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| Author(s): |
Gabriel Floriano Costa
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Química |
| Defense date: | 2024-07-05 |
| Examining board members: |
Raphael Nagao de Sousa;
René Alfonso Nome Silva;
Juliana Ferreira de Brito;
Janaina de Souza Garcia;
Marcos Roberto de Vasconcelos Lanza
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| Advisor: | Raphael Nagao de Sousa |
| Abstract | |
The nitrogen cycle is globally disturbed by the excessive use of fertilizers for food production. One of the most harmful symptoms of such disturbance is the accumulation of reactive nitrogen into the environment, especially nitrate, the most oxidized nitrogenous species, being a serious pollutant in groundwater, rivers, and lakes. Additionally, the ammonia production from Haber-Bosch is the most carbon dioxide-emitting industrial process due to the use of natural gas to obtain hydrogen, and the development of sustainable alternatives for ammonia production is crucial to moving toward an electrified future. The electrochemical nitrate reduction is a sustainable alternative to remove nitrates from aquatic systems and industrial wastewater, as well as to synthesize ammonia with a lower carbon footprint. This work aims to evaluate both catalyst and electrolyte aspects of the nitrate electrochemical reduction on copper-based materials. We kinetically and spectroscopically investigate how electrochemical cathodic conditions for nitrate conversion to ammonia impact the structure and content of Cu/Cu2O composite. Combining the kinetic evaluation of differently pre-reduced Cu/Cu2O catalysts compared with pure Cu alongside in-situ Raman and X-ray absorption spectroscopies, we found that since copper oxide reduces during nitrate reduction, oxygen vacancies boost ammonia production at lower overpotentials (from ?0.6 to ?0.77 V vs. SHE), while copper itself is active at ?1.1 V vs. SHE. Using neutral non-buffered electrolyte, we detected an increase in catholyte’s pH from 5.8 to up to 12.0, since nitrate reduction to ammonia involves the consumption of 8 moles of protons for each mole of nitrate. We also investigated the impact of the solution pH on the nitrate electrochemical reduction to ammonia on copper catalysts within a pH range of 4.4 to 9.3. Through electrochemical experiments and differential electrochemical mass spectrometry measurements, we elucidate how variation in solution pH at mildly acidic and basic conditions modulate both the rate of nitrate reduction and distribution of reaction products. Our findings provide valuable insights into the role of electrolyte in modulating nitrate reduction mechanisms, particularly within the critical pH range from 4.4 to 9.3, contributing to a deeper understanding of this important electrocatalytic process (AU) | |
| FAPESP's process: | 19/18847-6 - Ammonia electrochemical synthesis from nitrate reduction at metal oxides: an in operando investigation |
| Grantee: | Gabriel Floriano Costa |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |