A paper on materials for fuel cells, written by three professors at DTU Energy, has been cited more than 1000 times. This makes it among the 0.03 per cent most cited scientific papers of all time.
When researchers want to acknowledge that they find the work of colleagues relevant and exciting, they do do not give each other ‘likes’ as is done on social media. Instead they cite the results of their colleagues in their own research articles. This means that the papers that have been cited heavily by others have also been – all things being equal – very influential within their scientific field. Indeed, one way of measuring the track record of researchers is by the number of citations, their papers have received.
"We are happy that the paper has proven so useful. Reviews take a lot of work to write, but if they are well written, they are highly appreciated by others."
Professor Qingfeng Li
In 2003 four DTU researchers, Qingfeng Li, Ronghuan He, Jens Oluf Jensen and Niels J. Bjerrum, wrote a review paper in the journal Chemistry of Materials about a new and rapidly growing research field: materials for polymer fuel cells for operation above 100 °C. Traditional polymer fuel cells (PEMFC) only operate below 100 °C, which creates a number of problems related to cooling during operation and a low tolerance towards impurities in the fuel. However, in the mid-1990s it was discovered that by impregnating phosphoric acid into a polymer called polybenzimidazole (PBI) it can be used as an electrolyte for fuel cells high above 100 °C. DTU became active in the field early, and the researchers’ review paper gave an invaluable overview of the properties and possibilities of the new materials. This was also reflected in the subsequent verdict of their colleagues: by 2016 the article has been cited more than 1000 times.
To put this number into perspective, it is useful to look at a bit of citation statistics: It is estimated that of the order of 60 million scientific papers have been published worldwide, with 1.5 million being added every year. Of all these many papers, close to half, 44%, have never been cited – not even by their own authors. Close to a third of all papers have received 1-9 citations, below a quarter have 10-99 citations, and 2% have 100-999 citations. Only 3 out of every 10,000 papers (0.03%) have received more than 1000 citations. This select company now includes the paper “Approaches and Recent Development of Polymer Electrolyte Membranes for Fuel Cells Operating above 1000 °C”, making it a member of what Chemistry of Materials slightly facetiously calls the ‘1k Club’.
Thus, the DTU paper has really helped set the agenda within this field. Today, He is leading a research group in China, while the three other authors are professors at DTU Energy. They are still working on polymer fuel cells: although a lot has happened since the publication of their review paper in 2003, fortunately there remain plenty of scientific challenges that need to be solved!