Stimulating Electron Delocalization of Lanthanide Elements through High-Entropy Confinement to Promote Electrocatalytic Water Splitting.

ABSTRACT

High-entropy alloys (HEAs) have aroused extensive attention in the field of catalysis. However, due to the integration of multiple active sites in HEA, it exhibits excessive adsorption behavior resulting in difficult desorption of active species from the catalyst surfaces, which hinders the catalytic efficiency. Therefore, adjusting the adsorption strength of the active site in HEA to enhance the catalytic activity is of great importance. By introducing rare-earth (RE) elements into the high-entropy alloy, the delocalization of 4f electrons can be achieved through the interaction between the multimetal active site and RE, which benefits to regulate the adsorption strength of the HEA surface. Herein, the RE Ce-modified hexagonal-close-packed PtRuFeCoNiZn-Ce/C HEAs are synthesized and showed an excellent electrocatalytic activity for hydrogen evolution reaction and oxygen evolution reaction with ultralow overpotentials of 4, 7 and 156, 132 mV, respectively, to reach 10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH solutions, and the assembled water electrolysis cell only requires a voltage of 1.43 V to reach 10 mA cm-2, which is much better than the performance of PtRuFeCoNiZn/C. Combined with the results of in situ attenuated total reflection infrared spectroscopy and density functional theory (DFT), the fundamental reasons for the improvement of catalyst activity come from two aspects (i) local lattice distortion of HEA caused by the introduction of RE with large atomic radius induces 4f orbital electron delocalization of RE elements and enhances electron exchange between RE and active sites. (ii) The electronegativity difference between the RE element and the active site forms a surface dipole in HEA, which optimizes the adsorption of the active intermediate by the HEA surface site. This study provides an insightful idea for the rational design of high-performance HEA- and RE-based electrocatalysts.