Suchergebnisse

The manufacturing of three-dimensional (3D) graphene monoliths with remarkable electrical performance has become a challenging issue because their potential applications in the energy and electronic-based fields. Here we show the development of outstanding electrically conductive graphene patterned cellular structures combining a versatile and easily scalable filament printing method, such as Robocasting, with the use of highly crystalline graphene nanoplatelets (GNPs) as the graphene source. Robust 3D pure graphene-based monoliths have been manufactured by printing pseudoplastic aqueous-based GNPs inks with high graphene contents (36.6 wt %) and further thermal treatment by spark plasma sintering. Specific conductivities up to 385 S·cm have been assessed along the longitudinal direction of the 3D structure, i.e., where the current mainly flowed along the struts, being more conductor than reported 3D synthesized graphene structures and up to 2 orders of magnitude higher than 3D printed graphene monoliths. The present findings could open a straightforward pathway for creating, in a controlled way, a wide range of graphene-based hierarchical structures with an excellent electrical performance and robustness that could be employed for energy storage systems. ; Spanish Government (MAT2012-3294 and MAT2015-67437-R projects) and CSIC (PIE 201360E063 project). D. Pérez-Coll also acknowledges the financial support by FCT-BPD grant (SFRH/BPD/112282/2015). ; Peer Reviewed

[EN] The BaZrCeYO-BaPrO perovskite system, of interest for high-temperature electrochemical applications involving mixed protonic-electronic conductivity, forms a solid-solution with a wide interval of Ba substoichiometry in the range Ba(CeZr)PrYO, 0 ≤ x ≤ 1. Structural phase transitions mapped as a function of temperature and composition by high-resolution neutron powder diffraction and synchrotron X-ray diffraction reveal higher symmetry for lower Pr content and higher temperatures, with the largest stability field observed for rhombohedral symmetry (space group, R3c). Rietveld refinement, supported by magnetic-susceptibility measurements, indicates that partitioning of the B-site cations over the A and B perovskite sites compensates Ba substoichiometry in preference to A-site vacancy formation and that multiple cations are distributed over both sites. Electron-hole transport dominates electrical conductivity in both wet and dry oxidizing conditions, with total conductivity reaching a value of 0.5 S cm for the x = 1 end-member in dry air at 1173 K. Higher electrical conductivity and the displacement of oxygen loss to higher temperatures with increasing Pr content both reflect the role of Pr in promoting hole formation at the expense of oxygen vacancies. In more reducing conditions (N) and at low Pr contents, conductivity is higher in humidified atmospheres (0.023 atm pHO) indicating a protonic contribution to transport, whereas the greater electron-hole conductivity with increasing Pr content results in lower conductivity in humidified N due to the creation of protonic defects and the consumption of holes. ; We thank the MINECO, Spain (ENE2015-66183-R and MAT2016-78362-C4-1-R), CSIC, Spain (i-link0743), and CAPES, Brazil (PVE, Proceso 88881.03418/2013-1). Access to the neutron facilities at the Institut Laue Langevin (Grenoble, France) and the National Synchrotron Light Laboratory (LNLS, Campinas, Brazil) under grant 5-24-55(D2B) and research proposal D10B-XRD1-16166, respectively, is gratefully acknowledged. We also thank the FCT, PTDC/CTM-EME/6319/2014, QREN, FEDER, and COMPETE Portugal and the European Social Fund, European Union. U.A. acknowledges the Universidad San Pablo for financial support. We would also like to thank Steven Kermorvant and Alexandre Bosser of the IUT, University of Rennes (France), for assistance.