Computational determination of a graphene-like TiB 4 monolayer for metal-ion batteries and a nitrogen reduction electrocatalyst.

As an emerging two-dimensional (2D) material, the TiB 4 monolayer possesses intrinsic advantages in electrochemical applications owing to its graphene-like structure and metallic characteristics. In this work, we performed density functional calculations to investigate the electrochemical properties of the TiB 4 monolayer as an anode material for Li/Na/K ion batteries and as an electrocatalyst for the nitrogen reduction reaction (NRR). Our investigation reveals that Li/Na/K ions could be steadily adsorbed on the TiB 4 monolayer with moderate adsorption energies, and tended to diffuse along two adjacent C-sites with lower energy barriers (0.231/0.094/0.067 eV for Li/Na/K ions) compared to the currently reported transition-metal boride monolayers. Furthermore, a N 2 molecule can be spontaneously captured by the TiB 4 monolayer with a negative Gibbs free energy (-0.925 eV and -0.326 eV for end-on and side-on adsorptions, respectively), hence provoking a conversion into NH 3 along the most efficient reaction pathway ( i.e. , N 2 * → N 2 H* → HNNH* → H 2 NNH* → H 3 NNH* → NH* → NH 2 * → NH 3 *). In the hydrogenation process, the TiB 4 monolayer exhibits much higher catalytic activity for the NRR as compared with other electrocatalysts, which should be attributed to the spontaneous achievement (Δ G < 0) at all hydrogenation reaction steps except the potential-determining step. Moreover, the TiB 4 monolayer exhibits higher selectivity toward the NRR than the hydrogen evolution reaction. Our work advances the mechanistic understanding on the electrochemical properties of the TiB 4 monolayer as an anode material for metal-ion batteries and as a NRR electrocatalyst, and provides significant guidance for developing high-performance multifunctional 2D materials.