Ionic Liquid-Assisted Synthesis of Ce-Doped NiCo-Based Composite Electrocatalysts for Hydrogen Evolution

Abstract Developing efficient and low-cost electrocatalysts is an urgent need for water splitting. Water splitting relies on a wide range of catalysts. Owing to its flexible coordination chemistry and outstanding redox properties, cerium (Ce) not only functions as an active catalyst on its own but also serves as an effective promoter for other catalytic species. This paper prepared NiCo-PBA based on the “nanoregions” formed in an ionic liquid mixture system, synthesized Ce-doped nickel–cobalt-based Prussian blue analogues through ion exchange reactions, and successfully prepared porous composite materials CeNiCo@NC with different Ce contents by calcination in an inert atmosphere. The research results show that the resulting Ce-doped NiCo@NC materials with rationally optimized Ce contents deliver remarkable HER activity, making them promising candidates as efficient water-splitting catalysts. In particular, CeNiCo@NC-3 exhibits the highest electrocatalytic performance among the series, delivering 10 mA cm–2 at only 99 mV overpotential, 57 mV (36.5%) lower than that of Ce-free NiCo@NC-500. Additionally, its Tafel slope of 61 mV dec–1 corresponds to a 15.3% improvement over NiCo@NC-500. The origin of this enhanced activity lies in the enlarged electrochemically active surface area, expedited charge transfer, and the promotion of Ce3+ ↔ Ce4+ conversion in CeO2 after the introduction of Ce.