In-situ Hard Templating Assisted Facet Engineered Two-Dimensional Non-van der Waals CuInS2 for Efficient CO2 Reduction Reaction

Abstract

Selective facet exposure in two-dimensional (2D) materials is highly sought after but typically achieved using complex techniques such as Molecular Beam Epitaxy (MBE) or Chemical Vapor Deposition (CVD). Existing wet-chemical routes—whether diffusion-controlled or ligand-assisted—mainly focus on morphology control or facet tuning via shape regulation but rarely accomplish both simultaneously. Here, we report a distinctive hard-templating strategy that enables concurrent 2D formation and facet engineering in non-van der Waals CuInS₂ (CIS). In this method, an in-situ formed 2D van der Waals CuInP₂S₆ (CIPS) with a hexagonal atomic arrangement acts as the template. Crucially, the use of highly reactive white phosphorus allows CIPS formation within wet-chemical temperature limits—otherwise requiring ~2 weeks at 600 °C using red phosphorus in solid-state synthesis. This facilitates a one-pot, greener conversion to non-vdW CIS, replacing conventional multi-step procedures. The resulting 2D CIS retains a cubic zincblende structure yet preserves the hexagonal atomic arrangement of the template, yielding dominant (111) facet exposure. The template also dictates flake thickness. Owing to both facet exposure and intrinsic phosphorus doping, the material delivers significantly enhanced formate selectivity in electrochemical CO₂ reduction compared to non-2D or non-faceted counterparts with similar electrochemically active surface area (ECSA).