Hollow nanostructured rare-earth-containing high-entropy carbides: Facile electrochemical synthesis and effective electrocatalytic performance for hydrogen evolution

High-entropy carbides (HECs) have attracted growing attention as promising noble-metal catalyst alternatives for the hydrogen evolution reaction. Nevertheless, the reported HEC nanocrystals remain confined to dense solid structures with metallic components limited to groups IVB-VIB. The first synthesis of hollow nanostructured high-entropy carbides (HfNbTaTiZr)C, (HfNbTaTiZrRE)C (RE=Gd, Ce, Y) and (HfNbTaTiZrCeY)C was achieved by a direct electroreduction process. Electrolysis was conducted at 3.1 V using a graphite anode and a cathode prepared from mixed oxides/carbon additive powders in molten CaCl₂-NaCl at 800 °C. The effects of carbon sources on the microstructure of the product were systematically investigated. The results show that the microstructure of HECs can be easily tailored from solid to hollow particles by selecting different carbon sources. All as-synthesized HECs exhibit a single face-centered cubic phase and compositional homogeneity from the nanoscale to the microscale. It was found that the engineered hollow nanostructure, coupled with the incorporation of rare-earth elements, significantly enhanced electrocatalytic performance of HECs for hydrogen evolution in an alkaline electrolyte. Specifically, the HECs incorporated with dual rare-earth elements exhibited superior performance to those with a single element. Among them, (HfNbTaTiZrCeY)C demonstrates superior hydrogen evolution reaction performance with a low overpotential of 167 mV, a small Tafel slope of 58.8 mV·dec^-1, and a low charge transfer resistance of 2.7 Ω. This work not only establishes a facile method for synthesizing various hollow rare-earth-containing high-entropy carbide nanoparticles, but also provides a novel strategy for the design of high-performance non-noble metal-based catalysts.