Research

            
We are utilizing knowledge developed in the advanced Li-ion, Li-battery, and CO2 conversion fields to develop new gas-to-solid, gas-to-liquid, and solid-solid electrochemical reactions, and to explore new frontiers in electrochemical science opened up by identification and design of novel reaction mechanisms.

 

Novel metal-gas battery chemistries  
Nonaqueous metal-gas batteries are a growing family of primary and secondary batteries with higher theoretical capacities and energy densities than current Li-ion batteries, as exemplified by the prototypical Li-oxygen (Li-O2) battery. To further unlock the advantage of the metal-gas battery, we are exploring the use of previously unexplored gas molecules, i.e., fluorinated gases such as sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3), as the cathode gas-to-solid reaction. Metal-gas batteries employing these fluorinated gases can not only deliver high theoretical voltages (> 3 V) because of the strong oxidizing power of the fluorinated gas, but also serve as a great platform to understand the thermodynamics and kinetics of the multiple electron transfer (3 < n < 8) process of these fluorinated molecules. Knowledge from these efforts can provide insights into the design of gas-to-solid electrochemical systems which have broad application in areas such as energy storage/conversion, gas sensors, and environmental pollutant removal.
 

References

(1) Li, Y.; Khurram, A.; Gallant, B. M. A High-Capacity Lithium–Gas Battery Based on Sulfur Fluoride Conversion. J. Phys. Chem. C 2018, 122 (13), 7128–7138.

(2) He, M.; Li, Y.; Guo, R.; Gallant, B. M. Electrochemical Conversion of Nitrogen Trifluoride as a Gas-to-Solid Cathode in Li Batteries. J. Phys. Chem. Lett. 2018, 9 (16), 4700–4706.

(3) Gao, H.; Li., Y.; Guo, R.; Gallant, B. M., Controlling Fluoride‐Forming Reactions for Improved Rate Capability in Lithium‐Perfluorinated Gas Conversion Batteries. Adv. Energy Mater. 2019, 1900393.

 

 

 

CO2 capture and electrochemical conversion
Innovative approaches for CO2 management are crucial not only for developing mitigation technologies to address sustainability challenges, but also for enhancing our scientific understanding of CO2 reactivity for the design of CO2-centric reactions. Our work in this area focuses broadly on identifying innovative strategies for enhancing CO2 reactivity. Our current focus is on reactions conducted in organic media, given the opportunities to design simpler and selective reactions that lend themselves to more facile characterization without competing water reactions. Currently, we are working on the design and characterization of nonaqueous electrolytes incorporating amine-based motifs that offer the possibility of designing integrated chemical capture and electrochemical conversion systems. In such an approach, activation of the normally inert CO2 occurs through chemical reaction of the CO2 with the amine. Our group recently discovered that this process, which alters the electronic structure around the –COO moiety, renders the captured CO2 highly active for subsequent electrochemistry at inexpensive, metal-free carbon electrodes. This approach advantageously combines two conventionally separate methods – capture and electrochemical conversion – for CO2 mitigation. The feasibility of the aforementioned scheme has been demonstrated in rechargeable Li-based batteries to date, where Li2CO3 was the major discharge product. However, to circumvent the high material cost of Li, we are continuing to explore earth-abundant metals as negative electrode materials which could enable more cost-effective sequestration of the captured CO2 as a densely packed solid. We are also interested in understanding how protic donors may alter the reaction pathway in future work, possibly yielding protonated products such as chemicals or fuels.
 

References

(1) Khurram, A.; He, M.; Gallant, B. M. Tailoring the discharge reaction in Li-CO2 batteries through incorporation of CO2 capture chemistry. Joule 2018, 2, 2649-2666

(2) Khurram, A.; Yan, L.; Yin, Y.; Zhao, L.; Gallant, B. M. Promoting Amine-Activated Electrochemical CO2 Conversion with Alkali Salts. J. Phys. Chem. C 2019 (in press)

 

Novel materials and interface design for next-generation rechargeable batteries  
Fluoride-forming reactions. Fluoride-based materials are increasingly promising for future high-capacity and stable Li-ion cathode materials and stable Li metal interfaces. Our laboratory is developing expertise in fluoride-forming electrochemical reactions, particularly those conducted in Li+ environments, where the LiF amount, morphology, and structure can be carefully tuned by modulating the electrochemical conditions. We are currently exploring how fluoride-based materials can be synthesized in new ways, opening new opportunities to introduce this important yet normally intransigent precursor to future energy storage materials. Fundamentally, we are interested in studying how fluoride becomes incorporated in materials, imparting exciting new properties such as improved stability and high energy density.
 
Modifying the solid electrolyte interphase (SEI). The SEI plays a critical role in stability of the interphase of graphite materials, yet the native SEI that forms on metal surfaces such as Li remains highly unstable and challenging to characterize. We are developing selective, gas-based synthesis approaches to generate model ‘deconstructed’ interphases on Li that are amenable to fundamental study. This work aims to provide improved understanding of physical parameters of interfacial materials on Li, which normally evade characterization owing to their nanoscopic thickness, heterogeneity, and air reactivity. Our long-term interest is to integrate this knowledge to obtain better fundamental understanding of the individual contributions of common SEI phases, and use this understanding to develop rational guidelines for designing interfaces with improved stability over long-term cycling, bringing metal anodes a step closer to commercial feasibility.