Catalysts in electro-, photo- and photoelectrocatalytic CO2 reduction reactions

Carbon dioxide (CO2) is regarded as a main contributor to the greenhouse effect. As a potential strategy to mitigate its negative impacts, the reduction of CO2 is environmentally critical, economically meaningful and scientifically challenging. Being both thermodynamically and kinetically unfavored, CO2 reduction requires catalysts as a crucial component irrespective of the reaction modes, be it electrocatalytic, photoelectrocatalytic or photocatalytic. In an effort to systematically review the types of catalysts that have been studied for CO2 reduction, we categorize them into two major groups: those being activated by external sources and those being photoexcited and activated themselves. Attention is focused on the detailed mechanisms for each group by which the reduction of CO2 proceeds, yielding a summary of the guiding principles for catalyst designs. This review highlights the importance of mechanistic studies, which permits us to discuss our perspectives on potential directions of catalyst investigation for future catalytic CO2 reduction research. (C) 2019 Elsevier B.V. All rights reserved.