Preparation of a branched hierarchical Co3O4@Fe2O3 core-shell structure with high-density catalytic sites for efficient catalytic conversion of nitrate in wastewater to ammonia

This work employs a high-efficiency, low cost and environmentally friendly electrochemical nitrate reduction (NO3RR) strategy to realize the highly selective conversion of a typical environmental pollutant-nitrate to an extremely important chemical product-ammonia. To ensure high ammonia selectivity and Faradaic efficiency, a branched hierarchical Co3O4@Fe2O3 core-shell structure was synthesized on carbon cloth (CC) using a simple two-step hydrothermal method. After material characterization and parameter optimization, a nitrate conversion rate of 88.4 %, ammonia selectivity of 89.4 %, Faradaic efficiency of 87.2 % and NH3-N yield rate of 3810 mu g h- 1 cm- 2 were obtained at Co3O4@Fe2O3|CC, which also displayed durability by retaining a high Faradaic efficiency of 79.3 % after six consecutive NO3RR cycles. Investigation of the mechanism reveals that active atomic *H plays a key role in the NO3RR. The excellent NO3RR performance of Co3O4@Fe2O3|CC is attributed to its branched hierarchical core-shell structure with large electrochemical surface area and fully exposed catalytic sites. In addition, both experimental and density functional theory (DFT) calculations indicate that the Co3O4@Fe2O3 core-shell structure is superior to Co3O4|CC and Fe2O3|CC in catalyzing NO3RR due to the synergistic effect between Co3O4 and Fe2O3. This synergistic effect can promote the adsorption of NO3-, release of NH3 and inhibition of hydrogen evolution, ensuring the highly selective and efficient conversion of NO3 - to NH3. This work demonstrates that the morphology of an electrocatalyst can significantly affect its performance for the NO3RR, and has potential for practical application purposes.