Analysis of Transition from Compact to Mossy Structures During Galvanostatic Zinc Electrodeposition and Its Implications for CO2 Electroreduction

The galvanostatic electrodeposition of zinc on carbon paper from mildly acidic solutions (ZnCl2: 0.05–0.1 M; H3BO3: 0.05 M) was investigated. The deposits’ growth mechanisms were analyzed through the study of the electrodeposition potential transients and the physical characterization of the electrodes synthesized by varying the current density, transferred charge, and zinc precursor concentration. The analysis reveals that the transition from crystalline to amorphous mossy deposits takes place via the electrodeposition of metallic zinc followed by the formation of oxidized zinc structures. The time required for this transition can be controlled by varying the zinc precursor concentration and electrodeposition current density, allowing for the synthesis of composite zinc/oxidized zinc electrodes with varying ratios of the oxidized to underlying metallic phases. The impact of this ratio on the electrode activity for CO2 electroreduction is analyzed, highlighting that composite zinc/oxidized zinc electrodes can achieve a faradaic efficiency to CO equal to 82% at −1.8 V vs. Ag/AgCl. The mechanisms behind the variations in the catalytic activity with varying morphologies and structures are discussed, providing guidelines for the synthesis of composite zinc/oxidized zinc electrodes for CO2 electroreduction.