HDCFC Performance as a Function of Anode Atmosphere (N 2 -CO 2 )

Abstract

The mechanism for the oxidation of solid carbon in a fuel cell made as a hybrid between a molten carbonate fuel cell and a solid oxide fuel cell, known as a hybrid direct carbon fuel cell (HDCFC), was investigated. Fuel cell performance was measured by electrochemical impedance spectroscopy (EIS) and using current-Cpotential-Cpower density curves (I-CV-CP) between 700 to 80-C. The impacts of the gas species introduced at the cathode (air vs. pure O 2) and at the anode (pure N2, pure CO2, and mixed N2-CO2) were investigated, as well as the influences of temperature and anode gas flow rate. The majority of the impedance data could be modeled using an equivalent circuit consisting of a resistor (Rs) in series with three resistor-Cconstant phase element units (RQ, in parallel), depending on anode gas atmosphere. An explanation was proposed for each impedance element, and the literature relating to impedance data acquired for carbon-Ccarbonate mixture in a DCFC anode were discussed. By varying of the anode gas mixtures between pure N2 and pure CO2, together with variations in their flow rates, it was suggested that CO2 is a chemically active species which is not electrochemically active, a chemical intermediate in the oxidation of solid carbon in such a HDCFC. © 2013 The Electrochemical Society.