Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

Summary

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

Abstract

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.

In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.

In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

Introduction

The bipolar plate is a multi-functional key component of energy conversion systems and energy storage systems such as fuel cells and batteries. The key functional requirements of the bipolar plate are as follows: high electrical conductivity in the through-thickness direction to reduce ohmic-loss, high mechanical properties to withstand high compaction pressure and external impacts, and high productivity for mass production.

Compared with the graphite and metals that were conventionally adopted as materials for the bipolar plate, carbon fiber/epoxy composites have a higher specific strength and stiffness, which indicates that the weight of ....

Protocol

1. Material Preparation

1. Preparation of the composite material
   NOTE: CAUTION, Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these methods may be toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterparts. Please use all appropriate safety practices when performing an experiment, including the use of engineering controls (fume hood, glove box) and personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes).
   NOTE: Depending on the application, the type of reinforcing fiber can be one ....

Results

The fabricated specimens are observed using scanning electron microscopy (SEM) (Figure 1). Because the resin-rich layer that covers the top of the fibers is only a few micrometers thick, an optical microscopic image observed at the top of the specimen is not appropriate. A SEM image observed by tilting the specimen by 5° provides a more representative image. Compared to the composites fabricated by conventional compression molding, which has its surface cover.......

Discussion

The soft layer method provides significant advantages compared with the conventional methods, and with a lower manufacturing cost. All three types of composites manufactured by the soft layer method show unique characteristics in terms of the electrical properties, mechanical properties, gas permeability, and adhesion properties.

For the measurement of the electrical property, a four-point probe method was used. ASR was measured 5 times and the average value was taken as a representative value.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Unidirectional carbon/epoxy prepreg	SK Chemicals	USN020	Used to fabricate unidirectional carbon composite
Plain weave carbon fabric/epoxy prepreg	SK Chemicals	WSN 1k	Used to fabricate fabric carbon composite
Plain weave carbon fabric	SK Chemicals	C-112	Used to fabricate fabric carbon composite
Non-woven carbon felt	Newell	Graphite felt 3 mm	Used to fabricated felt carbon composite
Film type epoxy resin	SK Chemicals	K51	Used as a matrix of the composite
Acetone 99.5%	Samchun	67-64-1	Used to cleanse the carbon fiber and the soft layers
Mold release	ShinEtsu	KF-96	Used to coat the mold
Release film	Airtech	A4000V	Used as a soft layer
Compression mold	N/A	N/A	Machined in lab. Material: NAK80
Hot press	Hydrotek 100	N/A	Used to apply pressure and heat
Scanning electron microscope	FEI Compnay	Magellan 400	Used to investigate the surface of the composite