Rational design of a low-cost, durable and efficient bifunctional oxygen electrode for rechargeable metal-air batteries

Economic viability of the electrochemical stationary storage of electricity produced by intermittent renewables is the bottleneck for a transition towards a fully green energy landscape. Abundance, inexpensiveness and facile preparation for novel active materials and performant electrodes facilitate scale-up and costs lowering upon their further integration into already existing manufacturing processes. Herein, we demonstrate the relevance of a low-cost approach and a design strategy for the preparation of an efficient material for bifunctional O-2 electrocatalysis, and detail its further embedding into a gas diffusion electrode (GDE) architecture tested under relevant load conditions for rechargeable zinc-air battery application. A plain preparation of the active material combines alpha-MnO2, obtained from a simplified synthesis procedure, commercially available carbon black and Ni/NiO nanoparticles. A systematic optimization of the surface concentration of the most active catalytic ensemble and synergetic effects for both oxygen reduction and oxygen evolution reactions, taken separately, shapes the design of a bifunctional electrocatalyst. Performances of GDEs surpass the vast majority of the previous concepts, with stable overpotentials (ca. 0.35 V for each reaction, 55 % energy efficiency) over 400 h at 20 mAh.cm(-2) load cycles (for both charge and discharge), bridging the gap between promising electrocatalyst material and realistic functional electrode.