The Mercedes-Benz fuel cell system, © Daimler AG

Prof. Dr. Mohrdieck (Daimler): “In the long term I expect a diversification of drivetrains and fuels”

This is the second part of a two-part interview with Prof. Dr. Mohrdieck, Daimler’s Fuel Cell Director. Here the discussion focuses on extending the network of hydrogen refueling stations, the development of different drivetrains and issues such as carbon emissions, renewable energy and the possible innovations of tomorrow.

Prof. Dr. Christian Mohrdieck, Daimler’s Fuel Cell Director.

Are hydrogen-refueling facilities usually provided through new purpose-built stations or added to existing refueling stations?

Our main approach involves what we call multi-fuel or multi-energy stations, which means having an additional hydrogen pump at existing gas stations. These stations then provide up to five different fuels: gasoline, diesel, CNG, chargers and hydrogen. This is the most cost effective solution. You don’t have to look for land to build a new station, but can simply identify the most appropriate existing stations where a hydrogen pump can be added.

Some local governments, such as in Hamburg for example, have taken an even more aggressive approach. Here an oil company wanted to install a new gasoline station. The local government agreed but on the condition that the station provided hydrogen refueling facilities as well.

Do you think in future we will see the coexistence of different fuels or is one likely to dominate?

In the long term I foresee a diversification of drivetrains and fuels, depending on the application. For example, if you need to commute to work and back home in the evening, let’s say 30km each way, then a battery electric vehicle is a very good solution. You can recharge it at home overnight and many employers offer charging at the workplace. But if you need to drive long distances, perhaps in a business premium Sedan, traveling across Europe, Germany or other countries, then you’ll want shorter refueling times and a long range, so you’ll probably choose a fuel cell car. So I see a coexistence of the different technologies in the mid and long-term.

Intelligent drive train solutions for all vehicle classes — from small passenger cars to trucks. Electric vehicles: smart fortwo electric drive, smart BRABUS electric drive, B 200 e, SLS AMG Coupé Electric Drive, B-Class F-CELL & prototypes GLC F-CELL and smart fortwo electric drive / Plug-in-Hybrids: S 500 e, C 350 e Sedan and Estate, E 350 e, GLC 350 e 4MATIC, GLC 350 e Coupé 4MATIC, GLE 500 e 4MATIC, © Daimler AG
“Fuel cell vehicles will reach higher production numbers soon.”

It should be noted that high volume production has already started with battery electric vehicles, so at this point in time they are already further down the high volume production curve. My expectation is that fuel cell vehicles will reach higher production numbers soon. Judging by recent announcements in the media, this view is shared by Japanese companies such as Toyota.

“If you make hydrogen from natural gas by steam reforming and then use this hydrogen in fuel cell vehicles, the well-to-wheel CO2 emissions are still about 25% lower than with gasoline.”

How do you address some of the negative points raised by the media about the use of hydrogen, such as carbon emissions from hydrogen production and efficiency?

Regarding carbon emissions, we need to put this into perspective. If you make hydrogen from natural gas by steam reforming and then use this hydrogen in fuel cell vehicles, the well-to-wheel CO2 emissions, so that’s across the whole life cycle, are still about 25% lower than with gasoline. So even moving to hydrogen made from CNG is a big first step. This reduction is due to the fact that the fuel cell is twice as efficient as an ICE. It is an electrochemical device and therefore not limited by what engineers call the Carnot efficiency, which is an upper limit to the efficiency of thermodynamic processes.

The drive system of the Mercedes-Benz GLC F-CELL: the fuel cell drive system (black), hydrogen tanks (green), lithium-ion battery (yellow) and electric motor (red) © Daimler AG

Our ultimate goal is to produce hydrogen from renewable energy, wind and solar energy for example, which means zero carbon footprint hydrogen production. But we should not wait until this happens, because a 25% reduction in CO2 emissions compared to gasoline is already really significant. It’s a major step forward.

A very popular argument in the public discussion is that battery electric vehicles are more efficient than hydrogen. This is true on vehicle level because the conversion of hydrogen is an extra step that is not involved in battery electric vehicles. However, this is not taking the whole picture into account. If we drive a battery vehicle today, using electricity from the European electricity mix, then the well-to-wheel energy balance of this vehicle is slightly worse than the energy balance of a fuel cell vehicle that uses hydrogen made from natural gas. This is due to the fact that electricity production is not very energy efficient in Europe. We still have a lot of coal and nuclear energy involved, which is very energy intensive.

“Renewable energy isn’t always generated exactly when you need it. So the big challenge is how can we store huge amounts of electricity over a long time.”

We want battery electric vehicles that run on renewable energy, and this means we also need to store electricity because wind and solar power fluctuate. Renewable energy isn’t always generated exactly when you need it. So the big challenge is how can we store huge amounts of electricity over a long time, even from one season to the next. We are talking about storing terawatt hours of electricity over a long time. Very few technologies can do this, but hydrogen is one of them. Batteries cannot, because they leak too much current.

“If we want to move to renewable energy then we have to consider all aspects.”

Once you factor in the need for hydrogen in the storage of renewable electricity, then hydrogen and battery electric vehicles become very close in terms of efficiency. This is a complex picture, but if we want to move to renewable energy then we have to consider all aspects.

Are there any potential innovations, not yet under the media spotlight, that you think might be important in future?

Anything that can drive costs down will be important, such as reducing the platinum loading of catalysts and finding platinum alternatives. A non-noble metal-based catalyst would be a big innovation for fuel cells. There are many scientific groups working on this, but as the expression goes, there’s no such thing as a free lunch. Good results on catalyst loading have been obtained, but so far at the cost of reduced lifetime or durability. I’m optimistic that it will be possible to find a good solution in all dimensions, not just cost. We are continuously working on this and many other topics in our laboratories.

The other big change that could be revolutionary is finding new methods of storing hydrogen. Today, the best technology for storing hydrogen onboard a vehicle is compressed gaseous hydrogen. In thirty years of research, since the 1980s, nobody has found an alternative solution. However, we shouldn’t give up. Thirty years is a long time but sometimes innovation is just around the corner.


This is the second part of two. In part 1, Prof. Dr. Mohrdieck discusses the new Mercedes-Benz GLC F-CELL — a groundbreaking vehicle with a compact hydrogen fuel cell system which it combines with a lithium-ion battery as an additional energy source — the engineering challenges involved in its development and the territories currently leading the way in hydrogen infrastructure.

To read the previous part of the interview, click here.

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