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Sökning: WFRF:(Zhang Chi) > Stockholms universitet

  • Resultat 1-10 av 21
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1.
  • Han, Ning, et al. (författare)
  • Achieving Efficient Electrocatalytic Oxygen Evolution in Acidic Media on Yttrium Ruthenate Pyrochlore through Cobalt Incorporation
  • 2023
  • Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 33:20
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y2-xCoxRu2O7−δ results in an ultrahigh OER activity because of the charge redistribution at eg orbitals between Ru and Co atoms. The Y1.75Co0.25Ru2O7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H2SO4 at the current density of 10 mA cm−2, which is smaller than that of parent Y2Ru2O7−δ (360 mV) and commercial RuO2 (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen-mediated mechanism.
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2.
  • Zhang, Wei, et al. (författare)
  • Critical Role of Phosphorus in Hollow Structures Cobalt-Based Phosphides as Bifunctional Catalysts for Water Splitting
  • 2022
  • Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 18:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Cobalt phosphides electrocatalysts have great potential for water splitting, but the unclear active sides hinder the further development of cobalt phosphides. Wherein, three different cobalt phosphides with the same hollow structure morphology (CoP-HS, CoP2-HS, CoP3-HS) based on the same sacrificial template of ZIF-67 are prepared. Surprisingly, these cobalt phosphides exhibit similar OER performances but quite different HER performances. The identical OER performance of these CoPx-HS in alkaline solution is attributed to the similar surface reconstruction to CoOOH. CoP-HS exhibits the best catalytic activity for HER among these CoPx-HS in both acidic and alkaline media, originating from the adjusted electronic density of phosphorus to affect absorption–desorption process on H. Moreover, the calculated ΔGH* based on P-sites of CoP-HS follows a quite similar trend with the normalized overpotential and Tafel slope, indicating the important role of P-sites for the HER process. Moreover, CoP-HS displays good performance (cell voltage of 1.67 V at a current density of 50 mA cm−2) and high stability in 1 M KOH. For the first time, this work detailly presents the critical role of phosphorus in cobalt-based phosphides for water splitting, which provides the guidance for future investigations on transition metal phosphides from material design to mechanism understanding. 
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3.
  • Ding, Lijie, et al. (författare)
  • Smoking, heavy drinking, physical inactivity, and obesity among middle-aged and older adults in China : cross-sectional findings from the baseline survey of CHARLS 2011-2012.
  • 2020
  • Ingår i: BMC Public Health. - : BioMed Central. - 1471-2458. ; 20:1
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: Prevention and control of cardiometabolic conditions and cardiovascular disease (CVD) in China may contribute to sustainable CVD reduction globally, given the fact that one-fifth of the worldwide population is in China. Knowing the distribution of behavioral risk factors (e.g., smoking and physical inactivity), especially at a national level in China, would be extremely relevant to the field of public health and CVD prevention. The objectives of this study were to investigate the nationwide prevalence of obesity, smoking, heavy drinking, and physical inactivity in Chinese adults, and further explore whether cardiometabolic conditions would modify the distribution of behavioral risk factors.METHODS: This population-based study is based on the China Health and Retirement Longitudinal Study (2011-2012), including 17,302 adults (≥45 years, mean age 59.67 years, female 51.66%) from 25 provinces in China. Data on demographics, lifestyle factors, health status and history of diseases were collected via structured interviews and laboratory tests. Smoking, heavy drinking, obesity, and physical inactivity were defined following standard guidelines. We performed descriptive analysis and logistic regressions in this study.RESULTS: The overall prevalence of heavy drinking, obesity, current smoking, and physical inactivity among middle-aged and older adults was 7.23% (95% confidence interval 6.53-7.29%), 11.53% (10.43-12.62%), 27.46% (26.30-28.62%), and 44.06% (41.19-46.92%), respectively. The prevalence varied between rural and urban areas as well as among geographic areas, with higher prevalence in the Northern and Northeastern regions. Heavy drinking and obesity were significantly associated with incident hypertension, diabetes, and high cholesterol; while current smoking was significantly associated with incident hypertension. Compared with healthy individuals, participants who self-reported a diagnosis of hypertension, high cholesterol, or diabetes were less likely to smoke currently and drink alcohol heavily, but more likely to be physically inactive and obese.CONCLUSIONS: Among Chinese middle-aged and older adults, the prevalence of behavioral risk factors varies by geographic region. Further effort is required to improve physical activity and fitness for Chinese adults, especially those with cardiometabolic conditions.
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4.
  • Gambetta, Filippo M., et al. (författare)
  • Exploring the Many-Body Dynamics Near a Conical Intersection with Trapped Rydberg Ions
  • 2021
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 126:23
  • Tidskriftsartikel (refereegranskat)abstract
    • Conical intersections between electronic potential energy surfaces are paradigmatic for the study of nonadiabatic processes in the excited states of large molecules. However, since the corresponding dynamics occurs on a femtosecond timescale, their investigation remains challenging and requires ultrafast spectroscopy techniques. We demonstrate that trapped Rydberg ions are a platform to engineer conical intersections and to simulate their ensuing dynamics on larger length scales and timescales of the order of nanometers and microseconds, respectively; all this in a highly controllable system. Here, the shape of the potential energy surfaces and the position of the conical intersection can be tuned thanks to the interplay between the high polarizability and the strong dipolar exchange interactions of Rydberg ions. We study how the presence of a conical intersection affects both the nuclear and electronic dynamics demonstrating, in particular, how it results in the inhibition of the nuclear motion. These effects can be monitored in real time via a direct spectroscopic measurement of the electronic populations in a state-of-the-art experimental setup.
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5.
  • Gambetta, Filippo M., et al. (författare)
  • Long-range multi-body interactions and three-body anti-blockade in a trapped Rydberg ion chain
  • 2020
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 125:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Trapped Rydberg ions represent a flexible platform for quantum simulation and information processing which combines a high degree of control over electronic and vibrational degrees of freedom. The possibility to individually excite ions to high-lying Rydberg levels provides a system where strong and long-range interactions between pairs of excited ions can be engineered and tuned via external laser fields. We show that the coupling between Rydberg pair interactions and collective motional modes gives rise to effective long-range multi-body interactions, consisting of two, three, and four-body terms. Their shape, strength, and range can be controlled via the ion trap parameters and strongly depends on both the equilibrium configuration and vibrational modes of the ion crystal. By focusing on an experimentally feasible quasi one-dimensional setup of 88Sr+ Rydberg ions, we demonstrate that multi-body interactions are enhanced by the emergence of a soft mode associated, e.g., with a structural phase transition. This has a striking impact on many-body electronic states and results, for example, in a three-body anti-blockade effect. Our study shows that trapped Rydberg ions offer new opportunities to study exotic many-body quantum dynamics driven by enhanced multi-body interactions.
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6.
  • Higgins, Gerard, et al. (författare)
  • Coherent Control of a Single Trapped Rydberg Ion
  • 2017
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Trapped Rydberg ions are a promising novel approach to quantum computing and simulations. They are envisaged to combine the exquisite control of trapped ion qubits with the fast two-qubit Rydberg gates already demonstrated in neutral atom experiments. Coherent Rydberg excitation is a key requirement for these gates. Here, we carry out the first coherent Rydberg excitation of an ion and perform a single-qubit Rydberg gate, thus demonstrating basic elements of a trapped Rydberg ion quantum computer.
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7.
  • Higgins, Gerard, et al. (författare)
  • Highly Polarizable Rydberg Ion in a Paul Trap
  • 2019
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 123:15
  • Tidskriftsartikel (refereegranskat)abstract
    • Usually the influence of the quadratic Stark effect on an ion's trapping potential is minuscule and only needs to be considered in atomic clock experiments. In this work we excite a trapped ion to a Rydberg state with polarizability similar to 8 orders of magnitude higher than a low-lying electronic state; we find that the highly polarizable ion experiences a vastly different trapping potential owing to the Stark effect. We observe changes in trap stiffness, equilibrium position, and minimum potential, which can be tuned using the trapping electric fields. These effects lie at the heart of several proposed studies, including a high-fidelity submicrosecond entangling operation; in addition we demonstrate these effects may be used to minimize ion micromotion. Mitigation of Stark effects is important for coherent control of Rydberg ions; we illustrate this by carrying out the first Rabi oscillations between a low-lying electronic state and a Rydberg state of an ion.
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8.
  • Higgins, Gerard, 1989, et al. (författare)
  • Micromotion minimization using Ramsey interferometry
  • 2021
  • Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:12
  • Tidskriftsartikel (refereegranskat)abstract
    • We minimize the stray electric field in a linear Paul trap quickly and accurately, by applying interferometry pulse sequences to a trapped ion optical qubit. The interferometry sequences are sensitive to the change of ion equilibrium position when the trap stiffness is changed, and we use this to determine the stray electric field. The simplest pulse sequence is a two-pulse Ramsey sequence, and longer sequences with multiple pulses offer a higher precision. The methods allow the stray field strength to be minimized beyond state-of-the-art levels. Using a sequence of nine pulses we reduce the 2D stray field strength to (10.5 +/- 0.8) mV m(-1) in 11 s measurement time. The pulse sequences are easy to implement and automate, and they are robust against laser detuning and pulse area errors. We use interferometry sequences with different lengths and precisions to measure the stray field with an uncertainty below the standard quantum limit. This marks a real-world case in which quantum metrology offers a significant enhancement. Also, we minimize micromotion in 2D using a single probe laser, by using an interferometry method together with the resolved sideband method; this is useful for experiments with restricted optical access. Furthermore, a technique presented in this work is related to quantum protocols for synchronizing clocks; we demonstrate these protocols here.
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9.
  • Higgins, Gerard, et al. (författare)
  • Observation of second- and higher-order electric quadrupole interactions with an atomic ion
  • 2021
  • Ingår i: Physical Review Research. - 2643-1564. ; 3:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of matter to fields underlies the physical sciences, from particle physics to astrophysics, and from chemistry to biophysics. We observe an atom's response to an electric quadrupole field to second- and higher orders; this arises from the atom's electric quadrupole polarizability and hyperpolarizabilities. We probe a single atomic ion which is excited to Rydberg states and confined in the electric fields of a Paul trap. The quadrupolar trapping fields cause atomic energy level shifts and give rise to spectral sidebands. The observed effects are described well by theory calculations.
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10.
  • Higgins, Gerard, et al. (författare)
  • Single Strontium Rydberg Ion Confined in a Paul Trap
  • 2017
  • Ingår i: Physical Review X. - 2160-3308. ; 7:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Trapped Rydberg ions are a promising new system for quantum information processing. They have the potential to join the precise quantum operations of trapped ions and the strong, long-range interactions between Rydberg atoms. Combining the two systems is not at all straightforward. Rydberg atoms are severely affected by electric fields which may cause Stark shifts and field ionization, while electric fields are used to trap ions. Thus, a thorough understanding of the physical properties of Rydberg ions due to the trapping electric fields is essential for future applications. Here, we report the observation of two fundamental trap effects. First, we investigate the interaction of the Rydberg electron with the trapping electric quadrupole fields which leads to Floquet sidebands in the excitation spectra. Second, we report on the modified trapping potential in the Rydberg state compared to the ground state that results from the strong polarizability of the Rydberg ion. By controlling both effects we observe resonance lines close to their natural linewidth demonstrating an unprecedented level of control of this novel quantum platform.
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