Fe-Regulated Sulfidation of Ni-MOF to Construct an Fe-Ni(OH)2/Ni3S2 Heterojunction for Efficient Hydrogen Evolution in Both Acidic and Alkaline Media.

Abstract

Developing efficient and durable non-precious electrocatalysts for the hydrogen evolution reaction (HER) in both acidic and alkaline media is a critical challenge. Herein, we report a Fe-regulated sulfidation strategy that converts a Ni-MOF precursor into a Fe-doped Ni(OH)2/Ni3S2 heterojunction catalyst. Fe acts as a kinetic phase regulator that suppresses the complete conversion of Ni(OH)2 into Ni3S2, stabilizing a mixed phase architecture with abundant heterointerfaces and enlarged electrochemically active surface area. The optimized catalyst delivers exceptional HER performance, requiring overpotentials of only 163.3 mV at -10 mA cm-2 in 1 M KOH and 214.3 mV at -100 mA cm-2 in 0.5 M H2SO4, along with outstanding durability (200 h at -500 mA cm-2 in alkaline electrolyte and 100 h at -100 mA cm-2 in acidic electrolyte). Post-stability characterizations reveal pH-dependent reconstruction: under alkaline conditions, the Ni(OH)2 phase partially dissolves while the Ni3S2 framework remains; under acidic conditions, Fe2+ oxidation to Fe3+ forms a protective M-OH-rich oxide layer on Ni3S2. Density functional theory calculations identify Ni as the primary active site, with Fe functioning as an electronic modulator that redistributes electron density toward Ni and optimizes the d-band center. In alkaline media, the cooperative charge effect and upshifted d-band center synergistically promote water dissociation, with OH* desorption identified as the rate-determining step; in acidic media, strong electrostatic attraction from the highly negatively charged Ni sites dominates H* adsorption. This work highlights the pivotal role of heterojunction engineering and phase regulation in designing durable pH-universal HER catalysts.

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