Marriage of Ultralow Platinum and Single-Atom MnN4 Moiety for Augmented ORR and HER Catalysis

Abstract

Hitherto, Pt-based catalysts still are state of the art for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), but high dosage, low atom-utilization efficiency, and uncontrollable size of Pt species seriously impede their applications. Given this, we propose an effective way by enhancing Pt–transition metal single-atom interaction. Due to the strong interaction between single-atom Mn sites in Mn–N–C and Pt species, the overgrowth of Pt species is effectively limited with an average size smaller than 2.5 nm. Meanwhile, the regulated electronic structure drives electron transfer from Mn to adjacent Pt sites, endowing catalysts with reduced reaction energy barrier and higher intrinsic activity. As expected, the obtained Pt@Mn-SAs/N-C nanocatalyst with ideal Pt size and ultralow Pt loading (1.98 wt %) exhibits extraordinarily high ORR mass activity at 0.9 V in acidic and alkaline media, which is 11.1 and 14.7 times larger than that of commercial Pt/C, respectively. Moreover, at 30 mV, its HER mass activity is even 33.4 and 18.7 times larger than that of Pt/C. Theory calculation results show that favorable charge density rearrangement and resulting electron-enriched Pt sites, with negatively shifted d-band centers, weaken surface adsorption of key intermediates, boosting ORR/HER activity. This work provides enlightenment for integration of multiple active centers in catalysts.