Improving the ORR Performance by Enhancing the Pt Oxidation Resistance

Proton exchange membrane fuel cells require oxygen reduction catalysts with high activity and stability. Pt based alloy materials are most widely applied ORR catalyst due to its high intrinsic activity, but usually suffer from rapid deactivation as a result of particle agglomeration, detachment, Ostwald ripening and/or Pt dissolution. Here we investigate the degradation of the PdPt alloys via in situ X-ray absorption fine structure, Δμ analysis, identical location-electron microscopy and DFT calculations. We conclude that the origin of high activity and stability of the PdPt catalyst stems from the oxidation resistance of metallic Pt, forming mainly surface adsorbed O species at high potentials. Two stage degradation process are observed, showing an evolution of dynamic surface dependent ORR performance along with the deactivation process. The careful design of Pt alloy structure leads to controlled surface oxygen behaviours. This opens a new way to increase the lifespan of fuel cells and improve the Pt utilization efficiency

Lessons from countries implementing find, test, trace, isolation and support policies in the rapid response of the COVID-19 pandemic: a systematic review.

OBJECTIVE: To systematically learn lessons from the experiences of countries implementing find, test, trace, isolate, support (FTTIS) in the first wave of the COVID-19 pandemic. DESIGN, DATA SOURCES AND ELIGIBILITY CRITERIA: We searched MEDLINE (PubMed), Cochrane Library, SCOPUS and JSTOR, initially between 31 May 2019 and 21 January 2021. Research articles and reviews on the use of contact tracing, testing, self-isolation and quarantine for COVID-19 management were included in the review. DATA EXTRACTION AND SYNTHESIS: We extracted information including study objective, design, methods, main findings and implications. These were tabulated and a narrative synthesis was undertaken given the diverse research designs, methods and implications. RESULTS: We identified and included 118 eligible studies. We identified the core elements of an effective find, test, trace, isolate, support (FTTIS) system needed to interrupt the spread of a novel infectious disease, where treatment or vaccination was not yet available, as pertained in the initial stages of the COVID-19 pandemic. We report methods used to shorten case finding time, improve accuracy and efficiency of tests, coordinate stakeholders and actors involved in an FTTIS system, support individuals isolating and make appropriate use of digital tools. CONCLUSIONS: We identified in our systematic review the key components of an FTTIS system. These include border controls, restricted entry, inbound traveller quarantine and comprehensive case finding; repeated testing to minimise false diagnoses and pooled testing in resource-limited circumstances; extended quarantine period and the use of digital tools for contact tracing and self-isolation. Support for mental or physical health and livelihoods is needed for individuals undergoing self-isolation/quarantine. An integrated system with rolling-wave planning can best use effective FTTIS tools to respond to the fast-changing COVID-19 pandemic. Results of the review may inform countries considering implementing these measures

The Arabin pessary to prevent preterm birth in women with a twin pregnancy and a short cervix:the STOPPIT 2 RCT

Background: Preterm birth is common in twins and accounts for significant mortality and morbidity. There are no effective preventative treatments. Some studies have suggested that, in twin pregnancy complicated by a short cervix, the Arabin pessary, which fits around the cervix and can be inserted as an outpatient procedure, reduces preterm birth and prevents neonatal morbidity. Objective: STOPPIT 2 aimed to evaluate the clinical utility of the Arabin cervical pessary in preventing preterm birth in women with a twin pregnancy and a short cervix. Design: STOPPIT 2 was a pragmatic, open label, multicentre randomised controlled trial with two treatment group – the Arabin pessary plus standard care (intervention) and standard care alone (control). Participants were initially recruited into the screening phase of the study, when cervical length was measured. Women with a measured cervical length of ≤ 35 mm were then recruited into the treatment phase of the study. An economic evaluation considered cost-effectiveness and a qualitative substudy explored the experiences of participants and clinicians. Setting: Antenatal clinics in the UK and elsewhere in Europe. Participants: Women with twin pregnancy at < 21 weeks’ gestation with known chorionicity and gestation established by scan at ≤ 16 weeks’ gestation. Interventions: Ultrasound scan to establish cervical length. Women with a cervical length of ≤ 35 mm at 18+ 0–20+ 6 weeks’ gestation were randomised to standard care or Arabin pessary plus standard care. Randomisation was performed by computer and accessed through a web-based browser. Main outcome measures: Obstetric – all births before 34+ 0 weeks’ gestation following the spontaneous onset of labour; and neonatal – composite of adverse outcomes, including stillbirth or neonatal death, periventricular leukomalacia, early respiratory morbidity, intraventricular haemorrhage, necrotising enterocolitis or proven sepsis, all measured up to 28 days after the expected date of delivery. Results: A total of 2228 participants were recruited to the screening phase, of whom 2170 received a scan and 503 were randomised: 250 to Arabin pessary and 253 to standard care alone. The rate of the primary obstetric outcome was 18.4% (46/250) in the intervention group and 20.6% (52/253) in the control group (adjusted odds ratio 0.87, 95% confidence interval 0.55 to 1.38; p = 0.54). The rate of the primary neonatal outcome was 13.4% (67/500) and 15.0% (76/506) in the intervention group and control group, respectively (adjusted odds ratio 0.86, 95% confidence interval 0.54 to 1.36; p = 0.52). The pessary was largely well tolerated and clinicians found insertion and removal ‘easy’ or ‘fairly easy’ in the majority of instances. The simple costs analysis showed that pessary treatment is no more costly than standard care. Limitations: There was the possibility of a type II error around smaller than anticipated benefit. Conclusions: In this study, the Arabin pessary did not reduce preterm birth or adverse neonatal outcomes in women with a twin pregnancy and a short cervix. The pessary either is ineffective at reducing preterm birth or has an effect size of < 0.4. Future work: Women with twin pregnancy remain at risk of preterm birth; work is required to find treatments for this. Trial registration: Current Controlled Trials ISRCTN98835694 and ClinicalTrials.gov NCT02235181. Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 44. See the NIHR Journals Library website for further project information

Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria

Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O2) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O2]3− site selectively adsorbs molecular O2, forming a rarely reported electrophilic η2-O2 species at 298 K. Assisted by neighbouring Ce(III) cations, η2-O2 is finally reduced to two O2−, that create two Cu–O–Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s−1 at 373 K and 0.01 bar PCO. The unique electronic structure of [Cu(I)O2]3− site suggests its potential in selective oxidation

Engineering Pt-Pt coordination environment to enhance the four-electron oxygen reduction reaction

The oxygen reduction reaction (ORR) in proton exchange membrane fuel cells plays an important role in the H2 economy. Pt-based alloy catalysts with tuned d-band centres are widely regarded as the most efficient catalysts. Here we report that the average size of Pt domains in a Pt-Pd alloy, described as the Pt-Pt coordination number (C.N.), may measure the coordination environment of Pt and its effect on the d-states, to serve as a key geometric descriptor for the ORR activity. The decrease of Pt-Pt C.N. from 10.8 in commercial Pt nanoparticles to 1.33 in Pt1Pd493 alloy leads to an exponential increase in the Pt mass activity from 0.18 to 4.86 A/mgPt. Density functional theory calculations show that low C.N. sites of Pt within the Pd host have low O-O dissociation barriers, favouring the four-electron dissociative pathway. The precise engineering of Pt-Pt C.N. in an alloy is critical for optimising metal use in the activation of chemically stable compounds, particularly in the context of catalysis for renewable energy

Oxygen vacancy formation as the rate-determining step in the Mars-van Krevelen mechanism

The Mars-van Krevelen mechanism (MvK) is a widely recognized model for describing the role of lattice oxygen in catalysis. Following the MvK mechanism, the formation and conversion of surface oxygen vacancy (VO) are considered as the key steps. CeO2-ZrO2 (CZ) mixed oxides are the typical catalyst support in MvK mechanism. They have the unique property of hosting remarkable amount of VO without significant change in lattice structure, offering O storage and release capability that maintains the required concentration of active O on the catalytic surface. In this regard, the rate of VO formation and conversion directly affect their catalytic performance. In this work, we obtained the VO formation and conversion kinetics by measuring the rate of the Ce4+ reduction and oxidation via operando energy dispersive Extended X-ray Absorption Fine Structure (EDE). The main conclusions are: 1) VO formation is 10 times faster than VO conversion; 2) VO formation rates are comparable with the CO oxidation rates, thereby serving as the rate-determining step in CO oxidation; 3) Pd and Cu serve as catalysts for VO formation by significantly improving its rate by 50 times at 250 C by weakening the metal-O bonding strength, whereas the activation energy have been reduced to 58.4 kJ/mol and 36.5 kJ/mol, respectively. Our method in measuring and analysing partial reaction rates within a turnover is therefore important for all chemical reactions

The decisive role of CuI-framework O binding in oxidation half cycle of selective catalytic reduction

Cu-exchanged zeolite is an efficient catalyst to remove harmful nitrogen oxides from diesel exhaust gas through the selective catalytic reduction (SCR) reaction. The SCR performance is structure dependent, in which a Cu with one adjacent framework Al (1AlCu) has lower activation energy in oxidative half-cycle than Cu with two adjacent framework Al (2AlCu). Using a combination of operando X-ray absorption spectroscopy, valence to core - X-ray emission spectroscopy and density functional theory calculations, here we showed that 1AlCu proceeds with nitrate mechanism, in which side-on coordination of O2 at a CuI(NH3)xOfw (fw = framework) is the rate-limiting step in the oxidation half-cycle. As a result, the CuI(NH3)xOfw at 1AlCu can easily yield a transient CuIINOx intermediate upon breaking of Cu-Ofw after interaction with NO. In the meantime, 2AlCu has high barriers for Cu-Ofw bond breaking and proceeds with dimer mechanism. Our results show the coexisting of both dimer and nitrate mechanism, in particular at high Cu loadings, in which controlling the strength of the Cu-Ofw coordination is key for the O-O split in the nitrate pathway

Designing Reactive Bridging O^2– at the Atomic Cu–O–Fe Site for Selective NH₃ Oxidation

Surface oxidation chemistry involves the formation and breaking of metal–oxygen (M–O) bonds. Ideally, the M–O bonding strength determines the rate of oxygen absorption and dissociation. Here, we design reactive bridging O2– species within the atomic Cu–O–Fe site to accelerate such oxidation chemistry. Using in situ X-ray absorption spectroscopy at the O K-edge and density functional theory calculations, it is found that such bridging O2– has a lower antibonding orbital energy and thus weaker Cu–O/Fe–O strength. In selective NH3 oxidation, the weak Cu–O/Fe–O bond enables fast Cu redox for NH3 conversion and direct NO adsorption via Cu–O–NO to promote N–N coupling toward N2. As a result, 99% N2 selectivity at 100% conversion is achieved at 573 K, exceeding most of the reported results. This result suggests the importance to design, determine, and utilize the unique features of bridging O2– in catalysis