Topological insulator path toward efficient hydrogen evolution catalysts in the ${\mathrm{Li}}_2\mathrm{Pt}$ family

Topological materials, such as topological semimetals and topological insulators, with robust topological surface states have bright application prospects in electrochemical catalysis. Here, the first-principles calculations indicate the strong topological insulator ${\mathrm{Li}}_2\mathrm{Pt}$ family promotes efficient catalytic response to the hydrogen evolution reaction. For ${\mathrm{Li}}_2\mathrm{Pt}$ and ${\mathrm{Li}}_2\mathrm{Pd}$, the calculated Gibbs free energy $\mathrm{\Delta }{G}_{{\mathrm{H}}^{*}}$ of the bridge site is 0.054 eV and 0.041 eV, while that for the top site is 0.187 eV and 0.641 eV, respectively. The better hydrogen evolution reaction performance of the bridge site can ascribe to H hybridizes with the $d_{xy}+d_{x^2-y^2}$ orbital, which donates the nontrivial topological surface states, while H hybridizes with the $d_{z^2}$ orbital that withholds contribution to topological surface states for the top site. Noticeably, the $\mathrm{\Delta }{G}_{{\mathrm{H}}^{*}}$ of the bridge site for ${\mathrm{Li}}_2\mathrm{Pt}$ (0.054 eV) and ${\mathrm{Li}}_2\mathrm{Pd}$ (0.041 eV) is nearly half of the value of Pt (0.09 eV), indicating an excellent hydrogen evolution reaction activity. This work uncovers the hybridization between adsorbate and topological surface states plays a vital role in enhancing the hydrogen evolution reaction performance and provides a promising route to design topological quantum catalysts.

Figure 1

(a) Top and side view of ${\mathrm{Li}}_2\mathrm{Pt}$. The top and bridge adsorption sites are highlighted by the red points in the top panel. (b) The Brillouin zone of ${\mathrm{Li}}_2\mathrm{Pt}$, in which the high symmetry points and the projected (001) plane are illustrated.

Figure 2

Calculated band structures of ${\mathrm{Li}}_2\mathrm{Pt}$ without spin polarization (a) and with SOC (d). The red and blue lines indicate the valence band (VB) and the conduction band (CB), respectively. The green points in (a) highlight the BCPs numbered as P1–P6. The inset is an enlarged view for the BCPs in the dashed rectangle. The $d$-orbital resolved band structures and the corresponding PDOSs for ${\mathrm{Li}}_2\mathrm{Pt}$ without spin polarization [(b) and (c)] and with SOC [(e) and (f)], respectively. (g) The calculated surface states along selected paths on the (001) surface for ${\mathrm{Li}}_2\mathrm{Pt}$. (h) The enlarged image for the dotted rectangle in (g).

Figure 3

Charge density difference for ${\mathrm{Li}}_2\mathrm{Pt}$ eight-layer bulk without H adsorption (a), eight-layer slab with H adsorption on the top site (b), and eight-layer slab with H adsorption on the bridge site (c). The charge accumulation and depletion is indicated by the yellow and cyan region, respectively. The isosurface is set as 0.009 electrons/Å${}^{-3}$ (a) and 0.006 electrons/Å${}^{-3}$ [(b) and (c)], respectively. The displayed thickness is set to one unit cell. Panels (d), (e), and (f) are the PDOSs of Pt $d$ and H $s$ orbitals on the top layer of (001) surface corresponding to (a), (b), and (c), respectively. Panels (g), (h), and (i) are the hole density of states of Pt $d_{xz}+d_{yz}, d_{z^2}, d_{xy}+d_{x^2-y^2}$ and H $s$ orbitals on the top layer of (001) surface, respectively.

Figure 4

Surface electronic structures of the (001) surface for ${\mathrm{Li}}_2\mathrm{Pt}$ 20-layer slab without H adsorption from MLWFs (a) and with H adsorption on the top site (b) and bridge site (c) from DFT calculations, respectively. The red lines highlight the TSS. Panels (d), (e), and (f) are the real wave functions of the TSS at the $\overline{\mathrm{M}}$ point as circled in blue in (a), (b), and (c), respectively. The isosurface is set to 0.0003 electrons/Å${}^{-3}$. The displayed thickness is set to one unit cell. The adsorbed H atoms are indicated by the black arrows in (e) and (f).

Figure 5

Charge density difference for ${\mathrm{Li}}_2\mathrm{Pd}$ eight-layer bulk without H adsorption (a), eight-layer slab with H adsorption on the top site (b), and eight-layer slab with H adsorption on the bridge site (c). The charge accumulation and depletion is indicated by the yellow and cyan region, respectively. The isosurface is set as 0.002 electrons/Å${}^{-3}$ (a) and 0.006 electrons/Å${}^{-3}$ [(b) and (c)], respectively. The displayed thickness is set to one unit cell. Panels (d), (e), and (f) are the PDOSs of Pd $d$ and H $s$ orbitals on the top layer of (001) surface corresponding to (a), (b), and (c), respectively. Panels (g), (h), and (i) are the hole density of states of Pd $d_{xz}+d_{yz}, d_{z^2}, d_{xy}+d_{x^2-y^2}$ and H $s$ orbitals on the top layer of (001) surface, respectively.

Figure 6

(a), (b) Sketch map for the HER activity on the top and bridge site of ${\mathrm{Li}}_2\mathrm{Pt}$, respectively. The bigger solid arrow indicates the stronger interaction between H and the TSS/substrate. (c) The $|\mathrm{\Delta }{G}_{\mathrm{H}*}|$ diagram of HER. The data of NiSi, Pt, and PtGa are taken from the literature [24, 28, 45]. (d) The volcano plot for the HER of ${\mathrm{Li}}_2\mathrm{Pt}$ and ${\mathrm{Li}}_2\mathrm{Pd}$ in comparison with that of various transition metal catalysts and TQCs [23, 28]. The data of ${\mathrm{Li}}_2\mathrm{Pt}$ and ${\mathrm{Li}}_2\mathrm{Pd}$ corresponds to the eight-layer slab with bridge site absorption.