R. Berenguer

Biomass-derived binderless fibrous carbon electrodes for ultrafast energy storage

The possibility of storing energy efficiently and sustainably at little cost is crucial to prevent climate change and the exhaustion of natural resources. In this work we demonstrate that interconnected and porous carbon fibers easily obtained from lignin exhibit ultrafast charge–discharge and excellent energy density and cyclability performances, to be used as binderless and flexible electrodes in supercapacitors.

Preparation of different carbon materials by thermochemical conversion of lignin

Lignin valorization plays a crucial role within the modern biorefinery scheme from both the economic and environmental points of view; and the structure and composition of lignin becomes it an ideal precursor for the preparation of advanced carbon materials with high added-value. This review provides an overview of the different carbonaceous materials obtained by thermochemical conversion of lignin, such as activated carbons, carbon fibers, template carbons; high ordered carbons; giving information about the new strategies in terms of the preparation method and their possible applications.

Cyanide and Phenol Oxidation on Nanostructured Co3O4 Electrodes Prepared by Different Methods

Financial support by the Generalitat Valenciana grant no. GV05/136, no. GV06/106, and no. RED ARVIV/2007/076) and Ministerio de Educacion y Ciencia (MAT2007-60621 and MAT2005-00262) projects.

Pt- and Ru-Doped SnO2–Sb Anodes with High Stability in Alkaline Medium

Different Pt- and Ru-doped Ti/SnO2-Sb electrodes were synthesized by thermal decomposition. The effect of the gradual substitution of Sb by Ru in the nominal composition on the physicochemical and electrochemical properties were evaluated. The electrochemical stability of the electrodes was estimated from accelerated tests at 0.5 A cm(-2) in 1 M NaOH. Both as-synthesized and deactivated electrodes were thoroughly characterized by scanning electron microscopy (SEM), energy-dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD). The incorporation of a small amount (about 3 at. %) of both Pt and Ru into the SnO2-Sb electrodes produced a 400-times increase in their service life in alkaline medium, with no remarkable change in the electrocatalysis of the oxygen evolution reaction (OER). It is concluded that the deactivation of the electrodes is promoted by alkaline dissolution of metal species and coating detachment at high potentials. The introduction of Pt has a coating compacting effect, and Ru(IV), at low amounts until 9.75 at. %, replaces the Sn(IV) cations in the rutile-like SnO2 structure to form a solid solution that strongly increases the stability of the electrodes. The observed Ru segregation and decreased stability for larger Ru contents (x > 9.75 at. %), together with the selective dissolution of Ru after deactivation, suggest that the formation of a homogeneous (RuδSn1-δ)O2 single-phase is crucial for the stabilization of these electrodes.

Phosphorus functionalization for the rapid preparation of highly nanoporous submicron-diameter carbon fibers by electrospinning of lignin solutions

This work presents a fast and versatile method to prepare carbon fibers from lignin. It involves the production of submicron-sized phosphorus-functionalized lignin fibers in only one step by electrospinning of lignin/H3PO4 solutions. The phosphorus functionalities enable shortening of the conventional stabilization process from more than 90 h to only 2 h thus avoiding fiber fusion or even stabilizing the lignin fibers in an inert atmosphere. The incorporation of H3PO4 into the initial lignin solution produces more oxidized spun lignin fibers, due to the reaction of phosphoric acid with the dissolved lignin, generating phosphate (and/or polyphosphate) esters throughout the structure of lignin fibers. These phosphate groups seem to be responsible for the production of cross-linking reactions during the stabilization step that are, in this case, very active and effective in increasing the glass transition temperature of the lignin fibers, reducing the time needed for the stabilization step and improving this process. Moreover, they promote the chemical activation of lignin fibers and greatly increase their oxidation resistance, avoiding their complete combustion during carbonization under a low concentration of O2 at temperatures as high as 900 °C. The resulting carbon fibers gather different interesting properties, such as sub-micron diameters (≤1 μm), large surface area (≈2000 m2 g−1), relatively high performance in relation to their mechanical properties for functional applications and a rich variety of uniformly distributed O and P surface functionalities, which make them very attractive for heterogeneous catalysis, adsorption and electrochemical applications.

Easy fabrication of superporous zeolite templated carbon electrodes by electrospraying on rigid and flexible substrates

Electrospraying of colloidal suspensions of superporous zeolite templated carbon (ZTC) nanoparticles in ethanol is herein proposed for the controlled deposition of continuous carbon coatings over different substrates, both rigid and flexible. By simple tuning of the concentration, feed rate, voltage and treatment time, different electrode thicknesses can be obtained avoiding the difficult manipulation of ZTC nanopowder formed by around 200 nm size particles. The addition of sulfonated tetrafluoropolyethylene (Nafion) in low amounts into the ZTC suspension improves the adhesion, increases the allowable surface loading and enhances the electrochemical performance of ZTC electrodes. ZTC/Nafion coatings from 0.1 to 1.5 mg cm−2 have been successfully arranged over graphite sheet and conductive carbon paper substrates. The obtained electrodes have been electrochemically characterized in 1 M H2SO4 electrolyte, demonstrating the unique and well-known pseudocapacitive features of ZTC, while showing capacitances as high as 700 mF cm−2 and outstanding rate performance thanks to the improved arrangement and connectivity of the ZTC nanoparticles. A supercapacitor using electrosprayed ZTC electrodes is constructed, showing specific capacitance higher than 60 F g−1, capacitance retention of 63% when the current density is raised from 2.5 to 80 A g−1, energy density of 6.6 W h kg−1 and maximum deliverable power greater than 240 kW kg−1. These are promising results that make feasible the use of electrospraying for processing nanostructured carbon materials into electrodes of tunable thickness and deposited on substrates of different compositions and morphologies.

Synthesis of Vanadium Oxide Nanofibers with Variable Crystallinity and V5+/V4+ Ratios

Tailoring the morphological, chemical, and physical properties of vanadium oxides (VOx) is crucial to optimize their performance in current and future applications. The present contribution proposes a new route to obtain VOx nanofibers with different V4+/V5+ ratios and crystallinity. The method involves the exclusive electrospinning of water-free NH4VO3-saturated solutions including a reductant. Subsequent air-annealing under suitable conditions yields vanadium oxide fibers of 20–90 nm diameter and 10–50 m2/g surface area. The presence of the reductant gives rise to VOx nanofibers with a considerable proportion of V4+. Then, the right choice of the calcination heating rate and temperature permits to modify the V4+/V5+ ratio as well as the crystalline phase and crystallite size of the fibers. With the proposed methodology, long-range continuous single-phase orthorhombic V2O5 and monoclinic V3O7 nanofibers are obtained.