Microfibrillated cellulose - its barrier properties and applications in cellulosic materials: a review.

To increase their electrochemically active surface area, catalysts supported on high surface area materials, commonly carbons, are widely used in low-temperature fuel cells. Recent studies have revealed that the physical properties of the carbon support can greatly affect the electrochemical properties of the fuel cell catalyst. It has been reported that carbon materials with both high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles, but also facilitate electron transfer, resulting in better device performance. On this basis, novel non-conventional carbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example microsphere). The examples are supports produced from ordered mesoporous carbons, carbon aerogels, carbon nanotubes, carbon nanohorns, carbon nanocoils and carbon nanofibers. The challenge is to develop carbon supports with high surface area, good electrical conductivity, suitable porosity to allow good reactant flux, and high stability in fuel cell environment, utilizing synthesis methods simple and not too expensive. This paper presents an overview of carbon supports for Pt-based catalysts, with particular attention on new carbon materials. The effect of substrate characteristics on catalyst properties, as electrocatalytic activity and stability in fuel cell environment, is discussed.

Carbon supports for low-temperature fuel cell catalysts

Temperature dependent ageing mechanisms in Lithium-ion batteries – A Post-Mortem study

Electrochemical advanced oxidation processes (EAOPs) have emerged as novel water treatment technologies for the elimination of a broad-range of organic contaminants. Considerable validation of this technology has been performed at both the bench-scale and pilot-scale, which has been facilitated by the development of stable electrode materials that efficiently generate high yields of hydroxyl radicals (OH˙) (e.g., boron-doped diamond (BDD), doped-SnO2, PbO2, and substoichiometic- and doped-TiO2). Although a promising new technology, the mechanisms involved in the oxidation of organic compounds during EAOPs and the corresponding environmental impacts of their use have not been fully addressed. In order to unify the state of knowledge, identify research gaps, and stimulate new research in these areas, this review critically analyses published research pertaining to EAOPs. Specific topics covered in this review include (1) EAOP electrode types, (2) oxidation pathways of select classes of contaminants, (3) rate limitations in applied settings, and (4) long-term sustainability. Key challenges facing EAOP technologies are related to toxic byproduct formation (e.g., ClO4− and halogenated organic compounds) and low electro-active surface areas. These challenges must be addressed in future research in order for EAOPs to realize their full potential for water treatment.

Critical review of electrochemical advanced oxidation processes for water treatment applications

Recently it was shown that enzymatic and mechanical processing of macroscopic cellulose fibers lead to disintegration of long and entangled native cellulose I nanofibers in order to form mechanically strong aqueous gels (Paakko et al., Biomacromolecules, 2007, 8, 1934). Here we demonstrate that (1) such aqueous nanofibrillar gels are unexpectedly robust to allow formation of highly porous aerogels by direct water removal by freeze-drying, (2) they are flexible, unlike most aerogels that suffer from brittleness, and (3) they allow flexible hierarchically porous templates for functionalities, e.g. for electrical conductivity. No crosslinking, solvent exchange nor supercritical drying are required to suppress the collapse during the aerogel preparation, unlike in typical aerogel preparations. The aerogels show a high porosity of ∼98% and a very low density of ca. 0.02 g cm−3. The flexibility of the aerogels manifests as a particularly high compressive strain of ca. 70%. In addition, the structure of the aerogels can be tuned from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphology and porosity by modifying the freeze-drying conditions. The porous flexible aerogel scaffold opens new possibilities for templating organic and inorganic matter for various functionalities. This is demonstrated here by dipping the aerogels in an electrically conducting polyaniline–surfactant solution which after rinsing off the unbound conducting polymer and drying leads to electrically conducting flexible aerogels with relatively high conductivity of around 1 × 10−2 S cm−1. More generally, we foresee a wide variety of functional applications for highly porous flexible biomatter aerogels, such as for selective delivery/separation, tissue-engineering, nanocomposites upon impregnation by polymers, and other medical and pharmaceutical applications.

Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalities

Cellulose-based aerogels

Niobium-doped nanofibers elaborated by facile, single-step electrospinning present a higher rate capability in electrochemical cycling experiments than nondoped materials. This is attributed to the reduction of Li+ diffusion path lengths and enhanced intimate interparticle contact, in combination with improved intraparticle conductivity. Niobium doping has a significant effect on the electronic structure and provokes a substantial decrease in particle size.

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Nb-Doped TiO2 Nanofibers for Lithium Ion Batteries

Lithium secondary batteries working at very high temperature: capacity fade and understanding of aging mechanisms

Use of cellulose-based carbon aerogels as catalyst support for PEM fuel cell electrodes: Electrochemical characterization

Li(Ni,Mn,Co)O2/graphite lithium-ion batteries designed to work at high temperature were tested upon cycling at 85°C in various voltage ranges. Aging processes in relation with changes in the electrode/electrolyte interfaces at both electrodes were investigated by X-ray Photoelectron Spectroscopy (XPS). Changes were observed in the composition of the solid electrolyte interphase (SEI) at the surface of graphite electrode due to the high cycling temperature: disappearance of carbonates and increase of inorganic compounds coming from degradation of the salt. A slight dissolution process of the PVdF positive electrode binder was evidenced. It was also observed that the formation and thickness of the passivation layer at the positive electrode surface at 85°C depends on the cycling voltage range. © 2012 The Electrochemical Society.

https://iopscience.iop.org/article/10.1149/2.061210jes/pdf

Florent Fischer

Papers

Cellulose-based aerogels

Nb-Doped TiO2 Nanofibers for Lithium Ion Batteries

Lithium secondary batteries working at very high temperature: capacity fade and understanding of aging mechanisms

Use of cellulose-based carbon aerogels as catalyst support for PEM fuel cell electrodes: Electrochemical characterization

Lithium-Ion Batteries Working at 85°C: Aging Phenomena and Electrode/Electrolyte Interfaces Studied by XPS