No abstract

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt-alloyw ith aP t-skin. The synthesis of ultrasmall and ordered L1 0 -PtCo nanoparticle ORR catalysts further doped with af ew percent of metals (W,G a, Zn) is reported. Compared to commercial Pt/C catalyst, the L1 0 -W-PtCo/C catalyst shows significant improvement in both initial activity and high-temperature stability.T he L1 0 -W-PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 8 8C, which is superior to the DOE 2020 targets.E XAFS analysis and density functional theory calculations reveal that Wd oping not only stabilizes the ordered intermetallic structure,but also tunes the Pt-Pt distances in such away to optimize the binding energy between Pt and O intermediates on the surface.

Understanding the Cu-catalyzed electrochemical CO 2 reduction reaction (CO 2 RR) under ambient conditions is both fundamentally interesting and technologically important for selective CO 2 RR to hydrocarbons. Current Cu catalysts studied for the CO 2 RR can show high activity but tend to yield a mixture of different hydrocarbons, posing a serious challenge on using any of these catalysts for selective CO 2 RR. Here, we report a new perovskite-type copper(I) nitride (Cu 3 N) nanocube (NC) catalyst for selective CO 2 RR. The 25 nm Cu 3 N NCs show high CO 2 RR selectivity and stability to ethylene (C 2 H 4 ) at −1.6 V (vs reversible hydrogen electrode (RHE)) with the Faradaic efficiency of 60%, mass activity of 34 A/g, and C 2 H 4 /CH 4 molar ratio of >2000. More detailed electrochemical characterization, X-ray photon spectroscopy, and density functional theory calculations suggest that the high CO 2 RR selectivity is likely a result of (100) Cu(I) stabilization by the Cu 3 N structure, which favors CO−CHO coupling on the (100) Cu 3 N surface, leading to selective formation of C 2 H 4 . Our study presents a good example of utilizing metal nitrides as highly efficient nanocatalysts for selective CO 2 RR to hydrocarbons that will be important for sustainable chemistry/energy applications.

Engineering the crystal structure of Pt-M (M = transition metal) nanoalloys to chemically ordered ones have drawn increasing attention in oxygen reduction reaction (ORR) electrocatalysis due to their high resistance against M etching in acid. Although Pt-Ni alloy nanoparticles (NPs) have demonstrated respectable initial ORR activity in acid, their stability remains a big challenge due to the fast etching of Ni. In this work, sub-6 nm monodisperse chemically ordered L1 0 -Pt-Ni-Co NPs are synthesized for the first time by employing a bifunctional core/shell Pt/NiCoO x precursor, which could provide abundant O-vacancies for facilitated Pt/Ni/Co atom diffusion and prevent NP sintering during thermal annealing. Further, Co doping is found to remarkably enhance the ferromagnetism (room temperature coercivity reaching 2.1 kOe) and the consequent chemical ordering of L1 0 -Pt-Ni NPs. As a result, the best-performing carbon supported L1 0 -PtNi 0.8 Co 0.2 catalyst reveals a half-wave potential (E 1/2 ) of 0.951 V vs. RHE in 0.1 M HClO 4 with 23-times enhancement in mass activity over the commercial Pt/C catalyst along with much improved stability (no performance degradation and Ni/Co loss in 5000 potential cycles). Density functional theory (DFT) calculations suggest that the L1 0 -PtNi 0.8 Co 0.2 core could tune the surface strain of Pt shells towards optimized Pt-O binding energy and facilitated reaction rate, thereby improving the oxygen reduction electrocatalysis.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))