Origin of surface-bonded oxygen on dendritic Ag particles towards 3D-nanocrystalline carbon formation during CO2 electrochemical reduction reaction

Abstract

Formation of nanocrystalline carbon allotropes under the electrocatalytic reduction reaction of CO2 (CO2RR) on the dendritic Ag electrocatalysts was investigated at the applied potential −1.6 V vs. Ag/AgCl under the electrolyte system containing [BMIM]+[BF4]-, propylene carbonate, and water. The surface Ag − O bonds play an important role in developing the N+ stabilized highly energetic negatively charged Ag nanoclusters on which the nanocrystalline solid carbon was formed. Herein, the surface-bonded oxygen on dendritic Ag particles was originated from (i) the ultrathin natural silver oxide layers (unmodified Ag), (ii) anodization treatment (AD), and (iii) cyclic voltammetry treatments at a scan rate 1 (CV1) or 200 mV/s (CV200) for 5 cycles. Their capability to catalyze CO2RR towards solid carbon products depends on the stabilization of the active state of negatively charged nascent Ag nanoclusters under [BMIM]+[BF4]-. Even though each catalytic system yielded a major crystalline solid carbon product, a slight shift towards gaseous CO formation was noted in the case of AD compared to the unmodified Ag, CV200, and CV1, respectively. The increased intricacy in the three-dimensional structure of dendritic Ag particles following CV1 post-treatment, coupled with a stronger Ag − O bond could hinder agglomeration of anion Ag clusters. The crystalline solid carbon films containing sp2 − sp3 hybridization were grown on the facets of Ag nanocrystals as the building blocks and were matched with graphite and Diamond-C structures. The discoveries have significance in propelling the progress of electrocatalysts containing oxides, aiming to attain enhanced yields of higher value nanocrystalline carbon products through CO2RR.