Potassium–oxygen batteries (KOBs) are a promising energy storage technology with high theoretical energy density, low overpotential and a long cycle life. The cathode microstructure plays a significant role in the electrochemical performance of KOB. In this article, hierarchical porosity was introduced to commercially available carbon paper cathodes by thermal pretreatment in air at different pretreatment times. This pretreatment modifies the properties, such as surface area, defects, oxygen functional groups, etc. The discharge performance was determined at three different current densities, i.e., 0.1 mA/cm², 0.5 mA/cm², and 1.0 mA/cm². It has been found that an increase in specific surface area with the introduction of micropores and mesopores is beneficial for the improvement in the discharge capacity by enabling homogeneous discharge product, KO₂ distribution and high degrees of pore filling over the volume of the cathode. A reduction in the discharge overpotentials was observed, which is attributed to the introduction of oxygenic functional groups and defects. Samples treated for the longest pretreatment time of 24 h showed the highest discharge capacity of 5 mAh/cm² and lowest discharge overpotential of 0.03 V.

Potassium-oxygen batteries (KOBs) are a promising energy storage technology with high theoretical en-ergy density, low overpotential and long cycle life. Cathode microstructure plays a significant role in the electrochemical performance of KOB. In this article, hierarchical porosity was introduced to commer-cially available carbon paper cathodes by the thermal pretreatment in air at different pretreatment times. This pretreatment modifies the properties, such as, surface area, defects, oxygen functional groups etc. and it has been found to enhance the discharge capacity and it result in reduction of dis-charge overpotentials.