A study of Ni + 8YSZ/8YSZ/La0.6Sr0.4CoO3−δ ITSOFC fabricated by atmospheric plasma spraying

An intermediate temperature solid oxide fuel cell (ITSOFC) based on 8YSZ electrolyte, La_0.6Sr_0.4CoO_3−δ (LSCo) cathode, and Ni − 8YSZ anode coatings were consecutively deposited onto a porous Ni-plate substrate by atmospheric plasma spraying (APS). The spray parameters including current, argon and hydrogen flow rate, and powder feed rate were investigated by an orthogonal experiment to fabricate a thin gas-tight 8YSZ electrolyte coating (80 μm). By proper selection of the spray parameters to decrease the particles velocity and temperature, the sprayed NiO + 8YSZ coating after reducing with hydrogen shows a good electrocatalytic activity for H₂ oxidation. With the same treatment, 100–170 μm dimensions LSCo particle could keep phase structure after spraying. And the deposited LSCo cathode shows a good cathode performance and chemical compatibility with 8YSZ electrolyte after operating at 800 °C for 50 h. Output power density of the sprayed cell achieved 410 mW cm⁻² at 850 °C and 260 mW cm⁻² at 800 °C. Electrochemical characterization indicated that IR drop of 8YSZ electrolyte, cathodic polarization, and the contact resistance at LSCo/8YSZ interface were the main factors restricting the cell performance. The results suggested that the use of APS cell allowed the reduction of the operating temperature of the SOFC to below 850 °C with lower production costs.     

Improvement of 12 V overcharge behavior of LiCoO2 cathode material by LiNi0.8Co0.1Mn0.1O2 addition in a Li-ion cell

The 12 V overcharge instability of the LiCoO₂ cathode material was improved by the physical blending it with LiNi_0.8Co_0.1Mn_0.1O₂. Even though a Li-ion cell containing a LiCoO₂ cathode did not exhibit thermal runaway at 12 V at the 1 C overcharging rate, it showed thermal runaway at the 2 C overcharging rate, and the cell surface temperature reached more than 400 °C. However, the LiCoO₂ cell containing 40, 50, and 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ did not exhibit thermal runaway at the 2 C overcharging rate. In conclusion, 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ in the LiCoO₂ cathode showed the lowest cell surface temperature of <90 °C even at a 3 C overcharging rate.     

Electrochemical and solid-state NMR studies on LiCoO2 coated with Al2O3 derived from carboxylate-alumoxane

The surface of LiCoO₂ cathodes was coated with various wt.% of Al₂O₃ derived from methoxyethoxy acetate-alumoxane (MEA-alumoxane) by a mechano-thermal coating procedure, followed by calcination at 723 K in air for 10 h. The structure and morphology of the surface modified LiCoO₂ samples have been characterized with XRD, SEM, EDS, TEM, BET, XPS/ESCA and solid-state ²⁷Al magic angle spinning (MAS) NMR techniques. The Al₂O₃ coating forms a thin layer on the surface of the core material with an average thickness of 20 nm. The corresponding ²⁷Al MAS NMR spectrum basically exhibited the same characteristics as the spectrum for pristine Al₂O₃ derived from MEA-alumoxane, indicating that the local environment of aluminum atoms was not significantly changed at coating levels below 1 wt.%. This provides direct evidence that Al₂O₃ was on the surface of the core materials. The LiCoO₂ coated with 1 wt.% Al₂O₃ sustained continuous cycle stability 13 times longer than pristine LiCoO₂. A comparison of the electrochemical impedance behavior of the pristine and coated materials revealed that the failure of pristine cathode performance is associated with an increase in the particle–particle resistance upon continuous cycling. Coating improved the cathode performance by suppressing the characteristic structural phase transitions (hexagonal to monoclinic to hexagonal) that occur in pristine LiCoO₂ during the charge–discharge processes.     

NiO–YSZ cermets supported low temperature solid oxide fuel cells

Solid oxide fuel cells with thin electrolyte of two types, Sm_0.2Ce_0.8O_1.9 (SDC) (15 μm) single-layer and 8 mol% Yttria stabilized zirconia (YSZ) (5 μm) + SDC (15 μm) bi-layer on NiO–YSZ cermet substrates were fabricated by screen printing and co-firing. A Sm_0.5Sr_0.5CoO₃ cathode was printed, and in situ sintered during a cell performance test. The SDC single-layer electrolyte cell showed high electrochemical performance at low temperature, with a 1180 mW cm⁻² peak power density at 650 °C. The YSZ + SDC bi-layer electrolyte cell generated 340 mW cm⁻² peak power density at 650 °C, and showed good performance at 700–800 °C, with an open circuit voltage close to theoretical value. Many high Zr-content micro-islands were found on the SDC electrolyte surface prior to the cathode preparation. The influence of co-firing temperature and thin film preparation methods on the Zr-islands’ appearance was investigated.     

Study of NiO cathode modified by ZnO additive for MCFC

The preparation and subsequent oxidation of nickel cathodes modified by impregnation with zinc oxide (ZnO) were evaluated by surface and bulk analysis. The electrochemical behaviors of ZnO impregnated NiO cathodes was also evaluated in a molten 62 mol% Li₂CO₃ + 38 mol% K₂CO₃ eutectic at 650 °C by electrochemical impedance spectroscopy (EIS) as a function of ZnO content and immersion time. The ZnO impregnated nickel cathodes showed the similar porosity, pore size distribution and morphology to the reference nickel cathode. The stability tests of ZnO impregnated NiO cathodes showed that the ZnO additive could dramatically reduce the solubility of NiO in a eutectic carbonate mixture under the standard cathode gas condition. The impedance spectra for cathode materials show important variations during the 100 h of immersion. The incorporation of lithium in its structure and the low dissolution of nickel oxide and zinc oxide are responsible of these changes. After that, the structure reaches a stable state. The cathode material having 2 mol% of ZnO showed a very low dissolution and a good catalytic efficiency close to the NiO value. We thought that 2 mol% ZnO/NiO materials would be able to adapt as alternative cathode materials for MCFCs.     

Performance and stability of SOFC anode fabricated from NiO–YSZ composite particles

Ni–YSZ cermet anodes for solid oxide fuel cells (SOFCs) were fabricated at various sintering temperatures from NiO–YSZ composite particles made by spray pyrolysis (SP) technique. NiO particles covered with fine YSZ (Y₂O₃ stabilized ZrO₂) particles were used as the composite particles, and the initial ratio of Ni and YSZ was set at 75:25 (mol%). As a result, the cermet anode sintered at 1350 °C showed the morphology in which fine YSZ grains were uniformly dispersed on the surface of Ni grain network. Electrical performance such as electrochemical activity and internal resistance of a Ni–YSZ cermet anode changed with sintering temperature. The anode fabricated at 1350 °C showed the highest electrical performance. Especially, a single cell voltage with the Ni–YSZ cermet anode kept very stable for 8000 h at 1000 °C in the SOFC operation condition of H₂—3% H₂O and air. The cermet anode after a long-term test had its initial morphology. It indicates that the Ni–YSZ cermet anode fabricated from NiO–YSZ composite particles is a very promising material for its practical use as SOFCs.     

Enhancing the thermal stability of LiCoO2 electrode by 4-isopropyl phenyl diphenyl phosphate in lithium ion batteries

To enhance the thermal stability of LiCoO₂ in lithium ion batteries, 4-isopropyl phenyl diphenyl phosphate (IPPP) was investigated as an additive in 1.0 M LiPF₆/EC + DEC (1:1 wt.%) electrolyte. The thermodynamics and kinetics parameters of the single LiCoO₂ and Li_xCoO₂–IPPP-electrolyte are detected and calculated based on the C80 microcalorimeter data. The results indicated that IPPP can enhance the thermal stability of LiCoO₂ electrode in lithium ion battery more or less corresponding to the IPPP content in electrolyte. Furthermore, the electrochemical performances of LiCoO₂/IPPP-electrolyte/Li cells become slightly worse after using IPPP additive in the electrolyte. This alleviated trade-off between thermal stability and cell performance provides a possibility to formulate an electrolyte containing 5–10% of IPPP and enhance the LiCoO₂ electrode thermal stability with minimum sacrifice in performance.     

Characterization of a LiCoO2 thick film by screen-printing for a lithium ion micro-battery

A thick film cathode has been fabricated by a screen-printing technique using LiCoO₂ paste to improve the discharge capacity in lithium ion micro-batteries. The LiCoO₂ thick film (about 6 μm) was obtained by screen-printing, but high discharge capacity and a suitable surface roughness of printed LiCoO₂ film cathodes could not be obtained by adding carbon black only to the LiCoO₂ paste. On the other hand, the printed cathode which was prepared using the mixture of carbon-coated LiCoO₂ powders and carbon black showed a typical discharge curve of a LiCoO₂ cathode with a high discharge capacity (179 μAh cm⁻²).     

Nanocrystalline TiO2 (anatase) for Li-ion batteries

Nanocrystalline TiO₂ (anatase) was synthesized successfully by the direct conversion of TiO₂-sol at 85 °C. The as-prepared TiO₂ at 85 °C were calcined at different temperatures and time in order to optimize the system with best electrochemical performance. The particle sizes of the synthesized materials were found to be in the range of 15–20 nm as revealed by the HR-TEM studies. Commercial TiO₂ anatase (micron size) was also studied for its Li-insertion and deinsertion properties in order to compare with the nanocrystalline TiO₂. The full cell studies were performed with LiCoO₂ cathode with the best performing nano-TiO₂ as anode. The specific capacity of the nanocrystalline TiO₂ synthesized at 500 °C/2 h in a half-cell configuration was 169 mAh g⁻¹ while for the cell with LiCoO₂ cathode, it was 95 mAh g⁻¹ in the 2 V region. The specific reversible capacity and the cycling performance of the synthesized nano-TiO₂ anode in full cell configuration across LiCoO₂ cathode are superior to that reported in the literature. Cyclic voltammetry measurements showed a larger peak separation for the micro-TiO₂ than the nano-TiO₂, clearly indicating the influence of nano-particle size on the electrochemical performance.     

Improvement of anode performance by surface modification for solid oxide fuel cell running on hydrocarbon fuel

A Ni/ yttria-stabilized zirconia (YSZ) cermet anode was modified by coating with samaria-doped ceria (SDC, Sm_0.2Ce_0.8O₂) sol within the pores of the anode for a solid oxide fuel cell (SOFC) running on hydrocarbon fuel. The surface modification of Ni/YSZ anode resulted in an increase of structural stability and enlargement of the triple phase boundary (TPB), which can serve as a catalytic reaction site for oxidation of carbon or carbon monoxide. Consequently, the SDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition and nickel sintering.The maximum power density of an anode-supported cell (electrolyte; 8 mol% YSZ and thickness of 30 μm, and cathode; La_0.85Sr_0.15MnO₃) with the modified anode was about 0.3 W/cm² at 700 °C in the mixture of methane (25%) and air (75%) as the fuel and air as the oxidant. The cell was operated for 500 h without significant degradation of cell performance.     

In situ screen-printed BaZr0.1Ce0.7Y0.2O3−δ electrolyte-based protonic ceramic membrane fuel cells with layered SmBaCo2O5+x cathode

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered SmBaCo₂O_5+x (SBCO) cathode, a dense BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY) electrolyte was fabricated on a porous anode by in situ screen printing. The porous NiO–BaZr_0.1Ce_0.7Y_0.2O_3?δ (NiO–BZCY) anode was directly prepared from metal oxide (NiO, BaCO₃, ZrO₂, CeO₂ and Y₂O₃) by a simple gel-casting process. An ink of metal oxide (BaCO₃, ZrO₂, CeO₂ and Y₂O₃) powders was then employed to deposit BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY) thin layer by an in situ reaction-sintering screen printing process on NiO–BZCY anode. The bi-layer with 25 μm dense BZCY electrolyte was obtained by co-sintering at 1400 °C for 5 h. With layered SBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H₂ as fuel and the static air as oxidant. A high open-circuit potential of 1.01 V, a maximum power density of 382 mW cm^?2, and a low polarization resistance of the electrodes of 0.15 Ω cm² was achieved at 700 °C.     

Organic polymer gel electrolyte for Li-ion batteries

The present paper describes a novel synthesis of organic polymer gel electrolyte for Li-ion cell, comprising of Polyethylene oxide (PEO), LiClO₄, LiOH, Li₂SO₄ and dimethyl formamide (DMF). The gel was obtained with a specific weight ratio of these components after appropriate heat treatment. The gel when layered over graphite plate and LiCoO₂ cathode, it forms laboratory model Li-ion cell. The cell shows an OCP value of 3.624 V at 298 K.The galvanostatic charge/discharge tests show performances comparable to liquid electrolyte system.     

In situ XRD studies of the structural changes of ZrO2-coated LiCoO2 during cycling and their effects on capacity retention in lithium batteries

Synchrotron based in situ X-ray diffraction was used to study the structural changes of a ZrO₂-coated LiCoO₂ cathode in comparison with the uncoated sample during multi-cycling in a wider voltage window from 2.5 to 4.8 V. It was found that the improved cycling performance of ZrO₂-coated LiCoO₂ is closely related to the larger lattice parameter “c” variation range, which is an indicator of how far the structural change has proceeded towards the two end members of the phase transition stream during charge–discharge cycling. At fifth charge, the lattice parameter variation ranges for both uncoated and ZrO₂-coated LiCoO₂ were reduced compared with those for the first charge, reflecting the capacity fading caused by the high voltage cycling. However, this variation range reduction is smaller in ZrO₂-coated LiCoO₂ than that in the uncoated sample, and so is the capacity fading. These results point out an important direction for studying the fading mechanism and coating effects: the key issues are the surface protection, the interaction between the cathode surface and the electrolyte and the electrolyte decomposition. In order to improve the capacity retention during cycling, the variation range of lattice parameter “c” of LiCoO₂ should be preserved, not reduced.     

Performance of Ni/ScSZ cermet anode modified by coating with Gd0.2Ce0.8O2 for an SOFC running on methane fuel

A Ni/scandia-stabilized zirconia (ScSZ) cermet anode was modified by coating with nano-sized gadolinium-doped ceria (GDC, Gd_0.2Ce_0.8O₂) prepared using a simple combustion process within the pores of the anode for a solid oxide fuel cell (SOFC) running on methane fuel. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the anode characterizations. Then, the short-term stability for the cells with the Ni/ScSZ and 2.0 wt.%GDC-coated Ni/ScSZ anodes in 97%CH₄/3%H₂O at 700 °C was checked over a relative long period of operation. Open circuit voltages (OCVs) increased from 1.098 to 1.179 V, and power densities increased from 224 to 848 mW cm⁻², as the operating temperature of an SOFC with 2.0 wt.%GDC-coated Ni/ScSZ anode was increased from 700 to 850 °C in humidified methane. The coating of nano-sized Gd_0.2Ce_0.8O₂ particle within the pores of the porous Ni/ScSZ anode significantly improved the performance of anode supported cells. Electrochemical impedance spectra (EIS) illustrated that the cell with Ni/ScSZ anode exhibited far greater impedances than the cell with 2.0 wt.%GDC-coated Ni/ScSZ anode. Introduction of nano-sized GDC particles into the pores of porous Ni/ScSZ anode will result in a substantial increase in the ionic conductivity of the anode and increase the triple phase boundary region expanding the number of sites available for electrochemical activity. No significant degradation in performance has been observed after 84 h of cell testing when 2.0 wt.%GDC-coated Ni/ScSZ anode was exposed to 97%CH₄/3%H₂O at 700 °C. Very little carbon was detected on the anodes, suggesting that carbon deposition was limited during cell operation. Consequently, the GDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition.     

Durability of (Pr0.7Sr0.3)MnO3±δ/8YSZ composite cathodes for solid oxide fuel cells

Half cell SOFCs with (Pr_0.7Sr_0.3)MnO_3±δ/8YSZ composite cathodes on 8YSZ electrolytes were aged up to 1000 h at 1000 °C in air with/without 0.318 A cm⁻² cathodic polarization. During the aging, the performance of the half cell SOFCs was measured using electrochemical impedance spectroscopy (EIS). After aging, the surface of the composite cathode and the interface between the composite cathode and the electrolyte was investigated with scanning electron microscopy (SEM). Chemical element analysis was performed with energy dispersive X-ray spectroscopy (EDS). The performance of the half cell SOFCs degraded after aging with/without polarization compared to the initial state. The SOFCs had a larger polarization resistance after 1000 h of aging. The cathodic current was shown to have an impact on the performance by slowing down the rate of decrease of polarization resistance of the SOFCs. After aging, the microstructural properties—mean pore size increased and cumulative pore volume decreased, and growth of grains was found on the (Pr_0.7Sr_0.3)MnO_3±δ phases.     

Phase-separated polymer electrolyte based on poly(vinyl chloride)/poly(ethyl methacrylate) blend

The characteristics of polymer electrolytes based on a poly(vinyl chloride) (PVC)/poly(ethyl methacrylate) (PEMA) blend are reported. The PVC/PEMA based polymer electrolyte consists of an electrolyte-rich phase that acts as a conducting channel and a polymer-rich phase that provides mechanical strength. The dual phase was simply developed by a single-step coating process. The mechanical strength of the PVC/PEMA based polymer electrolyte was found to be much higher than that of a previously reported PVC/PMMA-based polymer electrolyte (poly(methyl methacrylate), PMMA) at the same PVC content, and even comparable with that of the PVC-based polymer electrolyte. The blended polymer electrolytes showed ionic conductivity of higher than 10⁻³ S cm⁻¹ and electrochemical stability up to at least 4.3 V. A prototype battery, which consists of a LiCoO₂ cathode, a MCMB anode, and PVC/PEMA-based polymer electrolyte, gives 92% of the initial capacity at 100 cycles upon repeated charge–discharge at the 1 C rate.     

Preparation of LiCoO2 from spent lithium-ion batteries

A recycling process involving mechanical, thermal, hydrometallurgical and sol–gel steps has been applied to recover cobalt and lithium from spent lithium-ion batteries and to synthesize LiCoO₂ from leach liquor as cathodic active materials. Electrode materials containing lithium and cobalt can be concentrated with a two-step thermal and mechanical treatment. The leaching behavior of lithium and cobalt in nitric acid media is investigated in terms of reaction variables. Hydrogen peroxide in 1 M HNO₃ solution is found to be an effective reducing agent by enhancing the leaching efficiency. Of the many possible processes to produce LiCoO₂, the amorphous citrate precursor process (ACP) has been applied to synthesize powders with a large specific surface area and an exact stoichiometry. After leaching used LiCoO₂ with nitric acid, the molar ratio of Li to Co in the leach liquor is adjusted to 1.1 by adding a fresh LiNO₃ solution. Then, 1 M citric acid solution at a 100% stoichiometry is added to prepare a gelatinous precursor. When the precursor is calcined at 950 °C for 24 h, purely crystalline LiCoO₂ is successfully obtained. The particle size and specific surface-area of the resulting crystalline powders are 20 μm and 30 cm² g⁻¹, respectively. The LiCoO₂ powder is found to have good characteristics as a cathode active material in terms of charge–discharge capacity and cycling performance.     

Development and testing of anode-supported solid oxide fuel cells with slurry-coated electrolyte and cathode

A laboratory setup was designed and put into operation for the development of solid oxide fuel cells (SOFCs). The whole project consisted of the preparation of the component materials: anode, cathode and electrolyte, and the buildup of a hydrogen leaking-free sample chamber with platinum leads and current collectors for measuring the electrochemical properties of single SOFCs. Several anode-supported single SOFCs of the type (ZrO₂:Y₂O₃ + NiO) thick anode/(ZrO₂:Y₂O₃) thin electrolyte/(La_0.65Sr_0.35MnO₃ + ZrO₂:Y₂O₃) thin cathode have been prepared and tested at 700 and 800 °C after in situ H₂ anode reduction. The main results show that the slurry-coating method resulted in single-cells with good reproducibility and reasonable performance, suggesting that this method can be considered for fabrication of SOFCs.     

Thin yttria-stabilized zirconia electrolyte and transition layers fabricated by particle suspension spray

In order to develop high performance intermediate temperature (<800 °C) solid oxide fuel cells (SOFCs) with a lower fabrication cost, a pressurized spray process of ceramic suspensions has been established to prepare both dense yttria-stabilized zirconia (YSZ) electrolyte membranes and transition anode layers on NiO + YSZ anode supports. A single cell with 10 μm thick YSZ electrolyte on a porous anode support and ∼20 μm thick cathode layer showed peak power densities of only 212 mW cm⁻² at 700 °C and 407 mW cm⁻² for 800 °C. While a cell with 10 μm thick YSZ electrolyte and a transition layer on the porous anode support using a ultra-fine NiO + YSZ powder showed peak power densities of 346 and 837 mW cm⁻² at 700 and 800 °C, respectively. The dramatic improvement of cell performance was attributed to the much improved anode microstructure that was confirmed by both scanning electron microscopes (SEM) observation and impedance spectroscopy. The results have demonstrated that a pressurized spray coating is a suitable technique to fabricate high performance SOFCs and at lower cost.     

Manganese dioxide as a cathode catalyst for a direct alcohol or sodium borohydride fuel cell with a flowing alkaline electrolyte

The oxygen reduction reaction at a manganese dioxide cathode in alkaline medium is studied using cyclic voltammetry and by measuring volume of oxygen consumed at the cathode. The performance of the manganese dioxide cathode is also determined in the presence of fuel and an alkali mixture with a standard Pt/Ni anode in a flowing alkaline-electrolyte fuel cell. The fuels tested are methanol, ethanol and sodium borohydride (1 M), while 3 M KOH is used as the electrolyte. The performance of the fuel cell is measured in terms of open-circuit voltage and current–potential characteristics. A single peak in the cyclic voltammogram suggests that a four-electron pathway mechanism prevails during oxygen reduction. This is substantiated by calculating the number of electrons involved per molecule of oxygen that are reacted at the MnO₂ cathode from the oxygen consumption data for different fuels. The results show that the power density of the fuel cell increases with increase in MnO₂ loading to a certain limit but then decreases with further loading. The maximum power density is obtained at 3 mg cm⁻² of MnO₂ for each of the three different fuels.