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

The CO[sub.2] electrochemical reduction reaction (CO[sub.2]RR) is one of the most promising methods to reduce carbon dioxide emissions and store energy. At the same time, the pathways of CO[sub.2] reduction reaction are diverse and the products are abundant. Converting carbon dioxide to C[sub.2+] 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 C[sub.2+] 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 CO[sub.2]RR to ethanal. According to the in situ Raman spectra, the high local pH environment on the catalyst surface is favorable for CO[sub.2]RR. 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 [sup.13]CO is generated when we replace [sup.12]CO[sub.2] with [sup.13]CO[sub.2], 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 H[sub.2]O dissociation and proton transfer, feeding sufficient H* for CO[sub.2] 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 CO[sub.2] and the adsorption of intermediates.