Studying the Effect of Carbonous Fillers on the Properties of Conductive Polymer Composites As Flow Field Plates in Redox Flow Batteries
Authors: Asadipour Erfan , Ramani Vijay K 
Published: December 2024

Redox flow batteries (RFBs) are large-scale stationary energy storage technologies that are integrated with solar and wind power plants. Flow field plates guide the electrolyte inside the RFB and conduct electrons from the electrodes to the current collector; hence, designing thin, durable, and electrically conductive flow field plate benefits RFB performance.

Bipolar graphite plates (BGPs) are traditionally used in RFBs due to their high electrical conductivity. However, BGPs are brittle, difficult to machine, and have high contact resistance with electrodes1-4. Hence, conductive polymer composites (CPCs) were proposed as alternatives. the CPCs are composed of one (or multiple) carbonous filler(s) and a durable polymer; the former provides the electrical conductivity, and the latter ensures mechanical flexibility and durability. Although many articles have explored this area1-12, a comprehensive study on the effect of size and shape of the carbonous fillers (majority and minority ones) is absent from the literature.

Many methodologies to produce CPCs are proposed; however, most lead to polymer chain scission or non-homogeneous mixing of components. Solution blending of all components, casting the solution, drying, and hot pressing it afterwards (to ensure compactness) is one of the methodologies that avoids mentioned complications. Preliminary results with natural graphite flakes and PVDF-co-HFP utilizing this method showed very low conductivity (<0.1 S/cm). This result is attributed to the formation of a superficial polymer-rich layer, as shown in Fig. 1. Hence, producing CPCs either without hot pressing or utilizing surface treatments to remove the polymer-rich region are studied here. Additionally, this study focuses on understanding the effect of shape and size of the carbonous filler(s) within CPCs as flow field plates for RFBs.

Fig. 1. SEM images of PVDF-co-HFP and graphite (50/50% wt/wt) distribution in CPCs produced by solution blend method. Before hot pressing the composites, the polymer was homogeneously blend with the graphite. However, an insulating polymer-rich layer was formed on the surface of the CPCs after hot pressing.

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Figure 1