CBE Seminar: Engineering two-dimensional nanomaterials for efficient solar hydrogen production and gas mixture separations


Dr. Jesse D. Benck
Department of Materials Science and Engineering
Massachusetts Institute of Technology


Two-dimensional (2D) nanomaterials possess many unique physical, chemical, and electronic properties which make them useful for energy-efficient chemical reaction and separation processes. In this presentation, I will discuss how the catalytic activity and molecular impermeability of the 2D nanomaterials graphene and molybdenum disulfide (MoS2) make them useful for applications in solar hydrogen production and gas mixture separations. I will highlight my efforts to identify atomic-scale structure-property-function relationships which form design principles for improving the performance of these materials.

First, I will discuss how molybdenum sulfide nanomaterials can be used for efficient solar hydrogen production through electrochemical water splitting. Hydrogen is a critical chemical reagent and energy carrier, but it is currently produced from fossil fuels, which are limited in supply and create harmful CO2 emissions when consumed. Splitting water into H2and O2 using the energy from sunlight is a promising approach to sustainable hydrogen production, but developing active and stable water splitting systems using inexpensive materials is a significant challenge. I will show that wet-chemical synthesized amorphous molybdenum sulfide is a promising earth-abundant alternative to precious metal catalysts for the electrochemical hydrogen evolution reaction (HER). Through in situ spectroscopy and microscopy, I will reveal how changes to this material’s composition, chemical state, and atomic-scale structure during catalysis affect its performance. Next, I will focus on integrated water splitting photocathodes, which incorporate both HER catalysts and semiconductor light absorbers. I will demonstrate how the atomic structure of molybdenum sulfide nanomaterials can provide both corrosion protection and catalytic activity, resulting in photocathodes with excellent performance.

Second, I will discuss how nanoporous graphene membranes could enable energy-efficient gas mixture separations. Chemical mixture separations account for more than 10% of global energy use. While membrane separations could significantly reduce this energy consumption, the performance of conventional polymer membrane materials is not good enough to make these processes economical. Graphene sheets perforated with nanometer-scale pores could become ultra-high performance gas separation membranes due to their single atom thickness, which gives them the potential to achieve extremely high flux and selectivity, but these membranes remain difficult to fabricate and test, and the mechanisms of gas permeation through graphene nanopores are not well understood. I will describe how for the first time, I directly measured gas mixture separations through primarily single layer graphene membranes. These transport measurements demonstrate that graphene membranes can provide high mixture separation selectivity and reveal useful insights about the mechanisms of gas permeation through graphene nanopores.


Jesse Benck is currently a postdoctoral research associate in Professor Yet-Ming Chiang’s group in the Department of Materials Science and Engineering at the Massachusetts Institute of Technology, where his work focuses on in situ monitoring of electrochemically-induced phase transitions in solid materials. Previously, Jesse completed postdoctoral research with Professor Michael Strano in the Department of Chemical Engineering at MIT, where he studied nanoporous single layer graphene membranes for gas mixture separations. Jesse earned a Ph.D. in Chemical Engineering from Stanford University, where he worked with Professor Thomas Jaramillo on nanostructured molybdenum sulfide catalysts for the electrochemical hydrogen evolution reaction and semiconductor photocathodes for solar water splitting. Jesse also holds a M.S. in Chemical Engineering from Stanford University and a B.S. in Chemical Engineering from Northwestern University. His future research program will focus on developing atomic-scale understanding of electrochemical materials for catalysis, separation membranes, and sensors. He aims to generate design principles for engineering materials and devices with improved performance for emerging problems in water, energy, and the environment.