Detection and Measurement of Interfacial Charge Transfer Relaxation Time: FeNi/NF Electrocatalysts for Water Splitting to Hydrogen

A cost-effective nickel-iron (Ni-Fe) alloy with a predominant face-centered cubic(111) crystallographic orientation is demonstrated as a high-performance electrocatalyst for the hydrogen evolution reaction (HER). This alloy demonstrates mutual hybridization of Ni and Fe d-orbitals, bringing its valence energy level close to the Fermi level, comparable to that of the benchmark Pt/C catalyst. While water-splitting electrocatalysts typically undergo surface structural evolution after each reaction cycle, the time scale of surface reconstruction during HER remains uncharted. This study presents a NiFe/NF alloy with an enriched (111) orientation, an active surface area of 24,217 ± 0.1 cm², an average crystallite size of 14.5 nm, and 0.634% lattice strain as an HER electrocatalyst. The electrocatalyst exhibits excellent performance towards HER, achieving a current density exceeding 800 mA/cm², an overpotential of -133 mV, and a hydrogen turnover frequency of 2.8 × 10¹² s^-1, and maintaining stable operation over 100 h. The distribution of relaxation time (DRT) analysis is introduced to deconvolute the HER process. A distinct high-frequency peak is attributed to interfacial charge transfer with a 2.38 × 10^-6 s relaxation time. Additionally, medium- and low-frequency peaks represent ion transport and hydrogen adsorption/desorption at 277.4 × 10^-6 and 905.1 × 10^-6 s relaxation times, respectively. The assignments can serve as a reference on the bulk and interfacial relaxation times critical for understanding electrocatalyst surface evolution using the DRT method, regardless of the material or type of electrochemical reaction. These findings are useful for advancing the design of low-cost, transition-metal-based alloys as catalysts for clean energy systems.