探寻具有高导电性和高催化活性的析氢反应（HER）催化材料一直是可持续能源发展研究中的热点。Ti₂C具有表面活性位点多和优良的力学稳定性、导电性等,已成为潜在的制氢催化剂。然而,终端O修饰Ti₂C表面,会降低该材料的导电性,进而限制了电子在价带与导带间的输运。本研究通过Nb掺杂,构建双电层Janus-TiNbCO₂,并借助VASP软件研究了Janus-TiNbCO₂的能带结构、HER性能和HER反应路径过渡态。结果表明,Janus-TiNb-CO₂为导体材料,其在应力、氧空位缺陷和H*覆盖度的影响下,均表现出极优异的催化活性,计算获得的最优ΔG_H*值为0.02 eV。H*在Janus-TiNbCO₂上可能以Heyrovsky路径进行反应,该路径的迁移能势垒为0.23 eV。Janus-TiNbCO₂是一种具有HER应用前景的催化材料。

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 ΔG_H*(@Ti) = -0.55 eV,ΔG_H*(@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 ΔG_H* of Nb surface is approximate 0.02 eV, while Ti surface has an excellent catalytic activity at high H* coverages (θ = 7/9, ΔG_H* = -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.