Sol-gel derived nanostructure electrocatalysts for oxygen evolution reaction: A review

Abstract

In the hunt for alternative energy sources attributed to the depletion of fossil fuels, green energy hydrogen produced from water splitting reaction is considered to be a promising candidate due to its high energy density and zero carbon emission during the process. This reaction involves two electrons while producing hydrogen in the cathode and four electrons while producing oxygen in the anode. So, the Oxygen Evolution Reaction (OER) is also as crucial as the Hydrogen Evolution Reaction (HER). Due to the sluggish kinetics of OER and the low abundant, cost-effective state of art catalyst RuO2, IrO2 (noble metals); advancement of alternative low-cost, highly abundant, reasonably active, and stable catalysts for industrial application becomes essential. The sol-gel process is such a method that involves a wet chemical synthesis from low-cost transition metal precursor for the production of various nanostructures specifically oxide materials. In recent decades, a plethora of sol-gel synthesized materials comprising a metal oxide, hydroxide, phosphide, sulfides, and their derivatives, heterostructure catalysts have demonstrated remarkable efficiency in promoting water splitting activities including Oxygen evolution reaction. In this method, the precursor molecules are mainly dissolved in alcohols or water forming a sol, and then converted to gel via various approaches and eventually dried to get the resultant catalyst. Anticipating continuous growth in research on these materials due to their cost-effective, easy synthesis process, and ability to execute industrial applications, a comprehensive review addressing the enhancement of sol-gel synthesized composites becomes imperative. This review aims to provide a thorough analysis of the recent research advancements in the sol-gel approach and resulting materials for OER. It particularly focuses on recent developments, showcasing their potential applications and reasons for displaying elevated catalytic properties of the prepared materials. Lastly, detailed discussions on prospective avenues for future research are presented in this review.