A strategic approach for nanostructured Zn-based electrocatalyst for highly selective electrochemical conversion of CO2 to CO

Abstract

Electroreduction of carbon dioxide (CO₂) directly facilitates the conversion of intermittent recycling into value-added chemicals and fuel, presenting a favorable strategy to resolve the energy and environmental crises caused by CO₂ emissions. Therefore, there is a necessity to develop highly active and selective emerging electrocatalysts to perform electrochemical CO₂ reduction (ECR) to carbon monoxide (CO). This work identifies a low-cost, earth-abundant, and non-toxic Zinc (Zn)-based electrocatalyst as a promising electrocatalyst for CO selectivity. Zn-based electrocatalysts were synthesized using a facile electrodeposition (ED) method in two different configurations: an ex situ cell and an in situ cell. The ex situ cell utilized a conventional three-electrode system, yielding an electrocatalyst referred to as Zn₈₇. Conversely, the in situ cell employed a gas diffusion electrode (GDE), resulting in the formation of an electrocatalyst identified as ZnO₅₂. Based on the phase quantification of the electrocatalysts from XRD analysis, the Zn electrocatalyst shows Zn (87 %) and ZnO (13 %). Whereas, the ZnO electrocatalyst shows the Zn (48 %) and ZnO (52 %). Thus, based on the predominant phase values, the electrocatalysts name, Zn as Zn_87%, and ZnO as ZnO_52% respectively, were adapted. Here, the ZnO₅₂ electrocatalysts, grown by the in situ cell, showed a large electroactive surface area, demonstrating more efficient ECR activity toward CO production with a Faradaic efficiency (FE_CO) of 88.4 % at –0.87 V versus reversible hydrogen electrode (V_RHE). However, the Zn₈₇ electrocatalyst, grown by the ex situ cell exhibited a FE_CO of 65.6 % at –0.98 V_RHE at an applied current density of 100 mA cm⁻². Accordingly, the enhanced electrochemical activity of the ZnO₅₂ electrocatalyst can be attributed to the large surface area, which provides great adsorption capacity, and the predominant Zn²⁺ create more active sites. Additionally, the Zn counterpart of the electrocatalyst, helps to stabilize ZnO state from converting ZnO to metallic Zn during the CO₂R performance.