Conversion of renewable energy resources (such as solar and wind) through water splitting to hydrogen and oxygen has attracted increasing attention. The sole product of hydrogen combustion is water, rendering a carbon-neutral energy cycle. Water splitting consists of two redox half reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Both of these two transformations involve multi- electron/proton movement and thus are kinetically sluggish. In order to accelerate the reaction rates for practical application, efficient catalysts are needed. State-of-the-art catalysts for water splitting are usually composed of noble metals, such as platinum, ruthenium, and iridium, whose scarcity and high cost limit their wide employment. Consequently, it is of critical importance to develop competent and non-precious catalysts via low-cost preparation. Owing to the thermodynamic convenience and potential application in proton exchange membrane and alkaline electrolyzers, traditionally, most HER catalysts were developed under strongly acidic conditions while OER catalysts under strongly alkaline conditions. In order to accomplish overall water splitting, the coupling of HER and OER catalysts in the same electrolyte is mandatory. This thesis will summarize our recent efforts towards developing 1st-row transition metal-based sulfides and phosphides for electrocatalytic water splitting under ambient conditions.

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Les phosphures de métaux de transition nanométriques trouvent de nombreuses applications, notamment en catalyse hétérogène. Les silices mésoporeuses organisées (SMO) de type SBA-15, grâce à leurs paramètres physico-chimiques ajustables (surface spécifique, taille de pores, épaisseur de parois, etc.) et la reproductibilité de leurs synthèses, sont des supports de nanoparticules (NPs) de choix. Dans ce contexte, l'objectif de cette thèse est de synthétiser des NPs de phosphure de cobalt dans les pores de matrices de type SBA-15 à partir de clusters organométalliques comme uniques précurseurs. Dans une première partie, nous étudions le comportement de trois clusters contenant un ou plusieurs ligands phosphorés à haute température. Ceux-ci présentent des rapports Co/P différents, ce qui a un impact direct sur la phase phosphure obtenue après activation. Nous suivons également l'influence de l'atmosphère et de la température sur les phases formées lors du traitement thermique. Pour contrôler la taille et la polydispersité des NPs étudiées, nous avons imprégné le cluster précurseur [Co4(CO)10(µ-NH(PPh2)2)] dans des SMO de type SBA-15. L'atmosphère et la température choisies pour le traitement thermique influent sur la phase obtenue, comme précédemment, mais les conditions ne sont pas identiques. De plus, des phases parasites ferromagnétiques sont formées et des lavages à l'acide chlorhydrique concentré sont nécessaires pour s'en affranchir. Enfin, la préparation de grandes quantités de produit (transfert d'échelle) requiert l'utilisation d'un volume contrôlé lors du traitement thermique, pour assurer une homogénéité dans l'échantillon. / Nanosized transition metal phosphides find applications in various fields, including heterogeneous catalysis. Ordered mesoporous silica (OMS) such as SBA-15 are supports of choice for nanoparticles (NPs), since they feature adjustable microstructural parameters (specific surface area, pore size, wall thickness, etc.) and reproducible synthesis conditions. In this context, the goal of this PhD work is to synthesize cobalt phosphide NPs within the pores of SBA-15-type OMS, starting from organometallic clusters as single-source precursors. First, we study the behavior of three organometallic clusters bearing one or more phosphine-based ligands at high temperatures. Depending on the initial Co/P ratio, those clusters afford different phosphide phases. We also monitored the influence of the atmosphere and the temperature during the thermal treatment on the phases obtained. To control size and polydispersity of the NPs, we impregnated the cluster precursor [Co4(CO)10(µ-NH(PPh2)2)] in SBA-15-type OMS. As in the previous case, atmosphere and temperature influence the obtained phase, but the conditions are different. Moreover, ferromagnetic impurities are formed and it is necessary to wash the samples with concentrated hydrochloric acid to remove them. Finally, larger quantities of product can be prepared (scale-up) but the volume of sample thermally treated at once needs to be controlled precisely to ensure homogeneity of the final product.

The physical and chemical properties of In- and Au- interfaces with In[0.53]Ga[0.47]As/InP(100) and In[0.52]Al[0.48]As(100) formed at room and low temperatures have been studied. Current-voltage measurements have indicated that In contacts to Ino[0.53]Ga[0.47]As(100) formed at 80K exhibit significantly higher Schottky barriers (&phis;b=0.45 eV) than In diodes formed at 294K (&phis;b=0.30 eV), whereas Au diodes formed on In[0.53]Ga[0.47]As(100) at either low temperature or room temperature exhibit Ohmic behaviour. The reactions occurring during interface formation at room and low temperatures have been investigated using soft X-ray photoemission spectroscopy (SXPS) and Transmission Electron Microscopy (TEM).The results presented show that In metallisation of In[0.53]Ga[0.47]As(100) at room temperature results in a predominantly three dimensional mode of growth, accompanied by the out-diffusion of As. Low temperature (125K) metallisation appears to reduce clustering and inhibit As out-diffusion. Examination of the resulting interfaces by TEM confirm the more uniform nature of the metal layers formed at low temperature. Metallisation temperature seems to have little effect on the formation of Au-In[0.53]Ga[0.47]As(100) interfaces, other than to reduce the extent of overlayer clustering, with As out-diffusion apparent for both low and room temperature Au deposition. Interfaces formed between In and In[0.52]Al[0.48]As(100) at both low and room temperature were relatively abrupt with no out-diffusion of substrate species into the metal overlayer. Low temperature metallisation again appeared to reduce overlayer clustering, with TEM studies showing a smaller grain size at low temperature. Au deposition onto In[0.52]Al[0.48]As(100) produced similar interfaces formed at room and low temperature. As diffuses into the Au overlayer to form an Au/As compound at both temperatures, resulting in an interface that is complex and reacted. The degree of overlayer clustering is also thought to be much less pronounced for Au deposition compared to In deposition. Barrier heights measured by SXPS during the study, show good agreement with reported current-voltage measurements for Au and In diodes formed on both In[0.53]Ga[0.47]As/InP(100) and In[0.52]Al[0.48]As(100). Possible mechanisms for the observed adaptation of the pinning position are discussed in the context of current models of Schottky barrier formation.