Progress and perspectives for engineering and recognizing active sites of two-dimensional materials in CO_(2) electroreduction

Carbon dioxide electroreduction usually suffers from low catalytic activities and debatable reaction mechanisms at present. That may be primarily ascribed to the high energy barrier for carbon dioxide activation over the conventionally fabricated catalysts and the infeasibility of traditional characterization techniques for unveiling the evolution of active sites and reactive intermediates. Two-dimensional(2 D) materials, which possess the active sites with high proportion, high activity and high uniformity, can act as ideal models to manipulate the active sites and understand structure-property relationship. In this review, we overview the boosted carbon dioxide activation by the intrinsic peculiar electronic states of 2D catalysts and the charge localization effect induced by chemical modification of two-dimensional catalysts. We also summarize the recognition of the structural evolutions for active sites in two-dimensional catalysts by means of in situ X-ray diffraction pattern and in situ X-ray absorption spectroscopy. Moreover, we emphasize the detection of the reactive intermediates on active sites in two-dimensional catalysts via in situ Raman spectroscopy and in situ Fourier transform infrared spectroscopy. Finally, we end this review with an outlook on the unresolved issues and future development of carbon dioxide electroreduction.