Pt Nanoparticle-Mn Single-Atom Pairs for Enhanced Oxygen Reduction.

The intrinsic roadblocks for designing promising Pt-based oxygen reduction reaction (ORR) catalysts emanate from the strong scaling relationship and activity-stability-cost trade-offs. Here, a carbon-supported Pt nanoparticle and a Mn single atom (Pt NP -Mn SA /C) as in situ constructed Pt NP -Mn SA pairs are demonstrated to be an efficient catalyst to circumvent the above seesaws with only ∼4 wt % Pt loadings. Experimental and theoretical investigations suggest that Mn SA functions not only as the "assist" for Pt sites to cooperatively facilitate the dissociation of O 2 due to the strong electronic polarization, affording the dissociative pathway with reduced H 2 O 2 production, but also as an electronic structure "modulator" to downshift the d -band center of Pt sites, alleviating the overbinding of oxygen-containing intermediates. More importantly, Mn SA also serves as a "stabilizer" to endow Pt NP -Mn SA /C with excellent structural stability and low Fenton-like reactivity, resisting the fast demetalation of metal sites. As a result, Pt NPs -Mn SA /C shows promising ORR performance with a half-wave potential of 0.93 V vs reversible hydrogen electrode and a high mass activity of 1.77 A/mg Pt at 0.9 V in acid media, which is 19 times higher than that of commercial Pt/C and only declines by 5% after 80,000 potential cycles. Specifically, Pt NPs -Mn SA /C reaches a power density of 1214 mW/cm 2 at 2.87 A/cm 2 in an H 2 -O 2 fuel cell.