[ES] La presente tesis doctoral se centra en la investigación y desarrollo de catalizadores avanzados con aplicaciones en la industria química. Desde la síntesis de nanopartículas de Rh2P hasta la exploración de catalizadores de cobalto dopados con heteroátomos, se ha buscado no sólo la eficiencia catalítica, sino también minimizar el impacto de estos procesos, permitiendo la producción de productos químicos esenciales con un menor consumo de recursos. Se ha investigado el proceso de síntesis de nanopartículas de Rh2P soportadas por impregnación húmeda seguida de pirólisis para su uso en reacciones de hidroformilación. Para ello, se han descrito y comparado dos métodos que se diferencian en los precursores empleados: uno a partir de un único precursor de fósforo y rodio y el otro a partir de dos precursores separados. Posteriormente, se ha realizado una caracterización de los materiales que ha permitido relacionar la forma de incorporar el fósforo con la composición de las partículas, determinando que el contenido de óxido de rodio es mayor cuando se emplean dos precursores. Para analizar la contribución del fósforo en el sistema se han preparado nanopartículas de rodio metálico soportadas para estudiar la influencia del fósforo en la composición y el tamaño de partícula. Se han analizado otros aspectos como la carga metálica, la temperatura de pirólisis y el uso de diferentes soportes empleando la microscopía electrónica; y se ha estudiado su capacidad de disociación de hidrógeno mediante ensayos de intercambio isotópico. Tras la caracterización de los materiales, éstos se han empleado como electrocatalizadores en la reacción de evolución del hidrógeno, en la que se ha estudiado su aplicabilidad a pH ácido, básico y neutro con bajas cargas de metal. Se ha demostrado que las especies de Rh2P son más activas que las de Rh metálico en la producción de hidrógeno y que el método de síntesis influye en la actividad catalítica. Para completar los ensayos experimentales, se han realizado cálculos DFT que han permitido comprobar por un lado la influencia de los defectos en la red de Rh2P y por otro, si las capas de carbono son efectivas en la protección de las nanopartículas. Se han aplicado los materiales de Rh y Rh2P en la hidroformilación de olefinas donde se ha estudiado la actividad catalítica, la influencia del fósforo y la estabilidad de los catalizadores. Se ha demostrado que el material Rh2P-1@C, obtenido a partir de un solo precursor de rodio y fósforo, es un sustituto viable del catalizador homogéneo RhCl(PPh3)3 ya que las energías de activación calculadas son muy cercanas entre sí. Se ha estudiado la influencia de algunos parámetros en la estabilidad del catalizador, como la temperatura de pirólisis a la que se sintetiza el material, demostrando que existe una relación inversa entre la temperatura de pirólisis y la cantidad de metal lixiviado durante la reacción. Otro factor estudiado es el del soporte, donde además del carbón se han empleado óxidos inorgánicos (Al2O3, CeO2, La2O3, ZnO), poniendo de manifiesto la superioridad del carbón como soporte no sólo en términos de actividad catalítica, sino de estabilidad del material. El catalizador Rh2P-1@C ha sido satisfactoriamente probado en reacciones de hidroformilación de etileno en un reactor de lecho fijo y en la reacción de hidroaminometilación. Como alternativa a los materiales de rodio, se han desarrollado catalizadores de cobalto dopados con heteroátomos (fósforo y nitrógeno). Éstos se han empleado en la hidroformilación de olefinas, donde se ha evaluado la influencia del dopaje en la actividad catalítica y en su estabilidad. Se ha comprobado la efectividad del recubrimiento del carbón dopado con nitrógeno al aumentar su estabilidad en comparación con las nanopartículas de cobalto sin recubrir y se ha demostrado que las nanopartículas de Co2P, al contrario que las Rh2P, no son más activas que las de Co metálico. / [CA] Aquesta tesis doctoral es centra en la investigació i la síntesis de nous catalitzadors amb aplicacions en reaccions químics d'interès industrial. Durant el transcurs de la síntesis de les nanopartícules fins a l'estudi de nous catalitzadors, s'ha cercat no únicament l'eficiència catalítica dels processos sinó la disminució de l'impacte dels mateixos. S'ha investigat el procés de síntesis de nanopartícules de Rh2P suportades a través del mètode d'impregnació humida seguida d'un procés de piròlisis, per al posterior ús d'aquests materials en reaccions d'hidroformil·lació. Per tal fi, s'han descrit i comparat dos mètodes de síntesis que es diferencien en els precursors utilitzats: un a partir d'un únic precursor com a font de fòsfor i rodi, i l'altre a partir dels dos precursors - de rodi i fòsfor - per separats. Posteriorment, s'ha portat a terme una caracterització completa de cadascun dels materials preparats que a permès relacionar la forma com s'incorpora el fòsfor el material en funció de la composició de les partícules. Amb l'objectiu d'analitzar la contribució de les espècies de fòsfor en el sistema s'han preparat un material basat en nanopartícules de rodi metàl·lic suportades. S'han analitzat, mitjançant la microscòpia electrònic, com influeixen en aquest paràmetre altres aspectes, com ara: la càrrega metàl·lica, la temperatura de piròlisis i l'ús de diferents suports. Tanmateix, s'ha estudiat la capacitat dissociativa de l'hidrogen per part d'aquests materials mitjançant assajos d'intercanvi isotòpic. Després de la caracterització dels materials, aquests s'han utilitzat com a electrocatalitzadors en la reacció d'evolució de l'hidrogen en la què s'ha estudiat la utilització d'aquests materials, utilitzant una baixa càrrega metàl·lica, en diferents medis (pH àcid, bàsic i neutre). Els treballs han demostrat que les espècies de Rh2P són més actives que les de Rh metàl·lic i que el mètode de síntesis també influeix en l'activitat catalítica. Per a completar la part experimental, s'han realitzat càlculs DFT que han permès comprovar tan la influència dels defectes de la xarxa de Rh2P com la influència de les capes de carboni en quant a la protecció de les pròpies nanopartícules. Tot seguit, els materials de Rh y Rh2P s'han aplicat en la reacció d'hidroformil·lació d'olefines on s'ha estudiat l'activitat catalítica, la influència de les espècies de fòsfor i l'estabilitat dels catalitzadors utilitzats. S'ha demostrat que el material de Rh2P-1@C, obtingut a partir d'un sol precursor de rodi i fòsfor, pot convertir-se en un possible candidat per a substituir el catalitzador homogeni RhCl(PPh3)3. També, s'ha estudiat la influència d'alguns paràmetres relacionats amb l'estabilitat del catalitzador, com ara la temperatura de piròlisis i la quantitat de metall lixiviat durant la reacció. Una altre factor que ha estat objecte d'estudi és el suport, on a més a més del carboni s'han utilitzat òxids inorgànics - Al2O3, CeO2, La2O3 i ZnO - posant de manifest la superioritat del carboni com a suport; no només en termes d'activitat catalítica sinó d'estabilitat del propi material. A més a més, el catalitzador Rh2P-1@C s'ha provat satisfactòriament en reaccions d'hidroformil·lació de l'etilè en un reactor de tipus llit fix, i en la reacció d'hidroaminometil·lació. Com a alternativa als materials de rodi, s'han sintetitzat catalitzadores de cobalt dopats amb heteroàtoms (fòsfor i nitrogen). Aquests materials, s'han utilitzat en la reacció d'hidroformil·lació d'olefines, on s'ha estudiat la influència del dopatge en l'activitat catalítica i en la seva estabilitat. S'ha comprovat que l'efectivitat del recobriment del carbó dopat amb nitrogen augmenta l'estabilitat del catalitzador en front de les nanopartícules de cobalt sense recobriment, i s'ha aconseguit demostrar que les nanopartícules de Co2P, a diferència de les de Rh2P, no resulten ser més actives que les de Co metàl·lic. / [EN] The present doctoral thesis focuses on the research and development of advanced catalysts with applications in the chemical industry. From the synthesis of Rh2P nanoparticles to the exploration of cobalt catalysts doped with heteroatoms, the primary goal has been to enhance not only the catalytic efficiency but also to minimize the environmental impact of these processes. In a time where the transition to clean energy sources and environmentally friendly processes is of utmost importance, advances in catalysis and material synthesis play a crucial role in the quest for more sustainable solutions in the chemical industry. The synthesis of supported Rh2P nanoparticles by wet impregnation followed by pyrolysis has been investigated. Two methods, differing only in the precursors employed, have been described and compared: one using a single precursor of phosphorus and rhodium, and the other using two separate precursors. Material characterization has revealed the relationship between the method of phosphorus incorporation and particle composition, demonstrating that the rhodium oxide content is higher when two separate precursors are used. Additionally, supported metallic rhodium nanoparticles were prepared to study the influence of phosphorus on particle size and composition. In this chapter, other factors have also been analyzed such as metal loading, pyrolysis temperature, and the use of different supports, employing electron microscopy. Finally, the hydrogen dissociation capacity of the catalysts has been compared through isotopic exchange assays, and the presence of carbon patches around the nanoparticles has been studied using Raman spectroscopy. Following material characterization, these materials have been employed as electrocatalysts in the hydrogen evolution reaction, where their applicability at acidic, basic and neutral pH at one of the lowest metal loadings described has been studied. It has been demonstrated that Rh2P species are more active than metallic Rh species in hydrogen production, and the synthesis method influences catalytic activity. To complement experimental assays, DFT calculations have been performed, allowing for an examination of the influence of defects in the Rh2P lattice and an assessment of the effectiveness of carbon layers in protecting the nanoparticles. Rh and Rh2P materials have been applied in the hydroformylation of olefins, where catalytic activity, the influence of phosphorus, and catalyst stability have been investigated. It has been shown that the material Rh2P-1@C, obtained from a single precursor of rhodium and phosphorus, is a viable substitute for the homogeneous catalyst RhCl(PPh3)3, as their apparent activation energies are very close. The influence of parameters affecting catalyst stability, such as the pyrolysis temperature at which the material is synthesized, has been studied, demonstrating an inverse relationship between pyrolysis temperature and the amount of leached metal during the reaction. Another factor studied is that of the support, where, in addition to carbon, inorganic oxides (Al2O3, CeO2, La2O3, ZnO) have been employed, highlighting the superiority of carbon as support not only in terms of catalytic activity but also material stability. At the end of this chapter, the Rh2P-1@C catalyst has been applied in the hydroformylation of ethylene in a fixed-bed reactor and in the hydroaminomethylation reaction. As an alternative to rhodium materials, cobalt catalysts doped with heteroatoms (phosphorus and nitrogen) have been developed. These catalysts have been employed in the hydroformylation of olefins, where the influence of doping on the catalytic activity and leaching has been evaluated. The effectiveness of nitrogen-doped carbon coating in suppressing leaching has been demonstrated compared to undoped cobalt nanoparticles, and it has been shown that Co2P nanoparticles, unlike Rh2P, are not more active than metallic Co nanoparticles. / Galdeano Ruano, CP. (2024). Catalizadores heterogéneos de rodio y cobalto para la hidroformilación de olefinas y la reacción de evolución del hidrógeno [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203121

The ever increasing demand for energy due to over consumption of non-renewable fossil fuels has emphasized the need for alternate, sustainable and efficient energy conversion and storage systems. In this direction, electrochemical energy conversion and storage systems involving various fundamental electrochemical redox processes such as hydrogen evolution (HER), oxygen reduction (ORR), oxygen evolution (OER), hydrogen oxidation (HOR) reactions and others become highly important. Electrocatalysts are often used to accelerate the kinetics of these reactions. Platinum (Pt), ruthenium oxide and iridium oxide (RuO2 and IrO2) are known to be the state of the art catalysts for several of these reactions due to favouarable density of states (DOS) near the Fermi level, binding energy with the reactant species, chemical inertness etc. Apart from HER, OER and ORR, chlorine evolution reaction (Cl-ER) is another industrially important reaction associated with water purification, disinfection, bleaching, chemical weapons and pharmaceuticals. Dimensionally stable anodes (RuO2/IrO2 mixed with TiO2 on Ti) are the most commonly used catalysts for this process. Issues related to surface poisoning, corrosion and cost of the catalysts, in addition to selectivity and specificity towards a particular reaction are various aspects to be addressed. For example, Pt is not very specific for ORR in presence of methanol in addition to high cost and corrosion in certain media. On the other hand, DSA can efficiently catalyze both OER and Cl-ER, and hence there is overlap of the two processes in the potential range available. There is an on going search for efficient, cost-effective, stable catalysts that possess high specificity for a particular redox reaction. Towards this goal, the present study explores certain layered (phospho)chalcogenides for catalyzing HER, ORR, OER and Cl-ER. The present thesis is structured in two parts, where the first part explores the multi-functional catalytic aspects of new classes of compounds based on layered transition metal mixed chalcogenides (MoS2(1-x)Se2x) and ternary phosphochalcogenides (FePS3, FePSe3 and MoPS). In addition, lithium insertion and desinsertion has been studied with the aim of using the layered materials for rechargeable batteries. The second part of the thesis explores organic electrode materials with active carbonyl groups such as rufigallol, polydihydroxyanthrachene succinic anhydride (PDASA) as battery electrodes. Additionally, covalently functionalized transition metal phthalocyanines with reduced graphene oxide are studied as counter electrodes in dye sensitized solar cells (DSSCs). MoS2(1-x)Se2x (x = 0 to 1) compositions are solid solutions of MoS2 and MoSe2 in different ratios. They crystallize in hexagonal structure with space group P63/mmc (D6h4) having Mo in trigonal prismatic coordination like the pristine counterparts. X-Ray diffraction studies reveal that Vegard’s law (figure 1a) is followed and hence complete miscibility of MoS2 and MoSe2 is established. MoS2(1-x)Se2x (x = 0 to 1) are layered in nature and the layers are held together by long range, weak van der Waal’s forces. This gives us the flexibility of exfoliation to produce corresponding few-layer materials (figure 1b). Figure 1. (a) Variation of lattice parameter corresponding to (002) reflection of MoS2(1-x)Se2x with different x values. (b) Scanning electron micrograph of few-layer MoS2(1-x)Se2x (x = 0.5). The electrocatalytic activity of the few-layer sulphoselenides have been studied towards HER in aqueous 0.5 M H2SO4 and towards Cl-ER in 3 M aqueous NaCl (pH = 3) solution. The mixed chalcogenides exhibit very good activities for both HER and Cl-ER as compared to the activity of their pristine counter parts (i.e. MoS2 and MoSe2) (figures 2a and 2b). Electrocatalytic activity on different compositions reveal that MoS1.0Se1.0 exhibits the maximum activity. Additionally, it has been observed that MoS1.0Se1.0 shows high specificity for Cl-ER with negligible interference of OER. Figure 2. Voltammetric data for (a) hydrogen evolution reaction (in 0.5 M aqueous H2SO4) and (b) chlorine evolution reaction (in 3 M aqueous NaCl solution, pH = 3) on MoS2(1-x)Se2x (x = 0, 0.5, 1). Figure 3. (a) XRD pattern of MoS2(1-x)Se2x (x = 0.5) electrode after a cycle of Li insersion and deinsersion (red) along with as-synthesized material (black) (b) Cycling behaviour of rGO supported (black) and pristine (red) MoS2(1-x)Se2x (x = 0.5) as electrode in rechargeable lithium-ion battery. The equiatomic MoS1.0Se1.0 has also been studied as an anode material for rechargeable lithium batteries. The cyclic voltammogram and characterization after charge-discharge cycle (figure 3a) indicate intercalation of Li with in the layers followed by conversion type formation of Li-S and Li-Se type compounds. The pristine material shows continuous capacity fading while the composites of sulphoselenides functionalized with conducting carbon supports such as rGO, MWCNT, super P carbon, toray carbon show marked improvement in capacity as well as cycling behavior. The rGO functionalized MoS1.0Se1.0 reveals ~1000 mAh/g of stable specific discharge capacity for 500 cycles (figure 3b). In the next two chapters, new class of transition metal-based layered materials FePS3 and FePSe3, containing both P and chalcogen (S and Se) is indroduced for electrocatalysis. FePS3 crystallizes in monoclinic symmetry with an indirect band gap of ~1.55 eV while FePSe3 possesses rhombohedral crystal structure with comparatively low band gap (~1.3 eV) as shown in figure 4a. The FePS3 and FePSe3 have been exfoliated as has been done for MoS1.0Se1.0 (liquid exfoliation method) using acetone as the solvent. Stable colloids with few-layer nanosheets having lamellar morphology and lateral sizes of ~100 to 200 nm are obtained. Electrical characterization indicates that they are semiconducting and the conductivity of the Se analogue is ~50 times higher than that of the S analogue (figure 4b). Figure 4. (a) Catholuminescence of FePX3 ( X = S and Se) reveals the band gap of the material. Band gap of the S analogue is 1.52 eV and that of the Se analogue is 1.33 eV (b) Resistivity of FePX3 ( X = S and Se) as a function of temperature. The tri-functional electrocatalytic activities on rGO-few layer FePX3 (X = S and Se) have been evaluated for HER over a wide pH range (0.5 M H2SO4, 0.5 M KOH, phosphate Figure 5. Catalytic activity of rGO-few-layer FePX3 (X = S, Se) towards HER in (a) aqueous 0.5 M H2SO4 and (b) 3.5 wt % NaCl solutions. (c) ORR activity of the catalysts in oxygen saturated 0.5 M KOH (d) OER behaviour on the catalysts in 0.5 M KOH at a rotation speed of 1600 rpm. buffer, pH 7 and 3.5 % NaCl), ORR and OER in alkaline media (0.5 M KOH). The studies clearly reveal that both rGO-FePS3 and rGO-FePSe3 exhibit excellent HER activity in acidic media (figure 5a) with high stability. The HER studies in 3.5 wt % aqueous NaCl solution (figure 5b) suggests that the catalysts are effective in evolving hydrogen from sea-water environment. Studies on ORR activity (figure 5c) indicate that the rGO composites of both S and Se analogues follow 4-electron pathways to produce water as the final product. They are also found to be highly methanol tolerant. In the case of OER (figure 5d), XPS characterization of the electrodes after the voltammetric studies reveals the presence of very thin layer of Fe2O3 (not detectable by XRD). All the three reactions (HER, ORR and OER) catalyzed by the Se analogue are better than the S analogue (figure 5). This could be due to the low band gap and high conductivity of FePSe3 as compared to FePS3. The over potential to achieve 10 mAcm-2 current density is ~108 mV for rGO-few-layer FePS3 catalyst where in the case of rGO-few layer FePSe3, it is ~97 mV (table 1). Table 1. Catalytic activities of rGO-few layer FePS3 and rGO-few layer FePSe3 towards HER, ORR and OER. Reaction studied rGO-FePS3 rGO-FePSe3 HER (η @ 10mAcm-2) ~108 mV ~97 mV ORR (peak potential) ~0.81 V ~0.87 V OER (η @ 10mAcm-2) ~470 mV ~430 mV It is likely that there is a strong interaction between FePX3 (metal d-orbital) and rGO, as observed from the downward shift of Fe 2p peak in high resolution XPS studies. This interaction may extend the density of states of metal d-orbitals thereby improving the catalytic activities. The next chapter deals with molybdenum-based phosphosulphide compound (MoPS). Molybdenum-based phosphide catalysts have been explored recently as excellent catalysts for various electrochemical reactions such as HER. It is expected that the catalyst containing both S and P will show positive effects on catalytic activities due to the synergy between S and P. In the present study, P incorporated MoS2 is studied towards HER. The XRD pattern of the as-synthesized crystal suggests the presence of mixed phase of MoS2, MoP2 and MoP while the elemental mapping in microscopy indicates the ratio of Mo, P and S to be 1:1:1. The electrochemical HER in 0.5 M H2SO4 indicates that the activity is improved drastically as compared to bulk and few-layer MoS2. The next section explores the use of different organic electrode materials possessing active carbonyl groups for Li-storage studies. The advantage of the use of carbonyl-based compounds lies in the high reversible activity towards Li ion insersion and de-insersion. Rufigallol (figure 6a) exhibits very stable capacity of ~200 mAh/g (at C/20 rate) upto 500 Figure 6. (a) and (c) Schematic representation of rufigallol and poly-dihydroanthracene succinic anhydride (PDASA) respectively. (b) and (d) Cyclic behaviour of rufigallol (at C/20 rate) and PDASA (at 20 mAg-1 current rate) in Li-storage devices. (e) and (f) represent the coulombic efficiency of rufigallol (at C/20 rate) and PDASA (at 20 mAg-1 current rate) as a function of number of cycles. cycles along (figure 6b) and with very good rate capability. A triptycene-based mesoporous polymer, PDASA (figure 6c) is introduced and explored as efficient electrode material for Li-storage. PDASA exhibits very high capacity of ~1000 mAh/g at a current rate of 50 mA/g upto 1000 cycles (figure 6d). Even at very high current rates (3A/g) excellent cyclability is observed. The mechanistic details of lithium uptake and release are studied using various spectroscopic techniques. In both the cases the coulombic efficiency observed is ~80 to 90 % (figures 6e and f). Figure 7. (a) Digital photograph of the dye sensitized solar cell with rGO-Co-TAPc counter electrode. (b) Photoconversion efficiency of DSSCs with different counter electrodes as mentioned in the figure. (c) Photo conversion efficiency of Pt and rGO-Co-TAPc based DSSCs as function of storage time. (d) Schematic illustration of DSSC wherein the energy level of the counter electrodes and electrolyte are shown for different M-TAPcs. In a slightly different direction, metal phthalocyanine - rGO composites (rGO-M-TAPc; M = Co, Zn, Fe) have been explored as counter electrodes in DSSC. Figure 7a depicts the digital image of a DSSC constructed using rGO-Co-TAPc as the counter electrode. It has been observed that rGO-cobalt tetraamino phthalocyanine (rGO-Co-TAPc) counter electrode exhibits ~6.6 % of solar conversion efficiency (figure 7b) and is close to that of standard DSSC (Pt counter electrode) under identical experimental conditions and are highly stable (figure 7c). Other metal phthalocyanines show less efficiency and is analysed based on the relative positions of HOMO energy levels of the materials and the energy level of the redox system (I-/I3- system) as given in figure 7d. The thesis contains eight chapters on aspects discussed above along with summary and future perspectives given at the end. It is devided into various chapters in two sections, one comprising inorganic chalcogenide-based electrocatalysts and another comprising organic electrode materials. Appendix I discusses the Na-storage behaviour of MoS1.0Se1.0 and appendix II describes the Li-storage behaviour of rGO functionalized benzoquinone and diamino anthraquinone electrode materials.

In recent years, there has been an increasing interest on renewable energy sources as substitute to fossil fuels. Among various processes of energy generation, electrochemical methods such as storage and conversion systems, electrolysis of water (production of H2 and O2), fuel cells, batteries, supercapacitors and solar cells have received great attention. The core of these energy technologies is a series of electrochemical processes, which directly depend on the nature of ‘electro catalyst’. The design and preparation of an electro catalyst is based on new concepts such as controlled surface roughness, atomic topographic profiles, defined catalytic sites, atomic rearrangements, and phase transitions during electrochemical reactions. Good electro catalysts should possess low over potential, high exchange current density, high stability, low cost and high abundance. The most fundamental reactions in the area of electrochemistry are hydrogen evolution (HER) and oxygen reduction (ORR) reactions. They are important in different energy systems such as fuel cells and batteries. Platinum has been a favoured electro catalyst due to its high activity, favourable density of states at Fermi level and chemical inertness. The low abundance, however, limits its large scale applications. Alternate materials with high catalytic activities are always required. In this particular direction, metal chalcogenides such as sulphides and selenides have attracted attention in recent years. The present thesis describes the synthesis of different phases of palladium and nickel chalcogenides and their applicability in various electrochemical reactions, both in aqueous and organic media. First part includes the synthesis of highly crystalline palladium selenide phases namely Pd17Se15, Pd7Se4 and Pd4Se by employing facile single source molecular precursor method. Pure palladium selenide phases are prepared by thrombolysis of highly processable intermediate complexes formed from metal and selenium precursors. Continuous films of different dimensions on various substrates (glass, ITO, FTO etc.) could be prepared (figure 1). This is one of the requirements for processing any new material. Thickness of the films could be altered by changing the volume of precursor complex coated on the substrate. All the phases are found to be metallic in nature with resistivity values in the range of 30 to 180 µΩ.cm. Figure 1. (a) Scanning electron micrograph and (b) photographic image of Pd17Se15 prepared on different substrates glass (1), Si (2), fluorine doped tin oxide (FTO) (3) and DSSC solar cell fabricated using FTO coated Pd17Se15 as the counter electrode (4). Other components of DSSC are given in the experimental section. All the palladium selenides phases are shown to be catalytically active towards electrochemical reactions such as HER and ORR. It is observed that the activities of the phases depend on the stoichiometric ratio of palladium to selenium. Higher the palladium content in the phase, higher is the catalytic activity observed. Therefore, the activities of the chalcogenides can be easily tuned by varying the ratio of metal to chalcogen. Tafel slopes of 50–60 mV/decade are observed for all three phases towards HER indicating that Volmer- Heyrovsky mechanism is operative. The exchange current densities are in the range of 2.3 x 10-4 A cm-2 to 6.6 x 10-6 A cm-2 (figure 2a). Figure 2. (a) Linear sweep voltammograms of Pd17Se15, Pd7Se4 and Pd4Se in 0.5 M H2SO4 (HER) and (b) 0.1 M KOH (ORR) at a scan rate of 2 mVs-1. These phases are found to be highly robust and stable under different pH conditions. Stability of the phases is confirmed by characterizing the catalysts post-HER process, using various techniques such as XPS, XRD and SEM. High activities observed for Pd4Se is explained based on electrochemically active surface area values determined from under potential deposition studies and also based on DFT calculations. Computational studies reveal the presence of different charge distribution on palladium in all the three phases which is likely to be another reason for varied activities. Palladium selenides are also explored as catalysts towards ORR in alkaline medium. Kinetic parameters and reaction mechanism are determined using RDE studies. All the three phases are found to be active and Pd4Se shows the highest activity, following a direct 4 electron reduction pathway (figure 2b). Other two phases follow 2 electron pathway terminating at hydrogen peroxide stage. Catalytic activity of Pd17Se15 is further improved by Nano structuring of the material and by synthesizing the material on active supports such as rGO, acetylene black and today carbon. ORR plays an important role in metal-air batteries. The palladium chalcogenides are used as electrodes in metal-air batteries. Specific energy density observed in the case of Mg-air primary batteries is higher for Pd4Se than the other two phases (figure 3a). Figure 3. (a) Discharge curves of Mg-O2 battery with different phases of palladium selenides as cathodes. Constant current density of 0.5 mA cm-2 is used for discharge. (b) Characteristic J–V curves of DSSCs with Pd17Se15, Pd7Se4 and Pt as counter electrodes. Versatility of these phases is further studied towards redox reaction in non-aqueous medium (I3-/I-). This reaction plays a crucial role in the regeneration of the dye in dye-sensitized solar cells (DSSC). Palladium selenide phases prepared on FTO plates are employed as counter electrodes in DSSC. The solar light conversion efficiencies are found to be 7.45 and 6.8% for Pd17Se15 and Pd7Se4 respectively and are comparable to that of platinum (figure 3b). The reason for high activities may be attributed to high electronic conductivity and low work function of the phases. The following chapter deals with the synthesis of palladium sulphide phases (Pd4S and Pd16S7) using both hydrothermal and single source precursor methods. Electro catalytic activities of the phases are shown towards HER and ORR and Pd4S exhibits better catalytic activities than that of Pd16S7 phase. Direct electrochemistry of cytochrome c is achieved on Pd4S with ∆E of ~64 mV (figure 4a). Electrochemical oxidation of ethanol, ethylene glycol (EG) and glycerol are also studied on the Pd4S phase and the activity is found to follow the order, glycerol > ethylene glycol > ethanol (figure 4b). Figure 4. (a) Cyclic voltammograms of Pd4S in (1) 0.1 M phosphate buffer solution (pH 7.0) and (2) in presence of 0.2 mM cytochrome c at a scan rate of 50 mVs-1 and (b) Voltammograms of Pd4S in presence of different alcohols (ethanol, EG and glycerol) in 1 M KOH solution at sweep rate of 50 mVs-1. Concentration of alcohols used is 0.1 M. The effect of dimensionality on the electro catalytic activity of nickel selenide phases forms part of the next chapter. Nickel selenide (NiSe) nanostructures possessing different morphologies of wires, spheres and hexagons are synthesized by varying the selenium precursors namely, selenourea, selenium dioxide (SeO2) and potassium selenocyanate (KSeCN), respectively using hydrothermal method. The different selenium precursors result in morphologies that are probably dictated by the by-products as well as relative rates of amorphous selenium formation and dissolution. The three different morphologies are used as catalysts for HER, ORR and glucose oxidation reactions. The wire morphology is found to be better than that of spheres and hexagons for all the reactions. Among the reactions studied, NiSe is found to be good for HER and glucose oxidation while ORR seems to terminate at the peroxide stage. In alkaline medium, nickel forms hydroxides and oxy-hydroxides and these oxyhydroxides are catalytically active towards the oxidation of glucose. Therefore, nickel selenides are employed as highly selective non-enzymatic glucose sensors and detection limit of 5 µM is observed. Electrical measurements on a single nanowire and a hexagon morphology of NiSe are carried out on devices fabricated by focused ion beam (FIB) technique (figure 5). The semiconducting nature of NiSe is revealed in the I-v measurements. The band gap of the material is found to be 1.9 eV and hence the single nanowire and hexagon are shown to act as visible light photodetector. Figure 5. SEM images of (a) single NiSe nanowire and (b) single NiSe hexagon with Pt contacts fabricated by FIB technique. Figure 6. Cyclic voltammograms of NiSe nanowires in 0.5 M aqueous NaOH in the (i) absence and (ii) the presence of 0.5 mM glucose, at a scan rate of 20 mVs-1 and (b) Galvanostatic discharge performance of Ni3Se2 with different morphologies (A, B and C represent Ni3Se2 prepared from SeO2, selenourea and KSeCN respectively). The next chapter includes the synthesis of different morphologies of Ni3Se2 using three different selenium precursors (SeO2, KSeCN and selenourea) and the study of their activities towards electrochemical reactions such as HER and glucose oxidation (figure 6a). Electrical measurements demonstrated the metallic behaviour of the material. These are also shown to be efficient electrode materials in energy storage devices such as supercapacitors with high specific capacitance of 2200 F/g (figure 6b). The studies are summarized in the last chapter with scope for further work. The appendixes show preliminary studies on electrooxidation of glycerol and propanol on Pd supported on TiN, synthesis of other selenides of Ni, Cu, Ag and Ti, and electro synthesis of metal-organic frameworks. (For figures pl refer the abstract pdf file)

Monolayer two-dimensional (2D) materials have been regarded as a hot topic in the fields of condensed matter physics, materials science, and chemistry due to their unique physical, chemical, and electronic properties. However, the research on the preparation method and properties understanding of the 2D monolayer are inadequate. In this dissertation, taking 2D nickel-iron layered double hydroxides (NiFe LDHs) and molybdenum disulfide (MoS2) as examples, the practicability of the direct synthesis of NiFe LDHs monolayer and the thermal enhancement catalytic performance of 2D MoS2 monolayer (MoS2 ML) are discussed. First, a one-pot synthetic strategy (bottom-up method) is presented to synthesize 2D NiFe-based LDHs monolayers, including NiFe, Co-, Ru-, doped, and Au-modified NiFe LDHs. The prerequisite and universality of this strategy are investigated and confirmed. The features of LDHs are characterized by advanced technologies. The obtained LDH bulks own a large interlayer spacing up to 8.2 Å, which can be facilely exfoliated into monolayers in water by hand-shaking within 10 s. As a result, the as-prepared NiFe-based LDH monolayers display a good electrocatalytic oxygen evolution reaction (OER) performance. This facile strategy paves the way for designing easily exfoliated LDHs for highly active catalysts and energy conversion devices based on other monolayer LDHs. Second, with gold-modified tape, 2D MoS2 ML is exfoliated from the bulk crystal through a micromechanical exfoliation method (top-down strategy). The thermal effects of MoS2 ML are confirmed by Raman and photoluminescence (PL) spectra. Moreover, an on-chip MoS2 ML hydrogen evolution reaction (HER) reactor is designed and fabricated. The thermal effects generate efficient electron transfer in the MoS2 ML and at the electrolyte-catalyst (MoS2 ML) interface, leading to an enhanced HER performance. Compared to the results obtained at room temperature, the MoS2 ML shows a direct thermal enhanced HER performance at higher temperatures. In summary, the findings and understandings, the direct synthesis and direct thermal enhancement catalytic performance, of 2D monolayers offer a guideline for synthesizing and catalyst application of other 2D monolayers.

Research on new, environment-friendly, clean and efficient energy sources have contributed immensely to the development of new technologies for the generation and storage of electrical energy. Heterogeneous ‘electrocatalysis’ involves catalysis of redox reactions where the electrode material, termed as ‘electrocatalyst’ reduces the overpotential and maximizes the current for the processes occurring at the electrode/electrolyte interface. Efficient catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are of paramount importance for electrochemical energy generation and storage applications in water splitting, fuel cells and batteries. However, high cost of Pt catalysts that are commonly used for such applications restricts their commercial viability. In addition, there are issues related to poisoning of the surface under certain conditions. One particular case of direct methanol fuel cells involves problems of methanol tolerance as well. Hence, the on-going search in this direction, is to search for alternate catalysts that can match the performance of Pt. There is a quest for the development of stable and durable electrocatalysts/ supports for various electrochemical redox reactions particularly based on energy storage and conversion. The present thesis is structured in exploring the multi-functional aspects of ternary palladium phosphochalcogenides (PdPS and PdPSe) that possess layer-type structure with high crystallinity. They are semiconducting in nature and possess favorable electrochemical, electrical and optical properties. The chalcogenide compounds crystallize in orthorhombic symmetry with an indirect band gap close to 1.5 eV. The current study shows the versatility of ternary phosphochalcogenides in the bulk phase as well as in small sizes. The electrocatalytic activities of the chalcoenides are found to be dramatically improved by increasing the electrical conductivity by way of forming composites with reduced graphene oxide (rGO). The average crystallite size of the PdPS and PdPSe are 30 μm ±10 μm (figure 1). The composites are prepared by simple hydrothermal methods without use of any reducing agent and are characterized using various physico-chemical techniques. Figure 1. FESEM images of (a) PdPSe and (b) PdPS. In the present investigations, PdPS and its reduced graphene oxide composite (rGO-PdPS) are shown to be very efficient hydrogen evolution electrocatalysts (figure 2a). The bulk form of PdPS is found to be very active and the composite of PdPS with reduced graphene oxide improves the hydrogen evolution performance dramatically, even superior to state of the art, MoS2-based catalysts. Figure 2. (a) Linear sweep voltammograms of rGO, bulk PdPS, rGO-PdPS composite and 40 % Pt-C in 0.5 M H2SO4 solution (pH 0.8). Scan rate used is 1 mV s-1. (b) Tafel plots for PdPS, rGO, rGO-PdPS and 40 wt% Pt-C in 0.5 M H2SO4 at 1 mVs-1 scan rate. The Tafel slope and the exchange current density values associated with hydrogen evolution reaction are 46 mV dec-1 and 1.4 x 10-4 A cm-2 respectively (figure 2b). The stability of the PdPS-based catalyst is found to be excellent retaining same current densities even after thousand cycles. Moreover, post-HER characterization reveals the durability of the material even after cycling for a long time. Preliminary spectroelectrochemical investigations are attempted to gain further insight in to the HER. Subsequently, the PdPS and its composite are explored as ORR catalysts in alkaline medium. The composite of PdPS with rGO is formed to enhance the catalytic activity of pure PdPS and the electron transfer kinetics is found to be very favorable. The kinetics of the oxygen reduction reactions are followed by RDE/RRDE measurements. It is experimentally verified that the composite eletrocatalyst is very stable, efficient and methanol tolerant in alkaline medium. The characteristics of the composite catalyst are comparable with widely used standard Pt-C for ORR (figure 3a). Moreover, ternary phophochalcogenide, PdPS, combined with rGO shows good catalytic activity towards OER and it affords a current density of 10 mA cm-2 at an overpotential of η = 570 mV (figure 3b). Figure 3. (a) Comparative voltammograms for rGO, bulk PdPS, rGO-PdPS and 40 % Pt-C in 1M KOH at 1600 rpm. The potential is swept at a rate of 5 mVs-1. (b) Linear sweep voltammograms of oxygen evolution reaction on rGO-PdPS, PdPS and 40 % Pt-C in 1 M KOH electrolyte. Scan rate 5 mV s-1. Apart from its tri-functional electrocatalytic behavior, PdPS and its rGO composite act as an anode material for Li-ion batteries showing high storage capacity of lithium (figure 4). The capacity fading of bulk PdPS is analyzed using XRD and SEM. The introduction of rGO, a well-known conducting matrix, improves the performance. Palladium phosphorous selenide (PdPSe) and its composite with rGO (rGO-PdPSe) are also explored as electrocatalysts for HER, ORR and OER. They show the tri¬functional electrocatalytic behavior as well. Figure 4. Discharge capacity as a function of number of cycles for PdPS, rGO rGO-PdPS electrode at current density of 35 mAg-1 in rechargeable lithium ion battery. The next chapter deals with single or few layer PdPS where layer-type PdPS is exfoliated by several methods such as ultra-sonication and solvent exfoliation. Various microscopic and spectroscopic techniques have been used to characterize the material. These sheets show significantly improved electrocatalytic activity towards ORR and HER with notably low onset potential and low Tafel slopes. The charge storage capacity also increases by an order from its bulk counterpart. The catalyst shows excellent stability for HER and good methanol tolerance behavior towards ORR is also observed. This opens up possibilities for applications of few-layer ternary phosphosulphides in energy conversion and storage. However, one should be cautious since the exfoliation results in a slightly different composition of the material. Different aspects of electrodeposition of gallium nanoparticles on exfoliated graphite surfaces from aqueous acidic solution forms part of the next study. The electrodeposited surface is characterized by various microscopic and spectroscopic techniques. The presence of surface plasmon peak in the visible region has led us to explore the use of Ga on EG for SERS studies. This preliminary work shows that the Raman signal of R6G is enhanced in the presence of Ga deposited on EG surface. The research work presented in the next part of the thesis deals with the preparation, physicochemical, spectroscopic characterization of room temperature molten electrolytes based on amides. Room temperature ternary molten electrolyte involving a combination of acetamide, urea and gallium nitrate salt is prepared and the molten eutectic is characterized. An electrochemical process is developed for depositing gallium nitride from the ternary molten electrolyte on Au electrode. Gallium ion is reduced at low potentials while nitrate ion is reduced to produce atomic nitrogen, forming gallium nitride under certain conditions. Au coated TEM grid is used for patterning gallium nitride (figure 5). The deposited gallium nitride is further annealed at high temperature to increase the crystalinity and improve the stoichiometry of gallium nitride. Figure 5. The FESEM image of patterned gallium nitride deposited on Au coated TEM grid. Elemental mapping of Ga and N from the same region is given. The last chapter explores the prepration and uses of textured GaN tubes synthesized from GaOOH rod-like morphology. The precursor material is prepared by simple hydrothermal technique, maintaining certain value for the pH of the solution. The thermal treatment under ammonia atmosphere leads to highly crystalline, single phase textured tube- like morphology. The as-prepared material is explored as photoanodes in photoelectrochemical water splitting, dye sensitized solar cells and active substrate for SERS. The appendix-I discusses the Na-ion storage capacity by rGO-PdPS composite whereas appendix-II deals with the synthesis of InN and FeN from ternary molten electrolyte. (For figures pl refer the abstract pdf file)

Synopsis of thesis entitled “Electrochemical and Photoelectrochemical Investigations of Co, Mn and Ir-based Catalysts for Water Splitting” by Ahamed Irshad M (SR No: 02-01-02-10-11-11-1-08823) under the supervision of Prof. N. Munichandraiah, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore (India), for the Ph.D. degree of the Institute under the Faculty of Science. Hydrogen is considered as the fuel for future owing to its high gravimetric energy density and eco-friendly use. In addition, H2 is an important feedstock in Haber process for ammonia synthesis and petroleum refining. Although, it is the most abundant element in the universe, elemental hydrogen is not available in large quantities on the planet. Consequently, H2 must be produced from its various chemical compounds available on earth. Currently, H2 is produced in large scale from methane by a process called steam-methane reforming (SMR). This process releases huge amount of CO2 into atmosphere as the by-product causing serious environmental issues. The development of alternate clean methods to generate H2 is a key challenge for the realization of hydrogen economy. Production of H2 gas by water splitting using electricity or sunlight is known. Low cost, high natural abundance and carbon neutrality make water as the best source of hydrogen. Thermodynamically, splitting of H2O needs 237 kJ mol-1 of energy, which corresponds to 1.23 V according to the equation, ΔG = -nFE. However, commercial electrolyzers usually operate between 1.8 to 2.1 V, due to the need of large overvoltage. The high overvoltage and subsequent energy losses are mainly associated with the sluggish kinetics of oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode. The overvoltage can be considerably reduced using suitable catalysts. Hence, the design and development of stable, robust and highly active catalysts for OER and HER are essential to make water splitting efficient and economical. Attempts in the direction of preparing several novel OER and HER catalysts, physicochemical characterizations and their electrochemical or photoelectrochemical activity are described in the thesis. A comprehensive review of the literature on various types of catalysts, thermodynamics, kinetics and mechanisms of catalysis are provided in the Chapter 1 of the thesis. Chapter 2 furnishes a brief description on various experimental techniques and procedures adopted at different stages of the present studies. Chapter 3 explains the results of the studies on kinetics of deposition and stability of Nocera’s Co-phosphate (Co-Pi) catalyst using electrochemical quartz crystal microbalance (EQCM). The in-situ mass measurements during CV experiments on Au electrode confirm the deposition of Co-Pi at potential above 0.87 V vs. Ag/AgCl, 3 M KCl (Fig.1a and b). The catalyst is found to deposit via a nucleus mediated process at a rate of 1.8 ng s-1 from 0.5 mM Co2+ in 0.1 M neural phosphate solution at 1.0 V. Further studies on the potential and electrolyte dependent stability of the Co-Pi suggest that the catalyst undergoes severe corrosion at high overpotential and in non-buffer electrolytes. Current/ Fig.1 (a) Cyclic voltammograms and (b) mass variations vs. potential of Au-coated quartz crystal in 0.1 M potassium phosphate buffer solution (pH 7.0) containing 0.5 mM Co(NO3)2 Chapter 4 deals with the electrochemical deposition of a novel OER catalyst, namely, Co-acetate (Co-Ac) from a neutral acetate electrolyte containing Co2+ ions. Use of acetate solution instead of phosphate avoids the solubility limitations and helps to get thick layer of the catalyst in a short time from concentrated Co2+ solutions. In addition, the Co-Ac is found to be catalytically superior to Co-Pi (Fig. 2a). It is also observed that the Co-Ac catalyst undergoes ion exchange with electrolyte species during electrolysis in phosphate buffer solution, which results in the formation of a hybrid Co-Ac-Pi catalyst (Fig. 2b). The presence of both acetate and phosphate ions in the catalyst and their synergistic catalytic effect enhance the OER activity. Fig.2. (a) Linear sweep voltammograms of Co-Ac in (i) phosphate and (ii) acetate electrolytes, and that of Co-Pi in (iii) acetate and (iv) phosphate electrolytes. (b) SEM image showing the formation of two layers of the catalysts after electrolysis in phosphate solution. In Chapter 5, high OER activity of an electrodeposited amorphous Ir-phosphate (Ir-Pi) is investigated. The catalyst is prepared by the anodic polarization of a carbon paper electrode in neutral phosphate solution containing Ir3+ ions (Fig. 3). The Ir-Pi film deposited on the electrode has Ir and P in an approximate ratio of 1:2 with Ir in an oxidation state higher than +4. Phosphate ions play a major role for both the electrochemical deposition process and its catalytic activity towards OER. The Ir-Pi catalyst is superior to similarly deposited IrO2 and Co-Pi catalysts both in terms of onset potential and current density at any potential in the OER region. Tafel measurements and pH dependence studies identify the formation of a high energy intermediate during oxygen evolution. Fig.3. (a) Cyclic voltammograms during the Ir-Pi deposition and (b) SEM image of Ir-Pi on C. Chapter 6 is on the preparation of a composite of Mn-phosphate (MnOx-Pi) and reduced graphene oxide (rGO) and its utilization as an OER catalyst. The composite is prepared by the simultaneous electrochemical reduction of KMnO4 and graphene oxide (GO) in a phosphate solution (pH 7.0). Various analytical techniques such as TEM, XPS, Raman spectroscopy, etc. confirm the formation of a composite (Fig. 4) and electrochemical studies indicate the favourable role of rGO towards OER. Under identical conditions, MnOx-Pi-rGO gives 6.2 mA cm-2 at 2.05 V vs. RHE whereas it is only 2.9 mA cm-2 for MnOx-Pi alone. However, the catalyst is not very stable during OER which is ascribed to slow oxidation of Mn3+ in the catalyst. Fig.4. (a) Raman spectrum and (b) TEM image of MnOx-Pi-rGO. In Chapter 7, an amorphous Ni-Co-S film is prepared by a potentiodynamic deposition method using thiourea as the sulphur source. The electrodeposit is used as a catalyst for the HER in neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by varying the ratio of concentrations of Ni2+ and Co2+. The bimetallic Ni-Co-S catalyst exhibits better HER activity than both Ni-S and Co-S (Fig. 5a). Under optimized deposition conditions, Ni-Co-S requires just 150 mV for the onset of HER and 10 mA cm-2 is obtained for 280 mV overpotential. The Ni-Co-S shows two different Tafel slopes, indicating two different potential dependent HER mechanisms (Fig. 5b). Presence of two different catalytic sites which contribute selectively in different potential regions is proposed. Fig.5. (a) Linear sweep voltammograms of HER at 1 mV s-1 in 1 M phosphate solutions (pH 7.4) using (i) Ni-S, (ii) Co-S and (c) Ni-Co-S. (b) Tafel plot of Ni-Co-S showing two Tafel slopes. Photoelectrochemical OER using ZnO photoanode and Co-acetate (Co-Ac) cocatalyst is studied in Chapter 8 of the thesis. Randomly oriented crystalline ZnO nanorods are prepared by the electrochemical deposition of Zn(OH)2 followed by heat treatment at 350 ºC in air. Co-Ac is then photochemically deposited onto ZnO nanorods by UV illumination in the presence of neutral acetate buffer solution containing Co2+ ions. The hybrid Co-Ac-ZnO shows higher photoactivity in comparison with bare ZnO towards PEC water oxidation (Fig. 6). Co-Ac acts as a cocatalyst and reduces the charge carrier recombination at the electrode/electrolyte interface. Fig.6. (a) Linear sweep voltammograms of ZnO under (i) dark and (ii) light conditions, and that of Co-Ac-ZnO in (iii) dark and (iv) light in 0.1 M phosphate (pH 7.0) electrolyte. Chapter 9 deals with PEC water oxidation using α-Fe2O3 photoanode and Ir-phosphate (Ir-Pi) cocatalyst. α-Fe2O3 is prepared by direct heating of Fe film in air which in turn is deposited by the electrochemical reduction of Fe2+. Thickness of the film as well as calcination temperature is carefully optimized. In order to further enhance the OER kinetics, Ir-Pi is electrochemically deposited onto α-Fe2O3. Under optimized conditions, Ir-Pi deposited α-Fe2O3 shows around 3 times higher photocurrent than that of bare α-Fe2O3 at 1.23 V vs. RHE (Fig. 7). Ir-Pi acts as a cocatalyst for OER and reduces the photogenerated charge carrier recombination. Fig.7. Photocurrent variation of α-Fe2O3 electrode at 1.23 V vs. RHE for (i) front and (ii) back side illuminations, against Ir-Pi deposition time. The thesis ends with a short summary and future prospectus of studies described in the thesis. The research work presented in the thesis is carried out by the candidate as the part of Ph.D. program. Some of the results have already been published in the literature and some manuscripts are under preparation. A list of publications is included at the end of the thesis. It is anticipated that the studies reported in the thesis will constitute a worthwhile contribution.

[ES] Esta Tesis Doctoral se centra en la recuperación mediante electrodeposición del Sb presente en un efluente residual proveniente de la metalurgia del cobre. El efluente en el que se basa este estudio se produce en el proceso de regeneración con HCl concentrado de las resinas de intercambio iónico de una de las subetapas del electro-refinado del cobre. Se trata de un electrolito ácido que contiene diversas impurezas, entre las que destacan, Sb y Bi, que son considerados materias primas críticas por la Unión Europea, debido al riesgo de suministro que presentan y a su importancia en la economía. El objetivo de esta Tesis es la recuperación del Sb y la reutilización del HCl. Para alcanzar ambos propósitos se ha estudiado el empleo de la electrodeposición como operación de separación para el tratamiento del efluente. Este proceso se ha investigado mediante técnicas electroquímicas, en particular, voltametría cíclica y de barrido lineal. En primer lugar, se ha realizado el estudio con disoluciones sintéticas que emulan el efluente generado en las metalurgias chilenas. La caracterización electroquímica de la disolución de Sb en medio HCl ha evidenciado que la reducción del Sb(III) a Sb metálico está limitada por la transferencia de materia y que una concentración elevada de HCl favorece la recuperación del Sb. Los ensayos de electrodeposición han destacado la relevancia de las reacciones secundarias, la reacción de evolución del hidrógeno (HER) y la generación de cloro, y su influencia negativa sobre la deposición de Sb. La HER tiene lugar en el cátodo y conlleva la generación de burbujas de hidrógeno a elevadas densidades de corriente, que reducen la superficie útil del electrodo de trabajo e incluso causan el desprendimiento del depósito de Sb. Por su parte, la generación de cloro gas en el ánodo provoca la redisolución de los depósitos de Sb desprendidos a causa de la HER. Tras la realización de estos ensayos se ha concluido que se puede aumentar la tasa de recuperación de Sb si se tienen mayores concentraciones del elemento en la disolución o si se mejoran las condiciones hidrodinámicas. Se ha analizado también cómo influye la presencia de Bi en la disolución sintética durante la electrodeposición del Sb. El potencial de reducción de ambos elementos es similar, lo que implica que la recuperación individual de Sb sea compleja. No obstante, si se trabaja bajo condiciones en las que no se supere la densidad de corriente límite del sistema, se logra una elevada selectividad hacia el Sb. Si la concentración de Bi en la disolución es superior a la de Sb, se electrodepositan ambos elementos, pero se logra un elevado valor de eficiencia de corriente debido a que la influencia de la HER sobre el Bi no es tan fuerte. A continuación, se ha estudiado la aplicación de las técnicas previamente analizadas con un efluente real, facilitado por una empresa española. Se ha verificado que las conclusiones obtenidas con las disoluciones sintéticas son aplicables al efluente real. En particular, se ha confirmado que, al aumentar la densidad de corriente aplicada, la deposición de Sb se ve mermada debido a la relevancia del resto de reacciones: la reducción de los demás elementos y la evolución del medio. Los depósitos obtenidos contienen algunos de los elementos presentes en el efluente real: Sb, Bi, As y Cu, siendo mayoritario el primero. Como resultado, se ha concluido que es posible purificar el HCl mediante la electrodeposición de los elementos contenidos en el electrolito. Finalmente, se ha planteado la posibilidad de sustituir el HCl empleado como regenerante por un disolvente eutéctico profundo, debido a la alta solubilidad de metales y su procedencia de fuentes renovables. En particular, la investigación se ha llevado a cabo con la oxalina, la cual presenta una elevada capacidad de disolución para el Sb y una amplia ventana de potencial que beneficiaría la aplicación de la técnica de electrodeposición para la recuperación del Sb. / [CA] Esta Tesi Doctoral se centra en la recuperació mitjançant electrodeposició del Sb present en un efluent residual provinent de la metal·lúrgia del coure. L'efluent en què es basa este estudi es produïx en el procés de regeneració amb HCl concentrat de les resines d'intercanvi iònic d'una de les subetapes de l'electro-refinat del coure. Es tracta d'un electròlit àcid que conté diverses impureses, entre les quals destaquen, Sb i Bi, que són considerats matèries primeres crítiques per la Unió Europea, a causa del risc de subministrament que presenten i a la seua importància en l'economia. L'objectiu d'esta Tesi és la recuperació del Sb i la reutilització de l'HCl. Per assolir aquests dos propòsits s'ha estudiat l'ús de l'electrodeposició com a operació de separació per al tractament de l'efluent. Este procés s'ha investigat mitjançant tècniques electroquímiques, en particular, voltametria cíclica i de rastreig lineal. En primer lloc, s'ha realitzat l'estudi amb dissolucions sintètiques que emulen l'efluent generat a les metal·lúrgies xilenes. La caracterització electroquímica de la dissolució de Sb en medi HCl ha evidenciat que la reducció del Sb(III) a Sb metàl·lic està limitada per la transferència de matèria i que una concentració elevada de HCl afavorix la recuperació del Sb. Els assajos d'electrodeposició han destacat la rellevància de les reaccions secundàries, la reacció d'evolució de l'hidrogen (HER) i la generació de clor, i la seua influència negativa sobre la deposició de Sb. La HER té lloc al càtode i comporta la generació de bambolles d'hidrogen a elevades densitats de corrent, la qual cosa reduïx la superfície útil de l'elèctrode de treball i fins i tot causa el despreniment del depòsit de Sb. Per la seua banda, la generació de clor gas a l'ànode provoca la redissolució dels depòsits de Sb despresos a causa de la HER. Després de la realització d'estos assajos s'ha conclòs que es pot augmentar la taxa de recuperació de Sb si es tenen majors concentracions de l'element en la dissolució o si es milloren les condicions hidrodinàmiques. S'ha analitzat també com influïx la presència de Bi en la dissolució sintètica durant l'electrodeposició del Sb. El potencial de reducció dels dos elements és similar, la qual cosa implica que la recuperació individual de Sb siga complexa. No obstant això, si es treballa sota condicions en què no se supere la densitat de corrent límit del sistema, s'aconseguix una elevada selectivitat cap al Sb. Si la concentració de Bi en la dissolució és superior a la de Sb, s'electrodepositen ambdós elements, però s'aconseguix un elevat valor d'eficiència de corrent pel fet que la influència de la HER sobre el Bi no és tan forta. A continuació, s'ha estudiat l'aplicació de les tècniques prèviament analitzades amb un efluent real, facilitat per una empresa espanyola. S'ha verificat que les conclusions obtingudes amb les dissolucions sintètiques són aplicables al efluent real. En particular, s'ha confirmat que, en augmentar la densitat de corrent aplicada, la deposició de Sb es veu minvada a causa de la rellevància de la resta de reaccions: la reducció dels altres elements i l'evolució del medi. Els depòsits obtinguts contenen alguns dels elements presents en el efluent real: Sb, Bi, As i Cu, sent majoritari el primer. Com a resultat, s'ha conclòs que és possible purificar l'HCl mitjançant l'electrodeposició dels elements continguts en l'electròlit. Finalment, s'ha plantejat la possibilitat de substituir l'HCl emprat com regenerant per un dissolvent eutèctic profund, a causa de l'alta solubilitat de metalls i la seua procedència de fonts renovables. En particular, la investigació s'ha dut a terme amb l'oxalina, la qual presenta una elevada capacitat de dissolució per al Sb i una àmplia finestra de potencial que beneficiaria l'aplicació de la tècnica d'electrodeposició per a la recuperació del Sb captat durant el procés de regeneració de les resines. / [EN] This Doctoral Thesis focuses on the recovery by electrodeposition of Sb present in an effluent from the copper metallurgy. The effluent on which this study is based is generated during the regeneration with concentrated hydrochloric acid of the ion exchange resins used in one of the sub-stages of copper electro-refining. It is an acid electrolyte containing several impurities, among them, Sb and Bi, which are considered critical raw materials by the European Union due to their supply risk and economic relevance. The aim of this Thesis is the recovery of Sb and reuse of HCl. To achieve both objectives, electrodeposition has been studied as a separation operation for the treatment of the effluent. This operation has been investigated through electrochemical techniques, primarily, cyclic and linear sweep voltammetry. First, the study has been conducted with synthetic solutions emulating the effluent generated in the Chilean metallurgy industries. The electrochemical characterization of the Sb solution in the HCl medium has shown that, mass-transfer limits the reduction of Sb(III) to metallic Sb and a high HCl concentration favors the recovery of Sb. From the electrodeposition tests the relevance and negative influence on Sb deposition of the secondary reactions, the hydrogen evolution reaction (HER) and the chlorine generation, has been proven. The HER occurs at the cathode and involves the generation of hydrogen bubbles at high current densities, which decrease the effective surface area of the working electrode and even cause the detachment of the Sb deposits. The chlorine generation at the anode leads to the redissolution of the Sb deposits detached by the HER. After conducting these experiments, it has been concluded that it is possible to increase the Sb recovery rate, if higher concentrations of this element are present in the solution or the hydrodynamic conditions of the electrodeposition process are improved. The influence of the presence of Bi in the synthetic solution on the Sb electrodeposition has also been investigated. The reduction potential of both elements is similar, implying that the individual recovery of Sb by electrodeposition is challenging. However, if the operating conditions do not imply exceeding the limiting current density of the system, a high electrodeposition selectivity towards Sb is achieved. If the concentration of Bi in the solution is higher than that of Sb, the simultaneous electrodeposition of both elements takes place, but, on the contrary, a high value of current efficiency is obtained because the influence of the HER on Bi reduction is not as significant as that on Sb deposition. The application of the previously analyzed techniques has been studied with a real effluent, that was provided by a Spanish company. It has been proven that the conclusions obtained with the synthetic solutions can be applied to a real effluent. It has been confirmed that, as the applied current density increases, the Sb deposition worsens due to the relevance of the other reactions that take place during the process: the reduction of the other elements and the evolution of the medium. The deposits obtained contain some elements present in the real effluent: Sb, Bi, As and Cu, the most significant being the first. From this study, it has been concluded that purifying the HCl by removing the elements contained in the electrolyte via electrodeposition is possible. Finally, the possibility of replacing the HCl used as a regenerant with a deep eutectic solvent has been considered based on their properties, among which are a high solubility of metals and their synthesis from renewable sources. In particular, the research has been carried out with oxaline, which presents a high dissolution capacity for Sb and a wide potential window that would benefit the application of the electrodeposition technique to recover Sb captured during the resins regeneration process. / Me gustaría agradecer la financiación a la Agencia Estatal de Investigación (AEI/10.13039/501100011033) (España) bajo el proyecto PCI2019-103535, gracias al cual he podido desarrollar la presente Tesis Doctoral, y a FEDER Una manera de hacer Europa / Hernández Pérez, L. (2024). Estudio electroquímico para la recuperación de antimonio de efluentes del electro-refinado de cobre por electrodeposición [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203892