Performance Analysis with Various Amounts of Electrolyte in a Molten Carbonate Fuel Cell

Abstract

The effect of initial electrolyte loading (IEL) on cell performance in a coin-type molten carbonate fuel cell (MCFC) was investigated in this work. Since the material of MCFC depends on the manufacturer, optimisation requires experimental investigation. In total, four IEL values, 1.5, 2.0, 3.0, and 4.0 g, were used, corresponding to a pore filling ratio (PFR) of 38, 51, 77, and 102%, respectively. The cell performance with respect to the PFR was analysed via steady-state polarisation, step-chronopotentiomtery, and impedance methods. The electrochemical analyses revealed that internal resistance and overpotential of the cell decreased with increasing PFR, and a large overpotential was observed when the PFR was 102%, probably due to the flooding phenomenon. After operation, cross-section of the cell was analysed via surface analysis of SEM and EDS methods, and the remaining electrolyte was estimated by dissolution of the cell in 10 wt% acetic acid. A linear relationship between IEL and the weight reduction ratio by dissolution was obtained. Thus, the remaining amount of electrolyte could be measured after operation. The results of SEM and EDS showed that a PFR of 38 and 102% showed a lack and flooding of electrolytes at the cell, respectively, which led to a large overpotential. This work reports that MCFC performance is allowed only in the narrow range of PFR.

Characterization of Spatial Distribution of Electrolyte in Molten Carbonate Fuel Cell Cathodes

“…The electrolyte occupies about 30% of the pore volume, which is a low value compared to the fraction determined by other authors (70%) . This apparent discrepancy can be explained by the fact that the multi‐modal pore sized cathode structure requires a lower fraction of electrolyte to infiltrate the entire material since larger pores, serving as gas channels, are not flooded by the electrolyte.…”

“…The compromise between mass transport and specific surface area can be achieved by tailoring the pore size, since it determines the properties of open‐porous materials . Particularly, the variation of the pore size in the MCFC cathode material is providing two essential microstructure parameters: 1) the fraction of small pores formed after oxidation, which is responsible for capillary force based infiltration of the electrode with the electrolyte (in the range 15–30%), and 2) the enlarged internal surface area of pores (specific surface area). Summarizing, the specific surface area after oxidation should be as large as possible to form the longest possible TPB.…”

Analysis of Cell Performance with Varied Electrolyte Species and Amounts in a Molten Carbonate Fuel Cell

“…Therefore, it can be said that the equations above can be used to calculate the remaining amount of electrolyte in the cell. In addition, it can be seen that the WRR performed with vacuum filtering is larger than that of the equation y = 0.13x -0.08, which was reported by the previous study [14]. This implies that the paper filtering method used in the previous experiment permitted reaction between moisture in the air and the carbonate electrolyte during filtering, which caused further reduction in the weight of the electrolyte.…”

“…However, with 4 g electrolyte, the overpotential is increased largely because of an increase in the mass-transfer resistance caused by the thick layer of electrolyte formed on the surfaces of the electrodes. It was suggested that electrolyte conditions above 4 g caused flooding because excess electrolyte covered the electrode surface and pores [14].…”

“…The WRR was calculated using the masses of the components before and after dissolution. In addition, unlike previous experiments, this study used vacuum filtering to reduce the experimental error of the WRR from reactions between the cell components and atmospheric humidity [14].…”