Performance Of Molten Carbonate Fuel Cell Research Articles

Effects of minor alloying elements (Si, Mn and Al) on the corrosion behavior of stainless steels in molten carbonate fuel cell cathode environment

Abstract Effects of minor alloying elements (Si, Mn, and Al) on the corrosion resistance behaviors of stainless steel (SS) modified 310S used as a cathode current collector (CCC) material for molten carbonate fuel cells (MCFC) were examined in a mixture of 62 mol% Li2CO3–38 mol% K2CO3 at 650 °C by measuring the change in corrosion potential and the potentio-dynamic, potentio-static polarization responses. The corrosion potential of modified 310S gradually increased after 9 h of immersion due to an active to passive transition and that of SSs added with minor alloying elements drastically increased before 6 h of immersion due to the reactive alloys. Si, Mn, and Al addition to base SS led to a decrease in corrosion resistance due to the rapid corrosion rate at the cathode operation potential, −40 mV, of the MCFC. The steady state current densities of SSs added with minor alloying elements were higher than that of 310S and modified 310S. Addition of Si, Mn, and Al induced a decrease in corrosion resistance of CCC materials in molten carbonate fuel cell operating temperatures, 650 °C.

Model-based quantitative characterization of anode microstructure and its effect on the performance of molten carbonate fuel cell

This paper presents research on the impact of the material microstructure on the performance of Molten Carbonate Fuel Cells (MCFC). The study is motivated by the need to increase the operation time of MCFC stacks. As the MCFC stacks are mainly composed of porous materials, the paper shows the impact of the porosity on both fuel cell performance and degradation rate. The study is based on the mathematical model, validated through experiments with varying microstructure parameters, achieving an overall relative error of 8%. The study evaluated the performance of MCFC using anodes with different porosity and found that increasing anode porosity from 40% to 70% led to a nearly two-fold increase in maximum power density. However, from both the degradation test and polarization curves, the optimal level of porosity for the anode is around 55%. The porosity level at 55% ensures the highest catalytic surface of the electrodes and is a compromise between the mechanical properties of the electrode and its electrochemical properties.

An experimental study of the effects of key operating parameters on the molten carbonate fuel cell performance

Proper selection of the operating conditions of molten carbonate fuel cells (MCFCs) can not only effectively improve the efficiency of power generation, but also reduce carbon emissions and help achieve the great goal of “carbon neutrality”.

Integration of molten carbonate fuel cell and looped multi-stage thermoacoustically-driven cryocooler for electricity and cooling cogeneration

Thermal management is essential for high-temperature molten carbonate fuel cell (MCFC) because the accumulated waste heat may degrade the durability. In this paper, looped multi-stage thermoacoustically-driven cryocooler (LMTC) is proposed to reuse the waste heat from MCFC for cooling production, which not only can tackle with the thermal management issue but also can provide additional usages. Accounting various irreversible dissipation, the models of MCFC, LMTC and MCFC-LMTC hybrid system are analytically formulated. Performance features of MCFC-LMTC hybrid system are revealed and the advantages are expounded via calculation examples. Calculations indicate that the maximum power density and corresponding efficiency of the hybrid system are 1688.9 W m−2 and 39.7%, which are 11.4% and 1.3% bigger than that of the sole MCFC system, respectively. By comparing with other available systems, the superiority of using LMTC to recover MCFC waste heat for refrigeration is clearly demonstrated. Considerable parametric studies show that the heat-transfer coefficient of hot heat exchange for LMTC is not suggested to be greater than 2.5 × 10−3 W m−2 K−1. In addition, an increase in the working temperature, working pressure of MCFC, reactant concentration or engine stage number of LMTC positively benefits the hybrid system performance, while an increase in the thermodynamic loss coefficient worsens the hybrid system performance. The obtained results may offer new insights into improving the performance of MCFCs through thermal management approaches.

Investigation of the filling of a porous ceramic matrix by molten salts using nano X-ray tomography

High-resolution nano X-ray computed tomography (nano-XCT) was used to investigate the process of infiltration of a Molten Carbonate Fuel Cell (MCFC) matrix by liquid electrolyte. A ceramic matrix made of a LiAl 2O3 powder was infiltrated by a liquid electrolyte during the start-up process of the MCFC. Nano-XCT extends the state-of-the art techniques for characterizing the morphology of the ceramic matrix and for the study of the penetration kinetics with electrolyte. Quantitative morphology analysis using high-resolution nano-XCT provides 3D information for each MCFC component nondestructively. The spatially resolved volume fraction of the molten electrolyte calculated from the 3D XCT data is used for simulation and to improve MCFC performance. Based on the results obtained, a new start-up procedure is proposed for a single MCFC. This procedure is consistent with the morphology changes which occur during the melting process inside the ceramic matrix.

Experimental and Modeling Investigation of CO3=/OH– Equilibrium Effects on Molten Carbonate Fuel Cell Performance in Carbon Capture Applications

Molten Carbonate Fuel Cells (MCFCs) are used today commercially for power production. More recently they have also been considered for carbon capture from industrial and power generation CO2 sources. In this newer application context, our recent studies have shown that at low CO2/H2O cathode gas ratios, water supplements CO2 in the electrochemical process to generate power but not capture CO2. We now report the direct Raman observation of the underlying carbonate-hydroxide equilibrium in an alkali carbonate eutectic near MCFC operating conditions. Our improved electrochemical model built on the experimental equilibrium data adjusts the internal resistance terms and has improved the representation of the MCFC performance. This fundamentally improved model now also includes the temperature dependence of cell performance. It has been validated on experimental data collected in single cell tests. The average error in the simulated voltage is less than 4% even when extreme operating conditions of low CO2 concentration and high current density data are included. With the improvements, this electrochemical model is suitable for simulating industrial cells and stacks employed in a wide variety of carbon capture applications.

The Effect of Atomic Layer Deposition of ZrO2 on the Cathode on the Performance of Molten Carbonate Fuel Cell

Molten carbonate fuel cell (MCFC) is a high-temperature fuel cell for power plants. Since MCFC is operated at approximately 650 °C, the lifetime of the MCFC is limited by the thermal degradation of MCFC components. To reduce thermal degradation, the lower temperature for long-term operation is suggested. However, the electrochemical reaction on the cathode becomes slower at the lower operational temperature. To improve the performance for the long-term operation of MCFC, a ZrO2 coated cathode was fabricated by atomic layer deposition. The cell using the ZrO2 coated cathode showed a high voltage of 0.867 V at a temperature of 600 °C and a current density of 150 mA/cm2. The charge transfer resistance is also reduced dramatically at that same time. It can be confirmed that the high cell performance is presented when the electron-rich environment of NiO by ZrO2 coating improved the performance of the cell. Also, the cell using the ZrO2 coated cathode kept a stable performance over 2,000 h due to the prevention of NiO sintering by the uniform ZrO2 coating layer.

Optimal design of molten carbonate fuel cell combined cycle power plant and thermophotovoltaic system

A novel hybrid system consisting of a molten carbonate fuel cell (MCFC), a gas turbine (GT), a steam cycle and a thermophotovoltaic (TPV) system to generate power is introduced and investigated. For this purpose, a GT is coupled to a MCFC in order to utilize unused fuel, raise the gas components temperature, supply the required carbon dioxide, and further power generation. Moreover, in order to boost the power generation and ameliorate the overall efficiency, a TPV system together with a steam cycle has been added to the system for heat recovery from the combustion chamber radiation and cathode output stream, respectively. The simulation of the hybrid system was accomplished through ASPEN HYSYS and MATLAB software. The effect of different influential parameters on each sub-system as well as the proposed hybrid system was examined comprehensively through sensitivity analysis. The results obtained revealed that increasing MCFC temperature decreased the anode, cathode, and ohmic overpotentials, while augmented the output voltage of the MCFC led to enhanced MCFC performance. Furthermore, the output voltage, power density, and efficiency of the MCFC enhanced with increasing the operating pressure for both of the fuel consumption rates. The output voltage and power density of the MCFC decreased as the fuel consumption rate incremented due to increased polarization losses, while the electrical efficiency of the MCFC enhanced. Optimizing the output temperature of the first and second heat exchangers increased the power of the steam turbine by about 16 kW. The highest power density and performance of the TPV system was obtained at cell and emitter distance of 1 cm. Incorporating the GT to the MCFC enhanced the system’s efficiency to 54.83%. The efficiency of the proposed hybrid system was found to be 67.3%.

Preliminary theoretical and experimental analysis of a Molten Carbonate Fuel Cell operating in reversible mode

An isothermal electrochemical model of a Molten Carbonate Fuel Cell (MCFC) operating in reversible mode is presented. Firstly, the model has been fitted with experimental data of a single MCFC operating only in fuel cell mode. Then, the MCFC model was used to calculate the overpotentials of the cell operating as electrolyzer. Additionally, equations were added to calculate the concentration overpotentials in the fuel and oxygen electrode, useful to improve the prediction of the limiting current densities where the fuel started to lack. The validation of the model simulating the operation of the cell in reversible mode was carried out with experimental data obtained on a single MCFC operating in reversible mode. The results indicate that in general the model predicts cell performance well when several parameters like temperature, composition in the fuel electrode and composition in the oxygen electrode are varied around a nominal operating point. Concerning the electrolysis operation of the cell, the theoretical thermo-neutral voltage is presented, as well as the power consumption and hydrogen production when the cell operates at the thermo-neutral voltage. Finally, the hydrogen production was validated comparing the experimental and numerical hydrogen molar fraction present at the exit of the fuel electrode.

New, Dual-Anion Mechanism for Molten Carbonate Fuel Cells Working as Carbon Capture Devices

Molten Carbonate Fuel Cells (MCFCs) are commercially employed in MW-scale power production, and recently are being developed also for carbon capture. Past experiments showed that MCFC performance with wet cathode feeding was higher than with dry cathode feeds at otherwise similar conditions. This was ascribed to a mechanism that predicted the water increasing the apparent CO2 diffusion rate. However, recent tests performed at low CO2 cathode feed concentrations, as in carbon capture service, showed the emergence of a different water effect. Namely, there seems to be an electrochemical reaction path attributable to water, involving hydroxide ions that runs parallel with the main path involving CO2. This results in lower CO2 transfer from the cathode to the anode than what can be calculated from the electrical current. For the first time, here, a theoretical analysis will be presented to introduce a kinetic expression for MCFCs working under this dual-ion regime. Focus will be given to the expression of CO2 and water polarization to assess the ratio between the current due to the two anions. Simulation and experimental results will be discussed providing a reliable and effective basis for the performance optimization of the MCFCs both in power and in carbon capture applications.

Molten Carbonate Fuel Cell Performance for CO2 Capture from Natural Gas Combined Cycle Flue Gas

CO2 capture and sequestration (CCS) from stationary flue gas sources is one of the critical technologies needed as the future energy landscape shifts to low carbon intensity energy systems. Molten carbonate fuel cells (MCFCs) have the potential to capture CO2 from flue gas at higher thermal efficiency than traditional CCS technologies while simultaneously producing electricity. Herein, we present an investigation of molten carbonate fuel cell behavior at carbon capture conditions using simulated natural gas combined cycle flue gas. Measurements at these low CO2 and high current conditions reveal a lower than expected cathodic consumption of CO2 Based on the strong dependence of this deviation on water partial pressure as well as mass balances revealing a net consumption of water at the cathode, a parallel oxygen reduction mechanism is proposed. In this mechanism, water and oxygen are consumed at the cathode to produce hydroxide ions which migrate through the electrolyte to the anode. This parallel mechanism contributes to power generation but not to CO2 capture. Mass transport limitations in the molten carbonate fuel cell cathode were identified as the primary driver for this alternative mechanism which were heavily influenced by the design of the current collector and cathode interface.

Study on LiI and KI with low melting temperature for electrolyte replenishment in molten carbonate fuel cells

Molten carbonate fuel cells (MCFCs) are regarded as the closest fuel cell to commercialization due to their high capacity and energy efficiency. However, they are operated at a high temperature (620 °C or higher), where liquid electrolyte loss occurs during operation; hence, their lifetime is limited. For the long-term operation of MCFCs, it is essential to develop a novel method to replenish the electrolyte during operation. However, it is very difficult to directly inject the electrolyte, (Li0.62K0.38)2CO3, into each unit cell of the stack unless it is supplemented through liquid or gas phase at low temperature. It was verified whether LiI and KI, which have low melting points and high vapor pressures, could replenish the lost electrolyte in MCFCs. In this study, the LiI and KI injected into the unit cell in liquid phase showed a similar tendency to the Li/K carbonate electrolyte. This is because LiI and KI react with the CO2/O2 gases supplied to the cathode during MCFC operation to form Li/K carbonate electrolytes.

Review of Fuel Cell Technologies with CO2 Capture

In 2016, the IEA estimated that CO2 emissions from the production of energy represented 42% of the total global emissions. To limit the increase of the Earth’s temperature to 1.5oC above pre-industrial levels in the framework of the Paris agreement, more than 1,950 GWe must be decarbonised within the power sector. Currently, the most advanced CO2 capture (CC) technologies applied to large-scale power plants are post- and pre-combustion capture and oxyfuel combustion. However, the main drawback of these technologies is the energy penalty, and consequent efficiency loss, which leads to a high Levelized Cost of Electricity (LCOE). As a result, novel energy systems, which promise high efficiency and low CO2 emissions, such as fuel cell (FC) hybrid power cycles with CC, merit research, development and detailed analysis of their potential economics. The objective of this paper is to review the techno-economic status of Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC) technologies for CC application. This includes their development status, optimal configurations, economic analysis, challenges to reach commercial operation and time frame to develop as candidates for future deployment at commercial scale. SOFCs and MCFCs have emerged as potential technologies in CC systems, with the added advantage of providing additional power production. Although promising, neither SOFCs nor MCFCs are commercially available for CC applications, primarily due to their low technological maturity and high associated costs of the FCs. The current authors have identified gaps in the literature that requires a unique study, containing a number of potential configurations, with an updated and homogeneous approach to assess the techno-economic performance of SOFCs and MCFCs as CC systems in power plants.

Metal Oxides As Additives to Improve Anode Performance in Molten Carbonate Fuel Cells (MCFC)

In molten carbonate fuel cells (MCFC), oxidation of solid carbon fuels takes place at extended three-phase boundary (TPB) as molten carbonate electrolyte enhances the reaction interface in the anode compartment of the cell and facilitates diffusion of reactants. It also acts as an electrochemical mediator in oxidising carbon or carbon monoxide to carbon dioxide. Several studies have already been conducted to improve electrolyte’s performance in anode by either changing its composition or adding additives, i.e. metal oxides. Electrolyte composition effect, in terms of using different metal carbonates and their quantity in the mixture, on the performance of MCFC has been extensively investigated in the literature. However, comparing different additives effect on the overall performance of a cell using available data in the literature is not viable. This is because of lack of consistency in previous studies’ experimental conditions and specifically in anode composition. Also, there is not an agreement on mechanism that metal oxides improve the performance of MCFCs. In the current study, two different percentages (5 and 10 wt%) of SnO2, CeO2, Fe2O3, and Mn2O3 were used as additives to electrolyte and fuel mixture of the anode. Performances of the full cell with different additives were evaluated in the same conditions using polarisation (IV) and electrochemical impedance spectroscopy (EIS) tests. In addition, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were performed on anode slurry samples to further investigate details of the interactions between the anode electrolyte components. Based on the results, we provide a clear comparison on the effectiveness of these metal oxides in improving the cell performance and also suggest a mechanism that metal oxides enhance performance of anode in molten carbonate fuel cells.

Corrosion-resistant coating for cathode current collector and wet-seal area of molten carbonate fuel cells

High-temperature corrosion of metallic bipolar plates is a main problem to limit system reliability of molten carbonate fuel cells (MCFCs). In particular, cathode current collector (CCC) and wet-seal area in the bipolar plates suffer severe corrosion during MCFCs operation. Herein, we are trying to explore facile and cost-effective coating materials and methods to enhance corrosion resistance of CCC and wet-seal area of MCFCs. Cobalt (Co) layer was coated by using electrodeposition method for CCC, and aluminum (Al) layer was coated by using mechanical cladding method for wet-seal area. Co and Al layers were transformed into in-situ lithiated oxides, which are LiCoO2 and LiAlO2, by reacting with electrolytes without detachment. These in-situ formed oxides efficiently impede formation and growth of corrosion scales by preventing permeation of electrolytes. We believe that Co electrodeposition and Al cladding would be suitable and practical methods for making protective layers to enhance corrosion resistance of CCC and wet-seal area in the MCFCs bipolar plates.

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

High‐resolution computed X‐ray tomography (XCT) is applied in this study to characterize the microstructure of Molten Carbonate Fuel Cell (MCFC) cathodes after operation, where a “virgin cathode” formed by porous nickel has been in situ oxidized and infiltrated by liquid electrolyte. This technique extends state‐of‐the art methodology to characterize pores such as porosity analysis using Mercury porosimetry. XCT enables 3D imaging of the internal structure of the electrodes including all components present at the cathode side, particularly NiO, pores, and electrolyte. The quantitative 3D microstructure analysis based on high‐resolution XCT provides topological information for each component and their mutual spatial distribution, which is significant for the enhancement of the MCFC performance. In particular, volume fraction, specific surface area, continuity of each phase, as well as the Triple Phase Boundary (TPB) density are calculated from the experimental data. The results indicate that superior properties of the multi‐modal pore sized cathode, used in this study, can be attributed to the formation of three self‐interpenetrating networks of pathways for the transport of gasses, electrons, as well as ions throughout pores, NiO, and electrolyte, respectively.

Manufacturing of γ-LiAlO2 matrix for molten carbonate fuel cell by high-energy milling

Molten carbonate fuel cells (MCFCs) are promising high temperature power generating devices. However, unlike solid oxide fuel cells (SOFCs) they utilize a liquid electrolyte which must be immobilized in a porous matrix.In this paper, a slurry composition for lithium aluminate (γ-LiAlO2) matrix was developed and green matrices were subsequently formed by the tape casting method. In order to achieve the desired structure of the matrix (pore size, porosity) γ-LiAlO2 powder was milled in a planetary ball mill for 18 h with a solvent, dispersant and defoamer. After this step, other ingredients were added, including a binder and plasticizer to obtain optimal rheology of the slurry. Cell tests confirmed optimal performance of the matrix compared to the third party reference γ-LiAlO2 matrices. Burned out matrix was characterized by scanning electron microscopy (SEM) and laser diffraction in order to determine the γ-LiAlO2 powder particle size and morphology. The results show that high-energy milling enabled a fine pore structure and high specific surface area of the matrix to be obtained in a relatively short time, compared to conventional fabrication routes. The matrix structure obtained within this study is suitable for high performance operation of MCFC.

Multi-modal porous microstructure for high temperature fuel cell application

In this study, the effect of microstructure of porous nickel electrode on the performance of high temperature fuel cell is investigated and presented based on a molten carbonate fuel cell (MCFC) cathode. The cathode materials are fabricated from slurry consisting of nickel powder and polymeric binder/solvent mixture, using the tape casting method. The final pore structure is shaped through modifying the slurry composition - with or without the addition of porogen(s). The manufactured materials are extensively characterized by various techniques involving: micro-computed tomography (micro-XCT), scanning electron microscopy (SEM), mercury porosimetry, BET and Archimedes method. Tomographic images are also analyzed and quantified to reveal the evolution of pore space due to nickel in situ oxidation to NiO, and infiltration by the electrolyte. Single-cell performance tests are carried out under MCFC operation conditions to estimate the performance of the manufactured materials. It is found that the multi-modal microstructure of MCFC cathode results in a significant enhancement of the power density generated by the reference cell. To give greater insight into the understanding of the effect of microstructure on the properties of the cathode, a model based on 3D tomography image transformation is proposed.

Performance assessment of an integrated molten carbonate fuel cell-thermoelectric devices hybrid system for combined power and cooling purposes

In order to recover the waste heat produced in molten carbonate fuel cells (MCFCs), a new hybrid system mainly consisting of an MCFC, a thermoelectric generator, and a thermoelectric cooler is integrated for performance enhancement. The irreversible losses in each subsystem are fully considered. The relationship between the dimensionless electric current of the thermoelectric element and the electric current density of the MCFC is discussed in detail. Based on non-equilibrium thermodynamics, the analytical formulas for power density and efficiency of the hybrid system are specified under different operation conditions. The general performance characteristics of the hybrid system are revealed and the optimum regions for several parameters are given. Numerical calculations show that the power density and efficiency of the hybrid system are 3.4% and 4.0% larger than that of the stand-alone MCFC, respectively. The effects of some main operating and design parameters on the performance of the proposed system are discussed through parametric analyses. Abundant numerical calculation examples are provided to show how to improve the system performance. The results obtained may provide some theoretical bases for the MCFC performance improvement through heat management method.

Catalytic activity of NiO cathode in molten carbonate fuel cells

Molten carbonate fuel cells (MCFCs) have attracted significant attention because of their potential contribution to the development of a sustainable and clean-energy society. MCFC performance is governed by cathodic transformation of carbon dioxide to carbonate anion in complex: gas – molten carbonate – solid surface system. Based on our recently proposed reaction mechanism together with the density functional theory (DFT) calculated activation barriers we created a simplified microkinetic model to predict the catalytic activity of the NiO cathode. Under the MCFC operation condition the cathode surface in close proximity to the triple phase boundary (TPB) is highly active towards electro-reduction of oxygen and simultaneous formation of carbonate anion. Our results explain why, despite a great effort devoted to modify the chemical composition of the cathode, a substantial increase in the MCFC performance has not been observed, and the in-situ oxidized nickel remains state-of-the-art cathode material.