Electrochemical performance of reversible molten carbonate fuel cells

Abstract

Molten carbonate electrolysis cellNi electrode NiO electrodeReversible molten carbonate fuel cell a b s t r a c tThe electrochemical performance of a state-of-the-art molten carbonate cell was investigated in both fuel cell (MCFC) and electrolysis cell (MCEC) modes by using polarization curves and electrochemical impedance spectroscopy (EIS). The results show that it is feasible to run a reversible molten carbonate fuel cell and that the cell actually exhibits lower polarization in the MCEC mode, at least for the short-term tests undertaken in this study. The Ni hydrogen electrode and the NiO oxygen electrode were also studied in fuel cell and electrolysis cell modes under different operating conditions, including temperatures and gas compositions. The polarization of the Ni hydrogen electrode turned out to be slightly higher in the electrolysis cell mode than in the fuel cell mode at all operating temperatures and water contents. This was probably due to the slightly larger masstransfer polarization rather than to charge-transfer polarization according to the impedance results. The CO 2 content has an important effect on the Ni electrode in electrolysis cell mode. Increasing the CO 2 content the Ni electrode exhibits slightly lower polarization in the electrolysis cell mode. The NiO oxygen electrode shows lower polarization loss in the electrolysis cell mode than in the fuel cell mode in the temperature range of 600e675 C.The impedance showed that both charge-transfer and mass-transfer polarization of the NiO electrode are lower in the electrolysis cell than in the fuel cell mode.

Operating the nickel electrode with hydrogen-lean gases in the molten carbonate electrolysis cell (MCEC)

“…The electrolyte in the MCEC is based on molten carbonate salts and carbon dioxide may play a very complex role in the electrolysis cell. For example, CO2 is a reactant in the production of carbonate ions or when generating CO, and further CO2 is involved in the reverse water-gas shift reaction and other reactions [20]. The observations made in this study show that all components in the gas influence the mass-transfer polarization of the Ni electrode in the electrolysis cell.…”

“…In our previous studies [20,21] the gases used for the Ni electrode still contain a relatively high amount of hydrogen in the MCEC. If the electrochemical cell is mainly applied for fuel gas production, the inlet gases should contain low amounts of hydrogen or even no hydrogen.…”

“…However, none of the studies above were performed using porous electrodes. Our previous study [20] has proved the feasibility of operating the molten carbonate electrolysis cell by using conventional fuel cell (MCFC) materials, i.e. the cell components consist of Ni-based porous electrodes and carbonate electrolytes.…”

CO2 electrochemical reduction into CO or C in molten carbonates: a thermodynamic point of view

“…These authors showed the feasibility to producing energetic molecules (CO, C) with a solar efficiency reaching 50% using the so-called STEP (Solar Thermal Electrochemical Production) process. Apart from CO 2 electrochemical reduction, another important application of molten carbonates is water electrolysis yielding hydrogen; Hu et al [18] have very recently given the proof-ofconcept of such process. CO 2 valorisation can also be combined with water transformation into H 2 through co-electrolysis of CO 2 and CO in order to produce syngas.…”

Electrode kinetics of the NiO porous electrode for oxygen production in the molten carbonate electrolysis cell (MCEC)

“…Some researchers have evidenced the possibility of electrolysis in molten carbonates, but mainly by converting CO 2 into CO. [1][2][3][4] However, most experiments were performed on ag electrodes, which differ from porous electrodes with regards to the electrode surface and mass-transport properties. Our previous study 5 showed that it is feasible to run the molten carbonate fuel cell reversibly with conventional Ni-based porous electrodes at 650 C. A lower polarization loss has been found for the electrolysis cell compared to the fuel cell, mainly due to the NiO electrode performing much better as an anode in MCEC mode. 5 The activity of the NiO electrode provides a dominant contribution to the performance of the cell, regardless of fuel cell or electrolyzer operation.…”