Materials development for intermediate temperature fuel cells

The work in this thesis mainly focuses on the preparation and optimization of materials for intermediate temperature fuel cells (ITFCs) with the aim of achieving high fuel cell performance as well as good stability. The fuel cell fabrication was also studied in order to develop a cost-effective fabrication process. Methods such as solid state reaction, combustion and carbonate co-precipitation were adopted for the synthesis of the materials. The densification temperature of Ce0.8Gd0.05Y0.15O1.9 (GYDC) electrolyte was greatly reduced by the carbonate co-precipitation synthesis and subsequently a simple one-step co-press-sintering fabrication process was developed. LiNO3 as sintering additive further reduced the densification temperature of GYDC and up to 96% relative density was achieved at 800 °C. Lithiated NiO was employed as cathode for IT-SOFCs and demonstrated good electrocatalytic activity. In addition, lithiated NiO was also investigated as both anode and cathode for IT-SOFCs and its stability was studied. Oxide-carbonate composites have demonstrated very high ionic conductivity as the melting of carbonates greatly enhanced the mobility of ions in materials. High power densities up to 670 mW cm-2 at 550 °C were achieved for the composite electrolytebased ITFCs. However, the traditional lithiated NiO cathode can gradually dissolve into the carbonate melt and scanning electron microscopy studies found obvious morphology change nearby the cathode/electrolyte interface which may be due to the dissolution of nickel ions. Perovskite oxide Sm0.5Sr0.5Fe0.8Cu0.2O3-δ (SSFCu) has been demonstrated to be a compatible and stable cathode for the composite electrolyte based ITFCs, as a stable current output of about 0.4 A cm-2 was observed under a constant voltage of 0.7 V during a cell test lasting 100 h. Instead of GYDC, BaCe0.5Zr0.3Y0.16Zn0.04O3-δ (BCZYZn) was also employed as substrate material for the carbonate composite electrolyte and SrFe0.7Mn0.2Mo0.1O3-δ (SFMMo) was developed and used as cathode

Electrochemical processes and systems: application for tutors

The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та технології"

Review of molten carbonate-based direct carbon fuel cells

Abstract Direct carbon fuel cell (DCFC) is a promising technology with high energy efficiency and abundant fuel. To date, a variety of DCFC configurations have been investigated, with molten hydroxide, molten carbonate or oxides being used as the electrolyte. Recently, there has been particular interest in DCFC with molten carbonate involved. The molten carbonate is either an electrolyte or a catalyst in different cell structures. In this review, we consider carbonate as the clue to discuss the function of carbonate in DCFCs, and start the paper by outlining the developments in terms of molten carbonate (MC)-based DCFC and its electrochemical oxidation processes. Thereafter, the composite electrolyte merging solid carbonate and mixed ionic–electronic conductors (MIEC) are discussed. Hybrid DCFC (HDCFCs ) combining molten carbonate and solid oxide fuel cell (SOFC) are also touched on. The primary function of carbonate (i.e., facilitating ion transfer and expanding the triple-phase boundaries) in these systems, is then discussed in detail. Finally, some issues are identified and a future outlook outlined, including a corrosion attack of cell components, reactions using inorganic salt from fuel ash, and wetting with carbon fuels

Electrochemical processes and systems: application for tutors

The features of redox reactions and the principles of their balancing according to the medium composition are considered. The basic representations about electrochemical processes and systems are outlined. The reactions and principles of chemical sources of electric energy and electrolysis systems functioning are analyzed. A general idea is given about the chemical properties of metals, corrosion resistance in environments of various aggressiveness, and the protection principles are given. Multivariate tasks and exercises for students, and PhD student’s classroom and independent work are offered. For teachers, PhD students and students of universities of specialties "Chemical technologies and engineering", "Biotechnologies and bioengineering", "Oil and gas engineering and technologies".Розглянуто особливості окисно-відновних реакцій і принципи їх балансування залежно від складу середовища. Викладено фундаментальні уявлення про електрохімічні процеси і системи. Проаналізовано перебіг реакцій і принципи функціонування хімічних джерел електричної енергії та систем електролізу. Узагальнено уявлення щодо хімічних властивостей металів, корозійної стійкості у середовищах різної агресивності та наведено принципи організації захисту від руйнування. Запропоновано багатоваріантні завдання та вправи для аудиторної та самостійної роботи студентів і аспірантів. Розраховано на викладачів, аспірантів і студентів вищих навчальних закладів спеціальностей "Хімічні технології та інженерія”, "Біотехнології та біоінженерія", "Нафтогазова інженерія та технології"

Application of infiltrated LSCM-GDC oxide anode in direct carbon/coal fuel cells

The authors would like to thank the European project ‘Efficient conversion of coal to electricity- Direct Coal Fuel Cells’, funded by the Research Fund for Coal & Steel (RFC-PR-10007).Hybrid direct carbon/coal fuel cells (HDCFCs) utilise an anode based upon a molten carbonate salt with an oxide conducting solid electrolyte for direct carbon/coal conversion. They can be fuelled by a wide range of carbon sources, and offer higher potential chemical to electrical energy conversion efficiency and have the potential to decrease CO2 emissions compared to coal-fired power plants. In this study, the application of (La, Sr)(Cr, Mn)O3 (LSCM) and (Gd, Ce)O2 (GDC) oxide anodes was explored in a HDCFC system running with two different carbon fuels, an organic xerogel and a raw bituminous coal. The electrochemical performance of the HDCFC based on a 1–2 mm thick 8 mol% yttria stabilised zirconia (YSZ) electrolyte and the GDC–LSCM anode fabricated by wet impregnation procedures was characterized and discussed. The infiltrated oxide anode showed a significantly higher performance than the conventional Ni–YSZ anode, without suffering from impurity formation under HDCFC operation conditions. Total polarisation resistance (Rp) reached 0.8–0.9 Ω cm2 from DCFC with an oxide anode on xerogel and bituminous coal at 750 °C, with open circuit voltage (OCV) values in the range 1.1–1.2 V on both carbon forms. These indicated the potential application of LSCM–GDC oxide anode in HDCFCs. The chemical compatibility of LSCM/GDC with carbon/carbonate investigation revealed the emergence of an A2BO4 type oxide in place of an ABO3 perovskite structure in the LSCM in a reducing environment, due to Li attack as a result of intimate contact between the LSCM and Li2CO3, with GDC being stable under identical conditions. Such reaction between LSCM and Li2CO3 was not observed on a LSCM–YSZ pellet treated with Li–K carbonate in 5% H2/Ar at 700 °C, nor on a GDC–LSCM anode after HDCFC operation. The HDCFC durability tests of GDC–LSCM oxide on a xerogel and on raw bituminous coal were performed under potentiostatic operation at 0.7 V at 750 °C. The degradation mechanisms were addressed, especially on raw coal.PostprintPeer reviewe

Coupled Electrochemo-Mechanical Phenomena at the Anode/Electrolyte Interface in Solid-State Batteries

With the ever-increasing demands for safe, reliable energy storage, solid-state batteries have emerged as a potential candidate to accelerate widespread adoption of electrified technology. While lithium-ion batteries currently dominate the rechargeable battery market, it is becoming apparent that these systems cannot provide the energy and power densities, lifetime, safety, and costs for electric vehicles requiring large format cells. However, by replacing the conventional liquid electrolyte with a solid-state electrolyte, advanced electrodes like alkali metal anodes could be enabled, which would provide significant advances in energy density, safety, and lifetime. However, despite the tremendous progress made in the field of solid-state batteries in the past decade, current solid-state battery performance generally remain inferior to that of incumbent technology. In an effort to better understand the limitations of solid-state batteries, this dissertation explores the coupled electrochemical and mechanical interactions between ceramic solid-electrolytes and alkali metal anodes. Two relevant model electrolyte systems, the Li7La3Zr2O12 garnet and the Na-β”-alumina electrolytes, are studied when coupled with Li metal and Na metal anodes, respectively. First, the effect of temperature on short-circuiting caused by penetration of the electroplated metal through the solid-electrolyte is explored. It is observed that both systems exhibit an increase in critical current density with increasing temperature. While both systems behave similarly qualitatively, the critical current densities of the Na-based system are significantly higher (12 mA cm-2 at room temperature) than that of the Li-based system (1 mA cm-2). The differences between the two systems are then correlated to differences in the mechanical properties and conductivities of the electrolytes using a fracture mechanics based model. Second, the effect of external stack pressure on unstable metal depletion at the anode/electrolyte interface is examined. It is demonstrated that at low stack pressures and/or high current densities, significant increases in cell resistance are observed in both systems. These increases in cell resistance are shown to be isolated to the metal stripping reaction, suggesting that the formation of voids at the electrode/electrolyte interface results in significant contact loss. The evolution of these voids is then analytically modeled to correlate morphological changes of the interface with distinct features in the cell cycling behavior. Lastly, Li metal electrodeposition onto a blocking electrode is explored for the enabling of “Li-free” battery manufacturing. It is observed that significant capacities (>5 mAh cm-2) of Li metal could be reversibly plated and stripped onto/from a current collector over several cycles with high efficiencies and the nucleation behavior onto the current collector is examined. To demonstrate proof-of-concept, prototypical all-solid-state batteries are manufactured with the “Li-free” approach exhibiting high efficiency. These designs introduce a novel approach toward improving the energy density and low-cost manufacturability of solid-state batteries. Overall, this dissertation explores the fundamental coupling between electrochemistry and mechanics at the anode/electrolyte interface in these systems and provides practical guidelines for the design, manufacturing, and operation of next-generation solid-state batteries.PHDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163176/1/micwan_1.pd

Ionic conduction mechanisms in nano-composite electrolyte and their relationship to micro-structural features

This study is based on a nano-composite electrolyte that is made up of samarium doped cerium oxide (SDC) skeleton within a sodium carbonate matrix. These nanocomposites have high ionic conductivities, even at temperatures as low as 400 °C. Our work revealed that the high interfacial interaction enhanced the ionic conduction behavior of the nano-composites by forming an interlayer between the oxide phase particles and the carbonate matrix which also provided structural connectivity. Consequently, the objective in this work is to address how the inter-phase affects ionic transport mechanisms, and under which circumstances the ionic conduction properties can be improved, especially in a two-phase nano-composite. The strength of influence of interfaces in ionic transport was also controlled by varying the amount of specific interface areas of the samarium doped ceria (SDC) particles in the nano-composite. In addition, the measurements conducted with composites with different amounts of the specific interface area of the SDC oxide particles in the electrolyte revealed insights into ionic conductivity of the composite. To control the value of specific surface area (SSA), the inverse relationship between the average particle size and SSA for SDC particles was employed. SDC particles with micron and nano-meter size distributions were mixed in order to obtain differing amounts of SSA in the composites between 47 m2.g-1 and 203 m2.g-1. The micro-structural investigations with SEM and TEM revealed that the Na2CO3 phase served as the glue in the composite. The glass-transition-like behavior was apparent in the thermal response of the nano-composite at 350 °C. Furthermore, the experimental results demonstrated that the overall ionic conductivity below 400 °C was controlled by the SSA. The activation energies for ionic conductivity were determined in temperature range of 25-600 °C using the Arrhenius conductivity (σT) versus inverse temperature plots in order to identify the ionic conductivity mechanisms. The activation energies are consistent with the calculated dissociation energy of the carbonate phase. The spectral elemental mapping by TEM-EELS mode showed that carbonate phase constituted the majority of the matrix. A rim around the SDC oxide particles with a high concentration of carbon was imaged. The strong dependence of the conductivity on the SSA, the differences in the activation energies, and spectral elemental mapping results suggested that the oxide surface acted as a dissociation agent for the carbonate phase. As a conclusion, the high ionic conductivities in the nano-composite electrolyte were the consequence of the oxide surface "liberating" ions, which can move more easily in the interaction region surrounding the oxide particles. The dependence of the ionic conductivity on the oxide particle amount was consistent with percolation type behavior of this interaction region, termed the "interphase" in this work

Investigations of Ni-SDC carbonate (Ni-SDCC) as composite anode for low temperature solid oxide fuel cells

Systematic research regarding NiO-SDC carbonate (NiO-SDCC) as composite anode is limited despite great chemical compatibility and cell performance achieved with other low temperature solid oxide fuel cell (LTSOFC) components. This study focuses to investigate the correlation of powder composition and calcination temperature on the chemical compatibility, morphologies, thermal and electrochemical performance of NiO-SDCC composite anode. NiO-SDCC composite powders with the weight ratios of 50:50 (NC55), 60:40 (NC64), and 70:30 (NC73) were achieved using high-energy ball-milling. All powders were calcined at 600–800 °C, pelletized and sintered at 600 °C. Characterisation include the crystalline phases, thermogravimetry, thermal expansion coefficient (TEC), hardness and morphologies were conducted. Electrochemical impedance spectroscopy (EIS) was conducted under in-situ reduction process. The powder and pellet morphologies, thermal expansion, and hardness were mostly affected by the calcination temperature as compared to powder composition. NC55 was selected for anode reduction process in hydrogen due for the least TEC values as compared to NC64 and NC73. The Ni-SDCC exhibited porosity of 36-40% after reduction process. The lowest area specific resistance of 5.3 Ωcm2 was achieved with sample calcined at 800 ℃. In this study, unexpected mechanical failure has been observed after EIS measurements. Therefore, chemical reactions and anode failure mechanisms were successfully proposed in this study. This mechanism is a new finding that has not been reported in previous studies and must be given appropriate attention. In conclusion, this study significantly contributes to the development of Ni-SDCC as LTSOFC composite anode. Further enhancement on this material is required on improved durability for LTSOFC application