Synergistic Effect of Co(III) and Co(II) in a 3D Structured Co3O4/Carbon Felt Electrode for Enhanced Electrochemical Nitrate Reduction Reaction

• Published in: ACS applied materials & interfaces 2021-06, Vol.13 (24), p.28348-28358
• Main Authors: Fu, Wenyang, Du, Xuedong, Su, Pei, Zhang, Qizhan, Zhou, Minghua
• Format: Article
• Language: English
• Subjects: Energy, Environmental, and Catalysis Applications
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.1c07063

As nitrate contamination causes serious environmental problems, it is necessary to develop stable and efficient electrocatalysts for efficient electrochemical nitrate reduction reaction (ENRR). Here, a nonprecious Co3O4/carbon felt (CF) electrode with a 3D structure was prepared by integrating electrodeposition with calcination methods. This 3D structured Co3O4/CF electrode exhibits a high-rate constant of 1.18 × 10–4 s–1 cm–2 for the ENRR, surpassing other Co3O4 electrodes in previous literature. Moreover, it also has an excellent stability with a decrease of 6.4% after 10 cycles. Density functional theory calculations, electron spin resonance analysis, and cyclic voltammetry were performed to study the mechanism of the ENRR on the Co3O4/CF electrode, proving that atomic H* (indirect pathway) plays a prominent role in NO3 – reduction and clarifying the synergistic effect of Co­(III) and Co­(II) in the Co­(II)–Co­(III)–Co­(II) redox cycle for the ENRR: Co­(III) prefers the adsorption of NO3 – and Co­(II) favors the production of H*. Based on this synergy, a relatively large amounts of Co­(II) on the surface of the Co3O4/CF electrode (1.3 Co­(II)/Co­(III) ratio) was maintained by controlling the temperature of calcination to 200 °C with a lower energy barrier of H* formation of 0.46 eV than other ratios, which is beneficial for forming H* and enhancing the performance of the ENRR. Thus, this study suggests that building 3D structure and optimizing Co­(II)/Co­(III) ratio are important for designing efficient Co3O4 electrocatalyst for ENRR.