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.

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.