Adsorption Of Oxygen Molecules Research Articles

Determining the influence of relative humidity on the working parameters of a gas sensor based on zinc oxide

This paper investigates the dependence of operating parameters of a gas sensor based on zinc oxide obtained by the method of direct current magnetron sputtering. The production of gas sensor films was carried out using a VUP-5M vacuum unit with an original material-saving magnetron. The study of the dependence of the working parameters of the gas sensor was carried out under standard conditions. It was found that with increasing humidity, the electrical resistance of the gas sensor decreases and, accordingly, the sensitivity to the target gas decreases. A significant reaction of the gas sensor to an increase in humidity was observed in the range of 65–80 % relative humidity. The mechanism of influence of relative humidity on the sensitivity of a gas sensor based on ZnO was investigated. The change in resistance of the gas sensor is caused by trapped electrons on adsorbed oxygen molecules on the surface of the sensitive layer. The capture of electrons from the conduction zone leads to bending of the conduction zone and an increase in the space charge zone, respectively, to a change in the resistance of the sensitive layer of the gas sensor. In the atmosphere, when O2 molecules are adsorbed on the ZnO surface, they remove an electron from the conduction band. The reaction of oxygen adsorbed on the ZnO surface with reducing gases and the replacement of adsorbed oxygen with other molecules changes the bending of the conduction band and reduces the area of space charge. Adsorption of water on the surface of zinc oxide occurs according to the dissociation mechanism, which consists in the adsorption of steam molecules or hydroxyl groups with the subsequent displacement of previously adsorbed oxygen and free electrons and, accordingly, leads to a decrease in the sensitivity of the gas sensor. In addition, the adsorption of water vapor (H2O) molecules leads to less chemisorption of oxygen species on the ZnO surface due to the reduction of the surface area, which is responsible for the sensor response. Approaches to reduce the influence of relative humidity on the sensitivity of a gas sensor based on zinc oxide have been proposed

Ultrasensitive detection and sensitivity mechanism of SO2F2 in SF6 decomposition product based on TiO2-NiS heterojunction

SO2F2 is a typical fault product of SF6 electrical insulation equipment. Detecting SO2F2 can indicate whether the equipment is faulty. SO2F2 is a hazardous gas that can cause harm to the human body. This study reports on the development of the SO2F2 sensor using TiO2-NiS for the first time, and the investigation of its gas sensitivity to SO2F2 in SF6 background and air. The effective construction of the TiO2-NiS heterojunction was characterized via the XRD, SEM, and TEM. The TiO2-NiS heterojunction sensor for SO2F2 has a working temperature of 150°C in both SF6 and air environments with the response and recovery time of 6 s/2 s to 5 ppm SO2F2 in the air and 5 s/6 s in the SF6 environments, respectively. The sensor has a strong linear fit and a detection limit of 100 ppb. The long-term stability, selectivity, resistance to moisture, and responsiveness/recovery are features of this sensor. Furthermore, it was demonstrated that SO2F2 adsorption performance on the TiO2-NiS heterojunction outperformed that of TiO2 and NiS based on first principles, and density of states and differential charge density provided a more detailed description of the interaction between SO2F2 gas and the TiO2-NiS heterojunction. The oxygen competitive adsorption of SO2F2 and lattice oxygen molecules on the surface of TiO2-NiS heterojunction, as well as the interaction between adsorbed F2− on the TiO2-NiS heterojunction surface and SO2F2, may be used to characterise the sensing mechanism in the SF6. At the same time, the prepared SO2F2 sensor can effectively measure the concentration of SO2F2 through hardware, and give early warning when the concentration exceeds the safe value.

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Enhancing surface activity in MoTe2 monolayers through p-block doping: A comprehensive DFT investigation

Molybdenum ditelluride (MoTe2), a member of the transition metal dichalcogenides (TMDs), has recently garnered significant attention in the fast growing fields of two-dimensional electronics. However, despite its advantages, the intrinsic properties of MoTe2, like the low chemical activity of its basal plane, also resulted in several technological challenges. To overcome these limitations, several methods have been explored, with single atom doping emerging as a particularly promising approach. In this study, we employed density functional theory (DFT) to investigate the influence of single atom impurities on the chemical activity of MoTe2. A total of 22 dopants were selected from the p-block of the periodic table, ranging from boron to bismuth. Specifically, we examined the adsorption of oxygen molecules (O2) on the doped structures to assess their impact on layer chemical activity. Our findings revealed that doping was energetically favorable for all investigated atoms, and it had a significant effect on surface activity. Notably, doping with dopants from groups 13–15, especially those with low atomic number, results in significant increased adsorption strength, leading to weakening of the molecular bonding in O2 by up 5.72 eV, hinting at the potential use as catalyst. Additionally, we identified certain molecules, primarily from group 17, with a remarkably high adsorption energy to charge transfer ratio. This leads to excellent sensing characteristics, where the response to adsorption in their carrier concentration is increased 100-fold over the pristine MoTe2, while sensor recovery is estimated between 0.01 and 2 s.

Pauling-type adsorption of O2 induced by S-scheme electric field for boosted photocatalytic H2O2 production

The effective adsorption of oxygen (O2) molecules over photocatalysts is a critical step in promoting the performance of photocatalytic H2O2 production. However, g-C3N4 usually features a Yeager-type (side-on) adsorption configuration of O2 molecules, which causes the breaking of O–O bonds and severely hinders the H2O2 production activity. Herein, we synthesized an oxygen-vacancy-rich TiO2–x/g-C3N4 step-scheme (S-scheme) heterojunction to regulate the oxygen adsorption configuration and improve the 2e– ORR selectivity of H2O2 production. In-situ X-ray photoelectron spectroscopy (in-situ XPS) and density functional theory (DFT) calculations reveal that the S-scheme heterojunction is formed between TiO2–x and g-C3N4. The difference between their Fermi levels leads to the electron flow from g-C3N4 to TiO2–x, which increases the electron-deficient sites in g-C3N4. As a result, the cleavage of O–O bonds on the surface of g-C3N4 is avoided and the oxygen adsorption configuration is tuned from Yeager-type to Pauling-type (end-on). Consequently, the photocatalytic H2O2 production rate is dramatically improved to 1780.3 μmol h–1, which is about 5 times higher than that of pristine g-C3N4. This work paves a new way to tailor the oxygen adsorption configuration by rationally designing S-scheme heterojunction photocatalysts.

Addressing the effects of gas adsorption on monolayers beyond charge population analysis: the case of WS2

The optoelectronic properties of two-dimensional (2D) materials can be significantly influenced by charge transfer resulting from surface molecular adsorption. One noteworthy example is observed in WS2 monolayers, where the behavior undergoes an anomalous change when exposed to air, primarily due to the adsorption of oxygen molecules. While the acceptor nature of O2 is widely acknowledged as the underlying cause, the precise electron transfer mechanism remains in need of a comprehensive explanation at the atomistic level. Going beyond conventional charge population analysis, we develop an approach describing the process of molecular adsorption and surface charge transfer that relies on the formalism commonly adopted for charged defects in semiconductors. This method clearly identifies two key factors contributing to electron transfer upon O2 physisorption: the presence of sulphur vacancies and the intrinsic n-type nature of WS2. This approach provides an effective and general scheme to characterize the surface charge transfer in 2D materials exposed to a gas atmosphere.

Annealing-induced enhancement of TiO2-ZnO nanocomposites for high-performance room-temperature air pollutant detection in fiber optic sensors

Fiber optic sensors, promising for their compactness and remote sensing abilities, are explored in this study as a platform for detecting volatile organic compounds (VOCs) using nanocrystalline metal oxide composites like TiO2-doped ZnO. Hydrothermally synthesized (S1 sample)and annealed composites (500 °C (S2 sample) and 1200 °C (S3 sample) annealing) were investigated for their gas-sensing properties towards inorganic gas like ammonia and VOCs like acetone, and isopropyl alcohol. Remarkably, annealing at 1200 °C yielded S3 sample with higher response (7.5 %) towards ammonia at room temperature for 500 ppm concentration. This superior performance is attributed to increased surface area, narrowed bandgap, and faster response/recovery times (18/15 s) compared to other samples. The proposed sensing mechanism involves the adsorption and desorption of oxygen molecules on the sensor surface, altering refractive index and light scattering, ultimately modulating the transmitted light intensity. X-ray diffraction, SEM imaging, and UV–Vis absorption techniques confirmed the structure and morphology of the nanocomposites.

MOF-derived CdS@c/h-In2O3 hollow hexagonal prism with surface-grown nanofibers for ppb-level formaldehyde detection: an insight into synergistic enhancement of endogenous phase-homojunction and heterojunction

Detection of ppb-level formaldehyde at low temperatures is a great pursuit for metal oxide semiconductor sensors. To realize this goal, metal organic framework (MOF) derived hollow hexagonal prism with surface-grown nanofibers were successfully prepared and modified using quantum dots, affording a 3D/0D heterojunction with excellent sensing performance. The CdS@c/h-In2O3-2 hollow hexagonal prism exhibits outstanding sensing properties (107.37 for 100 ppm), ideal selectivity, and low detection limit (160 ppb) at 160 °C. Moreover, the possible formation mechanism of the hollow hexagonal prism and endogenous phase-homojunction are proposed. Further, an insight into the synergistic enhancement of endogenous phase-homojunction and heterojunction is presented, including the gas diffusion, density functional theory (DFT) calculations, and resistance-controlled mechanism. The distinguished HCHO-sensing performance can be attributed to MOF-derived endogenous phase-homojunction, 3D/0D heterostructure, hollow morphology, and confined internal space, which ultimately synergize to strengthen the adsorption and electron transfer behavior of oxygen and HCHO molecules. Overall, this work provides new insights into the feasible strategy and theoretical viewpoint concerning high-performance HCHO sensors.

Solvothermal synthesis of bismuth-based halide perovskites: Investigating the influence of alcohol solvents on photocatalytic performance

Our study explores the effect of different solvents on the synthesis of bismuth-based halide perovskite (BHP) crystals with distinct morphologies. BHP crystals were successfully synthesized using various alcohol solvents, including ethanol (EtOH), butanol (BuOH), ethylene glycol (EG), glycerol (GL), and without the use of alcohol solvents. The choice of solvent acted a crucial role in shaping the nucleation and growth of BHP crystals, as it affected key solvent characteristics, including dielectric constant, ion-coordination, and atomic chain length. The resulting BHP crystals exhibited varying geometrical and structural features, which, in turn, significantly impacted their photophysical properties and photocatalytic activity for the degradation of organic pollutants under visible light irradiation. The introduction of EtOH into the synthesis process led to larger crystallite sizes and an increased adsorption of oxygen molecules on BHP, thereby enhancing the separation of photo-excited electrons and holes. Consequently, the photodegradation efficiency of rhodamine B achieved an impressive 99.6% after 30 min of irradiation. The degradation rate of tetracycline hydrochloride over BHP photocalysts followed this order: mesoporous structure with strong agglomeration of particles (EtOH) > irregular agglomerates composed of spherical particles (BuOH) > irregular clusters of sheets (EG) > thick plates (GL) > flower-like agglomerates (without the use of an alcohol solvent). Our evaluation considered changes in morphological characteristics, surface properties, and photon absorption capacities of the BHP crystalline structures. This study provides valuable insights into the role of various alcohol solvents in tailoring the structure and improving the photocatalytic performance of BHP photocatalyst synthesized through the solvothermal route.

Suppression of deep-level traps via semicarbazide hydrochloride additives for high-performance tin-based perovskite solar cells

Tin perovskites with exemplary optoelectronic properties offer potential application in lead-free perovskite solar cells. However, Sn vacancies and undercoordinated Sn ions on the tin perovskite surfaces can create deep-level traps, leading to non-radiative recombination and absorption of nucleophilic O2 molecules, impeding further device efficiency and stability. Here, in this study, a new additive of semicarbazide hydrochloride (SEM-HCl) with a N–C=O functional group was introduced into the perovskite precursor to fabricate high-quality films with a low concentration of deep-level trap densities. This, in turn, serves to prevent undesirable interaction between photogenerated carriers and adsorbed oxygen molecules in the device’s operational environment, ultimately reducing the proliferation of superoxide entities. As the result, the SEM-HCl-derived devices show a peak efficiency of 10.9% with improved device stability. These unencapsulated devices maintain almost 100% of their initial efficiencies after working for 100 h under continuous AM1.5 illumination conditions.Graphical

(Keynote) Oxygen Reduction and Evolution Reactions on Faceted MnxCo1-XFe2O4 Nanoparticles Prepared By Induction-Coupled Plasma

Substantial research efforts are directed toward the development of precious metal-free catalysts for fuel cells, metal-air batteries and electrolyzers, because the deployment of these technologies requires the synthesis of low-cost catalysts with controlled properties in large quantities.Mixed spinel oxides are a promising class of catalytic materials for the oxygen evolution (OER) and oxygen reduction (ORR) reactions, and thus several works have been devoted to the understanding of the structure – composition – activity relationships. Examples include the correlation between activity of spinel oxides and the covalency of the bond formed between the oxygen species and the metal cation in the octahedral sites1, or the possible role of metal cations in the tetrahedral sites in the oxygen electrocatalysis2. However, studies highlighting the importance of the facet engineering on the electrocatalytic activity of spinel oxides3 are still rare.Here, we will present our recent work on facetted nanoparticles MnxCo1-xFe2O4 (0 ≤ x ≤ 1) prepared by thermal plasma induction; a one step4, cost-effective and scalable method allowing the synthesis of large amounts (up to 30 g h-1 for 50 kW units) of uniform and crystalline nanoparticles5.Structural characterization by X-ray diffraction and TEM-EELS analysis showed that the mixed ferrite nanoparticles are formed by individual nanocrystals with well-defined truncated octahedron shape and with {100} and {111} facets mainly exposed, have high crystallinity, a median particle size of 40 nm and a homogeneous composition down to the atomic level.Electrochemical studies conducted in 0.1M KOH using the rotating disk electrode showed the highest activity was found for carbon black + Mn0.5Co0.5Fe2O4 composite electrode: half-wave potential for oxygen reduction 140 mV more negative than that of 20 wt% Pt/C; 420 mV oxygen evolution overpotential at 10 mAcm-2 (identical to IrO2/C). These are among the best performances reported for ferrites considering the size of the nanocrystals.Computational studies using density functional theory used to study the adsorption of oxygen molecule on the {100} and {111} facets of both CoFe2O4 and Mn0.5Co0.5Fe2O4 demonstrated that the Mn0.5Co0.5Fe2O4 {111} surface appears to have a highest affinity for the O2 molecule. The sites with lowest adsorption energy on each surface were identified and further analysis of O-O bond length and frequency as well as the Mulliken charge and populations confirmed the activation of the adsorbed O2 molecule. The energy diagrams of the ORR and OER computed for both Mn0.5Co0.5Fe2O4 {100} and {111} surfaces also pointed for a higher electrocatalytic activity for the {111} facet.

Unraveling the origin of facet-dependent photocatalytic H2O2 production over anatase TiO2

A typical photocatalytic H2O2 production reaction primarily comprises three processes: photoabsorption, electron–hole separation and transfer, and surface oxygen reduction reaction. Previous researches have focused on revealing the origin of the facet effect in photocatalysis. However, a comprehensive understanding of the structure–activity relationship for facet effect at atomic scale remains limited. Herein, we provide fundamental insights into photocatalytic H2O2 production performance of three types of TiO2 with predominantly exposed (101), (100), or (001) facets. The TiO2 nanosheets with exposed (001) facet exhibit the highest H2O2 yield rate of 649.2 μmol g-1 h-1, which is 29.2 and 5.2 times higher than those of TiO2 with (101) facet and (100) facet, respectively. Band alignment, charge carrier behavior, and surface reaction are studied systematically and correlated with unique surface atom arrangement. Even with narrowed light-response range, short charge carrier lifetime, inferior charge separation, and inconspicuous specific surface area, the (001) facet exposed TiO2 still performs best. The experimental results and density functional theory (DFT) calculations reveal that the under-coordinated Ti atoms on (001) surface serve as active sites and have strong interaction with oxygen molecule, while the Ti atoms on (101) and (100) surface can hardly adsorb and activate oxygen molecule. Hence, we suggest that the significantly lowered barrier for oxygen molecule adsorption and activation results from intrinsic surface sites rather than band-alignment, and the charge carrier behavior plays the principal role in this case. This work may provide semiquantitative insights into the origin of facet effect in photocatalysis.

Langmuir-Blodgett Monolayer of Cobalt Phthalocyanine as Ultralow Loading Single-Atom Catalyst for Highly Efficient H2O2 Production.

The electrochemical production of H2O2 via the two-electron oxygen-reduction reaction (2e- ORR) has been actively studied using systems with atomically dispersed metal-nitrogen-carbon (M-N-C) structures. However, the development of well-defined M-N-C structures that restrict the migration and agglomeration of single-metal sites remains elusive. Herein, we demonstrate a Langmuir-Blodgett (LB) monolayer of cobalt phthalocyanine (CoPc) on monolayer graphene (LB CoPc/G) as a single-metal catalyst for the 2e- ORR. The as-prepared CoPc LB monolayer has a β-form crystalline structure with a lattice space for the facile adsorption of oxygen molecules on the cobalt active sites. The CoPc LB monolayer system provides highly exposed Co atoms in a well-defined structure without agglomeration, resulting in significantly improved catalytic activity, which is manifested by a very high H2O2 production rate per catalyst (31.04 mol gcat-1 h-1) and TOF (36.5 s-1) with constant production stability for 24 hours. To the best of our knowledge, the CoPc LB monolayer system exhibits the highest H2O2 production rate per active site. This fundamental study suggests that an LB monolayer of molecules with single-metal atoms as a well-defined structure works for single-atom catalysts.

Extrinsic oxygen defects in SnO/SnO2 heterostructure for efficient NO2 gas detection

High selectivity and fast response in the detection of NO2 are key factors in protecting human health in life-threatening environments. The p-n SnO/SnO2 heterostructure is a promising material as a metal oxide for effective chemical reactions with a target gas. It has a synergistic effect on the intrinsic semiconducting properties and the formation of an interfacial electric field in the heterojunction. The extrinsic oxygen vacancies in the SnO/SnO2 structure enhance the chemical reaction in the sensing property. In this study, we developed a defect-SnO/SnO2 heterostructure-based NO2 gas sensor. It shows excellent sensing performances with a high response of 100.86, fast response time of 5.83 s, and superior selectivity (approximately 23 times higher than those of other target gases) in the detection of 50 ppm NO2 at 150 °C. Raman and electron paramagnetic resonance (EPR) results supported the presence of oxygen vacancies in the defect-rich SnO/SnO2 crystal and X-ray photoelectron spectroscopy (XPS) and time-of flight secondary ion mass spectrometry (ToF-SIMS) analyses described the role of SnO/SnO2 heterostructure with oxygen defects as an effective electron donor for the adsorbed oxygen molecules and NO2 target gas. We believe that the direct formation of oxygen vacancies in the SnO/SnO2 heterostructures is a significant reference for the development of high-performance NO2 gas sensors.

Synergistically boosted photocatalytic production of hydrogen peroxide via protonation and oxygen doping on graphitic carbon nitride

Photocatalytic synthesis of hydrogen peroxide (H2O2) using modified graphitic carbon nitride (g-C3N4) has been recognized as a promising green and sustainable process. However, the effect of g-C3N4 modification on the surface properties of photocatalytic surface reactions still needs extended exploration. In this work, we design and synthesize a protonation induced oxygen doping in g-C3N4 (pCN1), which shows uniquely curled nanosheet structures in microscopic level. Under visible light irradiation, the photocatalytic H2O2 production rate of pCN1 reaches 707 μmol g−1 h−1, which is approximately eight times higher than that of primitive g-C3N4. The enhanced photocatalytic performance is attributed to the synergistic effect of protonation and oxygen doping, which not only dramatically facilitates the adsorption of oxygen molecules and the desorption of H2O2 product, but also promotes the charge separation. In addition, more abundant protons supplied via protonation process can combine with the adjacent oxygen atoms on catalyst surface, thus promoting the formation of OOH* intermediate and improving the H2O2 yield. This work provides a facile and effective strategy to prepare highly-efficient modified g-C3N4 photocatalyst for the clean and convenient synthesis of H2O2.

Phase boundary induced drastic sensing performance enhancement of mixed-phase N-Fe2O3 (α/γ) gas sensors for acetone

The development of high-performance, portable and miniaturized metal oxide semiconductor (MOS)-based chemiresistive materials is important for portable gas sensors. Phase boundaries provide lasting inspiration and a promising avenue for designing advanced functionalities using nanomaterials. However, the impact of different phase boundaries in a single MOS on the performance of MOS-based chemiresistive gas sensors has been rarely explored. Here, we report a mixed-phase N-Fe2O3 (α/γ) gas sensor with rich phase boundaries, which exhibits an enhancement of the response up to 386 towards 50 ppm of acetone at 240 °C. This is attributed to the generation of the internal electric field (IEF) and defects originating from lattice mismatch at the N-Fe2O3 (α) – N-Fe2O3 (γ) phase boundaries, which providing more active sites for adsorption of oxygen and acetone molecules. This work clearly shows that we can optimize the gas sensing catalyst of low-cost materials by regulating the phase boundaries of nanomaterials to develop high-precision portable gas sensors.

Prism rather than tetrahedron: low-energy structures for gaseous gold clusters Au10(O2)n + by density functional calculations

The purpose of this study is to reveal the adsorption mechanism of oxygen molecules on gold clusters. density functional theory is employed to investigate the low-energy structure of multiple O2 adsorption on the Au10 + cluster and findings are compared with IR spectra. The nature of bonding of the O2 molecule and Au10 + cluster has been characterised through several metrics like binding energy, dissociation energy, bond length, and vibrational frequencies. The result shows that the lowest-energy structures are prism-shaped rather than tetrahedron-shaped, where only one O2 is chemically adsorbed while others are physically adsorbed. Chemically adsorbed η2-O2 behaves like free O2 –, forming a single electron π bond with Au10 +, while physically adsorbed η1-O2 does not result in an effective chemical bond and behaves like free O2. This study provides insights into the mechanism of oxygen molecule adsorption on gold clusters and can contribute to further research on the catalytic mechanism of gold clusters. Highlights Lowest energy structures are prism-shaped rather than tetrahedron-shaped, which is supported by IR spectrum and chemical hardness. Chemically adsorbed O2 is activated and displays structural and spectral features of free O2 –, while physically adsorbed O2 is close to free O2 in vibrational frequency and bond length. Chemical adsorption is equivalent to a single electron π bond while physical adsorption forms no effective chemical bond due to the lack of electronic pairing between Au10 + and O2.

Linkage engineering in covalent organic frameworks as metal-free oxygen reduction electrocatalysts for hydrogen peroxide production

Covalent organic frameworks (COFs) are promising platforms with tailorable structures toward metal-free electrocatalytic oxygen reduction (ORR). Here, COFs with different linkages were constructed and explored in the selective two-electron ORR (2e- ORR) for hydrogen peroxide (H2O2) production. Interestingly, imine-linked Py-TD-COF delivers a remarkable H2O2 selectivity of 80–92 %, while amine-linked Py-TD-COF-NH exhibits relatively low H2O2 selectivity of 50–61 %. Experimental and theoretical results reveal that the donor-accepter property of Py-TD-COF enables proper activation of O2, while Py-TD-COF-NH shows relatively high activation of O2 due to the electronic modulation induced by the linkage transformation. Furthermore, the potential H-bonding between the amine group and the adsorbed oxygen molecules on Py-TD-COF-NH is proved to elongate the OO bond, thus accelerating the subsequent hydrogenation and lowering the barrier for the reduction of *OOH to *O intermediates. This work highlights the importance of suitable linkages and provides a guideline for designing metal-free COF catalysts for 2e- ORR.

Directional manipulation of electron transfer in copper/nitrogen doped carbon by Schottky barrier for efficient anodic hydrazine oxidation and cathodic oxygen reduction

Development of bifunctional hydrazine oxidation and oxygen reduction electrocatalysts with high activity and stability is of great significance for the implementation of direct hydrazine fuel cells. Combining zero-dimensional metal nanoparticles with three-dimensional nitrogen-doped carbon nanosheets is an attractive strategy for balancing performance and cost. However, the precise construction of these composites remains a significant challenge, and thorough study of their interaction mechanisms is lacking. Herein, the CuNPs/CuSA-NPCF catalyst was constructed by anchoring copper nanoparticles on a three-dimensional nitrogen-doped porous carbon nanosheet framework through coordination of polyvinyl pyrrolidone and copper ions. The Schottky barrier of metal–semiconductor matched the Fermi level of the rectifying contact, thus enabling directional electron transfer. The resulting electron-deficient Cu nanoparticles surface exhibited Lewis acidity, which was beneficial to adsorption of hydrazine molecule. While the electron-enriched Cu–N4/carbon surface improved the adsorption of oxygen molecule, and accelerated electron supply from Cu-N4 active sites to various oxygen intermediates. The CuNPs/CuSA-NPCF Mott-Schottky catalyst exhibited excellent catalytic activity for hydrazine oxidation reaction and oxygen reduction reaction in an alkaline media. The directional manipulation of electron transfer in heterogeneous materials was an attractive universal synthesis method, providing new approach for the preparation of efficient and stable hydrazine fuel cell catalysts.

Adsorption behavior of O2 on U-Nb surface: a first-principles study.

Oxygen is a chemically active gas. Metal uranium will be rapidly oxidized when exposed to oxygen directly, forming a complex and uncompacted oxide layer on the surface. The U-O2 reaction system is a very complex metal oxidation system. The surface oxidation reaction of uranium-niobium alloy is more complex, and it is also the main corrosion form of uranium-niobium alloy. Exploring the microscopic mechanism of surface oxidation corrosion of uranium-niobium alloy is of great significance for understanding the surface corrosion phenomenon in practical applications. The adsorption of O2 on U-Nb (5at.%) surface was investigated by first-principles calculation using a periodic slab model within the density functional theory (DFT). The effect of different levels of Nb doping on O adsorption was investigated, and the stability of O-U and O-Nb adsorption was studied in conjunction with the Bader charge distribution, differential charge density map, electron density of states, and surface work function. The results showed that physical adsorption happens when O2 is vertically adsorbed at the top site of Nb atom, whereas dissociative adsorption happened in all other configurations considered here. The interaction between adsorbed O2 and U-Nb surface was essentially the hybridization between the O/2p orbital electrons and the U/6d, U/5f, Nb/4p, Nb/5s, and Nb/4d orbital electrons to form a relatively stable ionic bond. When Nb was doped into the second layer of the surface, the most stable O2 adsorption configuration was top-site horizontal adsorption. The adsorption energy was - 22.38 eV, which was more negative than the adsorption energy of - 21.38 eV for the first doped layer horizontal adsorption at hollow-site. The interaction was essentially the hybridization between O/2p orbital electrons and U/6d and U/5f electrons and between O/2s orbital electrons and U/6p orbital electrons to form a relatively stable ionic bond. In this paper, the adsorption and dissociation of oxygen molecules on the surface of U-Nb system were systematically studied by first-principles calculations, in order to explore the surface oxidation corrosion mechanism of uranium-niobium alloy from the micro level. The VASP program uses PAW pseudopotential, which belongs to the density functional method, and uses DSP.