Mechanistic insights into the effect of halide anions on electroreduction pathways of CO 2 to C 1 product at Cu/H 2 O electrochemical interfaces

Various elementary reaction steps during CO 2 electroreduction into C 1 product are systematically studied at specifically adsorbed halide anions modified Cu(111)/H 2 O interfaces via theoretical calculations with the aim of identifying the effect of halide anions X − (X = F, Cl, Br, I) on CO 2 electroreduction reaction activity, mechanisms and product selectivity in this work. Our present studies show that halogen atoms can be adsorbed on the Cu electrodes during CO 2 electroreduction, thus leading to notable electronic interactions between halogen atoms and Cu(111)/H 2 O interface. It is found that halogen atoms can gain electrons in the order of F > Cl > Br > I, showing that the adsorbed halide anions can be formed. The presence of halide anions can notably be favor of CO formations. CO electroreduction pathways towards C 1 product at Br − and I − modified Cu(111)/H 2 O interfaces are examined due to poor selectivity of CO electroreduction into CHO at F − and Cl − modified Cu(111)/H 2 O interfaces. The calculated results indicate that the presence of Br − and I − facilitate CO 2 electroreduction into C 1 product since notably enhanced CO 2 electroreduction activity can be achieved, which may be ascribed to the formations of chemically adsorbed anion radical ˙CO 2 − and more positive onset potentials for CO formations. Notably, it is found that the electroreduction pathways of CO 2 into CH 4 and CH 3 OH product may be able to parallelly occur at Br − and I − modified Cu(111)/H 2 O interfaces, whereas only CH 4 production pathways can occur at clean Cu(111)/H 2 O interface. Thus, it can be concluded that the presence of halogen anions on Cu alter mechanism and product selectivity of CO 2 electroreduction. Our present mechanistic insights into this effect may be able to give a theoretical guideline for control of mechanisms and product selectivity during CO 2 electroreduction.