High-Index Exposed and Ultra-Layered Co3o4: A Bifunctional Catalyst for Electrochemical Urea Oxidation, and Rapid 4-Nitrophenol Reduction to 4-Aminophenol

Abstract

Release of urea-enriched wastewater from urea industries pose a big threat to human health and aquatic environments. Electrochemical urea oxidation reaction (UOR) offers a potential solution by reducing wastewater “pollution” and producing “green” hydrogen via wastewater splitting. In this study, one-pot hydrothermal post-air-annealing was employed to synthesize ultra-layered Co3O4 nanosheets with exposed high-index (220) facets, using cobalt acetate and urea without additives. The air-annealing temperature played pivotal role, with the sample annealed at 500°C (H120-500) exhibiting ultra-layered nanosheets with (220) high-index dominance. This configuration facilitates diffusion and electron transfer in UOR, contributing to its superior performance compared to control samples and commercial Co3O4. H120-500 achieved a high turnover frequency (TOF) of 0.1493 s-1, current density of 250 mA.cm-2, stability over 20 hours, Tafel slope of 22.4 mV.dec-1, and requires only 1.37 V vs RHE to reach 10 mA.cm-2, surpassing state-of-the-art cobalt-based UOR electrocatalysts. Moreover, H120-500 displayed exceptional efficiency in reducing 4-NP to 4-AP, achieving a 99.64% reduction in just 2 minutes with pseudo-first-order rate constant (k) of 2.63×10-2 s-1 and durability over seven cycles. This approach holds promise for mitigating environmental pollution and generating green H2 coupled with valuable chemicals.

Keywords: : Catalysis, Exposed high-index facets, Tafel slope, Ultra-layered Co3O4 nanosheets, Reduction efficiency