As future energy sources, fuel cells are considered to be a technology of interest as they help in the production of sustainable energy using simple hydrocarbons as fuels.
Fuel cells function by a simple operational mechanism with fuel oxidation on one side of a membrane and oxidant reduction on the other side, releasing electrons and thus contributing to the generation of electrical energy. So far, a wide range of fuels such as propanol, methanol and ethanol have been used but among these fuels, methanol continues to be a favorable candidate because of its ease of handling, high energy density and other operational characteristics.
Applications of Methanol Fuel Cells
Methanol fuel cells thus find their potential use in military applications, laptop chargers or other scenarios where it is difficult to access electricity.
However, the wider spectrum of commercial potential for methanol systems is significantly hindered by methanol cross over in the membrane. Cross over refers to the leaking of methanol from the anode to the cathode via the membrane, which produces a short circuit and adversely affects the performance of fuel cells.
Cross over is mitigated by using a barrier layer on top of the membrane used. Earlier work in this field tested a wide range of materials that yielded enhanced performance by reducing methanol crossover, but those materials also considerably reduced proton transport, thus drastically reducing performance, as membrane proton conductivity is considered to be one of the dominant factors for generating energy in fuel cells.
It is a well-known fact that Andre Geim and Co-workers (Nature, A.K. Geim et.al 2014), discovered proton transfer through single layer graphene and other 2D materials. Graphene is also known for its dense lattice packing structure, preventing the passage of hydrocarbon-based molecules, including methanol, across the membrane. However, the exact application of these 2D materials in fuel cell systems is yet to be realized.
Figure: Schematic showing proton transport through the membrane region of a methanol fuel cell.
Improving Cell Performance
A way to utilize these 2D materials in an actual operating direct methanol fuel cell has been developed by Researchers from the School of Chemical Engineering and Analytical Science at the University of Manchester.
In their recently published paper in the journal Advanced Energy Materials (Holmes et al, 2016), they have demonstrated that the addition of single layer graphene by chemical vapor deposition on to the membrane area has considerably reduced methanol cross over, while at the same time causing negligible resistance to proton transport, thereby improving the cell performance by as much as 50%. This first proof of concept highlights that 2D materials can be used as exceptional barrier materials for fuel cells.
The work also highlights the possibility of realizing high efficiency membraneless fuel cells in the near future. This technology could also be extended to other fuel cells types, such as hydrogen fuel cells.
Hydrogen fuel cells suffer from the usage of high cost humidifiers that keep the membrane in a humid atmosphere for enhanced proton conductivity. Graphene however, as reported in previous studies, exhibited enhanced proton conductivity with increasing temperature without the need for humidifier systems. Utilizing graphene in fuel cells could help satisfy future energy demands.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
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