This is an authorized reprint of a recent publication in Advanced Energy Materials journal (Impact Factor: 16) (http://dx.doi.org/10.1002/aenm.201601216), by Stuart M. Holmes (Reader) and Prabhuraj - (PhD student - http://www.prabhuraj.co.uk/) from the School of Chemical Engineering and Analytical Science, University of Manchester in collaboration with the School of Physics, reporting the usage of 2D materials in operating direct methanol fuel cells, showing zero resistance to protons enhancing cell performance, thereby opening the bottle neck for commercialization of fuel cells.
The content published is the sole responsibility of the authors.
Fuel cells are an interesting energy technology for the near future, as they aid in production of sustainable energy using hydrocarbons as fuels, such as methanol, ethanol, acetone etc by a simple oxidation-reduction reaction mechanism.
Among different liquid fuels, methanol is attractive as it has a higher energy density (compared to lithium ion batteries and hydrogen) and other features such as ease in handling, availability etc. Hence methanol fuel cells find their potential use in laptop chargers, military applications or other scenarios where the access to electricity is difficult.
However the wider spectrum of commercial potential for methanol systems is greatly hindered by methanol cross over occurring in the membrane area of fuel cells. This is defined as the passage of methanol from anode to the cathode through the membrane, hence creating short circuit and greatly affecting the fuel cell performance.
This is mitigated by using barrier layer, in addition to the membrane used.
Figure 1: Schematic illustration of methanol fuel cell and structure of graphene
So far many materials have been used as a barrier layer in methanol fuel cells, where the proton conductivity is balanced with the methanol cross over. Proton conductivity is one of the dominant factors, where slight reduction in proton conductivity can influence the fuel cell performance to a large extent. All the materials reported in the literature to date have seen a reduction in proton conductivity though methanol cross over is reduced.
It is known that Andre Geim and his co-workers (Nature, A.K. Geim et.al 2014), discovered proton transfer through single layer graphene and other 2D materials. Also graphene is known for its dense lattice packing structure, inhibiting the passage of methanol and other hydrocarbon based molecules across the membrane. However the actual application of these 2D materials in fuel cell systems has not yet been realized.
In this Advanced Energy Materials paper, the researchers have used single layer graphene and hBN, formed by chemical vapour deposition method, as a barrier layer in the membrane of methanol fuel cells. They have reported that this thinnest barrier layer ever used before shows negligible resistance to protons, at the same time reducing cross over, enhancing the cell performance by 50%. This is of significant interest, as this would lead to usage of 2D materials in fuel cells.
Based on the results of the research obtained, researchers have been granted EPSRC (Engineering and Physical Sciences Research council grant “Adventurers in Energy grant”) to pursue further research in this field. They have shown that as the surface coverage of the 2D material on the system improved, the performance improved. This would lead to the usage of fuel cells, operating with high concentrated methanol fuels, as the current fuel cells suffer from cross over phenomena, with increased concentration.
Moreover, this would pave the way for a membrane-less fuel cell system operating with higher efficiency. This technology could further be extended to other fuel cells types namely hydrogen fuel cells. Hydrogen fuel cells suffer from the usage of high cost humidifier, where the membrane needs to be humidified for improved proton conductivity. Whereas graphene, as reported in earlier studies, showed improved proton conductivity with temperature, without the need for humidifier systems. The future prospect could be realized in such a way that the fuel cells will make significant contribution to the future energy demand.