A personal retrospect on three decades of high temperature fuel cell research; ideas and lessons learned

In1986 the Dutch national fuel cell program started. Fuel cells were developed under the paradigm of replacing conventional technology. Coal-fired power plants were to be replaced by large-scale MCFC power plants fuelled by hydrogen in a full-scale future hydrogen economy. With today's knowledge we will reflect on these and other ideas with respect to high temperature fuel cell development including the choice for the type of high temperature fuel cell. It is explained that based on thermodynamics proton conducting fuel cells would have been a better choice and the direct carbon fuel cell even more so, with electrochemical gasification of carbon as the ultimate step. The specific characteristics of fuel cells and multisource multiproduct systems were not considered, whereas we understand now that these can provide huge driving forces for the implementation of fuel cells compared to just replacing conventional combined heat and power production technology.     

H2S removal from biogas for fuelling MCFCs: New adsorbing materials

Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na₂CO₃ solutions were studied as H₂S sorbents for biogas purification for fuelling molten carbonate fuel cells. H₂S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H₂S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h⁻¹) of 8 ppm H₂S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H₂S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H₂S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na₂CO₃ solutions improved the H₂S adsorption properties: AC treated with Na₂CO₃ was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC.     

An MCFC operation optimization strategy based on PID auto-tuning control

Molten Carbonate Fuel Cell (MCFC) has been emerging as a promising renewable power system. It is still challenging to operate the MCFC to meet its varying demands because of its nonlinearity and complex dynamics. This paper proposes a novel MCFC operation framework based on PID auto-tuning control. A case study is presented to illustrate the applicability of the strategy with some comments.     

Comparison study on different ITM‐integrated MCFC hybrid systems with CO2 recovery using sweep gas

Previous study shows the ITM (oxygen ion transfer membrane)‐integrated MCFC (molten carbonate fuel cell) hybrid system with CO₂ recovery can maintain high efficiency; however, the oxygen partial pressure on the ITM permeate side is usually 1 atm, which requires a very high pressure ratio of the ITM air compressor in order to separate the oxygen; using the sweep gas can solve this problem. In this paper the ITM‐integrated MCFC hybrid systems with CO₂ recovery using different sweep gases are studied. With the Aspen plus software, two systems with different sweep gases are established, and their performances are compared with the benchmark system without sweep gas; the effects of key parameters on the optimum system performance are also investigated. Results show that compared with the benchmark system, the efficiencies of the systems with sweep gases are increased and the pressure ratios of the air compressors are decreased; the system using pure CO₂ as sweep gas can improve the system efficiency by 1.25%, which is superior to the system using the mixture gas of CO₂ and H₂O as sweep gas. Achievements from this paper will provide a valuable reference for CO₂ recovery from the MCFC hybrid power system with lower energy consumption. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimization of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine hybrid system for distributed power generation

In a previous study, a new hybrid system of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine was developed, where the HCCI engine replaces the catalytic burner and produces additional power by using the left-over heating values from the fuel cell stack. In the present study, to reduce the additional cost and footprint of the engine system in a hybrid configuration, the possibility of engine downsizing is investigated by using two strategies, i.e. the use of a turbocharger and the use of high geometric compression ratio for the engine design, both of which are to increase the density of the intake charge and thus the volumetric efficiency of the engine. Combining these two strategies, we suggest a new engine design with ∼60% of displacement volume of the original engine. In addition, operating strategies are developed to run the new hybrid system under part load conditions. It is successfully demonstrated that the system can operate down to 65% of the power level of the design point, while the system efficiency remains almost unchanged near 63%.     

Improved performance of molten carbonate fuel cells with (Li/Na)2CO3 electrolytes by using BYS coated cathode at low operating temperatures

In order to improve the stack life time of MCFCs, it is necessary to reduce the operating temperature of MCFCs below 600 °C, because reduced operating temperature minimizes electrolyte loss due to evaporation and corrosion. However, at the low operating temperature below 600 °C, the cell performance of MCFCs with (Li/Na)₂CO₃ electrolyte is too low to operate the fuel cell stack and system. In this study, we have performed wettability control of the liquid molten carbonate electrolyte by coating NiO cathodes with poor wetting property of the mixed ionic and electronic conductor (MIEC) such as BYS (Bi_1.5Y_0.3Sm_0.3O_3-δ). From experiments with symmetrical cells, each polarization component with various temperatures and gas conditions were studied. To investigate effects of the BYS coated cathode on the performance of MCFCs, a 100 cm² single cell of MCFCs was employed. The performance of a 100 cm² single cell with BYS coated cathode was better than that with conventional cathode by a factor of 1.84, because BYS coated cathode reduces activation polarization and mass transfer resistance greatly.     

Carbon capture: Energy wasting technologies or the MCFCs challenge?

Carbon dioxide is more and more pointed out as one of the factors mostly responsible of climate changes. As a consequence the reduction of CO₂ emissions, especially in the energy generation field, is becoming a worldwide must.This paper presents an overview on the main issues that are expected to affect, from this standpoint, power generation scenario and a spur for a critical comparison among ways to capture CO₂ by proposing new aspects to be considered within the evaluation criteria.In particular attention is drawn on the fully innovative opportunities that are offered by Molten Carbonate Fuel Cells (MCFCs) as a unique option suitable to effectively combine carbon capture from thermal plants and typical benefits of hydrogen and fuel cell power generation.As an example, such a new option is compared with one of the most common technologies forecast for reducing carbon dioxide emissions and relevant results are shortly presented.     

TiO2 protective coating processed by Atomic Layer Deposition for the improvement of MCFC cathode

One of the main issues for optimizing the molten carbonate fuel cell (MCFC) is the control of the corrosion and dissolution of the state-of-the-art porous nickel oxide cathode. A protective coating constituted by more stable oxides seems to be the best solution. In this paper, very thin layers of TiO₂ (50 and 300 nm) are processed by a sequential CVD technique, Atomic Layer Deposition (ALD), which produces high quality, homogeneous and conformal layers. Structural, morphological and electrochemical behaviors of TiO₂-coated samples are tested in a Li₂CO₃–K₂CO₃ (62:38 mol%) eutectic melt under a standard cathode atmosphere: CO₂/air (70:30 bar%). Ni solubility is determined by ICP-AES. The protective role of TiO₂ layers and the consequent decrease in Ni solubility have been clearly evidenced.     

A comparison between molten carbonate fuel cells based hybrid systems using air and supercritical carbon dioxide Brayton cycles with state of the art technology

A proposal for high efficiency hybrid systems based on molten carbonate fuel cells is presented in this paper. This proposal is based on adopting a closed cycle bottoming gas turbine using supercritical carbon dioxide as working fluid as opposed to open cycle hot air turbines typically used in this type of power generators.First, both bottoming cycles are compared for the same operating conditions, showing that their performances do not differ as much as initially expected, even if the initial objective of reducing compression work is accomplished satisfactorily. In view of these results, a profound review of research and industrial literature is carried out in order to determine realistic specifications for the principal components of the bottoming systems. From this analysis, it is concluded that an appropriate set of specifications must be developed for each bottoming cycle as the performances of compressor, turbine and recuperator differ significantly from one working fluid to another. Thus, when the operating conditions are updated, the performances of the resulting systems show a remarkable advantage of carbon dioxide based systems over conventional air units. Actually, the proposed hybrid system shows its capability to achieve 60% net efficiency, what represents a 10% increase with respect to the reference system.     

熔融碳酸盐燃料电池/燃气轮机混合装置发展现状

被誉为绿色能源的熔融碳酸盐燃料电池具有高效无污染的突出优点,是21世纪最有吸引力的发电方法之一.高品位的废热使得它可以和燃气轮机组成混合装置系统,从而大幅度地提高装置整体效率,在分布式发电领域具有十分重要的意义.本文介绍了燃料电池及混合装置的基本工作原理,并对燃料电池/燃气轮机混合装置的国内外的发展现状做了综合评述.