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Density functional theory calculations are employed to systematically investigate the trend of hydrogen evolution reaction (HER) performance of oxygen-terminated MXenes. By studying 30 transition-metal carbides and 30 transition-metal nitrides, Mn+1CnO2 and Mn+1NnO2 (M = Sc, Cr, Hf, Mo, Nb, Ta, Ti, V, W, Zr; n = 1, 2, 3), the tendency of oxygen desorption after hydrogen adsorption is elucidated to play a key role in HER performance of oxygen-terminated MXenes. On the basis of these observations, we propose a suitable HER descriptor, oxygen vacancy formation energy (Ef), which scales linearly with the adsorption free energy of hydrogen, ΔGH. In addition, this new descriptor is linearly correlated with the lithium binding strength on oxygen-terminated MXenes. Therefore, Ef is a universal descriptor for identifying the trend of adsorption processes where adsorbed species donate electrons to oxygen-terminated MXenes. This work provides a general guideline for large-scale screening of promising MXene-based materials for energy storage and conversion. [ABSTRACT FROM AUTHOR]

The activated carbons (ACs) are prepared from mesophase pitch which is pre-carbonized by using potassium hydroxide as an activating agent. Nitrogen adsorption at 77 K is used to characterize the surface area and the porous structure of the ACs. By changing the pre-carbonization temperature from 560 to 750 °C, the arrangement of the ACs' microcrystallines might be controllable, and the pore size could be adjusted between 1.5 and 2.4 nm. The electrochemical performance of the ACs in organic solvent (1 M EtNBF in propylene carbonate) is investigated by voltage sweep cyclic voltammetry and constant current charge-discharge cycling tests. The results show that the ions can transfer rapidly and freely in the pore larger than or equal to 1.85 nm, even when the current density increases to 25 A g. [ABSTRACT FROM AUTHOR]

Deposition of platinum monolayers on Au substrate (denoted as Au@PtML) has been shown an efficient catalyst design strategy for the electrocatalysis of alcohol oxidation due to presumed 100% utilization of Pt atoms and substrate-enhanced catalytic activities. However, the atomic structure and stability of Pt (sub)monolayers on realistic nanoparticulate Au surface still remains elusive. Here, we reveal coverage-dependent atomic structures and electrocatalytic stabilities of Pt submonolayers (sML) on Au nanoparticles for methanol oxidation reaction (MOR) by using high-resolution transmission electron microscopy combined with energy dispersive X-ray spectrum imaging and electrochemical techniques. At lower Pt coverages, the PtsML more resembled monatomic-thick layers, whereas higher Pt coverages above 0.5 ML resulted in 3D subnanometer Pt nanoclusters leading to lower Pt utilization efficiencies. Moreover, the Au@PtsML catalysts with Pt coverage below 0.5 ML showed higher structural and electrocatalytic stability during MOR electrocatalysis. As a result, increasing the Pt coverage beyond 0.5 ML brought in no obvious gain in the overall catalytic performance. Our results suggest that the Au@Pt0.5 ML catalyst appears to be a more reasonable MOR catalyst than previously reported Au@Pt1.0 ML catalyst, providing more rational catalyst design for achieving high Pt utilization efficiency and high catalytic performance. [ABSTRACT FROM AUTHOR]

It has been indicated that anatase TiO2 is a promising anode material for lithium ion power battery from many previous researches. Whereas, in this work, we find that the anatase TiO2, when used as an anode for lithium ion battery, has high catalytic activity to initiate the decarboxylation reaction of electrolyte solution, resulting in the large generation of sole gaseous component, CO2. The ROLi species and the new phase of flake-like Li2TiF6 material are the main reaction products between anatase TiO2 and LiPF6 based electrolyte solution. This work provides important and urgent information that the surface chemistry of anatase TiO2 used as the anode material of lithium ion battery must be modified to suppress its catalytic activity for the decomposition of solvents. [ABSTRACT FROM AUTHOR]