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.