Unveiling the role of gas permeability in air cathodes and performance enhancement by waterproof membrane fabricating method

摘要

Air cathode is the most popular oxygen reduction reaction (ORR) cathode with various applications in energy conversion and environmental purification. Understanding the role of gas permeability in air cathodes is crucial for its fabrication and operation optimizations. Herein, the correlations between gas permeability and performance are investigated by two experimental setups. One measures the gas permeability and the other evaluates the pressure-dependent performance. The results show two distinct ORR performances with respect to the gas permeability. The performance in low gas permeability is shown to depend on the gas permeability, oxygen partial pressure and solution convection, with obvious limiting current observed. Once the gas permeability surpasses a threshold value, suggested as 2 x 10(-12) m, the performance becomes less dependent on those factors, without limiting current observed. These observations are further mathematically demonstrated by the rate limiting process based on an oxygen transport model of air cathodes. An appropriately high gas permeability can eliminate the oxygen gas transport limitation and is vital for the performance enhancement. Following this principle, a novel waterproof membrane-based air cathode with high gas permeability is proposed, enabling cost savings in operation and production, and thus has great potential in practice.