Cu²⁺ as a dynamic director for Ce-incorporated (CoFeNiCuCe)₉S₈ nanoballs for multifunctional electrocatalysis

High-entropy metal sulfides (HEMSs) have emerged as a new class of electrocatalysts, but their synthesis often faces challenges due to their inherent complexity arising from multi-metal interactions, especially with elements having large differences in atomic/ionic sizes, such as the redox-active rare-earth elements. Here, we report a low-temperature (200°C) hydrothermal strategy to fabricate Ce-incorporated (CoFeNiCuCe)9S8 nanoballs by leveraging Cu2⁺ as a dynamic director for this phase evolution. Time-resolved studies reveal a multistage growth pathway involving cation exchange, lattice strain-driven reconstruction, and coalescence of various low and medium entropy intermediates (CoFeNi)9S8, CuS/(CoFeNi)9S8, (CoFeNiCu)9S8, Ce2S3, Ce2S3/(CoFeNi)9S8, (CoFeNiCuCe)/S nanoplates) into monodisperse (CoFeNiCuCe)₉S₈ HEMS nanoballs. By systematically varying Cu:Ce ratios, we obtain five distinct configurations, and Ce-rich HEMS-4 (Cu:Ce = 1:4) exhibits superior multifunctional electrocatalytic performance, outperforming a series of lower- (Co9S8, (NiFe)9S8, and (CoNiFe)9S8), medium-((CoNiFeCu)9S8), and high-entropy ((CoNiFeCuCe)9S8) analogues in the oxygen evolution reaction (OER; η10 = 175 mV, η100 = 260 mV), urea oxidation reaction (UOR; 1.277 V and 1.336 V at 10 and 100 mA.cm⁻2), hydrogen evolution reaction (HER; η10 = 85 mV), and nitrite reduction (NO2RR; 0.112 V at 100 mA.cm⁻2). Post-catalytic and in-situ Raman analyses, in conjunction with density functional theory (DFT), show that metal (oxy)hydroxides form during the reaction, while d–f orbital interactions protect the active sites from over-oxidation. This work establishes a paradigm for integrating rare-earth elements into HEMSs via controlled solution-phase synthesis, advancing the design of high-entropy electrocatalysts. High-entropy metal sulfides have emerged as a new class of electrocatalysts, but their synthesis often faces challenges due to their inherent complexity arising from multi-metal interactions. Here, the authors report a low-temperature hydrothermal strategy to fabricate Ce-incorporated (CoFeNiCuCe)9S8 nanoballs by leveraging Cu2⁺ as a dynamic director for controlled solution-phase synthesis.