58 research outputs found
Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution
NASA requires a durable and efficient catalyst for the electrolysis of water in a polymer-electrolyte-membrane (PEM) cell. Ruthenium oxide in a slightly reduced form is known to be a very efficient catalyst for the anodic oxidation of water to oxygen, but it degrades rapidly, reducing efficiency. To combat this tendency of ruthenium oxide to change oxidation states, it is combined with iridium, which has a tendency to stabilize ruthenium oxide at oxygen evolution potentials. The novel oxygen evolution catalyst was fabricated under flowing argon in order to allow the iridium to preferentially react with oxygen from the ruthenium oxide, and not oxygen from the environment. Nanoparticulate iridium black and anhydrous ruthenium oxide are weighed out and mixed to 5 18 atomic percent. They are then heat treated at 300 C under flowing argon (in order to create an inert environment) for a minimum of 14 hours. This temperature was chosen because it is approximately the creep temperature of ruthenium oxide, and is below the sintering temperature of both materials. In general, the temperature should always be below the sintering temperature of both materials. The iridium- doped ruthenium oxide catalyst is then fabricated into a PEM-based membrane- electrode assembly (MEA), and then mounted into test cells. The result is an electrolyzer system that can sustain electrolysis at twice the current density, and at the same efficiency as commercial catalysts in the range of 100-200 mA/sq cm. At 200 mA/sq cm, this new system operates at an efficiency of 85 percent, which is 2 percent greater than commercially available catalysts. Testing has shown that this material is as stable as commercially available oxygen evolution catalysts. This means that this new catalyst can be used to regenerate fuel cell systems in space, and as a hydrogen generator on Earth
Fluoride-ion solvation in non-aqueous electrolyte solutions
Understanding the factors that influence ion-solvent properties for the fluoride ion in organic solvents is key to the development of useful liquid electrolytes for fluoride-ion batteries. Using both experimental and computational methods, we examined a range of chemical and electrochemical properties for a set of organic solvents in combination with dry N,N,N-trimethylneopentylammonium fluoride (NpâF) salt. Results showed that solvent electronic structure strongly influences NpâF dissolution, and the pK_a of solvent protons provides a good guide to potential Fâ» reactivity. We found a number of organic solvents capable of dissolving NpâF while providing chemically-stable Fâ» in solution and characterized three of them in detail: propionitrile (PN), 2,6-difluoropyridine (2,6-DFP), and bis(2,2,2-trifluoroethyl) ether (BTFE). Arrhenius analysis for NpâF/PN, NpâF/DFP, and NpâF/BTFE electrolytes suggests that DFP facilitates the highest Fâ» ion mobility of the three neat solvents. Electrolyte mixtures of BTFE and amide co-solvents exhibit higher ionic conductivity than the neat solvents. This improved ionic conductivity is attributed to the ability of BTFE:co-solvent mixtures to partition between Npââș and Fâ» ion-aggregates, promoting better ion dissociation
Fluoride-ion solvation in non-aqueous electrolyte solutions
Understanding the factors that influence ion-solvent properties for the fluoride ion in organic solvents is key to the development of useful liquid electrolytes for fluoride-ion batteries. Using both experimental and computational methods, we examined a range of chemical and electrochemical properties for a set of organic solvents in combination with dry N,N,N-trimethylneopentylammonium fluoride (NpâF) salt. Results showed that solvent electronic structure strongly influences NpâF dissolution, and the pK_a of solvent protons provides a good guide to potential Fâ» reactivity. We found a number of organic solvents capable of dissolving NpâF while providing chemically-stable Fâ» in solution and characterized three of them in detail: propionitrile (PN), 2,6-difluoropyridine (2,6-DFP), and bis(2,2,2-trifluoroethyl) ether (BTFE). Arrhenius analysis for NpâF/PN, NpâF/DFP, and NpâF/BTFE electrolytes suggests that DFP facilitates the highest Fâ» ion mobility of the three neat solvents. Electrolyte mixtures of BTFE and amide co-solvents exhibit higher ionic conductivity than the neat solvents. This improved ionic conductivity is attributed to the ability of BTFE:co-solvent mixtures to partition between Npââș and Fâ» ion-aggregates, promoting better ion dissociation
Fluoride-ion solvation in non-aqueous electrolyte solutions
Understanding the factors that influence ion-solvent properties for the fluoride ion in organic solvents is key to the development of useful liquid electrolytes for fluoride-ion batteries. Using both experimental and computational methods, we examined a range of chemical and electrochemical properties for a set of organic solvents in combination with dry N,N,N-trimethylneopentylammonium fluoride (NpâF) salt. Results showed that solvent electronic structure strongly influences NpâF dissolution, and the pK_a of solvent protons provides a good guide to potential Fâ» reactivity. We found a number of organic solvents capable of dissolving NpâF while providing chemically-stable Fâ» in solution and characterized three of them in detail: propionitrile (PN), 2,6-difluoropyridine (2,6-DFP), and bis(2,2,2-trifluoroethyl) ether (BTFE). Arrhenius analysis for NpâF/PN, NpâF/DFP, and NpâF/BTFE electrolytes suggests that DFP facilitates the highest Fâ» ion mobility of the three neat solvents. Electrolyte mixtures of BTFE and amide co-solvents exhibit higher ionic conductivity than the neat solvents. This improved ionic conductivity is attributed to the ability of BTFE:co-solvent mixtures to partition between Npââș and Fâ» ion-aggregates, promoting better ion dissociation
Room-temperature cycling of metal fluoride electrodes: Liquid electrolytes for high-energy fluoride ion cells
Fluoride ion batteries are potential ânext-generationâ electrochemical storage devices that offer high energy density. At present, such batteries are limited to operation at high temperatures because suitable fluoride ionâconducting electrolytes are known only in the solid state. We report a liquid fluoride ionâconducting electrolyte with high ionic conductivity, wide operating voltage, and robust chemical stability based on dry tetraalkylammonium fluoride salts in ether solvents. Pairing this liquid electrolyte with a copperâlanthanum trifluoride (Cu@LaF_3) core-shell cathode, we demonstrate reversible fluorination and defluorination reactions in a fluoride ion electrochemical cell cycled at room temperature. Fluoride ionâmediated electrochemistry offers a pathway toward developing capacities beyond that of lithium ion technology
Randomised controlled trial of the Community Navigator programme to reduce loneliness and depression for adults with treatment-resistant depression in secondary community mental health services: trial protocol
BACKGROUND: New treatments are needed for people with treatment-resistant depression (TRD), who do not benefit from anti-depressants and many of whom do not recover fully with psychological treatments. The Community Navigator programme was co-produced with service users and practitioners. It is a novel social intervention which aims to reduce loneliness and thus improve health outcomes for people with TRD. Participants receive up to 10 individual meetings with a Community Navigator, who helps them to map their social world and set and enact goals to enhance their social connections and reduce loneliness. Participants may also access group meet-ups with others in the programme every 2Â months, and may be offered modest financial support to enable activities to support social connections. METHODS: A researcher-blind, multi-site, 1:1 randomised controlled trial with Nâ=â306 participants will test the effectiveness of the Community Navigator programme for people with TRD in secondary community mental health teams (CMHTs). Our primary hypothesis is that people who are offered the Community Navigator programme as an addition to usual CMHT care will be less depressed, assessed using the PHQ-9 self-report measure, at 8-month, end-of-treatment follow-up, compared to a control group receiving usual CMHT care and a booklet with information about local social groups and activities. We will follow participants up at end-of-treatment and at 14Â months, 6Â months after end-of-treatment follow-up. Secondary outcomes include the following: loneliness, anxiety, personal recovery, self-efficacy, social network, social identities. We will collect data about health-related quality of life and service use to investigate the cost-effectiveness of the Community Navigator programme. DISCUSSION: This trial will provide definitive evidence about the effectiveness and cost-effectiveness of the Community Navigator programme and whether it can be recommended for use in practice. The trial is due to finish in August 2025. TRIAL REGISTRATION: Prospectively registered on 8th July 2022 at: ISRCTN13205972
Pulseâlabeling studies of carbon cycling in arctic tundra ecosystems: Contribution of photosynthates to soil organic matter
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95486/1/gbc827.pd
Racism and bullying in rural primary schools: protecting White identities post Macpherson
Randomised controlled trial of the Community Navigator programme to reduce loneliness and depression for adults with treatment-resistant depression in secondary community mental health services : trial protocol
BACKGROUND: New treatments are needed for people with treatment-resistant depression (TRD), who do not benefit from anti-depressants and many of whom do not recover fully with psychological treatments. The Community Navigator programme was co-produced with service users and practitioners. It is a novel social intervention which aims to reduce loneliness and thus improve health outcomes for people with TRD. Participants receive up to 10 individual meetings with a Community Navigator, who helps them to map their social world and set and enact goals to enhance their social connections and reduce loneliness. Participants may also access group meet-ups with others in the programme every 2 months, and may be offered modest financial support to enable activities to support social connections. METHODS: A researcher-blind, multi-site, 1:1 randomised controlled trial with Nâ=â306 participants will test the effectiveness of the Community Navigator programme for people with TRD in secondary community mental health teams (CMHTs). Our primary hypothesis is that people who are offered the Community Navigator programme as an addition to usual CMHT care will be less depressed, assessed using the PHQ-9 self-report measure, at 8-month, end-of-treatment follow-up, compared to a control group receiving usual CMHT care and a booklet with information about local social groups and activities. We will follow participants up at end-of-treatment and at 14 months, 6 months after end-of-treatment follow-up. Secondary outcomes include the following: loneliness, anxiety, personal recovery, self-efficacy, social network, social identities. We will collect data about health-related quality of life and service use to investigate the cost-effectiveness of the Community Navigator programme. DISCUSSION: This trial will provide definitive evidence about the effectiveness and cost-effectiveness of the Community Navigator programme and whether it can be recommended for use in practice. The trial is due to finish in August 2025. TRIAL REGISTRATION: Prospectively registered on 8th July 2022 at: ISRCTN13205972
What does an interferometer really measure? Including instrument and data characteristics in the reconstruction of the 21cm power spectrum
Combining the visibilities measured by an interferometer to form a
cosmological power spectrum is a complicated process in which the window
functions play a crucial role. In a delay-based analysis, the mapping between
instrumental space, made of per-baseline delay spectra, and cosmological space
is not a one-to-one relation. Instead, neighbouring modes contribute to the
power measured at one point, with their respective contributions encoded in the
window functions. To better understand the power spectrum measured by an
interferometer, we assess the impact of instrument characteristics and analysis
choices on the estimator by deriving its exact window functions, outside of the
delay approximation. Focusing on HERA as a case study, we find that
observations made with long baselines tend to correspond to enhanced low-k
tails of the window functions, which facilitate foreground leakage outside the
wedge, whilst the choice of bandwidth and frequency taper can help narrow them
down. With the help of simple test cases and more realistic visibility
simulations, we show that, apart from tracing mode mixing, the window functions
can accurately reconstruct the power spectrum estimator of simulated
visibilities. We note that the window functions depend strongly on the
chromaticity of the beam, and less on its spatial structure - a Gaussian
approximation, ignoring side lobes, is sufficient. Finally, we investigate the
potential of asymmetric window functions, down-weighting the contribution of
low-k power to avoid foreground leakage. The window functions presented in this
work correspond to the latest HERA upper limits for the full Phase I data. They
allow an accurate reconstruction of the power spectrum measured by the
instrument and can be used in future analyses to confront theoretical models
and data directly in cylindrical space.Comment: 18 pages, 18 figures, submitted to MNRAS. Comments welcome
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