(Invited) Electrochemistry Combined in Situ Neutron Reflectometry: A Powerful Tool for a More Sustainable Environment

Abstract

Neutrons, having extraordinary characteristics that include penetrating power, sensitivity to lighter elements (such as hydrogen and carbon), and magnetic moment, make neutron reflectometry an ideal candidate for examining surface and interfacial structures of thin films in a non-destructive and non-invasive fashion. Liquids Reflectometer (LR) at the Spallation Neutron Source at Oak Ridge National Laboratory measures specular and off specular neutron reflectivity in a horizontal sample geometry, and tracks changes of layer thickness, scattering length density, and roughness as a function of depth. The exceptional sample environment at LR offers the capability to conduct in situ electrochemistry to probe the morphological and structural changes of solid/liquid interfaces during operation as a function of chemical and electrochemical gradients over time. Furthermore, the time-resolved mode at LR can be carried out continuously over a reduced Q range and binned into 60-second intervals. The improved time resolution of the neutron reflectivity (NR) measurement can help elucidate the kinetic behavior of surface/interfaces under dynamic conditions and provide a unique perspective to the equilibrium study. In this talk, I will give a brief introduction on neutron reflectometry, the LR, and a variety of sample environments at the LR. I will focus on the electrochemical applications coupled with in situ NR measurement. In the end, I will provide a specific example of applications in electrochemically modulated separation for water remediation by using neutron reflectometry. With the rapid growth of human population, it is highly desirable to minimize energy and materials input in selective separations for a more sustainable environment. The study is critical for creating new, more selective separation systems through rationally design of the structure and operating conditions.