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 Cl2 selectivity. To address this, we present the first design of a ternary vanadate-based hollow nanocube, (LaCoZn)3V2O8@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 (VZn) 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 VZn 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)3V2O8@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 Cl2 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.