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Graphene hydrogels with high electrical conductivity were prepared by a one-step process using hydrazine hydrate as gel assembly agent (GH-HD). Conventional two-step process of gel formation and further reduction to prepare highly conducting gels was replaced by a single step involving equivalent amount of hydrazine. Optimized graphene oxide concentration was established to facilitate such monolith formation. Extensive characterization and control studies enabled understanding of the material properties and gel formation mechanism. The synthesized gel shows a high electrical conductivity of 1141 S/m. The supercapacitor based on GH-HD delivers a high specific capacitance of 190 F/g at a current density of 0.5 A/g and 123 F/g at very high current density of 100 A/g. Furthermore, excellent power capability and cyclic stability were also observed. 3D macroporous morphology of GH-HD makes it ideal for high rate supercapacitor applications. [ABSTRACT FROM AUTHOR]

The present work aims to better understand the effect of operating temperature on the degradation of Solid Oxide Electrolysis Cells (SOECs). The studied SOECs consist of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ -Ce 0.8 Gd 0.2 O 2-δ (LSCF-GDC) oxygen electrode, GDC diffusion barrier layer, Y 0.16 Zr 0.84 O 1.92 (YSZ) electrolyte and Ni-YSZ hydrogen electrode. Durability tests are carried out at 750, 800 and 850 °C for 2000 h at −1 A cm−2, using 10/90 vol% H 2 /H 2 O and dry air at the hydrogen and oxygen electrodes, respectively. The electrochemical impedance spectra measured before and after ageing reveal a strong evolution related to the hydrogen electrode, while the change in the oxygen electrode contribution remains negligible. A set of advanced characterization techniques are employed to study the cell degradation. For the hydrogen electrode, a large Ni depletion is observed after ageing, which increases with the operating temperature. The analysis of the oxygen electrode shows an elemental inter-diffusion between the LSCF-GDC/GDC/YSZ layers on the manufactured cells that seems to not evolve significantly upon operation. Moreover, the presence of SrZrO 3 is not detected in the pristine cell and in the operated ones. Besides, only a limited LSCF decomposition is found in good agreement with the electrochemical characterizations. Hypotheses that could explain the good oxygen electrode stability are discussed. • Effect of temperature on solid oxide electrolysis cells degradation. • Higher Ni depletion at 850 °C than 750 °C. • Role of the interdiffusion layer on the cell durability. • Intermixing between LSCF and GDC with diffusion of Ce and Gd into LSCF. • Limited Sr segregation after operation under electrolysis current. [ABSTRACT FROM AUTHOR]