Potassium Cobalt Pyrophosphate as a Nonprecious Bifunctional Electrocatalyst for Zinc-Air Batteries.

Economic and sustainable (ecological) energy storage forms a major pillar of the global energy sector. Bifunctional electrocatalysts, based on oxygen electrolysis, play a key role in the development of rechargeable metal-air batteries. Pursuing precious metal-free economic catalysts, here, we report K 2 CoP 2 O 7 pyrophosphate as a robust cathode for secondary zinc-air batteries with efficient oxygen evolution and oxygen reduction (OER||ORR) activity. Prepared by autocombustion, nanoscale K 2 CoP 2 O 7 exhibited excellent oxygen reduction and evolution reactions among all phosphate-based electrocatalysts. In particular, the OER activity surpassed that of commercial RuO 2 with low overpotential (0.27 V). First-principles calculations revealed that the bifunctional activity is rooted in the Co active site with the CoO 5 local coordination in the most stable (110) surface. This nanostructured (tetragonal) pyrophosphate can be harnessed as an economic bifunctional catalyst for zinc-air batteries.