In situ hard templating-assisted, facet-engineered, two-dimensional non-van der Waals CuInS2 for efficient CO2 reduction reaction

Abstract

In two-dimensional (2D) materials, selective facet exposure is highly sought after but can be typically achieved only through sophisticated methods like chemical vapour deposition (CVD) or molecular beam epitaxy (MBE). Existing wet-chemical methods, whether diffusion-controlled or ligand-assisted, mostly concentrate on morphology control or facet tuning through shape regulation, but they hardly ever achieve both at the same time. Herein, we report a distinctive hard-templating approach that permits simultaneous facet engineering and 2D structure formation 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. Importantly, the use of highly reactive white phosphorus permits the formation of CIPS within the wet-chemical temperature limit of 225 °C, whereas red phosphorus-based solid state synthesis requires 14 days of continuous heating at an elevated temperature of 600 °C. As a result, this straightforward method facilitates an energy-efficient, one-pot, greener conversion to non-vdW CIS with superior control over crystal facet exposure, replacing conventional multi-step complex procedures. The resulting 2D CIS possesses a cubic zincblende structure yet preserves the hexagonal atomic arrangement of the template, yielding dominant (111) facet exposure. Additionally, the template determines the flake thickness. Owing to both facet exposure and intrinsic phosphorus doping, this catalyst delivers significantly enhanced formate selectivity in the electrochemical CO₂ reduction reaction compared with its non-2D or non-faceted counterparts with similar electrochemically active surface areas (ECSAs).