Saltwater boosts microbial electrolysis cells to cleanly produce hydrogen

Sep 19, 2011
This is an electrolysis cell with RED stack. Credit: Bruce Logan, Penn State

A grain of salt or two may be all that microbial electrolysis cells need to produce hydrogen from wastewater or organic byproducts, without adding carbon dioxide to the atmosphere or using grid electricity, according to Penn State engineers.

"This system could produce hydrogen anyplace that there is wastewater near sea water," said Bruce E. Logan, Kappe Professor of Environmental Engineering. "It uses no grid electricity and is completely carbon neutral. It is an inexhaustible source of energy."

Microbial electrolysis cells that produce hydrogen are the basis of this recent work, but previously, to produce hydrogen, the fuel cells required some electrical input. Now, Logan, working with postdoctoral fellow Younggy Kim is using the difference between and seawater to add the extra energy needed to produce hydrogen.

Their results, published in today's (Sept. 19) issue of the , "show that pure can efficiently be produced from virtually limitless supplies of and river water and biodegradable organic matter."

Logan's cells were between 58 and 64 percent efficient and produced between 0.8 to 1.6 cubic meters of hydrogen for every cubic meter of liquid through the cell each day. The researchers estimated that only about 1 percent of the energy produced in the cell was needed to pump water through the system.

The key to these microbial electrolysis cells is reverse-electrodialysis or RED that extracts energy from the ionic differences between salt water and fresh water. A RED stack consists of alternating ion exchange membranes -- positive and negative -- with each RED contributing additively to the electrical output.

"People have proposed making electricity out of RED stacks," said Logan. "But you need so many membrane pairs and are trying to drive an unfavorable reaction."

For RED technology to hydrolyze water -- split it into hydrogen and oxygen -- requires 1.8 volts, which would in practice require about 25 pairs of membrane sand increase pumping resistance. However, combining RED technology with exoelectrogenic bacteria -- bacteria that consume organic material and produce an electric current -- reduced the number of RED stacks to five membrane pairs.

Previous work with microbial electrolysis cells showed that they could, by themselves, produce about 0.3 volts of electricity, but not the 0.414 volts needed to generate hydrogen in these fuel cells. Adding less than 0.2 volts of outside electricity released the hydrogen. Now, by incorporating 11 membranes -- five membrane pairs that produce about 0.5 volts -- the cells produce hydrogen.

"The added voltage that we need is a lot less than the 1.8 volts necessary to hydrolyze ," said Logan. "Biodegradable liquids and cellulose waste are abundant and with no energy in and hydrogen out we can get rid of wastewater and by-products. This could be an inexhaustible source of energy."

Logan and Kim's research used platinum as a catalyst on the cathode, but subsequent experimentation showed that a non-precious metal catalyst, molybdenum sulfide, had a 51 percent energy efficiency. The King Abdullah University of Science and Technology supported this work.

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User comments : 9

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not rated yet Sep 19, 2011
Great research. Hydrogen is the future energy carrier.Production of Hydrogen from waste water near sea water will be a major breakthrough.

Dr.A.Jagadeesh Nellore(AP),India
1 / 5 (2) Sep 19, 2011
It would be nice if someone could pencil this out.

That is, they may produce energy but the cost still looks prohibitive.
not rated yet Sep 19, 2011
Good things going on at Penn State, I used to sneak into lectures and use their libraries. lol. Years ago. How could you not love a town with a bar called Zeno's ? :)

I wonder how this could fare in an urban area, with modification of course, the salts could be recycled, no ?
1 / 5 (1) Sep 19, 2011
Maybe can use microbes to make bubbling wine also.

How does the cost and reliability stack up against other
processes ?

Is this hydrogen for laptop or enough for power plants ?

Sounds like limited GEO "anyplace that there is wastewater near sea water"

1 / 5 (4) Sep 19, 2011
wow. i read about the ion energy source months ago...amazing that this guy who figured out how to pull energy out of mixing of fresh and salt water kept up the effort and realize how it could be used to create large scale industrial processes.

pretty amazing. simple but seemingly very powerful technology. amazed.
not rated yet Sep 19, 2011
It would be nice if someone could pencil this out.

That is, they may produce energy but the cost still looks prohibitive.

This site reports mainly on research, not on products ready for market. If you want products, try
not rated yet Sep 20, 2011
wow. i read about the ion energy source months ago...amazing that this guy who figured out how to pull energy out of mixing of fresh and salt water kept up the effort and realize how it could be used to create large scale industrial processes.

Making electricity out of a salinity gradient is actually an old hat. Norway already has some plants in operation, only, they don't waste it on hydrogen.

1 / 5 (3) Sep 20, 2011
The problem of these systems is, that the process efficiency is around 60% and the hydrogen infrastructure efficiency is again around 60% with all the pumping and cooling and transporting, and the point-of-use efficiency is around 60% again because fuel cells aren't perfect.

So you end up with 80% of the energy gone to the wind. There's so many steps along the way that even if you do optimize every individual bit of the chain to 80%, which is unrealistic, you still lose half of the energy.

Just producing electricity would be much more worthwhile.
not rated yet Sep 20, 2011
You meant to tell me that the system would be self-sufficient and still have a sizeable output? And all we'd really be losing is more crap in a landfill?

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