Dictating CuO:Cu(OH) 2 Ratio and Microstructural Evolution by Varying the Temperature of Anodization of Cu for OER-Masking GOR!

Abstract

This study investigates the anodization of Cu foam substrate at various temperatures and examines its influence on the surface composition and subsequent electrocatalytic glucose oxidation reaction (GOR). It has been found that anodizing Cu at room temperature results in a higher proportion of Cu(OH) 2 compared to CuO with a better control over the typical nanoneedles obtained while anodizing Cu. Increasing the temperature of anodization increases the CuO proportion while shortening the average length of the nanoneedles from ~3 μm at room temperature to ~50 nm at 46 C. When all these were tested with a 0.15 M glucose solution in 1 M KOH, the one anodized at room temperature achieved the highest current density of approximately 500 mA cm -2 at 1.924 V vs. RHE. The superior performance is attributed to the unique surface chemistry featuring a relatively higher proportion of Cu(OH) 2 , which facilitates a more efficient electron transfer during the glucose oxidation process with their lattice OH groups, vital for glucose activation. With CuO, glucose oxidation demands the in-situ conversion of CuO into Cu(OH) 2 or CuOOH for the same and tends to be slower. Moreover, the Cu electrode anodized at room temperature demonstrates the critical advantage of effectively masking the oxygen evolution reaction (OER), and exceptional durability under operational conditions. These insights on anodization of Cu electrodes are crucial for the practical application of Cu-based electrodes in co-electrolysis-based sustainable hydrogen production.