Atomically Isolated Rh Sites within Highly Branched Rh₂Sb Nanostructures Enhance Bifunctional Hydrogen Electrocatalysis

Abstract Breaking the bottleneck of hydrogen oxidation/evolution reactions (HOR/HER) in alkaline media is of tremendous importance for the development of anion exchange membrane fuel cells/water electrolyzers. Atomically dispersed active sites are known to exhibit excellent activity and selectivity toward diverse catalytic reactions. Here, a class of unique Rh₂Sb nanocrystals with multiple nanobranches (denoted as Rh₂Sb NBs) and atomically dispersed Rh sites are reported as promising electrocatalysts for alkaline HOR/HER. Rh₂Sb NBs/C exhibits superior HER performance with a low overpotential and a small Tafel slope, outperforming both Rh NBs/C and commercial Pt/C. Significantly, Rh₂Sb NBs show outstanding HOR performance of which the HOR specific activity and mass activity are about 9.9 and 10.1 times to those of Rh NBs/C, and about 4.2 and 3.7 times to those of Pt/C, respectively. Strikingly, Rh₂Sb NBs can also exhibit excellent CO tolerance during HOR, whose activity can be largely maintained even at 100 ppm CO impurity. Density functional theory calculations reveal that the unsaturated Rh sites on Rh₂Sb NBs surface are crucial for the enhanced alkaline HER and HOR activities. This work provides a unique catalyst design for efficient hydrogen electrocatalysis, which is critical for the development of alkaline fuel cells and beyond.