Research

Energy Storage | Sustainable Fuels & Chemicals | Wastewater Remediation

1. Energy Storage

A major challenge for intermittent renewable energy sources, such as wind and solar, is economical energy storage. Redox flow batteries are a promising method of energy storage due to the high current and power densities achievable, the ability to decouple power and energy by external storage of electrolytes, and long lifetimes. One of the challenges in flow batteries is their cost per amount of stored energy, which can be reduced by increasing the current densities achievable while maintaining energy efficiency.¹ Several limitations on the rates of reaction exist, including mass transport, ohmic resistances, and kinetics. Much effort has gone into understanding and improving mass transport, but for some of the reactions of interest, the kinetics at the electrode surface are not well understood.

Three of the reactions of particular interest in our group are the V²⁺/V³⁺,^2-7 Ce³⁺/Ce⁴⁺,^8-10 and Fe²⁺/Fe³⁺ redox couples. The vanadium couple is part of the well-known vanadium redox battery.¹¹ The cerium redox couple has been used in organic electrosynthesis as well as in flow batteries including Zn-Ce,^12,13 and H₂-Ce.¹⁴ The iron redox couple was one of the first used for flow battery applications and has cost benefits because iron is abundant and inexpensive. By better understanding these redox reactions on different electrode surfaces and the role of metal ion structure on rates, we can improve charge transfer kinetics to make more efficient batteries. In addition, the fundamental understanding of these charge transfer reactions can lead to improvements of processes including other types of batteries, corrosion, specialty cleaning, and metal deposition (all heavily used in industrial electrochemistry).

Current Projects:

NSF 2407420: Molecular Structures and Electrochemical Activity of Supersaturated Electrolytes for High-Energy-Density Redox Flow Batteries

2. Sustainable Fuels & Chemicals

To minimize carbon dioxide emissions, but still produce the chemicals and fuels needed for society, sustainable routes of production must be developed. Renewable energy sources such as solar or wind can produce electricity that can be used to drive electrochemical reactions or solar photons can drive photoelectrochemistry to sustainably produce the necessary chemicals and fuels. One example in our group is the production of transportation fuels (specifically, more high value fuels such as jet fuels) from bio-derived species and biooils. To compete (economically) with conventionally produced chemicals and fuels, the systems that are developed must be efficient and with low capital cost. Aside from process design, this will include developing catalysts with the long lifetime, selectivity, and activity to drive these reactions. We also look at electrochemical carbon dioxide reduction to fuels^1-2 and photoelectrochemical and electrochemical water splitting.

The electrocatalytic conversion of biooil has been demonstrated^3–5 but there is still a need for improvement in turnover frequency and selectivity. In our group we look at the technoeconomics of fuel and chemical productions to understand the areas where greatest improvements can be made, and the mechanisms of electrocatalytic reactions^6-9 to selectively design catalysts that can drive sustainable fuel and chemical production.

Current Projects:

NSF 2320929: Understanding Synergistic Effects of Organic Mixtures for Electrocatalytic Hydrogenation for Fuel Production

Office of Naval Research

References

[1] L Yao, C Yin, K E Rivera-Cruz, C L McCrory, N Singh, ACS Applied Materials & Interfaces, 2023, 15, 31438-31448

[2] L Yao, K Rivera Cruz, P Zimmerman, N Singh, C McCrory, ACS Catalysis, 2024, 14, 366-372

[3] Y Song, O Y Gutiérrez, J Herranz, J A Lercher, Appl. Catal. B Environ. 2016, 182, 236

[4] Singh, N; Song, Y; Gutiérrez, O Y; Camaioni, D M; Campbell, C T; Lercher, J A, ACS Catal. 2016, 6, 7466

[5] J Lessard,  In Organic Electrochemistry 2016; 1712

[6] J Akinola, I Barth, B R Goldsmith, N Singh, ACS Catalysis, 2020, 10, 4929-4941

[7] J Akinola, N Singh, Journal of Applied Electrochemistry, 2021, 51 (1), 37-50

[8] I Barth, J Akinola, J Lee, O Y Gutiérrez, U Sanyal, N Singh, B R Goldsmith, The Journal of Chemical Physics, 2022, 156, 104703

[9] J Akinola, I Barth, B R Goldsmith, N Singh, Journal of Catalysis, 2024, 430, 115331

3. Wastewater Remediation

Remediating waste streams is an important way to mitigate human impact on the environment. Of particular importance is minimizing the effect on the nitrogen cycle from reactive nitrogen emissions such as nitrate.¹ Electrochemical wastewater treatment can provide a sustainable method to remove biological poisons (e.g. nitrate) in streams such as fertilizer runoff, low-level nuclear waste, and other industrial waste.^2,3 For many of these reactions, including nitrate, the material properties that control kinetics are not well understood, and there is a need to develop active and stable electrocatalysts. Research in our group consists of determining the properties that control nitrate reduction activity and selectivity through kinetic measurements, adsorption thermodynamics and in situ spectroscopy,^4-7 developing poison-resistant electrocatalysts,⁸ studying concentration and conversion, and testing flow reactors for their effectiveness in remediating waste streams.

Current Projects:

NSF 2236770: Understanding the Interdependence of Cation and Anion Adsorption for Electrocatalytic Nitrate Reduction

NSF 2247194: Elucidating the Electrocatalytic Coupling of Nitrate and Carbon Dioxide: Toward Electron Efficient C-N Coupling

Keck Foundation

NSF 2420528: ECO-CBET: A Photocapacitive/Electrolytic Reactor for Carbon Neutral Production of Clean Water and Value-added Products from Nitrate Contaminated Waters

References

[1] National Academy of Engineering, National Academy of Engineering Grand Challenges For Engineers 2017, 19-22

[2] V Rosca, M Duca, M T DeGroot, M T M Koper, Chem. Rev. 2009, 109, 2209-2244

[3] M Duca, M T M Koper, Energy Environ. Sci. 2012, 5, 9726-9742

[4] J X Liu, D Richards, N Singh, B R Goldsmith, ACS Catalysis, 2019, 9, 7052-7064

[5] Z Wang, S D Young, B R Goldsmith, N Singh, Journal of Catalysis, 2021, 395, 143-154

[6] G Costa, M Winkler, T Mariano, M Pinto, I Messias, J Souza, I Neckel, M Santos, C Tormena, N Singh, R Nagao, Chem Catalysis, 2023, 4, 100850

[7] Z Wang, E Ortiz, B R Goldsmith, N Singh, Catalysis Science & Technology, 2021, 11, 7098-7109

[8] D Richards, S D Young, B R Goldsmith, N Singh, Catalysis Science & Technology, 2021, 11, 7331-7346