No abstract

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.

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.

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....

Under ambient conditions, the catalytic and electrocatalytic syntheses of ammonia from nitrogen and various proton sources including wet tetrahydrofuran (THF) and the protic solvents methanol and water were performed using titanocene dichloride ((η5-C5H5)2TiCl2, commonly abbreviated to CP2TiCl2) in a two-electrode cell containing 1.0 M LiCl as the electrolyte. The highest rate of ammonia synthesis, 9.5 × 10–10 mol·cm–2·sec–1·M CP2TiCl2 –1, was achieved at −1 V in water, whereas the highest faradaic efficiency (0.95%) was achieved at −2 V in THF. On account of its lower Gibbs free energy, density functional theory calculations suggest that the nitrogen-reduction reaction catalyzed by CP2TiCl2 in the presence of THF, methanol, or water preferably occurs via the Cp2TiClN2 intermediate rather than Cp2TiN2N2. Future strategies to improve both the rate of ammonia synthesis and its faradaic efficiency must consider ways of maximizing nitrogen selectivity to the catalytic active sites by controlling the transfer rates of protons and/or nitrogen.

No abstract

No abstract

We propose a test case prioritization strategy for risk based testing, in which the risk exposure is employed as the key criterion of evaluation. Existing approaches to risk based testing typically employ risk exposure values as assessed by the tester. In contrast, we employ exposure values that have been determined by experts during the risk assessment stage of the risk management process. If a given method produces greater accuracy in fault detection, that approach is considered more valuable for software testing. We demonstrate the value of our proposed risk based testing method in this sense through its application.