Designing Binary Ru-Sn Oxides with Optimized Performances for the Air Electrode of Rechargeable Zinc-Air Batteries.

Because of the sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), binary ruthenium-tin oxides synthesized by a hydrothermal method with postannealing at 450 °C for 2 h are first proposed as bifunctional catalysts for these two reactions on the air electrode of rechargeable zinc-air batteries. The binary Ru-Sn oxides in various compositions show the typical oxide solid solution in the rutile phase. Among all binary Ru-Sn oxides, RuSn73 (70 atom % RuO2 and 30 atom % SnO2) and RuSn37 (30 atom % RuO2 and 70 atom % SnO2) show the highest catalytic activities toward the OER and ORR, respectively. Consequently, a novel design of the air electrode consisting of a RuSn37 coating on the carbon paper and a Ti mesh coated with RuSn73 (denoted RuSn(37-C|73-Ti)) is proposed to possess the optimal charge-discharge performances. A unique cell employing such an air electrode has been demonstrated to exhibit a very low charge-discharge cell voltage gap of 0.75 V at 10 mA cm-2. This cell with a peak power density of 120 mW cm-2 at the current density of 235 mA cm-2 also shows an outstanding charge-discharge stability over 80 h. This cell also exhibits an exceptionally high charge rate capability at 150 mA cm-2 with a low charging voltage of 2.0 V.