Charge state modulation in metal-organic framework-based porous cobalt-incorporated nickel sulfide for efficient hydrogen evolution in anion exchange membrane water electrolyzer

For practical water electrolysis-based hydrogen production, the development of efficient electrocatalysts based on earth-abundant materials is highly desirable. Herein, metal-organic framework (MOF) derived Co-incorporated nickel sulfide (MD-Co/NiS₂) is demonstrated as a promising hydrogen evolution reaction (HER) electrocatalyst in an anion exchange membrane water electrolyzer (AEMWE). The MD-Co/NiS₂ exhibits a porous structure packed with numerous nanoparticles while maintaining the primary spherical morphology of the MOF, resulting in a large surface area with enhanced porosity. Furthermore, the reaction kinetics is enhanced by alleviating the charge polarization of Ni and S after Co incorporation. Owing to the integrated benefits of the geometrical and chemical structures, MD-Co/NiS₂ requires a low overpotential of 117 mV with long-term stability for 50 h at a current density of 10 mA cm⁻² in 1 M KOH. Moreover, AEMWE using MD-Co/NiS₂ as a cathode catalyst requires a low cell voltage of 1.97 V at a high current density of 1 A cm⁻², comparable to that of commercial Pt/C (2.01 V) and maintains cell performance for 50 h with a small potential increase of 55 mV.