Fuel cells for hydrogen vehicles are becoming longer lasting

Date:
August 24, 2020
Source:
University of Bern
Summary:
An international research team has succeeded in developing an
electrocatalyst for hydrogen fuel cells which, in contrast to the
catalysts commonly used today, does not require a carbon carrier
and is therefore much more stable. The new process is industrially
applicable and can be used to further optimize fuel cell powered
vehicles without CO2 emissions.



FULL STORY ==========================================================================
Fuel cells are gaining in importance as an alternative to battery-operated electromobility in heavy traffic, especially since hydrogen is a
CO2-neutral energy carrier if it is obtained from renewable sources. For efficient operation, fuel cells need an electrocatalyst that improves
the electrochemical reaction in which electricity is generated. The platinum-cobalt nanoparticle catalysts used as standard today have good catalytic properties and require only as little as necessary rare and
expensive platinum. In order for the catalyst to be used in the fuel
cell, it must have a surface with very small platinum-cobalt particles
in the nanometer range, which is applied to a conductive carbon carrier material. Since the small particles and also the carbon in the fuel
cell are exposed to corrosion, the cell loses efficiency and stability
over time.


==========================================================================
An international team led by Professor Matthias Arenz from the Department
of Chemistry and Biochemistry (DCB) at the University of Bern has now
succeeded in using a special process to produce an electrocatalyst
without a carbon carrier, which, unlike existing catalysts, consists
of a thin metal network and is therefore more durable. "The catalyst we
have developed achieves high performance and promises stable fuel cell operation even at higher temperatures and high current density," says
Matthias Arenz. The results have been published in Nature Materials. The
study is an international collaboration between the DCB and, among
others, the University of Copenhagen and the Leibniz Institute for
Plasma Science and Technology, which also used the Swiss Light Source
(SLS) infrastructure at the Paul Scherrer Institute.

The fuel cell -- direct power generation without combustion In a
hydrogen fuel cell, hydrogen atoms are split to generate electrical power directly from them. For this purpose, hydrogen is fed to an electrode,
where it is split into positively charged protons and negatively charged electrons. The electrons flow off via the electrode and generate electric current outside the cell, which drives a vehicle engine, for example. The protons pass through a membrane that is only permeable to protons and
react on the other side on a second electrode coated with a catalyst
(here from a platinum-cobalt alloy network) with oxygen from the air,
thus producing water vapor. This is discharged via the "exhaust."
The important role of the electrocatalyst For the fuel cell to produce electricity, both electrodes must be coated with a catalyst. Without a catalyst, the chemical reactions would proceed very slowly.

This applies in particular to the second electrode, the oxygen electrode.

However, the platinum-cobalt nanoparticles of the catalyst can "melt
together" during operation in a vehicle. This reduces the surface of
the catalyst and therefore the efficiency of the cell. In addition,
the carbon normally used to fix the catalyst can corrode when used
in road traffic. This affects the service life of the fuel cell and consequently the vehicle. "Our motivation was therefore to produce an electrocatalyst without a carbon carrier that is nevertheless powerful," explains Matthias Arenz. Previous, similar catalysts without a carrier
material always only had a reduced surface area. Since the size of
the surface area is crucial for the catalyst's activity and hence its performance, these were less suitable for industrial use.

Industrially applicable technology The researchers were able to
turn the idea into reality thanks to a special process called cathode sputtering. With this method, a material's individual (here platinum or
cobalt) are dissolved (atomized) by bombardment with ions.

The released gaseous atoms then condense as an adhesive layer. "With
the special sputtering process and subsequent treatment, a very porous structure can be achieved, which gives the catalyst a high surface area
and is self- supporting at the same time. A carbon carrier is therefore superfluous," says Dr. Gustav Sievers, lead author of the study from
the Leibniz Institute for Plasma Science and Technology.

"This technology is industrially scalable and can therefore also be used
for larger production volumes, for example in the automotive industry,"
says Matthias Arenz. This process allows the hydrogen fuel cell to be
further optimized for use in road traffic. "Our findings are consequently
of importance for the further development of sustainable energy use,
especially in view of the current developments in the mobility sector
for heavy goods vehicles," says Arenz.


========================================================================== Story Source: Materials provided by University_of_Bern. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Gustav W. Sievers, Anders W. Jensen, Jonathan Quinson, Alessandro
Zana,
Francesco Bizzotto, Mehtap Oezaslan, Alexandra Dworzak, Jacob J. K.

Kirkensgaard, Thomas E. L. Smitshuysen, Shima Kadkhodazadeh,
Mikkel Juelsholt, Kirsten M. O/. Jensen, Kirsten Anklam, Hao Wan,
Jan Scha"fer, Kla'ra Če'pe, Mari'a Escudero-Escribano,
Jan Rossmeisl, Antje Quade, Volker Bru"ser, Matthias
Arenz. Self-supported Pt-CoO networks combining high specific
activity with high surface area for oxygen reduction.

Nature Materials, 2020; DOI: 10.1038/s41563-020-0775-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200824123403.htm

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