A Tohoku University group of researchers have unraveled the mysteries behind a recently identified material – zirconium nitride (ZrN) – that helps power clean energy reactions. Their proposed framework will help future designs for transition metal nitrides, paving a path for generating cleaner energy.
Anion exchange membrane fuel cells (AEMFC) are devices that use hydrogen and oxygen to make clean electricity through chemical reactions, specifically the hydrogen oxidation reaction and the oxygen reduction reaction (ORR). AEMFCs, with their ability to operate in alkaline conditions, provide a suitable environment for earth-based catalysts, offering a cheaper alternative to other efficient catalyst materials, such as platinum.
Recent studies have shown that ZrN exhibits efficient performances – even outperforming platinum – when used for the ORR in alkaline media. ZrN, whilst not an earth-abundant material, is still more cost-effective than alternatives. But what lay behind its impressive performance has remained a mystery to scientists.
Hao Li, associate professor at Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR) and corresponding author of the paper explained, “To implement our new theoretical framework for ZrN, we decided to employ surface state analysis, electric field effect simulations, and pH-dependent microkinetic modeling.”
Surface analysis revealed that ZrN has a very thin layer of HO when it is undergoing ORR. This thin layer helps molecules stick to it in a way that is beneficial for the ORR. Moreover, the electric field effect simulations demonstrate that atomic oxygen sticking to this thin-covered surface undergo minimal changes, thereby sticking moderately.
After performing computer simulations, the researchers found that ZrN reaches the sweet spot of ORR in alkaline conditions.
“Our tested theory works well not just for ZrN but also for other materials like Fe3N, TiN, and HfN, which are similar to ZrN, meaning our idea explains how these materials can be utilized for clean energy too,” noted Hao. “Our framework will help rationalize and design transition metal nitrides for alkaline ORR.”
In the future, Hao and his team plan to extend this framework to study other industrially significant reactions, such as the oxygen evolution reaction.
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Platinum qualifies as a rare earth as it is quite hard to find and little has been found after decades of looking. A few thousand bits of jewelry is not a realistic comparison to hundreds of million of fuel cells.
Platinum is just not economically practical, and baring a miracle discovery in many locations, unlikely to ever be practical. Even a lot on one place is no assurance of midrange pricing.
Fuel cells have a lot of practical sense in application. Economics and fuelling for fuel cells is not ready yet, but a cost efficient long lasting fuel cell would go a very long way to incite more capital input into research and testing processes for scaling up.
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Better yet would be a non-pressurized liquid fuel for fuel cells, but one shouldn’t get to greedy at the start.
By Brian Westenhaus via New Energy and Fuel
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