Influence of CeO2 support morphology on the structural and NO2−RR performance of CeO2@Au catalyst†

Abstract

Gold nanoparticles are extensively employed in the field of electrocatalytic nitrite reduction for ammonia synthesis, due to their exceptional conductivity and remarkable stability. However, the performance of a single metal is often limited and by combining different metals, the overall performance can be significantly improved to meet specific needs and application scenarios. The regulation of the interaction between loaded gold nanoparticles and metal oxide support materials represents an effective strategy for facilitating the reduction of nitrite to ammonia. In this work, we prepared three different structural morphologies of cerium dioxide (CeO₂) – cubic (c-CeO₂), rod-like (r-CeO₂) and granular (p-CeO₂), by modulating the hydrothermal temperature. The effect of the morphology of the CeO₂ carriers on the surface structure of the composite catalyst, CeO₂@Au, was systematically studied and its performance of the electrocatalytic reduction of ammonia from nitrite was explored. It was found that c-CeO₂ loaded with Au nanoparticles possessed better electrocatalytic performance with an ammonia yield of 4007.9 μg h⁻¹ mg_cat⁻¹ and a Faraday efficiency of 91.2% compared to r-CeO₂ and p-CeO₂. The results of the characterisation tests, conducted using scanning electron microscopy (SEM), elemental mapping analysis (EDS) and inductively coupled plasma (ICP), demonstrate that c-CeO₂ exhibits enhanced crystallinity, a reduced particle size and a more uniform dispersion. Therefore, c-CeO₂ is able to load more Au nanoparticles during the complexation process with Au, which in turn possesses more reactive active sites. In addition, the results of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) showed that after the complexation of c-CeO₂ with Au, some of the lattice fringes of c-CeO₂ were distorted with defects leading to an increase in the content of oxygen vacancies, which greatly improved the active area of the catalyst. These physicochemical properties endow the c-CeO₂@Au catalysts with excellent electrocatalytic nitrite-to-ammonia activity.