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Owing to the flammability of dendrites and organic liquid electrolytes, the safety performance of lithium-ion batteries cannot be effectively ensured. The sodium-ion solid electrolyte is anticipated to become the leading next generation battery in commercial applications due to the high thermal stability and low price. Yet, the insufficient ionic conductivity of Na3Zr2Si2PO12 solid electrolytes, along with the large interfacial resistance between the cathode material and the solid electrolyte, substantially restricts the performance of room-temperature all-solid-state sodium rechargeable batteries. In the present study, the effects of Bi2O3 additive on the phase, microstructure and ionic conductivity of Na3.1Y0.1Zr1.9Si2PO12 ceramic electrolyte are reported. Moreover, a significant room temperature conductivity of 1.21 × 10-3 S cm-1 and the dense microstructure was attained by adding 1 wt% Bi2O3 to Na3.1Y0.1Zr1.9Si2PO12 sintered at 1100 °C for 6 h. Simultaneously, an electrochemical test exhibited that the electrochemical stability window increased to 4.8 V and revealed good cycle stability.

Inorganic ceramic as one of the most promising candidate for solid state electrolytes (SSEs) have received extensive attention due to their excellent thermal stability, good electrochemical stability and wide electrochemical window. The sodium super ionic conductor (NASICON, Na3Zr2Si2PO12) structure possesses a three-dimensional network, which helps the migration of Na+. However, because of its low Na+ ion conductivity and poor sintering performance, Na3Zr2Si2PO12 is difficult to achieve application. Therefore, it is quite urgent to solve these questions. In this study, we have reported the effects of additive antimony-tin oxide (ATO) on the phase, microstructure and ionic conductivity of Na3Zr2Si2PO12 ceramic electrolytes. With the ATO sintering additive added, the Na+ ion conductivity and density of Na3Zr2Si2PO12 ceramic electrolytes were improved. The Na3Zr2Si2PO12 ceramic with 5 wt% ATO additive sintered at 1100 °C shows a relatively high ionic conductivity of 1.43 × 10 − 3 S cm-1 at room-temperature, most densest microstructure and wide electrochemical window up to 4.6 V (vs. Na/Na+). In addition, Na/NASICON/Na symmetrical cells were assembled and exhibited good cycling stability which implied good compatibility between sodium (Na) metal and NASICON electrolyte.

Silver-coated carbon fibers successfully fabricated by a modified electroless plating process were characterized by scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). The electroless plating process was modified by replacing the conventional pretreatment and sensitization steps by only using surface hydroxylation step. And the activation and electroless plating steps were merged into one step. The silver layer was successfully coated onto the surface of carbon fibers under the given coating conditions. The effects of AgNO3 solution concentration and reaction temperature on the conductivity of silver-coated carbon fibers were studied in detail. The results indicated that the optimum AgNO3 solution concentration was 0.05 mol/L, and the optimum range of reaction temperature was from 45°C to 65°C.

Oxygen reduction reaction (ORR) of La 0.8 Sr 0.2 Co 0.5 Fe 0.5 O 3-δ (LSCF) cathode on La 9.5 Si 6 O 26.25 (LSO) apatite electrolyte is studied by electrochemical impedance spectroscopy over the temperature range 700–850 °C and the oxygen partial pressure range 0.01–0.21 atm. Different to the ORR on the LSCF electrode on Gd-doped ceria (GDC) electrolyte, the impedance response for the ORR on the LSCF electrode on LSO apatite electrolyte is characterized by clearly separable arcs at high, intermediate and low frequencies. The high frequency electrode process has activation energy of 231 ± 7 kJ mol −1 and is basically independent of oxygen partial pressure, which is most likely associated with the oxygen ion transfer from the LSCF electrode to LSO electrolyte at the interface. On the other hand, the electrode processes associated with the low and intermediate frequency arcs are dependent on the oxygen partial pressure with activation energies of 192 ± 12 kJ mol −1 and 124 ± 28 kJ mol −1 , respectively, are related to the dissociative adsorption and diffusion of oxygen on the LSCF surface and through the bulk and/or pores of LSCF electrodes to the reaction sites. The results show that the diffusion and migration of silica from the LSO apatite electrolyte to the LSCF surface particularly at the interface region have significant adverse effect on the electrochemical activity of LSCF cathode.

Lanthanum silicate oxyapatites with and without calcium (Ca) and iron (Fe) doping, La 10 Si 5 FeO 26.5 (LSFO) and La 9.5 Ca 0.5 Si 5.5 Fe 0.5 O 26.5 (LCSFO), are synthesized by sol–gel process (SGP) and solid state reaction process (SSP). The phase formation, microstructure and conductivities of LSFO and LCSFO oxyapatites are characterized by X-ray diffraction (XRD), scanning electron spectroscopy (SEM) and complex impedance analysis. The morphologies of LCSFO oxyapatite nanoparticles synthesized by SGP were characterized by transmission electron microscope (TEM). The thermal and decomposition properties of the LCSFO gel were analyzed by simultaneous differential scanning calorimetry and thermal gravimetric analysis (DSC–TGA). The results show that the phase formation of LCSFO synthesized by SGP occurs at temperatures as low as 750 °C, significantly lower than ∼1500 °C required for LCSFO synthesized by SSP. Co-doping of Ca and Fe significantly improves the densification, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites. The best results were obtained on LCSFO synthesized by SGP, achieving oxide-ion conductivity of 2.08 × 10 −2 S cm −1 at 800 °C, which is higher than 5.68 × 10 −3 S cm −1 and 1.04 × 10 −2 S cm −1 for LSFO and LCSFO synthesized by SSP, respectively, under the identical test conditions.

Electroless silver coating of carbonyl iron powder is demonstrated in the present investigation. The carbonyl iron powders are characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD) before and after the coating process. The relatively uniform and continuous silver coating is obtained under the given coating conditions. In this paper, the electromagnetic interference (EMI) shielding mechanism of the silver-coated carbonyl iron powder is suggested. The reflection of silver coating and absorption of carbonyl iron powder dominate the shielding mechanism of the silver-coated carbonyl iron powder. The silver-coated carbonyl iron powders are used as conductive filler in electroconductive adhesive for electromagnetic interference shielding applications. The effect of the thickness of electroconductive adhesive on the shielding effectiveness (SE) is investigated. The results indicate that the SE increases obviously with the increase of the thickness of electroconductive adhesive. The SE of the electroconductive adhesive with 0.35 mm thickness is above 38 dB across the tested frequency range.

The effect of co-doping of Sr and Al or Fe on the microstructure, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites is investigated in detail at 300–800 °C by the electrochemical impedance spectroscopy. The oxide-ion conductivity is 1.46 × 10 −2 S cm −1 for La 9.5 Sr 0.5 Si 5.5 Fe 0.5 O 26.5 (LSSFO) and 1.34 × 10 −2 S cm −1 at 800 °C for La 9.5 Sr 0.5 Si 5.5 Al 0.5 O 26.5 (LSSAO), respectively, which is one order of magnitude higher than 6.16 × 10 −3 S cm −1 measured on La 9.67 Si 6 O 26.5 (LSO) oxyapatite under the identical test conditions. The grain bulk and grain boundary resistances of co-doped oxyapatite are significantly smaller than that of LSO oxyapatite, and decrease significantly with the increase of the sintering temperature. LSSFO and LSSAO also show significantly higher density as compared to that of LSO. The results indicate that co-doping of Sr and Al or Fe significantly improves the densification, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites.

The co-doped lanthanum silicate oxyapatites, La9.5A0.5Si5.5Fe0.5O26.5 (A = Ba, Sr, and Ca), are synthesized by the high-temperature solid state reaction process. The phase formation and structure properties of undoped lanthanum silicate oxyapatite (La9.67Si6O26.5, LSO), Fe-doped lanthanum silicate oxyapatite (La10Si5FeO26.5, LSFO) and co-doped lanthanum silicate oxyapatites (La9.5A0.5Si5.5Fe0.5O26.5, A = Ba, Sr, and Ca) are characterized by X-ray diffraction (XRD) and scanning electron spectroscopy (SEM). The effect of co-doping of A (A = Ba, Sr, Ca) and Fe on the microstructure, sinterability and oxide ion conductivity of lanthanum silicate oxyapatites is investigated in detail. The results show that, as compared to LSO and LSFO oxyapatites, co-doping of A (A = Ba, Sr, and Ca) and Fe significantly benefits the sintering and densification process, and enhances the oxide ion conductivity. For co-doped oxyapatites, the oxide ion conductivities are related to the dopant size, the best properties are obtained for the oxyapatite co-doped with Ca and Fe. The co-doped La9.5Ca0.5Si5.5Fe0.5O26.5 (LCSFO) oxyapatite is a good electrolyte for SOFCs, with an oxide ion conductivity of 1.39 × 10−2 S cm−1 at 800 °C and a low activation energy of 90.71 kJ mol−1. The bulk density and oxide ion conductivities of co-doped oxyapatite ceramics increase significantly with the increase of the sintering temperature. The grain bulk and grain boundary resistances of La9.5Ba0.5Si5.5Fe0.5O26.5 (LBSFO), La9.5Sr0.5Si5.5Fe0.5O26.5 (LSSFO) and LCSFO oxyapatite ceramics are significantly smaller than those of LSO and LSFO oxyapatite ceramics sintered under the identical conditions.

Yb:YAG transparent ceramic nano-powder was prepared by chemical co-precipitation method, with ammonium bicarbonate as the precipitant and polyethylene glycol as surfactant. The addition of polyethylene glycol can reduce the agglomeration and particle size of the prepared Yb:YAG powder. The morphology, thermal stability and phase structure of Yb:YAG nano-powder were charactered by scanning electron microscopy (SEM), thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. The results show that well-crystallized nano-powder was obtained by calcining the precursors at 900 °C for 3 h. The average particle size of Yb:YAG powder is about 100–200 nm. When the volume amount of polyethylene glycol is 2.0%, well-dispersed Yb:YAG powder with spherical particles of 100 nm diameter was obtained.

Oxygen reduction reaction of (La,Sr)MnO3 (LSM) cathode on La9.5Si6O26.25 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 P 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.

Electroless Ag-coating of cenosphere particles is demonstrated in the present investigation. The electroless Ag-coating process is modified by replacing the conventional pretreatment and sensitization steps by only using a surface hydroxylation step with NaOH hydroxylating agent to simplify the steps and reduce the overall cost of the coating process. Furthermore, the activation and electroless plating steps are merged into one step. The cenosphere particles are characterized by scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDX), X-ray diffraction analysis (XRD), and fourier transform infrared (FT-IR) before and after the coating process. The relatively uniform and continuous coating is obtained under the given coating conditions. The possible mechanism of electroless Ag-coating of cenosphere particles utilizing surface hydroxylation of cenospheres is suggested.

Electroless silver coating on copper powder and its effects on oxidation resistance were investigated. In general, silver-coated copper powder is prepared by an electroless type of substitution plating making use of the substitution reaction between copper and silver. However, [Cu (NH 3 ) 4 ] 2+ is produced during the electroless plating process and absorbed onto the surface of the copper particles, which prevent substitution reactions proceeding. In the new electroless plating process, RE-608 copper-specific extractant was used as chelating reagent to formed chelate compound with Cu 2+ and the chelate compound was extracted to organic phase, which confirmed substitution reaction to be proceeding. As-coated copper particles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). When the silver content reached 6.86 wt.%, silver was homogeneously distributed around the copper particles and few free silver particles were detected. The results indicated that the properties of oxidation resistance were improved with increasing the dosage of RE-608 copper-specific extractant and reaction time, and with decreasing AgNO 3 concentration. It was also found that the optimum reaction temperature was 80 °C.

Electroless silver coating on copper powder and its effects on oxidation resistance were investigated by varying the fabrication parameters. Using acetylacetone (C5H8O2) as chelating reagent, silver-coated copper powder was fabricated by displacement reaction method. In the process, acetylacetone forms chelating compound with Cu 2+, which prevent the formation of [Cu (NH3)4]2+. Therefore, Ag + can be reduced continully and deposited on the surface of copper particles. As-coated copper particles were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and x-ray energy dispersive spectroscopy (EDS). The oxidation resistance of silver coated copper powder was investigated by gravimetric method. It was found that a fairly continuous silver layer was formed on the surface of copper powder by the electroless type of substitution plating. When the silver content reached 10 wt. %, silver was homogeneously distributed around the copper particles and few free silver particles were detected. The results showed that the silver coated copper powder with the best oxidation resistance was prepared at 40°C and the C5H8O2/AgNO3 molar ratio was 1:1.

Apatite ceramics are interesting alternative solid oxide fuel cells (SOFCs) electrolytes because of their open structure for the transportation of oxide ions and their good chemical stability. This study reports the influence of barium doping on the microstructure, sinterability and oxide conductivity properties of the aluminium lanthanum oxyapatite La9.5Ba0.5Si5.5Al0.5O26.5. SEM results show that lanthanum substitution with barium improves the sinterability of apatite ceramics. The barium doping also enhances the conductivity of the aluminium lanthanum silicates. The oxygen ion conductivity of La9.5Ba0.5Si5.5Al0.5O26.5 sintered at 1600 °C is 2.21 × 10−2 S cm−1 at 800 °C, higher than 9.81 × 10−3 S cm−1 of La10Si5AlO26.5 sample prepared under the same conditions. The results in the present study demonstrate that doping Ba on the La site for aluminium lanthanum oxyapatite reduces the sintering temperature and improves the ion conductivity. The enhancement of Ba dopant is mainly on the improvement of the densification and thus substantially reduced grain boundary resistance of aluminium lanthanum oxyapatite particularly at low temperatures

Hydrogen generation through high temperature solid oxide electrolysis cells (SOEC) has recently received increasingly international interest in the large-scale, highly efficient nuclear hydrogen production field. To achieve cost competitive electrolysis cells that are both high performing i.e. minimum internal resistance of the cell, and long-term stable, it is critical to develop electrode materials that are optimal for steam electrolysis. In this paper, the cathode materials of SOEC are reviewed. Ni-YSZ and Ni-SDC/GDC cermets are promising cathode materials for SOEC working at high temperature. The solid oxide matierials are promising cathode materials for SOEC working in atmospheres with low content of H2,e.g. in smaller scale generators used intermittently without H2 purging. More works, both experimental and theoretical, are needed to further develop SOEC cathode materials.