Dodecagonal GaN Microrods: Chemical Stability of a-, m-, and c-Plane Walls and Their Application to Water-Splitting

Abstract

Photoelectrolysis of water is a sustainable option for the production of hydrogen fuel. GaN nano- or microstructures are considered for water-splitting due to their general high chemical stability and high surface-to-volume ratio enhancing the process effectiveness. In this study GaN structures with dodecagonal microrods are used as a working electrode for the water-splitting process. Microrods are grown using a plasma-assisted molecular beam epitaxy process allowing tailoring of microrod height and density. Their unique property is the of presence twelve sidewalls with alternating a- and m-plane orientations. This enables a simultaneous study of the chemical stability of c-, a-, and m-plane walls of GaN. The water-splitting process is performed using a 1 mol l⁻¹ NaOH electrolyte solution. Non-zero current measured at zero bias under illumination indicates that the process takes place. A degradation of the GaN structure is observed after a prolonged process time. In short-term exposures, etching of microrod sidewalls is observed. Roughening of the a-plane walls studied by transmission electron microscopy indicates that this orientation is etched with a fastest rate. The internal crystalline structure is not influenced by the etching and remains stable as shown by the X-ray absorption spectroscopy study.