Medium-Entropy Effect Balances Cation Vacancy Concentration: Unlocking Efficient Chlorine Evolution in Ternary Vanadates

The chlorine evolution reaction (CER) in chlor-alkali processes faces significant challenges due to the similarity of thermodynamic potential with the oxygen evolution reaction, leading to competitive occupation for active sites and poor Cl 2 selectivity. To address this, we present the first design of a ternary vanadate-based hollow nanocube, (LaCoZn) 3 V 2 O 8 @C), and propose a novel strategy for steady-state regulation of cation vacancies driven by a medium-entropy effect for CER enhancement. Controlled Zn leaching generates cationic vacancies (V Zn ) that upshift the d -band center of adjacent Co sites. This electronic modulation strengthens Cl – adsorption while suppressing the competitive binding of the *OH species. Meanwhile, the inherent lattice distortion and sluggish diffusion of the medium-entropy system pin these cation vacancies against migration or annihilation. Notably, La incorporation into the medium-entropy system serves dual functions: it appropriately increases V Zn formation energy to establish a dynamic equilibrium between vacancy concentration and lattice stability, while simultaneously modulating the local charge density around Co sites to reduce the energy barrier of the rate-determining Heyrovsky step. The optimized (LaCoZn) 3 V 2 O 8 @C catalyst demonstrates outstanding CER performance, requiring only 163 mV overpotential at 50 mA cm –2, exhibiting a low Tafel slope of 46 mV dec –1, and achieving Cl 2 selectivity as high as 92%. Remarkably, the catalyst maintains operational stability over 300 h of continuous electrolysis, outperforming both commercial dimensionally stable anodes and certain noble-metal-based electrocatalysts. In addition, it delivers long-term stability for 350 h at a high current density of 500 mA cm –2 in a simulated flow electrolyzer, further demonstrating its robustness under industrially relevant conditions. This work provides a rational design strategy for highly selective and durable non-noble-metal CER catalysts.