The Hope and Hype for Hydrogen Part II

Can hydrogen become a viable replacement for fossil fuels? While the advantages are many, the drawbacks are troubling.

 

Hydrogen can be used to fuel vehicles. Image courtesy of Toyota Motor Sales 

 

Part I of this two-part series examined the fundamentals of hydrogen. Part II digs deeper into the use of hydrogen in a zero-carbon world as we separate the hype from the hope and examine the benefits and costs of increasing hydrogen use.

 

Uses For Hydrogen

As we have seen, the two most important uses for hydrogen are oil refining and as a source of ammonia for fertilizer. Another growing application is steel making, where hydrogen has several potential applications that take advantage of its zero-carbon emission possibilities. 

 

Renewable Energy Storage

Hydrogen can be stored on-site where renewable energies like wind and solar can be used to electrolyze water. It can then be burned in a gas turbine to produce electricity when renewables are intermittent. Hydrogen can also be mixed with natural gas and used in furnaces for home heating to reduce carbon emissions from straight natural gas. 

 

Transportation

As a transportation, fuel hydrogen is getting a lot of attention. Burning crude oil in ships is a major source of transportation pollution, and studies are underway to use hydrogen as a replacement. Similarly, hydrogen is being studied as an aviation fuel to dramatically reduce aviation's carbon footprint. 

For land transportation, there are three primary ways that hydrogen can be used as a fuel. The energy contained in hydrogen can be extracted by combustion in a modified internal combustion engine. Hydrogen acts much like burning natural gas but has none of the carbon emissions because there is no carbon in the fuel. Modifications to the engine to run hydrogen include revised sealing provided by the piston rings to prevent hydrogen from leaning into the crankcase, which could cause an explosion if the hydrogen mixes with the engine oil. The hydrogen must be stored, either cryogenically or in 10,000 psi high-pressure tanks, and these must be protected to prevent damage in a collision. 

But here’s the thing: Even with these upgrades, the efficiency of an internal combustion engine is around 25 percent, so most of the energy that the hydrogen can provide will be wasted as heat during the combustion process. The hydrogen-powered BMW has a range of 125 miles on ten gallons of cryogenically stored hydrogen. 

 

Formulated Synthetic Fuels

Gasoline consists primarily of chains and rings of carbon atoms bonded to hydrogen atoms. If you remove carbon dioxide from the atmosphere and produce green hydrogen through electrolysis, you can make a synthetic version of gasoline with effectively zero carbon emissions when burned in an ICE. 

 

Bentley is testing synthetic fuels in its latest performance machines and earliest sports cars. Image used courtesy of Bentley Motors 

 

Porsche is examining the potential for such fuels, particularly to be used to keep its older classic sports cars on the road and track after conventional fossil fuels are discontinued. An ICE engine will still produce nitrogen oxides during combustion, but these can be largely eliminated using a catalytic converter on the exhaust. 

A German company called P1 Fuels is developing high-performance synthetic gasoline, already finding motorsports applications. The company uses its fuels in World Rally Cup competitions and older sports and racing cars at vintage and historic races in Europe and the U.K. In the long term, this will likely be a niche usage for hydrogen, but one that will continue to allow the use of cherished older vehicles.

 

Fuel Cells

A more efficient way to use hydrogen in transportation is through a fuel cell. By combining hydrogen and oxygen using a catalyst, the fuel cell can produce electricity that can be used to power an electric traction motor to drive the vehicle. 

Recent improvements in proton exchange membrane (PEM) fuel cells use a permeable sheet of polymer material that allows hydrogen protons stripped of their electrons at the anode electrode to travel through the membrane to the cathode electrode. Only protons, not electrons, gaseous hydrogen, or oxygen, can pass through the membrane. Each PEM cell produces a small amount of electricity, and the cells must be connected to produce a stack with enough energy to power the vehicle. In addition to electricity and a bit of heat, the only output from the fuel cell is water vapor. The input hydrogen must be more than 99 percent pure, or it will foul the PEM stack. 

 

Toyota fuel cell stack. Image used courtesy of Toyota Motors 

 

In 2008, Honda introduced the first fuel cell-powered vehicle, the FCX Clarity, into the California market—specifically Los Angeles—available for lease only. Other automakers like Daimler (Mercedes-Benz), General Motors, and Toyota have had significant hydrogen fuel cell research programs. In 2014, Toyota introduced the Mirai, its first fuel cell vehicle, to customers.

 

2008 Honda Clarity FCX. Image used courtesy of Honda Motor Co., Inc. 

 

Three Miracles Needed

There are three big limitations with hydrogen fuel cells in everyday transportation. As with hydrogen combustion in an ICE vehicle, the hydrogen must be safely stored either cryogenically or in extremely high-pressure tanks—neither of which is particularly easy nor appealing. 

Next, fuel cell costs are high enough to make them unaffordable in an ordinary vehicle. Those costs are coming down as development has continued, but using platinum as a catalyst to speed up the hydrogen-oxygen reaction still makes them expensive. 

The biggest problem with using hydrogen in a fuel cell for land transportation comes from the efficiency of a fuel cell—at best, a PEM stack is about 50 percent efficient. That means half the energy that the onboard hydrogen contains is wasted. 

With the electrolysis efficiency to make green hydrogen at 67 percent, the combined efficiency is low enough that the better play is to just take the electricity created by renewable energy and place it in storage batteries that can then be used to charge a battery-powered EV, whose efficiency is over 90 percent, and forget the hydrogen altogether. 

 

A Silver Lining for Hydrogen?

One exception to this bleak outlook for hydrogen may be in land transportation—buses and heavy trucks.  A vehicle that travels the same route and carries roughly the same loads will have consistent and predictable fuel needs. These vehicles could be designed with ample fuel capacity and onboard storage to travel between strategically placed fueling stations.

If you build the hydrogen fueling station in a place with good solar and wind energy, you could produce green hydrogen on-site and eliminate the need to transport the H2. Bigger vehicles could accommodate larger hydrogen tanks to make the range sufficient, whereas just a few dedicated stations on a specified route could make zero-emission transcontinental shipping possible. 

 

Volvo testing its fuel cell truck in winter conditions. Image used courtesy of Volvo 

 

Why Bet on Hydrogen?

With all the limitations hydrogen presents, particularly as a transportation fuel, why are oil companies and governments worldwide so eager to jump on the hydrogen bandwagon? 

First, if you ignore all of the limitations presented by inefficiencies, the problems of transporting and storing it, and the issues with making it, the idea of hydrogen is appealing. Here is a completely recognizable fuel that, just like gasoline, can be pumped into a vehicle in just a few minutes and doesn’t require the recharging times of 30 minutes that an EV needs. If you are a politician or an oil company executive, you can spin that as an advantage and justify huge expenditures in the research and development of hydrogen infrastructure. 

Because oil companies are already producing and using hydrogen as part of their refining process, they are familiar with it. Because nearly all of the commercial hydrogen we use today comes from steam-reforming fossil fuels, the oil companies can also see a way for them to be part of the transportation system, even after gasoline and diesel fuel fall by the wayside. It keeps them in the game, even if the carbon capture technology that will be needed is far from ready for prime time.

That approach is fine, except that we are running out of time to make any meaningful reductions in the atmosphere's carbon dioxide level. Because we have spent the past three decades denying and debating the existence of human-caused climate change, we have seen the amount of carbon dioxide in the atmosphere rise to record levels. Now that we are finally willing to act, through the adoption of renewable energy resources, the gradual acceptance of EVs, and the building of a more robust carbon-neutral infrastructure, putting too many eggs into a hydrogen transportation basket will likely be a waste of the efforts and resources that we need for effective solutions.