Utilisation of coal in direct carbon fuel cells
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Hybrid Direct Carbon Fuel Cells merge Solid Oxide Fuel Cell (SOFC) and MCFC technologies, using a solid oxide electrolyte to separate the cathode and anode compartments, while a molten carbonate electrolyte is utilised to extend the anode/electrolyte region. Oxygen is reduced to O2- ions at the cathode and transported across the solid electrolyte membrane to the anode compartment, where carbon is oxidised to CO2. Molten carbonate could enhance the carbon oxidation in two ways as a fuel carrier or as an electrochemical mediator. The maximum energy density can be achieved by fully oxidising carbon to CO2 offering very high efficiencies. This concept has been demonstrated using a wide range of carbons and carbon-rich fuels such as coal, plastics, carbon colloids, activated carbons and charcoals. In a short stack of 3 cells delivered a maximum power output at 650°C of 5.4 W, at over 100mWcm-2. The underlying chemical processes in DCFCs are complex involving a series of catalytic and electrochemical reactions of a complex fuel. Coal and biochars are quite far from pure carbon comprising of high hydrogen content and often significant oxygen, sulphur and nitrogen contents as well as inorganic, ash components. Here we report on the pyrolysis and oxidation reactions and processes that occur in situ and in DCFC relevant conditions. Of key importance is interplay between carbon and its oxides as direct oxidation of carbon to carbon dioxide delivers the ultimate efficiency. There is a change in process above 750°C where the reverse Boudouard reaction becomes dominant and our focus is on understanding the lower temperature electrochemical processes.
Irvine , J T S , Fuente Cuesta , A , Mottram , A , Jiang , C , Savaniu , C D & Jain , S L 2015 , Utilisation of coal in direct carbon fuel cells . in S C Singhal & K Eguchi (eds) , 14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015 . ECS Transactions , no. 1 , vol. 68 , Electrochemical Society , pp. 2681-2684 , ECS Conference on Electrochemical Energy Conversion & Storage with SOFC-XIV , Glasgow , United Kingdom , 26/07/15 . https://doi.org/10.1149/06801.2681ecstconference
14th International Symposium on Solid Oxide Fuel Cells, SOFC 2015
© The Electrochemical Society, Inc. 2015. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published here: https://dx.doi.org/10.1149/06801.2681ecst
DescriptionThe authors thank the Research fund for coal and steel for supporting this research, Grant Agreement Number: RFCR CT-2011-00004.
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