Synergistic Defect-Interface Coupling in CoFe/NiFe/CoFe Layered Double Hydroxides for Efficient Oxygen Evolution Reaction.

The oxygen-evolution reaction for hydrogen generation is a slow reaction process, thus requiring electrocatalysts of high efficiency and earth abundance. Here, we report CoFe-NiFe-CoFe (CNC), a layered double hydroxide heterostructure fabricated on nickel foam by layer-by-layer electrodeposition. This approach allows for relatively better control of elemental distribution compared to typical hydrothermal procedures. The CNC electrode achieved a 10 mA cm-2 current density at an overpotential of only 210 mV and showed stability for 50 h at 200 mA cm-2. XPS results highlighted that surfaces terminated by CoFe exhibit significantly higher densities of defect-related oxygen species than those terminated by NiFe, which in turn is directly related to higher activity. From the electrochemical perspective, CNC has both a higher electrochemically active surface area and the lowest charge-transfer resistance compared to other configurations of CoFe and NiFe. Density functional theory calculations suggest that vacancy formation may be energetically more favorable in CoFe than in NiFe, and that interfacial synergy could plausibly contribute to optimizing the OER pathway. Especially, the calculations indicate that NiFe and CoFe derived sites may preferentially handle the early intermediate adsorption, while CoFe-NiFe interface could further influence the final OOH* → O2(g) step.