Search

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 O2 electrocatalysis, and detail its further embedding into a gas diffusion electrode (GDE) architecture tested under relevant load conditions for rechargeable zinc-air battery application. One of the most promising ORR electrocatalyst, α-MnO2, was synthetized through a microwave-assisted hydrothermal process, which delivered highly reproducible, rapid and scalable synthesis products. The physical, chemical and electrochemical properties of the electrocatalyst were then investigated. The synthetized α-MnO2 was further combined with commercially available carbon black and Ni/NiO nanoparticles to create the bifunctional catalyst composite. 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. Finally, this thesis investigates the different degradation processes occurring at the GDE under successive charge/discharge current loads, and of their interactions/relationships. This study reveals the interplay between the four major degradation processes that contribute to the deterioration of the ORR/OER electrocatalysts and ultimately to the overall GDE failure: i) chemically- and (partially electrochemically)-driven degradation of the polytetrafluoroethylene binder component, ii) incremental surface restructuring of the Ni/NiO nanoparticles, iii) formation of carbonate / hydrogen carbonate through oxidation of the carbon component, iv) pore clogging of the GDE by potassium carbonate / hydrogen carbonate formed by the reaction of the alkaline electrolyte with the CO2 from the ambient air. Last, this work provides a roadmap of where to act/leverage for enhancing the stability of the electrode, in which the composition should be tailored according to the specific application.