Transition metal-based self-supported anode for electrocatalytic water splitting at a large current density

Hydrogen produced from water electrolysis is a promising alternative to fossil fuels. The oxygen evolution reaction (OER), which occurs at the anode, involves a four-electron transfer process and requires a large potential to overcome the energy barrier. To address this challenge and reduce the cost associated with noble-metal catalysts, transition metal (TM) based catalysts offer a cost-effective solution. Compared to powder catalysts, TM-based catalysts in situ grown on conductive substrates are more suitable for industrial hydrogen production at large current density. Additionally, oxidation reactions with lower thermodynamic potential than OER have been explored as alternatives to reduce power consumption in electrohydrolysis hydrogen production. In this review, we provide an overview of the evaluation criterion, selection of substrate, preparation methods for self-supporting catalysts and their respective advantages and disadvantages. We also discuss the principle of active site selection and various strategies for enhancing the activity of catalysts, including metal doping, heteroatom doping, co-doping of both, heterojunctions, amorphization, compositing with conductive materials, morphology engineering, and creating superhydrophilic and superaerophobic surface. We then examine alternative anode reactions, such as urea oxidation, hydrazine oxidation, glucose oxidation and alcohol oxidation reactions. Finally, we outline the current challenges in the design of electrocatalysts and anodic oxidation reactions and provide an outlook on the future of hydrogen production using TM-based self-supported electrocatalysts.