The architecture of bifunctional Mn-Ni oxide-based Zn-air battery GDEs: Fabrication, functional testing and ageing analysis

Electrically rechargeable alkaline zinc-air batteries (RZAB) are still under development, yet they offer significant potential for both stationary and emerging mobile energy storage applications. The primary advantages arise from using materials that are abundanlt, low-cost, inherently safe, and environmentally benign, combined with established recycling methods and favourable life-cycle economics. However, a major bottleneck in current RZAB technology lies in is the air gas-diffusion electrode (GDE). Fabrication and testing protocols for GDEs remain poorly defined. Morevoer, these electrodes face substantial challenges in terms of efficiency and durability. This study focuses on the fabrication, testing, and ageing analysis of GDEs produced via spray coating. The electrodes studied employ a dual-catalyst system: α-MnO₂ for the oxygen reduction reaction (ORR) and Ni/NiO nanoparticles for the oxygen evolution reaction (OER). The electrodes were evaluated in a half-cell configuration, using a custom cycling protocol. Their overpotential response is modelled using a thin-film flooded agglomerate model. Additionally, post mortem analyses were undertaken: scanning electron microscopy (SEM) examined morphological changes in the active layer and Raman spectroscopy probed catalyst phase changes following cycling. The results indicate that GDE depends critically on effective porosity both in the as-fabricated state and as the electrode evolves during operation. The former aspect can be controlled by thickness tuning and fabrication protocols, while the latter can be mitigated by advanced OER management stategies. In this study, following a degradation-mode analysis, we propose two strategies to minimize damaging of the porosity network: one, by engineering the spatial distribution of the OER through tailored Ni/NiO synthesis; and two, by implementing a novel dual-air-electrode configuration.