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

• A branched hierarchical Co 3 O 4 @Fe 2 O 3 core–shell composite is prepared. • The composite can realize selective and efficient electroreduction of NO 3 – to NH 3. • The experimental and DFT results verify a synergistic effect between Co 3 O 4 and Fe 2 O 3 . • The composite can enhance nitrate adsorption, suppress HER and promote NH 3 release. This work employs a high-efficiency, low cost and environmentally friendly electrochemical nitrate reduction (NO 3 RR) 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 Co 3 O 4 @Fe 2 O 3 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 NH 3 -N yield rate of 3810 μg h −1 cm −2 were obtained at Co 3 O 4 @Fe 2 O 3 |CC, which also displayed durability by retaining a high Faradaic efficiency of 79.3 % after six consecutive NO 3 RR cycles. Investigation of the mechanism reveals that active atomic *H plays a key role in the NO 3 RR. The excellent NO 3 RR performance of Co 3 O 4 @Fe 2 O 3 |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 Co 3 O 4 @Fe 2 O 3 core–shell structure is superior to Co 3 O 4 |CC and Fe 2 O 3 |CC in catalyzing NO 3 RR due to the synergistic effect between Co 3 O 4 and Fe 2 O 3 . This synergistic effect can promote the adsorption of NO 3 – , release of NH 3 and inhibition of hydrogen evolution, ensuring the highly selective and efficient conversion of NO 3 – to NH 3 . This work demonstrates that the morphology of an electrocatalyst can significantly affect its performance for the NO 3 RR, and has potential for practical application purposes.