(7jk) Reinforced anion exchange membrane (AEM) Separators Based on Triblock Copolymers for Electrode-decoupled redox flow batteries (RFBs)

Energy consumption is one of the barometers of economic and human well-being and the equitable development of humankind requires sustainable energy equity. Achieving this overarching goal requires us to address issues such as the intermittency of ecologically non-disruptive renewable energy technologies (solar and wind), decarbonize the transportation sector, and find alternative chemical pathways for large scale, energy intensive industrial processes. I aim to help address these key issues by leveraging my training and experience in multi-scale theoretical and experimental investigations of electrochemical systems.

Postdoctoral Project – “Reinforced anion exchange membrane (AEM) Separators Based on Triblock Copolymers for Electrode-decoupled redox flow batteries (RFBs)”

Supervisor: Prof. Vijay K. Ramani, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis

PhD Dissertation – “Investigation of the oxygen reduction reaction at the lithium-oxygen cell cathode”

Supervisor: Prof. Jai Prakash, Department of Chemical and Biological Engineering, Illinois Institute of Technology

Research Interests:

My research journey began with my undergraduate work on continuum scale modeling of the capacity fade mechanisms in lithium-ion batteries with Prof. Balaji Krishnamurthy. An internship at Tata Power Solar, where I assisted in formulating a new silicon texturing bath composition (resulting in a ~1% improvement in final cell efficiency), whetted my appetite for translational research.

During my PhD research with Prof. Prakash at Illinois Institute of Technology, I: 1) evaluated novel lithium-ion cell chemistries for use in sub-zero temperatures (in conjunction with Hydro-Quebec), 2) performed the first ever accelerating rate calorimetry study of the thermal safety of lithium-sulfur cells (again with Hydro-Quebec), and 3) performed a multi-year theoretical and experimental investigation of catalysts, solvents and kinetics of the oxygen reduction reaction (ORR) in lithium-oxygen cells in collaboration with Toyota Motors. Over the course of these projects, I extensively employed density functional theory (DFT) simulations, continuum scale kinetic modeling, and classical electrochemical and electroanalytical experimental techniques.

As an integral part of my postdoctoral research project, I am investigating anion exchange membranes for use in electrode-decoupled redox flow batteries (RFBs). Herein, I am applying my knowledge of electrochemistry and transport phenomena to understand the transport of ions across a functionalized membrane. The final goal of this project, funded by ARPA-E, is to develop selective membranes that allow for the deployment of low-cost, electrode-decoupled RFBs such as the Fe-Cr system.

Future Research Directions:

I plan to leverage my training and experience in multi-scale theoretical and experimental investigations of electrochemical systems to carry out transformative, translational research into next generation, beyond lithium-ion batteries, grid scale energy storage using redox flow batteries, and the electro-synthesis of bulk and fine chemicals.

Project 1: Metal- (metal superoxide) batteries – Lithium-oxygen batteries have been the holy grail of next generation battery systems due to their unmatched theoretical specific energy (3458 Wh kg^-1). Despite years of extensive work on catalysts, redox mediators and ever-more-stable electrolytes, a practical lithium-oxygen battery has not been realized. As part of this project I will examine sodium- and potassium- oxygen batteries whose reduction products are superoxides instead of the peroxides, allowing me to circumvent the columbic efficiency and degradation problems of lithium-oxygen batteries. I will combine insights from electrochemical kinetics studies with oxygen impermeable membranes and water tolerant ionic liquids to demonstrate long life alkali metal- (metal superoxide) batteries. The end goal will be the development of a true metal-ambient air battery.

Project 2: Low-cost, grid scale energy storage – The adoption of intermittent renewable energy sources calls for the large-scale deployment of energy storage solutions to maintain grid reliability. The DOE estimates that $100/kWh is the cost at which storage solutions become cost competitive. This cost target precludes both the Li-ion battery and the all-vanadium redox-flow battery. I will investigate alternative, low cost, earth abundant chemistries for redox-flow batteries. The use of catalytic inhibitors to suppress the hydrogen evolution and oxygen evolution reactions, in conjunction with electrolyte systems that increase the nominal redox potential of the redox couple of choice, will pave the way for >2V RFBs utilizing couples such as Cr-Ce and provide an unparalleled cost advantage compared to existing technologies. Further, I will develop highly perm-selective, high anion transference number anion-exchange membranes for this system both in-house and in collaboration with polymer scientists and material chemists.

Project 3: Electro-synthetic alternatives to energy intensive chemical production –

Ammonia production – Ammonia is produced to the tune of 140 million tons a year via the energy intensive Haber-Bosch process with a massive carbon footprint. Biomimetic or electro-catalytic ammonia production is a low CO₂ alternative to this process that will allow for low capital cost and distributed production of ammonia at the demand site. Further, the elimination of steam reforming to produce hydrogen and the avoidance of transportation costs and associated emissions makes this an extremely tantalizing proposition. I will examine metal, metal oxide, carbide, nitride and alloy catalysts for electrochemical ammonia synthesis from water and air. Combining DFT screening of catalyst candidates (nitrides, carbides, Pt and Pd alloys) with robust half-cell and device-level testing, I will identify candidate catalysts at the top of the activity pyramid, evaluate their nitrogen reduction kinetics and design, test and optimize larger-scale cells to produce ammonia.

CO₂ capture, concentration and conversion (C3)- Any realistic timeline of a transition to renewables envisions significant dependence on fossil fuels in the near-term. Thus, it is imperative that efficient CO₂ capture technologies be developed. In collaboration with other groups working on CO₂ capture, I will develop alkali metal-O₂/CO₂ batteries for direct conversion of CO₂ to electricity. An intriguing idea that will be investigated is a combined N₂ electro-reduction/ alkali metal-O₂/CO₂ system wherein the ammonia produced is used to capture and concentrate the CO₂ before use in the battery.

Teaching Interests:

The experience I have gained assisting in the teaching of 9 courses across the spectrum of ChE, from the sophomore level to the advanced PhD level, has prepared me well to serve as an instructor teaching the traditional chemical engineering core. I have served as Assistant to instructor and Support to instructor respectively for courses on Electrochemical Engineering and Energy Conversion and Storage at Washington University, where I have been actively involved in class planning and laboratory sessions in addition to traditional teaching assistant roles. During my PhD, I served as a Teaching assistant for 7 courses including thermodynamics, transport phenomena, undergraduate laboratory and electives in energy technology. The experience of assisting in the teaching of thermodynamics as an introductory first course, an intermediate course for 1^st year master’s students and as an advanced course for PhD students provided invaluable insights into the nuances of balancing depth and clarity without sacrificing technical accuracy. The mentor-mentee relationships I formed with high school, undergraduate and graduate students in the lab redoubled and renewed my commitment to excellence in teaching and training. I look forward to bringing this passion to my future role as a ChE faculty member.

Invention and Technology Translation:

I have always wanted to see my work changing society in a reasonable timeframe. My PhD work on Pd and Pt alloy catalysts for lithium-oxygen batteries with Toyota resulted in a patent and is the basis of their continued research in this field. My on-going postdoctoral work on reinforced membranes for flow batteries has already resulted in a $50,000 Leadership in Entrepreneurial Acceleration Program (LEAP) grant from Washington University to serve as a pre-seed fund for a start-up. My future independent research career will maintain that same strong practical, inventive and translational emphasis.

Publications (9 published, 1 in review and 4 under preparation)

1. Sankarasubramanian, and B. Krishnamurthy, A Capacity Fade Model for Lithium ion batteries including kinetics and diffusion, Electrochim. Acta 70, 248-254 (2012).
2. Seo, S. Sankarasubramanian, C-S Kim, P. Hovington, J. Prakash, and K. Zaghib, Thermal characterization of Li/sulfur, Li/ S-LiFePO₄ and Li/S-LiV₃O₈ cells using Isothermal Micro-Calorimetry and Accelerating Rate Calorimetry, J. Power Sources 289, 1-7 (2015).

3. Sankarasubramanian*, N. Singh, F. Mizuno, J. Prakash, Ab initio investigation of the Oxygen Reduction Reaction activity on noble metal (Pt, Au, Pd), Pt₃M (M=Fe, Co, Ni, Cu) and Pd₃M (M=Fe, Co, Ni, Cu) alloy surfaces, for Li-O₂ cells, J. Power Sources, 319, 202-209 (2016).
4. Sankarasubramanian*, J. Seo, F. Mizuno, N. Singh, J. Prakash, Rotating ring-disc electrode investigation of the aprotic superoxide radical electrochemistry on multi-crystalline surfaces and correlation with Density functional theory modeling – implications for Lithium-air cells, J. Electrochem. Soc., 163(10), A2377-A2384 (2016).
5. Sankarasubramanian*, J. Seo, F. Mizuno, N. Singh, K. Takechi, J. Prakash, Enhancement of oxygen reduction reaction rate by addition of water to an oxidatively stable ionic liquid electrolyte for lithium-air cells, Electrochem. Commun., 73, 55-57 (2016).
6. Sankarasubramanian*, J. Seo, F. Mizuno, N. Singh, J. Prakash, Elucidating the Oxygen reduction reaction kinetics and the origins of the anomalous Tafel behavior at the Li-O₂ cell cathode, J. Phys. Chem. C, 121, 4789-4798 (2017).
7. Zhang, J. Parrondo, S. Sankarasubramanian, V. Ramani, Detection of Reactive Oxygen Species in AEM Fuel Cells using in situ Fluorescence Spectroscopy, ChemSusChem, 10, 3056-3062 (2017).
8. Seo^#, S. Sankarasubramanian*^{, #}, F. Mizuno, N. Singh, K. Takechi, J. Prakash, Effect of cathode porosity on the Lithium air cell oxygen reduction reaction – a rotating ring-disk electrode investigation, Electrochim. Acta, 248, 570-577 (2017).
9. He, G. Wang, J. Parrondo, S. Sankarasubramanian, V. Ramani, Pt/RuO_2.-TiO₂ electrocatalysts exhibit excellent hydrogen evolution activity in alkaline media, J. Electrochem. Soc., 164(12), F1234-F1240 (2017).