From Structure to Power: Monolithic Carbon Air Cathodes with an Optimized Active Distribution for Direct-Formate Fuel Cells

Abstract

Non-noble metal cathodes often suffer from limited oxygen reduction reaction (ORR) activity due to poor mass transport and insufficient active site availability, which restricts their application. This study presents a carbon-based air cathode featuring a monolithic, binder-free design aimed at enhancing the mass transfer and distribution of active sites. Characterization results indicate that the carbon-based monolithic air cathodes with a thickness of 1.5 mm (Fe@AC-1.5) possess a well-distributed pore structure that improves the oxygen transport capacity, thereby facilitating catalytic activity. Additionally, evaluation of the active site distribution of the cathode with a thickness of 2.4 mm (Fe@AC-2.4) revealed a comparable exponential distribution pattern. Furthermore, the findings demonstrate that the 1.5 mm thick monolithic air cathode prepared with agar (Fe@AC-1.5) contains numerous active sites for the ORR and an optimal pore distribution, resulting in an improved ORR activity. The direct-formate fuel cell utilizing Fe@AC-1.5 achieves a maximum power density of 22.63 mW cm^–2. This study introduces easily prepared carbon-based monolithic air cathodes with remarkable ORR properties and offers insights into active site distribution, thereby guiding future enhancements in the ORR performance.