High-performance lithium-ion batteries require electrolytes that are stable over wide operating voltages. We used density functional theory to investigate the degradation of ethylene carbonate (EC) electrolytes activated by interactions with LiCoO cathode surfaces and PF species in the electrolyte. We report detailed mechanisms for the activation of EC ring-opening reactions by Lewis acids to form CO, organics, or organofluorines. We find that Lewis acid-base complexation between EC and either PF or LiCoO weakens the C-O bonds of the EC ring and consequently lowers the barrier to and energy of EC ring-opening reactions. Our results predict that ring opening activated by the LiCoO cathode surface forms a cathode-electrolyte interphase primarily composed of an organic and organofluorine film. Simultaneous degradation of an EC molecule and PF forms PF and a surface organofluorine with an activation barrier of 1.28 eV and reaction energy of -0.26 eV. Ring opening of EC activated by the cathode to form short organic oligomers results from sequential ring-opening reactions at the surface with an activation barrier of 1.04 eV and an overall reaction enthalpy of -1.15 eV for the case of EC dimer formation. Complexation of EC with PF lowers the barrier to EC ring opening to form CO from 1.96 to 1.68 eV and the reaction energy from 0.02 eV to -1.38 eV relative to unactivated CO formation. We expect that EC electrolyte degradation at the cathode surface will be dominated by EC dimer formation reactions activated by PF because of their low reaction barriers relative to CO formation.

The tritium aspects of the DT fuel cycle embody some of the most challenging feasibility and attractiveness issues in the development of fusion systems. The review and analyses in this paper provide important information to understand and quantify these challenges and to define the phase space of plasma physics and fusion technology parameters and features that must guide a serious R&D in the world fusion program. We focus in particular on components, issues and R&D necessary to satisfy three ‘principal requirements’: (1) achieving tritium self-sufficiency within the fusion system, (2) providing a tritium inventory for the initial start-up of a fusion facility, and (3) managing the safety and biological hazards of tritium. A primary conclusion is that the physics and technology state-of-the-art will not enable DEMO and future power plants to satisfy these principal requirements. We quantify goals and define specific areas and ideas for physics and technology R&D to meet these requirements. A powerful fuel cycle dynamics model was developed to calculate time-dependent tritium inventories and flow rates in all parts and components of the fuel cycle for different ranges of parameters and physics and technology conditions. Dynamics modeling analyses show that the key parameters affecting tritium inventories, tritium start-up inventory, and tritium self-sufficiency are the tritium burn fraction in the plasma (f b), fueling efficiency (η f), processing time of plasma exhaust in the inner fuel cycle (t p), reactor availability factor (AF), reserve time (t r) which determines the reserve tritium inventory needed in the storage system in order to keep the plant operational for time t r in case of any malfunction of any part of the tritium processing system, and the doubling time (t d). Results show that η f f b > 2% and processing time of 1–4 h are required to achieve tritium self-sufficiency with reasonable confidence. For η f f b = 2% and processing time of 4 h, the tritium start-up inventory required for a 3 GW fusion reactor is ∼11 kg, while it is <5 kg if η f f b = 5% and the processing time is 1 h. To achieve these stringent requirements, a serious R&D program in physics and technology is necessary. The EU-DEMO direct internal recycling concept that carries fuel directly from the plasma exhaust gas to the fueling systems without going through the isotope separation system reduces the overall processing time and tritium inventories and has positive effects on the required tritium breeding ratio (TBRR). A significant finding is the strong dependence of tritium self-sufficiency on the reactor availability factor. Simulations show that tritium self-sufficiency is: impossible if AF < 10% for any η f f b, possible if AF > 30% and 1% ⩽ η f f b ⩽ 2%, and achievable with reasonable confidence if AF > 50% and η f f b > 2%. These results are of particular concern in light of the low availability factor predicted for the near-term plasma-based experimental facilities (e.g. FNSF, VNS, CTF), and can have repercussions on tritium economy in DEMO reactors as well, unless significant advancements in RAMI are made. There is a linear dependency between the tritium start-up inventory and the fusion power. The required tritium start-up inventory for a fusion facility of 100 MW fusion power is as small as 1 kg. Since fusion power plants will have large powers for better economics, it is important to maintain a ‘reserve’ tritium inventory in the tritium storage system to continue to fuel the plasma and avoid plant shutdown in case of malfunctions of some parts of the tritium processing lines. But our results show that a reserve time as short as 24 h leads to unacceptable reserve and start-up inventory requirements. Therefore, high reliability and fast maintainability of all components in the fuel cycle are necessary in order to avoid the need for storing reserve tritium inventory sufficient for continued fusion facility operation for more than a few hours. The physics aspects of plasma fueling, tritium burn fraction, and particle and power exhaust are highly interrelated and complex, and predictions for DEMO and power reactors are highly uncertain because of lack of experiments with burning plasma. Fueling by pellet injection on the high field side of tokamak has evolved to be the preferred method to fuel a burning plasma. Extrapolation from the DIII-D penetration scaling shows fueling efficiency expected in DEMO to be <25%, but such extrapolations are highly uncertain. The fueling efficiency of gas in a reactor relevant regime is expected to be extremely poor and not very useful for getting tritium into the core plasma efficiently. Gas fueling will nonetheless be useful for feedback control of the divertor operating parameters. Extensive modeling has been carried out to predict burn fraction, fueling requirements, and fueling efficiency for ITER, DEMO, and beyond. The fueling rate required to operate Q = 10 ITER plasmas in order to provide the required core fueling, helium exhaust and radiative divertor plasma conditions for acceptable divertor power loads was calculated. If this fueling is performed with a 50–50 DT mix, the tritium burn fraction in ITER would be ∼0.36%, which is too low to satisfy the self-sufficiency conditions derived from the dynamics modeling for fusion reactors. Extrapolation to DEMO using this approach would also yield similarly low burn fraction. Extensive analysis presented shows that specific features of edge neutral dynamics in ITER and fusion reactors, which are different from present experiments, open possibilities for optimization of tritium fueling and thus to improve the burn fraction. Using only tritium in pellet fueling of the plasma core, and only deuterium for edge density, divertor power load and ELM control results in significant increase of the burn fraction to 1.8–3.6%. These estimates are performed with physics models whose results cannot be fully validated for ITER and DEMO plasma conditions since these cannot be achieved in present tokamak experiments. Thus, several uncertainties remain regarding particle transport and scenario requirements in ITER and DEMO. The safety standard requirements for protection of the public and release guidelines for tritium have been reviewed. General safety approaches including minimizing tritium inventories, reducing tritium permeation through materials, and decontaminating material for waste disposal have been suggested.

Liquid ammonia is a high-density (17.7 wt %) hydrogen carrier with a well-established production and distribution infrastructure. Efficient decomposition and purification are essential for its use as a hydrogen-storage material. Here we demonstrate the production of high-purity (>99.7%) H 2 from NH 3 using a catalytic membrane reactor (CMR) in which a Ru catalyst is impregnated within a porous yttria-stabilized zirconia (YSZ) tube coated with a thin, 6 μm Pd film by electroless deposition. The intimate proximity of catalyst and membrane eliminates transport resistances that limit performance in the conventional packed-bed membrane reactor (PBMR) configuration. The addition of a Cs promoter enabled complete NH 3 conversion at temperatures as low as 400 °C, exceeding equilibrium constraints without the need for a sweep gas. A reactor model was developed that captured CMR performance with high fidelity. NH 3 decomposition was observed to follow first-order kinetics due to efficient H 2 removal. Relative to a comparable PBMR, the Ru loading in the CMR was reduced an order of magnitude and the H 2 recovery increased 35%, enabling record volumetric productivity rates (>30 mol m −3 s −1 ) that validate its promise for efficient, compact H 2 delivery from ammonia.

We utilized density functional theory to examine HF generation in lithium-ion battery electrolytes from reactions between H 2 O and the decomposition products of three electrolyte additives: LiPF 6 , LiPOF 4 , and LiAsF 6. Decomposition of these additives produces PF 5 , AsF 5 , and POF 3 along with LiF precipitates. We found PF 5 and AsF 5 react with H 2 O in two sequential steps to form two HF molecules and POF 3 and AsOF 3 , respectively. PF 5 (or AsF 5) complexes with H 2 O and undergoes ligand exchange to form HF and PF 4 OH (AsF 4 OH) with an activation barrier of 114.2 (30.5) kJ mol-1 and reaction enthalpy of 14.6 (-11.3) kJ mol-1. The ethylene carbonate (EC) electrolyte forms a Lewis acid-base complex with the PF 4 OH (AsF 4 OH) product, reducing the barrier to HF formation. Reactions of POF 3 were examined and are not characterized by complexation of POF 3 with H 2 O or EC, while PF 5 and AsF 5 complex favorably with H 2 O and EC. HF formation from POF 3 occurs with a reaction enthalpy of-3.8 kJ mol-1 and a 157.7 kJ mol-1 barrier, 43.5 kJ mol-1 higher than forming HF from PF 5. HF generation in electrolytes employing LiPOF 4 should be significantly lower than those using LiPF 6 or LiAsF 6 and LiPOF 4 should be further investigated as an alternative electrolyte additive.

We utilized density functional theory (DFT) to systematically investigate the ability of B, C and N interstitial and O substitutional surface and near-surface dopants in TiO 2 to facilitate O 2 reduction and adsorption. Periodic boundary condition calculations based on the PBE+U DFT functional show that dopants that create filled band gap states with energies higher than that of the near surface O 2 π z * molecular orbital enable O 2 adsorption and reduction. Sites that create unoccupied band gap states with energies below that of the O 2 π z * orbital reduce TiO 2 's reduction ability as these states result in photoexcited electrons with insufficient reduction potential to reduce O 2 . B dopants in interstitial and relaxed substitutional sites, whose gap states lie > 1.5 eV above the valence band maximum (VBM) and hence above O 2 's π z * level, facilitate the reduction of O 2 to the peroxide state with adsorption energies on TiO 2 of -1.22 to -2.77 eV.However, N dopants, whose gap states lie less than ~1 eV above the VBM impede O 2 adsorption and reduction; O 2 on N doped (101) anatase relaxes away from the surface. Interstitial and substitutional N dopants require two photoexcited electrons to enable O 2 adsorption. C doping, which introduces gap states between those introduced by N and B, aids O 2 adsorption as a peroxide for interstitial doping, although substitutional C does not facilitate O 2 adsorption. Dopants for enhancing the photocatalytic reduction of O 2 in order of predicted effectiveness are interstitial B, relaxed substitutional B, and interstitial C. In contrast, substitutional C, and interstitial and substitutional N hinder O 2 reduction despite increasing visible light absorption.Dopants within the surface layer likely deactivate quickly due to the high exothermicity of O 2 reacting with them to form BO 2 , CO 2 , and NO 2 .