Catalysts of 2 wt % Pd supported on CeO2, Sm2O3, and CeO2/Sm2O3 (in a 4:1 molar ratio) were studied in detail by high-resolution transmission electron microscopy and elemental mapping, both as-prepared and after undergoing one of three reduction pretreatments of increasing severity. The evolution in the nanostructure, composition, and disposition of the phases were studied in detail as a function of starting composition and of pretreatment conditions. The trends observed were compared with the trends in activity and selectivity of the catalysts for hydrogen generation from methanol fuel, with a view to their application in direct methanol intermediate-temperature solid oxide fuel cells. The catalyst preparation conditions had a dramatic effect on the Sm-containing materials but not on the Pd/CeO2. The Pd/CeO2/Sm2O3 catalyst was seen to develop a beneficial hierarchical structure in which Pd particles were supported on fine Sm2O3 crystallites, which were in turn supported on larger CeO2 particles. This effect may be useful for the deliberate design of such nanostructured catalysts.

Soft actuators based on Ionic Polymer–Metal Composites (IPMCs) are of considerable interest for applications in biomedical devices and robotics. In this work, thin commercial and thick laboratory-prepared Nafion membranes were made into model IPMC actuator devices by incorporation of Pt electrode layers. In extensive electromechanical tests the maximum average tip displacement and maximum force generated were recorded. The effect of amplitude and frequency of the applied voltage on both displacement and force was examined as were the effects of the origin of the Nafion membrane, the Pt loading, the structure of the electrode and the presence or absence of an Au overlayer. The cast samples generated much smaller displacements but much larger forces than the commercial Nafion samples. For all samples, displacement and force increased with increasing applied voltage, with increased number of Pt plating cycles and when an Au overlayer was present but decreased with increasing applied voltage frequency. Waveform analysis of applied voltage, current and force was performed by considering the capacitive nature of the IPMC actuators.

In a systematic study, Samarium doped ceria (SDC) nanopowders, SmxCe1−xO2−x/2 (x = 0.1, 0.2 or 0.3), were prepared by a low temperature citrate complexation route. The synthesis and crystallisation of the SDC powders were followed by thermochemical techniques (TGA/DTA), X-ray diffraction, elemental analysis, specific surface area determination (BET) and electron microscopy (SEM and TEM). Mean crystallite sizes were found to be around 10 nm for all compositions calcined at 500 °C. Dense electrolyte bodies were prepared at 1300 °C, 1400 °C and 1450 °C using two sintering times, 4 h or 6 h. Densities of 91–97% of theoretical were obtained, with a marked improvement in density on going from 1300 °C to higher sintering temperatures. Grain size analysis was conducted using SEM. Grain size distributions were related to %Sm and sintering conditions. Impedance spectroscopy was used to determine the total, bulk and grain boundary conductivities, the related activation energies and enthalpies of defect association and ion migration. Sintering at 1400 °C/6 h or 1450 °C/4 h gave superior grain structure and conductivity, with oversintering occurring after more severe treatments. At 600 °C the highest total ionic conductivity was 1.81 × 10−2 S cm−1 for Sm0.2Ce0.8O1.9. The relationships between chemical composition, sintering parameters, grain structure and electrochemical performance are discussed.Graphical abstractResearch highlights▶ A compositional series of high purity, nanoparticulate SDC materials was successfully prepared by a low temperature, inexpensive citrate complexation method in order to perform a detailed study of the effect of chemical composition, sintering temperature and sintering time on the densification, grain structure and ionic conductivity of the resulting dense pellets. ▶ Crystallization of the SDC product occurred from the gel at a temperature below 300 °C to give foam-like, single-phase materials with high porosity and with primary crystalline particles of about 10 nm diameter. ▶ Densities of over 95% of theoretical were achieved for all three compositions after sintering at 1400 °C or higher for 4 h or longer and both density and average grain size increased with increasing sintering temperature and sintering time. Samples sintered at 1400 °C for 6 h or 1450 °C for 4 h showed excellent microstructure for all compositions. ▶ Arrhenius-type plots of electrolyte conductivity showed an inflexion at around 500 °C and this was interpreted in terms of a defect association enthalpy, ΔHa, and an oxygen migration enthalpy, ΔHm. ΔHa was less sensitive to Sm content and had values of around 0.4 eV. ΔHm increased significantly with %Sm and had values of 0.4–0.7 eV. ▶ At 600 °C, the highest total conductivity was 1.81 × 10−2 S cm−1 for the 20SDC sample sintered at 1450 °C for 6 h.

Solid Oxide Fuel Cells (SOFCs) represent an attractive technology for the conversion of chemical to electrical energy because of their high efficiencies and low environmental impact, and because of the useful, high grade heat also generated. Direct utilisation of hydrocarbons in SOFCs would contribute to the more sparing utilisation of remaining fossil fuel reserves. In the longer term, this technology could be extended to work with more sustainable biofuel and waste-derived feedstocks. In this work, nanoparticulate Ceria–Zirconia mixed oxides, Ce1−xZrxO2 (x = 0.1, 0.25, 0.5, 0.75 and 0.9), were studied with a view to their application as anode materials in intermediate temperature (IT) SOFCs using hydrocarbon fuels. Impedance spectra were recorded in symmetrical cells under reducing conditions using gadolinium-doped ceria (GDC) as the electrolyte material. The spectra were analysed in terms of a double fractal finite length Gerischer impedance model. The model parameters were found to have monotonic dependences on temperature and more complex relationships with respect to Zr content. Diffusion-related processes and the electrochemical reaction were fastest for intermediate Zr contents while the chemical exchange reaction rate increased with decreasing Zr content. As a result, anode catalysts with 10 and 25 mol% Zr showed the lowest polarisation resistances of only 0.17 and 4.52 Ω cm2 at 700 °C in humidified 5% H2 and humidified 5% CH4, respectively. These values represented an approximately two-fold improvement on the pure ceria electrode. This performance compares very favourably with the currently most promising candidate anode materials applied in SOFCs for use with hydrocarbon fuels.

A variant of the sol–gel technique known as cation complexation is used to prepare a nanocrystalline Gd0.1Ce0.9O1.95 (GDC) solid solution. A range of techniques including thermal analysis (TGA/DTA), X-ray diffraction, specific surface area determination (BET) and electron microscopy (SEM and TEM) are employed to characterise the GDC powders. GDC calcined at 500 °C is found to have an average crystallite size of 11 nm. Specific surface areas are found to be 29.7 m2 g−1 for the as-calcined powder and 57.5 m2 g−1 after ball milling at 400 rpm. Dense ceramic pellets are prepared from unmilled and ball-milled GDC powders employing different thermal treatments. Their electrical properties are studied by impedance spectroscopy. Those samples sintered at 1300 °C for 30 h (starting from ball-milled powders) exhibit the highest density (96% of theoretical density) and the highest total ionic conductivity (1.91 × 10−2 S cm−1 at 600 °C).

SrCe0.95Yb0.05O3 (SCY) and related materials are under consideration as a proton conductors for Solid Oxide Fuel Cell (SOFC) electrolytes. Sintered pellets of SCY are used to perform impedance spectroscopy (IS) studies and fuel cell tests on cells with Pt electrodes of two different morphologies. Electrodes are applied to the SCY pellets by two routes: either by firing on a layer of Pt paint (denoted electrode P) or by magnetron sputtering (electrode S). In impedance spectra recorded over a wide temperature range under humidified hydrogen, in symmetrical cell conditions, cells with S electrodes give rise to a much smaller low frequency impedance feature than the cells with P electrodes. This is tentatively attributed to faster diffusion-related processes taking place at the S electrodes. The behaviour of working fuel cells with S and P electrode morphologies is evaluated in terms of maximum power output and Area Specific Resistance in two-atmosphere tests. The fuel cell anode with the S morphology results in superior fuel cell performance, in agreement with the impedance study. The influence of the two different electrode morphologies on the behaviour of the cells is discussed with reference to their morphology, as determined by SEM and AFM.

The synthesis of nanocrystalline solid solutions of general formula CexZr1−xO2 (x = 0.1, 0.25, 0.5, 0.75, and 0.9) using a citrate complexation technique was followed with thermochemical methods, and the resulting powders were characterized using X-ray diffraction (XRD) and electron microscopy (scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM)). Qualitative analysis of XRD data indicated that the samples exhibited either a cubic (Fm3m) or a tetragonal (P42/nmc) phase, depending on CeO2 content. Electron diffraction results were consistent with the XRD findings. In HRTEM, the internal crystal structure of the nanoparticles was observed to be highly ordered and primary particle size data were collected. Average crystallite size, obtained from the XRD data, was 4.8−8.3 nm, with the larger values at the compositional extremes. A similar trend was observed in HRTEM, although values were generally slightly higher. The Ce0.5Zr0.5O2 solid solution had the smallest crystallites (4.8 nm) and the highest specific surface area (45.8 m2·g−1).

In this work, ZrO2−CeO2 mixed oxide nanotubes with 50, 70, and 90 mol % CeO2 were synthesized following a very simple, high yield procedure, and their properties were characterized by synchrotron radiation XRD and by high resolution electron microscopy. The 50, 70, and 90 mol % CeO2 nanotubes exhibited the tetragonal phase (t′-form and t′′-form, P42/nmc space group) or the cubic phase (Fm3m space group). The nanotube walls were composed of nanoparticles with an average crystallite size ranging from 4.7 to 7.6 nm. Electron microscopy observations confirmed the size of these nanoparticles by direct observation. The SEM and TEM results showed that individual nanotubes were composed of a curved sheet of these nanoparticles. By SEM analysis, the nanotubes were found to have lengths of around 1−8 μm, diameters of around 500 nm, and wall thicknesses of 20 nm. Elemental analysis showed that Ce:Zr ratios appeared to be constant across space, suggesting compositional homogeneity in the samples. The 90 mol % CeO2 nanotubes exhibited the highest value of specific surface area, 101 m2·g−1, which compared with about 28 m2·g−1 for the other two compositions.

In this work, nanostructured gadolinia-doped ceria tubes (GdxCe1−xO2−x/2 with x = 0.1 and 0.2) were synthesised following a very simple, high yield procedure and their properties were characterised by XRD and by electron microscopy (SEM and HRTEM). Tubes of both oxide compositions were comprised of nanocrystals that exhibited the cubic phase (Fmm space group). In SEM, the tubes were found to have lengths of around 2 µm, diameters of around 700 nm and wall thicknesses of about 10 nm. The SEM and TEM results showed that individual tubes were composed of a thin sheet of nanoparticles curved round to form the tubular structure. The size of these primary nanoparticles was calculated from the peak-broadening seen in the XRD results. Average crystallite sizes of 7.8 and 9.4 nm were found for Gd0.1Ce0.9O1.95 and Gd0.2Ce0.8O1.9, respectively. Electron microscopy observations confirmed the size range of these nanoparticles by direct observation. The nanostructured Gd0.1Ce0.9O1.95 tubes exhibited a higher value of specific surface area, at 97 m2 g−1, than the other composition (61 m2 g−1).

SBA-15 was employed as the hard template in the preparation of ordered mesoporous ZrO2 by the replica method. The resultant ZrO2-SR product was characterized by XRD, TEM, EDX, SEM and nitrogen physisorption. The starting material, intermediate and product were studied by FT-IR. The formation of Zr–O–Si crosslinks made it impossible to obtain a pure ZrO2 product, although the material did have a similar ordered mesoporous structure to the SBA-15 template. The results showed that the replica method itself could be successfully used to prepare ordered mesoporous ZrO2, but that the use of mesoporous silica as the hard template meant that the silicon could not be completely removed from the product. The product was seen to contain both the normally stable monoclinic form of zirconia as well as the metastable tetragonal phase. The presence of the latter was considered to be related to the constriction of particle size by the SBA-15 template and by the Si-containing surface layer. These could both hinder sintering of the zirconia particles and prevent crystallite growth to sizes above the critical size, where the tetragonal phase would not be expected. The mesoporous zirconia product had a specific surface area of 220 m2 g−1 and a pore volume of 0.57 cm3 g−1, making it of great interest for applications as a support in catalysis and electrocatalysis.

The physical structure and the actuation mechanism of a Nafion-based soft actuator – a Pt-containing ionic polymer–metal composite (IPMC) – were investigated using in situ magnetic resonance imaging (MRI) during application of four different electrical regimes. Importantly, the raw MRI data were used to generate spatial maps of both proton density (PD) and proton spin–spin relaxation time (T2) across the sample. These were successfully employed to study changes in the distribution and chemical environment of water molecules absorbed within the operating actuator device. The IPMC sample was mapped in this way during the application of a small d.c. potential across its thickness. Three main phenomena were observed in the results: initial rapid increase in T2 at both electrodes, without an observed change in PD; slower formation of a region of high T2 and high PD at the IPMC cathode; and contraction of the polymer along the anode and its expansion along the cathode, giving rise to bending actuation. Reversing the polarity of the applied potential resulted in the reversal of the direction of the bending deformation of the IPMC sample and of the distribution of PD and T2 within it. These phenomena were explained in terms of the unusual structure of Nafion and its interaction with host ions and the electric field. Up to 20% of the total water content of the IPMC was found to be involved in long-range electro-diffusion.

In this work, a variant of the sol–gel technique known as cation complexation was used for the preparation of Gadolinum-doped ceria (GDC) solid solution. This method has the advantage of low cost and relative simplicity. A range of techniques including X-ray diffraction (XRD), specific surface area determination (BET) and scanning electron microscopy (SEM) were employed to characterize the GDC powder. GDC calcined at 500∘C was found to have an average crystallite size of 10 nm. To obtain an insight into any changes in the electrolyte material during operation, the electrochemical properties of dense GDC samples were studied by impedance spectroscopy (IS) before and after simple ageing treatment in dry air at 800∘C for 40 h. A reduction in grain boundary conductivity was observed after thermal treatment in the sample with the lower density.

Diffusion-weighted imaging was employed to spatially map the distribution of the diffusion coefficient of water, D, in bare, water-soaked, Li+-exchanged, cast Nafion and in an ionic polymer−metal composite (IPMC) soft actuator element, prepared from this bare Nafion by impregnation with Pt electrodes. D was evaluated in two orthogonal directions: along one of the long dimensions of the sample (Dx) and through its thickness (Dz). D-maps of the IPMC element were obtained both in the absence of an applied potential and in situ during the application of a 3 V dc potential across the thickness of the sample. In the bare Nafion, D-maps showed uniform values of both Dx and Dz of about 6 × 10−10 m2 s−1. In the IPMC two effects were observed: (i) D at the electroded surfaces of the IPMC was higher than at the center of the sample; (ii) this difference was much greater in Dz than in Dx. Both effects were explained by the influence of the impregnated Pt electrodes on polymer structure. The D-maps in the electrochemical measurements showed high values of D (up to 8 × 10−10 m2 s−1) at the cathode and low values (from 1 × 10−10 m2 s−1) at the anode. This was explained in terms of the effect on the Nafion nanostructure of the forced electro-migration of Li(H2O)x+ species toward the cathode.

Arrhenius plots of conductivities and capacitances associated with the bulk, overall electrolyte, charge transfer and electrode processes taking place in a symmetrical cell with well-defined Pt electrodes and electrolyte based on the ceramic proton conductor, SrCe0.95Yb0.05O3, were obtained under wet and dry air, wet and dry hydrogen and wet and dry argon over the temperature range, 200 °C–800 °C. Results for all six gas atmospheres are discussed in order to gain insight into the conduction mechanisms taking place within the electrolyte and, especially, the conduction, sorption and diffusion processes occurring at the electrodes, in this model system.

Solid Oxide Fuel Cells (SOFCs) represent an attractive technology for the conversion of chemical to electrical energy because of their high efficiencies and low environmental impact, and because of the useful, high grade heat also generated. Direct utilisation of hydrocarbons in SOFCs would contribute to the more sparing utilisation of remaining fossil fuel reserves. In the longer term, this technology could be extended to work with more sustainable biofuel and waste-derived feedstocks. In this work, nanoparticulate Ceria–Zirconia mixed oxides, Ce1−xZrxO2 (x = 0.1, 0.25, 0.5, 0.75 and 0.9), were studied with a view to their application as anode materials in intermediate temperature (IT) SOFCs using hydrocarbon fuels. Impedance spectra were recorded in symmetrical cells under reducing conditions using gadolinium-doped ceria (GDC) as the electrolyte material. The spectra were analysed in terms of a double fractal finite length Gerischer impedance model. The model parameters were found to have monotonic dependences on temperature and more complex relationships with respect to Zr content. Diffusion-related processes and the electrochemical reaction were fastest for intermediate Zr contents while the chemical exchange reaction rate increased with decreasing Zr content. As a result, anode catalysts with 10 and 25 mol% Zr showed the lowest polarisation resistances of only 0.17 and 4.52 Ω cm2 at 700 °C in humidified 5% H2 and humidified 5% CH4, respectively. These values represented an approximately two-fold improvement on the pure ceria electrode. This performance compares very favourably with the currently most promising candidate anode materials applied in SOFCs for use with hydrocarbon fuels.

Soft actuators based on Ionic Polymer–Metal Composites (IPMCs) are of considerable interest for applications in biomedical devices and robotics. In this work, thin commercial and thick laboratory-prepared Nafion membranes were made into model IPMC actuator devices by incorporation of Pt electrode layers. In extensive electromechanical tests the maximum average tip displacement and maximum force generated were recorded. The effect of amplitude and frequency of the applied voltage on both displacement and force was examined as were the effects of the origin of the Nafion membrane, the Pt loading, the structure of the electrode and the presence or absence of an Au overlayer. The cast samples generated much smaller displacements but much larger forces than the commercial Nafion samples. For all samples, displacement and force increased with increasing applied voltage, with increased number of Pt plating cycles and when an Au overlayer was present but decreased with increasing applied voltage frequency. Waveform analysis of applied voltage, current and force was performed by considering the capacitive nature of the IPMC actuators.

SBA-15 was employed as the hard template in the preparation of ordered mesoporous ZrO2 by the replica method. The resultant ZrO2-SR product was characterized by XRD, TEM, EDX, SEM and nitrogen physisorption. The starting material, intermediate and product were studied by FT-IR. The formation of Zr–O–Si crosslinks made it impossible to obtain a pure ZrO2 product, although the material did have a similar ordered mesoporous structure to the SBA-15 template. The results showed that the replica method itself could be successfully used to prepare ordered mesoporous ZrO2, but that the use of mesoporous silica as the hard template meant that the silicon could not be completely removed from the product. The product was seen to contain both the normally stable monoclinic form of zirconia as well as the metastable tetragonal phase. The presence of the latter was considered to be related to the constriction of particle size by the SBA-15 template and by the Si-containing surface layer. These could both hinder sintering of the zirconia particles and prevent crystallite growth to sizes above the critical size, where the tetragonal phase would not be expected. The mesoporous zirconia product had a specific surface area of 220 m2 g−1 and a pore volume of 0.57 cm3 g−1, making it of great interest for applications as a support in catalysis and electrocatalysis.

In this work, nanostructured gadolinia-doped ceria tubes (GdxCe1−xO2−x/2 with x = 0.1 and 0.2) were synthesised following a very simple, high yield procedure and their properties were characterised by XRD and by electron microscopy (SEM and HRTEM). Tubes of both oxide compositions were comprised of nanocrystals that exhibited the cubic phase (Fmm space group). In SEM, the tubes were found to have lengths of around 2 µm, diameters of around 700 nm and wall thicknesses of about 10 nm. The SEM and TEM results showed that individual tubes were composed of a thin sheet of nanoparticles curved round to form the tubular structure. The size of these primary nanoparticles was calculated from the peak-broadening seen in the XRD results. Average crystallite sizes of 7.8 and 9.4 nm were found for Gd0.1Ce0.9O1.95 and Gd0.2Ce0.8O1.9, respectively. Electron microscopy observations confirmed the size range of these nanoparticles by direct observation. The nanostructured Gd0.1Ce0.9O1.95 tubes exhibited a higher value of specific surface area, at 97 m2 g−1, than the other composition (61 m2 g−1).