Cobalt Phosphate-Modified (GaN)1–x(ZnO)x/GaN Branched Nanowire Array Photoanodes for Enhanced Photoelectrochemical Performance

Abstract

Photoelectrochemical water splitting based on suitable catalysts has attracted wide attention as a promising strategy to utilize solar energy to produce clean and renewable hydrogen fuel. Herein, we reported cobalt phosphate-modified (GaN)1–x(ZnO)x/GaN nanowire arrays on a high-temperature conductive GaN substrate toward enhanced photoelectrochemical water splitting by a facile two-step Au-assisted chemical vapor deposition method. The highly conductive Si-doped GaN substrate is designed to serve as a current collector and epitaxial substrate to grow GaN nanowires at high temperature. Meanwhile, high density of branched (GaN)1–x(ZnO)x nanowires with a tunable band gap, strong visible-light absorption, and high catalytic activity is deposited on the surface of GaN nanowires to act as active components to harvest light toward the oxygen evolution reaction. Such multi-junction heterostructures effectively enhance wide spectral utilization and light absorption and simultaneously accelerate the separation of electrons and holes and the transfer of photogenerated electrons from (GaN)1–x(ZnO)x nanowires to the GaN substrate collector and Pt electrode. The photocurrent density of the (GaN)1–x(ZnO)x/GaN nanowire array photoanode can reach 37.5 μA cm–2 at 1.23 V vs reversible hydrogen electrode and could be further enhanced to 186 μA cm–2 by modifying the cobalt phosphate cocatalyst, showing promising potential in clean hydrogen production.