In Operando neutron Imaging of Enzymatic Electrochemical Cells

Abstract

Enzymatic electrochemical cells (EECs) convert sugars, alcohols, and other fuels into electrical energy through electrochemical reactions catalyzed by naturally occurring enzymes. These devices typically consist of porous carbon electrodes, which may be separated by a polymer membrane. The porous electrodes in EECs are typically saturated with aqueous solutions to support electrochemical activity. The anode contains fuel within the liquid solution, while EECs often incorporate an air-breathing cathode. This work focuses on the characterization of the active anode assembled in a prototype three electrode cell developed to support investigation of the effects of varying environmental conditions on EEC performance. The aluminum three electrode cell reactor was designed and fabricated for in operando neutron imaging. This reactor consisted of two compartments for housing the working and counter electrodes. These halves of the reactor were separated by a Teflon gasket and filter paper. A three electrode cell arrangement was completed by embedding a silver reference electrode in the filter paper. Utilizing neutron tomography the active regions of the three electrode cell were mapped in the absence of the aqueous fuel solution. The reactor was then opened and wetted with a solution of 0.1 M glucose and 0.01 M hydroquinone in an aqueous sodium phosphate buffer. Cyclic voltammetry (CV) was performed to ensure proper function of the cell. Following CV in operando imaging was performed to generate radiographic representations of the anodic components prior to, during, and after discharge. Simultaneous chronoamperometry was performed to provide a connection between the dynamics of the aqueous fuel and buffer solutions and cell performance. Following discharge, tomographic scans were performed to allow for the observation of changes in the active regions of the half-cell. Following the initial measurements the three electrode cell was opened and flushed with fuel solution. The CV, in operando imaging, and tomographic measurements were then repeated. Increased aqueous solution content was found to improve the overall response of the system, yielding higher current in CV and a more consistent discharge behavior during chronoamperometry. Solution content is quantified based on tomographic scans and the related effects on performance are addressed. In general, the studies presented demonstrate a means of controlling test cell geometry to permit the study of EECs using neutron imaging techniques.