Dual-MOF-derived Ni@Fe-based core–shell heterostructures as trifunctional catalysts for methanol valorization-coupled H2 production via hybrid water electrolysis

Abstract

Developing efficient electrocatalysts for H₂ production via renewable resource-powered water electrolysis is a crucial aspect in replacing fossil fuels. Herein, Ni- and Fe-based dual metal organic framework (MOF)-derived core–shell NiO@Fe₃O₄/NF and trifunctional Ni₂P@Fe₂P/NF electrocatalysts are reported. Ni₂P@Fe₂P/NF required 268 and 229 mV overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at 50 mA cm⁻², while NiO@Fe₃O₄/NF required 375 and 311 mV, respectively, along with remarkable durability over 50 h. For the methanol oxidation reaction (MOR), Ni₂P@Fe₂P/NF required 109 mV lower potential than the OER. The fabricated alkaline conventional (OER + HER) Ni₂P@Fe₂P/NF(±) electrolyzer requires only 1.464 V cell voltage at 10 mA cm⁻² for overall water electrolysis (OWE), surpassing NiO@Fe₃O₄/NF(±) (1.679 V). The symmetrical hybrid (MOR + HER) water electrolyzer (HWE) fabricated using Ni₂P@Fe₂P/NF by replacing the anodic OER with the MOR reduces the required cell voltage to 1.458 V at 10 mA cm⁻². The electrolyzers also demonstrated remarkable durability over 70 h. The faradaic efficiency for H₂ production of the conventional Ni₂P@Fe₂P/NF(±) and NiO@Fe₃O₄/NF(±) electrolyzers is ∼90% and ∼88%, costing $1.48 and $1.59 per kg, respectively. Interestingly, the H₂ production cost of the hybrid Ni₂P@Fe₂P/NF(±) electrolyzer significantly reduces to $1.08 per kg with increasing faradaic efficiency to 99.7%, while simultaneously valorizing methanol to formate. This admirable performance underscores the viability of Ni₂P@Fe₂P/NF as a promising candidate for sustainable and efficient H₂ production.