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+, Ce3+/Ce4+, and Fe2+/Fe3+ redox couples. The vanadium couple is part of the well-known vanadium redox battery.2 The cerium redox couple has been used in organic electrosynthesis as well as in flow batteries including Zn-Ce,3,4 and H2-Ce.5 The iron redox couple was one of the first used for flow battery applications and iron is abundant and inexpensive. By better understanding these redox reactions on different catalyst surfaces, 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).

[1] Singh, N; McFarland, E W, J. Power Sources 2015, 288, 187

[2] Ding, C; Zhang, H; Li, X; Liu, T; Xing, F, J. Phys. Chem. Lett. 2013, 4 (8), 1281

[3] Xie, Z; Liu, Q; Chang, Z; Zhang, X, Electrochim. Acta 2013, 90, 695

[4] Walsh, F C; Lé on, C P de; Berlouis, L; Nikiforidis, G; Arenas-Martínez, L F; Hodgson, D;
Hall, D,Chempluschem 2015, 80 (2), 288

[5] Hewa Dewage, H; Wu, B; Tsoi, A; Yufit, V; Offer, G; Brandon, N,
J. Mater. Chem. A 2015, 3 (18), 9446

2. Sustainable Fuels & Chemicals

In order 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 in electrochemistry or solar photons can drive photoelectrochemistry to sustainably produce the necessary chemicals and fuels. Two examples in our group are the production of halogens and transportation fuels (specifically, more high value fuels such as jet fuels) from halides and biooils, respectively. Other specialty chemicals, such as adiponitrile, or pharmaceuticals can be produced by electrochemical methods. In order 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.

Photoelectrochemical production of halogens has been done in several examples,1–3 but catalyst efficiency and low cost absorbers are still a challenge, as well as methods for scale-up. The electrocatalytic conversion of biooil has been studied,4–6 but there is still a need for improvement in turnover frequency and selectivity, and its coupling with photoelectrochemistry is almost non-existent. 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 in order to selectively design catalysts that can drive sustainable fuel and chemical production.

[1] Mubeen, S; Lee, J; Singh, N; Moskovits, M; McFarland, E W, Energy Environ. Sci. 2013, 6 (5), 1633

[2] Singh, N; Mubeen, S; Lee, J; Metiu, H; Moskovits, M; McFarland, E W, Energy Environ. Sci. 2014, 1

[3] RG, M, Hydrogen-bromine generation utilizing semiconducting platelets suspended in a vertically flowing electrolyte solution, 1981

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

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

[6] Lessard, J. In Organic Electrochemistry 2016; 1712

3. Wastewater Remediation

Remediating waste streams is an important way to mitigate human impact on the environment. Of particular importance is minimizing the 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, developing poison-resistant electrocatalysts, and testing flow reactors for their effectiveness in remediating waste streams.

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

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

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