Noble‐Metal‐Free Oxygen Evolution Reaction Electrocatalysts Working at High Current Densities over 1000 mA cm⁻²: From Fundamental Understanding to Design Principles

Abstract

Alkaline water electrolysis provides a promising route for “green hydrogen” generation, where anodic oxygen evolution reaction (OER) plays a crucial role in coupling with cathodic hydrogen evolution reaction. To date, the development of highly active and durable OER catalysts based on earth‐abundant elements has drawn wide attention; nevertheless, their performance under high current densities (HCDs ≥1000 mA cm−2) has been less emphasized. This situation has seriously impeded large‐scale electrolysis industrialization. In this review, in order to provide a guideline for designing high‐performance OER electrocatalysts, the effects of HCD on catalytic performance involving electron transfer, mass transfer, and physical/chemical stability are summarized. Furthermore, the design principles were pointed out for obtaining efficient and robust OER electrocatalysts in light of recent progress of OER electrocatalysts working above 1000 mA cm−2. These include the aspects of developing self‐supported catalytic electrodes, enhancing intrinsic activity, enhancing the catalyst–support interaction, engineering surface wettability, and introducing protective layer. Finally, summaries and outlooks in achieving OER at industrially relevant HCDs are proposed.

Confinement Accelerates Water Oxidation Catalysis: Evidence from In Situ Studies

“…Third, the surface O * combines with OH − and forms adsorbed OOH species (OOH * ) [O* + OH − → OOH * + e − ], and the additional OH − reacts with the OOH * leading to the formation of adsorbed O 2 and H 2 O [OOH * + OH − → * + O 2 + H 2 O + e − ]. [ 36 ] Electrochemically, these reaction intermediates occur in three different potential regions: at the low potential (region ➀), * OH generation; in the mid potential (region ➁), metal redox transition; then, O 2 will be generated under high potential (region ➂, water oxidation regions). The three simplified processes of water oxidation involve the * OH species adsorption, * O radical formation, and * OOH transformation and desorption.…”

“…This redox process happens together with the formation of the O * , which is an essential intermediate (coupling with one OH − group to generate * OOH) for oxygen evolution. [34,35] Basically, the OER begins with the adsorption and discharge of OH [36] Electrochemically, these reaction intermediates occur in three different potential regions: at the low potential (region ➀), * OH generation; in the mid potential (region ➁), metal redox transition; then, O 2 will be generated under high potential (region ➂, water oxidation regions). The three simplified processes of water oxidation involve the * OH species adsorption, * O radical formation, and * OOH transformation and desorption.…”

Rational Design of Hydrogen Evolution Reaction Electrocatalysts for Commercial Alkaline Water Electrolysis

“…Under alkaline conditions, the slow and complex four‐electron transfer process of the OER has been fully emphasized in academia as well as industry, which has promoted the development of a large number of valid Ni‐based catalysts. [ 12,13 ] In contrast, although HER seems to have a simpler activation mechanism requiring two‐electron transfer steps, the lack of clarity in the HER mechanism under alkaline conditions often limits further exploitation of HER catalysts. [ 14 ] Meanwhile, the limitation of mass transfer at high current densities and catalyst stability issues likewise affect the industrial application of laboratory‐stage HER catalysts.…”

Deep Reconstruction of the NiFeSP Nanosheet Catalyst for Large Current–Density Water Oxidation

“…Hydrogen from electrochemical water splitting is viewed as a potentially game-changing solution to the world’s enormous energy demands in the face of rising energy and environmental challenges due to its high efficiency, reliability, and environmental protection. , However, the four-electron oxygen evolution reaction (OER) half-reaction in the water splitting process has sluggish kinetics, a large overpotential, and a complex mechanism that significantly impede the development of water electrolysis systems. , Although noble metals (Ru and Ir) and their oxides are still electrocatalysts for a commercial OER, their high cost seriously affects commercial benefits . Therefore, how to design OER catalysts with high activity, long life, and low cost, which are composed of rich earth elements, has become the focus of more and more researchers.…”