Construction of Fe3O4@Au catalysts via the surface functional group effect of ferric oxide for efficient electrocatalytic nitrite reduction

Abstract

Surface modification is one of the effective strategies to control the morphology and electrocatalytic performance of noble metal/transition metal oxide matrix composite catalysts. In this work, we successfully introduced modification groups such as –NH₂, –COOH, and –SH on the surface of Fe₃O₄ using the hydrothermal method. It was found that when the modification group –COOH was introduced, the regular spherical morphology of Fe₃O₄ was still maintained in Fe₃O₄–COOH, while Fe₃O₄–COOH had a relatively smaller spherical particle size (≈155.9 nm). Due to its smaller particle size, Fe₃O₄–COOH has a larger active area than Fe₃O₄, exposing more active sites. The abundant active sites in Fe₃O₄–COOH provide more nucleation and growth sites for Au particles, which is beneficial for the recombination between Fe₃O₄–COOH and Au. In addition, the experimental results of exploring the effect of Au precursor dosage on the synthesis of the Fe₃O₄–COOH@Au structure and performance show that the synthesized Fe₃O₄–COOH@Au_1.0 catalyst has higher electrocatalytic activity. Due to the larger electrochemically active surface area of the Fe₃O₄–COOH@Au_1.0 catalyst compared to those of Fe₃O₄–COOH@Au_0.5 and Fe₃O₄–COOH@Au_1.5 catalysts, the adsorption and activation of NO₂⁻ reactants were accelerated, thereby improving the electrocatalytic performance. Therefore, owing to the morphological and structural characteristics of Fe₃O₄–COOH combined with the high activity of Au nanoparticles, the synthesized Fe₃O₄–COOH@Au exhibits effective electrocatalytic activity in the electrocatalytic NO₂⁻RR synthesis of ammonia. At a voltage of −0.8 V (vs. RHE), the ammonia yield reached 2092.8 μg h⁻¹ mg_cat⁻¹ and Faraday efficiency reached 81.2%. The findings of this work will enrich our understanding of the construction of efficient Fe₃O₄@Au catalysts based on surface functionalization and help to design efficient electrocatalytic NO₂⁻RR catalysts for practical applications.