Porous silicon-nanowire-based electrode for the photoelectrocatalytic production of hydrogen

Photoelectrochemical water splitting is a sustainable and environmentally friendly way to produce green hydrogen, for which the practical fabrication of low-cost photoelectrodes remains a challenge. Here we report a porous photocathode assembly based on silicon nanowires (SiNW) as a light absorber and non-precious molybdenum sulfide (MoSx) as a hydrogen-evolution catalyst. Tuning the SiNW diameter is key to select the light absorption wavelength range of the system. We demonstrate a facile and robust route to synthesize SiNWs with a controlled diameter from 13 to 48 nm directly on a porous conductive support. The high quality and homogeneity of the SiNWs grown by this method also allowed drawing unprecedented conclusions on the growth process, hinting towards a silylene path. Photocathodes baring SiNWs covered with MoSx perform photoelectrocatalytic production of hydrogen for several hours with a faradaic yield over 98%. Building a porous photocathode for solar hydrogen production with earth-abundant materials: silicon nanowires to harvest light, molybdenum sulfide to turn protons into hydrogen.