A thiomolybdate cluster for visible-light-driven hydrogen evolution: comparison of homogeneous and heterogeneous approaches

Abstract

This study investigates the hydrogen evolution reaction (HER) efficiency of two photosystems incorporating an all-inorganic molecular thiomolybdate [Mo₃S₁₃]²⁻ cluster as a HER catalyst. First, we delve into the performance of a homogeneous [Mo₃S₁₃]²⁻/[Ru(bpy)₃]²⁺ (Mo₃/Ru) dyad which demonstrates high turnover frequencies (TOFs) and apparent quantum yields (AQYs) at 445 nm approaching the level of 0.5%, yet its performance is marked by pronounced deactivation. In contrast, a heterogeneous approach involves anchoring [Mo₃S₁₃]²⁻ onto graphitic carbon nitride (GCN) nanosheets through weak electrostatic association with its triazine/heptazine scaffold. [Mo₃S₁₃]²⁻/GCN (Mo₃/GCN) displays effective H₂ generation under visible light, with TOF metrics on par with those of its homogeneous analog. Although substantial leaching of [Mo₃S₁₃]²⁻ species from the Mo₃/GCN surface occurs, the remaining {Mo₃}-based centers demonstrate impressive stability, leading to enduring HER performance, starkly distinguishing it from the homogeneous Mo₃/Ru photosystem. Photoluminescence (PL) quenching experiments confirm that the performance of Mo₃/GCN is not limited by the quality of the inorganic interface, but could be optimized by using higher surface area supports or a higher concentration of [Mo₃S₁₃]²⁻ sites. Our findings showcase complexities underlying the evaluation and comparison of photosystems comprising well-defined catalytic centers and pave the way for developing analogous surface-supported (photo)catalysts with broad use in energy applications.