Dr Zoe Schnepp, School of Chemistry, University of Birmingham
Hydrogen fuel cells are being investigated as a promising way to power the future because of their green credentials – the only waste product they create when producing electricity is water.
Existing fuel cells typically use platinum as a catalyst to drive the chemical reactions inside. Although platinum is an effective catalyst, it is costly and in short supply. If everyone in the world is going to drive hydrogen-powered cars, we will need the fuel cells inside them to be both cheap and sustainable.
An alternative catalyst material we have been exploring at the University of Birmingham is iron carbide (Fe3C), which is abundant, naturally occurring and cheap.
Iron carbide is quite a familiar material, and people have been able to make great big lumps of it during steelmaking processes.
However, we are only interested in making it as nanoparticles. The idea is that the tiny particles have a large surface area so will work really well as a catalyst, driving the chemical reaction in the carbon fuel cell.
Making iron carbide nanoparticles is a challenging process because the material is produced in a big furnace at temperatures of around 800°C, rather than in a controlled environment in a round-bottomed flask.
A few years ago, our research group showed that nanoparticles of iron carbide could be made using a biopolymer called gelatin (the same gelatin you would use in cooking). This material shows really promising activity as a fuel-cell catalyst. While we found that the gelatin makes nanoparticles, we wanted to understand the process better in the hope that we could control the reaction and make those nanoparticles even smaller, therefore creating a more efficient catalyst.
You can study iron carbide by firing X-rays at the compound and measuring the diffracting light, which produces a pattern. That pattern is like a fingerprint which you can analyse and pick apart to understand what is in the mixture.
But to truly understand the reaction you need to replicate the dynamic conditions and high temperatures used to create it in a huge furnace. However, X-rays would not be able to pass through such thick walls.
Instead we used I11 beamline at the Diamond Light Source, one of the world’s most powerful synchrotrons, at Harwell in Oxfordshire. We put our sample into a tiny quartz capillary and the synchrotron X-ray beam was fired through the sample so that we were able to observe changes as it was being heated.
At Diamond, the very bright X-ray beam is combined with a really powerful detector which means you can take the fingerprints of the material really quickly – every couple of seconds, rather than every half an hour to an hour as in the lab. This allowed us to capture changes that happen very quickly during the reaction.
Using the data from this experiment we were able to see all of the stages involved in heating the gelatin starting material to form iron carbide. What was most interesting was that the data gave us information about the size of the particles in the system. So we learned where in the heating process most particle growth occurred. Since we want our nanoparticles to be as small as possible, this means we can focus on controlling that stage where most growth occurs.
Now we can go back to the lab and play around with the system, making the reaction happen slower and faster, to find out how to make the catalyst even better.
There are other interesting technologies that use platinum catalysts, so research is also being carried out to look at where else iron carbide could be used as a cheap and sustainable alternative.