Fabrication of all-solid-state lithium battery with lithium metal anode using Al2O3-added Li7La3Zr2O12 solid electrolyte

Li₇La₃Zr₂O₁₂ (LLZ) solid electrolyte is one of the promising electrolytes for all-solid-state battery due to its high Li ion conductivity and stability against Li metal anode. However, high calcination temperature for LLZ preparation promotes formation of La₂Zr₂O₇ impurity phase. In this paper, an effect of Al₂O₃ addition as sintering additive on LLZ solid electrolyte preparation and electrochemical properties of Al₂O₃-added LLZ were examined. By the Al₂O₃ addition, sintered LLZ pellet could be obtained after 1000 °C calcination, which is 230 °C lower than that without Al₂O₃ addition. Chemical and electrochemical properties of the Al₂O₃-added LLZ, such as stability against Li metal and ion conductivity, were comparable with the LLZ without Al₂O₃ addition, i.e. σ_bulk and σ_total were 2.4 × 10⁻⁴ and 1.4 × 10⁻⁴ S cm⁻¹ at 30 °C, respectively. All-solid-state battery with Li/Al₂O₃-added LLZ/LiCoO₂ configuration was fabricated and its electrochemical properties were tested. In cyclic voltammogram, clear redox peaks were observed, indicating that the all-solid-state battery with Li metal anode was successfully operated. The redox peaks were still observed even after one year storage of the all-solid-state battery in the Ar-filled globe-box. It can be inferred that the Al₂O₃-added LLZ electrolyte would be a promising candidate for all-solid-state battery because of facile preparation by the Al₂O₃ addition, relatively high Li ion conductivity, and good stability against Li metal and LiCoO₂ cathode.     

Nanoscale bismuth oxide impregnated (La,Sr)MnO3 cathodes for intermediate-temperature solid oxide fuel cells

Bismuth oxide based oxygen ion conductors are incorporated into (La,Sr)MnO₃ (LSM), the classical cathode material for solid oxide fuel cells (SOFC), to improve the cathode performance. Yttria-stabilized bismuth oxide (YSB) is taken as an example and is impregnated into a preformed porous LSM frame, forming a highly active cathode for intermediate-temperature SOFCs (IT-SOFCs) with doped ceria electrolytes. X-ray diffraction indicates that YSB is chemically compatible with LSM at intermediate temperatures below 800 °C. The impregnated YSB particles are nanosized and are deposited on the surface of the framework. Significant performance improvement is achieved by introducing nanosized YSB into the LSM electrodes. At 600 °C, the interfacial polarization resistance under open-circuit conditions for electrodes impregnated with 50% YSB is only 1.3% of the original value for a pure LSM electrode. The resistance is further reduced dramatically when current is passed through. In addition, the YSB impregnated LSM electrodes has the highest electrochemical performance among those based on LSM. Single cell with 25% of YSB impregnated LSM cathode generates maximum power density of 300 mW cm⁻² at 600 °C, indicating the promise of using LSM-based electrodes for IT-SOFC.     

Performance and durability of nanostructured (La0.85Sr0.15)0.98MnO3/yttria-stabilized zirconia cathodes for intermediate-temperature solid oxide fuel cells

In this communication we report the fabrication of nanostructured (La_0.85Sr_0.15)_0.98MnO₃ (LSM)/yttria-stabilized zirconia (YSZ) composite cathodes consisting of homogeneously distributed and connected LSM and YSZ grains approximately 100 nm large. We also investigate for the first time the role of the cathode nanostructure on the performance and the durability of intermediate-temperature solid oxide fuel cells. The cathodes were fabricated using homogenous LSM/YSZ nanocomposite particles synthesized by co-precipitation, using YSZ nanoparticles of 3 nm as seed crystals. Detailed microstructural characterization by transmission electron microscopy with energy-dispersive X-ray spectroscopy revealed that many of the LSM/YSZ junctions in the cathode faced the homogeneously connected pore channels, indicating the formation of a considerable number of triple phase boundaries. The nanostructure served to reduce cathodic polarization. As a result, these anode-supported solid oxide fuel cells showed high power densities of 0.18, 0.40, 0.70 and 0.86 W cm⁻² at 650, 700, 750 and 800 °C, respectively, under the cell voltage of 0.7 V. Furthermore, no significant performance degradation of the cathode was observed during operation at 700 °C for 1000 h under a constant current density of 0.2 A cm⁻².     

Identification of oxygen reduction processes at (La,Sr)MnO3 electrode/La9.5Si6O26.25 apatite electrolyte interface of solid oxide fuel cells

Oxygen reduction reaction of (La,Sr)MnO₃ (LSM) cathode on La_9.5Si₆O_26.25 apatite (LSO) electrolyte is studied over the temperature range 750–900 °C and the oxygen partial pressure range 0.01–1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (σ₁) is basically independent of oxygen partial pressure. The activation energy of σ₁ is 188 ± 15 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 1150 °C, and decreases to 120 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 850 °C, which is close to 80–110 kJ mol⁻¹ observed for the same electrode process at LSM/YSZ interface. The reaction order with respect to PO₂$P_{{\text{O}}_2}$ and the activation energy of the electrode process associated with low frequency arc (σ₂) are generally close to that of σ₂ at the LSM/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSM/LSO interface as compared to that at LSM/YSZ interface. The impedance responses of O₂ reduction reaction at the LSM/LSO interface are significantly higher than that at the LSM/YSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSM electrode on LSO electrolyte. At the sintering temperature of 1000 °C, the impedance responses of O₂ reduction reaction is 1.74 Ω cm² at 900 °C, which is significantly smaller than that of LSM electrode sintered at 1150 °C.     

CeO2 nanoparticles improved Pt-based catalysts for direct alcohol fuel cells

We developed an ultrasonic co-deposition technique to enhance the activity of Pt/C catalyst (and Pt/CNT, PtRu/C catalysts) for direct alcohol fuel cells (DAFCs) by CeO₂ nanoparticles. The composite catalyst architecture is obtained by an ultrasonically mixing commercial Pt/C catalyst and CeO₂ nanoparticles. Both Pt and CeO₂ are dispersed uniformly in the electrodes resulting in a great deal of CeO₂–Pt–C triple junction interfaces. Unlike traditional preparation of metal oxide supported Pt catalysts, CeO₂ will not cut the connection between Pt and C in this composite catalyst structure. Electrochemical measurements confirm that CeO₂ can improve almost all Pt based catalysts (Pt/C, Pt/CNT, and PtRu/C) for almost all small molecular alcohols (methanol, ethanol, ethylene glycol, and glycerol) electro-oxidation. EIS measurement shows that reaction resistance between Pt and alcohols is decreased much by adding small CeO₂ nanoparticles. Besides, these composite catalysts have high stability. It proves CeO₂ a very promising co-catalyst of Pt based catalysts for DAFCs.     

Synthesis of bimetallic iron ferrite Co0.5Zn0.5Fe2O4 as a superior catalyst for oxygen reduction reaction to replace noble metal catalysts in microbial fuel cell

A low-cost electrochemically active oxygen reduction reaction (ORR) catalyst is obligatory for making microbial fuel cells (MFCs) sustainable and economically viable. In this endeavour, a highly active surface modified ferrite, with Co and Zn bimetal in the ratio of 1:1 (w/w), Co_0.5Zn_0.5Fe₂O₄ was synthesised using simple sol-gel auto combustion method. Physical characterisation methods revealed a successful synthesis of nano-scaled Co_0.5Zn_0.5Fe₂O₄. For determination of ORR kinetics of cathode, using Co_0.5Zn_0.5Fe₂O₄ catalyst, electrochemical studies viz. cyclic voltammetry and electrochemical impedance spectroscopy were conducted, which demonstrated excellent reduction current response with less charge transfer resistance. These electrochemical properties were observed to be comparable with the results obtained for cathode using 10% Pt/C as a catalyst on the cathode. The MFC using Co_0.5Zn_0.5Fe₂O₄ catalysed cathode could produce a maximum power density of 21.3 ± 0.5 W/m³ (176.9 ± 4.2 mW/m²) with a coulombic efficiency of 43.3%, which was found to be substantially higher than MFC using no catalyst on the cathode 1.8 ± 0.2 W/m³ (15.2 ± 1.3 mW/m²). Also, the specific power recovery per unit cost for MFC with Co_0.5Zn_0.5Fe₂O₄ catalysed cathode was found to be 4 times higher as compared to Pt/C based MFC. This exceptionally low-cost cathode catalyst has enough merit to replace costly cathode catalyst, like platinum, for scaling up of the MFCs.     

Ni3(PO4)2-coated Li[Ni0.8Co0.15Al0.05]O2 lithium battery electrode with improved cycling performance at 55 °C

To improve the cycling performance of LiNi_0.8Co_0.15Al_0.05O₂ at 55 °C, a thin Ni₃(PO₄) layer was homogeneously coated onto the cathode particle via simple ball milling. The morphology of the Ni₃(PO₄)₂-coated LiNi_0.8Co_0.15Al_0.05O₂ particle was characterized using SEM and TEM analysis, and the coating thickness was found to be approximately 10-20 nm. The Ni₃(PO₄)₂-coated LiNi_0.8Co_0.15Al_0.05O₂ cell showed improved lithium intercalation stability and rate capability especially at high C rates. This improved cycling performance was ascribed to the presence of Ni₃(PO₄)₂ on the LiNi_0.8Co_0.15Al_0.05O₂ particle, which protected the cathode from chemical attack by HF and thus suppressed an increase in charge transfer resistance. Transmission electron microscopy of extensively cycled particles confirmed that the particle surface of the Ni₃(PO₄)₂-coated LiNi_0.8Co_0.15Al_0.05O₂ remained almost undamaged, whereas pristine particles were severely serrated. The stabilization of the host structure by Ni₃(PO₄)₂ coating was also verified using X-ray diffraction.     

Electrode performance of a new La0.6Sr0.4Co0.2Fe0.8O3 coated cathode for molten carbonate fuel cells

To improve the cathode performance in molten carbonate fuel cells (MCFCs), Lanthanum Strontium Cobalt Ferrite (La_0.6Sr_0.4Co_0.2Fe_0.8O₃, LSCF) of perovskite structure was coated on a porous Ni plate by a vacuum suction method. The electrochemical performance of modified cathode was examined and compared with that of uncoated conventional cathode via single cell operation and electrochemical impedance analysis (EIS). The cell voltage of the single cell using the LSCF coated cathode, measured at 650 °C with current density of 150 mA/cm² is 0.837 V and it is higher than that of the cell with uncoated conventional cathode, 0.805 V. The higher performance and the lower charge transfer resistance were obtained at 600–700 °C after LSCF coating. The lower activation energy of oxygen reduction reaction was also obtained. The lower activation energy of oxygen reduction reaction after LSCF coating shows that LSCF on lithiated NiO cathode plays a role of catalyst on the oxygen reduction reaction in cathode.     

Preparation and electrochemical properties of Sr-doped Nd2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Cathode materials Nd_2 − xSr_xNiO₄ were prepared by the glycine-nitrate process and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impendence spectroscopy and DC polarization method, respectively. The results show that no reaction occurred between the electrode and the CGO electrolyte at 1100 °C and the electrode formed good contact with the electrolyte after being sintered at 1000 °C for 4 h. The rate-limiting step for oxygen reduction reaction on Nd_1.6Sr_0.4NiO₄ electrode changed with oxygen partial pressure and measurement temperature. The Nd_1.6Sr_0.4NiO₄ electrode gave a polarization resistance of 0.93 Ω cm² at 700 °C in air, which indicates that Nd_2 − xSr_xNiO₄ electrode is a promising cathode material for intermediate-temperature solid oxide fuel cell (IT-SOFC).     

Compatibility of LiCoO2 and LiMn2O4 cathode materials for Li0.55La0.35TiO3 electrolyte to fabricate all-solid-state lithium battery

In order to improve performance of all-solid-state lithium ion battery with honeycomb structure, a compatibility of two commonly used cathode materials, LiCoO₂ and LiMn₂O₄, to Li_0.55La_0.35TiO₃ (LLT) solid electrolyte was studied. LiCoO₂/honeycomb LLT and LiMn₂O₄/honeycomb LLT half cells were fabricated by the impregnation of mixture of the cathode material with its precursor sol into honeycomb holes followed by the calcination. Impurity phases were observed at interface between LiCoO₂ and honeycomb LLT, while no impurity phase was confirmed in the case of LiMn₂O₄. In half cell test, the LiMn₂O₄/honeycomb LLT cell showed about 6 times larger discharge capacity than the LiCoO₂/honeycomb LLT cell, because of high internal resistance of the LiCoO₂/honeycomb LLT cell caused by the impurity phases. It can be said that the formation of low resistance interface at active material/electrolyte is one of the most important key to improve performance of the all-solid-state battery. Using LiMn₂O₄ instead of LiCoO₂, better interface between cathode material and LLT was obtained.     

Deposited RuO2–IrO2/Pt electrocatalyst for the regenerative fuel cell

A bifunctional RuO₂–IrO₂/Pt electrocatalyst for the unitized regenerative fuel cell (URFC) was synthesized by colloid deposition and characterized by analytical methods like TEM, XRD, etc. The result reveals that RuO₂–IrO₂ was well dispersed and deposited on the surface of Pt black. With deposited RuO₂–IrO₂/Pt as the catalyst of oxygen electrode, the performance of fuel cell/water electrolysis of unitized regenerative fuel cell (URFC) was studied in detail. URFC with deposited RuO₂–IrO₂/Pt shows better performance than that of URFC with mixed RuO₂–IrO₂/Pt catalyst. Cyclic performance of URFC with deposited RuO₂–IrO₂/Pt is very stable during 10 cyclic tests.     

Non precious metal catalysts for the PEM fuel cell cathode

Low temperature fuel cells, such as the proton exchange membrane (PEM) fuel cell, have required the use of highly active catalysts to promote both the fuel oxidation at the anode and oxygen reduction at the cathode. Attention has been particularly given to the oxygen reduction reaction (ORR) since this appears to be responsible for major voltage losses within the cell. To provide the requisite activity and minimse losses, precious metal catalysts (containing Pt) continue to be used for the cathode catalyst. At the same time, much research is in progress to reduce the costs associated with Pt cathode catalysts, by identifying and developing non-precious metal alternatives. This review outlines classes of non-precious metal systems that have been investigated over the past 10 years. Whilst none of these so far have provided the performance and durability of Pt systems some, such as transition metals supported on porous carbons, have demonstrated reasonable electrocatalytic activity. Of the newer catalysts, iron-based nanostructures on nitrogen-functionalised mesoporous carbons are beginning to emerge as possible contenders for future commercial PEMFC systems.     

La0.84Sr0.16MnO3−δ cathodes impregnated with Bi1.4Er0.6O3 for intermediate-temperature solid oxide fuel cells

La_0.84Sr_0.16MnO_3−δ–Bi_1.4Er_0.6O₃ (LSM–ESB) composite cathodes are fabricated by impregnating LSM electronic conducting matrix with the ion-conducting ESB for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performance of LSM–ESB cathodes is investigated at temperatures below 750 °C by AC impedance spectroscopy. The ion-impregnation of ESB significantly enhances the electrocatalytic activity of the LSM electrodes for the oxygen reduction reactions, and the ion-impregnated LSM–ESB composite cathodes show excellent performance. At 750 °C, the value of the cathode polarization resistance (R_p) is only 0.11 Ω cm² for an ion-impregnated LSM–ESB cathode, which also shows high stability during a period of 200 h. For the performance testing of single cells, the maximum power density is 0.74 W cm⁻² at 700 °C for a cell with the LSM–ESB cathode. The results demonstrate the ion-impregnated LSM–ESB is one of the promising cathode materials for intermediate-temperature solid oxide fuel cells.     

Preparation and characterization of silver-modified La0.8Sr0.2MnO3 cathode powders for solid oxide fuel cells by chemical reduction method

Herein a chemical reduction method is proposed in order to modify the solid oxide fuel cells (SOFC) traditional cathode material La_0.8Sr_0.2MnO_3−x (LSM). Silver nanoparticles were prepared by the reduction of ammoniacal silver nitrate with ascorbic acid in dilute aqueous solutions containing PVP. The obtained LSM–Ag composite powders were characterized by XRD, SEM, EDX, and STEM. The results showed that the LSM–Ag composite powder possess an elaborated fine structure with a homogeneous distribution of Ag and LSM, which effectively shortens the diffusion pathway for electrons and adsorbed oxygen. The electrochemical performance of the LSM–Ag cathode with different Ag loadings was investigated. A cathode loading with 1 wt.% Ag exhibited an area specific resistance as low as 0.45 Ω cm² at 750 °C, compared to around 1.1 Ω cm² for a pure LSM electrode. Similarly an anode-supported SOFC with 1 wt.% Ag in the cathode shows a peak power density of 1199 mW cm⁻¹, higher than the value of 717 mW cm⁻¹ achieved for a similar cell with a LSM cathode. Increasing the Ag loading is shown to have an insignificant effect on improving electrocatalytic performance at 750 °C, however it can increase output power at 650 °C.     

Direct NaBH4/H2O2 fuel cells

A fuel cell (FC) using liquid fuel and oxidizer is under investigation. H₂O₂ is used in this FC directly at the cathode. Either of two types of reactant, namely a gas-phase hydrogen or an aqueous NaBH₄ solution, are utilized as fuel at the anode. Experiments demonstrate that the direct utilization of H₂O₂ and NaBH₄ at the electrodes results in >30% higher voltage output compared to the ordinary H₂/O₂ FC. Further, the use of this combination of all liquid fuels, provides numerous advantages (ease of storage, reduced pumping requirements, simplified heat removal, etc.) from an operational point of view. This design is inherently compact compared to other cells that use gas phase reactants. Further, regeneration is possible using an electrical input, e.g. from power lines or a solar panel. While the peroxide-based FC is ideally suited for applications such as space power where air is not available and a high energy density fuel is essential, other distributed and mobile power uses are of interest.     

Enhancing the electrochemical properties of NiFe2O4 anode for lithium ion battery through a simple hydrogenation modification

Nanocrystal NiFe₂O₄ (NFO) octahedron with a spinel structure has been successfully synthesized by a one-step hydrothermal method. The effects of hydrogenation on the crystal structure, morphology, surface structure, and the electrochemical performance of NFO are comprehensively investigated for the first time. After hydrogenation, the well-defined octahedron morphology of NFO disappears and a small fraction of metallic Ni and some oxygen vacancies are generated after hydrogenation which has been characterized by X-ray diffraction (XRD), X-ray photoelectronic spectrometer (XPS) and Positron annihilation lifetime spectroscopy (PALS). Compared to the pristine NFO or the annealed NFO in air, the hydrogenated samples exhibit much better capacity retention (60% higher than un-hydrogenated NFO at 50th cycle) and rate capability (3 times higher at 1 A/g), which can be largely attributed to the synergetic effect of the conductive metallic Ni and oxygen vacancies resulting from H₂ reduction. Furthermore, this facile hydrogenation modification method may also be applied to improve the electrochemical performances of other transition metal oxides electrodes.     

Study of oxygen reduction mechanism on Ag modified Sm1.8Ce0.2CuO4 cathode for solid oxide fuel cell

Different amount of metal silver particles are infiltrated into porous Sm_1.8Ce_0.2CuO₄ (SCC) scaffold to form SCC–Ag composite cathodes. The chemical stability, microstructure evolution and electrochemical performance of the composite cathode are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance spectroscopy respectively. The composite cathode exhibits enhanced chemical stability. The metal Ag remains un-reacted with SCC and Ce_0.9Gd_0.1O_1.95 (CGO) at 800 °C for 72 h. The polarization resistance of the composite cathode decreases with the addition of metal Ag. The optimum cathode SCC-Ag05 exhibits the lowest area specific resistance (ASR, 0.43 Ω cm²) at 700 °C in air. Investigation shows that metal Ag accelerates the charge transfer process in the composite cathode, and the rate limiting step for electrochemical oxygen reduction reaction (ORR) changes to oxygen dissociation and diffusion process.     

Performances of LnBaCo2O5+x-Ce0.8Sm0.2O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskite oxides, LnBaCo₂O_5+x (LnBCO) (Ln = Pr, Nd, Sm, and Gd), are prepared using a solid-state reaction as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performances of LnBCO-Ce_0.8Sm_0.2O_1.9 (SDC) composite cathodes were investigated for IT-SOFCs on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The thermal expansion coefficient can be effectively reduced in the case of the composite cathodes. No chemical reactions between LnBCO cathodes and SDC electrolyte, and LnBCO and LSGM are found. The electrochemical performances of LnBCO cathodes and LnBCO-SDC composite cathodes decrease with decreasing Ln³⁺ ionic radii, which is closely related to the decrease of the electrical conductivity and fast oxygen diffusion property. The area specific resistances of the LnBCO cathodes and LnBCO-SDC composite cathodes on LSGM electrolyte are all lower than 0.13 Ω cm² and 0.15 Ω cm² at 700 °C, respectively. The maximum power densities of single-cell consisted of LnBCO-SDC composite cathodes, LSGM electrolyte, and Ni-SDC anode achieve 758-608 mW cm⁻² at 800 °C with the change from Ln = Pr to Gd, respectively. These results indicate that LnBCO-SDC composite oxides are candidates as a promising cathode material for IT-SOFCs.     

Ti4O7 supported IrOx for anode reversal tolerance in proton exchange membrane fuel cell

Fuel starvation can occur and cause damage to the cell when proton exchange membrane fuel cells operate under complex working conditions. In this case, carbon corrosion occurs. Oxygen evolution reaction (OER) catalysts can alleviate carbon corrosion by introducing water electrolysis at a lower potential at the anode in fuel shortage. The mixture of hydrogen oxidation reaction (HOR) and unsupported OER catalyst not only reduces the electrolysis efficiency, but also influences the initial performance of the fuel cell. Herein, Ti₄O₇ supported IrO_x is synthesized by utilizing the surfactant-assistant method and serves as reversal tolerant components in the anode. When the cell reverse time is less than 100 min, the cell voltage of the MEA added with IrO_x/Ti₄O₇ has almost no attenuation. Besides, the MEA has a longer reversal time (530 min) than IrO_x (75 min), showing an excellent reversal tolerance. The results of electron microscopy spectroscopy show that IrO_x particles have a good dispersity on the surface of Ti₄O₇ and IrO_x/Ti₄O₇ particles are uniformly dispersed on the anode catalytic layer. After the stability test, the Ti₄O₇ support has little decay, demonstrating a high electrochemical stability. IrO_x/Ti₄O₇ with a high dispersity has a great potential to the application on the reversal tolerance anode of the fuel cell.     

Cobalt-free layered perovskite GdBaFe2O5+x as a novel cathode for intermediate temperature solid oxide fuel cells

A cobalt-free layered perovskite oxide, GdBaFe₂O_5+x (GBF), was investigated as a novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). Area-specific resistance (ASR) of GBF was measured by impedance spectroscopy in a symmetrical cell. The observed ASR was as low as 0.15 Ω cm² at 700 °C and 0.39 Ω cm² at 650 °C, respectively. A laboratory sized Sm_0.2Ce_0.8O_1.9 (SDC)-based tri-layer cell of NiO-SDC/SDC/GBF was tested under intermediate temperature conditions of 550-700 °C with humidified H₂ (∼3% H₂O) as a fuel and the static ambient air as an oxidant. A maximal power density of 861 mW cm⁻² was achieved at 700 °C. The electrode polarization resistance was as low as 0.57, 0.22, 0.13 and 0.08 Ω cm² at 550, 600, 650 and 700 °C, respectively. The experimental results indicate that the layered perovskite GBF is a promising cathode candidate for IT-SOFCs.