High-Throughput Screening of 2D Photocatalyst Heterostructures with Suppressed Electron-Hole Recombination for Solar Water Splitting

TL;DR

Efficient solar-to-hydrogen production via photocatalysis faces challenges from recombination and limited visible-light absorption. The authors implement a high-throughput, first-principles workflow to screen 482 bilayers formed from 60 experimentally realizable 2D monolayers and identify 148 stable type-II vdW heterostructures, of which 65 satisfy water-splitting redox criteria across broad pH. Top candidates MoTe2/Tl2O, MoSe2/WSe2, and MoTe2/HfNCl show strong visible absorption (absorption coefficient above 0.6×10^6 cm^-1) and power conversion efficiencies up to about 2%, with nearly barrierless hydrogen evolution and built-in interlayer fields that promote charge separation. The work provides a practical design framework for tunable, experimentally accessible 2D photocatalysts for sustainable hydrogen production and guides future experimental realization.

Abstract

Efficient and scalable photocatalysts for solar water splitting remain a critical challenge in renewable energy research. The work presents a high-throughput first-principles discovery of two-dimensional (2D) type-II van der Waals heterostructures (vdWHs) optimized for visible-light-driven photocatalytic water splitting. We screened 482 heterostructures constructed from 60 experimentally realizable 2D monolayers and identified 148 stable type-II vdWHs with spatially separated valence and conduction band edges, out of which 65 satisfy the thermodynamic redox conditions for water splitting over a broad pH range. Among these, the best two, MoTe2/Tl2O and MoSe2/WSe2, exhibit a high visible-light absorption coefficient exceeding 0.6X10^6 cm-1, resulting in a high power conversion efficiency of 2%. Quantum kinetic analysis of the hydrogen evolution reaction (HER) reveals nearly barrierless free energy profiles across multiple adsorption sites. Our study further reveals that intrinsic interlayer electric fields in these vdWHs drive directional charge separation, suppressing carrier recombination. Our results establish a design framework for using type-II 2D heterostructures as tunable and experimentally accessible 2D photocatalysts for efficient hydrogen production.

Figures (5)

• Figure 1: (a) Schematic workflow of high-throughput first-principles calculations. Sixty-five type-II vdWHs were suitable for photocatalytic water-splitting applications out of 482 heterostructures made by combining 60 monolayers with less than 5% lattice mismatch. (b) Schematic working principle of photocatalysis for water splitting in MoTe$_2$ (top)/HfNCl (bottom) heterostructure. The oxygen evolution reaction (OER, 2H$_2$O+4h$^+_{VB}$ = O$_2$+4H$^+$) and Hydrogen evolution reaction (HER, 2H$^+$ + 2e$^-_{CB}$=H$_2$) requires photogenerated holes, and electrons, respectively. (c) Schematic showing redox potentials at pH=0 (dashed lines), band edge alignments, and charge transfer pathways of a type-II heterostructure. (d) Band structure and density of states, (e) highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the MoTe$_{2}$/HfNCl heterostructure, showing its type-II nature.
• Figure 2: The band edge alignment of the 65 heterostructures is depicted in relation to the reduction potential (H${^+}$/H${_2}$) and oxidation potential (O$_2$/H$_2$O) at pH$=$4, pH$=$7, and pH$=$10, offering valuable insights into their viability for photocatalytic reactions. The y-axis shows band edges' energy ($E - E_0$), where $E_0$ is the vacuum potential energy obtained from the DFT calculations [see Eq. \ref{['eq:0']}]. The pH values indicate the range in which the heterostructures satisfy the conditions for water splitting. Blue and red lines represent the VBM and CBM, respectively.
• Figure 3: The power conversion efficiency of the heterostructures. Among the 65 van der Waals heterostructures (vdWHs), 10 vdWHs are presented here, exhibiting a power conversion efficiency greater than 0.60%, indicating their strong potential for effective energy conversion at the nanoscale. In the inset, the absorption coefficients for the three most efficient heterostructures (MoTe$_{2}$/Tl$_{2}$O, MoSe$_{2}$/WSe$_{2}$, and MoTe$_{2}$/HfNCl) are shown.
• Figure 4: The electronic band structures and DOS of (a) MoTe${2}$/Tl${_2}$O, (b) MoSe${2}$/WSe${2}$, (c) MoTe$_{2}$/HfNCl heterostructures, confirming their type-II nature. Band edges and oxidation-reduction potentials at pH = 10 [marked by dotted lines, calculated using Eq. \ref{['eq:9']}] of (d) MoTe${2}$/Tl${_2}$O, (e) MoSe${2}$/WSe${2}$, (f) MoTe$_{2}$/HfNCl heterostructures. The valence band offset (VBO) and conduction band offset (CBO) are indicated, emphasizing their critical role in charge transfer. The plane-averaged electrostatic potential energies [Eq. \ref{['eq:0']}] of (g) MoTe$_{2}$/Tl$_{2}$O, (h) MoSe$_{2}$/WSe$_{2}$, and (i) MoTe$_{2}$/HfNCl heterostructures. The vertical dashed line shows the interface between two monolayers. The potential difference creates an electric field in the out-of-plane direction.
• Figure 5: Reaction paths for the hydrogen evolution reaction (HER) at different atomic sites on the MoTe$_2$ and Tl$_2$O surfaces for (a) U $=$ 0 and (b) U $=$ 0.78 V, MoSe$_2$ and WSe$_2$ surfaces for (c) U $=$ 0 and (d) U $=$ 0.94 V, and MoTe$_2$ and HfNCl surfaces for (e) U $=$ 0 and (f) U $=$ 0.74 V. * denotes the system and H$^*$ denotes the system + H. The photogenerated electrons generate an additional potential U, resulting in a reduction in Gibbs free energy. The free energy profile ($\Delta G$), depicted in (b, d, and f), confirms that HER proceeds through a barrierless pathway.