THEGREENGROK    Planetary Watch

Hydrogen Economy on the March?

by Bill Chameides | September 28th, 2011
posted by Erica Rowell (Editor)

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For hydrogen gas to be renewable it must be produced from renewable sources, as in this method of using proton exchange membrane electrochemical systems to split the hydrogen from water. Still, other issues surround hydrogen as an alt fuel. (NREL)

New research advances hydrogen-energy technologies.

One way to get to a low-carbon economy is to switch to an energy infrastructure that is powered using hydrogen gas (H2) instead of carbon-based fuels — often referred to as a “hydrogen economy.”

Great idea in theory, but how? Two separate papers surfacing in the scientific literature last week (here and here) may provide answers.

You Gotta Make It Before You Can Burn It

When it comes to renewable sources of energy, hydrogen isn’t just sitting there waiting to be tapped like the sun or the wind; and it’s not to be obtained by drilling a hole into the ground. If you want to use hydrogen gas as a fuel, you have to produce it — for example by splitting water molecules into hydrogen gas. Maybe you did just this in your high school science class by sending an electric current through water (H2O) to generate hydrogen gas (H2) at one electrode and oxygen (O2) at the other. But that method requires an input of energy (in this case in the form of electricity). In many current-day industrial processes that produce hydrogen gas, that energy is derived from fossil fuels (see here for example). That’s great if you’re in the business of buying or selling hydrogen gas, but the hydrogen gas hardly represents a carbon-free fuel.

So technologists have been hard at work developing methods for producing hydrogen gas in a renewable way, without the need for fossil fuels. Many of the methods being pursued have involved tapping solar energy (read about an example in action).

Now, Younggy Kim and Bruce Logan of Penn State University report on a new and quite novel approach. It uses the salinity difference between seawater and fresh water in conjunction with a special kind of microbe called exoelectrogenic bacteria (which has the ability to convert energy from organic matter, including waste, into electricity) to produce a current that in turn can generate hydrogen gas just like in your high school class.

Generating electricity from salinity differences via reverse electrodialysis is not new, but by adding the exoelectrogenic bacteria to the experiment, the authors were able to do away with the need for input energy to drive the system (thank you, bacteria). And only about one percent of the energy generated was consumed by pumping water through the system. Could coastal wastewater treatment plants be transformed into power plants of the hydrogen variety?

It’s premature to answer that question, but if this pans out and is scalable, it is a pretty cool approach and certainly renewable — we’ve got quite a lot of water (and waste) to tap.

You Also Gotta Transport It … Safely

OK, let’s say you’ve produced your hydrogen gas, and now you want to use it to power an automobile or an industrial plant. To do this, you’re going to have to move the H2 from its place of production to where it’s going to be used. And that turns out to be a bit of a problem. Hydrogen gas is very flammable. Ideally, you’d want to be able to embed it in some material where it would be safe and then pull it out of that material when it’s needed.

One such material to do that is formic acid (HCOOH). But there’s a problem — while it’s easy to embed the hydrogen gas into the acid, it’s not so easy to get it back out. And the catalysts generally relied on for the difficult liberation are rare precious metals of the platinum group — which makes the process less than economic and not entirely sustainable.

Maybe not such a big problem, say Albert Boddien of the Leibniz Institute for Catalysis at the University of Rostock, Germany, et al, who report on a new method involving iron catalysts to pull the hydrogen gas out. Suffice it to say there’s a good deal more iron on our rock than precious metals.

But there is a related issue — where does the formic acid come from? If it is generated using fossil fuels, you’re back to square one where a low-carbon economy is concerned. Sascha Ott of Uppsala University in Sweden suggests in the journal Science in a perspective piece on the Boddien et al paper that the formic acid could be generated from biomass — which raises its own potential sustainability issues. (See for example, here.) Maybe the answer to the sustainability issue is to forgo biomass and use a different production method. Maybe something involving saltwater, freshwater, and exoelectrogenic bacteria?

filed under: bacteria, energy, faculty, fossil fuels, Planetary Watch, zero emissions
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