High hopes for hydrogen - A look at future technologies
What role does hydrogen play in designing logistics without greenhouse gas emissions? A check on the energy source H2.
Transport and logistics have high hopes for using hydrogen (H2) as a fuel, hopes that are entirely justified. It is the most common chemical element in the universe and the only one to offer three options that underpin climate protection—even if there are still a number of obstacles to overcome.
First, this volatile gas can be produced while generating zero local emissions. In a process called electrolysis, an electric current is applied to water (H2O), splitting it into oxygen and hydrogen. Provided the electricity comes from a renewable source such as solar, wind, or hydropower, this process can be deemed climate-friendly.
Since electrolysis consumes almost one-third more energy than is stored in the hydrogen it yields, a basic challenge to overcome on the way to a sustainable hydrogen economy will be to provide sufficient affordable green electricity.
An often forgotten aspect is that at the moment, electrolysis still requires freshwater with the purity of drinking water—and almost ten liters of it per kilogram of hydrogen. This means that arid regions with an abundance of sunshine—which puts them in the running to become key centers of H2 production—would also have to invest in the desalination of seawater.
Second, so many hopes are pinned on hydrogen because it is the building block for all synthetic fuels, also referred to as synfuels, powerfuels, power-to-liquid fuels, or power-to-gas fuels. The first element in the periodic table can bond with carbon and oxygen to form a variety of hydrocarbon chains, including methane, methanol, diesel, and kerosine. The challenge here is that these processes are also energy-intensive.
What is often overlooked is that these fuels require not just green hydrogen, but also carbon dioxide, which must first be extracted from the atmosphere. Only if this is done without producing any emissions is the resulting synfuel climate-neutral. Depending on the powerfuel, only 40 to 60 percent of the energy present in the renewable power used at the start of the process chain is carried over. This is why such processes are often deemed uneconomical. But synfuels are a worthwhile option wherever electricity or hydrogen can’t be used to directly power engines or transport energy, for instance in maritime and aviation applications.
H2 as the “engine” of the fuel cell
Third, and most importantly, H2 is a key part of the solution because it can be converted back into electricity without emitting any greenhouse gases or air pollutants. This is what happens inside a fuel cell, and can be considered as the counterpart to electrolysis. As part of what’s known as a redox reaction, electrons pass from hydrogen to atmospheric oxygen. This produces electricity that can be used to power motors or charge batteries. The only “waste products” are clean steam and heat. Commercial vehicles use proton-exchange membrane (PEM) fuel cells, which have proven to be highly efficient. Dachser simulations indicated that a PEMFC swap-body truck would consume just under ten kilograms of H2 per 100 kilometers.
Despite initial positive results with PEM prototype and small-batch trucks, there are still several details to iron out before this kind of fuel cell really becomes a practical option. For instance, both the hydrogen fuel and the atmospheric oxygen sucked in must be extremely pure to prevent the fuel cell’s sensitive components from becoming contaminated too quickly and compromising the system’s service life. Alongside expensive air filtration technology, this requires automakers to use H2 5.0, which means that the hydrogen must have a certified purity of at least 99.999 percent—a tall order for the overall H2 supply system.
Another challenge is to determine the best way of storing the hydrogen on the truck. Should it be in tanks pressurized to 350 bar, as is common in today’s buses? Or liquified at extremely low temperatures like liquified natural gas (LNG)? Manufacturers are taking different approaches, but it is expected that wherever maximizing storage capacity and range are the decisive factors, a tank containing cold liquid H2 will likely be the best option.
To summarize: hydrogen has the potential to establish itself alongside the direct use of renewable power as the decisive technology for transport and logistics. Whether or not it will manage to meet the high expectations placed on it will become clear before the end of this decade. More and more manufacturers of commercial vehicles are setting out to transform this future technology into an innovation in climate protection and logistics.