Search

[EN] The flash phenomenon in flash sintering of ceramic materials is closely related to electrical conductivity of the material. However, our understanding of how particle-to-particle contact of ceramic powders affects this phenomenon and, consequently, the microstructure and electrical properties of flash-sintered materials remains limited. To address this, we utilized “pseudo-in-situ” impedance spectroscopy to investigate the effect of particle-to-particle contact in nanometric powders of ZnO and 8YSZ, both before and after flash sintering. The powders were prepared using two different procedures, either grinding with a binder or employing multiple milling and calcining steps. After compacting into pellets, the samples were characterized before and after flash sintering, either with current-to-voltage control or with the application of current density ramps until the flash event occurred. Pseudo-in-situ impedance was employed to demonstrate that preparing powders using multiple milling and calcining steps improved charge-carrier mobility paths, facilitated homogeneous passage of electric current, reduced thermal gradients, and consequently resulted in better microstructural homogeneity and electrical conductivity. In addition, the use of the electric-current ramp control retained microstructural homogeneity to a greater degree.

The potential of interactive layers of mixed-conducting oxides for improving the performance of air electrodes of solid oxide cells in the intermediate-temperature range is demonstrated. Active layers of CeGdO (CGO), CePrO (CPO), and SrFeMoO (SFM) with thickness in the range 200-400 nm are deposited on CGO-based electrolyte by spray pyrolysis, followed by deposition of a SFM/CGO composite air electrode by painting. The morphologies and phase composition of the active layers are examined by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis. The electrochemical performance of the electrolyte-electrode assemblies is determined by impedance spectroscopy in the range 600-800 °C. Significant improvements in the performance of the electrode process and the geometrically normalized ohmic conductance are observed for the assembly with a CPO active layer with mixed-oxide-ionic-electronic conductivity, especially in the low-temperature range, attributable to extension of the surface path of the electrochemical reactions. The CGO intermediate layer also improves performance but to a lesser degree, most likely due to better ionic-current collection in comparison to the assemblies with either SFM as the active layer or no active layer.

The impact of energy production by conventional technologies on the environment and human health has promoted transition policies towards a new model for the energy sector. In this context, it is essential to identify the key challenges which favour the global implementation of a clean, safe and efficient energy system, focused on the ways in which energy is produced and stored, and the management of existing resources and their emissions.

Protonic ceramic fuel cells (PCFCs) are promising electrochemical devices for the efficient and clean conversion of hydrogen and low hydrocarbons into electrical energy. Their intermediate operation temperature (500–800 °C) proffers advantages in terms of greater component compatibility, unnecessity of expensive noble metals for the electrocatalyst, and no dilution of the fuel electrode due to water formation. Nevertheless, the lower operating temperature, in comparison to classic solid oxide fuel cells, places significant demands on the cathode as the reaction kinetics are slower than those related to fuel oxidation in the anode or ion migration in the electrolyte. Cathode design and composition are therefore of crucial importance for the cell performance at low temperature. The different approaches that have been adopted for cathode materials research can be broadly classified into the categories of protonic–electronic conductors, oxide-ionic–electronic conductors, triple-conducting oxides, and composite electrodes composed of oxides from two of the other categories. Here, we review the relatively short history of PCFC cathode research, discussing trends, highlights, and recent progress. Current understanding of reaction mechanisms is also discussed.

[EN] The authors regret the mistake made when transcribing the gravimetric capacitance data reported in the previous article, the corrected values are as follows: The gravimetric capacitance was calculated using the discharge curves at different current densities, reaching 50.3, 39.1 and 41.3 F g−1 for 0.06, 0.60 and 2.40 A g−1, respectively. The authors wish to comment that these values do not alter the conclussions of the article, but rather accentuate the capacitive performance of the structures. The authors would like to apologise for any inconvenience caused.

[EN] Reduced graphene oxide (rGO) scaffoldings are used as templates to create lightweight 3D rGO/silica and rGO/silico-aluminate hybrids by a simple impregnation route and the sol-gel method. The printed rGO assemblies are infiltrated by the corresponding alkoxide precursor solution and gelled by exposure to ammonia vapours, producing an hybrid replica of the rGO structure. The hybrids show a significant prevalence of mesopores, with total porosity above 94 %, density of ~ 0.1 g¿cm¿3 and high specific surface area (¿ 190 m2¿g¿1). As a result, the 3D composite materials show enhanced water adsorption capacity and hydrophilicity, display compressive strengths in the range 0.1 ¿ 0.4 MPa, which scale with the proportion of silica (or Al-modified silica) on the hybrid scaffold, and electrical conductivities are above 60 S¿m¿1. These properties are very attractive for applications in the removal of pollutants, water filtering, catalysis, drug delivery, or energy production and storage.

[EN] Steady graphene oxide (GO) scaffolds created by direct ink writing are used to develop a silicon carbonitride (SiCN) -graphene oxide hybrid material through a preceramic polymer route. For achieving mechanically stable GO scaffolds, the drying method is critical as the ink contains about 5 wt.% of GO, 10 wt.% of polyelectrolytes and 85 wt.% of water. The liquid preceramic polymer (polysilazane type) quickly infiltrates the 3D scaffolds, under vacuum conditions, entirely covering the GO network creating a replica of the original scaffold. The hybrid cellular structure -once thermally treated for GO reduction and ceramic conversion- consists of a network of reduced GO (∼10 wt.%) embedded in an amorphous SiCN matrix following the designed architecture. The 3D hybrid structures show notable electrical conductivity (890 S m at room temperature), thermal stability and considerable strength, about 20 times higher than the single GO scaffold. The structures are tested as electrodes for supercapacitors, reaching a gravimetric capacitance of 39 F g that remains stable after 7000 charge/discharge cycles.

The arrangement of 2D graphene-type structures into strong and self-supported architectures by filament printing depends critically on the ink characteristics. Printable inks are normally achieved by controlling the electro-steric interactions in the particle dispersion by different means. This research shows that is possible to use just a single surfactant for graphene-type inks, such as graphene oxide (GO), graphene nanoplatelets (GNP) and their mixtures, to achieve characteristics of gelled inks, in other words, shear-thinning behavior and a high elastic modulus at rest. The surfactant is a commercial hydrogel former of the poloxamer family that contains both hydrophilic and hydrophobic blocks. These inks do not require lyophilization or supercritical drying processes, accordingly the method is simple, scalable and produces lightweight 3D printed structures that exhibit high strength and prominent electrical conductivity after heat treating at 1200 °C. Furthermore, it makes possible to adjust the proportion of GO and GNP in the ink to tailor the properties of the structure according to the pursued application.