In-situ photochemical fabrication of transition metal-promoted amorphous molybdenum sulfide catalysts for enhanced photosensitized hydrogen evolution

Abstract

Amorphous molybdenum sulfide catalysts (MoSx) can efficiently catalyze the H2 evolution reaction (HER); however, their catalytic activities are still limited that need to be improved. Herein, transition metal-promoted MoSx H2 evolution catalysts were facilely fabricated through an in-situ photochemical reduction with inexpensive organic dye as photosensitizers. Under visible light (λ ≥ 420 nm), the promotional effect of transition metals on the H2 evolution over MoSx follows the order of Co > Fe ≈ Ni > unpromoted > Cu > Zn in Erythrosin B-triethanolamine (ErB-TEOA) system. The most active Co-promoted MoSx (Co-MoSx) catalyst is amorphous and composed of inter-connected nanoparticles with diameters of 30–50 nm. The Co-MoSx catalyst contains both CoMoS phase and Co oxides/hydroxides. At the optimal reaction conditions, the Co-MoSx catalyst with Co:Mo ratio of 4:6 exhibits enhanced H2 evolution activity by 2 times as compared to unpromoted MoSx and turnover numbers (TONs) of 30 and 60 based on ErB and catalyst used, respectively. The Co-MoSx catalyst also shows a long-term stability without noticeable activity degradation. The formation pathways of Co-MoSx catalyst and the photocatalytic mechanism for enhanced H2 evolution performance were studied and a two-step reaction mechanism involved an oxidative quenching pathway of dye was proposed. This study demonstrates that in-situ concurrent photochemical fabrication with transition metal modification of amorphous MoSx catalyst is an effective strategy for development of MoSx-based HER catalysts with enhanced performances.