A practical way to store hydrogen: remapping the route to the hydrogen economy

Mention the phrase “hydrogen economy” these days, and most people will laugh at you. That’s because the phrase reminds most people of the endlessly unfulfilled promises of fuel cell–powered cars and hydrogen refueling stations. Even Arnold Schwarzenegger, with his famous hydrogen powered Hummers, has dropped talk of the Hydrogen Highway in favour of something a bit more practical: pushing the nuclear renaissance into California. U.S. energy secretary Steven Chu’s recent words and deeds echo those of the Terminator: Chu defended budget cuts to fuel cell research earlier this year (see article), and has stepped up his pro-nuclear rhetoric.

Does this mean we should just forget about the hydrogen economy? Of course not. Hydrogen is the most abundant element in the universe, and the most widely used energy carrier on our home planet. Bonded with elements like carbon or nitrogen, it releases enough energy—when burned in an engine—to move planes, trains, automobiles, and Great Lakes freighters like the massive Paul R. Tregurtha.

As a stand-alone fuel, however, it is inferior to the conventional fuels of which it is a vital ingredient. Together with its fussiness when it comes to storing it in its pure form, and the necessity of creating a fueling infrastructure from scratch, this is why people like secretary Chu have grown skeptical enough to focus money and effort on other energy solutions.

But what if we dropped the idea of using hydrogen as a stand-alone fuel, and looked at ways to polymerize it with carbon or nitrogen? If hydrogen came from low- or zero-emitting sources and processes, like water-splitting through photoelectrochemical or thermal methods, and if it were polymerized with carbon from captured power plant exhaust, the hydrogen economy could become a low-carbon reality.

I have spoken before about the concept of carbon capture and recycle (see article), in which carbon dioxide from captured power plant exhaust is reformed into carbon monoxide, mixed with hydrogen, and then polymerized via the Fischer-Tropsch synthesis into gasoline, diesel, and jet fuel. Such a scheme has the potential to effectively wipe out an entire category of greenhouse gas (GHG) emissions—electric power generation or transportation, depending on how you do the accounting.

Unlike current visions of the hydrogen economy, this would involve no change at the retail end of the fuel distribution system: there would still be gas stations. Nor would it involve radical changes to transportation equipment: we would use these fuels in the same internal combustion engines (ICEs) we use today. Large-scale use of such fuels, made from recycled carbon and burned in ICEs paired with electric motors in plug-in hydbrid vehicles, would represent a quantum leap in GHG emission reduction.

You could do the same with nitrogen. If you polymerize hydrogen with nitrogen you produce ammonia. As a fuel ammonia has, according to a study by researchers at the University of Ontario Institute of Technology, a higher energy density than natural gas. Ammonia can also be used in existing ICEs. When burned, it produces no carbon emissions.

This all depends on a radical increase in hydrogen production from water splitting. How likely is that? Very. Stay tuned.

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