Electrocatalyst or support? Circumventing corrosion for long-lived zinc–air batteries

Hundreds of air-electrode variations exist for electrically rechargeable zinc–air batteries, but few studies rigorously compare their performance. Here, we review metrics from 100 reported zinc–air studies, which focus on air electrodes, to understand how to improve zinc–air longevity. We discuss how top performers in discharge voltage, charge voltage, and voltage hysteresis use air electrodes prone to carbon corrosion, but top performers in total areal discharge energy (>2 Wh cmgeo–2) use air electrodes that are either carbon free or resistant to carbon corrosion. Few zinc–air cells to date are evaluated at areal discharge capacity > 10 mAh cmgeo–2, which complicates identifying the more promising oxygen electrocatalysts and their supported expressions for further development. Our metrics-based assessment suggests that eliminating carbon or minimizing its corrosion in air electrodes offers an effective but still underappreciated route to improve the longevity of rechargeable zinc–air batteries. A key strategy to circumvent corrosion of carbon in the air cathode is to lower the charging voltage below 2 V, which requires improving the performance of oxygen-evolution catalysts (preferably cobalt free).