Ultralow-Loading Ruthenium-Iridium Fuel Cell Catalysts Dispersed on Zn-N Species-Doped Carbon

Developing low-loading platinum-group-metal (PGM) catalysts is one of the key challenges in commercializing anion-exchange-membrane-fuel-cells (AEMFCs), especially for hydrogen oxidation reaction (HOR). Here, ruthenium-iridium nanoparticles being deposited on a Zn-N species-doped carbon carrier (Ru₆Ir/Zn-N-C) are synthesized and used as an anodic catalyst for AEMFCs. Ru₆Ir/Zn-N-C shows extremely high mass activity (5.87 A mg_PGM ^-1) and exchange current density (0.92 mA cm^-2), which is 15.1 and 3.9 times that of commercial Pt/C, respectively. Based on the Ru₆Ir/Zn-N-C AEMFCs achieve a peak power density of 1.50 W cm^-2, surpassing the state-of-the-art commercial PtRu catalysts and the power ratio of the normalized loading is 14.01 W mg_{PGM anode} ^-1 or 5.89 W mg_PGM ^-1 after decreasing the anode loading (87.49 µg cm^-2) or the total PGM loading (0.111 mg cm^-2), satisfying the US Department of Energy's PGM loading target. Moreover, the solvent and solute isotope separation method is used for the first time to reveal the kinetic process of HOR, which shows the reaction is influenced by the adsorption of H₂O and OH^-. The improvement of the hydrogen bond network connectivity of the electric double layer by adjusting the interfacial H₂O structure together with the optimized HBE and OHBE is proposed to be responsible for the high HOR activity of Ru₆Ir/Zn-N-C.