Development of a polymer composite with high electrical conductivity and improved impact strength for the application as bipolar plate

Abstract

Effects of high energy electrons on the properties of polyethylene / multiwalled carbon nanotubes composites: Comparison of as-grown and oxygen-functionalised MWCNT AIP Conference Proceedings 1593, 290 (2014) Abstract. Bipolar plates constitute the most important structural component in fuel cell stacks. Highly filled thermoplastic composites with high electrical conductivity obtain an increasing importance in the design of bipolar plates as alternative to conventional metallic systems. Thermoplastics (e.g. PP) have suitable properties such as a good processability, chemical resistance, light weight and low production costs. As thermoplastics have low electrical conductivities, conductive fillers have to be included in the matrix. A high content of such fillers (e.g. graphite) in excess of 80 wt.-% is necessary to achieve the desired electrical properties. However, materials with such high filler contents embrittle readily. The workability in injection and compression molding is difficult and the mechanical stability is insufficient in case of strain deformation. As consequence, material failure and an inacceptable amount of damaged goods can be observed during the processing. As no suitable thermoplastic system is available for better mechanical properties, the induction and dispersion of a rubber phase in the thermoplastic matrix can be used to increase the impact strength of the conductive composite. In this research work a ternary composite, based on PP as matrix, EPDM as impact modifier and synthetic graphite as conductive filler, was developed. The material was produced using a 26 mm co-rotating, intermeshing twin-screw extruder. The amounts of PP, EPDM and graphite were varied systematically and a process window was defined that enables improved impact strength and high electrical conductivity of the new material. The results indicate that impact strength can be enhanced by about 99 % with an EPDM content of 30 wt.-% in the PP matrix. The electrical conductivity decreases in a small range with increasing content of EPDM, but the conductivity is still excellent for producing bipolar plates.

Extruded polycarbonate/Di-Allyl phthalate composites with ternary conductive filler system for bipolar plates of polymer electrolyte membrane fuel cells

“…As thermoplastic polymers offer recyclability, they have been used numerously in preparing CPCs for BPPs. Examples include polypropylene (PP) [19,[28][29][30], polyethylene (PE) [31], and polyphenylene sulfide (PPS) [32,33], filled with carbon fiber (CF) [17], Graphite (G) [16,34], carbon nanotube (CNT) [35,36], carbon black (CB) [37,38], and graphene (Gr) [17,39], or combinations of these fillers [40].…”

“…Through-plane and in-plane electrical conductivities of 1.1 and 1.9 S cm −1 , respectively, were reported for PE filled with 63 wt% G [41]. Filler loadings as high as 80 wt% [42,43] and 90 wt% [28] have been used to increase the conductivity; this is however at the expense of the mechanical properties. Adding a modifier such as impact modifier can improve the mechanical properties [44].…”

“…Adding a modifier such as impact modifier can improve the mechanical properties [44]. For instance, Hopmann et al [28] reported a 99% increase in the impact strength of PP-60 wt% graphite composite by introducing 30 wt% EPDM rubber relative to PP mass, accompanied with only a small range decrease in conductivity. Another strategy for the enhancement of electrical, thermal, or mechanical properties in nanocomposites is the surface treatment of the nanofillers or the addition of a third component compatible with both nanomaterial and the matrix [45][46][47].…”

Hybrid conductive filler/polycarbonate composites with enhanced electrical and thermal conductivities for bipolar plate applications

“…Several thermoplastic materials such as polypropylene (PP) [13,[26][27][28][29][30], polyethylene [31][32][33], polycarbonate (PC) [34][35][36], and polyphenylene sulfide [37,38] have been studied as the matrix for CPCs, including bipolar plate applications [39]. Different carbon-based fillers such as carbon fiber (CF) [9,26,[40][41][42], graphite (G) [43][44][45], carbon nanotube (CNT) [45][46][47][48][49][50], and graphene (Gr) [51][52][53][54][55] have been used as conductive fillers. In particular, PC has shown promises in preparing composites with high electrical, thermal and mechanical properties.…”