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Hydrogen production and the future of fuel

 

By: Hannah Pell

“The most important car in 100 years.” Such is how James May, co-host of the British car show Top Gear, described the Honda Clarity during his test drive several years ago. “This is the future of motoring.”

What is it about this car that seemed so revolutionary? It’s the fact that it’s not powered by an engine or a battery — but by a hydrogen fuel cell. Hydrogen technology has been getting a lot of coverage lately, and I wanted to know a bit more about the science behind it, as well as its role in the future of fuel.

Hydrogen production 
Hydrogen is the lightest element at #1 on the periodic table and the most abundant in the universe. Its chemical structure contains only one proton and one electron, making it highly reactive (flammable!) and therefore not freely found in nature. In order to get hydrogen by itself, it must be extracted from naturally occurring compounds. There are several processes for producing hydrogen: steam methane reforming, gasification, and electrolysis.

Steam methane reforming is the process of catalyzing a reaction between steam and methane to produce hydrogen, carbon monoxide, and a small amount of carbon dioxide (collectively known as “syngas”). Most of the world’s hydrogen is produced by this method, utilizing natural gas as the primary source of methane.

Gasification is the process of converting either biomass (agricultural residues, some crops, organic municipal and animal wastes) or carbonaceous materials (i.e. coal) into syngas as well. This process goes back more than two centuries when coal and peat were used to produce town gas, which powered the first public street lighting system in London in 1807. A more modern application of hydrogen gasification is to make ammonia which, although is useful for numerous household cleaning and pharmaceutical products, is classified as an extremely hazardous substance in the United States.

A cleaner alternative is electrolysis, the process of producing hydrogen using an electric current. Housed within an electrolyzer, a voltage is applied to a cathode and anode submerged in water or a liquid alkaline solution, setting off a reaction releasing hydrogen and oxygen in their gaseous forms. Hydrogen is then collected and stored in high-pressure tanks for future use.

Image credit: U.S. Department of Energy.
 
Hydrogen is often labeled using four different colors — brown, grey, blue, and green — to describe the source and process from which it was produced. Brown hydrogen is sourced from coal gasification and is the most pollutive method. Grey hydrogen comes from natural gas and steam methane reforming. Blue hydrogen is also produced from steam methane reforming but incorporates carbon capture and storage (CCS) technologies, thereby lessening its negative environmental impact. Finally, green hydrogen is produced entirely from renewable sources (such as wind and solar) powering the electrolysis process.

Hydrogen as a fuel source 
Hydrogen has been considered an alternative fuel source since the Energy Policy Act of 1992, authored with the aim of reducing the Unites States’ dependence on petroleum by encouraging voluntary alternative fuel deployment.

Once produced, how can hydrogen be transformed into fuel? Hydrogen is an energy carrier, not an energy source itself, so it must be transformed into energy through a fuel cell stack. Within the fuel cell, the air is fed to the cathode and hydrogen is fed to the anode. A catalyst separates the hydrogen protons and electrons, leaving the electrons to flow along a different path to create electricity that powers the car. When they recombine, they form water (H2O) and heat, the only byproducts.

One major issue regarding hydrogen fuel availability is the lack of infrastructure. As of 2020, there were just over forty public hydrogen fueling stations in the United States, and all but one of them are located in California. Additionally, hydrogen must be kept in high-pressure tanks, so both its storage and transportation is relatively expensive compared to other fuel sources. According to the U.S. Energy Information Administration’s Annual Energy Outlook 2021 report, the capital cost of fuel cells is more than six times that of battery storage and on par with nuclear when compared according to the levelized cost of energy (LCOE) estimates.

Although cars powered by hydrogen fuel cells require much less refueling time (approximately 5 minutes at the pump versus 45 minutes charging), the number of battery cars far exceeds the number of hydrogen cars on the road. Only Toyota, Honda and Hyundai so far produce hydrogen fuel cell cars. However, additional efforts to design and utilize hydrogen fuel cell trucks, buses, and trams are underway at several car manufacturers and other large companies.

How soon could we all be pumping hydrogen into our cars instead of gasoline? Unfortunately, the future that James May predicted still seems a bit of a ways off.

Image Credit: Department of Energy.
 

The harmony of “and”
 The future of widespread hydrogen fuel cell cars may not seem so bright, but hydrogen is important for a myriad of other applications. Apart from automobiles, hydrogen fuel cells are utilized at large-scale data centers as a potential backup in case electricity is lost and batteries drain. Additionally, liquid hydrogen is used to fuel NASA spacecrafts, and the electrical systems onboard are powered by hydrogen fuel cells.

Reaching net-zero carbon emissions by 2050 will require a complex combination of clean energy solutions. Dr. Arun Majumdar — professor of mechanical engineering and materials science at Stanford University and former Under Secretary of Energy — recently summarized this succinctly on the Columbia Energy Exchange podcast: “The scale and urgency of the problem is such that we cannot have either-or solutions. We fall into the tyranny of ‘or’, and we need the harmony of ‘and’. We need and.”

Despite present limitations, hydrogen technology will remain an important option in our future, greener energy landscape, because when it comes to combating climate change, there is no either-or.

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