Direct Carbon Fuel Cells DCFCs

When Wilhelm Ostwald, toward the end of the nineteenth century, formulated his idea of using an electrochemical mechanism for the direct conversion of natural fuels chemical energy to electrical energy, coal was the chief kind of fuel in the hands of mankind. Even today, notwithstanding the widespread use of petroleum products and the development of nuclear power, coal remains a very important component of world energy supply. Its share of all known natural fuel reserves worldwide is about 60%. In China today, about 80% of the electrical energy is produced by coal-fired power stations, these being responsible for 70% of the carbon dioxide emissions and 90% of the sulfur dioxide emissions in this country (Cao et al 2007). 

There are two possibilities for an electrochemical utilization of the chemical energy of coal (i) via prior coal gasification and the subsequent use of hydrogen and/or of carbon monoxide, thus produced, in various fuel cells and (ii) by a direct electrochemical oxidation within the fuel cell. For the first of these possibilities no insurmountable technical or scientific problems arise. Gasification units and proton-conducting membrane fuel cells are well known and very reliable devices, so, their use is connected only with economic and lifetime problems. 

Some attempts to realize the second approach that, basically, is a much simpler one-step process, are discussed in this section. 

Antoine Cesar Becquerel in France (1855) and Pavel Yablochkov in Russia (1877) have built electrochemical devices, using coal anodes in a molten potassium nitrate electrolyte. William Jacques (1896) obtained a US patent for his invention of a coal stack with a coal anode and an iron cathode immersed into molten alkali hydroxide. Despite the great doubts raised, as to the nature of the processes taking place in the stack, the electrical performance of this fuel cell stack, operating at temperatures from 400 to 500°C, had a rather impressive total power 1.5 kW, and current densities up to 

It was shown that an effective anodic oxidation of carbon cannot take place in low-temperature aqueous solutions, but only at high temperatures and in other electrolytes (particularly, in molten carbonates or alkali hydroxides). Thus, in molten carbonates at 600 C, the equation can be formulated as follows  

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A new version of MCFC technology - the direct carbon fuel cell (DCFC) - is under development at the Lawrence Livermore National Laboratory in the USA. Instead of using gaseous fuel, a slurry of finely divided carbon particles dispersed in molten alkali metal carbonates is fed to the cell. The carbon is made by the pyrolysis of almost any waste hydrocarbon e.g., petroleum coke), a process that is already carried out industrially on a large scale to produce carbon black for use in the manufacture of tyres, inks, plastic fillers, etc. The pyrolysis reaction yields hydrogen that can itself be utilized in another fuel cell ... 

Direct Carbon Fuel Cells (DCFC). In direct carbon fuel cells, solid carbon (presumably a fuel derived from coal, pet-coke or biomass) is used directly in the anode, without an intermediate gasification step. Concepts with solid oxide, molten carbonate, and alkaline electrolytes are all under development. The thermodynamics of the reactions in a DCFC allow very high efficiency conversion. Therefore, if the technology can be developed into practical systems, it could ultimately have a significant impact on coal-based power generation. 

Direct carbon fuel cell (DCFC) Molten hydroxide 600-850 Power generation... 

Balachov II, Hombostel MD, lipilin AS (2005) Direct coal fuel cells (DCFC) clean electricity from coal and carbon based fuels. The carbon fuel cell seminar. Palm Springs, CA Cao D, Sun Y, Wang G (2007) J Powtr Sources 167 250... 

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