Cu-ACF Composite Catalyst: Synthesis, Characterization, and Electrocatalytic Properties toward Ammonia Oxidation in Acid Solution

Abstract

Oxidation of ammonia (NH3) using electrocatalyst is highly important because of its usage in fuel cells. In this study, a Cu-ACF composite catalyst was synthesized by the liquid phase deposition (LPD) method with immobilizing copper serving as the active component onto activated carbon fiber (ACF) matrix for the electrochemical oxidation (ECO) of inorganic compounds exemplified by NH3. The electrochemical behavior and surface characteristics of the catalyst, including its redox and corrosion properties, were assessed using cyclic voltammetry (CV), fluorescence spectroscopy (FS), UV-Vis absorption spectroscopy, zeta potential measurements, environmental scanning electron microscopy (ESEM), and transmission electron microscopy–energy dispersive X-ray spectrometer (TEM-EDX). Results demonstrated that applying the CV reversible redox capability could illustrate the catalytic activity of the Cu-ACF catalysts, and the NH3 oxidation current density on the Cu-ACF catalyst increases with increasing scan rate. The wavelengths of the fluorescence peaks for the fresh catalyst varied from those of the exhausted catalyst, which reveals that FS is a valid method to the characterization of the formation of copper oxide nano-clusters in intrinsic fluorescence emission from Cu-ACF catalyst. The ESEM and TEM-EDX results demonstrate that CuO crystal nanoparticles are highly dispersed on the ACF-supported surface. These crystal structures can explain the high activity of the electrocatalyst, which is also responsible for the strong metal-support interaction.