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

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.