Technologies that store electrical energy or convert solar and electrical energies to fuels are emerging as critical to our ability to deploy decentralized cost-effective energy equivalents from renewable and inexpensive sources, such as solar, wind, biomass, and carbon dioxide. Our research program is in theory, modeling, and simulation, with emphasis on multi-scale, multi-physics, and high performance computing, focused on selected fundamental science topics that limit these technologies. These include: i) photo-electro conversions and ii) electrical energy storage. The overarching theme of the research is about the fundamentals of charge and ion transport and reactivity in complex molecular, solid state, and interfacial environments relevant to electrical-to-fuel conversions and electrical energy storage. Our computation program includes method development as appropriate.

Nanostructured transition metal oxide semiconductors are viewed as essential photoelectron-active materials for future generation photoelectrochemical solar cells, batteries, energy conversion substrates, and nanoscale integrated circuit components because of their flexibility in synthesis, low cost, and high chemical stability.  For example earth-abundant metal oxides such as nanocrystalline TiO₂ and α-Fe₂O₃ have received much attention for solar production of H₂ and electricity.  Mixed TiO₂/perovskites show great potential for solar cells with unprecedented efficiencies. TiO₂ is also widely utilized for photocatalytic and catalytic conversions, including biomass conversion. A critical property in nanostructured assemblies is efficient transport of electron/hole (e⁻/h⁺) carriers within the material and across interfaces.

The general focus of our program is on the computational characterization of the structure, dynamics, and reactivity of charge carriers in the solid state and at solid/solid and solid/electrolyte interfaces. The fundamental knowledge emerging from this research will lead to a enhanced understanding of carrier processes (generation, separation, recombination, trapping) and transport. The processes are most often investigated with band theory. In contrast our approach will be molecularly-based and provide complementary chemical insights. Our efforts will also include studies of e^-/h⁺ driven reactions at interfaces, with special attention given to specificity, kinetics, and over-potentials.  As much as possible the research will be correlated to experimental measurements such as photoluminescence, NMR and EPR, and others.

Planned efforts include:

• Modeling the processes of e^-/h⁺ generation, separation, and recombination proper (in bulk titania as model system); we will also characterize the influence of defects on these processes. We will learn about fundamentals of photo-efficiency.
• Modeling the dynamics of redox reactivity by e^-/h⁺ carriers at solid/liquid interfaces. We will learn about the role of dynamics vs. thermodynamics in reactivity.
• Modeling carrier generation and transport in the recently discovered TiO₂/perovskites systems with our ‘localized polaron” models. We will learn the basis of their enhanced charge separation ability and superior photo-efficiency.

Redox flow batteries (RFBs) hold considerable promise for grid energy storage, but are hampered by low energy density, capacity decay, and high cost. Li-based batteries for vehicle power face challenges associated with safety, cycle life, and cost.  There is a critical need to go beyond current battery chemistries and presently usedpolymer membranes, but experimental research in this area has made only incremental progress. The goal of our research will be to advance the fundamental understanding of redox potentials, solvation structures, selective ion transport, water diffusion, chemical stability of electrolytes, and membrane morphology for RFBs.  This will be achieved through computational characterization of redox species and couples, organic solvents, ionic liquids, and polymer membrane separators that are of interest in RFB technology. Predictive computer simulations, ideally in conjunction with synthesis and electrochemical characterization, have the potential to define science-based rules for the selection of redox active species, solvents, ionic liquids, and polymer membranes for these energy storage applications.