The practical utility of ternary nickel-cobalt-manganese oxide-supported platinum catalysts for room-temperature oxidative removal of formaldehyde from the air

Formaldehyde (FA), a carcinogenic oxygenated volatile organic compound, is present ubiquitously in indoor air. As such, it is generally regarded as a critical target for air quality management. The oxidative removal of FA under dark and room-temperature (RT) conditions is of practical significance. A series of ternary nickel-cobalt-manganese oxide-supported platinum catalysts (Pt/NiCoMnO4) have been synthesized for FA oxidative removal at RT in the dark. Their RT conversion values for 50 ppm FA (XFA) at 5,964 h-1 gas hourly space velocity (GHSV) decrease in the following order: 1 wt% Pt/NiCoMnO4 (100 %) > 0.5 wt% Pt/NiCoMnO4 (25 %) > 0.05 wt% Pt/NiCoMnO4 (14 %) > NiCoMnO4 (6 %). The catalytic performance of 1 wt% Pt/NiCoMnO4 has been examined further under the control of various process variables (e.g., catalyst mass, flow rate, relative humidity, FA concentration, time on stream, and molecular oxygen content). The catalytic oxidation of FA at low temperatures (e.g., RT and 60 °C) is accounted for by Langmuir-Hinshelwood mechanism (single-site competitive-adsorption), while Mars van Krevelen kinetics is prevalent at higher temperatures. In situ diffuse-reflectance infrared Fourier-transform spectroscopy reveals that FA oxidation proceeds through a series of reaction intermediates such as DOM, HCOO-, and CO32-. Based on the density functional theory simulations, the unique electronic structures of the nearest surface atoms (platinum and nickel) are suggested to be responsible for the superior catalytic activity of Pt/NiCoMnO4.

Defect engineered ternary metal spinel-type Ni-Fe-Co oxide as bifunctional electrocatalyst for overall electrochemical water splitting

Transition metal spinel oxides were engineered with active elements as bifunctional water splitting electrocatalysts to deliver superior intrinsic activity, stability, and improved conductivity to support green hydrogen production. In this study, we reported the ternary metal Ni-Fe-Co spinel oxide electrocatalysts prepared by defect engineering strategy with rich and deficient Na+ ions, termed NFCO-Na and NFCO, which suggest the formation of defects with Na+ forming tensile strain. The Na-rich NiFeCoO4 spinel oxide reveals lattice expansion, resulting in the formation of a defective crystal structure, suggesting higher electrocatalytic active sites. The spherical NFCO-Na electrocatalysts exhibit lower OER and HER overpotentials of 248 mV and 153 mV at 10 mA cm-2 and smaller Tafel slope values of about 78 mV dec-1 and 129 mV dec-1, respectively. Notably, the bifunctional NFCO-Na electrocatalyst requires a minimum cell voltage of about 1.67 V to drive a current density of 10 mA cm-2. The present work highlights the significant electrochemical activity of defect-engineered ternary metal oxides, which can be further upgraded as highly active electrocatalysts for water splitting applications.

FeCoNi molybdenum-based oxides for efficient electrocatalytic oxygen evolution reaction

The search for highly efficient and inexpensive electrocatalysts is crucial to the advancement of environmentally friendly and sustainable energy sources. Here, adopting a one-step hydrothermal method, we have effectively fabricated a self-supported multi-metal molybdenum-based oxide (FeCoNi-MoO4) on nickel foam (NF). In addition to changing the catalyst's microstructure, the introducing of Fe and Co, enhanced its active center count, improved its electronic structure, and in turn reduced the difficulty for high-valence Ni and Fe species to form, which accelerates the oxygen evolution reaction (OER) kinetics by promoting the development of the actual active materials, NiOOH and FeOOH. FeCoNi-MoO4 has outstanding OER performance, requiring just 204 mV overpotentials at 10 mA cm-2 and 271 mV at 100 mA cm-2. Its exceptional OER kinetics at both low and high currents are indicated by a Tafel slope of 50.6 mV dec-1, which is attributed to the combined effect of its multi-metal composition and a higher number of active sites. Moreover, the FeCoNi-MoO4 electrode was operated continuously for over 48 h. Furthermore, the density functional theory (DFT) results demonstrated that the introducing of Fe and Co, which quickens the rate of electron transfer during the electrocatalytic process, improves the ability of oxygen intermediate species to adsorb, and ultimately lowers the overpotential, is responsible for the increased electrocatalytic activity of FeCoNi-MoO4. This work offers hope for further developments in the sector by proposing an efficient approach for creating multi-active electrocatalysts that are stable, economical, and efficient.

Design and synthesis of hierarchical MnO-Fe3O4@C/expanded graphite composite for sensitive electrochemical detection of bisphenol A

Hierarchically nanostructured binary transition metal oxide-based materials with high conductivity and catalytic activity are quite attractive for the electrochemical quantitative detection of environmental pollutants due to their natural abundance, variable oxidation state, and excellent synergies between metal sites. Herein, a new hierarchical MnO-Fe3O4@C/expanded graphite (EG) composite is designed and synthesized through a simple and in situ annealing method with the utilization of bimetallic organic framework (FeMn-MOF)/EG precursor. The synthesized MnO-Fe3O4@C/EG composite possesses a unique hierarchical nanoarchitecture that small-sized bimetallic oxide nanoparticles of 10-40 nm completely encapsulated by amorphous carbon layers of 2-4 nm are uniformly distributed on the EG platform. This distinctive structure combines the advantages of high conductivity, excellent catalytic activity, and strong stability. Resultantly, when it is applied to monitor environmental endocrine disruptors, the sensor exhibits a significant catalytic effect on the electrochemical oxidation of bisphenol A (BPA), inducing an amplified response current. In addition, the sensor shows a wide linear range of 1-50 μM and 50-400 μM for the BPA monitor, giving a sensitivity of 5208.8 and 1641.9 μA mM-1 cm-2, respectively. This study offers a new approach to design hierarchical binary metal oxide-based sensing materials as well as to explore their electrochemical properties and applications for the determination of emerging contaminants.

Three dimensional nickel foam carried sea urchin-like copper-cobalt-cerium cathode for enhanced tetracycline wastewater purification in photocatalytic fuel cell

Photocatalytic fuel cells (PFCs) regarded as a potential sustainable technique, have been broadly reported. In this work, the carbon quantum dot-loaded TiO2 photoanode and sea urchin-like CuCoCe ternary metal oxide cathode materials are successfully synthesized and used to construct PFC systems for efficient tetracycline (TC) degradation (45 mg/L) and simultaneous electricity generation. The results demonstrate that the CQDs-modified TiO2 photoanode has improved absorption intensity in both the UV and visible regions, and the photocurrent density at 1.23 V vs RHE reached 1.31 mA cm-2, which is 1.3 times higher than that of the original TiO2 photoanode. The established PFC system achieves the highest removal ratio of 96.9 % for TC in 60 min with a maximum power density of 0.77 mW cm-2. The PFC system can operate efficiently over a wide pH range (3.0-9.0). Furthermore, quenching experiments and ESR spectra show that the main reactive oxygen species in the degradation process are •O2-, 1O2 and •OH. This study provides meaningful way to develop multiple metal oxides as cathode of PFC system for efficient organic pollutant degradation and energy recovery.

Nitrogen and fluoride co-doped graphdiyne with metal-organic framework (MOF)-derived NiCo(2)O(4)-Co(3)O(4) nanocages as sensing layers for ultra-sensitive pesticide detection

Heteroatom doped graphdiyne (GDY) has been demonstrated to be an effective strategy for achieving outstanding electrochemical properties, including improved electrocatalytic activity, tunable electronic properties and high electronic conductivity, by producing numerous heteroatomic defects as well as active sites. Extensive efforts have been devoted to the issue of single element doping of GDY. Introducing two or more kinds of heteroatoms into GDY materials may create a synergic effect between the co-dopants, thus generating superior electrochemical performance. Nevertheless, little research on multiple elements co-doped GDY, especially in the application of constructing electrochemical biosensor. Herein, nitrogen and fluoride co-doped GDY (N-F-GDY) has been synthesized and employed to combine with NiCo₂O₄-Co₃O₄ hollow multishelled nanocages to establish an ultrasensitive electrochemical biosensor for the assay of pesticide residue. The as-prepared electrochemical biosensor possesses a wide linear range of 0.448 pM-44.8 nM for monocrotophos detection and a low detection limit of 0.0166 fM (S/N = 3).

The Status of Representative Anode Materials for Lithium-Ion Batteries

Since the invention of lithium-ion batteries as a rechargeable energy storage system, it has uncommonly promoted the development of society. It has a wide variety of applications in electronic equipment, electric automobiles, hybrid vehicles, and aerospace. As an indispensable component of lithium-ion batteries, anode materials play an essential role in the electrochemical characteristics of lithium-ion batteries. In this review, we described the development from lithium-metal batteries to lithium-ion batteries in detail on the time axis as the first step; This was followed by an introduction to several commonly used anode materials, including graphite, silicon, and transition metal oxide with discussions the charge-discharge mechanism, challenges and corresponding strategies, and a collation of recent interesting work; Finally, three anode materials are summarized and prospected. Hopefully, this review can serve both the newcomers and the predecessors in the field.

In Situ Reconstruction of Metal Oxide Cathodes for Ammonium Generation from High-Strength Nitrate Wastewater: Elucidating the Role of the Substrate in the Performance of Co3O4-x

In situ electrochemical reconstruction is important for transition metal oxides explored as electrocatalysts for electrochemical nitrate reduction reactions (ENRRs). Herein, we report substantial performance enhancement of ammonium generation on Co, Fe, Ni, Cu, Ti, and W oxide-based cathodes upon reconstruction. Among them, the performance of a freestanding ER-Co₃O_4-x/CF (Co₃O₄ grown on Co foil subjected to electrochemical reduction) cathode was superior to its unreconstructed counterpart and other cathodes; e.g., an ammonium yield of 0.46 mmol h^-1 cm^-2, an ammonium selectivity of 100%, and a Faradaic efficiency of 99.9% were attained at -1.3 V in a 1400 mg L^-1 NO₃^--N solution. The reconstruction behaviors were found to vary with the underlying substrate. The inert carbon cloth only acted as a supporting matrix for immobilizing Co₃O₄, without appreciable electronic interactions between them. A combination of physicochemical characterizations and theoretical modeling provided compelling evidence that the CF-promoted self-reconstruction of Co₃O₄ induced the evolution of metallic Co and the creation of oxygen vacancies, which promoted and optimized interfacial nitrate adsorption and water dissociation, thus boosting the ENRR performance. The ER-Co₃O_4-x/CF cathode performed well over wide ranges of pH and applied current and at high nitrate loadings, ensuring its high efficacy in treating high-strength real wastewater.

·H effectively enhance electrocatalytic nitrogen fixation

Nowadays, most reported ammonia (NH₃) yields and Faradaic efficiency (FE) of electrocatalysts are very low in the field of electrocatalytic nitrogen reduction reactions (NRR). Here, we are reported ·H for the first time in the field of electrocatalytic NRR, which are generated by sulfite (SO₃^2-) and H₂O in electrolyte solutions upon exposure to UV light. The high NH₃ yields can achieve 100.7 μg h^-1 mg_cat^-1, while stability can achieve 64 h and the FE can achieve 27.1% at -0.3 V (vs. RHE) with UV irradiation. In situ Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR), density functional theory (DFT) and ¹H nuclear magnetic resonance (NMR) tests showed that the ∙H effectively lowered the reaction energy barrier at each step of the NRR process and inhibits the occurrence of competitive hydrogen evolution reaction (HER). This explores the path and provides ideas for the field of electrocatalysis involving water.

Modification of glassy carbon electrode with manganese cobalt oxide-cubic like structures incorporated graphitic carbon nitride sheets for the voltammetric determination of 2,4,6 -trichlorophenol

Novel cube-like transition metal oxide embedded on graphitic carbon nitride (MCO@GCN) formed a hybrid composite via hydrothermal assisted sonochemical synthesis. The synthesized composite was examined with various physical characterizations such as morphological SEM, EDX, XRD, and FT-IR spectroscopy. The electrocatalytic activity of MCO@GCN composite was further investigated when used  to modify a glassy carbon electrode (GCE). The electrochemical sensor was investigated using modified MCO@GCN/GCE towards environmental pollutant 2,4,6-trichlorophenol (2,4,6-TCP) detection with at a potential of (+ 0.654 V vs Ag/AgCl) in pH-7. The structural features have favored a high charge transfer ratio with excellent conductivity which showed a low detection limit (LOD) of 0.0068 μM and sensitivity of 23.57 μA·μM^-1·cm^-2 comprising a wide linear working range of 0.01-1720 μM by using differential pulse voltammetry. Besides, the MCO@GCN/GCE displayed excellent selectivity , repeatability, reproducibility, storage, and operational stability. Notably, the proposed MCO@GCN/GCE was validated with different environmental samples (tap, river, and industrial water) with RSD 0.62-2.86% and 96.51-99.66% (n = 3) recovery.

Interior and Exterior Decoration of Transition Metal Oxide Through Cu0/Cu+ Co-Doping Strategy for High-Performance Supercapacitor

Although CoO is a promising electrode material for supercapacitors due to its high theoretical capacitance, the practical applications still suffering from inferior electrochemical activity owing to its low electrical conductivity, poor structural stability and inefficient nanostructure. Herein, we report a novel Cu⁰/Cu⁺ co-doped CoO composite with adjustable metallic Cu⁰ and ion Cu⁺ via a facile strategy. Through interior (Cu⁺) and exterior (Cu⁰) decoration of CoO, the electrochemical performance of CoO electrode has been significantly improved due to both the beneficial flower-like nanostructure and the synergetic effect of Cu⁰/Cu⁺ co-doping, which results in a significantly enhanced specific capacitance (695 F g^-1 at 1 A g^-1) and high cyclic stability (93.4% retention over 10,000 cycles) than pristine CoO. Furthermore, this co-doping strategy is also applicable to other transition metal oxide (NiO) with enhanced electrochemical performance. In addition, an asymmetric hybrid supercapacitor was assembled using the Cu⁰/Cu⁺ co-doped CoO electrode and active carbon, which delivers a remarkable maximal energy density (35 Wh kg^-1), exceptional power density (16 kW kg^-1) and ultralong cycle life (91.5% retention over 10,000 cycles). Theoretical calculations further verify that the co-doping of Cu⁰/Cu⁺ can tune the electronic structure of CoO and improve the conductivity and electron transport. This study demonstrates a facile and favorable strategy to enhance the electrochemical performance of transition metal oxide electrode materials.

Enhanced Oxygen Evolution Electrocatalysis in Strained A-Site Cation Deficient LaNiO3 Perovskite Thin Films

As the BO₆ octahedral structure in perovskite oxide is strongly linked with electronic behavior, it is actively studied for various fields such as metal-insulator transition, superconductivity, and so on. However, the research about the relationship between water-splitting activity and BO₆ structure is largely lacking. Here, we report the oxygen evolution reaction (OER) of LaNiO₃ (LNO) by changing the NiO₆ structure using compositional change and strain. The 5 atom % La deficiency in LNO resulted in an increase of the Ni-O-Ni bond angle and an expansion of bandwidth, enhancing the charge transfer ability. In-plane compressive strain derives the higher d_z² orbital occupancy, leading to suitable metal-oxygen bond strength for OER. Because of the synergistic effect of A-site deficiency and compressive strain, the overpotential (η) of compressively strained L_0.95NO film is reduced to 130 mV at j = 30 μA/cm² compared with nonstrained LNO (η = 280 mV), indicating a significant enhancement in OER.

Nanoporous metal oxide composite materials: A journey from the past, present to future

Along with the progress of porous metal oxides, the development of multi-metal oxide composite materials have received a significant attention in the last few decades owing to the interesting physical and chemical properties of the hybrid oxide nanostructures. Consequently, a large number of national and international articles, communications etc. related to these oxide composites have come to light. This review conveys a comprehensive overview of those nanoporous metal oxide composites, illustrating various synthetic pathways and formation mechanisms for composite oxides based on template and non-templated routes. Also, characteristic properties of the synthesized materials analyzed using various techniques have been discussed systematically here. Moreover, the current review will also focus on a thorough literature survey of significant potential applications of these oxide composites in different fields including catalysis, biosensing, adsorption, energy conversion, toxic chemical removal, solar cell etc. demonstrating the impact of the metal compositions, nanostructures on the performances of the materials. Finally, a brief perspective is mentioned indicating the future prospects of these porous composites. Though, the scope of this review is limited to porous metal oxide composites, the information presented here can be helpful for any researchers working in other emerging fields.

Design of NiO Flakes@CoMoO4 Nanosheets Core-Shell Architecture on Ni Foam for High-Performance Supercapacitors

As typical electrode materials for supercapacitors, low specific capacitance and insufficient cycling stability of transition metal oxides (TMOs) are still the problems that need to be solved. Design of core-shell structure is considered as an effective method for preparation of high-performance electrode materials. In this work, NiO flakes@CoMoO4 nanosheets/Ni foam (NiO flakes@CoMoO4 NSs/NF) core-shell architecture was constructed by a two-step hydrothermal method. Interestingly, the CoMoO4 NSs are vertically grown on the surface of NiO flakes, forming a two-dimensional (2D) branched core-shell structure. The porous core-shell architecture has relatively high surface area, effective ions channels, and abundant redox sites, resulting in excellent electrochemical performance. As a positive electrode for supercapacitors, NiO flakes@CoMoO4 NSs/NF core-shell architecture exhibits excellent capacitive performance in terms of high specific capacitance (1097 F/g at 1 A/g) and outstanding cycling stability (97.5% after 2000 circles). The assembled asymmetric supercapacitor (ASC) of NiO flakes@CoMoO4 NSs/NF//active carbon (AC)/NF possesses a maximum energy density of 25.8 Wh/kg at power density of 894.7 W/kg. The results demonstrate that NiO flakes@CoMoO4 NSs/NF electrode displays potential applications in supercapacitors and the design of 2D branched core-shell architecture paves an ideal way to obtain high-performance TMOs electrodes.

Solution-phase synthesis of transition metal oxide nanocrystals: Morphologies, formulae, and mechanisms

In this review, we provide a broad overview of solution-phase synthesis of transition metal oxide nanocrystals (NCs), including a substantial catalog of published methods, and a unifying classification and discussion. Prevalent subcategories of solution-phase synthesis are delineated and general features are summarized. The diverse morphologies achievable by solution-phase synthesis are defined and exemplified. This is followed by sequential consideration of the solution-phase synthesis of first-row transition metal oxides. The common oxides of Ti, V, Mn, Fe, Co, Ni, Cu, and Zn are introduced; major crystal lattices are presented and illustrated; representative examples are explained; and numerous synthesis formulae are tabulated. Following this presentation of experimental studies, we present an introduction to theories of NC nucleation and growth. Various models of NC nucleation and growth are addressed, and important concepts determining the growth and structure of colloidal NCs are explained. Overall, this review provides an entry into systematic understanding of solution-phase synthesis of nanocrystals, with a reasonably comprehensive survey of results for the important category of transition metal oxide NCs.

Quantitative comparison of bright field and annular bright field imaging modes for characterization of oxygen octahedral tilts

Octahedral tilt behavior is increasingly recognized as an important contributing factor to the physical behavior of perovskite oxide materials and especially their interfaces, necessitating the development of high-resolution methods of tilt mapping. There are currently two major approaches for quantitative imaging of tilts in scanning transmission electron microscopy (STEM), bright field (BF) and annular bright field (ABF). In this paper, we show that BF STEM can be reliably used for measurements of oxygen octahedral tilts. While optimal conditions for BF imaging are more restricted with respect to sample thickness and defocus, we find that BF imaging with an aberration-corrected microscope with the accelerating voltage of 300kV gives us the most accurate quantitative measurement of the oxygen column positions. Using the tilted perovskite structure of BiFeO₃ (BFO) as our test sample, we simulate BF and ABF images in a wide range of conditions, identifying the optimal imaging conditions for each mode. We show that unlike ABF imaging, BF imaging remains directly quantitatively interpretable for a wide range of the specimen mistilt, suggesting that it should be preferable to the ABF STEM imaging for quantitative structure determination.