Understanding the limitations of catalytic processes enables the design of optimized catalysts. Here, femtosecond transient absorption spectroelectrochemistry is used to explore the photophysics of polyoxometalate-based covalent photosensitizer-hydrogen evolution catalyst dyads. The study shows that the presence of light-driven forward and backward electron transfer, i.e. ‘‘electron ping-pong’’, is a limiting factor for charge accumulation on the polyoxometalate. Based on this insight, chemical means of optimizing catalyst performance are proposed.