Synthesis of hydroxide nanoparticles of Co/Cu on carbon nitride surface via galvanic exchange method for electrocatalytic CO2 reduction into formate

Abstract

Herein we report Co and Cu based metal hydroxides (Co(OH)2/Cu(OH)2) on carbon nitride (C3N4) surface via replacement of Co nanoparticles (NPs) through galvanic exchange method for electrocatalytic carbon dioxide reduction. The lower value of reduction potential in case of cobalt ([Co+(aq) + 2e− → Co(s)], −0.28 eV) compared to copper ([Cu2+(aq) +2 e− → Cu(s)], +0.34 eV) makes Co(0) easily susceptible to galvanic exchange process. On the basis of this significant difference in the reduction potential of Cu(0) and Co(0), 0.62 V, Cu2+ can replace Co(0) via galvanic exchange without using any external bias. The synthesis of (Co(OH)2/Cu(OH)2) involves two steps, where in the first step on surface of C3N4, Co NPs were synthesized via reducing of Co2+ ions with a strong reducing agent NaBH4. In presence of aqueous medium, formation of cobalt hydroxide also takes place. In the second step these cobalt nanoparticles on C3N4 were subjected to the process of galvanic exchange in which the sacrificial Co NPs were exchanged by Cu atoms and forming Cu(OH)2 in presence of an aqueous medium. Overall, the whole synthesis process results in deposition of hydroxides of cobalt and copper (C3N4/(Co(OH)2/Cu(OH)2) on C3N4 surface. The synthesized materials were characterized using PXRD, EDS, XPS, TEM and SEM. The two electrocatalysts C3N4/(Co/Co(OH)2 C3N4/(Co(OH)2/Cu(OH)2 were evaluated for their performance towards carbon dioxide reduction. C3N4/(Co(OH)2/Cu(OH)2 showed superior performance with electrocatalytic activity more than three times of C3N4/(Co/Co(OH)2. The product of CO2 electro-reduction was identified, using a rotating ring disc electrode (RRDE) system, to be primarily formate.