Since the discovery of the first single-layer graphene (GR) in 2004, numerous graphene-like two dimensional (2D) materials have aroused widespread interest inartificial photosynthetic systems. 2D materials in AP systems can act as light absorbers to capture solar light, and simultaneously produce the high-energy state electron-hole pairs.
Recently, Academician Sun Licheng and others from Westlake University published a Perspective article in "National Science Review" (NSR), analyzing the research progress, scientific problems and challenges of artificial photosynthesis systems constructed based on 2D materials in the field of solar fuel synthesis.
2D materials in AP systems can act as light absorbers to capture solar light, and simultaneously produce the high-energy state electron-hole pairs. Due to the merit of the nanoscale thickness of 2D materials, the photogenerated electrons can be swiftly conveyed to co-catalysts for the reduction reactions (HER, CO2 reduction, N2 fixation etc.), while the photogenerated holes are quickly transferred to water oxidation catalysts for O2 evolution reaction (OER). In addition to the rapid migration of photogenerated carriers, the large specific surface area of 2D materials can by themselves provide more accessible active sites, thus facilitating their catalytic activity. Furthermore, the planar structures of 2D materials allow their chemical modification via various strategies for AP.
In this article, the authors elaborate on strategies to enhance solar energy conversion efficiency in artificial photosynthesis systems based on two-dimensional (2D) materials:
(1) From the perspective of the 2D materials themselves, strategies include designing 2D materials with different structures, reducing their thickness, introducing vacancies and heteroatoms, and constructing 2D/2D heterojunctions.
(2) From the perspective of co-catalysts, combining heterogeneous catalysts or molecular catalysts with 2D materials to construct "co-catalyst-2D material" composite catalysts, thus accelerating surface reaction kinetics and effectively promoting catalytic reactions.
Furthermore, the author also identified the current scientific issues and challenges faced by the 2D materials-based artificial photosynthesis systems:
·many breakthroughs are being made in promoting photocatalytic water splitting, CO2 reduction and N2 fixation properties via 2D-material-based AP under lab conditions, while industrial application is still in its infancy. The lack of facile and economic technologies for large-scale production of 2D materials with a precisely controllable layer number and atomic structure is a non-negligible factor.
·as for photocatalytic CO2 reduction, the products are mainly limited to C1 chemicals instead of the C2+ chemicals with higher energy density and market value.
·the relatively low photocatalytic activity of N2 fixation (micromole or below) caused by the high N≡N triple bond energy, weak adsorption and activation of N2 on catalytic
sites.
·the systematic optimization of 2D materials and co-catalysts is the cornerstone to achieving large-scale production of solar fuels via AP.