Design of active and stable Co-Mo-S_x chalcogels as pH-universal catalysts for the hydrogen evolution reaction

Three of the fundamental catalytic limitations that have plagued the electrochemical production of hydrogen for decades still remain: low efficiency, short lifetime of catalysts and a lack of low-cost materials. Here, we address these three challenges by establishing and exploring an intimate functional link between the reactivity and stability of crystalline (CoS₂ and MoS₂) and amorphous (CoS_x and MoS_x) hydrogen evolution catalysts. We propose that Co²⁺ and Mo⁴⁺ centres promote the initial discharge of water (alkaline solutions) or hydronium ions (acid solutions). We establish that although CoS_x materials are more active than MoS_x they are also less stable, suggesting that the active sites are defects formed after dissolution of Co and Mo cations. By combining the higher activity of CoS_x building blocks with the higher stability of MoS_x units into a compact and robust CoMoS_x chalcogel structure, we are able to design a low-cost alternative to noble metal catalysts for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.