Aqueous air cathodes and catalysts for metal–air batteries

Metal–air batteries hold the promise of high specific energy and benign, recyclable components, which are critical to the long term goal of eliminating the use of fossil fuels. The critical components of metal–air batteries include the cathode electrocatalysts and the compatible electrolyte, which together enable the oxygen evolution (OER) and oxygen reduction (ORR) reactions, determining much of the battery's performance. In this review, we summarize the current status of research on bifunctional oxygen electrocatalysts for aqueous electrolytes and look forward to the advances which need to be made to achieve the promise of metal–air batteries.