Year: 2025
Type: dissertation
Abstract: Electrochemical nitrogen fixation presents a promising sustainable pathway for producing ammonia, nitrate, and nitrite with zero-carbon emissions when renewable sources of electricity are used. These compounds are essential for fertilizers in agriculture, feedstock for chemicals and pharmaceuticals, and ammonia as potential future energy carrier. The current more efficient manufacturing process for ammonia and nitrate is the CO2-emitting Haber-Bosch (H-B) process and the nitrous oxideemitting Ostwald process, respectively, which are heavily dependent on the use of fossil fuels (primarily coal and natural gas) to produce the hydrogen feedstock, to provide process heat, and to produce electricity. Carbon dioxide and nitrous oxide are significant greenhouse gases. Annually, 150 million tons of NH3 are produced globally using the H−B process, which consumes 3−5% of the annual natural gas production worldwide, or approximately 1−2% of the yearly global energy supply. Due to the limited supply of fossil fuels, there is a critical demand to use renewable energy, including electricity from renewables, as a replacement for fossil fuels. Also, it is highly desirable to develop an alternative, efficient process for ammonia and nitrate manufacturing, which can simultaneously reduce CO2 and N2O emissions. Electrochemical nitrogen fixation under mild conditions is an emerging alternative to the current nitrogen industry. In this study, the electrochemical one-pot cell design has four unique features compared to the traditional method: simultaneous production of ammonium, nitrate, and nitrite due to the bifunctionality of the electrocatalyst, a two-electrode electrochemical cell design with constant current, hermetically sealed metal cells to prevent any contamination, and a fixed volume of headspace gas that can hold pressure up to 17 bars. This study includes optimization of experimental parameters, including palladium monometallic and bimetallic nanoparticles and different headspace gases to assess their electrocatalytic activity, as well as the headspace pressure, temperature, and applied current. The dependence of nitrogen species on the initial oxygen concentration in the headspace of an electrochemical cell with Pd-EGCG nanoparticles as the electrocatalyst was studied. Electrocatalytic activity was observed. Further, the palladium-based bimetallic nanoparticles PdRu, PdFe, and PdRh, were investigated. PdRu-EGCG and PdFe-EGCG showed no electrocatalytic performance. Whereas PdRh-EGCG nanoparticle showed the electrocatalytic activity with 25 mA of applied current at 5 bar pressure of ultra-zero air of headspace gas with simultaneous production of ammonium, nitrite, and nitrate with the yield rate of 0.38±0.10, 24.25± 1.39, and 4.25 ± 0.33 𝜇g/h/mgcat, respectively, with the faradaic efficiency (FE%) of 2.17 ± 0.105 %. A time-dependent study was performed that showed the linear timedependence up to 18 hours in the total fixed nitrogen with a slope of 89 ± 1.08 𝜇g/h of atomic nitrogen with a constant faradaic efficiency of 2.05 ± 0.08 %. After 18 hours, due to the solubility limitation of N2, a lower production rate was observed.
Author: Farooq, Muhammad Umer
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7134147590
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