PNNL

Abstract

In this paper, we describe a flexible three-dimensional (3-D) pore-scale model that can be used to construct multi-scale fibrous electrodes for redox flow batteries (RFB). The fibrous electrode provides active sites for electrochemical reactions, and its design is closely related to battery performance. Recent electrode designs, such as biporous electrodes, can modify electrode structures by creating secondary pores on a single carbon fiber to reduce internal resistance within the battery. Existing pore-scale models only resolve electrodes to the single carbon fiber scale and cannot incorporate new multi-scale electrode designs in numerical models. Our flexible 3-D pore-scale model aims to bridge this gap and provide a tool that can be used to rapidly screen a wide array of electrode configurations. We used our model to analyze two types of multi-scale electrodes—laser-perforated electrodes and biporous electrodes. Both types of electrodes were investigated at varying electrolyte flow velocities. The laser-perforated electrode exhibited a reduced pressure drop under the operating conditions while maintaining similar permeability conditions to those observed for the pristine electrode. We studied the electrochemical process occurring in the biporous electrode and found that the increased specific surface area and enhanced reaction kinetics from the secondary pores are the most influential factors leading to improved battery efficiency. However, operating the biporous electrode in limiting current density regions should be avoided, because decreased mass transfer efficiency leads to a more significant voltage loss. We believe that our 3-D pore-scale model can accelerate the flow battery electrode design process and provide insights into electrode geometry optimization.