(2ia) Electrochemical Systems with Flowable Suspension Electrolytes for Sustainable Future

Research Interests

Transitioning towards a sustainable future requires essential measures including generating and storing renewable energy, manufacturing materials with clean energy and less energy-intensive methods, and implementing efficient technologies for water treatment. Through my research, I envision to establish design principles for new electrochemical architectures for addressing challenges along the path to sustainability.

Research Vision

Electrochemical systems with flowable suspension electrolytes (FSEs) have the potential to address sustainability challenges as they enable large scale renewable energy storage, less energy-intensive chemical synthesis via electrochemical pathways, energy efficient metal recovery and processing, waste water treatment, separations etc. In this new architecture, FSEs—mixture of conductive colloidal particles and solvent—are pumped through the reactor for electrochemical conversion after which the suspension is stored in external tanks or directed for downstream processing depending on the application. FSEs have the advantage of reconfigurable electrode microstructures, extremely high surface areas, tunable charge and mass transport profiles and regenerable materials. In addition, they offer new reactor and process design opportunities. However, the choice of solid particles (conductive, redox-active, catalysts, metals, mediators, with bio-film coatings, etc.) and solvents (aqueous, non-aqueous) result in FSEs with widely varying rheological and electrochemical behaviors under various operating conditions (flow rates, potentials, current densities, etc.), often with high viscosities and poor conductivities. Designing efficient, application-specific electrochemical cells with FSEs requires knowledge of various tradeoffs between rheology, transport and electrochemistry as a function of multitude of input parameters related to material properties, reactor geometry and operating conditions.

My research group will leverage fundamentals colloidal science and electrochemical engineering principles to establish design rules for building efficient electrochemical systems with flowable suspension electrolytes for applications in diverse fields (energy storage, metals recovery and processing, separations etc.) that accelerate the transition to sustainable future. Within this context, we will build and employ simulation tools to explore rheology of and transport (charge and mass) in various FSE formulations related to different applications. Through this exploration, we aim to establish constitutive relations that describe the bulk properties. In addition, we will integrate rheology, transport and electrochemistry to build computationally inexpensive continuum full-cell models and optimize the system performance as a function of input design space for a given application. Furthermore, we will design experimental workflows to validate the models and collaborate with experimental electrochemical researchers to build lab scale reactors. Using this integrated approach, my group will establish design principles that help inform best material sets and operating conditions for a given application. Finally, advancement in the science of FSEs from our research will benefit other fields such as consumer care, pharmaceutical, food, material processing etc. A diverse set of research expertise in experiments and modeling related to suspension flows and electrochemical engineering places me at a unique advantage to address these challenges.

Research Experience:

Through graduate and postdoctoral research, I explored the fundamental aspects of microstructure, rheology and flow behavior of fluid-particle suspensions using experiments and modeling. In addition, the knowledge was leveraged to study biological and electrochemical systems with flowing suspensions.

Postdoctoral research:

Advisors: James Swan and Fikile Brushett, Massachusetts Institute of Technology; Eric Shaqfeh, Stanford University

I investigated the effect of particle roughness on the microstructure and rheology of colloidal gels using Stokesian dynamics simulations. For this purpose, I developed a pair-wise model for hydrodynamically interacting rough particles, integrated with the Stokesian dynamics simulations and computed the microstructure and bulk properties of colloidal gels subjected to linear shear rate. I explored the effect particle roughness on the structure-property relations for various inert-particle interaction strengths and applied shear rates relative to thermal energies. The research can help with formulation and processing of gels in pharmaceutical, food, energy storage and oil industries.

In addition, I studied the electronic charge transport across sheared suspensions of conductive non-Brownian particles for electrochemical applications. As part of the effort, I developed a kinetic Monte Carlo based charge hopping model to model the charge transport across suspension microstructure and integrated with the Stokesian dynamics simulation tool. I explored the effect of particle concentration and shear rate on charge carrier diffusivity which is linearly related to electrical conductivity of the suspension. The model predictions agree well with experiments.

Parallelly, I developed a continuum-based one dimensional model to predict the performance of a redox flow battery with suspension-based electrolyte. Rheology, charge and mass transport and electrochemistry were integrated to explore the tradeoffs between flow and electrochemical behaviors of the suspension electrolyte. This computationally inexpensive model allowed me to investigate the system performance (cell over potentials, net power output etc.) for a wide range of input parameters related to material properties and operating conditions. This research has applications in large scale energy storage.

Furthermore, I investigated how microparticles (dust or aerosols embedded with viruses) travel through and deposit in the human airways and to assess the consequent negative health effects. I employed computational fluid dynamics simulations coupled with point particles with stokes drag to compute the flow of air-particle mixture through airways of humans and rhesus monkeys.

Graduate research:

Advisors: Jeffrey Morris and Sanjoy Banerjee, City College of New York.

My graduate research was focused on understanding the inertial flow behavior of non-Brownian suspensions using experiments, simulations and linear stability analysis. Motivation for this work arose from lack of fundamental understanding and accurate transport models necessary to design pumping and mixing systems for industry. For this purpose, I designed and built Taylor-Couette experimental flow setup and employed flow visualization and particle tracking techniques and linear stability analysis. I investigated the effect of particle size and concentration on the inertial flow transitions and the type of flow structures when the suspension is sheared in the annulus between concentric rotating cylinders of the Taylor-Couette setup. I explored how inertial migration of particles contributes to non-uniform concentrations in the flow cross sections, ultimately effecting the flow stability of the suspensions.

Teaching Interests

I am passionate about teaching in an engaging and effective way with the help of visualizations and real-life examples while encouraging curiosity and critical thinking. I strive to create inclusive and respectful environments suitable for a diverse set of students to flourish. As a faculty, I am happy to teach any of the fundamental chemical engineering courses both at the undergraduate and graduate level. My past teaching and research experiences have helped me prepare best for designing and teaching courses related to complex fluids, fluid dynamics, heat and mass transfer, chemical engineering thermodynamics, and numerical methods.

I have thoroughly enjoyed my teaching experiences at all levels of chemical engineering in academia as well as in industry. During my Ph.D., I served as a teaching assistant for two undergraduate level thermodynamics courses and one graduate level mass transport course. I particularly enjoyed recitations, where I had the opportunity to deconstruct the complexity of a problem and devise easily accessible approaches to solve problems. I also learned effective ways of preparing course material and delivering content when I got the opportunity to give two lectures on the reaction equilibria for the undergraduate thermodynamics course and one lecture on linear stability analysis for a graduate level fluid particle systems course. In addition, during my work in the nuclear industry, I designed and delivered a short course on computational methods related to fluid flow and heat transfer to the new batch of engineers as part of their training where I motivated the problems with the real systems of the nuclear plants. I believe these experiences have prepared me to design courses and deliver them in an effective way.

Selected Publications

• Madhu Majji, Bertrand Neyhouse, Nicholas Matteucci, Kyle Lennon, Christopher Mallia, Alexis Fenton Jr, James Swan, and Fikile Brushett. Modeling Electrochemical and Rheological Characteristics of Suspension-Based Electrodes for Redox Flow Cells. Journal of The Electrochemical Society, 170(5), p.050532, (2023).

• Madhu Majji, James Swan, Parameterization of hydrodynamic friction in a model for sheared suspensions of rough particles. Physical Review Fluids, submitted. Preprint arXiv:2203.06300

• Madhu Majji, Sanjoy Banerjee, and Jeffrey Morris, Inertial flow transitions of a suspension in Taylor–Couette geometry. Journal of Fluid Mechanics, 835, pp.936-969, (2018).

• Madhu Majji, and Jeffrey Morris, Inertial migration of particles in Taylor-Couette flows, Physics of Fluids, 30(3), p.033303, (2018).

• Han Lin, Madhu Majji, Noah Cho, John Zeeman, James Swan, and Jeffrey Richards., Quantifying the hydrodynamic contribution to electrical transport in non-Brownian suspensions. Proceedings of the National Academy of Sciences119, no. 29: e2203470119, (2022).

• Taylor Geisler, Madhu Majji, Jana Kesavan, V. J. Alstadt, Eric S. G. Shaqfeh, G. Iaccarino, Simulation of microparticle inhalation in rhesus monkey airways. Physical Review Fluids, 4, 083101, (2019).