O2 Desorption Research Articles

Lattice oxygen-mediated Ni[sbnd]O[sbnd]O[sbnd]M formation for efficient oxygen evolution reaction in MOF@LDH core–shell structures

Two-dimensional (2D) layered double hydroxides (LDHs) are promising as an effective electrocatalyst towards oxygen evolution reaction (OER), but their poor conductivity and tendency to stack together limits their activity and durability as an electrocatalyst. Herein, a three-dimensional (3D) core–shell catalyst, in which numerous LDH nanoplates are vertically grown on cuboidal metal organic framework (MOF) structures, is synthesized through a facile one-pot reaction strategy. The representative electrocatalyst (CoNi-BDC@LDH) achieves an excellent OER performance (with an overpotential of 282 mV at 100 mA cm−2) and stability. A series of quasi-operando and ex-situ characterization reveals a lattice oxygen-mediated mechanism where Ni and its neighboring metal site collaboratively forms Ni-O-O-M (M = Ni, Co) bridges, and the high valence state of Ni facilitates O2 desorption from the bridges. The high OER performance is additionally attributed to γ-NiOOH and CoOOH phases, and a large electrochemically active surface area.

Efficient catalytic decomposition of N2O over Cd-doped NiO in the presence of O2

A series of Cd-doped NiO catalysts were prepared and tested in the N2O catalytic decomposition reaction. In comparison with NiO, it was found that the Cd0.04Ni catalyst showed higher N2O decomposition activity in the temperature range of 300–450 °C with or without O2, and lower activation energy (77.8 kJ mol−1). The incorporation of Cd into the NiO lattice was verified by X-ray diffraction (XRD) patterns and Raman spectra. This led to the distortion of the original NiO structure and weakened the Ni-O bond. X-ray photoelectron spectroscopy (XPS) results showed that compared with NiO and CdO, Cd0.04Ni possessed higher Ni2+ and Cd(n+1)+ contents, which might have been induced by the electron transfer behavior between CdO and NiO. A possible mechanism for active site regeneration and O2 desorption over Cd0.04Ni was proposed. The Cd0.04Ni catalyst also exhibited good resistance to NO and O2.

Strong Electronic Orbit Coupling between Cobalt and Single-Atom Praseodymium for Boosted Nitrous Oxide Decomposition on Co3O4 Catalyst.

Nitrous oxide (N2O) has gained increasing attention as an important noncarbon dioxide greenhouse gas, and catalytic decomposition is an effective method of reducing its emissions. Here, Co3O4 was synthesized by the sol-gel method and single-atom Pr was confined in its matrix to improve the N2O decomposition performance. It was observed that the reaction rate varied in a volcano-like pattern with the amount of doped Pr. A N2O decomposition reaction rate 5-7.5 times greater than that of pure Co3O4 is achieved on the catalyst with a Pr/Co molar ratio of 0.06:1, and further Pr doping reduced the activity due to PrOx cluster formation. Combined with X-ray photoelectron spectroscopy, X-ray absorption fine structure, density functional theory and in situ near-ambient pressure X-ray photoelectron spectroscopy, it was demonstrated that the single-atom doped Pr in Co3O4 generates the "Pr 4f-O 2p-Co 3d" network, which redistributes the electrons in Co3O4 lattice and increases the t2g electrons at the tetracoordinated Co2+ sites. This coupling between the Pr 4f orbit and Co2+ 3d orbit triggers the formation of a 4f-3d electronic ladder, which accelerates the electron transfer from Co2+ to the 3π* antibonding orbital of N2O, thus contributing to the N-O bond cleavage. Moreover, the energy barrier for each elementary reaction in the decomposition process of N2O is reduced, especially for O2 desorption. Our work provides a theoretical grounding and reference for designing atomically modified catalysts for N2O decomposition.

The promoting effect of alkali metal and H2O on Mn-MOF derivatives for toluene oxidation: A combined experimental and theoretical investigation

In this work, different alkali metal (Na or K)-doped manganese-based metal–organic framework (Mn-MOF) derivative materials were obtained from Mn-MIL-100 through ex situ posttreatment method, and their catalytic activities were studied by toluene oxidation. A series of characterization results (N2 adsorption–desorption, X-ray absorption spectroscopy, temperature programmed O2 desorption, etc.) showed that Na-doped Mn-MOF derivatives presented larger specific surface area, lower average manganese valence, and better adsorbed oxygen mobility, which displayed higher catalytic activity. Interestingly, both the addition of alkali metal and the introduction of water in the reaction atmosphere promoted the mineralization of toluene, as demonstrated by in situ diffuse reflectance infrared Fourier transform spectroscopy and thermal desorption-gas chromatography-mass spectrometry. Density functional theory calculations further confirmed that alkali metals and H2O were conducive to the adsorption of toluene, benzyl alcohol, benzaldehyde, benzoic acid and O2. This work provides new ideas for developing high-efficiency and water-promotion Mn-based materials for VOC control.

Enhancement of Cs on Co3O4 for N2O Catalytic Decomposition: N2O Activation and O2 Desorption

In this work, a series of cesium (Cs) modified metal oxide (Co3O4, CuO, Mn2O3, and NiO) catalysts were synthesized and investigated for N2O catalytic decomposition. More than 95% N2O conversion was obtained with the Cs-supported Co3O4 (Cs/Co) catalyst at 300 °C, but only a slight increase or even suppression was obtained with the other catalysts. The activation energy (Ea) varied significantly for Cs modified catalysts. It was found that both of N2O adsorption–dissociation (from N2O-TPD) and O2 desorption capacities (from O2-TPD) were highly correlated with the N2O decomposition activity. Highly optimized N2O activation and O2 desorption capacities contributed to the boosting performance of the Cs/Co catalyst. Moreover, the improved electron transfer property inferred from H2-temperature-programmed reduction and X-ray photoelectron spectroscopy was likely to facilitate the reaction processes and promote N2O catalytic decomposition performance.

High-Temperature Abatement of N2O over FeOx/CeO2-Al2O3 Catalysts: The Effects of Oxygen Mobility

CeO2-Al2O3 oxides prepared by co-precipitation (Ce+Al) or CeOx precipitation onto Al2O3 (Ce/Al) to obtain dispersed CeO2 and samples with further supported FeOx (2.5–9.9 weight% in terms of Fe) were characterized by XRD, XPS, DDPA and Raman. Fe/Ce/Al samples with lower surface concentrations of Fe3+ were substantially more active in N2O decomposition at 700–900 °C. It was related to higher oxygen mobility, as estimated from 16O/18O exchange experiments and provided by preferential exposing of (Fe-)Ce oxides. Stabilization of some Ce as isolated Ce3+ in Fe-Ce-Al mixed oxides dominating in the bulk and surface layers of Fe/(Ce + Al) samples retards the steps responsible for fast additional oxygen transfer to the sites of O2 desorption.

Pyrolysis of mass-selected (V2O5)NO- (N = 1-6) clusters in a high-temperature linear ion trap reactor.

A high-temperature linear ion trap that can stably run up to 873K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5)NO- (N = 1-6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5)NO- clusters with N = 2-5 at 873K. However, novel dissociation channels involving fragmentation of (V2O5)NO- to small-sized VxOy - anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3-6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V2O5)NO- monotonically increased with the increase in cluster size. The internal energies carried by the (V2O5)NO- clusters at 873K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis.

Soot Oxidation over γ-Al2O3-Supported Manganese-Based Binary Catalyst in a Dielectric Barrier Discharge Reactor

In this work, soot oxidation was conducted over a series of Mn-X/γ-Al2O3 (M = Ce, Co and Cu) binary catalysts in a dielectric barrier discharge reactor. The soot conversion in the plasma–catalytic system was in the order of Mn/γ-Al2O3 (57.7%) > Mn-Co/γ-Al2O3 (53.9%) > Mn-Ce/γ-Al2O3 (51.6%) > Mn-Cu/γ-Al2O3 (47.7%) during the 30 min soot oxidation process at 14 W and 150 °C. Meanwhile, the doping of Ce, Co and Cu slightly improved the CO2 selectivity of the process by 4.7% to 10.3% compared to soot oxidation over Mn/γ-Al2O3.It is worth to note that the order of CO2 selectivity was in the opposite order with soot oxidation rate. The effects of discharge power, oxygen content in the carrier gas and reaction temperature on plasma–catalytic soot oxidation was systematically analyzed. The catalyst characterizations, including N2 adsorption–desorption, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction by H2 and temperature-programmed desorption of O2, were conducted to illustrate the reaction mechanisms of plasma–catalytic soot oxidation and reaction pathways.

Imaging the facet surface strain state of supported multi-faceted Pt nanoparticles during reaction

Nanostructures with specific crystallographic planes display distinctive physico-chemical properties because of their unique atomic arrangements, resulting in widespread applications in catalysis, energy conversion or sensing. Understanding strain dynamics and their relationship with crystallographic facets have been largely unexplored. Here, we reveal in situ, in three-dimensions and at the nanoscale, the volume, surface and interface strain evolution of single supported platinum nanocrystals during reaction using coherent x-ray diffractive imaging. Interestingly, identical {hkl} facets show equivalent catalytic response during non-stoichiometric cycles. Periodic strain variations are rationalised in terms of O2 adsorption or desorption during O2 exposure or CO oxidation under reducing conditions, respectively. During stoichiometric CO oxidation, the strain evolution is, however, no longer facet dependent. Large strain variations are observed in localised areas, in particular in the vicinity of the substrate/particle interface, suggesting a significant influence of the substrate on the reactivity. These findings will improve the understanding of dynamic properties in catalysis and related fields.

Desorption of physisorbed molecular oxygen from coronene films and graphite surfaces.

We present a study on the adsorption and desorption of molecular oxygen (O2) on highly oriented pyrolytic graphite and coronene films deposited on it. To this end, density functional theory calculations were performed and experiments were made using the FORMOLISM device, which combines ultra-high vacuum, cryogenics, atomic or molecular beams, and mass spectrometry techniques. We first studied the desorption kinetics of dioxygen (O2) on a coronene film and graphite at 15K using the thermally programed desorption technique. We observed that the desorption of O2 occurs at a lower temperature on coronene than on graphite. We deduce the binding energies that are 12.5 kJ/mol on graphite and 10.6 kJ/mol on coronene films (pre-exponential factor, 6.88 × 1014 s-1). The graphite surfaces partially covered with coronene show both adsorption energies. In combination with theoretical density function theory (DFT) calculations using graphene and coronene as surfaces, we observe that the experimental results are in good agreement with the theoretical calculations. For the adsorption of the O2 molecule, two orientations are possible: parallel or perpendicular to the surface. It seems that O2 is best bound parallel to the surface and has a preference for the internal sites of the coronene.

Ligand Modulation of Active Sites to Promote Electrocatalytic Oxygen Evolution.

Rationally designed catalysts hold the key to address the sluggish kinetics of oxygen evolution reaction (OER). However, engineering the active sites of such catalysts still faces grand challenges. This study proposes a feasible ligand modulation strategy to boost the OER catalytic activity of cobalt-iron oxyhydroxide ((Fe,Co)OOH). The 2-methylimidazole (MI) ligand coordination on (Fe,Co)OOH reduces the orbital overlap between the Fe/Co 3d and O2p, which weakens the adsorption to oxygen-containing intermediates and thus facilitates the unfavorable O2 desorption. As a result, the MI ligand modulated (Fe,Co)OOH achieves an excellent OER performance with low overpotentials (230/290mV at 10/100mAcm-2 ) and excellent durability (>155h). This study provides a novel ligand modulation strategy for the design of OER catalysts.

Insight into the underlying competitive mechanism for the shift of the charge neutrality point in a trilayer-graphene field-effect transistor

Layer-number modulation in graphene has become a recent focus of research due to the superior degree of freedom that can be achieved in terms of magic-angle, wettability, superconductivity, and superlattices. However, the intrinsic transport of multilayer graphene is indistinguishable in atmospheric adsorbates and supporting environment, and its underlying charge transfer mechanism has not yet been thoroughly determined. In this study, a shift in the charge neutrality point of trilayer graphene (TLG) is demonstrated to be regulated by three governing factors: oxygen gas (O2), water molecules (H2O), and thermally activated electrons. Absorbed O2 ​induces a high work function in semimetallic TLG, while H2O is not an evident dopant but can strengthen binding against O2 ​desorption. A simplified model is developed to elucidate the competitive mechanism and charge transfer among these two dopants (O2, H2O) and thermal electrons, and the model is demonstrated by work function regulation and Bader charge transfer based on density functional theory calculations. This study provides a strategy to explore transport modulation of multilayer graphene in the fields of ballistic transport and low power consumption of graphene field-effect transistors.

A Theoretical Study of the Oxygen Release Mechanisms of a Cu-Based Oxygen Carrier during Chemical Looping with Oxygen Uncoupling

The Cu-based oxygen carrier is a promising material in the chemical looping with oxygen uncoupling (CLOU) process, while its performance in the CLOU is significantly dependent on the oxygen release properties. However, the study of oxygen release mechanisms in CLOU is not comprehensive enough. In this work, the detailed oxygen release mechanisms of CuO(110) and CuO(111) are researched at an atomic level using the density functional theory (DFT) method, including the formation of O2, the desorption of O2 and the diffusion of O anion, as well as the analysis of the density of states. The results show that (1) the most favorable pathway for O2 formation and desorption occurs on the CuO(110) surface of O-terminated with energy barriers of 1.89 eV and 3.22 eV, respectively; (2) the most favorable pathway for O anion diffusion occurs in the CuO(110) slab with the lowest energy barrier of 0.24 eV; and (3) the total density of states for the O atoms in the CuO(110) slab shifts to a lower energy after an O vacancy formation. All of the above results clearly demonstrate that the CuO(110) surface plays a significantly important role in the oxygen release reaction, and the oxygen vacancy defect should be conducive to the reactivity of oxygen release in a Cu-based oxygen carrier.

Influence of water molecule on active sites of manganese oxide-based catalysts for ozone decomposition

Developing an efficient approach to decompose ground-level O3 in humidity is crucial for preventing O3 pollution in practical application scenes. In this study, MnOx, CuO, and Cu/MnOx were synthesized to investigate the influence of H2O on the variation of active sites during O3 decomposition. The structural characterizations of the as-synthetic catalysts were measured by N2 physisorption, XRD, SEM, O2-TPD, H2-TPR, TG, and FT-IR analyses. In dry conditions, the elimination rate of O3 followed the sequence of MnOx > Cu/MnOx > CuO. The introduction of Cu to MnOx enhanced the surface area and pore volume of Cu/MnOx, accordingly diminishing the amounts of surface defects and the participation of sub-surface lattice oxygen for catalytic cycle, indicating that surface defects and oxygen vacancies (VO) determined the catalytic activity for O3 decomposition. In humid conditions, the elimination rate of O3 changed to the sequence of Cu/MnOx > MnOx > CuO, with a variation rate compared to dry conditions of −62.9% for MnOx, 14.2% for CuO, and 27.7% for Cu/MnOx. The decrease of participant sub-surface lattice oxygen and the accumulation of intermediates in humidity diminished the decomposition of O3 on MnOx, while the active species such as superoxide radicals generating from the reaction of H2O and Cu/MnOx facilitated the participation of VO and the desorption of O2 from the occupied active sites, accelerating the catalytic cycle on Cu/MnOx. This work developed a deeper understanding of the influence of H2O on catalytic activity, promoting the performance of MnOx-based catalysts for practical O3 decomposition.

Effects of electric field and biaxial strain on the (NO2, NO, O2, and SO2) gas adsorption properties of Sc2CO2 monolayer

Herein, we present a first-principles study of the effects of electric field and biaxial strain on the adsorption properties of Sc2CO2 monolayer in respect of O2, SO2, NO, and NO2 gases. We calculated the optimized configuration, adsorption energy, charge transfer, band structure, and densities of states of the adsorption systems under various electric fields and biaxial strains. We found that the adsorption intensities of NO2, NO, O2, and SO2 on the Sc2CO2 monolayer decrease with increasing the positive electric field. However, the electric field of 0.408 ​V/Å is not large enough to cause the desorption of O2, SO2, NO, and NO2 molecules, and it does not change their chemisorption nature on the Sc2CO2 monolayer. On the other hand, the gas adsorption intensity increases with increasing the biaxial strain from −10% to 10%. The Sc2CO2 monolayer with the −10% compressive strain physisorbs NO2, NO, O2, and SO2 molecules as compared to the chemisorption on the pristine one. The biaxial strains ϵ≥2% change the selectivity in gas adsorption of Sc2CO2 monolayer to NO2 molecule, compared with the O2 molecule on the pristine Sc2CO2 monolayer. The present work suggests an effective way to obtain attractive gas adsorption properties of two-dimensional materials using strain engineering for future gas sensors, gas capture or toxic gas filtration applications.

An Investigation of the Electrochemical Activity of (Ba/Sr)FeO3-y Anodes

FeOx, SrFeO3-y (SF), and Ba0.5Sr0.5FeO3−y (BSF) were studied for application as fuel oxidation catalysts in solid oxide fuel cells (SOFC) anodes. Electrodes were prepared by impregnation into porous yttria-stabilized zirconia (YSZ), with La0.3Sr0.7TiO3−y (LST) added for electronic conductivity. The electrode impedances decreased dramatically upon addition of SF and BSF and much less when only SrO or FeOx were added. Temperature Programmed Desorption (TPD) of O2 from oxidized BSF showed O2 desorbing between 200 °C and 700 °C, while no O2 desorbed from Fe2O3 below 900 °C. The results, together with thermodynamic analysis, suggest that stabilization of Fe+4 in the perovskite lattice plays an important role in enhancing the catalytic activity of SF and BSF by providing access to a Fe3+/Fe4+ redox couple that can accept oxygen anions from the yttria-stabilized zirconia (YSZ) electrolyte. Oxygen is weakly bound to these sites facilitating its reaction with adsorbed H2.

Role of Al pairs on effective N2O decomposition over the ZSM-5 zeolite catalyst

Series of ZSM-5 zeolites with diverse contents and locations of Al pairs were synthesized, and Co2+ ions were subsequently anchored at the Al pairs of ZSM-5 zeolites by wet ion-exchange with H protons. The Co-ZSM-5 sample derived from the mixtures of AlCl3 and TEOS of Si/Al=30.3 showed the best deN2O performance. Analysis on Co (Ⅱ) ion exchange capacity demonstrated the content of Al pairs followed the sequence: AlCl3 (0.84) > Al(NO3)3 (0.73) > aluminum isopropoxide (0.65) and TEOS (0.84) > silicic acid (0.57). More Al pairs coordinated with protons or cobalt ions were essentially associated with better performances for N2O catalytic dissociation. Moreover, Si source had a significant effect on the location of Al pairs determined by UV–vis–DRS of bare Co (Ⅱ), Al pairs of ZSM-5 zeolite synthesized from TEOS were enriched in the sinusoidal channel (γ site), whereas those synthesized from silicic acid were concentrated in the channel intersections (6-MRs β site). The theoretical calculation revealed that the O2 desorption at γ-site Co2+ of ZSM-5 zeolite required to overcome less energy barrier (23.8 kcal/mol) than that at β-site one.

ZIF-8 derived ZnO-CsPbBr3 polyhedrons for efficient triethylamine detection

Triethylamine, as a typical gas of volatile organic compounds, is a growing threat to human health due to its extensive applications in industry. In this study, ZIF-8 derived ZnO polyhedrons are decorated by CsPbBr3 quantum dots via electrostatic adsorption. Then a highly sensitive sensor towards triethylamine based on ZnO-CsPbBr3 composite is successfully fabricated. Compared with sensors based on pristine ZnO and ZnO (nanoparticles)-CsPbBr3, ZnO-CsPbBr3 displays a higher response value (~ 60 towards 100 ppm of TEA), shorter response/recovery time (2/18 s), and lower detection limit (5 ppb). Thus, highly-sensitive detection and efficiently-catalytic oxidation of trimethylamine can be achieved. Such distinguished performance can be ascribed to its unique architecture and n-n heterojunction. Notably, the sensing mechanism is thoroughly interpreted by X-ray photoelectron spectroscopy, temperature programmed desorption of O2 and in-situ diffuse scattering Fourier transform infrared spectra.

Hollow carbon nanospheres@graphitic C3N5 heterostructures for enhanced oxygen electroreduction

Improving the electrocatalytic activity of metal-free catalysts for the oxygen reduction reaction (ORR) is of great significance as promising alternatives to the Pt group precious catalysts in fuel cells. This paper proposes a simple template-based strategy to fabricate a catalyst with enhanced ORR activity. The resulting material contained 3D heterojunction and consisted of hollow carbon nanospheres and graphitic C3N5 (HCNs@g-C3N5). The fast electron/charge transports between g-C3N5 and HCNs was achieved because of the conductive heterojunction presence. This heterojunction provided the potential difference, which is beneficial for O2 activation and desorption of the intermediate reaction products. Compared with stand-alone HCNs and g-C3N5, the HCNs@g-C3N5 composite demonstrated significantly enhanced ORR activity with a more positive half-wave potential and faster kinetics in the alkaline medium. Furthermore, linear sweep voltammetry demonstrated that the water generation from O2 occurred through a four-electron transfer reaction. According to calculations performed using density functional theory (DFT), a built-in electronic field (IEF) formed at the heterojunction because of the charge density difference between C and N atoms. This IEF reduced the O2 activation energy and lowered the charge transfer resistance, which, in turn, enabled the rapid formation and desorption of the intermediates and significantly enhanced ORR activity of HCNs@g-C3N5.

ZnO nanowire optoelectronic synapse for neuromorphic computing

Artificial synapses that integrate functions of sensing, memory and computing are highly desired for developing brain-inspired neuromorphic hardware. In this work, an optoelectronic synapse based on the ZnO nanowire (NW) transistor is achieved, which can be used to emulate both the short-term and long-term synaptic plasticity. Synaptic potentiation is present when the device is stimulated by light pulses, arising from the light-induced O2 desorption and the persistent photoconductivity behavior of the ZnO NW. On the other hand, synaptic depression occurs when the device is stimulated by electrical pulses in dark, which is realized by introducing a charge trapping layer in the gate dielectric to trap carriers. Simulation of a neural network utilizing the ZnO NW synapses is carried out, demonstrating a high recognition accuracy over 90% after only 20 training epochs for recognizing the Modified National Institute of Standards and Technology digits. The present nanoscale optoelectronic synapse has great potential in the development of neuromorphic visual systems.