Modulation of the microstructure of the Ag/C-based alkaline cathode via the ionomer content for a bipolar membrane fuel cell

Abstract

Abstract Ag/C is evaluated as a cathode catalyst for a bipolar membrane fuel cell (BPMFC). The microstructure of the cathode catalyst layer is modulated via ionomer content, and the effects on BPMFC performance are studied. When the ionomer content is increased from 10 wt% to 30 wt%, the fuel cell performance is optimized at 19.3 mW/cm2 with an ionomer content of 20 wt%. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) are conducted on the catalyst layer. EIS indicates that the charge transfer resistance is minimum, while CV suggests that the highest electrocatalytic activity of the catalyst is achieved with an ionomer content of 20 wt%. The microstructure of the catalyst layer is characterized using scanning electron microscopy (SEM) and nanometer-scale X-ray computed tomography (nano-CT). The SEM results show that excess ionomer cover on the surface of the catalyst, and the catalyst seems to form larger aggregates. Nano-CT, however, produces quite different results. The reconstructed 3D image of the catalyst layer reveals that the Ag/C catalyst tends to aggregate at low ionomer content. When the ionomer content is increased from 10 wt% to 30 wt%, the average diameter of the catalyst aggregation decreases from 313 nm to 210 nm.