Oxide-based precious metal-free electrocatalysts for anion exchange membrane fuel cells: from material design to cell applications

The shortage of fossil fuel has triggered global concern due to environmental issues. Consequently, fuel cells have been designed to efficiently generate electricity from clean and renewable fuels and have gained increasing attention. In recent years, the development of earth-abundant and cost-effective materials for application in fuel cells has become a key objective worldwide to push the commercialization of this technology. Anion exchange membrane fuel cells (AEMFCs) have become one of the most popular research topics because their alkaline environment allows a wider range of cost-effective materials to be employed as membranes and electrodes. Unitized regenerative AEMFCs (UR-AEMFCs) have also attracted great research interest because of their additional energy storage capability. The electrode performance plays critical role in the practical application of (UR-)AEMFCs. Oxide-based precious metal (PM)-free electrocatalysts have been developed as one class of promising candidates for application in (UR-)AEMFCs due to their many advantages, such as low cost, earth-abundant resources, intrinsic tunable electronic structures and surface properties, and structural flexibility, which can be utilized to lower the kinetic and thermodynamic barriers of oxygen electrocatalysis in an alkaline environment. Herein, we provide a comprehensive review of recent advances in oxide-based PM-free electrocatalysts used for (UR-)AEMFCs considering their synthetic strategies, such as morphology and structure control, electronic and surface properties. In addition, their design principles and corresponding catalytic performances are summarized. The current challenges with their wide application are also discussed to provide some guidelines for the design of next-generation oxide-based electrocatalysts for (UR-)AEMFCs.