Effective Nitrate Electroconversion to Ammonia Using an Entangled Co₃O₄/Graphene Nanoribbon Catalyst

Author(s)

Souza, Marcielli K. R. ; Cardoso, Eduardo S. F. ; Pinto, Leandro M. C. ; Crivelli, Isabela S. C. ; Rodrigues, Clauber D. ; Souto, Robson S. ; Rezende-Filho, Ary T. ; Lanza, Marcos R. V. ; Maia, Gilberto

• Document type: Journal article
• Source: ACS APPLIED MATERIALS & INTERFACES; v. 17, n. 1, p. 16-pg., 2024-12-27.

Abstract

There has been huge interest among chemical scientists in the electrochemical reduction of nitrate (NO3-) to ammonia (NH4+) due to the useful application of NH4+ in nitrogen fertilizers and fuel. To conduct such a complex reduction reaction, which involves eight electrons and eight protons, one needs to develop high-performance (and stable) electrocatalysts that favor the formation of reaction intermediates that are selective toward ammonia production. In the present study, we developed and applied Co3O4/graphene nanoribbon (GNR) electrocatalysts with excellent properties for the effective reduction of NO3- to NH4+, where NH4+ yield rate of 42.11 mg h(-1) mg(cat)(-1), FE of 98.7%, NO3- conversion efficiency of 14.71%, and NH4+ selectivity of 100% were obtained, with the application of only 37.5 mu g cm(-2) of the catalysts (for the best catalyst & horbar;Co3O4(Cowt %55)GNR, only 20.6 mu g cm(-2) of Co was applied), confirmed by loadings ranging from 19-150 mu g cm(-2). The highly satisfactory results obtained from the application of the proposed catalysts were favored by high average values of electrochemically active surface area (ECSA) and low R-ct values, along with the presence of several planes in Co3O4 entangled with GNR and the occurrence of a kind of "(Co-3(Co(CN)(6))(2)(H2O)(12))(1.333) complex" structure on the catalyst surface, in addition to the effective migration of NO3- from the cell cathodic branch to the anodic branch, which was confirmed by the experiment conducted using a H-cell separated by a Nafion 117 membrane. The in situ FTIR and Raman spectroscopy results helped identify the adsorbed intermediates, namely, NO3-, NO2-, NO, and NH2OH, and the final product NH4+, which are compatible with the proposed NO3- electroreduction mechanism. The Density Functional Theory (DFT) calculations helped confirm that the Co3O4(Cowt %55)GNR catalyst exhibited a better performance in terms of nitrate electroreduction in comparison with Co3O4(Cowt %75), considering the intermediates identified by the in situ FTIR and Raman spectroscopy results and the rate-determining step (RDS) observed for the transition of *NO to *NHO (0.43 eV). (AU)

• FAPESP's process: 19/04421-7 - Production and characterization of metal-graphene or graphene oxide nanocomposites for the electrocatalytic production of hydrogen peroxide: Application to the degradation of endocrine disrupting chemicals by electrochemical advanced oxidation processes
• Grantee: Guilherme Vilalba Fortunato
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 22/12895-1 - Advanced processes for the degradation of emerging pollutants: catalytic materials, electroanalytical sensors and scientific dissemination
• Grantee: Marcos Roberto de Vasconcelos Lanza
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 23/01425-7 - Development of carbon/non-noble metal based electrocatalysts for hydrogen peroxide generation in environmental applications
• Grantee: Marcos Roberto de Vasconcelos Lanza
• Support Opportunities: Regular Research Grants
• FAPESP's process: 23/10772-2 - Development of carbon/non-noble metal based electrocatalysts for hydrogen peroxide generation in environmental applications
• Grantee: Eduardo dos Santos Freitas Cardoso
• Support Opportunities: Scholarships in Brazil - Support Program for Fixating Young Doctors