MOF-on-MOF-Derived Ultrafine Fe₂P-Co₂P Heterostructures for High-Efficiency and Durable Anion Exchange Membrane Water Electrolyzers

Abstract

The alkaline hydrogen evolution reaction (HER) in an anion exchange membrane water electrolyzer (AEMWE) is considered to be a promising approach for large-scale industrial hydrogen production. Nevertheless, it is severely hampered by the inability to operate tolerable HER catalysts consistently under low overpotentials at ampere-level current densities. Here, we develop a universal ligand-exchange (MOF-on-MOF) modulation strategy to synthesize ultrafine Fe₂P and Co₂P nanoparticles, which are well anchored on N and P dual-doped carbon porous nanosheets (Fe₂P-Co₂P/NPC). In addition, benefiting from the downshift of the d-band center and the interfacial Co-P-Fe bridging, the electron-rich P site is triggered, which induces the redistribution of electron density and the swapping of active centers, lowering the energy barrier of the HER. As a result, the Fe₂P-Co₂P/NPC catalyst only requires a low overpotential of 175 mV to achieve a current density of 1000 mA cm^-2. The solar-driven water electrolysis system presents a record-setting and stable solar-to-hydrogen conversion efficiency of 20.36%. Crucially, the catalyst could stably operate at 1000 mA cm^-2 over 1000 h in a practical AEMWE at an estimated cost of US$0.79 per kilogram of H₂, which achieves the target (US$2 per kg of H₂) set by the U.S. Department of Energy (DOE).