Concentration Of Oxygen Defects Research Articles

Insights into the surface Structure-Sensitive photocatalytic oxidation of gaseous toluene on Pd/TiO2 catalysts

Indoor volatile organic compounds (VOCs), represented by toluene, can pose a serious threat to human health. In this work, a series of Pd/TiO2 catalysts with different surface structures (i.e., dispersion/valence of Pd species, surface Ti3+/oxygen defect concentration and Pd-TiO2 interactions, etc.) was constructed by various methods. It was found that the Pd/TiO2 catalyst prepared by one-step reduction of NaBH4 method (Pd/TiO2-N) with metallic Pd particles possessed more surface Ti3+/oxygen defects and stronger Pd-TiO2 interaction than Pd/TiO2 catalysts prepared by ethylene glycol reduction loading method (Pd/TiO2-E) and incipient wetness impregnation method (Pd/TiO2-I). Further photochemical characterizations and reaction mechanism study revealed that the relatively higher concentration of Pd0 species on Pd particles, stronger Pd-TiO2 interaction, and more surface Ti3+/oxygen defects on Pd/TiO2-N could facilitate the generation of more reactive oxygen species (ROS) under light irradiation. The partial oxidation of toluene to benzyl alcohol/benzaldehyde/benzoic acid and the subsequent ring-opening process were found to be highly determined by the valence states of Pd particles and the concentration of surface Ti3+/oxygen defects. This work provides instructive insights into the construction of highly efficient Pd/TiO2 catalysts for the removal of indoor VOCs.

Enhanced mechanism of molten alkali nitrates on triple-phase interface during the carbonation of MgO

Thermochemical energy storage has broad application prospect with the advantages of high energy density and trans-regional storage capability. For MgCO3/MgO reaction couple, conversion rate of MgO carbonation with molten alkali nitrates is significantly enhanced. However, its kinetic mechanism is still controversial. In this work, molecular dynamics research on MNO3-MgO-CO2 (M is Li/Na/K/Na0.n5K0.5) interface was carried out to reveal the mechanism and regulate its performance. Results indicate that MNO3 plays a dominant role in facilitating MgO(s) → Mg2+ + O2− after melting. Lattice distortion is observed on the surface of MgO due to oxygen ion exchange between NO3– and MgO, breaking MgO balance. Interestingly, generated oxygen vacancies become highly reactive sites. Overall, the participation of molten MNO3 gives rise to triple-phase boundary that works as a efficient pathway for CO2 to penetrate deeper into MgO. Subsequently, structure-activity relationships between microstructure and carbonation kinetics was proposed. Among all the dopants studied, Na0.5K0.5NO3 not only creates strong distortion of the MgO lattice with oxygen defect concentration of 0.0787 mol%, but also exhibits a small-contact angle of 67.5° on MgO at 320 °C and 0.1 MPa, boosting MgO carbonation. The ambient temperature plays opposite effects on interface wettability of molten MNO3 and thermodynamic driving force, causing a parabolic kinetics with a peak rate at 332 °C. Small and uniformly dispersed dopants are beneficial for energy carriers to adsorb CO2. The above regulation provides a guiding principle for the preparation of thermochemical energy carriers in subsequent applications.

CuNi Nanoalloys with Tunable Composition and Oxygen Defects for the Enhancement of the Oxygen Evolution Reaction**

AbstractColloidal synthesis is an excellent tool for the study of cooperative effects in nanoalloys. In this work, bimetallic CuNi nanoparticles of defined size and composition are fully characterized and tested for the oxygen evolution reaction. Copper addition to nickel leads to modifications in the structural and electronic properties, showing a higher concentration of surface oxygen defects and formation of active Ni3+ sites under reaction conditions. The ratio OV/OL between oxygen vacancies and lattice oxygen shows a clear correlation with the overpotential, being an excellent descriptor of the electrocatalytic activity. This is attributed to modifications in the crystalline structure, leading to lattice strain and grain size effects. Bimetallic Cu50Ni50NP showed the lowest overpotential (318 mV vs RHE), low Tafel slope (63.9 mV dec−1), and excellent stability. This work unravels the relative concentration between oxygen defects and lattice oxygen (OV/OL) as an excellent descriptor of the catalytic activity of bimetallic precatalysts.

CuNi Nanoalloys with Tunable Composition and Oxygen Defects for the Enhancement of the Oxygen Evolution Reaction.

Colloidal synthesis is an excellent tool for the study of cooperative effects in nanoalloys. In this work, bimetallic model CuNi nanoparticles of defined size and composition are fully characterized and tested for the oxygen evolution reaction. Copper addition to nickel leads to modifications in the structural and electronic properties, showing a higher concentration of surface oxygen defects and formation of active Ni3+ sites under reaction conditions. The ratio OV/OL between oxygen vacancies and lattice oxygen shows a clear correlation with the overpotential, being an excellent descriptor of the electrocatalytic activity. This is attributed to modifications in the crystalline structure, leading to lattice strain and grain size effects. Bimetallic Cu50Ni50NP showed the lowest overpotential (318 mV vs RHE), low Tafel slope (63.9 mV dec-1), and excellent stability. This work unravels the relative concentration between oxygen defects and lattice oxygen (OV/OL) as an excellent descriptor of the catalytic activity of bimetallic precatalysts.

Chemical bath deposited SnO2 for high-efficiency perovskite solar cells on Ti substrates

Perovskite solar cells fabricated on metal substrates, such as Ti, can effectively reduce manufacturing costs. However, the SnO2 electron transport layers (ETL) deposited using most methods is not suitable for Ti substrates, resulting in low-efficiency devices. This study improved the chemical bath technology to facilitate the easy deposition of SnO2 layers with a low oxygen defect concentration and high conductivity on Ti substrates by adjusting the reaction time. The devices fabricated on Ti substrate using optimized SnO2 showed a much higher short-circuit current density (Jsc) and fill factor (FF) compared to control devices. The champion device demonstrated a Jsc of 20.1 mA/cm2 and a power conversion efficiency (PCE) of 15.21%. Additionally, we proposed solutions to fabricate a large perovskite solar cell module with a 12.96 cm2 aperture area and 95.8% geometric filling factor (GFF). This metal substrate–based approach was developed by taking the preparation technology of C–Si solar cells as a reference.

CuCeOx/CuO Catalyst Derived from the Layered Double Hydroxide Precursor: Catalytic Performance in NO Reduction with CO in the Presence of Water and Oxygen.

Valencies of metal species and lattice defects, such as oxygen vacancies, play a pivotal role in metal oxide-catalyzed reactions. Herein, we report a promising synthetic strategy for preparing CuO-supported CuCeOx catalysts (CuCeOx/CuO) by calcination of a hydrotalcite precursor [Cu6Ce2(OH)16]CO3·nH2O. The structural and chemical properties of catalysts were characterized by XRD, ICP-AES, TEM, TPR, NH3-TPD, XPS, Raman spectroscopy, and N2 adsorption, which revealed that the thermal pretreatment in an oxidative atmosphere caused segregation and reconstitution processes of the precursor, resulting in a mesoporous catalyst consisting of well-dispersed CuO-supported CuCeOx clusters of 1.8-3.2 nm in size with a high population of oxygen vacancies. The as-prepared catalyst shows excellent catalytic performance in the reduction of NO by CO in the absence as well as in the presence of water and oxygen. This behavior is attributed to its high oxygen defect concentration facilitating the interplay of the redox equilibria between Cu2+ and reduced copper species (Cu+/Cu0) and (Ce4+/Ce3+). The high surface population of oxygen vacancies and in situ-generated metallic copper species have been evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. The layered double hydroxide-derived CuCeOx/CuO also showed good water tolerance and long-term stability. In situ infrared spectroscopy investigations indicated that adsorbed hyponitrite species are the main reaction intermediates of the NO conversion as also corroborated by theoretical simulations.

Temperature Ramp Strategy for Regulating Oxygen Vacancies in NiCo2O4 Nanoneedles Towards Enhanced Electrocatalytic Water Splitting.

The oxide-based systems often suffer from higher overpotentials compared to transition metal sulphides and phosphides for the electrochemical hydrogen evolution reaction. Interestingly, the generation of oxygen vacancy has been seen as strategy for further activating transition metal oxides (NiCo2O4 as a model system) for electrochemical watersplitting. Herein, we employ the temperature ramp strategy (ambient air calcination) for the generation of oxygen vacancies in NiCo2O4 (NCO) towards tuning of electrocatalytic enhancements. The NiCo2O4 synthesized at temperature ramp rates of 2 (NCO-2), 5 (NCO-5), and 10ºC/ min (NCO-10) depicts contrasting structural features and varying Ni:Co:O surface composition. The decrease in the crystallite size and converse trend in the particle strain were observed from NCO-2 to NCO-10. Interestingly, the surface Ni:Co:O ratios of 1:0.78:3.6, 1:0.81:3.3, and 1:0.69:2.8 for NCO-2, NCO-5, and NCO-10, respectively, were observed. The reduced relative oxygen ratio in the latter implies generation of ample amount of oxygen vacancy defects. HER performance depicts a consistent trend with enhanced oxygen defect concentration with the overpotential requirement of 700, 647, and 597 mV for NCO-2, NCO-5, and NCO-10, respectively, for the generation of a cathodic current of 25 mA cm-2. The same trend in an electrocatalytic enhancement is observed for other cathodic currents.

Improved electrocatalytic methanol oxidation of NiO nanosheet arrays with synergistic high surface oxygen vacancy and Ni3+/Ni2+ ratio

The combination of anodic biomass electrooxidation and cathodic hydrogen evolution reaction is an effective strategy to realize energy saving hydrogen production and high value chemical products. Herein, we synthesized dense NiO nanosheet arrays on Ni foam using different heat-treatment temperature, including 400, 450 and 500 °C. The NiO prepared under 500 °C owns the highest oxygen defect concentration (58.1%) and Ni3+/Ni2+ ratio (3.13), giving the highest intrinsic activity for methanol electrocatalytic oxidation reaction. However, the NiO prepared at 400 °C (named as NiO-400) owns highest catalyst surface area and electrochemical surface area, giving the highest practical activity. Based on the above results, a facile method of surface modification by ultraviolet oxidation is proposed to improve the oxygen defect concentration (from 34.7% to 36.8%) and Ni3+/Ni2+ ratio (from 2.94 to 3.19) of NiO-400, and the catalytic current was increased by about 48.9%. This work provides some theoretical basis for improving the activity of biomass electrocatalytic oxidation of Ni-based materials.

Hydrogen Spillover-Accelerated Selective Hydrogenation on WO3 with ppm-Level Pd.

Hydrogen spillover from the metal to the support opens a fresh avenue to design dual-active site catalysts for selective hydrogenation. However, very limited knowledge has been obtained to reveal the relationship between the capacity of hydrogen spillover and catalytic performance of hydrogenation. Herein, hydrogen spillover-dependent selective hydrogenation has been demonstrated on WO3-supported ppm-level Pd (PdHD/WO3), where the *H species generated and spilled from Pd to WO3 are readily utilized for addition of a reactant. The WO3 supports with a hexagonal phase and a suitable oxygen defect concentration can enhance the capacity of hydrogen spillover, significantly accelerating the catalytic activity of PdHD/WO3. For the hydrogenation of 4-chloronitrobenzene, the PdHD/WO3 catalysts with the highest capacity of hydrogen spillover yielded a turnover frequency (TOF) of 47,488 h-1 (33 times higher than that of traditional Pd/C). Meanwhile, benefiting from the hydrogen spillover, the unique adsorption of 4-chloronitrobenzene via the nitro group on the oxygen vacancy of WO3 guaranteed >99.9% selectivity of 4-chloroaniline during the whole hydrogenation. This work thus helps to create an effective method for fabricating cost-effective nanocatalysts with an extremely low Pd loading for the ideal hydrogenation with extremely high activity and selectivity.

Oxygen vacancy regulated valence states of Pt on rutile TiO2 promote catalytic oxidation of HCHO

Anatase-TiO2-supported Pt (Pt/TiO2(A)) is a well-known supported catalyst for catalyzing the oxidation of formaldehyde (HCHO). However, rutile TiO2 (TiO2(R)) has not been widely utilized for this reaction due to its inferior performance. In this study, we have developed a novel approach involving NaBH4-induced oxygen vacancy manipulation to regulate the valence states of Pt on TiO2(R). By employing a large excess of NaBH4 (nNaBH4/nPt = 2000), we were able to generate an extraordinary concentration of oxygen defects and electron-rich sites on the surface of TiO2(R), resulting in the concentration of Pt0 on Pt/TiO2(R)− 2000 exceeding that on Pt/TiO2(A)− 2000. The newly synthesized Pt/TiO2(R)− 2000 catalyst exhibited a remarkably high turnover frequency (TOF) of 160.2 h−1, which is approximately five times that of Pt/TiO2(R)− 20. The discrepancy in the reaction mechanisms between rutile and anatase was identified as the critical factor underlying the vastly different performances observed.

Defect Formation Thermodynamics of (A,A′)(B,B′)O3 (A = Mg,Ca,Sr and B = Ti,Mn,Cr,Fe,Mo) Perovskites

In a previous theoretical study [B. Grimm and T. Bredow, Oxygen Defect Formation Thermodynamics of CaMnO3: A Closer Look. Phys. Status Solidi B 2022, https://doi.org/10.1002/pssb.202200427], the structural, thermodynamic, and electronic properties of have been studied. The present study increases the range of compounds to ternary perovskites in a search for suitable anode materials for high‐temperature water electrolysis. compounds containing the abundant elements A = Mg,Ca,Sr and B = Ti,Mn,Cr,Fe,Mo are studied theoretically on hybrid density functional theory level. Criteria for a suitable electrode material are low‐oxygen defect formation energy and high reaction energy for decomposition into other phases. Based on these criteria, the most suitable perovskites are chosen as starting points to create stable mixed compounds. The compound δ is found to be the optimal choice as electrode material, with an oxygen defect concentration of at least δ present at 520 K and highly endothermic decomposition reactions.

Surface modification of Co3O4 nanostructures using wide range of natural compounds from rotten apple juice for the efficient oxygen evolution reaction

In this study, a new strategy has been produced to use a rotten apple juice as a source for the surface modification of Co3O4 nanostructures, giving rise to efficient electro-catalysts for driving oxygen evolution reaction (OER) at relatively low over potential. We have studied the morphology, chemical composition, and crystalline aspects of Co3O4 nanostructures using different analytical techniques. The Co3O4 nanostructures grown with rotten apple juice were observed with low impurity of Fe and P, surface modification, reduced particle size, high concentration of oxygen vacancies, defects and cubic phase of Co3O4. Furthermore, we have used the surface modified Co3O4 nanostructures for water electrolysis and noticed the significant performance towards OER in alkaline conditions. The electrochemical characterization revealed that the Co3O4 nanostructure prepared with 20 mL of rotten apple juice exhibits an overpotential value of 269 mV at 20 mA/cm2 current density. The charge transport resistance (Rct) at the interface was estimated around 118.9 Ω, confirming an excellent reaction kinetics on the Co3O4 nanostructures and highly supported efficient performance towards OER. The Co3O4 nanostructures prepared with 20 mL of rotten apple juice has shown an acceptable durability for 40 h, verifying the long-term use. The performance of Co3O4 nanostructures with apple juice could be attributed to high oxygen vacancies due to high density of Co2+ ions on the surface, impurities of Fe and P, reduced nanoparticle size, defects in the structures, and favorable chemical composition. At the end, surface modified Co3O4 nanostructures was observed as an outperformed electrocatalyst when prepared with rotten apple juice. Therefore, this can be used in diverse purposes including energy conversion and storage applications.

Green, Water-Based Synthesis of ZnO Nanostructures

We report on the synthesis of zinc oxide (ZnO) nanostructures using a simple, green, waterbased process, without the aid of any chemical precursor or external energy source. Zinc plates were immersed in deionized water and kept at ambient conditions in a dark cabinet for up to 21 days. After immersion, the reaction products were analyzed using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and Raman spectroscopy. After short immersion times (1-3 days), ZnO agglomerates with a high concentration of oxygen defects were formed, which overlapped along the c axis to form ZnO nanoflowers. After long immersion times (21 days), ZnO microswords with smooth surfaces, well-defined tips, and less oxygen defects were formed. This low-cost, low-energy synthesis process is an attractive alternative to produce ZnO nanostructures with low impact on the environment.

High thermoelectric power factor in LaVO3/KTaO3 heterostructure

Perovskite oxides are well-known for exhibiting semiconducting properties and widely used for electronic applications. The combination of two different perovskite oxides form heterojunction interface that tailors the charge transfer mechanism. Here, the thermoelectric(TE) electrical transport properties are investigated of pervoskite oxide heterostructure (HS) L a V O 3 / K T a O 3 ( L V O / K T O ) using Boltzmann transport equation (BTE) for symmetric and asymmetric termination in [001] orientation. The electron–phonon scattering and defect scattering due to oxygen vacancies are incorporated with BTE. A strong electron–phonon scattering is observed. The effect of oxygen defect concentration on electrical transport is also studied. These HS exhibits high electrical conductivity 2 . 9 × 1 0 4 S/m at room temperature due to n-type conducting interface and highly dispersive degenerate conduction bands. Besides moderate Seebeck coefficient, a relatively high thermoelectric power factor of 222 μ V m − 1 K − 2 for symmetric termination HS is obtained at 300 K as compared to bulk K T a O 3 and S r T i O 3 . The high power factor and low electronic thermal conductivity (0.19 Wm − 1 K − 1 ) designate L V O / K T O HS as an efficient material for photothermoelectric-based detectors and photovoltaic applications. • Electrical transport is predicted using Boltzmann transport theory. • Defect scattering due to oxygen vacancies is implemented. • Electron phonon scattering dominant at all temperatures. • High electrical conductivity of 2.9 x 10 4 S/m is obtained at 300 K. • Enhancement in power factor compared to bulk KTO and STO.

Ag decorated sea urchin-MoO3 based hierarchical micro-nano structures as surface - enhanced Raman spectroscopy substrates for the detection of a nitrosamine industrial pollutant

Sea urchin MoO3 with low loading of silver (Ag/SUMoO3) forming hierarchical micro-nano structures are explored as surface-enhanced Raman scattering (SERS) substrates. Owing to the high concentration of oxygen defects and consequently, Mo+5 states, possessing unique morphology of sea urchins, SUMoO3 are beneficial for achieving superior SERS properties. Silver nanoparticles are decorated on SUMoO3 by photoreduction, achieving an excellent Ag-MoO3 interface without the use of any coupling agents and the underlying scaffold prevents the silver from aggregation and oxidation. Ag/SUMoO3 substrate shows a high enhancement factor of 9.2 × 109 and a detection limit of 1 nM for 4-mercaptobenzoic acid. The synergetic effect of charge transfer enhancement from defect-rich SUMoO3 coupled with electromagnetic enhancement from silver nanoparticles is responsible for the high enhancement factor. Further, the detection of an environmental pollutant and a potent carcinogenic, N-nitrosodiphenylamine (NDPhA) up to 10−5 M is demonstrated using Ag/SUMoO3 as a SERS substrate for the first time. Antibacterial testing reveals the higher zone of inhibition achieved for Ag/SUMoO3 against E. coli than for bulk MoO3-Ag revealing the superior role of the unique morphology and composition of Ag/SUMoO3.

Lithiation‐Induced Defect Engineering to Promote Oxygen Evolution Reaction

AbstractExploring efficient electrocatalysts for oxygen evolution reaction (OER) is an urgent need to advance the development of sustainable energy conversion. Though defect engineering is considered an effective strategy to regulate catalyst activity for enhanced OER performance, the controllable synthesis of defective oxides electrocatalysts remains challenging. Here, oxygen defects are introduced into NiCo2O4 nanorods by an electrochemical lithiation strategy. By tuning in situ lithiation potentials, the concentration of oxygen defects and the corresponding catalytic activity can be feasibly regulated. In addition, the relationship between the changes in the defect density and electronic structure and the lithiation cut‐off voltages is revealed. The results show that NiCo2O4 nanorods undertook intercalation and two‐step conversion reaction, in which the lithiation‐induced conversion reaction gives rise to a CoO@NiO‐based structure with higher defect density and lower oxidation states. As a result, the defective CoO@NiO‐based catalyst exhibits exceptional OER activity with an overpotential of 270 mV at 10 mA cm−2, which is about 74 mV below the pristine nanomaterials. This research proposes a novel strategy to explore high‐performance catalysts with structural stability and defect control.

Intrinsic oxygen defects in UO2 (1 1 1) and PuO2 (1 1 1) surfaces

Density functional theory (DFT) + U combined with the first principle atomistic thermodynamic method was employed to study the physical properties of intrinsic oxygen defects in (111) surfaces of UO2 and PuO2. The calculated formation energy indicates that the oxygen interstitial (Oi) defects are dominant in UO2, while the oxygen vacancy (Ov) and Oi defects can coexist in PuO2. Such a difference can be attributed to the distinct electronic properties of U and Pu elements. Moreover, the formation energy of Ov is found to be sensitive to the surface depth, and Ov prefer to form on the sub-surface layer for both UO2 and PuO2. Comparatively, the formation of Oi is insensitive to the incorporation depth. The strain effect of formation energy is mainly contributed by the local structural distortion, rather than the electronic hybridization. Through thermodynamic calculation, the strain-modulated formation energy phase diagrams of the oxygen defects have been established over a wide range of temperature and pressure, providing the potential strategy for controlling the type and concentration of intrinsic oxygen defects in UO2 and PuO2. Our results shed some light on the defect behaviors of actinide dioxide, and thereby the oxidation properties of actinide metals.

(Invited) Effect of Atomic-Scale Surface Overcoat By Atomic Layer Deposition on Dopant Segregation of Perovskite Cathodes

Intense research has been performed to advance the solid oxide cell (SOC) technology because of their excellent efficiency for clean energy conversion and storage, but the lack of long-term durability, particularly of perovskite (ABO3)-based air electrodes, is currently the main technological bottleneck for wider commercial adoption. Long-term durability of SOC air electrodes has been mainly hampered by surface segregation of A-site dopant and morphological agglomeration. Since a deposition of an atomically thin oxide has proven to be highly effective in suppressing electrode agglomeration, a successful suppression of dopant segregation with the same approach will enhance the durability of air electrodes significantly by killing two birds with one stone. In the previous study [1], we demonstrated the effectiveness of an atomic scale overcoat in suppressing particle agglomeration. In this presentation, we demonstrate that even a few angstroms of metal oxide overcoat by atomic layer deposition (ALD) affects the behavior of Sr segregation in the underlying La0.8Sr0.2MnO3 (LSM) electrode significantly. By leveraging angle-resolved X-ray photoelectron spectroscopy (ARXPS), we provide a quantitative analysis of the relative atomic concentration on both the very surface and bulk of the electrode. Compared to bare LSM electrodes, those with 2 – 3 Å ALD overcoat show relatively high resistivity against Sr segregation when exposed to of 750 °C for 250 h. Particularly, an oxide overcoat with multi-valent cations (CeO2 and TiO2) tends to suppress Sr segregation effectively and even drive Sr species back into the bulk of LSM while an overcoat with single valent cations (ZrO2 and Y2O3) exhibits little effect on Sr segregation. It was further demonstrated that the segregation behavior is nicely aligned with the electrode performance; those coated with CeO2 and TiO2 showed better thermal stability in terms of polarization resistance. Based upon the time evolution of Sr content, cationic valence states, and oxygen defect concentration in the vicinity of surface, we conjecture that the amount of oxygen defects formed by the overcoat and the resulting chemical potential gradient at the interface between the overcoat underlying LSM surface plays a pivotal role in the Sr segregation behavior. The authors acknowledge the support from National Science Foundation (DMR 1753383) and NASA MIRO program (NNX15AQ01A).

Oxygen Defect Formation Thermodynamics of CaMnO3: A Closer Look

Sustainable hydrogen production is one of the most important topics in modern energy economics. Of technological relevance are, for example, electrochemical and thermal splitting of water. For such processes anode materials with a variable concentration of oxygen defects are required. Herein, the oxygen defect thermochemistry of a possible anode material, the perovskite CaMnO3, is investigated theoretically. The aim of this work is to identify reliable quantum chemical methods for the calculation of oxygen defect formation enthalpies and entropies, including configuration entropy, which is usually neglected. All possible defect configurations in a supercell are computed to obtain the configuration entropy using Boltzmann statistics. Various generalized gradient approximation (GGA), meta‐GGA, and hybrid functionals as implemented in the solid‐state programs CRYSTAL and VASP are evaluated for the calculation of structure parameters, electronic and magnetic properties, and reaction energies of CaMnO3. The global hybrid functional PW1PW gives the most accurate overall description of CaMnO3 and is therefore recommended for future theoretical studies of more efficient water‐splitting catalysts based on calcium manganate.

NiO-Based Gas Sensors for Ethanol Detection: Recent Progress

In this review, we summarized the state-of-the-art progress on the ethanol performance of NiO by means of morphology, doping, loading noble metal particles, and forming heterojunctions. We first introduced the effect of modulating NiO morphology on ethanol performance that has been reported in recent years. The morphology with large specific surface area and high porosity was considered to be the one that can bring high gas response. Then, we discussed the enhanced effect of the doping of metal cations and noble metal particle loading on the ethanol-sensitive properties of NiO. Doping ions increased the ground-state resistance and increased the oxygen defect concentration of NiO. The effects of noble metal particles on the performance of NiO included chemical sensitization and electronic sensitization. Finally, the related contents of NiO forming complexes with metal oxides and bimetallic oxides were discussed. In this section, the specific improvement mechanism was discussed first, and then, the related work of researchers in recent years was summarized. At the same time, we presented a reasonable outlook for NiO-based ethanol sensors, imagining future directions.