Seemingly Negligible Amounts of Platinum Nanoparticles Mislead Electrochemical Oxygen Reduction Reaction Pathway on Platinum Single-Atom Catalysts

Abstract

A few studies have claimed that Pt single-atom catalysts (SACs) can catalyze the oxygen reduction reaction (ORR) following a four-electron pathway (O-2+4H(+)+4e(-)-> 2H(2)O). Here, we show that, in the presence of a seemingly negligible amount of Pt nanoparticles, the ORR can mistakenly be thought to occur via a four-electron pathway on Pt SACs. Various weight percentages (1, 2, 4, 8 wt%) of Pt SACs were prepared on C(3)N(4)layers deposited on a carbon support (C@C3N4). Through a combination of H-2/CO uptakes and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) results, the amount of Pt nanoparticles could be estimated when they were mixed with Pt single atoms. Particularly, most of Pt in the 4 wt% Pt catalyst existed as single atoms, but a small number of Pt nanoparticles co-existed. Although this catalyst seemed to follow the four-electron pathway, the reaction actually occurred on Pt nanoparticles, not Pt single-atoms.