Electrochemical intercalation of cationic and anionic species from a lithium perchlorate–propylene carbonate system—a rocking-chair type of dual-intercalation system

The reductive and oxidative intercalation of ionic species of lithium perchlorate (LiClO₄) in propylene carbonate (PC) medium are carried out to develop a dual-intercalation battery system. Cyclic voltammetry (CV), potentiostatic transients (i-t), galvanostatic charging, thermogravimetry (TG) and differential thermal analysis (DTA) are performed to establish the intercalation behaviour of both lithium and perchlorate ionic species. A polypropylene graphite composite electrode material containing 20 wt.% polypropylene as a binder is found to be a suitable host material for dual intercalation studies. The intercalation/de-intercalation efficiency (IDE) increases with increasing sweep rate and reaches up to 90% for Li⁺ and 65% for ClO₄⁻ ions at a sweep rate of 40 mV s⁻¹. The formation of a passive film decreases the IDE during the first intercalation/de-intercalation cycle. The open-circuit potential for a battery assembly involving these two electrodes is in the range 3.8 to 4.0 V.     

Lithium cycling efficiency of ternary solvent electrolytes with ethylene carbonate—dimethyl carbonate mixture

Lithium cycling efficiency for ternary solvent (mol ratio 1:1:1) electrolytes of different molar conductivities containing LiPF₆ and LiClO₄ with ethylene carbonate (EC)—dimethyl carbonate (DMC) binary mixture of constant mixed ratio (mol ratio 1:1) was investigated by galvanostatic experiments at 25 °C. The solvents applied to the EC-DMC mixture are 1,2-dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF) and ethylmethyl carbonate (EMC). The molar conductivity of the EC-DMC-DME ternary solvent electrolytes gradually increased with the addition of DME. However, the molar conductivities of the EC-DMC-2-MeTHF and EC-DMC-EMC ternary solvent electrolytes gradually decreased with the addition of 2-MeTHF and EMC. The decrease of the molar conductivity for these solutions is attributed to a decrease of the dissociation degree for electrolytes versus a decrease of the dielectric constant rather than that of the viscosity of the EC-DMC-2-MeTHF and EC-DMC-EMC ternary solvent mixtures. The lithium cycling efficiency of every ternary electrolyte containing LiPF₆ was larger than those of the EC-DME, EC-EMC and EC-DMC binary electrolytes containing LiPF₆ at about 20 cycles. Especially, the efficiency of LiPF₆/EC-DMC-DME electrolyte became about 80% at 40 cycles. The nickel (working) electrode surface in binary and ternary electrolytes after dissolution by cyclic voltammetry was observed by atomic force microscopy. The formation of lithium dendrite was already observed during the first cycle in the LiPF₆/EC-DMC electrolyte. However, it was found that the addition of ethers such as DME and 2-MeTHF to the LiPF₆/EC-DMC electrolyte was helpful to suppress the formation of lithium dendrite on the nickel electrode.     

Electrochemical characterization of LixNiyCo1−yO2 electrodes in a 1 M LiPF6 solution of the ethylene carbonate–diethyl carbonate

The electrochemical characteristics of Li_xNi_yCo_1−yO₂ (0.5<y<0.9) prepared by a co-precipitation method were reported. Slow scan cyclic voltammetry (SSCV) and electrochemical impedance spectroscopy (EIS) were used to investigate the kinetic behavior of the composite electrodes. Kinetic data such as the Tafel slope and the charge-transfer resistance were determined based on the experimental results. An equivalent circuit model was proposed to simulate the impedance spectra and gave a good data fit. The present study also demonstrated that the kinetic data were composition-sensitive to varying lithium content and nickel content in the mixed oxide electrodes.     

Study of molten carbonate fuel cell—microturbine hybrid power cycles

The interaction realized by fuel cell—microturbine hybrids derive primarily from using the rejected thermal energy and combustion of residual fuel from a fuel cell in driving the gas turbine. This leveraging of thermal energy makes the high temperature molten carbonate fuel cells (MCFCs) ideal candidates for hybrid systems. Use of a recuperator contributes to thermal efficiency by transferring heat from the gas turbine exhaust to the fuel and air used in the system.Traditional control design approaches, consider a fixed operating point in the hope that the resulting controller is robust enough to stabilize the system for different operating conditions. On the other hand, adaptive control incorporates the time-varying dynamical properties of the model (a new value of gas composition) and considers the disturbances acting at the plant (load power variation).     

Structural optimization of graphite for high-performance fluorinated ethylene–propylene composites as bipolar plates

This paper presents a novel method of structural optimization by using graphite particles ranging in size from 35 to 500 μm to fabricate conductive fluorinated ethylene–propylene composites for high-temperature bipolar plates. To investigate the effects of dispersion and packing density, the large graphite particles were decorated with fluorinated ethylene–propylene powders by ball milling, and the master batch of well-dispersed small graphite particles and polymer master batch was mixed with large graphite particles. The resulting fluorinated ethylene–propylene/graphite composite bipolar plates, which contained 65 wt% graphite, exhibited high electrical conductivity of 550 S cm^?1. In particular, by modulating the electrical transportation paths between the large graphite particles with the well-dispersed fluorinated ethylene–propylene/graphite master batch, the orientation and dispersion of the graphite particles in the matrix resulted in enhanced electrical conductivity and mechanical properties. The preparation of structurally optimized fluorinated ethylene–propylene/graphite composite bipolar plates with well-dispersed graphite particles of different sizes provides a robust and scalable strategy for realizing high-performance and large-area bipolar plates.     

Direct internal reforming molten carbonate fuel cell with core–shell catalyst

A sort of core–shell catalyst as a novel anti-alkali-poisoning concept was prepared, tested and applied in the direct internal reforming molten carbonate fuel cell (DIR-MCFC). Results showed that the core–shell catalyst possessed good alkali-poisoning resistance capacity, which was explained well by the micropore model of the catalyst. And the cell performance could keep above 0.75V during 100 h test. When the steam carbon ratio was 2 (S/C = 2) and the current density was 150 mA cm⁻², the cell potential varied from 0.826 to 0.751 V and the voltage fluctuant phenomenon was explained specifically. Furthermore, the short stack (three cells) was also assembled, and the maximum output power density of the short stack was 338.4 mW cm⁻². The above results indicated that the core–shell catalyst could be applied into the DIR-MCFC successfully.     

Oxide ion and proton conduction in doped ceria–carbonate composite materials

The direct current four-probe method has been employed to investigate the conduction of oxide ion and proton in a doped ceria–carbonate composite electrolyte for fuel cells. The measurements are conducted in oxygen and in hydrogen atmospheres in the temperature range of 425–650 °C. The conductivities of both of O²⁻ and H⁺ increase with the increase of carbonate content above the melting point of the carbonate. The ionic conductivities of the composite electrolytes have also been simulated using the effective medium percolation theory. The deviations between experimental results and simulated values of O²⁻ conductivity are caused by the associating effect of ceramic and carbonate phases, which leads to a higher O²⁻ migration energy through the phase interface. According to the comparison of experimental data and simulated values, the conduction mechanisms of O²⁻ and H⁺ have been proposed.     

Effective fabrication method of rod-shaped γ-LiAlO2 particles for molten carbonate fuel cell matrices

An effective fabrication method for rod-shaped γ-LiA1O₂ particles for molten carbonate fuel cell matrices via the synthesis of porous β-LiAlO₂ agglomerates that are easily washed and dispersed with deionized water has been investigated. In order to make large pores and high porosity in the reaction mixture, powder types of carbon and ammonium carbonate that make little ash and undesired material during the whole process are utilized. Regardless of the kind of pore-formers used, most of the rod-shaped β-/γ-LiAlO₂ particles are 1 μm in diameter and 10–15 μm long (aspect ratio of 10–15). The crystal structure of rod-shaped γ-LiAlO₂ particles synthesized from the reaction mixture with pore-formers coincides exactly with that of commercial γ-LiAlO₂ powders. As a consequence, cell performance using rod-shaped γ-LiAlO₂ particle reinforced matrices is highly improved in comparison with non-reinforced standard matrices.     

Degradation behaviour of Al–Fe coatings in wet-seal area of molten carbonate fuel cells

The corrosion resistance of Al–Fe coatings increases as a protective LiAlO₂ layer forms. If, however, the Al–Fe coatings lack sufficient aluminium for maintaining this protective layer, the corrosion resistance of the coating is degraded by the growth of non-protective scales, such as LiFeO₂. In this study, the degradation behaviour of Al–Fe coatings is investigated in the wet-seal environment of molten carbonate fuel cells (MCFC). Al–Fe coated specimens with various amounts of aluminium in the range 8–70 at.% and bulk specimens of Fe–23.9 Al (at.%) are prepared. A corrosion test is performed in Li/K carbonate systems at 650 °C with a single-cell and an immersion test. Test results reveal that aluminium contents in the coatings should be higher than 25 at.% in order to form and maintain a protective LiAlO₂ layer. In addition to aluminium content, the influence of microstructural features on the degradation behaviour of Al–Fe coatings is discussed.     

Durability study of an intermediate temperature fuel cell based on an oxide–carbonate composite electrolyte

It was reported that ceria–carbonate composites are promising electrolyte materials for intermediate temperature fuel cells. The conductivity stability of composite electrolyte with co-doped ceria and binary carbonate was measured by AC impedance spectroscopy. At 550 °C, the conductivity dropped from 0.26 to 0.21 S cm⁻¹ in air during the measured 135 h. At a constant current density of 1 A cm⁻², the cell performance keeps decreasing at 550 °C, with a maximum power density change from 520 to 300 mW cm⁻². This is due to the increase of both series and electrode polarisation resistances. Obvious morphology change of the electrolyte nearby the cathode/electrolyte interface was observed by SEM. Both XRD and FT-IR investigations indicate that there are some interactions between the doped ceria and carbonates. Thermal analysis indicates that the oxide–carbonate composite is quite stable at 550 °C. The durability of this kind of fuel cell is not good during our experiments. A complete solid oxide-carbonate composite would be better choice for a stable fuel cell performance.     

Preparation of creep-resistant Ni–5 wt.% Al anodes for molten carbonate fuel cells

Ni–5 wt.% Al anodes for molten carbonate fuel cells (MCFCs) are fabricated using relatively cheap elemental powders instead of expensive alloy powders. The tape-cast green sheets are sintered in various atmospheres: reduction, full oxidation–reduction, and partial oxidation–reduction atmospheres. The anode sintered in a reduction atmosphere shows a morphology of a network structure of an NiAl solid solution with its surface covered with thin Al₂O₃ films, and has relatively low creep resistance. On the other hand, the anode sintered in a full oxidation–reduction atmosphere or the one sintered in a partial oxidation–reduction atmosphere has a morphology of small Al₂O₃ particles dispersed in a network structure. In the former, however, a large number of micropores are created during sintering. The latter does not have the micropore problem and generally exhibits high creep resistance. The highest creep resistance is shown by the anode sintered in a partial oxidation–reduction atmosphere with an oxidation time of 2.5 h.     

Novel doped barium cerate–carbonate composite electrolyte material for low temperature solid oxide fuel cells

A composite of a perovskite oxide proton conductor (BaCe_0.7Zr_0.1Y_0.2O_3−δ, BCZ10Y20) and alkali carbonates (2Li₂CO₃:1Na₂CO₃, LNC) is investigated with respect to its morphology, conductivity and fuel cell performance. The morphology shows that the presence of carbonate phase improves the densification of oxide matrix. The conductivity is measured by AC impedance in air, nitrogen, wet nitrogen, hydrogen, and wet hydrogen, respectively. A sharp increase of the conductivity at certain temperature is seen, which relates to the superionic phase transition at the interface phases between oxide and carbonates. Single cell with the composite electrolyte is fabricated by dry-pressing technique, using nickel oxide as anode and lithiated nickel oxide as cathode, respectively. The cell shows a maximum power density of 957 mW cm⁻² at 600 °C with hydrogen as the fuel and oxygen as the oxidant. The remarkable proton conductivity and excellent cell performance make this kind of composite material a good candidate electrolyte for low temperature solid oxide fuel cells (SOFCs).     

Validation of H/O conduction in doped ceria–carbonate composite material using an electrochemical pumping method

A hydrogen and oxygen electrochemical pump technique has been employed to elucidate the conduction of proton and oxygen ion in a doped ceria–carbonate composite electrolyte for intermediate temperature solid oxide fuel cells. The composite material shows efficient conductivities of both of the two ions at 650 °C. The molten carbonate phase is important for the migration of both of the two ions. The mechanism of the conduction of proton and oxygen ion is also discussed.     

Experimental investigation of heat transfer and friction factor with water–propylene glycol based CuO nanofluid in a tube with twisted tape inserts

Convective heat transfer and friction factor characteristics of water/propylene glycol (70:30% by volume) based CuO nanofluids flowing in a plain tube are investigated experimentally under constant heat flux boundary condition. Glycols are normally used as an anti-freezing heat transfer fluids in cold climatic regions. Nanofluids are prepared by dispersing 50 nm diameter of CuO nanoparticles in the base fluid. Experiments are conducted using CuO nanofluids with 0.025%, 0.1% and 0.5% volume concentration in the Reynolds numbers ranging from 1000 < Re < 10000 and considerable heat transfer enhancement in CuO nanofluids is observed. The effect of twisted tape inserts with twist ratios in the range of 0 < H/D < 15 on nanofluids is studied and further heat transfer augmentation is noticed. The increment in the pressure drop in the CuO nanofluids over the base fluid is negligible but the experimental results have shown a significant increment in the convective heat transfer coefficient of CuO nanofluids. The convective heat transfer coefficient increased up to 27.95% in the 0.5% CuO nanofluid in plain tube and with a twisted tape insert of H/D = 5 it is further increased to 76.06% over the base fluid at a particular Reynolds number. The friction factor enhancement of 10.08% is noticed and increased to 26.57% with the same twisted tape, when compared with the base fluid friction factor at the same Reynolds number. Based on the experimental data obtained, generalized regression equations are developed to predict Nusselt number and friction factor.     

Cobalt carbonate hydroxide assisted formation of self-supported CoNi-based Metal–Organic framework nanostrips as efficient electrocatalysts for oxygen evolution reaction

The development of efficient and low-cost electrocatalysts is crucial for improving the efficiency of electrochemical oxygen evolution reaction (OER). Herein, self-supported CoNi-based metal-organic framework (MOF) nanostrips grown on Ni foam (NF) were synthesized with cobalt carbonate hydroxide (CoCH) nanoneedles as a sacrificial template and demonstrated to be highly efficient electrocatalysts for OER. In this approach, the CoCH nanoneedles play a key role in modulating the morphology of CoNi-MOF with reduced thickness and sizes through affording Co source and slowing down the leaching of Ni ions from the NF substrate. The resultant CoNi-MOF/CoCH/NF electrode possesses higher catalytically active surface area and smaller electrochemical impedance than CoCH template-free electrodes, which enable rapid mass transport and charge transfer during OER, thus showing enhanced electrocatalytic activity for OER. In alkaline media (1.0 M KOH), it needs a low overpotential of 251 mV to deliver a current density of 10 mA cm⁻² and exhibits a small Tafel slope of 40.7 mV dec⁻¹ as well as excellent durability. The developed approach may inspire further capability on constructing more promising catalysts for energy related applications.     

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.     

Effects and properties of various molecular weights of poly(propylene oxide) oligomers/Nafion acid–base blend membranes for direct methanol fuel cells

Various molecular weights of poly(propylene oxide) diamines oligomers/Nafion^® acid–base blend membranes were prepared to improve the performance of Nafion^® membranes in direct methanol fuel cells (DMFCs). The acid–base interactions were studied by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The performance of the blend membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The proton conductivity was slightly reduced by acid–base interaction. The methanol permeability of the blend D2000/Nafion^® was 8.61 × 10⁻⁷ cm² S⁻¹, which was reduced 60% compared to that of pristine Nafion^®. The cell performance of D2000/Nafion^® blend membranes was enhanced significantly compared to pristine Nafion^®. The current densities that were measured with Nafion^® and 3.5 wt% D2000/Nafion^® blend membranes were 62.5 and 103.5 mA cm⁻², respectively, at a potential of 0.2 V. Consequently, the blend poly(propylene oxide) diamines oligomers/Nafion^® membranes critically improved the single-cell performance of DMFC.     

Investigation of La2NiO4+δ-based cathodes for SDC–carbonate composite electrolyte intermediate temperature fuel cells

Lanthanum nickelate based oxides, including La₂NiO_4+δ (LN), La₂Ni_0.8Co_0.2O_4+δ (LNC82) and La₂Ni_0.8Fe_0.2O_4+δ (LNF82), were investigated as cathodes for intermediate temperature fuel cells with samaria doped ceria (SDC)–carbonate composite electrolytes. These oxides were synthesized by glycine–nitrate process and characterized by XRD and SEM, showing that all samples annealed at 800 °C for 2 h exhibit a K₂NiF₄ phase and a foam-like structure. The electrochemical properties of these cathodes were evaluated by fabricating and testing fuel cells with two kinds of composite electrolytes, SDC-20 wt.% (0.53Li/0.47Na)₂CO₃ and SDC-30 wt.% (0.67Li/0.33Na)₂CO₃, referred to as SDC(53L47N)20 and SDC(67L33N)30, respectively. Among these three cathodes, LNC82 shows the best cell performances at 500–600 °C. Moreover, fuel cells with SDC(67L33N)30 composite electrolyte present much higher power output than those with SDC(53L47N)20 composite electrolyte. It reveals that cobalt doping greatly enhances the electrochemical property of lanthanum nickelate, and such cathodes are more compatible with the SDC(67L33N)30 composite electrolyte.     

Effect of heat treatment and chemical composition on the corrosion behavior of Ni–Al intermetallics in molten (Li + K) carbonate

The corrosion performance of several Ni–Al alloys in 62 mol% Li₂CO₃–38 mol% K₂CO₃ at 650 °C has been studied using the weight loss technique. Alloys included 50Ni–50Al at.% (NiAl) and 75Ni–25Al at.% (Ni₃Al) alloys with additions of 1, 3 and 5 at.% Li each one, with or without a heat treatment at 400 °C during 144 h. For comparison, AISI-316L type stainless steel was also studied. The tests were complemented by X-ray diffraction, scanning electronic microscopy and micro-analyses. Results showed that NiAl-base alloy without heat treatment presented the lowest corrosion rate even lower than Ni₃Al alloy but still higher than conventional 316L-type stainless steel. In general terms, by either by heat treating these base alloys or by adding Li, the mass loss was increased. This effect was produced because by adding Li the adhesion of the external protective layer was decreased by inducing a higher number of discontinuities inside the grain boundaries. When the alloys were thermally annealed, these irregularities in the grain boundaries disappeared, decreasing the number of paths for the outwards diffusion of Al from the alloy to form the external, protective Al₂O₃ layer.     

H2 production from oxidative steam reforming of 1-propanol and propylene glycol over yttria-stabilized supported bimetallic Ni–M (M = Pt,Ru, Ir) catalysts

This paper reports hydrogen production from oxidative steam reforming of 1-propanol and propylene glycol over Ni–M/Y₂O₃–ZrO₂ (10% wt/wt Y₂O₃; M = Ir, Pt, Ru) bimetallic catalysts promoted with K. The results are compared with those obtained over the corresponding monometallic catalyst. The catalytic performance of the calcined catalysts was analyzed in the temperature range 723–773 K, adjusting the total composition of the reactants to O/C = 4 and S/C = 3.2–3.1 (molar ratios). The bimetallic catalysts showed higher hydrogen selectivity and lower selectivity of byproducts than the monometallic catalyst, especially at 723 K. Ni–Ir performed best in the oxidative steam reforming of both 1-propanol and propylene glycol. The presence of the noble metal favours the reduction of the NiO and the partial reduction of the support. The NiO crystalline phase present in the calcined catalysts was transformed to Ni° during oxidative steam reforming. The adsorption and subsequent reactivity of both 1-propanol and propylene glycol over Ni–Ir and Ni catalysts were followed by FTIR; C–C bond cleavage was found to occur at a lower temperature in propylene glycol than in 1-propanol.