Corresponding Author

Li-Li Xu(ll-xu2008@163.com);
Xiao-Feng Zhao(xfz_33@126.com)


Exploring the potential hydrogen evolution reaction (HER) catalysts with the high activity and high conductivity has always been a hot spot in the research of renewable energy development. Ti2C, as one of the 2D-MXene, has excellent properties relating to many active sites, mechanical stability, conductivity, etc., and has become a potential HER catalyst. However, the modification of the surface of Ti2C by terminal O will reduce the conductivity, thereby limiting the transport of electrons between the valence band and the conduction band. In this study, an electric double layer Janus-TiNbCO2 was constructed by Nb doping. The band property, HER activity and HER reaction path of Janus-TiNbCO2 are studied by the first-principles calculations. The results show that Nb doping increases the distance between Ti and O atoms, which increases the lattice parameters of Janus-TiNbCO2 comparing with that of Ti2CO2 structure. The Janus-TiNbCO2 structure is stable by calculating the thermodynamic stability at 500 K using AIMD method. The band gap of Ti2CO2 is approximate 0.9 eV. After Nb doping, the orbital hybridization between Nd-3d and O-2p affects the electronic rearrangement of Ti-3d, leading that Janus-TiNbCO2 has the metal band structure. In Janus-TiNbCO2, both Ti and Nb surfaces adsorb H* by O site, where the ΔGH*(@Ti) = -0.55 eV,ΔGH*(@Nb) = 0.02 eV, showing Ti and Nb surfaces have different catalytic activities. Comparing with graphenes, e.g., h-B2O, Pt, and g-C3N4, Janus-TiNbCO2 has better catalytic activity. The charge distribution of Janus-TiNbCO2 near the Fermi level was analyzed by HSE-06 function. The result reveals that O atoms on the Ti surface exhibit charge unsaturation at the Fermi level, while those on Nb surface strong saturation. Moreover, the effects of H* coverage and strains(+2% ~ +4%) on the catalyst activity of Janus-TiNbCO2 are studied. When the H* coverage is low, the optimal ΔGH* of Nb surface is approximate 0.02 eV, while Ti surface has an excellent catalytic activity at high H* coverages (θ = 7/9, ΔGH* = -0.06 eV). Under the strain action, the H* coverage on surface is not affected. However, strains will reduce the HER activity of Nb surface, and increase the HER activity of Ti surface. Furthermore, oxygen defect is a stable point defect in Janus-TiNbCO2 . Oxygen defect will increase the HER activity of Ti surface and decrease the HER activity of Nb surface. Comparing to the Tafel pathway, the Heyrovsky is a more suitable pathway for the HER, in which the migration barrier of Heyrovsky is 0.23 eV for H* on Nb surface. Janus-TiNbCO2 can be used as a potential HER catalyst.

Graphical Abstract


MXene, Janus-TiNbCO2, band, hydrogen evolution reaction

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