Photo: Lisbeth Holten

Recommendations for catalysis research in electrolysis

Friday 07 Jun 19

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Jakob Kibsgaard
Associate Professor
DTU Physics
+45 45 25 32 90

Contact

Ib Chorkendorff
Professor
DTU Physics
+45 45 25 31 70
Two leading Danish catalysis researchers have prepared a comment for the distinguished scientific journal Nature Energy with three clear recommendations for their colleagues in the field.

One of the keys to solving tomorrow’s challenge of storing renewable energy and ensuring substitutes for fossil fuels is the development of better catalysts. The first and most straightforward step in the process is to split water to create hydrogen. This can be done through electrocatalysis which involves two half-cell reactions that convert water to hydrogen and oxygen, respectively.

The best catalysts for this process in acid-based electrolysis are platinum and iridium, which, however, are scarce resources that are only extracted in a few places in the world. Research has therefore focused on finding substitutes that are equally effective.

The scientific journal Nature Energy has asked two leading Danish researchers in the field, Professor Ib Chorkendorff and Associate Professor Jakob Kibsgaard, both from DTU Physics, to draw up a comment for the research field. It’s based on the substantial experience the two researchers have in catalysis research, as well as the countless readings of articles from other researchers in the field. This has led to three clear recommendations.

Greater focus on the oxygen reaction

The first recommendation is to increase focus on the part of the water splitting process comprising the oxygen reaction. A large part of the research so far has primarily focused on the process of developing hydrogen. It turns out, however, that the biggest energy loss is on the oxygen side of the process, which results in excessive energy loss overall.

“If we’re to succeed in making hydrogen through electrolysis on a larger scale, we must not overlook the part of the process that produces oxygen. With excessive energy loss on that side of the process, the total electrolysis process will not be a financially viable alternative. It’s therefore important to have a major research focus on the oxygen part of the process,” says Jakob Kibsgaard.

A large amount of catalysts not necessarily the solution

The second recommendation is about the amount of catalysts. Many seemingly good results from electrolysis research turn out to be the result of substantially increasing the amount of catalysts. However, this will not necessarily solve the challenge of replacing scarce resources such as platinum and iridium. If you use a much greater amount of another perhaps cheaper metal instead, it may eventually be more expensive than using the precious metals.

“You therefore get a better idea of the scale-up potential if you measure the catalyst activity per atom, in order to get an accurate image of how good the catalyst really is,” says Jakob Kibsgaard.

Grafik: Jakob Kibsgaard 
Measuring pitfalls

As the third recommendation, Ib Chorkendorff and Jakob Kibsgaard call attention to the large number of measuring pitfalls that researchers must be aware of in order to ensure that their results are valid. One of the most important points is that researchers generally measure a current assumed to be a proportional expression for the production of hydrogen and oxygen, respectively. Yet this is not always the case.

“Part of the measured current can potentially be caused by other processes that have nothing to do with the development of oxygen or hydrogen, especially when very large catalyst amounts are used. For instance, it could be caused by an outright corrosion of the catalyst, if it isn’t stable. The amount of hydrogen and oxygen gas, respectively, should therefore be measured directly, rather than simply relying on the measured current,” says Ib Chorkendorff.

Especially regarding the last recommendation on measuring pitfalls, Ib Chorkendorff and Jakob Kibsgaard express concern that the publication of metrologically unsound data can dilute the research field in the long run by making it more difficult to know the good from the bad.

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