The Evolution of Hexagonal Cobalt Nanosheets for CO 2 Electrochemical Reduction Reaction.

The CO2 electrochemical reduction reaction (CO2RR) is one of the most promising methods to reduce carbon dioxide emissions and store energy. At the same time, the pathways of CO2 reduction reaction are diverse and the products are abundant. Converting carbon dioxide to C2+ products, a critical feedstock, requires a C–C coupling step with the transfer of more than 10 electrons per molecule and, hence, is kinetically sluggish. The production of some key adsorptions is conducive to the formation of C2+ products. In this work, we used in situ techniques to figure out the reason why hexagonal-close-packed (hcp) Co nanosheets (NSs) have high activity in CO2RR to ethanal. According to the in situ Raman spectra, the high local pH environment on the catalyst surface is favorable for CO2RR. The high pH at low potentials not only suppresses the competing hydrogen evolution reaction but also stimulates the production of COCO* intermediate. The isotopic labeling experiment in differential electrochemical mass spectrometry (DEMS) provides a possible sequence of the products. The 13CO is generated when we replace 12CO2 with 13CO2, which identifies the origin of the products. Besides, in situ electrochemical impedance spectroscopy (EIS) shows that the hcp Co at −0.4 V vs. RHE boosts the H2O dissociation and proton transfer, feeding sufficient H* for CO2 to *COOH. In the end, by analyzing the transmission electronic microscopy (TEM), we find that the Co (002) plane may be beneficial to the conversion of CO2 and the adsorption of intermediates. [ABSTRACT FROM AUTHOR]