A comprehensive review on the recent developments in transition metal-based electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) is one of the key electrocatalysis technologies for the development of renewable energy conversion and storage systems like water splitting, metal-air batteries, and fuel cells. For the large-scale application of these technologies, highly efficient, low cost and stable electrocatalysts are very important. Recently, non-noble metal-based OER electrocatalyst has drawn fabulous research interest. Albeit, it may be difficult to include all the studies, this review aims to look over the recent progress and offer a comprehensive insight toward the OER. It begins with a fundamental introduction to the electrochemistry of OER electrocatalyst including the synthesis, and mechanism. In this review, a comprehensive investigation is made on various types of nanostructured materials including Co, Ni, Mn, Fe, Cu, and Zn-based transition metal oxide and multi-metal oxides such as spinels, perovskites, and layered double hydroxides. The crucial factors that are used to tune the activity of the catalyst towards OER are summarized, including nanostructure development, phase, morphology, crystal facet, defect, mixed-metal, and strain engineering for metal oxide, heteroatom doping, topological defects, and formation of metal-N-C composites. Finally, major applications, the current states challenges, and some perspectives for non-noble-metal-based OER electrocatalysts are discussed. This review will help to explore and develop better catalysts and units for practical applications and will offer a basic understanding of the OER process along with the standard parameters to evaluate the performance.