Ni and Co oxide water oxidation electrocatalysts: Effect of thermal treatment on catalytic activity and surface morphology

Research on renewable energy is flourishing, as it promises to reduce costs and deliver clean energy for the future. Water oxidation (WO) is one of the most promising and fascinating research fields, offering environmentally friendly renewable fuel sources. However, to make this a reality, efficient WO electrocatalysts (WOEs) have to be prepared from readily available and cost-effective sources. The catalytic activity of WOEs is directly related to their structure and synthesis process. Thus, researchers have focused on preparing Ni and Co (Ni/Co) oxide WOEs through various thermal treatment processes (TTPs) owing to their simplicity, cost effectiveness, and ability to tune the physicochemical properties of the WOEs. In this review, the effect of TTPs on the catalytic activity of Ni/Co oxide-based WOEs were carefully evaluated. To do so the effect of TTPs on the structure-activity relationship (SAR), their advantages and limitations, and how these methods can be properly optimized for preparing Ni/Co oxide WOEs has been discussed based on published reports. Also, the electrochemical techniques and parameters that are most commonly utilized in determining the catalytic activity of WOEs has been discussed along with a general mechanism for WO at the Ni/Co oxide electrocatalysts.