Suchergebnisse

Altres ajuts: Authors appreciate the award to DPD with the support of the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia and the Co-fund programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union" and the award of Humboldt Fellowship of the Alexander von Humboldt Foundation (AvH), Germany. ; This work presents a facile reactive template route to prepare polypyrrole (PPy) with a given, chosen nanostructure among three different morphologies (i.e., nanotubes, nanofibers and urchins). This approach exploits the variability of MnO morphologies and its versatility as sacrificial template. The morphological evolution for this template-assisted growth of PPy nanostructures has been briefly explained. These unique architectures significantly enhance the electroactive surface area of the PPy nanostructures, leading to better interfacial/chemical distribution at the nanoscale, fast ion and electron transfer and good strain accommodation. Thus, when used as supercapacitor electrodes, a maximum specific capacitance of 604 F/g at a current density of 1.81 A/g was reached for PPy nanofibers. Even after more than 1000 cycles at 9 A/g, a capacitance of 259 F/g with 91% retention was achieved. Moreover, the same PPy nanofibers can be used as cathode material for lithium-ion batteries (LIBs), showing a capacity of 70.82 mAh/g at a rate of 0.10 C with good cycling stability and rate capability. Our results provide sound evidences that PPy nanostructures can be properly tuned and make the difference for the practical application of these materials in electrochemical energy storage devices.

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that polarization occurs when a conducting material is immersed in an electrolyte in presence of electric fields, and bipolar electrochemistry processes may occur. This work demonstrates the dramatic drop in resistance for electrochemical cells with just a few macroscopic conducting pieces immersed in the electrolyte, in the absence of any electrical contact, through bipolar induction. Furthermore, mediation of soluble redox species between adjacent induced poles of opposite charge results in an additional mechanism for charge transfer, contributing further to the decrease in impedance. Relevant parameters like size, geometry, and spatial occupation of inducible pieces within the electric field, are relevant. Remarkably, the effects observed can explain some empirical observations previously reported for carbon suspensions and slurries. Thus, no electronic percolation requiring particle contact, nor ordering, are needed to explain the good performance associated to lowered impedance These results suggest new engineering designs for electrochemical cells with enhanced currents. ; The authors thank financing from the Ministry of Science of Spain (MAT2015-65192-R, and RTI2018-097753-B-I00, RTI2018-099826-B-I00, MAT2017-91404-EXP), and Severo Ochoa Program (SEV-2015-0496 and CEX2019-000917-S). LLA thanks the Ramon y Cajal Program contract (RYC-2013-12640). ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed