Regulating the Interlayer Anion Microstructure of NiFe LDH toward Efficient Electrocatalytic Water Splitting for Hydrogen Evolution

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Chinese explanation / 中文解读

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Original abstract

NiFe-layered double hydroxides (NiFe-LDH) are highly efficient electrocatalysts for water splitting, and their unique two-dimensional layered structure makes it possible to precisely regulate active sites and interfacial reaction environments. However, conventional modification strategies often face limitations due to the inherently narrow interlayer spacing of LDH materials. Herein, an anion-exchange strategy was employed to introduce five different anions (NO3−, Cl−, CO32−, SO42−, and PO43−) into the interlayer space. This study systematically investigated the regulatory effects of these intercalated anions on the structural features, electronic properties, and HER catalytic performance of the catalyst. On one hand, the size and charge differences of the anions effectively tune the interlayer spacing of LDH, which increases in the order of CO32−, NO3−, Cl−, PO43−, and SO42− intercalation. The enlarged interlayer spacing promotes electrolyte transport and optimizes the local microenvironment around the active sites, thereby accelerating the HER kinetics, as manifested by a progressively lower onset overpotential with increasing interlayer spacing. On the other hand, the introduction of anions regulates the electronic structure of Ni and Fe in the LDH layers, with the metal oxidation state gradually increasing in the order of SO42−, NO3−, CO32−, Cl−, and PO43− intercalation. Electron-rich (low-valence) metal centers promote electron transfer and lower the deprotonation energy barrier, thereby offering a kinetic advantage for the HER. As a result, the overpotential decreases as the valence state of the layer metal decreases. Under the combined effects, SO42− intercalation expands the interlayer spacing of NiFe-LDH from 0.768 to 0.855 nm, increases the electrochemical double-layer capacitance (Cdl) by 66% (from 2.24 to 3.72 mF·cm−2), and reduces the HER overpotential by 55 mV at 10 mA·cm−2 compared to the pristine LDH. In addition, the NiFe-SO42−-LDH-NFs catalysts exhibited outstanding electrocatalytic stability, with the photovoltaic-electrolysis system combined with GaInP2/InGaAs/Ge solar cells maintaining the STH efficiency above 25% over 100 h.

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