Carbon-based metal-free catalysts for electrochemical CO2 reduction: Activity, selectivity, and stability

Zero or negative emissions of carbon dioxide (CO2) is the need of the times, as inexorable rising and alarming levels of CO2 in the atmosphere lead to global warming and severe climate change. The electrochemical CO2 reduction (eCO2R) to value-added fuels and chemicals by using renewable electricity provides a cleaner and more sustainable route with economic benefits, in which the key is to develop clean and economical electrocatalysts. Carbon-based catalyst materials possess desirable properties such as high offset potential for H2 evolution and chemical stability at the negative applied potential. Although it is still challenging to achieve highly efficient carbon-based catalysts, considerable efforts have been devoted to overcoming the low selectivity, activity, and stability. Here, we summarize and discuss the recent progress in carbon-based metal-free catalysts including carbon nanotubes, carbon nanofibers, carbon nanoribbons, graphene, carbon nitride, and diamonds with an emphasis on their activity, product selectivity, and stability. In addition, the key challenges and future potential approaches for efficient eCO2R to low carbon-based fuels are highlighted. For a good understanding of the whole history of the development of eCO2R, the CO2 reduction reactions, principles, and techniques including the role of electrolytes, electrochemical cell design and evaluation, product selectivity, and structural composition are also discussed. The metal/metal oxides decorated with carbon-based electrocatalysts are also summarized. We aim to provide insights for further development of carbon-based metal-free electrocatalysts for CO2 reduction from the perspective of both fundamental understanding and technological applications in the future