p-Block-metal bismuth-based electrocatalysts featuring tunable selectivity for high-performance oxygen reduction reaction

For oxygen reduction reaction (ORR), replacing the conventional electrocatalysts based on platinum-group metals (PGMs) with alter-natives based on non-noble metals is vital for the large-scale appli-cations of green energy conversion and chemical synthesis. Here, we report the discovery of ORR catalysts based on the p-block-metal bismuth (Bi); the selectivity in ORR pathways could be controlled by tailoring the size of Bi. Specifically, the metallic Bi nanoparticles gave a high selectivity (>96%) for 2e- ORR, an ultra-high kinetic cur-rent density (3.8 mA$cm-2 at 0.65 V), and an excellent stability; in contrast, the single-atomic-site Bi catalysts gave a good selectivity for 4e- ORR and a corresponding half-wave potential of 0.875 V, ap-proaching that of the best-known Fe/NC catalysts. This work pre-sents new high-performance ORR catalysts based on the p-block -metal Bi, in contrast to the intensively studied d-block transition metals, and thus would provide new perspectives for developing PGM-free ORR catalysts.