MOF-on-MOF-Derived Ultrafine Fe<sub>2</sub>P-Co<sub>2</sub>P Heterostructures for High-Efficiency and Durable Anion Exchange Membrane Water Electrolyzers.

Zhang, Hua; Chen, Anran; Bi, Zenghui; Wang, Xinzhong; Liu, Xijun; Kong, Qingquan; Zhang, Wei; Mai, Liqiang et al. · ACS Nano · 2023

basic_science · Level V

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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 Fe<sub>2</sub>P and Co<sub>2</sub>P nanoparticles, which are well anchored on N and P dual-doped carbon porous nanosheets (Fe<sub>2</sub>P-Co<sub>2</sub>P/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 Fe<sub>2</sub>P-Co<sub>2</sub>P/NPC catalyst only requires a low overpotential of 175 mV to achieve a current density of 1000 mA cm<sup>-2</sup>. 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<sup>-2</sup> over 1000 h in a practical AEMWE at an estimated cost of US$0.79 per kilogram of H<sub>2</sub>, which achieves the target (US$2 per kg of H<sub>2</sub>) set by the U.S. Department of Energy (DOE).