CAREER: Understanding the Interdependence of Cation and Anion Adsorption for Electrocatalytic Nitrate Reduction

Providing fuels and chemicals without negative environmental impacts requires new catalysts and processes that can be driven by renewable electricity instead of fossil fuels. Electrocatalysis is a method to use renewable electricity to drive low temperature and pressure reactions for distributed sustainable fuel generation, waste treatment, and energy storage. Understanding electrocatalytic reaction rates will increase the energy efficiency and economic viability of new electrocatalytic processes. This CAREER project will study electrocatalysis to convert waste nitrate species to valuable products such as ammonia as a case study for sustainable chemical processes. Nitrate is a harmful pollutant that results from industrial effluents and agricultural runoff, while ammonia is a useful fuel and fertilizer. For electrocatalytic nitrate conversion to be viable, the negatively charged nitrate anion must interact with an electrified electrocatalyst surface in the presence of positively charged cations to reduce nitrate at the desired rates. This project will step-by-step add in the complexity of these factors to develop an understanding of what impacts electrocatalytic reaction rates. In addition to studying this model electrocatalytic reaction, the next generation of scientists and engineers will be trained for the new challenges for a switch to a more sustainable, environmentally friendly chemical economy through coursework and hands on training. The complex interaction of reactants, ions, and the electrocatalyst is incompletely understood for electrocatalysis. This project will study the interplay of the reacting molecule (i.e., nitrate), cations, the electrocatalyst surface, and potential in controlling electrocatalytic rates and selectivities of nitrate reduction. Structure-activity relations will be derived by measuring reaction rates on controlled metal and alloy surfaces and comparing to the measured adsorption energy of nitrate and other intermediates on those surfaces. By studying the interaction of the cations with the nitrate anion through UV-Vis, Raman, and X-ray absorption spectroscopy and comparing to kinetics, how these cation-anion interactions impact the adsorption energies and rates will be identified. The understanding of nitrate electrocatalytic reduction in electrolytes of interest to wastewater treatment will be improved by combining knowledge gained of these interactions. The new insights will be used to evaluate reaction rates for nitrate reduction in continuous electrocatalytic reactor systems. This project will develop methods to apply chemical reactor engineering principles to electrochemical reactors necessary for future advances in sustainable chemical and fuel generation. Specific broader impacts include updating undergraduate core curriculum for modern technologies, an electrochemistry applications and engineering course, Chem-E Car mentorship and outreach, and leveraging NSF I-CORPS to identify practical applications of electrocatalytic nitrate reduction. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.