Research
The Moreno Lab aims to integrate engineering and related disciplines to solve challenges in water and energy and strive for a cleaner environment. Much of the research conducted in Dr. Moreno's lab involved the multidisciplinary field of electrochemistry, which integrates various concepts from physics, chemistry, and materials science. As a result, many lab members (including Dr. Moreno himself!) get exposure to fundamental knowledge in a range of different fields that they would otherwise not have received during training in their major. Nevertheless, Dr. Moreno strives to ensure that the research maintains some sort of connection to his strengths in Thermodynamics and Heat Transfer, and as such, emphasis is placed on topics such as long-term cycling effects and stability, thermal management of battery systems, and the complicated influence of temperature of the systems studied. The headings below reflect the current activities of the lab as of June 2023.
Electrochemical CO2 Utilization:
As we progress toward renewable energy resources, it is also important to consider how we can decrease CO2 emissions from our existing resources. This can be done via carbon capture and subsequently conversion to a range of value-added fuel products - essentially, the inverse of combustion (Fig. 1A). Common value-added products include carbon monoxide, methanol, formic acid, hydrogen, among higher ordered carbon products.
The exact formation of these fuel products can get complicated, and electrochemical methods are often preferred due to their ability to select certain fuel products based on the catalyst used (Fig. 1B). Additionally, traditional CO2 conversion processes employ high temperatures and pressures, reducing cost/manufacturing concerns with an electrochemical processes [3]. While operating an electrochemical system for CO2 conversion does not require increased temperature/pressure, studies have shown that conditions slightly above ambient can have more favorable results [4].
Higher pressures can increase the solubility of CO2 in an aqueous solution, provided the system built is capable of handling higher pressures and the increased solubility does not significantly alter the solution pH. While CO2 solubility decreases at higher temperatures, other factors such as diffusion coefficient and conductivity can enhance the performance at higher temperatures. The Moreno Lab is presently studying the effects of increased temperatures and pressures for electrochemical CO2 conversion, using an in-house H-cell (Fig. 2), and later scaling up to a flowable system for increased fuel production.
In the future, the lab aims to integrate solar energy for photoelectrochemical (PEC) CO2 conversion. Using solar energy for electrochemical CO2 conversion can result in a net decrease of overall emissions, in lieu of electricity that is derived from fossil fuel-based sources. When employing solar energy for PEC conversion, the influx of heat naturally coincides and can result in increased temperature values up to 35°C.
Fig. 1. (A) Schematic illustrating process of electrochemical CO2 reduction and relevant influential parameters to consider [1]. (B) Product speciation and corresponding efficiencies based on the type of metal catalyst that is selected; note that copper is unique and can produce a wide range of products [2].
Fig. 2. In-house H-cell batch reactor with components labelled.
In order to effectively harness renewable energy, we must be able to effectively store it. Batteries are often characterized both on their ability to store energy as well as the rate at which they are able to provide it (Fig. 3). Lithium-ion batteries are preferred to their capability to excel in both factors, in addition to lighter overall weight. However, challenges involving safety and cycling life must be considered for greater system scale-up, such as in electric vehicles [6].
It is critical to understand the aging of Li-ion batteries for optimizing the performance in larger-scale applications. This aging is largely affected by a multitude of factors, including temperature, size, chemical composition, voltage cutoff, and depth of discharge. Experimentally, the Moreno Lab is constructing smaller-scale lithium-ion batteries in coin cells (Fig. 4) and studying their characteristics to determine their long-term performance. Computational models are being developed to predict changes in performance on scale-up, considering equivalent electrical circuits to simulate cycling, and energy balance to account for temperature changes. Electrochemical impedance spectroscopy (EIS) testing can be used to best fit experimental parameters to the model.
Nickel-zinc batteries (Fig. 5, 6A) have shown to be a promising alternative to lithium-ion batteries, possessing a long cycle life, safer materials, and can maintain a strong discharge current. The Moreno Lab is studying the cycling characteristics of nickel-zinc batteries, and also characterizing the formation of different gaseous products in the system via mass spectroscopy (Fig. 6B). This research is being done in collaboration with Aesir Technologies, Inc., situated in Joplin, Missouri.
Energy Storage:
Fig. 3. Ragone chart of various rechargeable battery chemistries [5].
Fig. 4. Schematic of Li-ion coin cell battery construction [6].
Fig. 6. (A) Schematic of Ni-Zn battery and relevant reactions, (B) Gassing setup with cycling apparatus and components labelled.
Fig. 5. Comparison of nickel-zinc batteries with other battery chemistries [7].
Adsorption Thermodynamics:
In thermodynamics, it is well-known that input work is required to maintain a space as hot or cold (refrigeration). Desalination (Fig. 7A) can be thought a mixing or "blue" analog to this, to maintain a purified stream against a natural concentration gradient. The inverse process of mixing high and low concentration water streams to extract "blue" energy may serve as a viable alternative to wind/solar in regions where such salinity gradients are naturally available. This energy from mixing can be thought of as analogous to a heat engine.
Analogous thermodynamic terms can be developed for electrosorption-based cycles to improve cycle efficiency based on different cycle operations (Fig. 7B). By using cycles under operations analogous to Carnot-like operation in a blue refrigeration (desalination) cycle, theoretical efficiency can be boosted from 9% to almost 35% [8]. Conversely, for the reverse mixing process, several different analogies for different heat cycles (such as Carnot and Stirling) can be developed, showing performance changes based on cycle operation [9].
For real electrodes constructed and tested experimentally, the thermodynamic limits can be understood by examining the adsorption characteristics of the electrodes (including properties such as enthalpy and entropy). Thermodynamic adsorption isotherms for desalination (Fig. 7C) have been published experimentally [10], but these require many individual experiments varying both concentrations and temperatures. The theory involved in electrochemical adsorption isotherms could be of interest to a diverse range of disciplines. The project will also integrate with experiments to more easily determine adsorption characteristics of electrodes for salt water treatment.
Fig. 7. (A) Concept of capacitive electrosorption (deionization) desalination process. (B) Charge-voltage diagram showing different cycle operations [9]. (C) Electrosorption isotherm example.
References:
1. Tufa RA, Chanda D, Ma M, Aili D, Demissie TB, Vaes J, Li Q, Liu S, Pant D. Towards highly efficient electrochemical CO2 reduction: Cell designs, membranes and electrocatalysts. Applied Energy. 2020 Nov 1;277:115557.
2. Bagger A, Ju W, Varela AS, Strasser P, Rossmeisl J. Electrochemical CO2 reduction: a classification problem. ChemPhysChem. 2017 Nov 17;18(22):3266-73.
3. Moreno D, Omosebi A, Jeon BW, Abad K, Kim YH, Thompson J, Liu K. Electrochemical CO2 conversion to formic acid using engineered enzymatic catalysts in a batch reactor. Journal of CO2 Utilization. 2023 Apr 1;70:102441.
4. Lin R, Guo J, Li X, Patel P, Seifitokaldani A. Electrochemical reactors for CO2 conversion. Catalysts. 2020 Apr 26;10(5):473.
5. Meesala Y, Jena A, Chang H, Liu RS. Recent advancements in Li-ion conductors for all-solid-state Li-ion batteries. ACS Energy Letters. 2017 Dec 8;2(12):2734-51.
6. Alyakhni A, Boulon L, Vinassa JM, Briat O. A comprehensive review on energy management strategies for electric vehicles considering degradation using aging models. IEEE Access. 2021 Oct 15;9:143922-40.
8. Moreno D, Hatzell MC. Constant chemical potential cycles for capacitive deionization. Physical Chemistry Chemical Physics. 2019;21(44):24512-7.
9. Moreno D, Hatzell MC. Using Thermodynamics Principles to Optimize Performance of Capacitive Mixing Cycles for Salinity Gradient Energy Generation. InASME Power Conference 2019 Jul 15 (Vol. 59100, p. V001T12A007). American Society of Mechanical Engineers.
10. Mossad M, Zou L. Evaluation of the salt removal efficiency of capacitive deionisation: Kinetics, isotherms and thermodynamics. Chemical engineering journal. 2013 May 1;223:704-13.