Enhancing Ammonia Oxidation in Direct Ammonia Fuel Cells with Cauliflower-Structured NiCu Alloy Anode

Nickel (Ni) has become a nonprecious metal catalyst of great interest in direct ammonia fuel cell (DAFC) research owing to its low cost and plentiful reserves. However, in the ammonia oxidation reaction (AOR), the poor electrocatalytic activity of Ni limits the DAFC performance and application. Here, we design a cauliflower-like NiCu nanosphere alloy (Ni@NiCu/CP) by cyclic voltammetry (CV) and square wave potential (SWP) electrodeposition on carbon paper (CP) with a Ni substrate layer. The formation of NiCu alloys and the cauliflower-like structure with abundant catalytic active sites enhances the conductivity, reduces the internal resistance of charge transfer, improves the reaction kinetics, and thereby increases the AOR performance. The maximum current density of Ni@NiCu/CP electrode reaches 241.2 mA cm–2, which is at a relatively high level in the previously reported studies. Moreover, a membrane-free DAFC is constructed utilizing catalyst-free carbon paper as the cathode and Ni@NiCu/CP as the anode. It has an open-circuit voltage (OCV) of 1.3 V and a peak power density of 15.46 mW cm–2. The results indicate that this cost-effective alloy catalyst has good prospects for application in direct ammonia fuel cells.