「2019年に、ダイムラーとして2050年までにCO2ニュートラル輸送を実現することが、私たちの最終目標であることを発表しました。ここで掲げた、2050年までにすべての車種をリニューアルするプランの実行には約10年かかる見込みです。まずは2039年までに、主要地域である欧州、日本、北米において『Tank To Wheel (TTW)』の走行時CO2ニュートラル車両のみを提供する、これが目標です」
また、「最終的に車両のTCO（Total Cost of Ownership／総所有コスト）は、どの技術が、どの目的に適しているかによって決定されます。ダイムラーは今後数年間で、バッテリー電気駆動（BEV）と、水素ベース駆動（F-Cell）の両方に多額の投資を行い、それらを使用して幅広い車両を構築します」とも話す。
An international research team led by the University of Bern 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
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.
A research team from the Technical University of Munich (TUM) led by chemist Johannes Lercher has developed a synthesis process which drastically increases the activity of catalysts for the desulfurization of crude oil. The new process could perhaps also be used for catalysts in fuel cells.
Crude oil contains a great deal of sulfur. To turn the crude oil into fuel, the sulfur compounds must be removed using hydrogen. Experts call this process hydrotreating. The process is carried out using catalysts.
Under the leadership of Prof. Johannes Lercher and Dr Hui Shi, a team of researchers at the Professorship of Chemical Technology at the Technical University of Munich have now developed a process to increase the activity of these catalysts many times over by treating the catalytically active metal sulfides with concentrated hydrochloric acid beforehand.
Important for the environment
Hydrotreating is one of the most important catalytic processes - both with regard to the quantity of catalyst used and the quantity of processed raw material. With highly pressurized hydrogen, impurities such as sulfur or nitrogen compounds are removed from the crude oil as completely as possible.
"These kinds of impurities would later combust to form sulfur dioxide and nitrogen oxides, which would result in negative effects on the environment especially the air quality," says Manuel Wagenhofer, first author of the study. In addition, sulfur and nitrogen compounds would also damage precious metals in catalytic converters in modern vehicles, and drastically reduce their effectiveness.
An amazing effect of hydrochloric acid
The TUM chemists examined such mixed metal sulfide catalysts for their effectiveness in hydrotreating by first synthesizing nickel molybdenum sulfides over several process stages, and then treating them with acid.
"It was amazing how much adding concentrated hydrochloric acid increased the catalytic performance," says Wagenhofer. "Hydrochloric acid improves the accessibility of active centers in the catalysts by removing less active components, mainly nickel sulfides. Purer, and therefore more active, mixed metal sulfides are formed."
Great advantages for fundamental research
The TUM chemists' results are also very important for fundamental research. The purified mixed metal sulfides are also easier to examine, scientifically.
"For example, we were able to identify and quantify active centers on the catalysts that were treated in this way," explains Lercher. "This was only possible because the surface was no longer covered in nickel sulfide."
In principle, the acid treatment could apparently be used as an investigation instrument for a series of similar catalysts, to optimize these, for example, for use with oils from renewable raw materials which are to be transformed into climate-friendly fuels in the future via a refining process.
"If we understand mixed metal sulfide catalysts better, we can perhaps improve them considerably for use in other important fields of the future, such as water electrolysis or hydrogen fuel cells," says Johannes Lercher.
Publication:
Enhancing hydrogenation activity of Ni-Mo sulfide hydrodesulfurization catalysts. Manuel F. Wagenhofer, Hui Shi, Oliver Y. Gutierrez, Andreas Jentys, Johannes A. Lercher. Science Advances 2020, Vol. 6, no. 19, eaax5331, DOI: 10.1126/sciadv.aax5331 https://advances.sciencemag.org/content/6/19/eaax5331
More information:
Parts of this work were funded by Chevron Energy Technology Company and the Federal Ministry of Education and Research (BMBF) in the framework of the MatDynamics joint project. X-ray absorption spectrums were recorded at the PETRA III Synchrotron source of the German Electron Synchrotron (DESY) in Hamburg.
Contact:
Prof. Dr. Johannes A. Lercher Professorship of Chemical Technology and Catalysis Research Center Technical University of Munich Lichtenbergstr. 4, 85748 Garching, Germany Tel.: +49 89 289 13540 - E-Mail: johannes.lercher@ch.tum.de
Isuzu Motors Limited and Honda R&D Co. Ltd, a research-and-development subsidiary of Honda Motor Co. Ltd., today signed an agreement to undertake joint research on heavy-duty trucks, utilizing fuel cells (FC) as the powertrain.
Today, the automobile industry is facing demand to reduce exhaust gas/carbon emissions from mobility products in order to address the ongoing global challenge of reducing humanity’s environmental footprint. Moreover, from the perspective of energy security, the industry is required to take initiatives to promote utilization of renewable energy.
Under these circumstances, as a commercial vehicle manufacturer committed to support transportation, Isuzu has been striving to promote the utilization of low-carbon and sustainable energy.
To that end, Isuzu has been researching and developing various powertrains including clean diesel engine, engines for natural gas vehicles (NGVs) and electric vehicle (EV) powertrains, which accommodate a broad range of customer needs and how vehicles are used. In parallel, Honda has been working toward the realization of a carbon-free society and, to this end, in addition to hybrid and battery electric vehicles, Honda has been researching and developing fuel cell vehicles (FCVs), the ultimate environmental technology, for more than 30 years.
There are still some issues that need to be addressed to popularize the use of FC and hydrogen energy, including issues related to cost and infrastructure. These issues need to be tackled not only by individual companies but more expansively through industry-wide initiatives. Against this backdrop, Isuzu was striving to expand its lineup of next-generation powertrains for heavy-duty trucks, and Honda was striving to expand application of its FC technologies beyond use for passenger vehicles, which will represent progress toward the realization of a hydrogen society. Sharing the same technological research goals, the two companies reached an agreement to conduct joint research on heavy-duty FC trucks.
Taking advantage of the respective strengths each company has amassed over a long period of time, that is, Isuzu’s strengths in the development of heavy-duty trucks and Honda’s strengths in the development of FC, the two companies will strive to establish the foundation for basic technologies such as FC powertrain and vehicle control technologies. Moreover, through this joint research, Isuzu and Honda will not only realize clean, low-noise, low-vibration heavy-duty trucks customers are waiting for, but also promote expansive discussions by the industry so that the use of FC trucks and hydrogen energy can contribute to the future prosperity of the logistics industry and all other industries in our society and to the early realization of hydrogen society.
