Graphite microporous bipolar plates, a novel device

Graphite microporous bipolar plates, a novel device

An attractive clean-energy technology, the proton exchange membrane (PEM) fuel cell, has the potential to provide a viable alternative to the extensive burning of fossil fuels in vehicles powered by internal combustion engines [1, 2]. A PEM fuel cell stack is comprised of several components, such as bipolar plates, which serve a variety of functions. In addition to providing cell-to-cell electrical contact in the stack, they also generate uniform fields of flow for hydrogen and air, act as heat transfer surfaces, and prevent the leakage of gases and coolant. There is also a significant contribution of the bipolar plates to almost 80 % of the total weight and 45 % of the total cost of the fuel cell stack [3]. As a result, finding new materials for bipolar plates has become of significant interest. There are currently two types of bipolar plates available on the market: metal based or graphite based. In the corrosive environment of the fuel cell (pH of 2-4 and temperatures around 80 °C), metal based bipolar plates are susceptible to chemical attack. It is important to note that there are several problems associated with metal plates, such as electrocatalyst poisoning, ion exchange with the membrane, and formation of a high resistance oxide surface layer. The chemical stability of graphite plates is higher than that of metals, but the plates are brittle. On the other hand, carbon-based composite bipolar plates have been found to have better flexural strength (albeit at the expense of a lower electrical conductivity) than Graphite bipolar plates. Other characteristics of carbon-based polymer composites, such as their lower density and the fact that they can be manufactured relatively easily, make them an attractive alternative to either metallic plates or purely graphite plates.

 

The management of water is one of the most critical factors for a PEM fuel cell to work effectively [4]. To maintain high levels of ionic conductivity, it is imperative that the PEM is sufficiently hydrated. On the other hand, excessive accumulation of water inside a fuel cell, referred to as flooding, is a significant problem that needs to be addressed adequately. Due to the oxygen reduction reaction that occurs at the cathode of the fuel cell, water is produced. In addition, humidity in the reactant feeds can result in water condensation.tion. In addition, the protons that are transferred from the cathode to the anode are also carrying their hydration water with them. These processes lead to water accumulation in the gas flow channels that feed oxygen to the cathode as a result of water accumulation. In the fuel cell, oxygen transport is blocked, which results in a loss of power that occurs intermittently.rs intermittently. As a result of having water present in the gas flow channels or the gas diffusion layer, the reaction products will be distributed in an inhomogeneous and discontinuous manner across the active catalyst area, affecting the performance of an individual cell as well as cell-to-cell performance variations within a stack. In the PEM fuel cell technology, water management is hence an important issue.

 

The present study describes the production and characteristics of novel graphite-polymer composite plates that can provide solutions to water management problems [5]. Graphite, water-based resins, and micropore-forming additives were combined to produce microporous plates whose porosity could be tailored for the desired uptake of water during fuel cell operation through capillary action, while still offering sufficient resistance to permeability and leakage of gaseous fuel. We measured and correlated bipolar plate properties such as water uptake via wicking and suction (vacuum fill), the pressure required to force gas through the water seal within the plates, throughplane, and inplane electrical conductivities, and flexural strength of the plates. The DOE (US Department of Energy) 2020 requirements were met or exceeded with bipolar plates [6]. 

 

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