Construction of Fe 3 O 4 @Au catalysts via the surface functional group effect of ferric oxide for efficient electrocatalytic nitrite reduction.

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 -NH 2 , -COOH, and -SH on the surface of Fe 3 O 4 using the hydrothermal method. It was found that when the modification group -COOH was introduced, the regular spherical morphology of Fe 3 O 4 was still maintained in Fe 3 O 4 -COOH, while Fe 3 O 4 -COOH had a relatively smaller spherical particle size (≈155.9 nm). Due to its smaller particle size, Fe 3 O 4 -COOH has a larger active area than Fe 3 O 4 , exposing more active sites. The abundant active sites in Fe 3 O 4 -COOH provide more nucleation and growth sites for Au particles, which is beneficial for the recombination between Fe 3 O 4 -COOH and Au. In addition, the experimental results of exploring the effect of Au precursor dosage on the synthesis of the Fe 3 O 4 -COOH@Au structure and performance show that the synthesized Fe 3 O 4 -COOH@Au 1.0 catalyst has higher electrocatalytic activity. Due to the larger electrochemically active surface area of the Fe 3 O 4 -COOH@Au 1.0 catalyst compared to those of Fe 3 O 4 -COOH@Au 0.5 and Fe 3 O 4 -COOH@Au 1.5 catalysts, the adsorption and activation of NO 2 - reactants were accelerated, thereby improving the electrocatalytic performance. Therefore, owing to the morphological and structural characteristics of Fe 3 O 4 -COOH combined with the high activity of Au nanoparticles, the synthesized Fe 3 O 4 -COOH@Au exhibits effective electrocatalytic activity in the electrocatalytic NO 2 - 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 Fe 3 O 4 @Au catalysts based on surface functionalization and help to design efficient electrocatalytic NO 2 - RR catalysts for practical applications.