Real-Time Monitoring of Surface Effects on the Oxygen Reduction Reaction Mechanism for Aprotic Na–O2Batteries

Discharging of aprotic sodium–oxygen (Na–O2) batteries is driven by the cathodic oxygen reduction reaction in the presence of sodium cations (Na+-ORR). However, the mechanism of aprotic Na+-ORR remains ambiguous and is system dependent. In-situelectrochemical Raman spectroscopy has been employed to study the aprotic Na+-ORR processes at three atomically ordered Au(hkl) single-crystal surfaces for the first time, and the structure–intermediates/mechanism relationship has been identified at a molecular level. Direct spectroscopic evidence of superoxide on Au(110) and peroxide on Au(100) and Au(111) as intermediates/products has been obtained. Combining these experimental results with theoretical simulation has revealed that the surface effect of Au(hkl) electrodes on aprotic Na+-ORR activity is mainly caused by the different adsorption of Na+and O2. This work enhances our understanding of aprotic Na+-ORR on Au(hkl) surfaces and provides further guidance for the design of improved Na–O2batteries.