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Correction for ‘Carbon dioxide and nitrogen reduction reactions using 2D transition metal dichalcogenide (TMDC) and carbide/nitride (MXene) catalysts’ by Zhaodong Li et al. , Energy Environ. Sci. , 2021, 14 , 6242–6286, DOI: 10.1039/D1EE03211A.
Carbon dioxide-assisted coupling of methane offers an approach to chemically upgrade two greenhouse gases and components of natural gas to produce ethylene and syngas. Prior research on this reaction has concentrated efforts on catalyst discovery, which has indicated that composites comprised of both reducible and basic oxides are especially promising. There is a need for detailed characterization of these bifunctional oxide systems to provide a more fundamental understanding of the active sites and their roles in the reaction. We studied the dependence of physical and electronic properties of Ca-modified ZnO materials on Ca content via X-ray photoelectron and absorption spectroscopies, electron microscopy, and infrared spectroscopic temperature-programmed desorption (IR-TPD). It was found that introduction of only 0.6 mol% Ca onto a ZnO surface is necessary to induce significant improvement in the catalytic production of C 2 species: C 2 selectivity increases from 5% on un-modified ZnO to 58%, at similar conversions. Evidence presented shows that this selectivity increase results from the formation of an interface between the basic CaO and reducible ZnO phases. Furthermore, the basicity of these interface sites correlates directly with catalytic activity over a wide composition range, and this relationship indicates that moderate CO 2 adsorption strength is optimal for CH 4 coupling. These results demonstrate, for the first time to our knowledge, a volcano-type relationship between CO 2 -assisted CH 4 coupling activity and catalyst surface basicity, which can inform further catalyst development.
The sustainability potential of carbon capture, concentration, and utilization technologies motivates accelerated discovery of carbon dioxide sorbents, for which we present a high throughput screening instrument.
Correction for ‘Thorium amidates function as single-source molecular precursors for thorium dioxide’ by Mark D. Straub et al. , Chem. Commun. , 2021, 57 , 4954–4957, https://doi.org/10.1039/D1CC00867F.
The electrochemical carbon dioxide reduction reaction (CO 2 RR) using renewable energy sources is a promising solution for mitigating CO 2 emissions. In particular, CO 2 RR to formate represents a commercially profitable target. However, a comprehensive understanding of the catalytic mechanisms of Sn-based catalysts under reaction conditions, including the real-time structural evolution of catalysts and the role of all key reaction intermediates in influencing the CO 2 RR selectivity, is still lacking. The current study reports a framework to study the selectivity preference of Sn-based bimetallic catalysts using a combination of electrochemical measurements, in situ characterization, and density functional theory (DFT) calculations. The addition of a second metal (Co, Ni, Ag, Zn, Ga, Bi) was found to play a vital role in affecting the CO 2 RR performance. In situ X-ray absorption near edge structure (XANES) measurements revealed a dynamic evolution in the Sn valence state induced by different secondary metals. A multidimensional descriptor involving all the key reaction intermediates was developed to assess formate selectivity using a 2-dimensional volcano plot. Finally, this research offers an effective framework for understanding CO 2 RR catalytic selectivity by considering both the real-time structural evolution of catalysts and all the key intermediates involved.
Correction for ‘Acid–base concentration swing for direct air capture of carbon dioxide’ by Anatoly Rinberg and Michael J. Aziz, Energy Adv. , 2024, https://doi.org/10.1039/d4ya00251b.
The interaction of xenon (Xe) bubbles with small self-defects in uranium dioxide (UO2) has been studied using molecular statics simulations. The results show that the pressure and size of bubbles have a minimal impact on the heterogeneity of the interaction between a charge neutral Xe bubble and charged point defects, while the local charge distribution around the bubble overwhelmingly determines the interaction strength and critical interaction distance. The charge effect on the interactions between Xe bubbles and defects was further confirmed by assessing the point defect interaction energies with negatively or positively charged Xe bubbles. The Xe density, or pressure, has a much smaller effect on the interaction energy between charged bubbles and small defects at least for low and medium pressure bubbles. The interactions between charged Xe bubbles and point defects basically follow the Coulomb electrostatic interaction law, which is independent of the empirical potentials employed for the Xe–UO2 system in this work.
A vanadium dioxide (VO 2 ) based solid-to-solid phased changing material has been attracting great interest in smart window applications. However, achieving high solar modulation and high transparency simultaneously in visible light is the major challenge for the practical application of this smart material. To resolve this issue, in this paper, a smart film composed of a VO 2 nanoparticle matrix and a patterned VO 2 film is presented. Furthermore, numerical modeling and electromagnetic simulation are carried out to characterize the performance in terms of solar modulation and luminous transmittance, and a parametric study is carried out to optimize the proposed smart window film. Compared with the VO 2 nanoparticle matrix, the proposed structure can obtain 23% solar modulation and 57% luminous transmittance but with a much thinner thickness, which will significantly reduce the cost and fabrication complexity and extend the environment stability.
The low temperature monoclinic, insulating phase of vanadium dioxide is ordinarily considered nonmagnetic, with dimerized vanadium atoms forming spin singlets, though paramagnetic response is seen at low temperatures. Here, we find a nonlocal spin Seebeck signal in VO 2 films that appears below 30 K and that increases with a decrease in temperature. The spin Seebeck response has a nonhysteretic dependence on the in-plane external magnetic field. This paramagnetic spin Seebeck response is discussed in terms of prior findings on paramagnetic spin Seebeck effects and expected magnetic excitations of the monoclinic ground state.
Thermal transport in nuclear fuels used for nuclear energy applications is directly tied to performance and reliability. Uranium dioxide (UO 2 ), one of the most important nuclear fuels, can accumulate excess oxygen atoms as interstitial defects, which significantly impacts thermal transport properties. In this study, thermal conductivities and inelastic neutron scattering (INS) measurements on UO 2+ x were performed at low temperatures (2–300K). The thermal conductivity of UO 2+ x (x = 0, 0.03, 0.04, and 0.11) is significantly suppressed compared to UO 2 except near the Néel temperature T N = 30.8 K, where it is independent of x. INS measurements demonstrate that the heat capacities and phonon group velocities of UO 2 and UO 2.08 are similar, and the suppressed thermal conductivity results from smaller phonon lifetimes. These perceptions advance our understanding of thermal transport properties in advanced nuclear fuels and guide safe and economic utilization of nuclear energy.
Vanadium dioxide (VO 2 ) undergoes a metal–insulator phase transition at ~70 °C and has attracted substantial interest for potential applications in electronics, including those in neuromorphic computing. The vanadium–oxygen system has a rather complicated phase diagram, and controlling the stoichiometry and the phase of thin films of vanadium oxides is a well-known challenge. Here, we explore the novel combination of two methods of VO 2 thin film deposition using off-axis RF magnetron sputtering on (100)- and (111)-oriented yttria-stabilized zirconia (YSZ) substrates: reactive sputtering of vanadium in an oxygen environment and sputtering of vanadium metal followed by oxidation to VO 2 . Interestingly, the reactive sputtering process on both substrate orientations yields the metastable semiconducting VO 2 (B) phase, which is structurally stabilized by the YSZ surface. The metal sputtering and oxidation process on YSZ produces mainly the equilibrium monoclinic (or M1) phase of VO 2 that exhibits a metal–insulator transition. Using this method, we obtained thin films of (010)-textured polycrystalline VO 2 (M1) that show a metal–insulator transition with an on/off ratio larger than 1000.
Titanium dioxide (TiO 2 ) is a wide-gap semiconductor with numerous applications in photocatalysis, photovoltaics, and neuromorphic computing. The unique functional properties of this material critically depend on its ability to transport charge in the form of polarons, namely narrow electron wavepackets accompanied by local distortions of the crystal lattice. It is currently well established that the most important polymorphs of TiO 2 , the rutile and anatase phases, harbor small electron polarons and small hole polarons, respectively. However, whether additional polaronic species exist in TiO 2 , and under which conditions, remain open questions. Here, we provide definitive answers to these questions by exploring the rich landscape of polaron quasiparticles in TiO 2 via recently developed ab initio techniques. In addition to the already known small polarons, we identify three species, namely a large hole polaron in rutile, a large quasi-two-dimensional electron polaron in anatase, and a large exciton polaron in anatase. These findings complete the puzzle on the polaron physics of TiO 2 and pave the way for systematically probing and manipulating polarons in a broad class of complex oxides and quantum materials.
Abstract Ocean-based carbon dioxide (CO 2 ) removal (CDR) strategies are an important part of the portfolio of approaches needed to achieve negative greenhouse gas emissions. Many ocean-based CDR strategies rely on injecting CO 2 or organic carbon (that will eventually become CO 2 ) into the ocean interior, or enhancing the ocean’s biological pump. These approaches will not result in permanent sequestration, because ocean currents will eventually return the injected CO 2 back to the surface, where it will be brought into equilibrium with the atmosphere. Here, a model of steady state global ocean circulation and mixing is used to assess the time scales over which CO 2 injected in the ocean interior remains sequestered from the atmosphere. There will be a distribution of sequestration times for any single discharge location due to the infinite number of pathways connecting a location at depth with the sea surface. The resulting probability distribution is highly skewed with a long tail of very long transit times, making mean sequestration times much longer than typical time scales. Deeper discharge locations will sequester purposefully injected CO 2 much longer than shallower ones and median sequestration times are typically decades to centuries, and approach 1000 years in the deep North Pacific. Large differences in sequestration times occur both within and between the major ocean basins, with the Pacific and Indian basins generally having longer sequestration times than the Atlantic and Southern Oceans. Assessments made over a 50 year time horizon illustrates that most of the injected carbon will be retained for injection depths greater than 1000 m, with several geographic exceptions such as the Western North Atlantic. Ocean CDR strategies that increase upper ocean ecosystem productivity with the goal of exporting more carbon to depth will have mainly a short-term influence on atmospheric CO 2 levels because ∼70% will be transported back to the surface ocean within 50 years. The results presented here will help plan appropriate ocean CDR strategies that can help limit climate damage caused by fossil fuel CO 2 emissions.
Abstract Accounting for temporal changes in carbon dioxide (CO 2 ) effluxes from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of flux measurements of CO 2 based on the eddy covariance method from 13 lakes and reservoirs in the Northern Hemisphere, and quantify dynamics at multiple temporal scales. We found pronounced sub-annual variability in CO 2 flux at all sites. By accounting for diel variation, only 11% of site-months were net daily sinks of CO 2 . Annual CO 2 emissions had an average of 25% (range 3%–58%) interannual variation. Similar to studies on streams, nighttime emissions regularly exceeded daytime emissions. Biophysical regulations of CO 2 flux variability were delineated through mutual information analysis. Sample analysis of CO 2 fluxes indicate the importance of continuous measurements. Better characterization of short- and long-term variability is necessary to understand and improve detection of temporal changes of CO 2 fluxes in response to natural and anthropogenic drivers. Our results indicate that existing global lake carbon budgets relying primarily on daytime measurements yield underestimates of net emissions.
Abstract How quickly the US can decarbonize light-duty vehicle (LDV) transportation depends on the rates of change of electric vehicle (EV) sales, stock turnover, and grid decarbonization. We build a stock turnover model to assess how sensitive achieving 2050 LDV decarbonization targets is to these rates. We estimate carbon dioxide (CO 2 ) reductions of 70%–85% by 2050, including emissions from vehicles and upstream electricity generation, provided that new vehicle sales transition to 100% EVs and substantial grid decarbonization are accomplished by 2050. This result is robust to continuation of long-term trends of increasing vehicle longevity, and to whether the timing of EV sales growth and grid decarbonization are coordinated. If the two key goals are met, the annual contribution of EV electricity use to CO 2 emissions will be small over the entire period.
Abstract Marine carbon dioxide removal (mCDR) is gaining interest as a tool to meet global climate goals. Because the response of the ocean–atmosphere system to mCDR takes years to centuries, modeling is required to assess the impact of mCDR on atmospheric CO 2 reduction. Here, we use a coupled ocean–atmosphere model to quantify the atmospheric CO 2 reduction in response to a CDR perturbation. We define two metrics to characterize the atmospheric CO 2 response to both instantaneous ocean alkalinity enhancement (OAE) and direct air capture (DAC): the cumulative additionality ( α ) measures the reduction in atmospheric CO 2 relative to the magnitude of the CDR perturbation, while the relative efficiency ( ϵ ) quantifies the cumulative additionality of mCDR relative to that of DAC. For DAC, α is 100% immediately following CDR deployment, but declines to roughly 50% by 100 years post-deployment as the ocean degasses CO 2 in response to the removal of carbon from the atmosphere. For instantaneous OAE, α is zero initially and reaches a maximum of 40%–90% several years to decades later, depending on regional CO 2 equilibration rates and ocean circulation processes. The global mean ϵ approaches 100% after 40 years, showing that instantaneous OAE is nearly as effective as DAC after several decades. However, there are significant geographic variations, with ϵ approaching 100% most rapidly in the low latitudes while ϵ stays well under 100% for decades to centuries near deep and intermediate water formation sites. These metrics provide a quantitative framework for evaluating sequestration timescales and carbon market valuation that can be applied to any mCDR strategy.
The ferroelectric phase (𝑃𝑐𝑎2 1 , which is in orthorhombic symmetry) of hafnium dioxide (HfO 2 ) has gained much attention due to its potential applications in nanoelectronics and advanced memory devices. However, its complex phase behavior under external stimuli, such as pressure and temperature, remains a subject of intense investigation. This study focuses on developing a machine learning-based interatomic potential (MLIP) that is trained with data from density-functional theory (DFT) calculations to simulate phase transitions and mechanical properties of HfO 2 . The developed MLIP predicts lattice parameters, equations of state, bulk and shear moduli, and elastic constants that closely align with DFT predictions for several phases and at various pressures. Once validated, the MLIP is used to investigate the phase transitions of ferroelectric HfO 2 (𝑃𝑐𝑎2 1 ) under both isobaric and constant stress conditions at elevated temperatures ranging from 200 to 2500 K. We used several complementary methods, including local symmetry identification, radial distribution function, and x-ray diffraction characterization, to identify interesting phase transitions among several competitive hafnia phases predicted from our simulations. The suggested methods uniformly reveal that under pure deviatoric condition, the system favors a transition from the orthorhombic 𝑃𝑐𝑎2 1 phase to a tetragonal (𝑃4 2 /𝑛𝑚𝑐) phase, whereas a zero stress condition drives the system from the 𝑃𝑐𝑎2 1 phase to another orthorhombic (𝑃𝑏𝑐𝑛) phase. These findings provide crucial insights into stress and temperature-induced phase behavior of hafnia, guiding future experimental and theoretical studies for optimizing hafnia-based ferroelectric devices.
In this work, we experimentally study the angle-dependent single ionization of carbon dioxide (CO 2 ) by linearly and circularly polarized pulses. The angle dependence of the ionization probability by linearly polarized pulses extracted from time-domain measurements on an impulsively excited rotational wave packet is compared with data obtained from a direct angle-scan measurement. The results from the measurement with linear and circular polarization are consistent with the adiabatic ionization approximation. Further, we extend the time-domain method to extract the dependence of the asymptotic momentum distribution of fragment ions on the orientation of the molecular axis, and apply it to investigate dissociative double ionization of CO 2 . We show that such measurements can directly test the validity of the axial recoil approximation.