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Modified microbial fuel cell produces electricity and desalinates water

Source : fcw

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Bruce Logan, Kappe Professor of Environmental Engineering (right) and Maha Mehanna, postdoctoral fellow (left) are already at work on the next generation of microbial desalination cells based on using air cathodes.

University Park, Pa. — A process that cleans wastewater and generates electricity can also remove 90 percent of salt from brackish water or seawater, according to an international team of researchers from China and the U.S.

Clean water for drinking, washing and industrial uses is a scarce resource in some parts of the world. Its availability in the future will be even more problematic. Many locations already desalinate water using either a reverse osmosis process — one that pushes water under high pressure through membranes that allow water to pass but not salt — or an electrodialysis process that uses electricity to draw salt ions out of water through a membrane. Both methods require large amounts of energy.

“Water desalination can be accomplished without electrical energy input or high water pressure by using a source of organic matter as the fuel to desalinate water,” the researchers report in a recent online issue of Environmental Science and Technology.

“The big selling point is that it currently takes a lot of electricity to desalinate water and using the microbial desalination cells, we could actually desalinate water and produce electricity while removing organic material from wastewater,” said Bruce Logan, Kappe Professor of Environmental Engineering, Penn State

The team modified a microbial fuel cell — a device that uses naturally occurring bacteria to convert wastewater into clean water producing electricity — so it could desalinate salty water.

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Three chambered microbial desalination cells at work in Bruce Logan’s, Kappe Professor of Environmental Engineering, laboratory
“Our main intent was to show that using bacteria we can produce sufficient current to do this,” said Logan. “However, it took 200 milliliters of an artificial wastewater — acetic acid in water — to desalinate 3 milliliters of salty water. This is not a practical system yet as it is not optimized, but it is proof of concept.”

A typical microbial fuel cell consists of two chambers, one filled with wastewater or other nutrients and the other with water, each containing an electrode. Naturally occurring bacteria in the wastewater consume the organic material and produce electricity.

The researchers, who also included Xiaoxin Cao, Xia Huang, Peng Liang, Kang Xiao, Yinjun Zhou and Xiaoyuan Zhang, at Tsinghua University, Beijing, changed the microbial fuel cell by adding a third chamber between the two existing chambers and placing certain ion specific membranes — membranes that allow either positive or negative ions through, but not both — between the central chamber and the positive and negative electrodes. Salty water to be desalinated is placed in the central chamber.

Seawater contains about 35 grams of salt per liter and brackish water contains 5 grams per liter. Salt not only dissolves in water, it dissociates into positive and negative ions. When the bacteria in the cell consume the wastewater it releases charged ions — protons — into the water. These protons cannot pass the anion membrane, so negative ions move from the salty water into the wastewater chamber. At the other electrode protons are consumed, so positively charged ions move from the salty water to the other electrode chamber, desalinating the water in the middle chamber.

The desalination cell releases ions into the outer chambers that help to improve the efficiency of electricity generation compared to microbial fuel cells.

“When we try to use microbial fuel cells to generate electricity, the conductivity of the wastewater is very low,” said Logan. “If we could add salt it would work better. Rather than just add in salt, however in places where brackish or salt water is already abundant, we could use the process to additionally desalinate salty water, clean the wastewater and dump it and the resulting salt back into the ocean.”

Because the salt in the water helps the cell generate electricity, as the central chamber becomes less salty, the conductivity decreases and the desalination and electrical production decreases, which is why only 90 percent of the salt is removed. However, a 90 percent decrease in salt in seawater would produce water with 3.5 grams of salt per liter, which is less than brackish water. Brackish water would contain only 0.5 grams of salt per liter.

Another problem with the current cell is that as protons are produced at one electrode and consumed at the other electrode, these chambers become more acidic and alkaline. Mixing water from the two chambers together when they are discharged would once again produce neutral, salty water, so the acidity and alkalinity are not an environmental problem assuming the cleaned wastewater is dumped into brackish water or seawater. However, the bacteria that run the cell might have a problem living in highly acidic environments.

For this experiment, the researchers periodically added a pH buffer avoiding the acid problem, but this problem will need to be considered if the system is to produce reasonable amounts of desalinized water.

King Abdullah University of Science and Technology, Saudi Arabia and Ministry of Science and Technology, China, supported this work.

August 9, 2009 - 10:59 AM No Comments

Dr. Ihara Further Evolves His Technologies on Direct Hydrocarbon Sofc

Source :

Associate professor Ihara Manabu, Research Center for Carbon Recycling Energy, Tokyo Institute of Technology, has further evolved his technologies on the SOFC, which directly uses hydrocarbon of the primary fuel for electric power generation.

As known, this fuel cell is superior to the fuel cell of the type using the reformer in many respects. When this type of the fuel cell is operated with use, carbon accumulatively deposits on the surface of the fuel electrode of the fuel cell, so that the fuel electrode gradually deteriorates in performance.
Dr. Ihara has succeeded this time in minimizing the deterioration of the fuel electrode, and in developing, based on this, a new fuel electrode which leads to the fuel cell having high output power and high durability.

Dr. Ihara has also succeeded in developing a called “rechargeable direct carbon fuel cell (RDCFC)”. The RDCFC operates using the depositing solid carbon as the fuel. Accordingly, during the power generation operation, there is no need of supplying additional gas to the fuel cell.
Dr. Ihara has succeeded in increasing the output power of the fuel cell by controlling the equilibrium reaction at the fuel electrode. The output power density of the fuel cell was increased up to 0.26W/cm2. This figure is the highest in the world when it is considered as the figure representative of the output power of this type of the fuel cell. The RDCFC has a high possibility of reducing the size. In this respect, it is expected to use the RDCFC as the micro fuel cell.

Fuel Electrode Improvement:
A trace of proton conductor was added to the fuel electrode of the direct carbon fuel cell by using the infiltration process. More exactly, SrZr0.95Y0.05O3-alpha (SZY) was added to Ni/YSZ, and SrCe0.95Yb0.05 O3-alpha (CYB) was added to Ni/GDC.
The result is that the fuel electrode was highly activated, and the deterioration of the depositing carbon was minimized.

Rechargeable Direct Carbon Fuel Cell:
The rechargeable direct carbon fuel cell (RDCFC) is developed by associate professor Ihara Manabu et al, Research Center for Carbon Recycling Energy, Tokyo Institute of Technology in 1998. #1
The RDCFC is based on the solid oxide fuel cell (SOFC).
The operation principle of the RDCFC is quite different from the conventional fuel cell. Carbon, not hydrogen, is used for the fuel of the RDCFC.
The carbon has been a nuisance material in the conventional fuel cell.
Electricity is extracted through a process in which carbon reacts with oxygen to generate carbon dioxide.

Specifically, the hydrocarbon is thermally decomposed at the fuel electrode to deposit the carbon on the surface. At the fuel electrode the carbon couples with oxide ions to generate carbon oxide and electrons. Electrons flow through an external circuit and reach the air electrode. At the air electrode oxide couples with electrons into oxide ions. The oxide ions pass through the electrolyte to the fuel electrode, and couple with carbon. This process is repeated to continuously generate electricity.

A micro fuel cell using oxide conductive ceramic for the electrolyte was trially manufactured.
The approximate size of the fuel cell was 20 mm in diameter and 0.3 mm in thickness. A porous structure containing nickel and GDC (gadolinium doped ceria ) was used for the fuel electrode. The fuel was solid carbon obtained by thermally decomposing hydrocarbon gas such as propane gas.
The power density of the trial product was 52 mW/cm2.
Note that the figure is substantially equal to that of DMFC and that the product is still in the trial stage.
The fuel is solid and provides high energy density. No need of using the fuel tank and the fuel pump is required. From those facts, it is readily senn that with future improvement of the RDCFC, its output density will exceed that of the DMFC and its size will be further reduced.

It is noted that in the RDCFC, after hydrocarbon gas of the fuel is thermally decomposed, power generation is performed and continues without the supply of fuel gas.
In the experimental operation, when 5 minutes were taken for the thermal decomposition, power generation continued for a maximum of 83 minutes. In the experiment, a cycle of the thermal decomposition and the power generation was repeated six times. From the result, it was confirmed that the power generation characteristic of the RDCFC was stable.

#1:
In 1998, he engaged in studying electrochemical reaction at the electrodes of the fuel cell. He awared that carbon deposited on the electrode, which had been considered as a nuisance material, will be the fuel for the fuel cell. He proposed a basic concept of the rechargeable direct carbon fuel cell (RDCFC). His proposal was flatly rejected and criticized strongly “It is impossible”.
In 2001, he constructed a model of the RDCFC. Solid carbon was used for the fuel. The RDCFC successfully generated electric power. However, the output power was low. In 2002, the RDCFC was adopted for further promoting his study by Precursory Research for Embryonic Science and Technology (PRESTO).

In 2007, he reached an idea of infiltrating a proton conductor into the fuel electrode of the RDCFC. By the infiltration of the carbon conductor, the output power density of the fuel cell was increased to practical use levels. Common practice to increase the output power of the fuel cell was to use a material of which oxide ion conductivity or electron conductivity is high. However, he focused attention on the proton coverage at three-phase interface (electron, oxide ion, fuel).

Source and references:
1) Press release from NEDO
2) “Development Of SOFC Directly Using Dry Hydrocarbon as Secondary Fuel, Based on Fuel Electrode Reaction Mechanism”
3) “New Technology Implementable into Micro Fuel Cell, Much Smaller Than Conventional One”

From author:
Medias are reporting the start of selling the micro fuel cell devices for mobile devices. Medis and Tohsiba. In this circumstance, Ihara’s technologies on “Rechargeable Direct Carbon Fuel Cell (RDCFC)” caught my eye.  RDCFC uses direclty hydrocarbon for its fuel.  No need of using the fuel tank and the pump is required. After the hydrocarbon is thermally decomposed, the fuel cell automatically and continuously operates without the supply of fuel gas. Its size may be reduced to be much smaller than that of the curren micro fuel cell.

August 9, 2009 - 10:48 AM No Comments

Improving solid oxide fuel cells with nanostructured electrolyte layers

Source : nanowerk

In today’s Spotlight we take a look at a specific example of the challenges researchers face in improving fuel cell technology and the important role that modern laboratory instruments such as electron microscopes play in their work.
Fuel cells have gained a lot of attention because they provide a potential solution to our addiction to fossil fuels. Energy production from oil, coal and gas is an extremely polluting, not to mention wasteful, process that consists of heat extraction from fuel by burning it, conversion of that heat to mechanical energy, and transformation of that mechanical energy into electrical energy. In contrast, fuel cells are electrochemical devices that convert a fuel’s chemical energy directly to electrical energy with high efficiency and without combustion (although fuel cells operate similar to batteries, an important difference is that batteries store energy, while fuel cells can produce electricity continuously as long as fuel and air are supplied). Read more here: Building better fuel cells with nanotechnology.
The scientific activities of the Institute of Energy Research at the Research Center Jülich (FZJ) – with a staff of about 4400 one of the largest research centers in Europe – are focused on the development of materials, structural elements and components for innovative systems of energy conversion, particularly in the area solid oxide fuel cell (SOFC) and thermal barrier coatings for advanced power stations. In this context, powder synthesis and production of ceramic and metallic materials, as well as mixed materials for bulk and layered elements, is carried out.
The FZJ scientists are also working in fields that are either closely related to these main research areas – like the high-temperature stable composites C/SiC as a possible alternative material for new generations of gas turbines – or those based on the central area of powder technology and coating process, like the manufacturing of powder-metallic elements consisting of NiTi shape memory alloys or the development of metals with improved functional porosity.
The Jü¨lich Research Center has been working on SOFCs since 1989. This includes all research fields like materials development, processing and coating techniques, stack assembling, and system analysis of SOFC power plants. The major task of the institute is the materials synthesis and the development and application of the processing and coating techniques.
Principle of a solid oxide fuel cell
Principle of a solid oxide fuel cell. A SOFC is based on two electrodes and an electrolyte. The reduction of air is assigned to the cathode electrode, while the fuel gas, e.g. hydrogen, is oxidized on the anode side. The two electrodes are separated by the gas tight electrolyte. In the SOFC the electrolyte is based on an oxygen ion-conducting ceramic material in which oxygen ions are diffusing. On reaching the anode side the ions react with the fuel gas to form water. This migration of ions constitutes a current pushing through an external load. (Images: FZJ)
A recent research focus in the development of SOFCs at the FZJ has been the lowering of the fuel cell’s operating temperature from above 800°C down to 600°C in order to achieve cost reduction and better long-term thermal stability. Specifically, this requires a further reduction of the thickness of the cell’s electrolyte layer and an optimization of its electrochemical properties with respect to higher ionic conductivity at intermediate temperature are the actual fields of research.
A team at FZJ has developed a planar anode supported SOFC – a concept that is based on the anode substrate as the mechanical supporting component. The sandwich structure of this SOFC stacks
  • a porous, 0.3 – 1.5 mm thick yttrium stabilized zirconium (YSZ)/NiO anode substrate
  • a porous YSZ/NiO anode functional layer
  • a dense, gas-tight 5-10 ?m thick 8YSZ electrolyte layer, and
  • a porous LSM or LSCF cathode with a thickness of ca. 50 µm.
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    So far, the researchers have achieved an average power output of 1.4 W/cm2 at 750°C and 0.7 V with their fuel cell.
    The manufacturing of the electrolyte layer is usually done by vacuum slip-casting or screen-printing. Thinning of this layer needs another deposition technique like the sol-gel process: In a liquid solution of an organometallic precursor a new phase – the sol – is formed by hydrolysis and condensation. This sol is a stable mixture of a solid phase dispersed in a liquid, in which the dispersed phase is much smaller than a micrometer, so that gravitational force is negligible and particle interactions are dominated by short range forces. The dispersed particles in the sol can condense in a gel, in which the solid is still immersed like in a liquid. By drying and firing of the gel during a subsequent low temperature thermal treatment, it is possible to obtain solid matrices with a tailored microstructure.
    SEM images of a layer from a colloidal sol deposited onto a tape-casted substrate sintered at 1400C
    SEM images of a layer from a colloidal sol deposited onto a tape-casted substrate sintered at 1400°C.(Images: FZJ)
    A fundamental property of the sol-gel process is the generation of a ceramic material at rather low temperature compared to traditional routes. By tuning hydrolysis and condensation reactions, the desired nano-sized ceramic particles are obtained for making advanced layers.
    Such thin layers can be deposited by spraying, spin coating, dip coating or even painting. The as-deposited gel layers contain still a large solvent amount. Drying (evaporation of the solvent) creates the final amorphous or crystalline layer, which is further processed by calcination (decomposition of starting materials and formation of reaction products) and sintering (densification).
    There are several problems that need to be investigated and solved when taking the sol-gel layer fabrication route: homogeneity of multi-layers by repeated coating; soaking of the sol into the substrate grain assembly due to capillary tension; and crack formation and their growth.
    The lab in Jülich uses a high end scanning electron microscopy (SEM) and several optical microscopes for studying the layer formation. The information retrieved from optical microscopy was not sufficient with respect to detail resolution. A high end SEM can overcome this problem, but the workload on it results in a long sample throughput. The way-out offers a microscope which imaging capabilities exceed those of an optical one and which allows quick access to shorten cycle time between coating manufacturing and microstructure evaluation. The team is using the table top scanning electron microscope Phenom from FEI for studying 1) improvement of the substrate surface quality, 2) optimization of coating process, and 3) evaluation of layer quality.
    A key argument for using the table top SEM has been a shortening of the cycle time while still being able to perform structural sample characterization at reasonable costs. Yet – with a magnification of 5000-10000x, a low accelerating voltage of 5 kV together with the high-sensitive backscattered electron detector – the instrument is powerful enough to generate detailed surface-enhanced images.
    Polymeric sol dip-coated and fired at 600ºC on tape-casted 3YSZ substrate with a well finished surface
    Polymeric sol dip-coated and fired at 600°C on tape-casted 3YSZ substrate with a well finished surface. (Images: FZJ)
    The SOFC researchers operated their table top Phenom in its two imaging modes – compositional (compo) and topographical (topo) contrast mode. In compo contrast mode, differences in the average atomic number of different phases and early stages in grain formation can be seen (see images above). Topo contrast mode shows that topographic features of the substrate prevent an even and homogenous layer. This leads to the conclusion that high quality thin electrolyte layers can be made only on well finished substrate surfaces and with a particle size of the solid constituent in the gel slightly larger than the size of remaining defects.
    By Michael Berger (based on material by Mark Kappertz at FZJ). Copyright 2009 Nanowerk LLC
    August 9, 2009 - 10:48 AM No Comments