Optimization of electrolyte to significantly improve photoelectrochemical water splitting performance of ZnO nanowire arrays

Highlights: • ZnO nanowire arrays were prepared by an electrochemical deposition method. • ZnO nanowire array was used as photoanode for PEC water splitting. • PEC water splitting activities were evaluated in Na₂SO₃ and Na₂SO₄ electrolytes. • The photoanode shows enhanced PEC water splitting activity in Na₂SO₃ electrolyte. • The enhanced PEC water splitting is ascribed to depletion of hole by SO₃²⁻ anion. - Abstract: In this work, a simple and facile strategy has been applied to improve the photoelectrochemical (PEC) water splitting performance of ZnO nanowire arrays by the optimization of Na₂SO₄ and Na₂SO₃ electrolytes. The ZnO nanowire array electrode exhibits significant PEC water splitting enhancement in Na₂SO₃ electrolyte solution compared to in Na₂SO₄ electrolyte solution. The photocurrent density of ZnO nanowire array photoanode in Na₂SO₃ electrolyte solution is 6 times higher than that in Na₂SO₄ electrolyte solution at 0.5 V vs. Ag/AgCl. Mott-Schottky (MS) and electrochemical impedance spectroscopy (EIS) studies of ZnO nanowire array electrodes in Na₂SO₄ and Na₂SO₃ electrolyte solutions reveal that SO₃²⁻ anions consume the holes and efficiently improve the separation of photogenerated electron-hole pairs, leading to significant improvement for PEC water splitting performance in Na₂SO₃ electrolyte solution. This work provides a promising strategy to improve the PEC water splitting performance of photoanode materials by the optimization of electrolytes.