Pore Surface Engineering of Fe-N-C Structure of Oxygen Electrocatalysis in an Alkaline Chemical Energy Conversion

Abstract

With the rise of the carbon-neutral era, hydrogen's importance as an energy source has surged. Its electrochemical production aligns well with carbon-neutral goals, minimizing emissions during use. Chemical energy conversion under alkaline conditions gains competitiveness by employing non-platinum catalysts. Various metal species, like Fe and Co, intentionally enhance Oxygen Reduction Reaction (ORR) catalytic activity in heteroatom-doped carbons. Among them, Fe-N decorated carbons (Fe-N-C) have been extensively studied due to synergistic interactions between Fe and N species on carbon substrates, boosting ORR activity. Despite substantial efforts by researchers to enhance the activity and durability of non-platinum catalysts, there are instances where the excellent performance observed in single-cell tests, creating Membrane-Electrode Assemblies (MEAs) with the catalyst, is not faithfully replicated. This discrepancy may be attributed to three factors: differences in reactant supply and reaction environments between half-cell and MEA, electrodeposition techniques, and the influence of interfaces in single cells. Among these factors, our study specifically investigates the impact of interfaces. MEA stands as a critical single-cell component, comprising electrolyte (membrane)/catalyst and catalyst/substrate interfaces. The reduction of interfacial resistance was anticipated to enhance overall performance, ultimately connected to homogeneous catalysis within the electrode. Focusing on increasing catalyst availability, we synthesized Fe-N-C catalysts with a porous particle structure. Our findings confirm that the porous structure and surface properties of the catalyst contribute to the formation of triple-phase boundaries above the electrode, reducing electrolyte/catalyst interfacial resistance and thereby enhancing single-cell performance. Additionally, the use of Fe-N-C, a porous N-doped carbon, as a substrate for the Oxygen Evolution Reaction (OER) catalyst, further improves electrolysis performance by densely loading high surface area exposed nanoparticles onto a three-dimensional conductive framework.