Unassisted HI photoelectrolysis using n-WSe2 solar absorbers

Abstract

Molybdenum and tungsten diselenide are among the most robust and efficient semiconductor materials for photoelectrochemistry, but they have seen limited use for integrated solar energy storage systems. Herein, we report that n-type WSe₂ photoelectrodes can facilitate unassisted aqueous HI electrolysis to H₂(g) and HI₃(aq) when placed in contact with a platinum counter electrode and illuminated by simulated sunlight. Even in strongly acidic electrolyte, the photoelectrodes are robust and operate very near their maximum power point. We have rationalized this behavior by characterizing the n-WSe₂|HI/HI₃ half cell, the Pt|HI/H₂||HI₃/HI|Pt full cell, and the n-WSe₂ band-edge positions. Importantly, specific interactions between the n-WSe₂ surface and aqueous iodide significantly shift the semiconductor’s flatband potential and allow for unassisted HI electrolysis. These findings exemplify the important role of interfacial chemical reactivity in influencing the energetics of semiconductor-liquid junctions and the resulting device performance.