Molecular and Material Engineering of Photocathodes Derivatized with Polyoxometalate-Supported {Mo₃S₄} HER Catalysts

Molecular engineering of efficient HER catalysts is an attractive approach for controlling the spatial environment of specific building units selected for their intrinsic functionality required within the multistep HER process. As the {Mo₃S₄} core derived as various coordination complexes has been identified as one as the most promising MoS-based HER electrocatalysts, we demonstrate that the covalent association between the {Mo₃S₄} core and the redox-active macrocyclic {P₈W₄₈} polyoxometalate (POM) produces a striking synergistic effect featured by high HER performance. Various experiments carried out in homogeneous conditions showed that this synergistic effect arises from the direct connection between the {Mo₃S₄} cluster and the toroidal {P₈W₄₈} units featured by a stoichiometry that can be tuned from two to four {Mo₃S₄} cores per {P₈W₄₈} unit. In addition, we report that this effect is preserved within heterogeneous photoelectrochemical devices where the {Mo₃S₄}-{P₈W₄₈} (thio-POM) assembly was used as cocatalyst (cocat) onto a microstructured p-type silicon. Using a drop-casting procedure to immobilize cocat onto the silicon interface led to high initial HER performance under simulated sunlight, achieving a photocurrent density of 10 mA cm^-2 at +0.13 V vs RHE. Furthermore, electrostatic incorporation of the thio-POM anion cocat into a poly(3,4-ethylenedioxythiophene) (PEDOT) film is demonstrated to be efficient and straightforward to durably retain the cocat at the interface of a micropyramidal silicon (SimPy) photocathode. The thio-POM/PEDOT-modified photocathode is able to produce H₂ under 1 Sun illumination at a rate of ca. 100 μmol cm^-2 h^-1 at 0 V vs RHE, highlighting the excellent performance of this photoelectrochemical system.