Developing an efficient electrocatalyst for the hydrogen evolution reaction (HER) working in both acidic and alkaline solutions is highly desirable, but still remains challenging. Here, PtxNi ultrathin nanowires (NWs) with tunable compositions (x = 1.42, 3.21, 5.67) are in situ grown on MXenes (Ti3C2 nanosheets), serving as electrocatalysts toward HER. Such PtxNi@Ti3C2 electrocatalysts exhibit excellent HER performance in both acidic and alkaline solutions, with the Pt3.21Ni@Ti3C2 being the best one. Specifically, Pt3.21Ni@Ti3C2 achieves record‐breaking performance in terms of lowest overpotential (18.55 mV) and smallest Tafel slope (13.37 mV dec−1) for HER in acidic media to date. Theory calculations and X‐ray photoelectron spectroscopy analyses demonstrate that the coupling of MXenes with the NWs not only approaches the Gibbs free energy for hydrogen adsorption close to zero through the electron transfer between them in acidic media, but also provides additional active sites for water dissociation in alkaline solution, both of them being beneficial to the HER performance.
Developing an efficient Pt‐based electrocatalyst with well‐defined structures for the methanol oxidation reaction (MOR) is critical, however, still remains a challenge. Here, a one‐pot approach is reported for the synthesis of Pd3Pb/PtnPb nanocubes with tunable Pt composition varying from 3.50 to 2.37 and 2.07, serving as electrocatalysts toward MOR. Their MOR activities increase in a sequence of Pd3Pb/Pt3.50Pb << Pd3Pb/Pt2.07Pb < Pd3Pb/Pt2.37Pb, which are substantially higher than that of commercial Pt/C. Specifically, Pd3Pb/Pt2.37Pb electrocatalysts achieve the highest specific (13.68 mA cm−2) and mass (8.40 A mgPt
−1) activities, which are ≈8.8 and 6.8 times higher than those of commercial Pt/C, respectively. Structure characterizations show that Pd3Pb/Pt2.37Pb and Pd3Pb/Pt2.07Pb are dominated by hexagonal‐structured PtPb intermetallic phase on the surface, while the surface of Pd3Pb/Pt3.50Pb is mainly composed of face‐centered cubic (fcc)‐structured PtxPb phase. As such, hexagonal‐structured PtPb phase is much more active than the fcc‐structured PtxPb one toward MOR. This demonstration is supported by density functional theory calculations, where the hexagonal‐structured PtPb phase shows the lowest adsorption energy of CO. The decrease in CO adsorption energy and structural stability also endows Pd3Pb/PtnPb electrocatalysts with superior durability relative to commercial Pt/C.
Hard carbon (HC) anodes have shown extraordinary promise for sodium‐ion batteries, but are limited to their poor initial coulombic efficiency (ICE) and low practical specific capacity due to the large amount of defects. These defects with oxygen containing groups cause irreversible sites for Na+ ions. Highly graphited carbon decreases defects, while potentially blocking diffusion paths of Na+ ions. Therefore, molecular‐level control of graphitization of hard carbon with open accessible channels for Na+ ions is key to achieve high‐performance hard carbon. Moreover, it is challenging to design a conventional method to obtain HCs with both high ICE and capacity. Herein, a universal strategy is developed as manganese ions‐assisted catalytic carbonization to precisely tune graphitization degree, eliminate defects, and maintain effective Na+ ions paths. The as‐prepared hard carbon has a high ICE of 92.05% and excellent cycling performance. Simultaneously, a sodium storage mechanism of “adsorption‐intercalation‐pore filling‐sodium cluster formation” is proposed, and a clear description given of the boundaries of the pore structure and the specific dynamic process of pore filling.
Sn-Doped Bi2O3 nanosheets showed enhanced catalytic selectivity and activity for CO2RR relative to undoped ones with 2.5% Sn-doped Bi2O3 NSs showing a highest FE of over 93% and a largest current density of nearly 50 mA cm−2 for formate in H-cell.
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