The sluggish kinetics of negative V 2+ /V 3+ reaction is the key factor limiting the performance of vanadium redox flow battery (VRFB). To further enhance the competitiveness of VRFB in the fields of energy storage, it is urgent to develop anode material with high catalytic activity toward V 2+ /V 3+ reaction. Taking the advantages of excellent conductivity and catalytic activity of MXene (Ti 3 C 2 T x , Nb 2 CT x , V 2 CT x ) with different transition metals are used as catalysts to improve the kinetics of V 2+ /V 3+ reaction. At the current density of 160 mA cm −2 , the battery equipped with Nb 2 CT X modified composite electrode shows the highest energy efficiency of 83.1 %, which is 12.3 % higher than that with pristine graphite felt (GF). Furthermore, the effect of MXene with different transition metals on hydrogen evolution reaction (HER) is studied based on density functional theory (DFT). HER occurred on Nb 2 CT x surface should overcome a higher energy barrier compared with Ti 3 C 2 T x and V 2 CT x , implying the ability to inhibit side reaction occurrence for Nb 2 CT x . Ascribing to the enhanced kinetics of V 2+ /V 3+ reaction and the effective inhibition of HER, the Nb 2 CT x -modified electrode exhibits the highest catalytic activity, reversibility and cycle stability. This work promotes the development and application of Nb-based MXene as a catalyst in VRFB.
Sen-Wang Wang,Zhen-Hong He,Jian-Gang Chen,Kuan Wang,Zhong-Yu Wang,Pan-Pan Guo,Jie Lan,Weitao Wang,Zhao-Tie Liu
Hydrogenolysis of biomass-derived lignin sources is highly important for the conversion of renewable biomass resources to biofuels. However, lots of developed catalysts suffer from the drawbacks of expensive precious metal catalysts and/or operation under harsh conditions. In the present work, Co–Ni bimetallic catalysts were prepared and applied in catalyzing hydrogenolysis of Caryl–O aromatic ethers with high activities under the promotion of Nb2C MXene additive. Especially, the hydrogenolysis of diphenyl ether (DPE), a 4–O–5 model compound, to cyclohexane (cy) and cyclohexyl alcohol (cy-ol) could be achieved over the Co2Ni1Ox–Nb2C MXene catalytic system at 120 °C and under 5 bar of H2, which are mild conditions in comparison with those for the developed heterogeneous precious-metal-free catalysts. The excellent catalytic performances stemmed from the strong interaction between Co and Ni species and the promotion of Lewis acidic sites offered by Nb2C MXene. The proposed reaction pathway involved the direct hydrogenolysis of DPE route, in which DPE was initially hydrogenolyzed to benzene and phenol. They were further hydrogenated to cy and cy-ol. The present work not only develops a noble-metal-free bimetallic catalyst for utilization of biomass-derived lignin sources, but also provides a novel strategy for using the Nb2C MXene material.
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