ZIF-8 is a zeolitic imidazolate framework with very good thermal and chemical stability that opens up many applications that are not feasible by other metal-organic frameowrks (MOFs) and zeolites. Several works report the adsorption properties of ZIF-8 for strategic gases. However, despite the vast experimental corpus of data reported, there seems yet to be a dearth in the understanding of the gas adsorption properties. In this work we provide insights at a molecular level on the mechanisms governing the ZIF-8 structural deformation during molecular adsorption. We demonstrate that the ZIF-8 structural deformation during the adsorption of different molecules at cryogenic temperature goes beyond the gas-induced rotation of the imidazolate linkers. We combine experimental and simulation studies to demonstrate that this deformation is governed by the polarizability and molecular size and shape of the gases, and that the stepped adsorption behavior is defined by the packing arrangement of the guest inside the host.

Organic photoactive materials are promising candidates for the generation of solar fuels in terms of efficiency and cost. However, their low stability in aqueous media constitutes a serious problem for technological deployment. Here we present organic photocathodes for the generation of hydrogen in aqueous media with outstanding stability. The device design relies on the use of water-resistant selective contacts, which protect a P3HT:PCBM photoactive layer. An insoluble cross-linked PEDOT:PSS hole-selective layer avoids delamination of the film, and an electron-selective TiO x layer in contact with the aqueous solution electrically communicates the organic layer with the hydrogen-evolving catalyst (Pt). We developed a novel method for the synthesis of the TiO x layer compatible with low-temperature conditions. Tuning the thickness of the TiO x /Pt layer leads to a trade-off between the achievable photocurrent (∼1 mAcm −2) and the stability of the photocathode (stable hydrogen generation of 1.5 μmol h −1 cm −2 for >3 h).

Efficient solar-to-fuel conversion could be a cost-effective way to power the planet using sunlight.

The investigation of the lithiation−delithiation kinetics of anodes comprising carbon-coated ZnFe 2 O 4 nanoparticles is reported in here. The study confirmed that, as occurring with other conversion electrodes, lithiation of ZnFe 2 O 4 nanoparticles is a multistep process involving the presence of intermediate Li−Zn−Fe−O phases as precursors for the formation of amorphous Li 2 O. A detailed knowledge on the reaction kinetics of the involved electrochemical mechanisms has been achieved by using impedance spectroscopy. It has been observed that lithiation reactions introduce a long delay that limits the electrode charging, not related to diffusion mechanisms. The sloping curve following the conversion plateau of the galvanostatic discharge is connected to a retardation effect in the reaction kinetics. This limitation is seen as an additional resistive process originated by the specific lithiation microscopic features. It is concluded that capacitance spectra allow distinguishing two separate processes: formation of kinetically favored intermediate Li−Zn−Fe−O phases and subsequent reaction to produce highly dispersed LiZn and Fe 0 in an amorphous Li 2 O matrix. A detailed electrical model is provided accounting for the overall electrode lithiation process. ■ INTRODUCTIONLi-ion batteries have become core devices for the consumer electronics industry. Materials for commercial battery electrodes are mostly chosen from a set of intercalation compounds that reversibly accommodate lithium ions in host sites in the lattice without severely distorting the structure. In most transition metal compounds such as LiCoO 2 , LiNi 1−y−z Mn y Co z O 2 , LiFePO 4 , and Li 4 Ti 5 O 12, redox activity is restricted to a few exchanged electrons. Therefore, intercalation materials exhibit intrinsic limitations that make them unviable when high capacity requirements have to be fulfilled as in the case of large scale or automotive applications.1−3 During the past decades a new family of electrode materials operating under the so-called conversion reaction has been intensely studied.4 For these compounds lithiation occurs through the reaction that involves a complete metal reduction as M a X b + (bn)Li ↔ aM + bLi n X, where M = transition metal, X = anion (O, S, N, P, and F), and n = anion formal oxidation state. Conversion reaction is able to accommodate larger amount of Li atoms into the lithium binary compound Li n X, which explains specific capacities exceeding 1000 mAh g −1 as reported for many compounds. Interestingly, conversion materials usually show good reversibility because of the formation of a nanostructured matrix that comprises metallic nanoparticles surrounded by amorphous Li n X phases. Intimate phase contact facilitates reactivity as evidenced by the observation of remaining metallic nanoparticles after extended oxidation/ reduction cycling. 4 Despite their potentialities, conversion compounds present a series of performance limitations that hinders their straightforward application in commercial devices. There...

A simple modification of the conventional sol-gel polymerization of resorcinol-formaldehyde mixtures allowed a facile preparation of ultrahigh mesoporous carbon gels. In the conventional synthesis the growth of the cluster polymer particles leading to the development of the porosity is controlled by the R/C ratio. In the presence of a carbon conductive additive, the polymerization of the reactants proceeded through the formation of less-branched polymer clusters resulting in carbon gels with large pore volumes within the micro/mesoporous range. The obtained materials displayed unusual heterogeneous pore systems characterized by large mesopores interconnected by necks of variable sizes, along with an enhanced electrical conductivity provided by the carbon black additive. The gels showed stable electrochemical response in neutral aqueous electrolyte, being reversibly charged/discharged at large potential windows, without significant losses in the current density, chemical modifications or structural collapse. The enhanced life cycle of these electrodes makes them good candidates for their use in electrochemical applications where a fast response and high cycleability is required.