Molten carbonate fuel cell (MCFC) technology continues to attract significant attention due to its high performance over a range of carbon-containing fuel gases and non-toxic chemistry of its ...carbonate electrolyte which makes it especially suitable for biofuels. Steady improvements in performance have been achieved by optimizing the properties of MCFC components, including anode, cathode and LiAlO
2
matrix. Issues related to creep and sintering of porous Ni anodes have been resolved by adding Al as an alloying element, which improves not only the mechanical strength but also the wettability of the anode. Ni electrodes oxidized and lithiated during initial operation of a fuel cell or fuel cell stack (“in situ lithiation”) are commonly used as the cathodes, which generates optimal pore structure while decreasing the dissolution of NiO into the molten carbonate electrolyte to an acceptably low level. Porous LiAlO
2
, as a bed of very fine particles tape-cast and sintered to form a matrix for the molten carbonate electrolyte, serves as the membrane between anode and cathode. Despite these continuing improvements, fundamental understanding of the factors which determine the long-term stability of the MCFC components (anode, cathode, and matrix) in the extremely corrosive molten carbonate environment is still incomplete. In particular, the wetting behavior of the complex solid/liquid/gas phase in MCFC system remains to be understood more completely, which is essential to reduce the cost and improve the lifetime of MCFC. In the present review, the technical issues of the components and their wetting properties are addressed and insights to guide future research are provided.
Synthesis of trifunctional inorganic/organic hybrid nanocomposites and their applications for recognition and elimination of heavy metal ions.
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•Core-shell nanoparticles with magnetic ...Fe3O4 as core and porous SiO2 as shell were synthesized, and the inorganic/organic hybrid nanocomposites based on core–shell Fe3O4@SiO2 was fabricated using “grafting-from” strategy.•The nanocomposites showed selective fluorescence response toward Fe3+.•The nanocomposites were an excellent adsorbent for Fe3+, Zn2+, Hg2+ and Pd2+, and could be recycled by desorption of Na2EDTA.•The nanocomposites had superparamagnetism and strong magnetic sensitivity in favour of the sustainable removal of heavy metal ions in practical applications.
The core–shell nanoparticles with magnetic Fe3O4 as core and porous SiO2 as shell were synthesized by the hydrolysis and condensation of tetraethyl orthosilicate on Fe3O4 seed in an alkaline medium. Subsequently, the inorganic/organic hybrid nanocomposites based on core–shell Fe3O4@SiO2 nanoparticles were fabricated using “grafting-from” strategy, in which a macrocyclic dioxotetraamine (1,4,8,11-tetraazacyclotetradecane-5,7-dione, TACTDD) was grafted onto the end of Fe3O4@SiO2 surface. The as-synthesized nanocomposites possessed three functionalities: Firstly, the nanocomposites showed a selective fluorescence response toward Fe3+ ion with a detection limit of 6.0 × 10−7 mol/L, the eye-perceived fluorescence quenching under ultraviolet light could be used for the qualitative recognition of Fe3+ ion; Secondly, the nanocomposites were an excellent adsorbent, the adsorption efficiency for Fe3+ could reach 99.6% when the initial concentration was 200 mg/L without pH preadjustment, and over 85% for Zn2+, Hg2+ and Pd2+ ions. Moreover, the nanocomposites could be recycled by Na2EDTA, the desorption ratio of Fe3+, Zn2+, Hg2+ and Pd2+ ions only reduced slightly with six cycles, and all remained above 91%; Thirdly, the nanocomposites had superparamagnetism with a magnetization of 29.6 emu/g, this strong magnetic sensitivity can facilitate the sustainable removal of heavy metal ions in practical applications.
The dynamic contact angle of molten carbonate in first contact with porous Ni was measured as a function of porosity and thickness of the substrate, and of the amount of carbonate as a fraction of ...the empty pore volume available (“degree-of-filling”). The spreading of molten carbonate on the outer surface, and its penetration inside the porous Ni substrate were observed separately, and the time to complete absorption of a known mass of melt was measured under different conditions of substrate porosity, thickness and degree-of-filling. The average absorption rate and the average linear velocity over the initial void cross-section were determined and correlated with substrate characteristics. A straightforward quasi-linear correlation with control variables was found. However, although initial filling is capillary-force controlled, later stages of absorption appear slowed down significantly by viscous and inertial effects. This helps to understand why capillary equilibrium models do not accurately predict electrolyte redistribution in long-term performance. Moreover, post-test analysis indicates that on first contact of porous Ni substrates with molten carbonate, sintering of Ni particles occurs even at the relatively low temperature of 580 °C. Models for initial filling need to account for this initial accelerated sintering. The result of this work may be used to optimize the infiltration process of electrolyte into the porous MCFC electrodes.
•Dynamic wetting of porous Ni substrate was investigated using sessile drop method.•Effects of porosity, thickness, and d.o.f. on dynamic wetting were revealed.•The initial filling is capillary-force controlled.•The later filling apparently appears slowed down by viscous and inertial effects.•Molten carbonate accelerates the sintering of Ni particles in the substrate.
Cracking of α-LiAlO2 matrices in molten carbonate fuel cells (MCFC) leads to reduction in the performance. It was demonstrated in this work that the mechanical strength of α-LiAlO2 matrices is ...improved by heat-treating at 800°C under ambient gas atmosphere. The mechanical strength (2.91MPa) of the heat-treated matrix was enhanced more than 5 fold compared to the non-heat-treated matrix (0.58MPa). The porosity and crystal structure of the α-LiAlO2 matrices were not changed after the heat-treatment. The wetting behavior and distribution of carbonate in the heat-treated and the non-heat-treated matrix were investigated and compared. Both non-heat-treated and heat-treated α-LiAlO2 matrices were completely wetted by molten carbonate. The molten carbonate distribution was concentrated right underneath the circular region formed by the molten carbonate drop in the matrix. Non-heat-treated α-LiAlO2 samples cracked as a result of the complete absorption of molten carbonate, however, the heat-treated α-LiAlO2 matrices did not crack, presumably due to their enhanced mechanical strength.
Doping CeO2 with Y cations was achieved in this study using three strategies: doping only during the hydrothermal process (H-Y-doped CeO2), doping only during the impregnation process (I-Y-doped ...CeO2), and doping during both the hydrothermal and impregnation processes (H/I-Y-doped CeO2). During the three synthesis strategies of Y-doped CeO2, these Y ions could be incorporated into the CeO2 lattice in the +3 state while holding the cubic fluorite structure, and no impurity phases were detected. Pure CeO2 crystal itself contained a certain number of intrinsic VO defects, and Y-doping was beneficial for the creation of extrinsic VO defects. The relative concentrations of VO defects were quantified by the values of A592/A464 obtained from Raman spectra, which were 1.47, 0.93, and 1.16 for the H-Y-, I-Y-, and H/I-Y-doped CeO2, respectively, and were higher than that of the undoped one (0.67). Moreover, the OSCs of the three Y-doped CeO2 were enhanced, and the sequence of OSCs was: H-Y-doped CeO2 (0.372 mmol/g) > H/I-Y-doped CeO2 (0.353 mmol/g) > I-Y-doped CeO2 (0.248 mmol/g) > Undoped CeO2 (0.153 mmol/g); this result was in good agreement with the Raman spectroscopy results.
Doping CeOsub.2 with Y cations was achieved in this study using three strategies: doping only during the hydrothermal process (H-Y-doped CeOsub.2), doping only during the impregnation process ...(I-Y-doped CeOsub.2), and doping during both the hydrothermal and impregnation processes (H/I-Y-doped CeOsub.2). During the three synthesis strategies of Y-doped CeOsub.2, these Y ions could be incorporated into the CeOsub.2 lattice in the +3 state while holding the cubic fluorite structure, and no impurity phases were detected. Pure CeOsub.2 crystal itself contained a certain number of intrinsic Vsub.O defects, and Y-doping was beneficial for the creation of extrinsic Vsub.O defects. The relative concentrations of Vsub.O defects were quantified by the values of Asub.592/Asub.464 obtained from Raman spectra, which were 1.47, 0.93, and 1.16 for the H-Y-, I-Y-, and H/I-Y-doped CeOsub.2, respectively, and were higher than that of the undoped one (0.67). Moreover, the OSCs of the three Y-doped CeOsub.2 were enhanced, and the sequence of OSCs was: H-Y-doped CeOsub.2 (0.372 mmol/g) > H/I-Y-doped CeOsub.2 (0.353 mmol/g) > I-Y-doped CeOsub.2 (0.248 mmol/g) > Undoped CeOsub.2 (0.153 mmol/g); this result was in good agreement with the Raman spectroscopy results.
Two kinds of Darboux-Bäcklund transformations (DBTs) are constructed for the q-deformed Nth KdV hierarchy with self-consistent sources (q-NKdVHSCS) by using the q-deformed pseudodifferential ...operators. Note that one of the DBTs provides a nonauto Bäcklund transformation for two q-deformed Nth KdV equations with self-consistent sources (q-NKdVESCS) with different degree. In addition, the soliton solution to the first nontrivial equation of q-KdVHSCS is also obtained.
Dynamic wetting of dense Ni foil by molten carbonate Gao, Liangjuan; Selman, J. Robert; Nash, Philip
Colloids and surfaces. A, Physicochemical and engineering aspects,
08/2018, Volume:
550, Issue:
C
Journal Article
Peer reviewed
Open access
Dynamic contact angles on dense Ni foil under reducing and pure CO2 atmospheres were measured and evidence detected of the water-gas shift reaction taking place on the nickel substrate if the ...atmosphere contains hydrogen.
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Wetting is an important factor that affects the active reaction area inside the porous Ni anode in molten carbonate fuel cell stacks. To provide a relatively simple base case, the dynamic wetting of the dense Ni foil was investigated under different atmospheres, including reducing atmosphere (80%H2 + 20%CO2 humidified at 45 °C), pure CO2 atmosphere and, oxidizing atmosphere (1%O2 + 99%N2). It was demonstrated that the water-gas shift reaction occurs at the interface of dense Ni foil and the molten carbonate under reducing atmosphere but not under CO2 atmosphere and oxidizing atmosphere. The contact angle was affected by the mass of the carbonate pellet under reducing atmosphere but not under CO2 atmosphere. The contact angle decreased rapidly under oxidizing atmosphere due to the formation of nickel oxides on the surface.
A cubic fluorite-type CeO
with mesoporous multilayered morphology was synthesized by the solvothermal method followed by calcination in air, and its oxygen storage capacity (OSC) was quantified by ...the amount of O
consumption per gram of CeO
based on hydrogen temperature programmed reduction (H
-TPR) measurements. Doping CeO
with ytterbium (Yb) and nitrogen (N) ions proved to be an effective route to improving its OSC in this work. The OSC of undoped CeO
was 0.115 mmol O
/g and reached as high as 0.222 mmol O
/g upon the addition of 5 mol.% Yb(NO
)
∙5H
O, further enhanced to 0.274 mmol O
/g with the introduction of 20 mol.% triethanolamine. Both the introductions of Yb cations and N anions into the CeO
lattice were conducive to the formation of more non-stoichiometric oxygen vacancy (
) defects and reducible-reoxidizable Ce
ions. To determine the structure performance relationships, the partial least squares method was employed to construct two linear functions for the doping level vs. lattice parameter and
vs. OSC/
.
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