A research team at the Korea Advanced Institute of Science and Technology (KAIST) has found a method to increase the performance of iron- and nitrogen-doped carbon electrodes in hydrogen fuel cells — which are reportedly 1,000 times cheaper than platinum catalysts currently used.
Platinum speeds up the oxygen reduction reaction that takes place at the cathode in a hydrogen fuel cell, increasing performance while also minimising the formation of intermediaries such as hydrogen peroxide which can damage the equipment over time.
According to a paper published in peer-reviewed journal ACS Catalysis, the KAIST research team found that iron- and nitrogen-doped carbon (Fe-N-C) electrodes bind to oxygen, preventing the final desorption step of intermediaries.
However, by treating the electrodes with phosphine gas, this creates a FeN3PO moiety in the molecule which sped up the oxygen reduction reaction without producing intermediaries. When tested for peroxides, this method produced a yield of less than 5%.
This was validated on the lab bench with small-scale proton exchange membrane (PEM) and anion exchange membrane (AEM) fuel cells using phosphine-treated Fe-N-C electrodes.
The researchers describe the test results as “one of the best performances among previously reported heteroatom-doped Fe−N−C catalysts”.
But in terms of actual cell voltage and power density, platinum electrodes still generally outperformed phosphine-treated Fe-N-C, which means that if this technology is brought to market, there may have to be a trade-off between cost and performance.
However, performance between the two materials was closer for AEM than PEM fuel cells, with the experimental electrode actually outperforming the precious metal at higher current densities.
While platinum in PEM electrolysers is used in small quantities, such that a 10% increase in price of the precious metal only bumps up the cost of the equipment by around 0.1%, the metal is a critical component used in larger amounts for both PEM and AEM fuel cells.
Around a third of the cost of a PEM fuel cell is down to the use of platinum, according to figures from the US Department of Energy and the European Commission.
But UK-based technology firm Johnson Matthey has argued that not only have fuel cells used in vehicles reduced platinum loading by 90% since the 1990s, but the metal can also be recovered during recycling at high purity, further reducing costs of new equipment.
Updated to include additional clarity from research team around fuel cell test results.
