Print Page | Contact Us | Report Abuse | Sign In | Register
Graphene Updates
Blog Home All Blogs

Graphene Membranes Enable a Novel Approach to Ubiquitous Photodetectors

Posted By Dexter Johnson, IEEE Spectrum, Monday, March 12, 2018

Image: University of Manchester

Back in January, scientists in Andre Geim’s research team at the University of Manchester reported that light could be used to enhance proton transport through graphene.  What this means is the possibility of an entirely new class of photodetectors, which are used in just about everything from high-speed optical communication networks to the remote control for your TV.

Needless to say, an entirely new class of photodetectors—based on proton transport as opposed to all current photodetectors today that are based on electron transport—is a pretty significant development. You add on to this the fact that the photodetectors made from graphene are 100,000 times more responsive than silicon and you have the basis of a transformative technology.

What regular readers of The Graphene Council may have missed earlier this month in an Executive Q&A with Jeffrey Draa, CEO of Grolltex, was that we got some indications in that interview that the technology being developed in Geim’s lab is ramping up for commercial applications.

Draa said in the interview: “…we’re also starting to get some inquiries for an application that actually Dr. Andre Geim at the University of Manchester, who, of course, was the discoverer of graphene was very passionate about. This is one of the very first applications that he thought futuristically would really make the world a better place, and that third application that we're starting to see on the horizon is graphene as a proton exchange membrane in a hydrogen fuel cell.”

Draa in this interview points to the initial applications that were discussed almost four years ago for this graphene-based proton exchange membrane. At the time, Geim had discovered that contrary to the prevailing wisdom that graphene was impermeable to all gas and liquids  it could, in fact, allow protons to pass through. This made scientists immediately conjure up the proton exchange membranes that are central to the functioning of fuel cells.

While there’s no reason to think that these graphene membranes won’t someday make for excellent proton exchange membranes for fuel cells, the problem is that fuel cells are not exactly ubiquitous. However, photodetectors certainly are ubiquitous, making for a much larger potential market for these graphene membranes.

Of course, it’s a pretty big step to make these graphene membranes go from being used for fuel cells to being used in photodetectors. So how did this application switch occur?

The University of Manchester scientists started with monolayer graphene decorated with platinum (Pt) nanoparticles. In operation, photons (light) strike the membrane and excite the electrons in the graphene around the Pt nanoparticles. This makes the electrons in the graphene become highly reactive to protons. This, in turn, induces the electrons to recombine with protons to form hydrogen molecules at the Pt nanoparticles. This process mimics the way in silicon-based photodetectors operate based on electron-hole recombination.

While there are similarities between the semiconductor approach to electron-hole recombination, the photon-proton effect used in this graphene membrane would represent a big departure from the previous approach and nobody is quite sure what the implications might be.

However, it is clear that this graphene membrane that Grolltex is working on with the scientists at Manchester may have a new set of applications that extends far beyond just typical membrane-based technologies.

Tags:  Andre Geim  fuel cells  membranes  photodetectors  University of Manchester 

Share |
PermalinkComments (0)
 

2D materials - Graphene and hBN (hexagonal boron nitride) enhances methanol fuel cell performance

Posted By Terrance Barkan, Tuesday, November 29, 2016

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. 


Tags:  Fuel Cells  Graphene  hBN  Hexagonal boron nitride  Methane 

Share |
PermalinkComments (0)