Rechargeable Zn–air batteries (ZABs) can play a significant role in the transition to a cleaner and more sustainable energy system due to their high theoretical energy density, high cell voltage, and environmental friendliness. ZAB’s air cathode is the principal determinant in predicting the battery’s overall performance, as it is responsible for catalyzing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharging and charging process, respectively. In this work, a detailed optimization study of the architecture of the air cathode was carried out using the benchmark bifunctional oxygen electrocatalyst (Pt/C-RuO₂). The air cathode composition and architecture were optimized regarding the choice of the commercial gas diffusion layer (GDL), the effect of hot pressing the catalyst layer (CL), and the optimum pore size of the current collector. The best cathode from this study shows a maximum power density (PD_max) of 167 mW/cm², with a round trip efficiency and a voltage gap (E_gap) of 59.8% and 0.78 V, respectively, indicating the air cathodes preparation approach proposed in this work as a promising strategy for the improvement of the overall performance of ZABs.

Microbial fuel cells (MFCs) are sustainable energy recovery systems because they use organic waste as biofuel. Using critical raw materials (CRMs), like platinum-group metals, at the cathode side threatens MFC technology’s sustainability and raises costs. By developing an efficient electrode design for MFC performance enhancement, CRM-based cathodic catalysts should be replaced with CRM-free materials. This work proposes developing and optimizing iron-based air cathodes for enhancing oxygen reduction in MFCs. By subjecting iron phthalocyanine and carbon black pearls to controlled thermal treatments, we obtained Fe-based electrocatalysts combining high surface area (628 m² g⁻¹) and catalytic activity for O₂ reduction at near-neutral pH. The electrocatalysts were integrated on carbon cloth and carbon paper to obtain gas diffusion electrodes whose architecture was optimized to maximize MFC performance. Excellent cell performance was achieved with the carbon-paper-based cathode modified with the Fe-based electrocatalysts (maximum power density-PD_max = 1028 mWm⁻²) compared to a traditional electrode design based on carbon cloth (619 mWm⁻²), indicating the optimized cathodes as promising electrodes for energy recovery in an MFC application.