Improving the OER Performance of NiFe-LDH electrocatalyst via Heterostructure Formation with NiB in Alkaline Media

Abstract

Nickel-iron layered double hydroxides (NiFe-LDH) present a promising alternative to precious metal electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. This potential stems primarily from the Ni-O-Fe bond, which facilitates the formation of catalytically active sites. However, Fe sites in NiFe-LDH are prone to leaching during the OER process, resulting in diminished activity and stability. This study investigates the catalytic activity of heterostructures NiFe-LDH with NiB (NiFe@NiB) compared pristine nickel boride (NiB) and NiFe-LDH. The properties of NiB, such as electrical conductivity, surface area, and coordination number, can be finely tuned through annealing temperature. Notably, boron, acting as an electron acceptor, induces changes in the nickel oxidation state (Ni³⁺ → Ni(³⁺δ)⁺), which drives a phase transformation from β-NiOOH to γ-NiOOH. The γ-NiOOH structure in the NiFe@NiB enhances the intrinsic catalytic activity compared to the β-NiOOH structure of NiFe-LDH. The NiFe@NiB composite exhibits an approximately fivefold increase in surface roughness and a 9.95-fold enhancement in electrochemical surface area (ECSA) relative to NiFe-LDH. Additionally, the intrinsic activity, as represented by turnover frequency, increased by 6.31%. Consequently, the NiFe@NiB achieved a significantly reduced overpotential of 280 mV at 10 mA cm⁻², compared to 355 mV for NiFe-LDH under alkaline OER conditions. Furthermore, the potential of NiFe-LDH increased by 39 mV over 130 hours, whereas NiFe@NiB exhibited only a 17 mV increase, reflecting a 41% improvement in stability. The NiFe@NiB catalyst demonstrated negligible changes in charge transfer resistance (Rct) and overall catalytic activity during durability testing, highlighting its robust performance and long-term stability.