Rational electronic control of carbon dioxide reduction over cobalt oxide

The selective reduction of carbon dioxide (CO 2 ) into fuels and chemicals is expected to play a key role in achieving a carbon–neutral sustainable energy economy. Activation of CO 2 is the most important step in this process. As the electron transfer to CO 2 is the rate-limiting step for CO 2 activation, it is significant to modulate the electronic structure of CO 2 reduction catalysts to enhance their activities. However, the intrinsic relationships between electronic properties of catalysts and their catalytic activities remains somewhat unclear, which limits the rational design of highly-efficient CO 2 reduction catalysts. Herein, a catalyst-insulator–metal system consisting of Al as an electron-donor material was designed to modulate the electronic structure of cobalt oxide (Co 3 O 4 ) catalyst. The electrons in Al can be efficiently tunneled to Co 3 O 4 across an ultrathin self-formed Al 2 O 3 insulating layer. Experimental and theoretical results undoubtedly confirm that high electron density on Co 3 O 4 favours the adsorption and activation of CO 2 , while lowers the energy barrier for the formation of COOH* and especially lowers the desorption energy barrier of CO* intermediates, thereby significantly accelerating the reaction kinetics of CO 2 -to-CO photoreduction. The turnover frequency per Co atom of Co 3 O 4 /Al 2 O 3 -Al is much higher than that of Co 3 O 4 . The apparent quantum yield (AQY) of Co 3 O 4 /Al 2 O 3 -Al catalyst highly reaches 3.8% at 420 nm, which is superior to those of most reported catalysts. Besides, the increase in electron density on Co 3 O 4 can effectively inhibit the competing hydrogen evolution reaction. The selectivity of CO increases from 57.9% for Co 3 O 4 to 82.4% for Co 3 O 4 /Al 2 O 3 -Al. Significantly, the catalytic efficiency can be rationally tuned through controlling the content and particle size of Al. This work stablishes the links between the electronic structure of catalysts and their catalytic activities toward CO 2 reduction reaction. Moreover, this Al 2 O 3 -Al structure reported here, may be used as an unprecedented platform for the electronic effect study of other heterogeneous catalysts.