Rate-determining Step Backshift Effectively Boost ORR Performance by Excess Electrons Transfer to O-O Antibonding Orbital

Abstract

Pt23Pd77 nanosheets (NSs) were successfully synthesized with a thickness of 1.33 nm and the mass activity (MA) of 6.78 A mgPGM-1, achieving excellent oxygen performance of 45.2 times higher than commercial Pt/C (0.15 A mgPt-1). Furthermore, the Tafel slope of Pt23Pd77 NSs is as low as 39.52 mV dec-1 compared to Pt/C (70.55 mV dec-1) indicating the rate-determining step (RDS) is transferred from *OOH cleavage to the second electron transfer. First-principles calculations show a decline in the barrier of *OOH → *O + *OH, thus the second electron transfer succeeds the RDS. In the kinetic-controlled region, the apparent activation energy (Ea) of Pt/C does not change with the change of overpotential, and the reaction order of OH- is close to 0, while the Ea of the NSs decreases with the increase of overpotential, and the reaction order is negative. All of this proves that the RDS moves backwards. This paper provides another idea for improving the performance optimization strategy of oxygen reduction, that is, the kinetic RDS backshift.