In situ spectroscopy and nanoscale imaging of electrochemical energy conversion and storage systems

            The first part of my talk will focus on solar energy conversion. The fundamental problem that limits the solar energy conversion efficiency of conventional semiconductors such as Si is that all absorbed photon energy above the band gap is lost as heat. The critical question that our research addresses is: Can we avoid energy losses in semiconductors? Ultrathin 2D semiconductors such as monolayer (ML) MoS₂ and WSe₂ have unique physical and photophysical properties that could make high-efficiency, hot-carrier energy conversion possible. Our research team has employed photocurrent spectroscopy, steady-state absorption spectroscopy, and in situ femtosecond transient absorption spectroscopy as a function of applied potential to characterize underlying steps in a ML MoS₂ photoelectrochemical cell. The rich data set informs us on the timescales for hot-carrier generation/cooling and exciton formation/recombination, as well as the magnitudes of changes in exciton energy levels, exciton binding energies, and the electronic band gap. These findings open the possibility of tuning the hot-carrier extraction rate relative to the cooling rate to ultimately utilize hot-carriers for solar energy conversion applications. The second part of my talk will focus on elucidating charge storage mechanisms in nanoscale materials, which underlies the performance of electrochemical technologies such as batteries and smart windows. I will discuss our high-throughput electro-optical imaging method that measures the battery-like and capacitive-like (i.e., pseudocapacitive) charge storage contributions in single metal oxide nanoparticles.  I will present our single particle-level measurements that show (1) individual particles exhibit different charge storage mechanisms at the same applied potential and (2) particle size-dependent pseudocapacitive charge storage properties.

Justin Sambur is the Monfort Associate Professor of Chemistry at Colorado State University. Justin earned his B.S. degree in 2006 from the State University of New York (SUNY)-Binghamton. His undergraduate honors thesis work under the direction of Dr. David Doetschmann focused on the degradation mechanisms of chemical warfare agents within zeolite pores. Justin traveled west to graduate school and earned his PhD under the direction of Dr. Bruce A. Parkinson at Colorado State University (CSU). Justin studied the photoelectrochemical energy conversion properties of semiconductor nanocrystals and light absorbing polymers on single crystal electrode surfaces. In 2011, Justin traveled back to NY to join Prof. Peng Chen’s lab at Cornell University. Justin’s NSF ACC-F Postdoctoral Fellow work integrated single molecule imaging methods in the area of photoelectrochemistry. Justin returned to CSU in 2016 as an Assistant Professor of Chemistry and the School of Advanced Materials Discovery (SAMD). His research has been recognized with the Royce Murray Young Investigator Award, Air Force Young Investigator Award, NSF CAREER Award, and DOE Early Career Award. Justin was also named a Sloan Research Fellow and a Scialog Fellow in Advanced Energy Storage.