Breaking the symmetry of high-entropy alloy surfaces for compressively strain-tuned oxygen reduction reaction

A largely unexplored approach for optimizing surface strains on terrace-type catalysts is the break of atomic symmetry to release surface stress. The key challenge lies in how to implement this approach into practical nanocatalysts, in particular the promising high-entropy alloys (HEAs). Herein, we design and synthesize a series of HEA nanorings (NRs) with abundant terrace-type defects for oxygen reduction reaction (ORR) electrocatalysis. The asymmetry-triggered release of surface stress enables the modulation of compressive strain for optimizing the electronic structure. On the optimally-tuned PtPdFeCoNi HEA NRs, we achieve mass and specific activities of 0.99 A mg^-1_{platinum group metal (PGM)} and 1.32 mA cm^-2_PGM at 0.95 V versus reversible hydrogen electrode (vs. RHE), demonstrating a competitive performance. Experimental and theoretical investigations unveil that the stress-released compressive strain lowers the d-band center of Pt sites in HEA NRs, resulting in favorable desorption of oxygenated intermediates and thus accelerated ORR kinetics.