Surface synergistic effect of sub-2 nm NiFeCr hydroxide nanodots yielding high oxygen evolution mass activities

Designing cost-effective electrocatalysts with high efficiency and stability for oxygen evolution reaction (OER) is crucial for hydrogen generation by water splitting and meta-air batteries. NiFe catalysts doped with transition-metal cations have offered an efficient approach to tuning the atomic and electronic structure, thus enhancing OER activity. However, most research focused on regulating the composition of atoms in large-sized catalysts, which remains a major challenge to achieving high atom utilization efficiency and optimal surface synergistic effect. Herein, a one-step co-precipitation method is presented to directly synthesize ultrafine NiFeCr trimetallic amorphous hydroxide nanodots (AND-NiFeCr, < 2 nm) to fully expose the atoms at the surface and near-surface region. Electronic-structure investigation revealed a strong synergistic electronic interaction between Ni, Fe, and Cr cations, which subtly tailors ternary catalysts' local atomic and electronic configuration. Due to the refined ultrafine nano-and electronic-structure modulation, the optimized AND-NiFeCr (Ni:Fe:Cr = 5:3:2) catalysts demonstrated superior OER activity with a low overpotential of 271 mV at 10 mA cm-2. Moreover, an extraordinarily high mass activity of 4926 A gMetal-1 at the overpotential of 300 mV was achieved. This work provides a novel surface synergistic effect strategy to design highly efficient NiFe-based ultrafine hydroxide OER catalysts with high atomic utilization efficiency.