Recent Trends in Artificial Leaves: Atomistic-design and Surface-probing Using Selective Two-dimensional Nanomaterials as Examples

Abstract

Photocatalytic CO2 conversion to hydrocarbon fuels, which makes possible simultaneous solar energy harvesting and CO2 reduction reaction (CO2RR), is considered a killing-two-birds-with-one-stone approach to solving the energy and environmental problems. However, the development of solar fuels has been hampered by the low photon-to-fuel conversion efficiency of the photocatalysts and lack of the product selectivity. Recent advances in development of integrated nanostructured materials have offered unprecedented opportunity for photocatalytic CO2RR. In 2D-layered nanomaterials (TMDCs and beyond), a perfect planar layer structure is usually inactive. Here, four cases with defect engineering (e.g. interstitial, vacancy, etc.) and heterostructures for enhancing CO2RR will be illustrated: (i) single-layer to few-layer MoS2 with vacancies controlled by plasma; (ii) reconstructed edge atoms of monolayer WSe2; (iii) the carbon-doped or carbon-implanted SnS2 nanosheets; and (iv) direct Z-scheme of ZnS/ZIS heterojunctions. Besides the challenges in materials, to make such energy conversion towards practical solutions, some key questions need to be addressed. For instance: Where does the reaction take place and what are the key steps for CO2RR? Nanoscale redox mapping using scanning tunnelling microscope at the TMDC–liquid interface shows layer-dependent redox behavior and also confirms that the edge is the most preferred region for charge transfer. Advancements in in situ and operando synchrotron radiation-based spectroscopies, including X-ray absorption and X-ray photoelectron spectroscopy (XPS), etc., along with various vibrational spectroscopies, such as Raman and Fourier transform infrared spectroscopy (FTIR), have enabled scientists to probe the geometric, bonding and electronic information of the catalyst and obtain atomic insights into the catalytic surfaces and reaction mechanisms.