Cascade Anchoring Strategy for Fabricating High-Loading Pt Single Atoms as Bifunctional Catalysts for Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions

Carbon supports containing single-atomically dispersedmetal-N (x) (denoted as M-SAC-N (x) C (y) , x, y: coordination number) have attracted increasingattention due to their superb performance in heterogeneous catalysis.However, large-scale controllable preparation of single-atom catalysts(SACs) with high concentration of supported metal-N (x) is still a big challenge because of the metal atom agglomerationduring synthesis at high density and temperatures. Herein, we reporta stepwise anchoring strategy from a 1,10-o-phenanthrolinePt chelate to an N (x) -doped carbon (N (x) C (y) ) with isolatedPt single-atom catalysts (Pt-SAC-N (x) C (y) ) containing Pt loadings upto 5.31 wt % measured via energy-dispersive X-ray spectroscopy (EDS).The results show that 1,10-o-phenanthroline Pt chelatepredominantly contributes to the formation of chelate single metalsites that bind tightly to platinum ions to prevent metal atoms fromaggregating, resulting in high metal loading. The high-loading Pt-SAC-N (x) C (y) exhibits a low hydrogen evolution (HER) overpotential of24 mV at 0.010 A cm(-2) current density with a relativelysmall Tafel gradient of 60.25 mV dec(-1) and excellentstable performance. In addition, the Pt-SAC-N (x) C (y) catalyst showsexcellent oxygen reduction reaction (ORR) catalytic activity withgood stability, represented by the fast ORR kinetics under high-potentialconditions. Theoretical calculations show that Pt-SAC-NC3 (x = 1, y = 3) offers alower H2O activation energy barrier than Pt nanoparticles.The adsorption free energy of a H atom on a Pt single-atom site islower than that on a Pt cluster, which is easier for H-2 desorption. This study provides a potentially powerful cascade anchoringstrategy in the design of other stable M-SAC-N (x) C (y) catalysts withhigh-density metal-N (x) sites for the HERand ORR.