A Review of Synthesis Techniques for Gallium-Zinc Oxynitride Solar-Activated Photocatalyst for Water Splitting

Converting a practically limitless energy source, such as sunlight, into chemical energy with very little or no carbon footprint will pose a major challenge in the coming decades. The technology exists to convert solar energy into chemical fuels, such as hydrogen, through overall water splitting to produce hydrogen and oxygen. However, the photocatalytic efficiency is still below the feasibility limit. Many photocatalyst materials have been developed for solar hydrogen generation through water splitting in the last four decades. Gallium-zinc oxynitride (GaN:ZnO) solid solution is reported to be a suitable photocatalyst for overall water splitting and to have the highest photocatalytic activity. The traditional synthesis method contains difficulties and inefficiencies, such as long nitridation of starting materials at high temperatures and low Zn content of the synthesized photocatalyst. A number of experiments have been conducted in recent years to develop new synthesis approaches. In this article, a comprehensive review of various synthesis techniques of GaN:ZnO solid solution, along with their advantages and disadvantages, are presented. This information is essential for improving the efficiency of the synthesis techniques of GaN:ZnO solid solution and its photocatalytic activity for overall water splitting.