Fewer photons, more hydrogen: effects of dynamic irradiation on light-driven hydrogen evolution by thiomolybdate catalysts

Abstract

Molecular molybdenum sulfide clusters such as [Mo₃S₁₃]²⁻ ({Mo₃}) are promising earth-abundant catalysts for the light-driven hydrogen evolution reaction (HER). Their catalytic performance strongly depends on the irradiation conditions, which can influence both activity and stability. In this study, the prototype thiomolybdate {Mo₃} was combined with [Ru(bpy)₃]²⁺ as a photosensitizer (PS) to evaluate HER performance under dynamic irradiation conditions, a combination that has not been systematically explored before. A statistical Design of Experiments (DoE) approach was applied to assess the impact of three key parameters, i.e., irradiation intensity, on/off frequency, and duty cycle on the catalytic performance (assessed based on the turnover number). The results identify irradiation intensity as the main control parameter for catalytic activity, followed by duty cycle and on/off frequency. Interactions between frequency and duty cycle underline the importance of dark periods in the irradiation sequence. Optimization of the three key parameters resulted in a 102% increase in hydrogen production compared to continuous irradiation while reducing the required energy input by 25%. Mechanistic studies provide initial insights into photosensitizer and catalyst deactivation under the given irradiation conditions. These findings highlight the potential of controlled pulsed irradiation to improve energy use in light-driven homogeneous HER.