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El hidrógeno es un portador de energía que ya ha demostrado su capacidad para reemplazar el petróleo como combustible. Sin embargo, los medios de producción actualmente en uso siguen siendo altamente emisores de gases de efecto invernadero. La foto-electrólisis del agua es un proceso que, a partir de la energía solar, separa los compuestos elementales del agua como el hidrógeno y el oxígeno utilizando un semiconductor con propiedades físicas adecuadas. La hematita (¿-Fe2O3) es un material prometedor para esta aplicación debido a su estabilidad química y su capacidad para absorber una porción significativa de la luz (con una banda prohibida entre 2.0 - 2.2 eV). A pesar de estas propiedades ventajosas, existen limitaciones intrínsecas al uso de óxido de hierro para la descomposición fotoelectroquímica del agua. La primera restricción es la posición de su banda de conducción que es menor que el potencial de reducción de agua. Esta limitación se puede superar mediante la adición en serie de un segundo material, en tándem, que absorberá una parte complementaria del espectro solar y llevar a los electrones a un nivel de energía más alto que el potencial para la liberación de hidrógeno. El segundo obstáculo proviene del desacuerdo entre la corta longitud de difusión de los portadores de carga y la profundidad de penetración larga de la luz. Por lo tanto, es necesario controlar la morfología de los electrodos de hematita en una escala de tamaño similar a la longitud de transporte del orificio. En esta tesis, se introduce un nuevo concepto para mejorar el rendimiento fotoelectroquímico de la hematita. Usando el método hidrotermal depositamos capas delgadas de hematita dopada con Cr en sustratos de vidrio conductivo. También se ha preparado por medios electroquímicos una heterounión del tipo p-CuSCN/n-Fe2O3 depositando secuencialmente una capa de ¿-Fe2O3 y una película de CuSCNsobre sustratos de FTO (SnO2: F).Finalmente, se ha preparado células solares de perovskitas y óxido de hierro. Para ello se depositó una capa delgada, densa y uniformede óxido de hierro (¿-Fe2O3) como capa de transporte de electrones (ETL) en lugar de dióxido de titanio (TiO2) que se utiliza convencionalmente en las células fotovoltaicas perovskitastipoCH3NH3PbI3 (SGP). Este último dispositivo mostró un aumento en la fotocorriente del 20% y un IPCE30 veces mayor que la hematita simple, lo que sugiere una mejor conversión de las longitudes de onda por encima de 500 nm. Palabras clave: Fotoelectroquímica, división de agua, producción de hidrógeno, evolución de oxígeno, semiconductores de óxido de metal, hematita, óxido de hierro, nanoestructuras / Hydrogen is an energy carrier that has already demonstrated its ability to replace oil as a fuel. However, the means of production currently used remain highly emitting greenhouse gases. Photo-electrolysis of water is a process that uses solar energy to separate the elemental compounds of water such as hydrogen and oxygen using a semiconductor with adequate physical properties. Hematite (¿-Fe2O3) is a promising material for this application because of its chemical stability and ability to absorb a significant portion of light (with a band-gap between 2.0 - 2.2 eV). Despite these advantageous properties, there are intrinsic limitations to the use of iron oxide for the photoelectrochemical cracking of water. The first constraint is the position of its conduction band, which is lower than the water reduction potential. This constraint can be overcome by the addition in series of a second material, in tandem, which will absorb a complementary part of the solar spectrum and bring the electrons to a higher energy level than the potential of hydrogen release. The second obstacle comes from the disagreement between the short diffusion length of the charge carriers and the long light penetration depth. It is therefore necessary to control the morphology of the hematite electrodes on a scale of similar size to the transport length of the hole. In this thesis a new concept is introduced to improve the photoelectrochemical performances. Using the hydrothermal method we deposited thin layers of Cr-doped hematite on conductive glass substrates. We also electrochemically prepared a p-CuSCN / n-Fe2O3 heterojunction by sequentially depositing ¿-Fe2O3 and CuSCN films on FTO (SnO2: F) substrates. Finally, we have used uniform and dense thin layers of iron oxide (¿-Fe2O3) as an electron transport layer (ETL) in place of titanium dioxide (TiO2) conventionally used in photovoltaic cells based on perovskites CH3NH3PbI3 (PSC). This latter concept showed a 20% increase of the photocurrent and an IPCE 30 times greater than the simple hematite, suggesting better conversion of high wavelengths (> 500 nm). Keywords: Photoelectrochemistry, Water Splitting, Hydrogen Production, Oxygen Evolution, MetalOxide Semiconductors, Hematite, Iron Oxide, Nanostructures, Surface. / L'hidrogen és un proveïdor d'energia que ja ha demostrat la seva capacitat per reemplaçar el petroli com a combustible, però els mitjans de producció actuals continuen essent fortament emissors dels gasos responsables d'efecte hivernacle. La fotoelectròlisi de l'aigua és un procés que, a partir de l'energia solar, separa els compostos elementals d'aigua com l'hidrogen i l'oxigen utilitzant un semiconductor amb propietats físiques adequades. La hematita (¿-Fe2O3) és un material prometedor per a aquesta aplicació a causa de la seva estabilitat química i capacitat d'absorbir una porció significativa de la llum (amb un gap entre 2,0 i 2,2 eV). Malgrat aquestes propietats avantatjoses, hi ha limitacions intrínseques per a l'ús d'òxid de ferro per a la descomposició fotoelectroquímica de l'aigua. La primera restricció és la posició de la seva banda de conducció que és inferior al potencial de reducció d'aigua. Aquesta limitació es pot superar mitjançant l'addició en sèrie d'un segon material, en tàndem, que absorbirà una part complementària de l'espectre solar i portar els electrons a un nivell d'energia més alt que el potencial per a l'alliberament d'hidrogen. El segon obstacle prové del desacord entre la curta durada de la difusió dels portadors de càrrega i la llarga profunditat de penetració de la llum. Per tant, és necessari controlar la morfologia dels elèctrodes d'hematita en una escala de mida similar a la longitud del forat del transport. En aquesta tesi, es presenta un nou concepte per millorar el rendiment fotoelectroquímic. Mitjançant el mètode hidrotermal es van dipositar capes primes de hematita Cr-doped sobre substrats de vidre conductor. També s'han preparat electroquímicamentheterounions de tipus p-CuSCN/n-Fe2O3 dipositant seqüencialment una capa de ¿-Fe2O3 i altra de CuSCN sobre substrats FTO (SnO2: F).Finalment, s'han produït cél·lules solars de perovskitesi óxid de ferro. Per això es va depositaruna capa prima,densai uniforme d'òxid de ferro (¿-Fe2O3) com a capa de transport d'electrons (ETL) en lloc de diòxid de titani (TiO2) que s'utilitza convencionalment en les cèl·lules fotovoltaiques de perovskita híbrida del tipus CH3NH3PbI3 (SGP). Aquest últim dispositiu va mostrar un augment del fotocorrent del 20% i una IPCE30 vegades superior a la hematita simple, la qual cosa suggereix una millor conversió a longitud d'ones per sobre de 500 nm. Paraules clau:Fotoelectroquímica, divisió d'aigua, producció d'hidrogen, evolució d'oxigen, semiconductors d'òxids metàl·lics, hematita, òxid de ferro, nanoestructures. / Bouhjar, F. (2018). Preparation et performance d'une cellule photocatalytique à base d'hématite pour la génération d'hydrogène [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/106345 / TESIS

The main objective of this doctoral thesis is explore the origin of the nanoporous carbons photoactivity for studying their applications in different fields of research covering their use as photocatalysts for pollutants degradation as well as photoelectrodes for water photooxidation reaction, either by themselves or as additives coupled to a semiconductor in hybrid electrodes. The first stage of this study mainly consisted in investigating the photoactivity of carbon materials by themselves (in the absence of semiconductors) towards different reactions, aiming at linking their photochemical response with the carbon material nature in terms of porosity, surface chemistry, composition and structure. The exploration of the photoassisted degradation of phenol nanoconfined in the pore voids of several nanoporous carbons showed a positive effect of the tight packing of the molecule in the carbon material porosity. This indicated the role of confinement to boost fast interactions between the photogenerated charge carriers at carbon material surface and the molecule adsorbed inside pores. The irradiation wavelength was found as a key variable upon phenol photooxidation reaction, with the best optimum performance at low and high wavelengths, and a minimum photodegradation yield at ca. 400 nm for all tested carbon materials. Another parameter strongly influencing the photoactivity of the nanoporous carbons was the surface functionalisation. When sulphur was incorporated to a carbon matrix, the light conversion towards the phenol photooxidation became more efficient and it was dependent on the nature of the S-containing groups. Further on, the analysis of photocurrent transients obtained by irradiating several nanoporous carbon electrodes exhibited different responses, with either anodic or cathodic photocurrent, and transient shapes, thus demonstrating the distinct nature of the catalysed reaction occurring onto electrode/electrolyte interface. The second stage deals with hybrid nanoporous carbon/semiconductor (i.e. WO3) electrodes which allowed to explore the role of nanoporous carbon as additive towards water oxidation reaction. The presence of carbon material had a notable effect on the hybrid electrode performance, in terms of conversion efficiency (IPCE), likely due to the improved collection of the photogenerated electrons by carbon matrix. An optimal amount of carbon additive of ca. 20 wt.% was obtained for the best performing hybrid electrode, with a twofold IPCE compared to that obtained for bare WO3 electrode. The effect of carbon matrix on WO3 performance was found dependent on semiconductor crystalline structure.

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Since the beginning of the Industrial Revolution, the global energy consumption has been continuously increasing, supplied mainly by coal, oil and natural gases. Unfortunately, this consumption is linked to the emission of greenhouse gasses such as CO2 to the atmosphere. For this reason, it is extremely important to look for sustainable and renewable energy sources in order to replace the commonly used fossil fuels. Within the different types of renewable energy sources, solar energy holds by far the largest potential capacity. In this respect, artificial photosynthesis is a promising technology not only to harvest solar energy, but also as a means of storage by producing energy-rich chemical fuels such as H2 from water. The main components of photoelectrochemical water splitting devices are the semiconductor light absorber photoelectrodes and the electrolyte. Chapter 1 reviews the fundamental aspects of photoelectrochemical water splitting and overviews the physics and electrochemistry of semiconductor materials. The second chapter describes the methodologies and techniques employed throughout the thesis. The experimental results are reported from Chapter 3 to 8, focusing on the development and further optimization of two photoelectrodes, concretely hematite and cupric oxide, besides the design and fabrication of tandem cells for standalone water splitting. In the case of hematite photoanodes, the main efforts have focused on its doping to enhance carrier density and mobility as a way of diminishing recombination. The major drawback present in cupric oxide photoelectrodes is their instability against photocorrosion, for this reason, research has focused on protecting them, both by impregnation and adsorption methodologies. Finally, a tandem cell composed by a hematite photoanode and a cupric oxide photocathode was developed. It is worth noting that a polymer electrolyte membrane (PEM) was employed as to facilitate upscaling and diminish the corrosion observed employing the typical acidic or basic liquid electrolytes.

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To meet the growing energy world demands, and in conjunction, lower CO2 production levels, near zero emission energy sources must be pushed to the forefront as alternatives to fossil fuels. Photoelectrochemical (PEC) cells are a potential alternative to fossil fuels and have recently generated much interest because of their potential to electrolyze water into hydrogen fuel from sunlight. But in order to be competitive with fossil fuels, understanding the mass-transfer limitations in PEC systems is critical. This work focuses on the addressing the mass-transfer limitations in a conceptually novel PEC cell reactor, the Dual Bed Colloidal Suspension Reactor (DBCSR). Mass-transfer correlations for the DBCSR are presented. The correlations are based on experimental data obtained using two fabricated diffusion cells. The working correlation representative of both cells is given. An analysis of the orientation of the gas sparger suggests that the transport phenomena in both cells is not the same, and therefore using two correlations to represent similar systems is justified. An energy analysis is presented that shows that gas sparging is a low energy consumption option to mitigate mass-transfer limitations. Future work is suggested for better understanding the mass-transfer behavior in the DBCSR.

Cette thèse porte sur la modification d'électrodes par des polymères électrogénérés, capables d'immobiliser une biomolécule et/ou de fournir des propriétés de transduction électrochimique afin d'élaborer des biocapteurs à ADN faisant intervenir différents types d'interactions : ADN/protéine de réparation, hybridation et aptamère/molécule cible.Dans un premier temps, nous avons immobilisé la protéine Formamidopyrimidine ADN Glycosylase (Fpg) de D. radiodurans portant un tag histidine sur un film de poly-(pyrrole-NTA) via l'interaction NTA/Cu2+/Histidine. Dans le but d'étudier, par spectroscopie d'impédance électrochimique et SPR, l'interaction de cette protéine avec un duplex d'ADN sans lésions et un duplex d'ADN portant une lésion -oxo-guanine (8-oxo-G), car la Fpg est une protéine impliquée dans la réparation de l'ADN lorsque celui-ci comporte un site 8 (8-oxo-G).Dans un second temps, nous avons élaboré un biocapteur photoélectrochimique à partir d'un complexe multifonctionnel, (Ru(bpy-pyrrole)2(dppn)]2+) (bpy-pyrrole=4-méthyl-4'-butylpyrrole-2,2'-bipyridine, dppn=benzo[i]dipyrido-[3,2-a:2'.3'-c]phénazine) pouvant être électropolymérisé, intercalé l'ADN et photoactivé. La preuve de concept a été réalisée pour une séquence type d'ADN du VIH. Une limite de détection de 10-15 mol.L-1 et une sensibilité de 0,01 unité par décade avec une gamme de linéarité allant de 10-15 à 10-10 mol.L-1 ont été obtenue. Puis, nous avons conçu un aptacapteur pour la détection de la cocaïne à l'aide d'un aptamère double-fragment, formant une seule entité en présence de cocaïne, pouvant être immobilisée par intercalation sur le ligand dppn du métallopolymère. Ainsi une gamme de linéarité comprise entre 10-6 et 5x10-4 mol L-1 a été obtenue pour une concentration d'aptamère de 10-7 mol L-1, avec une limite de détection de l'ordre de 10-6 mol L-1. / This work focuses on the conception and optimization of impedancemetric and photoelectrochemical DNA biosensors based on the modification of electrodes with electrogenerated polymers. Different types of interactions involving DNA were studied: DNA/DNA repair protein, hybridization and aptamer/target molecule.In the first part, a poly-(pyrrole-NTA)-modified electrode was used to immobilize a protein involved in DNA repair: the Fpg (Formamidopyrimidine DNA Glycosylase) from D. radiodurans. This protein was previously tagged with histidine to be immobilized via a (NTA)Cu-histidine interaction. This protein detects and removes 8-oxo-guanine (8-oxo-G), a DNA damage caused by irradiation in double stranded DNA. We studied the behavior of this Fpg with DNA duplexes with and without 8-oxo-G nucleotide by electrochemical impedance spectroscopy and SPR.In the second part, we report the design of novel photoelectrochemical biosensor based on a multifunctional complex, (Ru(bpy-pyrrole)2(dppn)]2+) (bpy-pyrrole=4-methyl-4'-butylpyrrole-2,2'-bipyridine, dppn= benzo[i]dipyrido-[3,2-a:2'.3'-c]phenazine) exhibiting photo-sensitive, DNA-intercalating and electro-polymerizable properties. This modified electrode achieves photoelectrochemical detection on planar electrode by intercalating HIV-DNA duplexes or aptamer–cocaine complexes. The photocurrent generated through visible irradiation was correlated to the oligonucleotides concentration. Low detection limits of 10-15 mol L-1 and sensitivity of 0.01 unit per decade were measured, demonstrating excellent adequacy of these modified electrodes towards duplex HIV DNA detection. For the cocaine detection, the photelectrochemical aptasensor was based on the immobilization of a 10-7 mol L-1 double-fragment anti-cocaine aptamer and finally exhibited a linear range between 10-6 and 5x10-4 mol L-1 and a detection limit of 10-6 mol L-1.

This paper deals with the construction of photoelectrochemical cell, used for detection of ultraviolet radiation as a UV sensor. Photoelectrochemical cell consists of three layers, layer of photoactive semiconductor titanium dioxide, carbon electrodes and poly(vinyl alcohol) polymer electrolyte. The sensor layer enables the detection of UV radiation with the subsequent generation of photocurrent. Material printing techniques, such as screenprinting, pad printing and inkjet printing were used to produce the cell. Gel electrolyte was characterized by optical microscopy and rheometry. Sensor functionality was verified by use of electroanalytical techniques.