Selection of an appropriate electrolyte medium is essential for successful NH 3 electro-synthesis at low temperature and pressure. In this study, 2-propanol was employed as an electrolyte medium and its effectiveness in the electro-reduction of N 2 to NH 3 under ambient conditions was evaluated. NH 3 synthesis and faradaic efficiency using a mixture of 2-propanol/water (9:1, v/v) surpassed those when electrosynthesis was carried out using solely water. The concentration of H 2 SO 4 and the applied current density influenced NH 3 synthesis in this 2-propanol-based system, and the optimal conditions led to maximized N 2 reduction, indicating that the competing and electron-losing reaction of H 2 evolution was relatively well suppressed.

Covalent organic frameworks (COFs) have emerged as a promising light-harvesting module for artificial photosynthesis and photovoltaics. For efficient generation of free charge carriers, the donor–acceptor (D-A) conjugation has been adopted for two-dimensional (2D) COFs recently. In the 2D D-A COFs, photoexcitation would generate a polaron pair, which is a precursor to free charge carriers and has lower binding energy than an exciton. Although the character of the primary excitation species is a key factor in determining optoelectronic properties of a material, excited-state dynamics leading to the creation of a polaron pair have not been investigated yet. Here, we investigate the dynamics of photogenerated charge carriers in 2D D-A COFs by combining femtosecond optical spectroscopy and non-adiabatic molecular dynamics simulation. From this investigation, we elucidate that the polaron pair is formed through ultrafast intra-layer hole transfer coupled with coherent vibrations of the 2D lattice, suggesting a mechanism of phonon-assisted charge transfer.

In this study, a novel electrolysis cell based on ethylenediamine (EDA) as a cathodic solvent was developed for NH 3 electro-synthesis. The NH 3 -generating cathode chamber was filled with 0.1 M LiCl/EDA and separated by a cation exchange membrane from the anodic compartment, which was filled with 0.05 M H 2 SO 4 aqueous solution. It appeared that EDA was cathodically stable, and thus electron-stealing medium destruction was substantially avoided. The faradaic efficiency for NH 3 synthesis was 17.2%, producing 7.73 × 10 −7 mol NH 3 for 1 h electrolysis at a cell voltage of 1.8 V with the charge consumption of 1.3 C.

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Lithium-mediated reduction of dinitrogen is ap romising methodt oe vade electron-stealing hydrogen evolution, ac ritical challenge which limits faradaic efficiency (FE) and thus hinders the success of traditional protic-solvent-based ammonia electro-synthesis. Av iable implementation of the lithium-mediated pathway using lithium-ion conducting glass ceramics involves i) lithium deposition, ii)nitridation,a nd iii)ammonia formation. Ammonia was successfully synthesized from molecular nitrogen and water,y ielding am aximum FE of 52.3 %. Witha n ammonia synthesis rate comparable to previously reported approaches, the fairly high FE demonstrates the possibility of using this nitrogen fixation strategya sasubstitute for firmly established, yet exceedingly complicated and expensivet echnology,a nd in so doing represents an ext-generation energy storagesystem.The Haber-Bosch process is aw ell-established ammonia (NH 3 ) synthesis technology that converts more than 120 million tons of N 2 into NH 3 annually. [1,2] However,this process is exceedingly energy intensiveo wing to harsh operating conditions, and exhibits extensive carbon emission. [1] Therefore, the development of more environmentally benign alternatives is crucial.Electrochemical synthesisi sa na ttractive candidatef or N 2 fixation ase nergy consumption, if optimized (i.e. with low overvoltage and high faradaic efficiency), could potentially be reduced as compared to the Haber-Bosch process while avoiding CO 2 emission. [3,4] If the required electricity for the process is supplied from renewable sources, this approach offers a meanstostore excess renewable energy in agreen energy carrier with an energy density comparable to fossil fuels. [5] True sustainability,h owever,w ill only be realized if the electrons required for the N 2 reduction originate from water rather than H 2 .Over the last three decades, such electrochemical processes have been developed, with state-of-the art technologiess ummarized in Ta ble S1 in the Supporting Information. [6][7][8][9][10][11][12][13][14][15][16] Unfortunately,t he faradaic efficiencies (FEs) in most cases were unbearably low (< 5%)a st he competing hydrogen evolution from water or ap rotonw as preferred over the intended N 2 reduction, which was particularly sluggish owing to the strong triple bond of N 2 (941 kJ mol À1 ). [3,17,18] Innovative strategies are thus indispensable to overcome such obstacles and achieve excellent selectivity in the N 2 reduction.One promisingw ay is to employ Li as amediator in the electro-synthesis. In contact with N 2 ,m etallicL i, on accounto fi ts strong reducing power,c auses dissociation to form lithium nitride (Li 3 N) even under ambient conditions. Thus-formed Li 3 N is ah igh-energyi ntermediate for NH 3 synthesis that is readily transformed into NH 3 upon reaction with protons or water. [17] This so-called "Li-mediated pathway" was firstly applied to synthesizing NH 3 in studies by Ts unetoe tal.,w hich reported an impressively high maximum FE of 59 %a t5 0atm of N 2 (1 atm = 0....

Electrical conductivity relaxation is used for monitoring the cubic-to-hexagonal phase transition in the perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3−δ. After in situ annealing at 1173 K, at which temperature the cubic polymorph is stable, electrical conductivity relaxation experiments are conducted during long-term annealing at 1073 K. The decreases in the surface exchange and chemical diffusion coefficients with time due to the sluggish phase transition are found to be correlated. It is demonstrated that B-site doping with Zr to an amount as low as 3 mol % stabilizes the high-temperature perovskite cubic phase of Ba0.5Sr0.5Co0.8Fe0.2O3−δ, with preservation of its high oxygen transport and exchange properties.

The surface oxygen exchange kinetics of bismuth oxide stabilized with 25 mol% erbia (BE25) has been studied in the temperature and pO 2 ranges 773-1,023 K and 0.1-0.95 atm, respectively, using pulse-response 18 O- 16O isotope exchange measurements. The results indicate that BE25 exhibits a comparatively high exchange rate, which is rate determined by the dissociative adsorption of oxygen. Defect chemical considerations and the observed pO 2 1=2 dependence of the rate of dissociative oxygen adsorption suggest electron transfer to intermediate superoxide ions as the rate determining step in surface oxygen exchange on BE25.

Dual-phase ceramic membranes with very high oxygen flux have been designed by taking into account the volume fraction of the fluorite phase, membrane thickness, and surface modification. The oxygen flux of Ce 0.9 Gd 0.1 O 2−δ −La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (GDC−LSCF) dual-phase membranes has been systematically investigated as a function of membrane thickness and volume fraction of the fluorite phase with or without surface modification. The percolation threshold of the composites for electronic conduction has been determined to be about 20 vol % of LSCF by general effective-medium theory. The oxygen flux of uncoated fluorite phase-rich membrane (80 vol % GDC−20 vol % LSCF) with 30-μm thickness exhibits a low oxygen flux (8.0 × 10 −3 mL• cm −2 •min −1 at 850 °C) under an air/He gradient, indicating that the permeation is controlled by only the surface-exchange kinetics of GDC. With both sides coated with La 0.6 Sr 0.4 CoO 3−δ (LSC), the flux of the membrane (3.6 mL•cm −2 •min −1 at 850 °C) has been dramatically enhanced by about 3 orders of magnitude in comparison with the oxygen flux of the membrane with a nonmodified surface. This observation implies that surface modification has a decisive role in dramatically enhancing the contribution of the GDC to the fluorite rich dual-phase membrane.