Study Concludes That Microbial Electrolysis Cells Are a Promising Approach to Renewable and Sustainable Hydrogen Production
10 November 2008
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| Schematics of a two-chamber (flat anode) (A) and single-chamber membraneless (brush anode) (B) MEC. Bacteria (green ovals) grow on the anode and donate electrons but can also function as the biocatalyst on the cathode (dotted green ovals). Click to enlarge. Credit: ACS |
A review of the materials, architectures, performance, and energy efficiencies of emerging microbial electrolysis cell systems (MECs) finds that MECs can efficiently convert a wide range of organic matter into hydrogen and are therefore a promising technology for renewable and sustainable hydrogen gas production from organic feedstocks.
However, the researchers conclude, there are a number of outstanding research questions that must be resolved for MECs to develop into a mature, commercial hydrogen production technology. The paper was published online 1 November in the ACS journal Environmental Science & Technology.
The review team included the two research groups who independently discovered several years ago that bacteria could be used to make hydrogen gas in an electrolysis-type process based on microbial fuel cells (MFCs). One group was led by Dr. Bruce Logan at Penn State, the other by Dr. René A. Rozendal at the University of Queensland (Australia).
MECs show high hydrogen yields and they need only a relatively small electrical energy input. Given these interesting properties, MECs could become viable technology to produce renewable hydrogen, provided a clean and renewable electricity input is used. Renewable hydrogen has many applications, the most prominent ones being for transportation and industry.
Transportation fuels are currently responsible for about 20 to 25% of the global fossil fuel consumption. Because of climate change, and instabilities in the fossil fuel market, there is great interest in hydrogen as a transportation fuel (i.e., the hydrogen economy). Moreover, even without a hydrogen economy, there exists a large hydrogen demand.
In 2000, the global hydrogen consumption was already estimated to be 50 million tons per year, with about two-thirds used by the petrochemical industry. This hydrogen is used for upgrading fossil fuels and synthesis of industrial chemicals such as ammonia and methanol. Other industries that consume significant amounts of hydrogen include the food industry (saturation of fats and oils) and the metal industry (as a reducing agent for metallic ores).
MECs can contribute significantly to these hydrogen demands by producing large quantities of hydrogen from renewable resources such as biomass and wastewaters. The MEC concept is now well proven, and significant advancements have been made with respect to the performance in only a few years since its discovery.
—Logan et al. (2008)
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| Hydrogen production rate (Q) and energy efficiency calculated from the electricity input and hydrogen output as a function of the applied voltage using experimental data (ηe real, based on heat of combustion) and theoretical maximum energy efficiencies based on Gibbs free energy (ηEΔG max) and heat of combustion (ηEΔH max). Click to enlarge. Credit: ACS |
In a microbial fuel cell, bacteria oxidize organic matter and release carbon dioxide and protons into solution and electrons to an electrode (anode). (Earlier post.) The electrons flow from the anode through an electrical circuit to the cathode where they are consumed in the reduction of oxygen. Without oxygen, current generation is not spontaneous. However, if a small voltage (>0.2 V in practice) is applied between the anode and the cathode, hydrogen gas is produced at the cathode through the reduction of protons. The system based on this latter process is termed a microbial electrolysis cell.
MEC systems are based on a number of components, each of which will require much additional investigation.
Microorganisms. Little is known about the composition of the microbial communities in MECs, the authors note. The only study of a community analysis of an MEC found that Pseudomonas spp. and Shewanella spp. were present on the anode. Microorganisms are observed to be attached to the cathode, but to what extent they affect the function of the MEC is not clear.
Nor is it clear to what extent the operation of an MEC is affected by the inoculum source.
Another production issue to be resolved is that high concentrations of hydrogen gas also favors the growth of methanogens, reducing hydrogen gas production and contaminating the product gas with methane.
Materials. The anode material in a MEC can be the same as the material in a MFC—e.g., carbon cloth carbon paper, graphite felt, graphite granules or graphite brushes. Hydrogen production in an MEC occurs at the cathode. Because the hydrogen evolution reaction (HER) on plain carbon electrodes is very slow, a high overpotential is required to drive hydrogen production. To reduce this overpotential, platinum is usually used as a catalyst.
There are many disadvantages to using platinum, the authors note, including the high cost and the negative environmental impacts incurred during mining/extraction. Exploration of biocathodes are underway.
Other materials issues include membranes (although some MECs are membraneless), and tubing and gas collection systems.
Potential feedstock sources for MECs include wastewater (and wastewater treatment is a major potential application for MECs) and cellulosic biomass.
So far, MECs have achieved hydrogen production of up to 3.12 m3H2/m3 d with energy input of 0.8 V, values which are in the same order as those of fermentation systems, according to the reviewers. MEC systems have reached a maximum current density of 186 A/m3. This, the authors note, is much lower than those in the more-extensively studied MFCs (5,600 A/m3, 10 A/m2), and thus it is likely that with additional research, higher current densities will be achieved in MECs in the future.
The reviewers suggest that for MECs to become a mature hydrogen production technology, several research questions still need to be addressed:
More experience is required with real organic feedstocks containing complex organic substrates such as polymeric and particulate substances;
Novel, more cost-effective chemical and/or biological cathodes need to be developed that show low potential losses and are not platinum-based;
Membrane pH gradients need to be eliminated, or membranes should not be used in the reactor;
Methanogenic consumption of the hydrogen product needs to be prevented (in case of membrane-less MECs and/or MECs with a biocathode); and, most critically,
A cost-effective, scalable MEC design needs to be developed.
Resources
Bruce E. Logan, Douglas Call, Shaoan Cheng, Hubertus V. M. Hamelers, Tom H. J. A. Sleutels, Adriaan W. Jeremiasse, and René A. Rozendal (2008) Microbial Electrolysis Cells for High Yield Hydrogen Gas Production from Organic Matter. ASAP Environ. Sci. Technol., doi: 10.1021/es801553z
Using Biomas for Hydrogen is good.
Destroying water for Hydrogen is bad, very bad. I don't care if it is wastewater. Destroying water in any form to make Hydrogen is an extremely bad idea.
Posted by: Joseph | 10 November 2008 at 12:12 PM
Renewable bio-mass energy was tried hundreds of years ago with much lower populations. It devastated whole areas including Iceland and England and North Africa. Much of the top soil of North Africa was washed into the Mediterranian sea because of farming to supply grain to the Roman Empire. There is nothing what so ever at all sustainable about hydrogen from bio-mass to provide any substantial part of the energy required by industrial civilizations.
There is plenty of water being produced by the combustion of fuels to make up for any used to make hydrogen. All plants use sunlight to split up water to make hydrogen that is used to form carbohydrates. There is enough water in the oceans for any use ever discovered by man. In fact the current worry is that there is going to be too much. There are cheap enough means to supply all drinking water from the ocean, but supplying water for crop growing is another problem. It may be that every town needs two water systems like some have already: one for drinking and one for watering plants. ..HG..
Posted by: Henry Gibson | 10 November 2008 at 12:41 PM
Joseph:
Most biomas production normally requires huge amount of fresh water.
Since fresh and specially sea water is available in huge quatities, wouldn't be an ideal feed stock for direct hydrogene production?
Posted by: HarveyD | 10 November 2008 at 12:55 PM
HarveyD
Getting water Dirty and Destroying water are two completely different things. The Earth is a closed system for H2O and has the exact same amount of water now that it had 10 million years ago. Water has so many uses and no matter how dirty you make water, given enough time it will be filtered and cleaned. If you seperate the Hydrogen from H2O and use the Hydrogen for fuel you destroy the water molecule. Lets say a hyrogen car uses a 100 units of water per day. If it's 70% effecient then 30 units is emmited out the tailpipe as water vapor exhaust. This means you are destroying 70 units of water per day per vehicle and ounce it's gone it's gone. With a couple hundred million Hyrogen vehicles on the road. Exactly how long do you think the oceans will last?
Posted by: Joseph | 10 November 2008 at 01:25 PM
In a microbial electrolysis cell, the microbes eat biomass and use the energy obtained to split water into hydrogen and oxygen.
When you "burn" hydrogen either in a fuel cell or by combustion, you make water by combining hydrogen and oxygen.
The putative advantage of the microbial electrolysis I would guess is higher efficiency.
No water is destroyed in the cycle.
Posted by: | 10 November 2008 at 01:54 PM
This is the 100th methods for making hydrogen i read in the last year??? The problem is there is no hydrogen cars available on the market.. It cost 500$ to 1000$ more to have a working hydrogen car. It take a compressed tank and some fittings like valves, hoses, connector, meter, injectors valves controled by electronic. O.k maybe 2000$ but if it's done at the factory to a new car on a production line then all cars can comes with a gazeous hydrogen tank and the cost is approx 1000$.
What is horrendous is not the lack of knowledge about it, it's so simple. What is horrendous is that no manufacturers and no tuner or mechanical shop is selling and installing a convertion so no one except good amators are building for themselfs hydrogen cars.
Someone have to install and sell hydrogen gas at a service station where the hydrogen is made on-site with water and sold at 40 cents a gallon. It take a water electrolyser and some machinery about double the size of a 110 volts air conditionner and a tank. It's so simple and nobody is commercializing anything and billions are spent by incompetants all over the world for nothing. It's a world of madscientist where nuclear weapons exists and no commercial hydrogen cars and trucks exist.
Posted by: a.b | 10 November 2008 at 01:55 PM
Joseph, are you at all serious with that statement?
Just in case you are;
A hydrogen powered car doesn't destroy water or hydrogen. Water is H2O, you don't create hydrogen from water so much as release it. You release it by putting energy into it. A fuel cell is only using the energy potential that's been created in the release of the hydrogen not the hydrogen itself. It gets the energy by combining it with oxygen, which makes water. For every unit of water that goes in a unit of water comes out because the hydrogen is only used as an energy carrier. The efficiency rating only refers to how well it uses the energy that's been put into the system. Only chemical bonds are being broken and recreated here, not atoms.
Posted by: ai_vin | 10 November 2008 at 02:11 PM
a.b you could do that or you could put the 40 cents of electricity into an electric scooter and travel 50 miles.
Hydrogen by its very nature as an energy carrier will always be more expensive than the electricity or natural gas used to create it. Its like saying we can power everything with steam, its not a resource.
Encouraging the use of more natural gas in transport would help as hydrogen can be used as a component of the gas (up to about 5% I think) in the same transport infrastructure. It could turn out to be ideal to fuel a small range extender engine.
We have to replace declining fossil fuels with high EROEI alternatives or we risk falling off the energy cliff chasing ethanol, hydrogen and tar sands.
Posted by: | 10 November 2008 at 03:43 PM
Hydrogen can be blended in with NG up 30% and transported through the same pipelines as NG without causing the enbrittlement problems you'd get with pure H2.
Posted by: ai_vin | 10 November 2008 at 06:15 PM
annon:
....we have to replace fossil fuels with high EROEI alternative energies....
Average EROEI for various energy sources vary a lot for each given geographical area and even for specific projects within the same area or country.
Using about half a dozen sources, the average EROEI for major current and future energy sources seem to be:
1) about 22.5 : 1 for hydro
2) close to 20 : 1 for coal
3) unrealized potential of 19.0 : 1 for highest efficiency cellulosic ethanol. Could be as low as 5 : 1
4) about 14.5 : 1 for recent discovery conventional oil.
5) about 13.0 : 1 for high quality geothermal.
6) about 9.0 : for coal produced electricity.
7) about 8.4 : 1 for sugar cane ethanol.
8) about 8.3 :1 for new high efficiency solar and large wind turbines in high quality wind areas.
9) about 8.0 : 1 for nuclear.
10) about 3.0 : 1 for shales and sands oil
11) about 2.0 : 1 for surgar beet ethanol
12) about 1.67 : 1 for grain ethanol.
All the above EROEI can change within a rather short time frame and will vary with the factors and geographical areas used for the data collection and who is financing the study. It is very far from being as reliable as many people think. The margin of error may be as high as 300% in many cases.
Posted by: HarveyD | 10 November 2008 at 06:54 PM
Harvey,
Not withstanding 300% margin of error, the solar and wind figures sound low as the energy inputs are substantially one off and the payback is is decades.
This should be seen in context of so many consumptive activities (never claimed as energy productive)such as a weeks holiday O/S (entertainment) or house makeover (fashion) just to say If the various energy creating activities seem humble, we should try and remember how much our other activities run in the red.
Am I confused?
Posted by: arnold | 10 November 2008 at 07:47 PM
arnold:
Wind and Solar vary tremendously from year to year, project to project and from one study to another. The current average 8.5 or so could be too high for some places and too low for others.
Those two technologies could have much higher EROEI in a decade or two while others (like oil and nuclear) may fall drastically.
EROEI for cellulosic ethanol is is not reliable. The claimed 19.0 may 300+% too high.
Very large Wind turbines coupled with huge hydro water reservoirs could give much better results. The Hudson Bay and Labrador shores could be excellent areas for such combo.
The EROIE battles and wild claims are not over. Is the average of many studies more reliable? May be...
Posted by: HarveyD | 10 November 2008 at 08:07 PM
As many have said, arguments about calculating EROEI will rage for a long time. Studies done on wind power have found increasing returns with larger turbines. The next generation of 5MW turbines are likely to improve this further.
I think we should be electrifying heating and transport and then generating as much carbon free electricity as possible. Fossil fuels should only be used in high efficiency power stations with the waste heat being used to heat digesters, fish farming or any industrial/agricultural process which requires lots of heat.
Posted by: | 10 November 2008 at 11:59 PM
Harvey? Have you seen this- http://www.theoildrum.com/story/2006/10/17/18478/085
wiki places the EROEI of wind at 5-35 and I've numbers as high as 40-50 for off-shore wind.
Posted by: ai_vin | 11 November 2008 at 12:36 AM
Sorry, I meant to say "I've heard numbers as high as". I don't know if they're true.
Posted by: ai_vin | 11 November 2008 at 03:58 AM
Wind EROEI can vary depending on the raw materials used. If recycled steel and aluminium is used for construction fuelled by non fossil electricity, the emissions are very low. Also new technologies using composite (eventually from plant materials) blades, lighter, stronger, less radar return and could even be formed on site (less transport issues.) Gear-less permanent magnet generators or even hydraulic drive trains. A 20MW wind turbine would 'only' have a blade diameter of 250m compared to over 100m with today's 2-5MW turbines. Doubling the blade size returns approximately 4 times the as much energy production as the original blade.
There is not much that can compete with wind charged batteries on cost, the speed of installation, EROEI, emissions savings and abundance.
Posted by: | 11 November 2008 at 04:32 AM
"Lets say a hyrogen car uses a 100 units of water per day. If it's 70% effecient then 30 units is emmited out the tailpipe as water vapor exhaust."
Are you joking or just that bad at math?
When you combine Hydrogen with oxygen you get water and energy released.
If 100 units of water are converted into the hydrogen required to run a car off of hydrogen, and the car is 70 % efficient ... that means that %30 of the "ENERGY" available was not used. This lost energy is in the form of the heat in the exhaust. Water is not being destroyed
Not at the rate you think it is ... some hydrogen will escape our car unburned ... and will react with something in the environment ... there is a pretty good chance it will be oxygen
The gas engine on my generator is only %15 efficient at converting gasoline to electricity.
This does not mean that 85% of the fuel was unburned, we would have to look at the Hydrocarbon emissions to determine this. The generator head is not 100% efficient at converting mechanical energy from the engine into electrical energy. The engine might be 27% efficient at converting the gasoline to mechanical energy and the alternator 55% - 65% efficient at converting mechanical energy to electricity.
This is the kind of efficiency you can expect from your cars alternator.
When I burn gasoline I am producing water and co2, co, some Nox, some gasoline escapes unburned and some only partially burned so you end up with shorter chains of hydrocarbons like methane.
We are generating new water every day you don't have to worry about running out.
Posted by: math | 11 November 2008 at 07:55 AM
ai-vin:
Yes, there are very wild EROEI numbers claimed for various energy sources.
Will we have internationally justified and accepted methods and results in the near future?
It seems that many studies on the same energy source come out we very different numbers. They may not use the same input and output factors and values. Everybody seems to have developped its own method and agenda.
I would like to see the figures for the best Hydro/Wind combined sites. It could probably go as high as 40 or 50 while some sites may be as low as 20 and even less.
Other combined power generation possibilities could also be very interesting.
Posted by: HarveyD | 11 November 2008 at 08:06 AM
Those inclined to work out the 'Fine Structure' please do so.
In laymen terms. Not all Hydrogen is created equal. Some Hydrogen molecules have the ability (are charged or state) to capture Oxygen molecules creating H2O, water. It is important to note that it is the hydrogen capturing the oxygen and not the other way around. When you force a hydrogen molecule to 'release' it's Oxygen the energy created comes from electrons on the hydrogen molecule. It is correct to say that neither the hydrogen nor the oxygen is destroyed. However, the hydrogen's STATE has been changed and it has lost it's ability to capture the oxygen molecule to make H2O.
Extrapolating = destroying water
The only water "created" by a fuel cell comes from the hydrogen molecules that were not altered and therefore recapture oxygen and exit the tailpipe.
Posted by: Joseph | 11 November 2008 at 08:27 AM
Joseph, I wonder what kind of hydrogen-state you call 'destroyed water'.
I could guess H2, H. or H+
In any form, the proton is unchanged. the only difference is the presence of respectively 2, 1 or 0 electrons. Electrons are destroyed neither.
In your logic, biomass is also partly destroyed water.
CO2 + H2O + sunlight --> biomass + O2 + wasteheat.
Posted by: Alain | 11 November 2008 at 09:46 AM
Wow, Joseph you have created a new property of matter. This is big news that you just can not keep secret. Soon Joseph will be receiving the Noble prize in Physic soon.
Seriously, a huge hydrogen economy already exits. There are many uses for H2 besides being an energy carrier. So any process that convert biomass to H2 would sell like hot cakes.
Posted by: Kit P | 11 November 2008 at 09:50 AM
Hydrogen is the most abundant element in the universe, why must you use water to get it. Use another source and build all the fuel cells you want. Just don't use water.
Hypothetical - You have a Honda fuel cell car. It's takes 5 gallons of water to provide a full tank of hydrogen for the car. You fill up the tank drive 100 miles. If you could capture all the tailpipe output you would have 1 gallon of water. So you used (destroyed) 4 gallons of water. How come you think that energy from hydrogen is free, its not.
Plants do not break down the H2O bond, plants break down the CO2 bond. Plants use H2O for several duties however, eventually it escapes through the plant wall intact and unmolested.
Posted by: Joseph | 11 November 2008 at 10:51 AM
In any case it will be dificult to move from oil (more of 100years old of research and technology) to NEWS energy.
The time it s too short to find something really performant and not so expensive...
Time and money for changing, but we need !
Business as usual is finish ! ACTION ! NOW !
Posted by: raoul | 11 November 2008 at 11:49 AM
I said many times to use water electrolysis to power the devices likes cars and trucks and the rest. Don't rush my mind anymore. Im sick of using gasoline that cost a lot. Water is free and can propel anything and don't make pollution. Many peoples here just guess the 'science' and are making confusing sound and im tired of that. And the couple of tousands people actually working on the water powered car are having a hard time with basic water-electrolyser desing and especially hydrogen carburation for making the engine work. Hydrogen engine need proper hydrogen carburation or injection and ignition timing for all rpm and all load on the engine, zero water car proponents and builders have even tought about that 'little' problem, LOL.
Posted by: a.b | 11 November 2008 at 01:28 PM
After reading a number of Joseph's contrarian posts, I had initially suspected that he was just a little dull witted. After reading about his 'water destruction by electrolysis' concerns, I am starting to think that he is just an attention whoring troll. No one is that stupid.
Posted by: Bob Bastard | 11 November 2008 at 02:37 PM