Synergistic effect of an atomically dual-metal doped catalyst for highly efficient oxygen evolution

Abstract

The oxygen evolution reaction (OER) involving multi-step electron transfer is a challenging approach for water-splitting due to its sluggish kinetics. It is desirable to explore more efficient electro-catalysts with earth-abundant elements. Herein, we employed a high-temperature polymerization method to develop a structure consisting of graphitic carbon nitride (g-C₃N₄) nanopatch enveloped carbon nanotubes (CNTs), where isolated Ni and Fe atoms were embedded into the tri-s-triazine units of g-C₃N₄ by forming a metal–N_x structure. The designed dual-metal catalyst exhibited remarkable OER performance with an extremely low overpotential (∼326 mV at 10 mA cm⁻²) and a small Tafel slope (67 mV per decade), which is superior to those of state-of-the-art electrocatalysts with metal–N_x coordination and the benchmark IrO₂/C catalyst. In combination with atomic microscopy observations, our synchrotron-based X-ray absorption spectroscopy results revealed that, as compared to single-metal (Fe or Ni) doped hybrids, the electronic structures of both Ni and Fe atoms were reconfigured in the obtained dual-metal samples. Notably, increase of the oxidative state in Ni sites after multi-metal doping directly contributed to more active sites and favored the OER process, assisted by the porous structure and good electrical contacts between CNTs and g-C₃N₄. This investigation clearly demonstrated a unique synergistic effect in atomically dual-metal doped catalysts, thus it may provide a versatile route to regulate the electronic structures of single atomic catalysts through engineering of neighboring elements and coordination number.