Electrochemical synthesis of ammonia from water and nitrogen catalyzed by nano-Fe2O3 and CoFe2O4 suspended in a molten LiCl-KCl-CsCl electrolyte

Comparing B3LYP and B97 Dispersion-corrected Functionals for Studying Adsorption and Vibrational Spectra in Nitrogen Reduction

Electrochemical ammonia synthesis is being actively studied as a low temperature, low pressure alternative to the Haber-Bosch process. This work studied pure iridium as the catalyst for ammonia synthesis, following promising experimental results of Pt-Ir alloys. The characteristics studied include bond energies, bond lengths, spin densities, and free and adsorbed vibrational frequencies for the molecules N2 , N, NH, NH2 , and NH3 . Overall, these descriptive characteristics explore the use of dispersion-corrected density functional theory methods that can model N2 adsorption - the key reactant for electrochemical ammonia synthesis via transition metal catalysis. Specifically, three methods were tested: hybrid B3LYP, a dispersion-corrected form B3LYP-D3, and semi-empirical B97-D3. The latter semi-empirical method was explored to increase the accuracy obtained in vibrational analysis as well as reduce computational time. Two lattice surfaces, (111) and (100), were compared. The adsorption energies are stronger on (100) and follow the trend EB3LYP >EB3LYP-D3 >EB97-D3 on both surfaces.

Recent Advances in Solar Thermal Electrochemical Process (STEP) for Carbon Neutral Products and High Value Nanocarbons

Climate change represents one of the most important environmental issues of our time. Due to high levels of anthropogenic CO₂ emissions, atmospheric CO₂ has for the first time ever exceeded 415 ppm and has increased from 315 ppm in 1950. An annual increase in atmospheric CO₂ of ∼2 ppm is equal to a net increase of ∼15.6 billion tons of CO₂. The combustion of fossil fuels for electricity and transportation is still the main reason accounting for the CO₂ accumulation. On the top of that, fossil fuels are widely used in our modern industry for the productions of indispensable social staples. For instance, the millennia old thermal reduction of iron ore by charcoal or baked coal (3C + 2Fe₂O₃ → 4Fe + 3CO₂) continues as the main method for the production of iron. The artificial fertilizer ammonia boosts the global population and is mainly produced from the Haber-Bosch process, in which hydrogen is generated via steam reforming of methane (CH₄ + 2H₂O → 4H₂ + CO₂). Sequestration and diminution of CO₂ require the development of a portfolio of technologies on (1) efficient and long-term harvesting of renewable energy, that is, solar, not only for electricity but also directly as the energy force in vital chemical processes, wherever possible, (2) carbon-neutral processes to replace current industrial processes that emit vast amounts of CO₂, such as iron and ammonia production, and (3) new, low-cost technologies for CO₂ capture and conversion with particular interests in the exploration of CO₂ as the feedstock for fuels or other valuable chemicals and materials. To this end, we conducted some studies on the sustainable synthesis of ammonia and iron with net-zero CO₂ emissions and large-scale CO₂ capture and conversion into fuels and high value nanocarbon products via electrolysis in molten salt(s) with the introduction of the Solar Thermal Electrochemical Process (STEP). In STEP, solar UV-visible energy is focused on a photovoltaic device that generates the electricity to drive the electrolysis, while concurrently the solar thermal energy is focused on a second system to generate heat for the electrolysis cell. The utilization of the full spectrum of sunlight in STEP results in a higher solar energy efficiency than other solar conversion processes. STEP has been applied to conduct (1) CO₂-free ammonia synthesis from nitrogen and water with the aid of nano-Fe₂O₃ in a molten hydroxide electrolyte, (2) CO₂-free production of iron via electrochemical reduction of iron ore in molten carbonate, (3) CO₂ capture and conversion into nanostructured carbon products as well as fuels in molten or mixed molten electrolytes, and (4) organic electrosynthesis of benzoic acid from benzene without overoxidizing into CO₂. In this Account, we highlight some recent achievements in these topics and propose that using STEP is a highly efficient strategy for saving energy and, consequently, the environment. STEP is an ideal tool that can theoretically be applied to all endothermic reactions.

Electrochemical Synthesis of Ammonia: Recent Efforts and Future Outlook

Ammonia is a key chemical produced in huge quantities worldwide. Its primary industrial production is via the Haber-Bosch method; a process requiring high temperatures and pressures, and consuming large amounts of energy. In the past two decades, several alternatives to the existing process have been proposed, including the electrochemical synthesis. The present paper reviews literature concerning this approach and the experimental research carried out in aqueous, molten salt, or solid electrolyte cells, over the past three years. The electrochemical systems are grouped, described, and discussed according to the operating temperature, which is determined by the electrolyte used, and their performance is valuated. The problems which need to be addressed further in order to scale-up the electrochemical synthesis of ammonia to the industrial level are examined.

Electrochemical Ammonia Generation Directly from Nitrogen and Air Using an Iron-Oxide/Titania-Based Catalyst at Ambient Conditions

Ammonia was produced electrochemically from nitrogen/air in aqueous alkaline electrolytes by using a Fe₂O₃/TiO₂ composite catalyst under room temperature and atmospheric pressure. At an applied potential of 0.023 V versus reversible hydrogen electrode, the rate of ammonia formation was 1.25 × 10^-8 mmol mg^-1 s^-1 at an overpotential of just 34 mV. This rate increased to 2.7 × 10^-7 mmol mg^-1 s^-1 at -0.577 V. The chronoamperometric experiments on Fe₂O₃/TiO₂/C clearly confirmed that Fe₂O₃ along with TiO₂ shows superior nitrogen reduction reaction activity compared to Fe₂O₃ alone. Experimental parameters such as temperature and applied potential have a significant influence on the rate of ammonia formation. The activation energy of nitrogen reduction on the employed catalyst was found to be 25.8 kJ mol^-1. Real-time direct electrochemical mass spectrometry analysis was used to monitor the composition of the evolved gases at different electrode potentials.

Electrochemical synthesis of ammonia from N2 and H2O using a typical non-noble metal carbon-based catalyst under ambient conditions

Ammonia is an important precursor of fertilizers and nitrogen compounds, and it is also a potential energy storage medium and alternative fuel for vehicles.