Nanocrystalline ceria is under study to improve performance in high-temperature catalysis and fuel cells. We synthesize porous ceria monolithic nanoarchitectures by reacting Ce(III) salts and epoxide-based proton scavengers. Varying the means of pore-fluid removal yields nanoarchitectures with different pore−solid structures: aerogels, ambigels, and xerogels. The dried ceria gels are initially X-ray amorphous, high-surface-area materials, with the aerogel exhibiting 225 m2 g-1. Calcination produces nanocrystalline materials that, although moderately densified, still retain the desirable characteristics of high surface area, through-connected porosity in the mesopore size range and nanoscale particle sizes (∼10 nm). The electrical properties of calcined ceria ambigels are evaluated from 300 to 600 °C and compared to those of commercially available nanoscale CeO2. The pressed pellets of both ceria samples exhibit comparable surface areas and void volumes. The conductivity of the ceria ambigel is 5 times greater than the commercial sample and both materials exhibit an increase in conductivity in argon relative to oxygen at 600 °C, suggesting an electronic contribution to conductivity at low oxygen partial pressures. The ceria ambigel nanoarchitecture responds to changes in atmosphere at 600 °C faster than does the nanocrystalline, non-networked ceria. We attribute the higher relative conductivity of CeO2 ambigels to the bonded pathways inherent to the bicontinuous pore−solid networks of these nanoarchitectures.
The description of the proton transport in multiscale hybrid membrane in their "dry state" and at various temperatures was performed by using broadband dielectric spectroscopy. Permittivity and conductivity have been measured on a wide frequency range from a few hertz to microwaves. We found that the proton transport is multiscale, and different electrical relaxations are evidenced, resulting from the polarizations at the different length scales of the hybrid membrane. When the frequency increases, four dielectric relaxations are detected due to (a) polarization of silica domains in micronic scale, (b) polarization in the micronic silica domain, (c) polarization of silica oblong (nanometric range) forming the micronic silica domain, and finally (d) polarization of −SO3H groups distributed in the silica network (angstroms scale). Thus, this experiment confirms that the ionic transport is severely restricted to the organization of the silica network.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A microbial fuel cell bioanode encapsulating electroactive bacteria in core–shell fibers mixed with a conductive scaffold was electrospun. This new design opens up perspectives of storable ready-to-use anodes for portable applications.
Summary: Hybrid membranes containing a continuous functionalized silica network were synthesized by combining electrospinning and the sol-gel chemistry. The in-plane proton conductivity was evaluated at 80°C under 80% relative humidity and values of 100 mS/cm have been measured. We investigated the proton transport in these multiscale membranes through different techniques including electrochemical impedance spectroscopy, FG-NMR and QENS. We demonstrated that hydrated protons interact with silica network, but connected pathways for hydrated proton exist in the all membranes that facilitate in fine the proton transport. Introduction Improvements need to be performed before Polymer Electrolyte Membrane Fuel cells will be commercialized for transport application. One of the challenges is to replace Nafion, the state of the art by membranes that are efficient at high temperature (³ 100°C) and low humidity (50% RH). Up to date, the development on polymer electrolyte membranes capable of working at higher temperatures with dry gases is still under consideration. Among the different approaches, the addition of inorganic materials capable of retaining water to perfluorosulfonated ionomers has been developed [1]. But, the results are often poor mechanical properties of the membrane, inorganic particle leaching out of the membrane when the fuel cell is running. Only few examples point out the benefit of these particles and how their size, distribution, functionalization can result in unexpected activity. [2, 3] We propose here to develop hybrid organic-inorganic membranes, exempt of Nafion. These membranes consist of two intermingled networks of PVDF-HFP and functionnalized silica network.[3] To avoid the phase separation between these two components, we synthesized the hybrid membrane by combining electrospinning and the sol-gel process. To achieve satisfactory proton conduction, a comprehensive study was performed on the proton transport in these multiscale membranes. To do so, we employed different techniques including electrochemical impedance spectroscopy, PG-NMR and QENS. Experimental Field Gun Emission-Scanning Electron Microscopy (FG-SEM), High Resolution Transmission Electron Microscopy were used to characterize the microstructure of the hybrid membranes while Small Angle Neutron Scattering (SANS) was performed to study the hybrid organic/inorganic interfaces. In-plane proton conductivity was determined as function of temperature and humidity. Electrochemical impedance spectroscopy (EIS), 2H NMR relaxation and 1H pulsed field gradient NMR (PFGNMR), quasielastic neutron scattering (QENS) were used to study the proton transport at various scales. Results Hybrid organic-inorganic membranes were fabricated by electrospinning in controlled atmosphere (Relative Humidity ~ 20% and T = 25°C) on aluminum foil which serves as counter electrode. The electrospun solution consists of dissolved polymer and pre-hydrolyzed silica precursors. After processing and heat treatment at 70°C, the hybrid membrane is homogenous, flexible with a thickness ranging from 10 to 100 mm depending on the volume of the used hybrid solution. Characterization techniques including FG-SEM, SANS and HR-TEM demonstrated that the fibers in the membrane are composed of an alternation of a thin layer of polymer and oblong functionalized silica domains connected to each other to form a continuous network. To characterize the proton transport in the electrospun hybrid organic-inorganic membranes, their proton conductivities were measured at 80°C under various relative humidity (RH) conditions. We found that this complex architecture gives rise to efficient proton transport as conductivity values superior to 100 mS/cm is achieved at 80°C under 80% relative humidity. Lately, macroscopic diffusion coefficient was measured by EIS and values compare well with Nafion, confirming the fast transport of hydrated proton through the membrane. Unexpectedly, hydrated proton and water molecule interact with the silica network, giving rise to local diffusion coefficient one order of magnitude lower than Nafion (PG-NMR and QENS) but diffuse rapidly throughout the membrane, as the diffusion coefficient of water is comparable to Nafion for the range of 1 to 10 mm. Conclusion In contrast to what it has been observed in Nafion, we found that the water diffusion coefficient (m to Å) can be locally slowdown (2 x 10 -6 cm 2 /s) due to weak interactions with the silica network but diffusion coefficient determined by EIS is high (9.6 x 10 -6 cm 2 /s) at least comparable to one observed in Nafion, the state of art at the mm scale. Acknowledgements The authors would like to thank ANR MéconPrhy for the financial support. References [1] Kreuer, K. et al. ; “Chem. Mater., 8, 610–641 (1996). [2] Mauritz, K.A. et al. Chem. Rev. , 104 , 4535–4585 (2004). [3] Laberty-Robert C. et al. , Chem Soc Rev , 40 (2011) 961.
Aqueous batteries face the challenge of limited energy density due to parasitic gas production from hydrogen and oxygen evolution reactions, particularly at the negative electrode. This study investigates the electrochemical properties and mechanisms of proton intercalation in anatase TiO2 featuring vacancies (Vac-TiO2), stabilized via a low-temperature sol–gel process. XRD refinement analysis, supported by thermal analysis, estimated 17% cationic vacancies, while 1H MAS NMR spectroscopy revealed stabilization of these vacancies by OH groups. The presence of cationic vacancies led to changes in the oxide anion sublattice, which accommodate proton insertion. Electrochemical assessments in acetate buffer electrolyte demonstrated Vac-TiO2's ability to delay the hydrogen evolution reaction and enhance proton capacity, validated by pH-dependent studies, DFT calculations, and kinetic analyses. Notably, the occurrence of undercoordinated oxide anions was shown to induce the insertion of H+ at higher potential values, and the insertion mechanism was suggested to occur via a solid-solution mechanism. Owing to these features, Vac-TiO2 exhibited superior cyclability and performance compared to pure anatase TiO2, highlighting its potential for sustainable proton intercalation processes. In half-cell configurations, Vac-TiO2 showed a high Coulombic efficiency (CE exceeding 90% after 48 cycles), while full cells (MnO2||Vac-TiO2) demonstrated an excellent cycling stability (CE exceeding 95.4% over 1000 cycles), high power density (10.5 kW·kg–1 vs 6.2 kW·kg–1), and improved self-discharge. This study paves the way for innovative approaches to improving proton intercalation materials, positioning Vac-TiO2 as a viable candidate for next-generation energy storage solutions.
