The trouble with hydrogen

Hydrogen has been touted as the clean alternative to our fossil-fuel-driven society. Cars of the future running on hydrogen will produce only water as a byproduct. However, this rosy view of a future hydrogen economy overlooks some serious drawbacks that make hydrogen not as green as advertised.

Most discussions of hydrogen play up the benefits of increased efficiency and negligible emissions without mentioning the source of the hydrogen. Although it is the most abundant element in the universe, hydrogen is almost never found in its pure form. Sources of hydrogen include water, metal hydrides, hydrocarbons and certain minerals. For example, Chrysler developed a concept van called the Natrium that runs on hydrogen derived from sodium borohydride fuel.

There are numerous technologies that have been producing hydrogen from fossil fuels for decades. The most common is a process called steam reforming that transforms natural gas into carbon dioxide and hydrogen gas. However, both coal and oil can be transformed into hydrogen via gasification. This means that the most likely source of hydrogen gas in the near future is fossil fuels.

Cost estimates also suggest that this will be the case. In 2006, Popular Mechanics estimated how much it would cost to produce hydrogen from six sources: natural gas, nuclear, solar, wind, biomass and coal. Their results showed that coal is the cheapest source of hydrogen, costing $1 per gallon of gas, while solar power was the most expensive, at $9.50 per gallon of gas.

Even if we decided to produce our hydrogen from water, it would still have significant environmental consequences. The process of releasing the hydrogen from water, called electrolysis, requires electricity. If taken from the U.S. grid, approximately 70 percent will be produced via fossil fuels with about half from coal. This shifts the pollutants from our tailpipes to power plants.

Does this mean that a hydrogen-powered future is doom and gloom? Hardly. In fact this scenario of hydrogen-derived environmental damage is a result of our determination to use hydrogen as an alternative fuel. Most research has focused on how to replace the gasoline or diesel engine with a hydrogen-powered fuel cell.

This is a poor application of hydrogen technology and provides the false analogy that a fuel cell is like an engine. In reality, a hydrogen fuel cell acts more like a battery.

The most common hydrogen fuel cell is the proton exchange membrane (PEM). This fuel cell uses hydrogen and oxygen gas to produce electricity and water. A special type of PEM fuel cell, called a unitized regenerative fuel cell (URFC), can work in the reverse direction, producing hydrogen and oxygen gas from water and electricity. When used in this manner it can act like a rechargeable battery, producing hydrogen gas when electrical demand is low and electricity when demand is high. Both NASA and the Stuart Island Energy Initiative, located here in Washington state’s San Juan Islands, have demonstrated this concept.

In the 1990s, NASA created an unmanned aircraft, the Helios, which used solar panels and an URFC for sustained, high-altitude flight. During the day, the solar panels would power the aircraft and produce hydrogen gas, while at night the URFC would produce electricity. A similar system was built on Stuart Island, to provide electricity for residents.

While hydrogen fuel cells are a promising technology, their misapplication can lead to serious environmental problems. However, if used as a battery substitute rather than an engine, we can benefit from hydrogen technology in an ecologically conscious manner.