Acidic Electrocatalytic CO 2 Reduction Using Space-Confined Nanoreactors.

Electrochemical CO 2 reduction reaction (CO 2 RR) is an attractive strategy for sustainable production of chemicals and has mainly been implemented in alkaline or neutral electrolytes. However, part of input CO 2 is consumed by the formation of carbonate under these conditions. Herein, a space-confined strategy is proposed for CO 2 RR in acidic media, and Ni nanoparticles are encapsulated inside N-doped carbon nanocages as yolk-shell nanoreactors. By confining CO 2 RR in the cavities of nanoreactors, a Faradaic efficiency (FE) of 93.2% for CO is achieved at pH 7.2 and 84.3% FE for CO at pH 2.5. The inhibited proton diffusion within the Nernst layer of a nanoreactor is responsible for suppression of competing hydrogen evolution in acid. Moreover, CO 2 RR in an acidic flow electrolysis system offers enhanced current density and sustainable operation, in comparison with the conventional neutral pH system. This work shows that steering of mass transport via a unique structure is a viable avenue toward selective CO 2 conversion, and it provides a further understanding of the structure-performance relationship of electrocatalysts.