(6ao) Understanding and Improving Electrocatalysts for Energy Conversion and Waste Remediation

The challenge of sustainably providing the increasing demand for energy and resources relies on improving existing renewable energy processes or developing new processes. Major issues include the storage of energy, conversion of renewable energy to storable transportation fuels, and the remediation of waste streams. Catalysis and electrocatalysis can play a major role in providing sustainable energy and remediating waste streams, but improvements are needed in electrocatalyst activity, selectivity and stability. My interest is in synthesizing and testing new classes of materials (such as doped and undoped metal sulfides) that can achieve activities, selectivities and stabilities that are unmet by the existing metal electrocatalysts. I am also interesting in characterization of electrocatalysts under operating conditions through the use of spectroscopy and kinetic analysis. To evaluate potential processes, I will also use technoeconomic analysis and sensitivity analysis to identify which factors have the largest impact on the final product. As a faculty member I will focus on the following research projects:

Project 1. Understand and improve the electrocatalytic activity of flow batteries. A focus of my graduate work was on new electrocatalysts for H₂/Br₂ flow batteries, whose activity and stability have a major impact on the feasibility of flow batteries. In this project, I hope to extend my previous work to other flow batteries including the H₂/Cerium battery (where competing oxygen evolution and changing oxidation states of the catalyst are a challenge)¹ or vanadium batteries (where the competition of hydrogen evolution is an issue). The specific aims of this project are to test new electrocatalyst materials, and characterize them under operating conditions using techniques such as X-ray absorption spectroscopy (XAFS) to understand the effects of applied potential on oxidation state or adsorption of reactant molecules.

Project 2. New methods to convert solar energy to transportation fuels. Research on solar fuels has focused on water splitting (to H₂ and O₂) and carbon dioxide reduction, but other processes are also achievable (and possibly more viable) if new electrocatalysts are developed. A sample reaction is using electrochemical potential provided from sunlight to hydrogenate waste biomass, which enables easier deoxygenation to fuel-grade hydrocarbons. Aqueous electrochemical hydrogenation of biomass has a low overpotential compared to CO₂ electro-reduction (~0.1 V compared to 1 V), important for solar driven processes where the voltage provided by photons is limited. However, electrocatalyst activities rates must be improved, and photoelectrochemical hydrogenation of biooil has not been demonstrated using sunlight. The specific aims of this project are to evaluate new electrocatalysts (such as metal sulfides) for the conversion of lignin-based biooils to hydrocarbons, and coupling the reaction with light absorbers powered by sunlight. The characterization techniques such as XAFS used to evaluate flow batteries in Project 1 can also be used here to understand reactant coverages and electronic properties of the catalyst.

Project 3. Remediation of wastewater through electrochemical treatment. One of the major concerns for a sustainable future is treatment of waste streams. Nitrate is a biological poison that is present in waste as varied as fertilizer run-off, electrochemical industrial waste and low-level nuclear waste, and can potentially be treated electrochemically through nitrate reduction. Yet, the mechanism of nitrate remediation is not well-understood, and active catalysts that can maintain activity in the presence of metal ions or other poisons do not exist. The specific aim of this project is to determine the properties of electrocatalysts that control the activity for nitrate reduction and develop catalysts with high activity and resistance to poisoning. Similar experimental techniques from the other two proposed projects can be applied to develop waste remediation electrocatalysts.

PhD Research:

My graduate research with Professor Eric McFarland and Professor Horia Metiu at the University of California, Santa Barbara focused on understanding new types of electrocatalysts for the conversion of energy. This consisted of identifying metal sulfides and doped metal sulfides for active and stable H₂/Br₂ flow battery electrocatalysts,^2â??5 and use of catalysts for the conversion of solar energy to hydrogen.^6,7 We coupled experiments with theory to understand molecular descriptors for catalyst activity (such as hydrogen binding energy on metal sulfides) and to identify active sites.^8,9 Through selective synthesis of particular phases of rhodium sulfide we were able to improve electrocatalytic activity and stability. I also completed a technoeconomic analysis of the H₂/Br₂ flow battery to identify key components in the levelized cost of electricity.¹⁰

Postdoctoral Research:

My postdoctoral research with Prof. Charles T. Campbell and Prof. Johannes Lercher at the University of Washington and Pacific Northwest National Laboratory consists of the interrogation of electrocatalysts for electrocatalytic hydrogenation (ECH) of phenol. This includes in situ characterization of the catalysts by XAFS to identify phenol and hydrogen coverages on the surface as well as electronic and structural properties of the catalyst. In addition, we identified the cause for deactivation at elevated temperatures by kinetic analysis and modified reaction conditions (e.g. hydrogen pressure) to prevent formation of poison species, and enable unprecedented rates at temperatures relevant for ECH (<100 °C). I am currently a Washington Research Foundation Innovation Fellow with the Clean Energy Institute at UW, and successfully presented for a PNNL Initiative as well as co-wrote a proposal for Laboratory Directed Research and Development (internal funding for PNNL).

Teaching Interests:

During my time as a student, the professors of my core Chemical Engineering courses helped me develop my interest in Catalysis and Reaction Engineering, and I hope to be able to do the same for future chemical engineers. I am comfortable with the core Chemical Engineering course structure, but feel best suited towards teaching Reaction Engineering and in developing elective courses in Electrochemistry or Energy. As a graduate student I was a Teaching Assistant for Undergraduate Chemical Reaction Engineering and an Energy elective. In terms of teaching in a research environment, I supervised six undergraduate students during my graduate work, including education on the experimental aspects of catalysis, electrochemistry and photoelectrochemistry.

References:

1. Tucker, M. C., Weiss, A. & Weber, A. Z. Improvement and analysis of the hydrogen-cerium redox flow cell. J. Power Sources 327, 591â??598 (2016).

2. Ivanovskaya, A., Singh N., Liu, R., Kreutzer, H., Baltrusaitis, J., Nguyen, T. V., Metiu, H. & McFarland, E. Transition Metal Sulfide Hydrogen Evolution Catalysts for Hydrobromic Acid Electrolysis. Langmuir 29, 480â??492 (2013).

3. Masud, J., Nguyen, T. V., Singh, N., McFarland, E., Ikenberry, M., Hohn, K., Pan, C.-J. & Hwang, B.-J. A RhxSy/C Catalyst for the Hydrogen Oxidation and Hydrogen Evolution Reactions in HBr. J. Electrochem. Soc. 162, F455â??F462 (2015).

4. Nguyen, T. Van, Kreutzer, H., Yarlagadda, V., McFarland, E. & Singh, N. HER/HOR Catalysts for the H2-Br2 Fuel Cell System. ECS Trans. 53, 75â??81 (2013).

5. Masud, J. Walter, J., Nguyen, T. V., Lin, G., Singh, N., McFarland, E., Metiu, H., Ikenberry, M., Hohn, K., Pan, C.-J. & Hwang, B.-J. Synthesis and Characterization of RhxSy/C Catalysts for HOR/HER in HBr. ECS Trans. 58, 37â??43 (2014).

6. Singh, N., Mubeen, S., Lee, J., Metiu, H., Moskovits, M. & McFarland, E. W. Stable electrocatalysts for autonomous photoelectrolysis of hydrobromic acid using single-junction solar cells. Energy Environ. Sci. 1â??4 (2014). doi:10.1039/c3ee43709d

7. Mubeen, S., Singh, N., Lee, J., Stucky, G. D., Moskovits, M. & McFarland, E. W. Synthesis of chemicals using solar energy with stable photoelectrochemically active heterostructures. Nano Lett. 13, 2110â??5 (2013).

8. Singh, N., Upham, D. C., Liu, R., Burk, J., Economou, N., Buratto, S., Metiu, H. & McFarland, E. Investigation of the active sites of rhodium sulfide for hydrogen evolution/oxidation using carbon monoxide as a probe. Langmuir 30, 5662â??8 (2014).

9. Singh, N., Upham, D. C., Metiu, H. & McFarland, E. W. Gas-Phase Chemistry to Understand Electrochemical Hydrogen Evolution and Oxidation on Doped Transition Metal Sulfides. J. Electrochem. Soc. 160, A1902â??A1906 (2013).

10. Singh, N. & McFarland, E. W. Levelized cost of energy and sensitivity analysis for the hydrogenâ??bromine flow battery. J. Power Sources 288, 187â??198 (2015).