Filling Oxygen Vacancies Research Articles

Synergistic dual-layer passivation boosts efficiency and stability in perovskite solar cells using naphthol sulfonate.

The performance and stability of perovskite solar cells (PSCs) are critically influenced by the interfacial properties between the perovskite absorption layer and the electron transport layer (ETL). This study introduces a novel interfacial engineering approach using dipotassium 7-hydroxynaphthalene-1,3-disulfonate (K-NDS) as a multifunctional passivator to enhance both the SnO2 ETL and the perovskite absorber layer. The sulfonic acid groups (-SO3-) in K-NDS effectively fill oxygen vacancies on the SnO2 surface, while the hydroxyl groups (-OH) passivate dangling bonds, improving the crystallinity of the perovskite film. Additionally, the diffusion of K+ from the SnO2 ETL into the perovskite layer optimizes energy level alignment, thereby enhancing charge carrier extraction and transport. This bifacial passivation strategy has significantly improved both the power conversion efficiency (PCE) and long-term stability of PSCs. The modified devices achieved a champion PCE of 23.00% and an open-circuit voltage (VOC) of 1.172 V. Furthermore, these devices maintained 75% of their initial PCE even after 1000 hours of storage under indoor environmental conditions. This work demonstrates the effectiveness of synergistic interfacial passivation in advancing the performance and durability of PSCs.

Nitrogen incorporated oxygen vacancy enriched MnCo2Ox/BiVO4 photoanodes for efficient and stable photoelectrochemical water splitting

Oxygen vacancies in oxygen evolution cocatalysts (OECs) can significantly improve the photoelectrochemical (PEC) water splitting performance of photoanodes. However, OECs with abundant oxygen vacancies have a poor stability when exposing to the highly-oxidizing photogenerated holes. Herein, we partly fill oxygen vacancies in a MnCo2Ox OEC with N atoms by a combined electrodeposition and sol-gel method, which dramatically improves both photocurrent density and stability of a BiVO4 photoanode. The optimized N filled oxygen vacancy-rich MnCo2Ox/BiVO4 photoanode (3 at.% of N) exhibits an outstanding photocurrent density of 6.5 mA·cm−2 at 1.23 VRHE under AM 1.5 G illumination (100 mW·cm−2), and an excellent stability of over 150 h. Systematic characterizations and theoretical calculations demonstrate that N atoms stabilize the defect structure and modulate the surface electron distribution, which significantly enhances the stability and further increases the photocurrent density. Meanwhile, other heteroatoms such as carbon, phosphorus, and sulfur are confirmed to have similar effects on improving PEC water splitting performance of photoanodes.

Frontispiz: Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution

Electrocatalysis. In their Research Article (e202301408), Zhao-Qing Liu et al. report the activation of lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies with fluorine, thus resulting in a highly active catalyst for electrocatalytic oxygen evolution.

Frontispiece: Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution

Electrocatalysis. In their Research Article (e202301408), Zhao-Qing Liu et al. report the activation of lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies with fluorine, thus resulting in a highly active catalyst for electrocatalytic oxygen evolution.

Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling the Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution.

The development of productive catalysts for oxygen evolution reaction (OER) remains a major challenge that requires significant progress in both mechanism and material design. Conventionally, the thermodynamic barrier of the lattice oxidation mechanism (LOM) is lower than that of absorbate evolution mechanism (AEM) because the former could bypass certain limitations. However, it remains a challenging task to control the OER pathway from the AEM to the LOM by taking advantage of the intrinsic properties of catalyst. Herein, we incorporate F anion into oxygen vacancies of spinel ZnCo2O4 and establish the link between electronic structure and the OER catalytic mechanism. Density theoretical calculation reveals that F upshifts O 2p center and activate the redox capability of the lattice O, successfully triggering the LOM pathway, achieving a low overpotential of 350 mV at 10 mA cm-2. Moreover, the large electronegativity of F anion is favorable for the balance of residual protonation, which can stabilize the structure and locally trigger LOM without surface reconstruction during OER reaction. This finding provides a feasible strategy to concurrently enhance the activity and stability of OER, and demonstrates the significance of considering lattice oxygen participation for understanding the OER trend of highly active spinel.

Activating Lattice Oxygen in Spinel ZnCo2O4 through Filling Oxygen Vacancies with Fluorine for Electrocatalytic Oxygen Evolution

AbstractThe development of productive catalysts for the oxygen evolution reaction (OER) remains a major challenge requiring significant progress in both mechanism and material design. Conventionally, the thermodynamic barrier of lattice oxidation mechanism (LOM) is lower than that of absorbate evolution mechanism (AEM) because the former can overcome certain limitations. However, controlling the OER pathway from the AEM to the LOM by exploiting the intrinsic properties of the catalyst remains challenging. Herein, we incorporated F anions into the oxygen vacancies of spinel ZnCo2O4 and established a link between the electronic structure and the OER catalytic mechanism. Theoretical density calculations revealed that F upshifts the O 2p center and activates the redox capability of lattice O, successfully triggering the LOM pathway. Moreover, the high electronegativity of F anions is favourable for balancing the residual protonation, which can stabilize the structure of the catalyst.

Resistive, Temperature-Independent Metal Oxide Gas Sensor for Detecting the Oxygen Stoichiometry (Air-Fuel Ratio) of Lean Engine Exhaust Gases.

This study presents a resistive sensor concept based on Barium Iron Tantalate (BFT) to measure the oxygen stoichiometry in exhaust gases of combustion processes. The BFT sensor film was deposited on the substrate by the Powder Aerosol Deposition (PAD) method. In initial laboratory experiments, the sensitivity to pO2 in the gas phase was analyzed. The results agree with the defect chemical model of BFT materials that suggests the formation of holes h• by filling oxygen vacancies VO•• in the lattice at higher oxygen partial pressures pO2. The sensor signal was found to be sufficiently accurate and to have low time constants with changing oxygen stoichiometry. Further investigations on reproducibility and cross-sensitivities to typical exhaust gas species (CO2, H2O, CO, NO, …) confirmed a robust sensor signal that was hardly affected by other gas components. The sensor concept was also tested in real engine exhausts for the first time. The experimental data showed that the air-fuel ratio can be monitored by measuring the resistance of the sensor element, including partial and full-load operation modes. Furthermore, no signs of inactivation or aging during the test cycles were observed for the sensor film. Overall, a promising first data set was obtained in engine exhausts and therefore the BFT system is a possible cost-effective alternative concept to existing commercial sensors in the future. Moreover, the integration of other sensitive films for multi-gas sensor purposes might be an attractive field for future studies.

Probing Local Environments of Oxygen Vacancies Responsible for Hydration in Sc-Doped Barium Zirconates at Elevated Temperatures: In Situ X-ray Absorption Spectroscopy, Thermogravimetry, and Active Learning Ab Initio Replica Exchange Monte Carlo Simulations

Proton-conducting oxides, specifically heavily Sc-doped barium zirconate perovskite, have attracted attention as electrolytes for intermediate-temperature protonic ceramic fuel cells because of their high proton conductivity and high chemical stability against carbon dioxide in that temperature regime. Hydration is a key reaction for incorporating protons by filling oxygen vacancies, VO, with hydroxyl groups and activating proton conduction in the perovskite. However, probing the local environment of oxygen vacancies responsible for hydration is challenging because the behavior depends on the temperature and water partial pressure, which necessitates in situ observations and calculations of the local environments at elevated temperatures. To obtain such information, we combined in situ X-ray absorption spectroscopy (XAS) for both the Sc and Zr K-edges, thermogravimetry, X-ray diffractometry, and active learning ab initio replica exchange Monte Carlo (RXMC) simulations in undoped and 20–40 at % Sc-doped barium zirconates at and below 800 °C. The presence of oxygen vacancies adjacent to Sc and Zr in the dehydrated samples and the hydration of these oxygen vacancies under a wet atmosphere were probed by in situ XAS for Sc and Zr pre-edges at elevated temperatures. Here, the microscopic hydration linearly responds to the macroscopic degree of hydration. RXMC sampling further supports the presence of Sc-VO-Zr and Sc-VO-Sc environments. An initial hydration occurs in the Sc-VO-Zr environment at and above 600 °C, but the Sc-VO-Sc environment contribution is greater at higher degrees of hydration. The Zr-Vo-Zr environment is the least abundant among them for the whole temperature range examined and thus has a negligible impact.

Evidence of redox cycling as a sub-mechanism in hydrogen production during ethanol steam reforming over La0.7Sr0.3MnO3-x perovskite oxide catalysts

Ethanol steam reforming (ESR) is of societal interest. In this work, experiments were conducted to ascertain if some of the H2 is produced by a redox cycle involving H2O filling oxygen vacancies over reducible oxide catalysts. Redox cycling experiments were performed over La0.7Sr0.3MnO3-x(100) in ultra-high vacuum. It was found that H2 was produced from redox cycling with alternating ethanol and water exposures over La0.7Sr0.3MnO3-x(100), with both half-cycles occurring at temperatures ≤800 K. In the first half-cycle, ethanol ‘directly’ reduced the surface to create oxygen vacancies (not by a CO intermediate), and in the second half-cycle water filled oxygen vacancies to make H2. The H2 production during the water exposure has a half-cycle turnover frequency of >3.2 × 10-2 molecules site-1 s−1 in the temperature range of 700–800 K, which is fast enough to be part of the ESR full catalytic cycle. Flowing both reactant gases together, ethanol and water, over La0.7Sr0.3MnO3-x(100) and La0.7Sr0.3MnO3-x powders significantly increases hydrogen production compared to pure ethanol. The results suggest that steady state ESR includes a sub-mechanism of ethanol ‘directly’ reducing the surface to create oxygen vacancy, and water filling oxygen vacancy to make some of the H2 by a Mars van Krevelen type mechanism.

Recent advances and perspectives of CeO2-based catalysts: Electronic properties and applications for energy storage and conversion.

Cerium dioxide (CeO2, ceria) has long been regarded as one of the key materials in modern catalysis, both as a support and as a catalyst itself. Apart from its well-established use (three-way catalysts and diesel engines), CeO2 has been widely used as a cocatalyst/catalyst in energy conversion and storage applications. The importance stems from the oxygen storage capacity of ceria, which allows it to release oxygen under reducing conditions and to store oxygen by filling oxygen vacancies under oxidizing conditions. However, the nature of the Ce active site remains not well understood because the degree of participation of f electrons in catalytic reactions is not clear in the case of the heavy dependence of catalysis theory on localized d orbitals at the Fermi energy E F . This review focuses on the catalytic applications in energy conversion and storage of CeO2-based nanostructures and discusses the mechanisms for several typical catalytic reactions from the perspectives of electronic properties of CeO2-based nanostructures. Defect engineering is also summarized to better understand the relationship between catalytic performance and electronic properties. Finally, the challenges and prospects of designing high efficiency CeO2-based catalysts in energy storage and conversion have been emphasized.

Enhanced Electrical Properties of Na0.5Bi4.5Ti4O15-Bi4Ti3O12 Ceramics After Filling Oxygen Vacancies with Y-Doping

Enhanced Electrical Properties of Na0.5Bi4.5Ti4O15-Bi4Ti3O12 Ceramics After Filling Oxygen Vacancies with Y-Doping

Tailored electronic structure by sulfur filling oxygen vacancies boosts electrocatalytic nitrogen oxyanions reduction to ammonia

Electrocatalytic reduction of nitrogen oxyanions (NOx−, x = 3 and 2) to ammonia (NH3) under ambient conditions is an alternative to the Haber-Bosch process (HBP). Recent catalysts are vulnerable to low-rate and -selectivity NH3 synthesis due to the multi-step electron–proton transfer process and water as a proton donor, especially in neutral media. Herein, we introduce sulfur species into Co3O4 spinel nanosheets (S-Co3O4) inspired by the bio-nitrogenase of metal-sulfur clusters to alleviate the above dilemma. The S5-Co3O4 exhibits an NH3 yield rate of 174.2 mmol h−1 g−1 at − 0.6 V versus reversible hydrogen electrode (RHE) with a Faradaic efficiency of 89.9 %, nitrate (NO3−) as feedstock. Furthermore, nitrite (NO2−) reduction possesses comparable NH3 Faradaic efficiency (87.6 %) and a higher yield rate (314.5 mmol h−1 g−1) at the same conditions. Theoretical calculations demonstrated that sulfur species reduce the free energy change of formation *H, boosting the activation of *NOx (x = 3 and 2). A two-electrode device, S5-Co3O4 as bifunctional catalysts, demonstrates excellent NH3 Faradaic efficiency (>95 %) over a wide voltage range for NO2−RR, while the anode produces high value-added benzoic acid.

A full range of defect passivation strategy targeting efficient and stable planar perovskite solar cells

Defects and inferior charge transport dynamics within devices are key issues that inhibit the improvements of photovoltaic performance and stability. Developing facile and feasible strategies for synchronous passivation of defects regarding charge transport layers (CTLs), perovskite films and their interfaces, and precise tuning of energy level structure, is a definite way to solve above problems. Herein, we develop a synergistic passivation strategy for perovskite films and bilateral interfaces to improve device performance. Firstly, an appropriate amount of phenylethylammonium chloride is adopted to modify SnO2 electron transport layer (ETL). The complexation reaction between N atoms in –NH2 and Sn4+ improve the agglomeration of SnO2 nanoparticles and film quality of SnO2 ETL. The presence of Cl− ions not only effectively fill oxygen vacancies within SnO2 ETL, but also participate in regulating crystal growth dynamics of perovskite films, thus improving electron transport properties at interface. Subsequently, p-type conducting material N,N'-Bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) is introduced into anti-solvent chlorobenzene during the preparation of perovskite films to further regulate the crystal quality and achieve full-range defect passivation. Particularly, the introduction of NPB helps to construct a gradient heterojunction between upper perovskite film and SpiroOMeTAD hole transport layer, thus reducing the accumulation of hole carriers near interface and further suppressing current–voltage hysteresis behavior of devices. Additionally, the hydrophobicity of NPB and full range of defect passivation greatly enhance the humidity and thermal stability of devices. Finally, a high power conversion efficiency of 21.88% is obtained with suppressed hysteresis and enhanced long-term stability. This work highlights the role of full-range defect passivation on CTLs, perovskite absorption layers and interfacial charge transport properties, which provide a novel concept for constructing high-performance and stable perovskite devices.

Chlorobenzenesulfonic Potassium Salts as the Efficient Multifunctional Passivator for the Buried Interface in Regular Perovskite Solar Cells

AbstractThe interfacial properties for the buried junctions of the perovskite solar cells (PSCs) play a crucial role for the further enhancement of the power conversion efficiency (PCE) and stability of devices. Delicate manipulation of the interface properties such as the defect density, energy alignment, perovskite film quality, etc., guarantees efficient extraction and transport of photogenerated carriers. Herein, chlorobenzenesulfonic potassium salts are presented as a novel multifunctional agent to modify the buried tin oxide (SnO2)/perovskite interface for regular PSCs. The increasing number of carbon‐chlorine bonds (CCl) in 2,4,5‐trichlorobenzenesulfonic potassium (3Cl‐BSAK) exhibit efficient interaction with uncoordinated Sn, effectively filling oxygen vacancies in the SnO2 surface. Importantly, synergistic effects of the functional group‐rich organic anions and the potassium ion are achieved for reduced defect density, carrier recombination, and hysteresis. A champion PCE of 24.27% and the open‐circuit voltage (VOC) up to 1.191 V for modified devices are obtained. The unencapsulated devices maintain 80% of their initial PCE after aging at 80 °C for 800 h in the atmosphere and 95% after aging for 100 d. With 3Cl‐BSAK decoration, a high efficiency semitransparent PSC with a PCE of 12.83% and an average visible light transmittance (AVT) over 27% is also obtained.

Atomic Sulfur Filling Oxygen Vacancies Optimizes H Absorption and Boosts the Hydrogen Evolution Reaction in Alkaline Media

AbstractThe hydrogen evolution reaction (HER) usually has sluggish kinetics in alkaline solution due to the difficulty in forming binding protons. Herein we report an electrocatalyst in which sulfur atoms are doping in the oxygen vacancies (VO) of inverse spinel NiFe2O4 (S‐NiFe2O4) to create active sites with enhanced electron transfer capability. This electrocatalyst has an ultralow overpotential of 61 mV at the current density of 10 mA cm−2 and long‐term stability of 60 h at 1.0 Acm−2 in 1.0 M KOH media. In situ Raman spectroscopy revealed that S sites adsorb hydrogen adatom (H*) and in situ form S‐H*, which favor the production of hydrogen and boosts HER in alkaline solution. DFT calculations further verified that S introduction lowered the energy barrier of H2O dissociation. Both experimental and theoretical investigations confirmed S atoms are active sites of the S‐NiFe2O4.

Atomic Sulfur Filling Oxygen Vacancies Optimizes H Absorption and Boosts the Hydrogen Evolution Reaction in Alkaline Media.

The hydrogen evolution reaction (HER) usually has sluggish kinetics in alkaline solution due to the difficulty in forming binding protons. Herein we report an electrocatalyst in which sulfur atoms are doping in the oxygen vacancies (VO ) of inverse spinel NiFe2 O4 (S-NiFe2 O4 ) to create active sites with enhanced electron transfer capability. This electrocatalyst has an ultralow overpotential of 61 mV at the current density of 10 mA cm-2 and long-term stability of 60 h at 1.0 Acm-2 in 1.0 M KOH media. In situ Raman spectroscopy revealed that S sites adsorb hydrogen adatom (H*) and in situ form S-H*, which favor the production of hydrogen and boosts HER in alkaline solution. DFT calculations further verified that S introduction lowered the energy barrier of H2 O dissociation. Both experimental and theoretical investigations confirmed S atoms are active sites of the S-NiFe2 O4 .

Atomic Origin of Interface-Dependent Oxygen Migration by Electrochemical Gating at the LaAlO3-SrTiO3 Heterointerface.

Electrical control of material properties based on ionic liquids (IL) has seen great development and emerging applications in the field of functional oxides, mainly understood by the electrostatic and electrochemical gating mechanisms. Compared to the fast, flexible, and reproducible electrostatic gating, electrochemical gating is less controllable owing to the complex behaviors of ion migration. Here, the interface‐dependent oxygen migration by electrochemical gating is resolved at the atomic scale in the LaAlO3–SrTiO3 system through ex situ IL gating experiments and on‐site atomic‐resolution characterization. The difference between interface structures leads to the controllable electrochemical oxygen migration by filling oxygen vacancies. The findings not only provide an atomic‐scale insight into the origin of interface‐dependent electrochemical gating but also demonstrate an effective way of engineering interface structure to control the electrochemical gating.

Ethanedithiol treatment on zinc oxide films for highly efficient quantum dot light-emitting diodes by reducing exciton quenching

Surface modification of ZnO nanoparticles with ethanedithiol (EDT) has been studied to minimize exciton loss at the ZnO/quantum dots (QDs) interface and to improve the efficiency of QD light-emitting diodes (QLEDs). The EDT treatment has been demonstrated to fill oxygen vacancies and reduce carboxylate and hydroxyl ligands on the surface of the ZnO nanoparticles from the x-ray photoelectron spectroscopy analysis. The reduction of oxygen vacancies makes the ZnO films more hydrophobic and maintains the optical bandgap under ambient conditions. EDT treatment shifts the energy level up by 0.47 eV by modifying the surface of ZnO. Non-radiative recombination processes at the ZnO/QDs interface such as interfacial charge transfer and energy transfer are reduced through the upshifted energy level and reduced surface defects. The brightness of the QLED with EDT treatment on ZnO was improved by more than 330% having a maximum luminance of 59 , 500 c d / m 2 compared to the QLED with pristine ZnO. The maximum current efficiency of the QLEDs has been improved from 54.3 cd/A to 73.4 cd/A, which is 35% higher than ZnO-based QLEDs.

Enhanced Hydrogen Evolution Reaction Performance of NiCo2P by Filling Oxygen Vacancies by Phosphorus in Thin-Coating CeO2.

A series of NiCo2P-based electrocatalysts, which were wrapped by CeO2 whose oxygen vacancies (VO) are partially filled with phosphorus atoms (named as NiCo2Px/PxFVo-CeO2, where x refers to the consumption of NaH2PO2·H2O), have been fabricated to improve the electrocatalytic reactivity of NiCo2P toward hydrogen evolution in alkaline solution. In the novel catalysts, the P atoms fill the oxygen vacancies, elevate the chemical valence state of Ni2+ and Co3+, and increase the hydride acceptors, whichreinforcing the promoting effect of CeO2 in the hydrogen evolution reaction (HER). Moreover, the negatively charged P atoms capture the positively charged protons more easily, benefiting the Volmer step during HER. Furthermore, the synergistic effect between oxygen vacancies and the filled P atoms accelerates the migration rate of electrons/ions and increases the electrochemical active area. All of the above are advantageous to the hydrogen evolution of NiCo2Px/PxFVo-CeO2 in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo2P0.3/P0.3FVo-CeO2 in alkaline media to drive a current density of 10 mA cm-2. The reactivity is superior to that of Pt/C at a large current density along with a Tafel slope of 61.24 mV dec-1 and long-term durability, which giving a new technology for efficient transition-metal catalyst candidates toward HER in alkaline solution.

Hierarchical nickel cobalt oxide spinel microspheres catalyze mineralization of humic substances during wet air oxidation at atmospheric pressure

Humic substance (HS) is a key pollutant in water supply or wastewater treatment. In this work, hollow microspheres constituted of NiCo2O4 (NCO) spinel were synthesized and used as the catalyst of catalytic wet air oxidation, aiming to remove HS at atmospheric pressure and low temperature. The results show that NCO had excellent hierarchical architectures with large surface area (66.88 m2/g), solid-state redox couples, numerous surface oxygen species, and low reduction temperature. When NCO was used to treat HS solution at 90°C, total organic carbon concentration decreased by 93.4% after 24 h. NCO itself had the ability to mineralize the HS adsorbed on the surface, and dissolved oxygen can fill oxygen vacancies and recover NCO to its original state. Hydroxyl radicals also assisted the HS degradation. These findings provide some insight into the HS degradation process and promise an inexpensive and easy way to clean HS-rich water or wastewater.