DFT calculations of double vacancies MoS2 catalyzing water gas shift reaction: S vacancies as electron bridge promote electron transfer to H2O and CO molecules

The poor activity of molybdenum disulfide (MoS₂) basal plane is the key scientific problem to limit efficient hydrogen production. In this paper, MoS₂ with single (V_S-MoS₂) and double sulfur vacancy (V_{S, S}-MoS₂) have been constructed and used for water gas shift reaction (WGSR). Results show that the adsorption energy of V_{S, S}-MoS₂ for CO molecule is −1.43 eV, which is 28.6 times and 1.1 times than original MoS₂ and V_{S, S}-MoS₂, respectively. The energy barrier of the rate-determining step in the association mechanism of V_{S, S}-MoS₂ is 1.78 eV, which is 21% lower than pristine MoS₂. S vacancies are active sites for CO and H₂O adsorption. The delocalized electrons enrichment in S vacancies break the electron transfer barrier between the surface and molecules. Sulfur vacancies as medium make electrons continuously transferred to CO and H₂O molecules.     

Defect-rich high-entropy oxide nanospheres anchored on high-entropy MOF nanosheets for oxygen evolution reaction

In this work, high-entropy oxide nanoparticles (HEO NPs)/high-entropy metal-organic framework (HE-MOF) heterostructure electrocatalysts for oxygen evolution reaction (OER) are constructed by in-situ growth of HEO NPs on HE-MOF using partial-localized pyrolysis strategy, and the effect of pyrolysis temperature on the OER performance are studied. The results indicate that the well-dispersed HEO NPs are rich in defects such as oxygen vacancy and lattice distortion, which can increase catalytic active centers. Meanwhile, the nanosheet-like HE-MOF not only acts as the support HEO NPs catalyst but also is kinetically beneficial for fast electrons and ions transportation. Among all the prepared nanostructures, HE-MOF-350-200 shows the best OER performance, achieving a low overpotential of 266 mV at 50 mA cm⁻² along with a satisfactory stability.     

Fabricating PdCe/OMS-2 catalysts with boosted low-temperature activity for toluene deep degradation

Porous cryptomelane-type octahedral molecular sieve(OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC) catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the p...     

An Atomistic View of Platinum Cluster Growth on Pristine and Defective Graphene Supports (Small 10/2023)

Density functional theory (DFT) is used to systematically investigate the electronic structure of platinum clusters grown on different graphene substrates. Platinum clusters with 1 to 10 atoms and graphene vacancy defect supports with 0 to 5 missing C atoms are investigated. Calculations show that Pt clusters bind more strongly as the vacancy size increases. For a given defect size, increasing the cluster size leads to more endothermic energy of formation, suggesting a templating effect that limits cluster growth. The opposite trend is observed for defect-free graphene where the formation energy becomes more exothermic with increasing cluster size. Calculations show that oxidation of the defect weakens binding of the Pt cluster, hence it is suggested that oxygen-free graphene supports are critical for successful attachment of Pt to carbon-based substrates. However, once the combined material is formed, oxygen adsorption is more favorable on the cluster than on the support, indicating resistance to oxidative support degradation. Finally, while highly-symmetric defects are found to encourage formation of symmetric Pt clusters, calculations also reveal that cluster stability in this size range mostly depends on the number of and ratio between Pt C, Pt Pt, and Pt O bonds; the actual cluster geometry seems secondary.     

Thermodynamics of surface and oxygen vacancy in rare earth stannates by first-principles calculations

The research of nanocrystalline pyrochlores highlights the importance of the surface structure, composition and segregated point defect in their thermal, electrical, optical, magnetic, and catalytic performances. In order to provide a basic view on the surface-related phenomena, thermodynamic stabilities of three low-index (100), (110), and (111) surfaces for A₂Sn₂O₇ (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd), together with their configurations, electronic structures and related oxygen vacancies are investigated using first-principles calculations. The (111) surfaces with A₃SnO₈ and ASn₃O₆ terminations are predicted to be stable due to their low surface energies. Meanwhile, the (110) surfaces with A₂Sn₂O₈ and A₂Sn₂O₆ terminations are found to may also form. For these surface structures, the amount of broken bonds play the main role in their structural stability, and the local coordination environment variation also has minor contribution to it. Moreover, oxygen vacancies are observed to segregate on the surface layer, owing to lower energy of breaking bonds accompanying with oxygen vacancy formation and the larger relaxation space comparing to the counterpart in bulk. These results are expected to provide guidance on optimizing the performances of these compounds through surface engineering.     

Band gap and oxygen vacancy engineering of honeycomb-like CuFe2O4 spinels toward enhanced high infrared emissivity

Recently, copper ferrites have acquired widespread attraction in high infrared radiation fields owing to their remarkable cost efficiency. However, to achieve broader applications under various operating conditions, it is essential to further improve the infrared emissivity, particularly at high temperatures. Herein, the Ni-doped CuFe₂O₄ (NCFO) honeycomb-like frameworks, which are constructed with single-crystal nano-subunits, are successfully fabricated via the scalable sol–gel avenue. The unique porous honeycomb framework endows NCFO with enhanced infrared absorption and relieves the stress between coatings and substrates meanwhile. With both band gap and oxygen vacancy (OV) engineering of CuFe₂O₄ itself via smart Ni doping, a maximum lattice strain, the richest OVs, and the narrowest band gap (∼1.63 eV) are simultaneously achieved for the CuFe₂O₄ with 15% Ni doping (denoted as CNFO-15). Benefiting from the synergy of these external and intrinsic contributions, the CNFO-15 possesses an ultrahigh infrared emissivity (∼0.975) in the wavelength range of 3–5 µm at a test temperature of 800°C. Moreover, the CNFO-15-based coating displays superior infrared radiation performance with outstanding high-temperature resistance. More meaningfully, the constructive design here will provide a distinctive perspective for future large-scale fabrication of advanced high-infrared-emissivity coatings.     

Ionic (O2−, H+) transport in novel Zn-doped perovskite LaInO3

For the first time the LaIn_1-xZn_xO_3-1/2x samples was synthesized via solid-state reaction method. The Zn²⁺−doping effect on the B-site of LaInO₃ on structure, water uptake and electrical properties was investigated. The results show that Zn²⁺ is good alternative to alkaline earth metals. The Zn-doping decreases the sintered temperature and makes it possible to obtain high-density ceramics. The substitution increases the conductivity by ∼2 orders of magnitude. Below ∼500 °C the phases exhibit the dominant oxygen-ionic transport (dry atmosphere), and the dominant protonic transport below 600 °C (wet atmosphere). The obtained results suggest the prospects for using these materials in the Hydrogen Energy field. A new concept of the ability of perovskite phases LaBO₃ to incorporate water has been proposed. In addition to the presence of oxygen vacancies, their size, which depends on the B-cation nature, is of decisive importance in the hydration process and the formation of proton conductivity.     

Dual-Defect Engineering of Bidirectional Catalyst for High-Performing Lithium-Sulfur Batteries

Practical applications of lithium-sulfur (Li-S) batteries have been hindered by sluggish reaction kinetics and severe capacity decay during charge-discharge cycling due to the notorious shuttle effect of polysulfide and the unfavored deposition and dissolution of Li₂S. Herein, to address these issues, a double-defect engineering strategy is developed for preparing Co-doped FeP catalyst containing P vacancies on MXene, which effectively improves the bidirectional redox of Li₂S. Mechanism analysis indicates that P vacancy accelerates Li₂S nucleation via increased unsaturated sites, and Co doping generates local electric field to reduce the reaction energy barrier and accelerate Li₂S dissolution. MXene provides highly conductive channels for electron transport, and effectively captures polysulfide. The double-defect catalyst enables an impressive reversible specific capacity of 1297.9 mAh g⁻¹ at 0.2 C, and excellent rate capability of 726.5 mAh g⁻¹ at 4 C. Remarkably, it demonstrates excellent cycling stability with capacity retention of 533.3 mAh g⁻¹ after 500 cycles at 2 C. The results can unlock the double-defect engineering of vacancy induction and heteroatomic doping towards practical Li-S batteries.     

Boosting Electrochemical Reduction of CO2 to Formate over Oxygen Vacancy Stabilized Copper–Tin Dual Single Atoms Catalysts

Designing reasonable atomic structures is essential in modulating the selectivity of the valuable products produced in the electrochemical CO₂ reduction. Herein, a Cu Sn diatomic sites electrocatalyst stabilized by double oxygen vacancies on CeO_2-x is constructed, which exhibits superior electrochemical selectivity toward formate, achieving a 90.0% Faradaic efficiency at formate partial current density of 216.8 mA cm⁻² with the applied bias of −1.2 V versus REH. The experimental characterizations and theoretical calculations highlight the significance of the synergistic effect of Cu and Sn diatoms on reducing the activation energy and promoting the formation of intermediate ^*OCHO, which accounts for its high selectivity toward formate. Meanwhile, the oxygen vacancies on the CeO_2-x also play a pivotal role in manipulating the electrochemical performance and stability, which underlines the importance of regulating the electronic metal-support interaction between Cu Sn diatoms and CeO_2-x. This work demonstrates an effective method to design efficient electrochemical CO₂ reduction catalysts by modulating the surface structures of single-atoms anchored support.