(3dj) Scratching the Surface: Simulating and Engineering the Interfaces of Materials for Sustainable Energy and Environmental Remediation

My research is broadly focused on theoretical materials innovation for renewable energy and environmental applications, with a special emphasis on the development of computational methods for more realistic modeling of interfacial phenomena in electrocatalysis and solar energy conversion. I am driven by the prospects of combining first-principles calculations, Monte Carlo simulations, and machine learning in a synergistic approach for developing a fundamental understanding of complex materials systems, discovering relationships between their structure and function, and identifying promising routes for device optimization.

The problems I am currently studying lie in an area of computational materials science where a number of different frontiers meet: the advancement of computational techniques capable of handling the complexity and scale of real materials, the judicious utilization of machine learning to facilitate the detection of hidden materials trends, and the discovery/optimization of materials for sustainable technologies that can combat climate change. In particular, I am interested in understanding how the effects of surface reconstruction and modification in real materials can give rise to changes in electrocatalytic rates for water splitting and CO₂ conversion, and solar cell efficiency. To this end, I employ analytical, numerical, and machine-learning techniques, and the questions I address range from the fundamental and phenomenological level to the more practical realization-oriented and materials-based level. Maintaining direct connections to experimental efforts is an important aspect of my approach.

Successful Proposals

U.S. Department of Energy, Office of Basic Energy Sciences, grant DE-SC0019281

PI: Prof. Andrew M. Rappe

Department of Defense, High-Performance Computing Modernization Program, Pathfinder

PI: Prof. Andrew M. Rappe

Postdoctoral Projects

“Suppressing Deep-Trap Formation in Cu₂ZnSnS₄-Based Solar Cells via Ion Substitution”

“Designing Materials for Solar Thermochemical Hydrogen Production Using Machine Learning”

“First Principles Modeling of Seawater-Based CO₂ Mineralization”

Under the supervision of Prof. Emily A. Carter, Mechanical and Aerospace Engineering, Princeton University

PhD Dissertation

“Toward Realistic Modeling of Catalytic Surfaces: From First Principles to Machine Learning”

Under the supervision of Prof. Andrew M. Rappe, Department of Chemistry, University of Pennsylvania

Research Experience

My PhD and postdoctoral research purposefully span a number of disciplines from chemistry and physics to materials science and engineering due to my passion for improving the realism of computational methods for materials modeling. To this end, I have applied and developed methods for (1) the modeling and design of catalysts for water splitting and semiconductors for solar cells using first-principles calculations (to compute accurate thermodynamic and kinetic quantities) and machine learning (to identify performance descriptors), (2) the prediction of surface phase diagrams using ab initio grand canonical Monte Carlo (to sample efficiently surface phase space), and (3) the simulation of ferroelectric phase transitions using molecular dynamics simulations (to include the effect of nanoscale fluctuations on these processes). For my work in electrocatalyst design for water splitting, I collaborate closely with an experimental research group at Rutgers University. This collaboration not only has developed a deeper understanding of the surface effects that govern the H₂ evolving activity of nickel phosphides but also has provided practical strategies for improving their catalytic efficiencies. Additionally, through this collaboration, I have acquired valuable and versatile experience in analyzing and interpreting measurements relevant to catalysis and engaging in productive discussions with experimentalists about their results and next steps. Moreover, as a result of serving as the Alternate HPC Contact for my PhD group’s DOD HPCMP accounts and my current group’s NREL HPC project, I have become proficient in high-performance supercomputing and have co-written five successful proposals for high-priority time (~15 million CPU hours).

Teaching Experience

Since my final year as an undergraduate, I have been honing my craft as an educator. As a senior undergraduate at Drexel University, I guest-lectured for “CHEM 355 Physical Chemistry IV”. As a PhD student at the University of Pennsylvania, I was a teaching assistant for general chemistry, physical chemistry lecture and laboratory, and graduate quantum chemistry, where, for physical chemistry lecture, I received a teaching assistant award. More recently, I started tutoring for the Princeton Online Tutoring Network, which provides tutoring assistance to underrepresented K-12 students during the COVID-19 pandemic. Additionally, I serve as an editor for Princeton Insights, which is a team of graduate and postdoctoral researchers that highlight some of Princeton University’s most exciting recent research through short, accessible reviews.

Future Directions

My career plans center around solving grand challenges in energy and the environment by designing and developing next-generation technologies for water splitting, CO₂ utilization, and solar energy conversion. More specifically, I aim, through theoretical innovations and experimental collaborations, (1) to develop state-of-the-art computational techniques for the realistic simulation of material surfaces, (2) to provide fundamental understanding and design principles for sustainable H₂ production and controllable CO₂ conversion, and (3) to improve solar cell efficiency via chemical modification and interfacial engineering.

Selected Publications

R. B. Wexler, G. S. Gautam, and E. A. Carter, 2020. “Optimizing kesterite solar cells from Cu₂ZnSnS₄ to Cu₂CdGe(S,Se)₄”. In preparation.

R. B. Wexler, G. S. Gautam, and E. A. Carter, 2020. “Exchange-Correlation Functional Challenges in Modeling Quaternary Chalcogenides”. Phys. Rev. B. Under revision.

R. B. Wexler, Y. Qi, and A. M. Rappe, 2019. “Sr-induced dipole scatter in Ba_xSr_1-xTiO₃: Insights from a transferable-bond valence-based interatomic potential”. Phys. Rev. B. 100 (17), 174109. doi: 10.1103/PhysRevB.100.174109

R. B. Wexler, T. Qiu, and A. M. Rappe, 2019. “Automatic Prediction of Surface Phase Diagrams Using Ab Initio Grand Canonical Monte Carlo”. J. Phys. Chem. C. 123 (4), 2321-2328. doi: 10.1021/acs.jpcc.8b11093

A. B. Laursen, R. B. Wexler, M. J. Whitaker, E. J. Izett, K. U. D. Calvinho, S. Hwang, R. Rucker, H. Wang, J. Li, E. Garfunkel, M. Greenblatt, A. M. Rappe, and G. C. Dismukes, 2018. “Climbing the Volcano of Electrocatalytic Activity while Avoiding Catalyst Corrosion: Ni₃P, a Hydrogen Evolution Electrocatalyst Stable in Both Acid and Alkali”. ACS Catal. 8 (5), 4408-4419. doi: 10.1021/acscatal.7b04466

R. B. Wexler, J. M. P. Martirez, and A. M. Rappe, 2018. “Chemical Pressure-Driven Enhancement of the Hydrogen Evolving Activity of Ni₂P from Nonmetal Surface Doping Interpreted via Machine Learning”. J. Am. Chem. Soc. 140 (13), 4678-4683. doi: 10.1021/jacs.8b00947

R. B. Wexler, J. M. P. Martirez, and A. M. Rappe, 2017. “Active role of phosphorus in the hydrogen evolving activity of nickel phosphide (0001) surfaces”. ACS Catal. 7 (11), 7718-7725. doi: 10.1021/acscatal.7b02761

C. H. Naylor, W. M. Parkin, Z. Gao, H. Kang, M. Noyan, R. B. Wexler, L. Z. Tan, Y. Kim, C. E. Kehayias, F. Streller, Y. R. Zhou, R. Carpick, Z. Luo, Y. W. Park, A. M. Rappe, M. Drndić, J. M. Kikkawa, and A. T. C. Johnson, 2017. “Large-area synthesis of high-quality monolayer 1T’-WTe₂ flakes”. 2D Mater. 4 (2), 021008. doi: 10.1088/2053-1583/aa5921

R. B. Wexler, J. M. P. Martirez, and A. M. Rappe, 2016. “Stable phosphorus-enriched (0001) surfaces of nickel phosphides”. Chem. Mater. 28 (15), 5365-5372. doi: 10.1021/acs.chemmater.6b01437