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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))

Core/shell nanocatalysts are ac lass of promising materials,w hicha chieve the enhanced catalytic activities through the synergy between ligand effect and strain effect. However,i th as been challenging to disentangle the contributions from the two effects,whichhinders the rational design of superior core/shell nanocatalysts.H erein, we report precise synthesis of PdCu/Ir core/shell nanocrystals,w hichc an significantly boost oxygen evolution reaction (OER) via the exclusive strain effect. The heteroepitaxial coating of four Ir atomic layers onto PdCu nanoparticle gives arelatively thickIr shell eliminating the ligand effect, but creates ac ompressive strain of ca. 3.60%. The strained PdCu/Ir catalysts can deliver al ow OER overpotential and ah igh mass activity.D ensity functional theory (DFT) calculations reveal that the compressive strain in Ir shell downshifts the d-band center and weakens the binding of the intermediates,c ausing the enhanced OER activity.The compressive strain also boosts hydrogen evolution reaction (HER) activity and the strained nanocrystals can be served as excellent catalysts for both anode and cathode in overall water-splitting electrocatalysis.

PtM alloy catalysts (e.g., PtFe, PtCo), especially in an intermetallic L1 0 structure, have attracted considerable interests due to their respectable activity and stability for oxygen reduction This article is protected by copyright. All rights reserved.3 reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, metal-catalyzed formation of •OH from H 2 O 2 (i.e., Fenton reaction) by Fe-or Co-containing catalysts causes severe degradation of PEM/catalyst layers, hindering the prospects in commercial applications. Zinc (Zn) is known as an antioxidant in Fenton reaction, but rarely alloyed with Pt owing to its relatively negative redox potential. Here, we synthesized sub-4 nm intermetallic L1 0 -PtZn nanoparticles (NPs) as high-performance PEMFC cathode catalysts. In PEMFC tests, the L1 0 -PtZn cathode achieves outstanding activity (0.52 A mg Pt -1 at 0.9 V iR-free , and peak power density of 2.00 W cm -2 ) and stabilityonly 16.6 % loss in mass activity after 30,000 voltage cycles), exceeding the U.S. DOE 2020 targets and most of the reported ORR catalysts. Density function theory (DFT) calculations reveal that biaxial strains developed upon the disorder-order (A1-L1 0 ) transition of PtZn NPs would modulate the surface Pt-Pt distances and optimize Pt-O binding for ORR activity enhancement, while the increased vacancy formation energy of Zn atoms in ordered structure accounts for the improved stability. PtZn slabs. (f) Correlations between the formation energy and vacancy formation energy of M in various L1 0 -PtM systems. TOC Structurally ordered L1 0 -PtZn nanoparticles are developed as catalysts for oxygen reduction in proton exchange membrane fuel cells (PEMFCs). The L1 0 -PtZn catalyst with a "Pt-skin" achieves outstanding activity, power density, and stability in a PEMFC. The extraordinary fuel cell performance of L1 0 -PtZn/Pt is ascribed to the optimized biaxial strains, the Fenton reaction resistance, and the increased vacancy formation energy of Zn.

Surface engineering has proved effective in enhancing activities of CO 2 reduction reaction (CO 2 RR) on Cu. However, predictive guidance is necessary for the surface engineering to reach its full potential. We propose that the generalized coordination number (GCN) can be used as a descriptor to characterize CO 2 RR on Cu surfaces. A set of linear scaling relations between the binding energy of CO 2 RR intermediates and GCN are established to construct a volcano-type coordination−activity plot and from which we can derive the theoretical overpotential limit on Cu surfaces. We predict that the dimerized (111) surface yields the lowest possible overpotential on Cu for CO 2 RR to methane, and surface engineering by creating adatoms could lower CO 2 RR overpotentials and simultaneously suppress the competing hydrogen evolution reaction.

Alkaline hydrogen evolution reaction (HER), consisting of Volmer and Heyrovsky/Tafel steps, requires extra energy for water dissociation, leading to more sluggish kinetics than acidic HER. Despite the advances in electrocatalysts, how to combine active sites to synergistically promote both steps and understand the underlying mechanism remain largely unexplored. Here, Density Functional Theory (DFT) calculations predict that NiO accelerates the Volmer step while metallic Ni facilitates the Heyrovsky/Tafel step. A facile strategy is thus developed to control Ni/NiO heterosurfaces in uniform and well-dispersed Ni-based nanocrystals, targeting both reaction steps synergistically. By systematically modulating the surface composition, we find that steering the elementary steps through tuning the Ni/NiO ratio can significantly enhance alkaline HER activity, and Ni/NiO nanocrystals with a Ni/NiO ratio of 23.7% deliver the best activity, outperforming other state-of-the-art analogues. The results suggest that integrating bicomponent active sites for elementary steps is effective for promoting alkaline HER, but they have to be balanced.