Oxygen Evolution Reaction in Alkaline Environment: Material Challenges and Solutions

Abstract

The oxygen evolution reaction (OER) generally exists in electrochemistry-enabled applications that are coupled with cathodic reactions like hydrogen evolution, carbon dioxide reduction, ammonia synthesis, and electrocatalytic hydrogenation. The OER heavily impacts the overall energy efficiency of these devices because the sluggish OER kinetics result in a huge overpotential, thus, a large amount of efficient catalysts are needed. The benchmark iridium and ruthenium (Ir/Ru)-based materials (mostly used in acid media) are, however, significantly limited by their scarcity. Non-precious metal-based catalysts (NPMCs) have emerged as the most promising alternatives; however, they tend to degrade quickly under the harsh operating conditions of typical OER devices. Another challenge is the unsatisfying performance of OER catalysts when integrated in real-world devices. Herein, the OER active sites for three mainstream types of NPMCs including non-precious transition metal oxides/(oxy)hydroxides, metal-free carbon materials, and hybrid non-precious metal and carbon composites are reviewed. In addition, possible degradation mechanisms for active sites and mitigation strategies are discussed in detail. This review also provides insights into the gaps between R&D of NPMCs for the OER and their applications in practical devices.