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An attempt has been made to synthesize a highly stable oxygen-deficient strontium cobaltite {SrCoO3-δ (δ = 5/16)} by decomposition of the sol-gel derived oxalate at 1000°C for 10 h in air. The product corresponds to the rhombohedral Sr6Co5O15 (93 wt%) and spinel cubic Co3O4 (7 wt%) phases at room temperature but displays the perovskite-type cubic structure with a ~ 3.953 Å at 900°C. It serves as an excellent material for separation of oxygen from the air and exhibits high oxygen permeability (JO2) of 3.0 ml/cm2.min at 1000°C for a 1.0 mm thick membrane. The activation energy of the process is found as 22 kJ/mol. Further, both JO2 and conductivity (σ) reveal good correlation with phases present at different temperatures. The system shows (i) reversible phase separation following the reaction SrCoO3-δ →Sr6Co5O15 + Co3O4 and (ii) hysteresis in oxygen permeability upon cooling but remains reusable.

Iron Cobaltite (FeCo2O4) is successfully prepared in a single-phase form via wet-chemical route with assistance from high power (150 W) ultrasound. The synthesis process was further hastened by utilizing the power of uniform microwave heating for solid-state reaction in lieu of conventional heating. We were able to achieve single-phase FeCo2O4 by calcinating sonicated solution at 400 °C for 6 h. The use of these accelerated synthesis techniques could accelerate the nucleation rate, and thus could result in reduction of phase formation temperature/time. This eventually resulted in nanoparticles formation with average particle size of ~ 200 nm. The electrochemical performance of the material was tested in a three-electrode system, with FeCo2O4 compound showing a high specific capacitance of 784 Fg−1 at 2 mVs−1. The electrochemical performance demonstrated by the FeCo2O4 put its candidature as a potential cathode material for supercapacitor application.

We report the electrochemical performance and structural characteristics of porous nanostructured ceramic cathodes for thin-film solid oxide fuel cells (TF-SOFCs) based on yttria-stabilized zirconi...

Comparative experimental studies of the structural and elastic characteristics of the YBaCo4O7 + x and DyBaCo4O7 + x (x = 0, 0.1, 0.2) cobaltite systems reveal their different behavior depending on excess oxygen content x. A relation between structural parameters aav = (a + b/ $$\sqrt 3 $$ )/2 and c and index x is determined, and the nonstoichiometric cobaltites are found to be separated into two phases with different values of x under certain synthesis and heat-treatment conditions. Stoichiometric samples with Y and Dy ions have ortho-rhombic lattice distortions eo = (a – b/ $$\sqrt 3 $$ )/a = –3.9 × 10–3 and eo = –4.1 × 10–3, respectively. These distortions remove frustrations and promote the formation of a long-range magnetic order in the cobalt subsystem. The Y cobaltite exhibits pronounced anomalies of the elastic properties at the magnetic phase transition temperature TN, and only their traces are detected in the Dy cobaltite. The structural distortion disappears in the samples of both series at a small oxygen nonstoichiometry, the frustrations are retained, the further development of a long-range magnetic order is hindered, and the anomalies of the elastic properties at TN are rapidly smeared and disappear. The qualitatively different behavior of the DyBaCo4O7 + x series is likely to be related to the rare-earth-ion-induced magnetic anisotropy.

The synthesis and characterization of thorn-shaped nickel cobaltite nanoparticles (NiCo2O4) via a simple, rapid hydrothermal synthesis method for different reaction durations of 7 h and 14 h, denoted as NCo-7 and NCo-14, are reported. Scanning and transmission electron microscopy images reveal that the synthesized NiCo2O4 sample shows a thorn-like morphology. Compared to NCo-7, NCo-14 exhibits good capacitive performance, with a large specific capacitance. The NCo-14 electrocatalyst exhibited excellent activity toward the oxygen evolution reaction and electrooxidation of methanol in alkaline medium.

NdCoO3 nanocrystals formed via glycine–nitrate combustion method followed by heat treatment has been systematically studied. Formation of NdCoO3 nanocrystals with minimal size of 7–10 nm from X-ray amorphous combustion products has been elucidated to be a very rapid process, occurring at the temperature of 550–600 °C for 5–30 min. The comparison of the minimum sizes of NdCoO3 crystallites obtained from the offered empirical relation dmin = lunit cell·N (where N is 7–12 and lunit cell is elementary cell parameter) and the data determined on the basis of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed good correlation. The existence of special nanoporous microstructure and spatial limitations prevent NdCoO3 particle growth. The kinetic equation based on Avrami–Erofeev nucleation model was offered to be correlated well with experimental data of fractional conversion (α) versus isothermal time (τ). The apparent activation energy (Ea = (338 ± 32) kJ) of formation of NdCoO3 nanocrystals from X-ray amorphous combustion products obtained in excess of oxidant followed by heat treatment at 550–600 °C was determined.

New nanocomposite electrode material of rGO/MnCo2O4 was freely loaded on flexible substrate on nickel foam and prepared by a simple, cost-effective, and eco-friendly pathway. The results show that the spinel manganese cobaltite (MnCo2O4) with reduced graphene oxide (rGO) nanocomposite forms a uniform deposit and densely covers on the nickel foam (NF). The electrochemical measurements were investigated in three methods, such as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The synergistic effects from rGO and MnCo2O4 deliver outstanding an excellent electrochemical performance that was not realized by any of these components alone. The electroactive material exhibits a high specific capacitance of Csp = 808 F/g at 2 mV/s in 1 M KOH solution. Furthermore, this device delivers an excellent power density of P = 7658 W/kg and a high energy density of E = 15.2 Wh/kg. More importantly, cycling retention is 135% after 1000 charge/discharge cycles. This study proposes that the as-prepared (rGO/MnCo2O4)/nickel foam has a potential application and a promising candidate for energy storage devices.

Developing cost-effective and more efficient nanocatalysts for the treatment of organic pollutants from process industry is always challenging for the researchers working in the field of chemistry, chemical, energy and environment engineering. In this work, a cost-effective and more efficient nanocatalysts, i.e., Nickel Cobaltite nanocomposites and its Lanthanum (La) doped derivatives with controlled surface morphology has been synthesized at 393.15 K through single step sol–gel method. The surface morphology, chemical composition, and crystal structure of the synthesized nanocomposites were analysed by scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and X-rays diffraction (XRD), respectively. The rough surface and well-crystallized metallic nanocomposites confirm the successful synthesis of nanocatalysts. The molar ratio of Lanthanum to Cobalt (Lax:Coy) showed a significant influence on the surface morphology and catalytic activity (Kapp = 0.15–0.47 min−1) of the products. Synthesized nanocomposites showed high catalytic activity for the reduction of methylene blue under solar irradiation. Photocatalytic results for the reduction of methylene blue show that the catalytic activity of synthesized nanocatalysts increases with the increase in the doping concentration of Lanthanum.

The present study is focused on synthesis and sintering of calcium cobaltite (Ca3Co4O9) by solid-state reaction of calcium carbonate (CaCO3) and cobalt oxide (Co3O4) using microwave heating at 850, 900, and 950 °C. Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) results show a weight loss of ~26% due to the decomposition of CaCO3 in the temperature range of 600–820 °C, resulting into single phase of Ca3Co4O9 which remains stable up to 920 °C. The Ca3Co4O9 phase is observed in samples heated at 850 °C and 900 °C, whereas at 950 °C, Ca3Co4O9 is transformed to Ca3Co2O6 as identified by X-Ray Diffractometry. 98.76% of relative density is obtained by microwave sintered sample at 950 °C with 1hr holding time. Changes in synthesis temperature did not show any effect on the Seebeck coefficient (119–155 μV/K). The specimens sintered at 900 °C exhibit a low resistivity (150-160 μΩ-m) and better power factor (94–145 μW/mK2) in the 35–500 °C temperature range.

A phase-heterogeneous ceramic based on layered calcium cobaltite Ca3Co4O9+δ was prepared by solid-phase reactions followed by hot pressing. The phase composition, microstructure, electrical conductivity, and thermoelectromotive force (thermo-emf) of the ceramic were studied, and the power factor (P) was calculated. Hot pressing allows preparation of a high-density ceramic with high electrical conductivity, and the phase heterogeneity considerably increases its thermo-emf coefficient, which in total can be considered as a procedure for preparing a ceramic with improved thermoelectric characteristics. The ceramic of the nominal composition Ca3Co4.4O9+δ, containing an impurity Co3O4 phase, has the highest power factor (P1100 = 427 μW m–1 K–2), which is 1.5 times higher than that of Ca3Co4O9+δ (P1100 = 280 μW m–1 K–2) and more than 4 times higher than that of the low-density ceramic Ca3Co4O9+δ prepared by the traditional solid-phase method.

The processes of gadolinium ferrite and gadolinium cobaltite vaporization was studied. It was shown that the predominant components of vapor are atomic iron and cobalt, which are characteristic for the vaporization of individual iron and cobalt oxides, respectively. The activities of iron and cobalt oxides in GdFeO3 and GdCoO3 were determined.

Recently Ni–Co mixed oxide nanoparticles have received tremendous attention for their application potential in electrochemical devices, biosensing, and biomedical treatments. However, the biomedica...

Zero thermal expansion (ZTE) materials are highly desired in modern industries where high-precision processing is necessary. However, ZTE materials in pure form are extremely rare. The most widely used are Invar alloys, where the ZTE is intimately associated with spontaneous magnetic ordering, known as the magnetovolume effect (MVE). Despite tremendous studies, there is still no consensus on the microscopic origin of MVE in Invar alloys. Here, we report the discovery of room-temperature isotropic ZTE in a pure-form cobaltite perovskite, A-site disordered La0.5Ba0.5CoO3-x. The temperature window of the anomalous thermal expansion shows large tunability by simply altering the oxygen content, making this material a promising candidate for practical applications. Furthermore, we unveil with compelling experimental evidence that the ZTE originates from an isostructural transition between antiferromagnetic large-volume phase and ferromagnetic small-volume phase, which might shed light on the MVE in Invar alloys.

In this study, nickel cobaltite/mesoporous carbon composites are synthesized by reacting CoCl2, Ni (NO3)2 and nitric acid-treated biogas slurry mesoporous carbon using urea as hydrolyzing agent and hexadecyltrimethylammonium bromide (CTAB) as surfactant. The presence of Ni, Co, C and O peaks in the EDX results confirm that the composites are successfully synthesized. Interestingly at 350 °C, the composite surface morphology switched to cross-linked nanoflake structures interconnected with mesoporous carbon. The X-ray diffraction analysis of the NiCo2O4/mesoporous carbon composites reveals that the spinel structure of the NiCo2O4 is maintained in the composites. The nitrogen uptake increases with increasing annealing temperature to 300 °C then decreases at higher temperature (400 °C). The type IV isotherms are exhibited by all the composites. The contribution of mesopores increases with increasing annealing temperature: 32% for BC-NCo-200, 41% for BC-NCo-250, 56% for BC-NCo-300, 66% for BC-NCo-350 and 86% for BC-NCo-400. The NiCo2O4/mesoporous carbon composites exhibit high specific capacitance of 835 F g−1 at scan rate of 5 mV s−1 for sample annealed at 350 °C. The cyclic stabilities of the electrodes are above 90% after 50,000 cycles indicating that the synthesized composites are suitable candidates for supercapacitors.

Lithium-ion transport in cathodes, anodes, solid electrolytes, and through their interfaces plays a crucial role in the electrochemical performance of solid-state lithium-ion batteries. Direct visualization of the lithium-ion dynamics at the nanoscale provides valuable insight for understanding the fundamental ion behaviour in batteries. Here, we report the dynamic changes of lithium-ion movement in a solid-state battery under charge and discharge reactions by time-resolved operando electron energy-loss spectroscopy with scanning transmission electron microscopy. Applying image denoising and super-resolution via sparse coding drastically improves the temporal and spatial resolution of lithium imaging. Dynamic observation reveals that the lithium ions in the lithium cobaltite cathode are complicatedly extracted with diffusion through the lithium cobaltite domain boundaries during charging. Even in the open-circuit state, they move inside the cathode. Operando electron energy-loss spectroscopy with sparse coding is a promising combination to visualize the ion dynamics and clarify the fundamentals of solid-state electrochemistry., Understanding lithium ion dynamics holds the key to unlocking better battery materials and devices. Here, by combining electron energy-loss spectroscopy and machine learning, the authors reveal how lithium is extracted from LiCoO2 cathode used in a solid-state battery.

A scheme is proposed to describe the spin state of the Co3+ ions in the layered TbBaCo2O5.5 cobaltite near the metal–insulator transition. The spin state of the Co3+ ions in the metallic phase corresponds to a mixture of the HS( $$t_{{2g}}^{4}$$ $$e_{g}^{2}$$ , S = 2) and LS( $$t_{{2g}}^{6}$$ $$e_{g}^{0}$$ , S = 0) states taken at approximately the same proportion. The transition into a nonmetallic state occurs due to the transformation of the HS state into the LS state in octahedra and part of the LS state into the IS( $$t_{{2g}}^{5}$$ $$e_{g}^{1}$$ , S = 1) state in pyramids (near TC ~ 280 K). The proposed scheme agrees with the well-known structural data obtained for the TbBaCo2O5.5 cobaltites. As follows from volumetric and linear expansion, the transition takes place over a wide temperature range T ≈ TMI ± 50 K. The study of thermal expansion shows that an LS/IS state is retained down to T = 80 K.

Mixed transition metal oxides have attracted great attention in supercapacitors applications due to their better electrochemical performance than their single oxides. In this work, iron cobaltite (FeCo2O4) and its single metal oxides i.e. iron oxide (Fe2O3) and cobalt oxide (Co3O4) were synthesized by a simple hydrothermal process. The structural, spectroscopic and morphological properties were studied using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and field-emission scanning electron microscope (FESEM). XRD and FTIR results show the composition of the products. The obtained iron oxide was α-Fe2O3. FESEM images show that FeCo2O4 and its single metal oxides exhibit different morphology even though they were synthesized via similar method. The electrochemical properties of the α-Fe2O3, Co3O4 and FeCo2O4 electrodes were examined by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) in a 6 M KOH electrolyte solution. At comparable current density, the FeCo2O4 electrode has the highest specific capacitance (Csp), followed by Co3O4 and α-Fe2O3. An asymmetric FeCo2O4/KOH/GO supercapacitor was fabricated. The supercapacitor exhibits maximum energy density of 14.5 Wh kg−1 and maximum power density of 2177 W kg−1. It demonstrates 60% rate capability after 1000 continuous charge-discharge cycles at 1 A g−1.

Nickel cobaltite composite electrodes were fabricated by a fast, scalable, and cost-effective electrophoretic deposition for supercapacitor applications. NiCo2O4/PANI/rGO composite electrode went t...

Conventional inorganic p-type conductive oxides, for example, NiO, CuOX, and CuCrOX, can serve as low-cost and efficient hole transport materials for wide-bandgap organolead halide perovskites [for...

It is shown that interlayer electron tunneling in the quasi-two-dimensional ensemble of Hubbard fermions leads to the realization of the gapless superconducting phase with the chiral (d + id)-wave order parameter symmetry, not for a single value of sodium ion concentration, but in a wide range of concentrations. Precisely this situation corresponds to experimental data on the layered sodium cobaltite intercalated by water (NaxCoO2 ⋅ yH2O). Intra-atomic electron repulsion that determines the strong electron correlation regime leads to the representation of Hubbard fermions, the interaction of which ensures Cooper instability. Intersite intralayer interactions between fermions considerably affect the positions of nodal points of the chiral order parameter and change the critical concentration at which a topological transition occurs in the 2D system of Hubbard fermions.

Half doped cluster glass compound Eu0.5Sr0·5CoO3 is prepared in polycrystalline form and is characterized by using x-ray diffraction, x-ray absorption spectroscopy, x-ray photoelectron spectroscopy and magnetization studies. The magnetic properties of this compound have been reinvestigated using DC magnetization studies. Magnetization versus Temperature (M-T) measurements revealed that the sample is ferromagnetic below 110 K with an additional transition observed around 230 K, which has not been reported in the previous studies on this compound. After analyzing the 1/M versus temperature data, the new transition was attributed to the onset of short range ferromagnetic interactions in the sample at ~230 K. Based on magnetization versus applied magnetic field (M − H) measurement, the sample has been projected as a coexistent state of ferromagnetic and antiferromagnetic clusters below 110 K. In view of the coexistent magnetic state, the possibility of the presence of exchange bias in the system has also been explored and it was established that this compound exhibits a negative exchange bias of about −4683Oe, making it technologically important.

Herein, we report a facile regulation of the interface of two immiscible solvents, n-butanol and water, to achieve the physicochemical tuning of the transition-metal oxide nickel cobaltite. The crystal nucleation and the growth of nickel cobaltite into distinct morphology are highly dependent on the orientation and the mass transfer of the reactive species through the reactive interface layer. A distinct two-dimensional flakelike (1 nm thickness) nickel cobaltite is formed at the interface of n-butanol/water in a 1:1 solvent ratio. Rather, one-dimensional needles and irregular interconnected networks are achieved, as aqueous and organic counterparts are, respectively, increased. The impact of the solvent ratio on doping metal ions (Co2+ and Ni2+) at the interstitial sites of fcc spinel structure is evident from the X-ray and electronic absorption investigations. It is presumed that the interface-assisted synthesis may provide a simple and novel way to develop and adopt various transition-metal oxides for wide applications.

7 Figures, 2 Tables.-- This article also appears in: Giornate dell’Elettrochimica Italiana (GEI 2019)., Transition‐metal‐based materials are among the most active and durable catalysts for the effective electrocatalysis of oxygen‐related reactions. Herein, we present a study on bifunctional catalysts as air electrodes aimed at metal‐air batteries based on nickel and cobalt spinel (NiCo2O4) supported on electrospun carbon nanofibers. The physicochemical features of these transition‐metal‐based catalysts are essential for the understanding of their electrochemical activity. Results show that the major presence of oxidized Ni and Co species (Ni3+ and Co3+) produces higher activity for the oxygen evolution reaction (OER), whereas lower oxidation states of the metals (Ni2+, Co2+, Ni0 and Co0) together with the presence of N‐doped carbon lead to enhanced oxygen reduction reaction (ORR) performance. This study highlights the importance of designing catalysts in terms of crystallographic structure and proper oxidation states of the elements for maximizing their performance., The research leading to these results has received funding from the “Accordo di Programma CNR‐MiSE, Gruppo tematico Sistema Elettrico Nazionale e Progetto: Sistemi elettrochimici per l′accumulo di energia”.

A unique single step method has been evolved for the formation of nickel cobalt binary hydroxide [(Ni-Co)(OH)2] floating film of thickness about 541 nm on the surface of precursor solution by purging NH3 gas over it. Then by transferring the as formed film on a glass substrate, it got transformed into the nickel cobaltite (NiCo2O4) film after its calcination at 300 °C. In this very unique and distinct approach the hierarchical porous interlaced 3-D nanostructured films of two different materials (Ni-Co)(OH)2 and (NiCo2O4) have been formed simultaneously using a single precursor solution. The transferability and uniform film thickness by and large have also been observed as additional features of this technique.

Spinel Nickel cobaltite oxide (NiCo2O4) have received great interest due to its usage in several industrial applications. The motivation of the present study is to explore the usefulness of spinel Nickel cobaltite oxide as inorganic charge transporting layer for standard perovskite solar cells (PSCs). This is the first demonstration of successful use of NiCo2O4 nanoparticles as hole transporting layer (HTL) in standard PSCs with the triple cation perovskite material. The synthesis of nanoparticles was done using a facile chemical precipitation method without the use of surfactant. The synthesized nanoparticles were characterized by the various techniques like X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Field emission scanning electron microscopy (FE-SEM), and UV–vis spectroscopy (UV–vis). The co-ordination of Ni in Co3O4 matrix, as well as M+n O bond lengths, were confirmed by the XAS studies. The standard mesoporous PSCs were fabricated by spin-coating a thin layer of NiCo2O4 (120 nm), and fabricated PSCs show an esteemed power conversion efficiency (PCE) of >14% (under standard illumination conditions) and long-term stability (under ambient condition RH = 30–40%) as compared to the spiro-based PSCs. To improve the device performance further we also fabricated the PSCs using the interfacial hole transporting layer, presenting a PCE of >16% with almost negligible hysteresis that is comparable to the normal standard PSCs based on spiro-OMeTAD as HTL. The performance of PSCs was further analysed by Electrochemical Impedance Spectroscopy (EIS), Photoluminescence (PL), Time-resolved Photoluminescence (TrPL) studies. The results showed the reduced recombination resistance in the PSCs using NiCo2O4 as well as interfacial layer. These outcomes indicate the effectiveness of NiCo2O4 interlayer for stable and highly efficient perovskite solar cells.

The exploration of efficient and cost-effective cathodes for flexible hybrid supercapacitors (HSCs) and microbial fuel cells (MFCs) is highly desirable but challenging. Benefiting from the strong points of abundant sources, low price and respectable theoretical capacity, nickel cobaltite (NCO) has a wide applicable prospect as a cathode for flexible HSCs and MFCs. Nevertheless, the capacity, rate capability and oxygen reduction reaction (ORR) activity of the NCO are far from ideal due to its intrinsic weak conductivity. Herein, a feasible and valid method is employed to modify NCO nanowires (NWs) as a high performance cathode for flexible HSCs and MFCs via introducing phosphate ions and oxygen defects. Due to the larger surface, more active sites and faster charge transfer, the assembled flexible HSC device delivers a high energy density of 211 W h kg−1, and the MFC device achieves a power density of 3276.1 mW cm−2. This work may shed light on the modulation of phosphate ions and oxygen defects in enhancing the electrochemical performance of metal oxide electrodes, holding great potential for future flexible multifunctional electrodes.

Novel divalent Co(II), Ni(II) and Zn(II) Schiff base complexes have been synthesized by reacting a prepared Schiff base (H2L, 2-(ethoxycarbonyl-hydrazono)-pentanedioic acid) with metal salts. Ligand H2L was prepared through condensation of α-ketoglutaric acid with ethyl carbazate. Solid solutions [Ni1/3Co2/3(HL)2] and [Zn1/3Co2/3(HL)2] were prepared by performing the reaction with stoichiometric proportions of metal ions. The crystal structures of metal (Co and Zn) and mixed metal (Ni–Co and Zn–Co) complexes were isomorphic and crystallized in a monoclinic system of space group C2/c. Interestingly, prepared solid solutions were employed as precursors for producing nanospinels such as nickel cobaltite (NiCo2O4) and zinc cobaltite (ZnCo2O4). As-synthesized spinel cobaltite nanoparticles (NPs) were characterized by Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HR-TEM) techniques. PXRD revealed a predominant spinel-type structure with a crystalline nature and high purity. Lattice parameters were calculated to be 8.1120 A for NiCo2O4 and 8.1178 A for ZnCo2O4. The morphology studies (by FESEM and HRTEM) revealed that the spinels were built by self-assembled aggregation of NPs with irregular shapes. Based on the TEM and HRTEM images, the mean sizes of the NPs synthesized by as-prepared solid solutions were 22–24 nm for NiCo2O4 and 16–18 nm for ZnCo2O4. In addition, photocatalytic degradation activity was evaluated using rhodamine dyes in visible light. Surprisingly, nanospinels employed as electrode materials showed a good specific capacitance Csp of 115 F g−1 (NiCo2O4), 177 F g−1 (ZnCo2O4) at a 0.25 A g−1 current density. Furthermore, the as-prepared nanospinels showed desirable stability in alkaline electrolyte with excellent cycling performance.

Cobaltite systems with spinel-type structures and Ni-based sulfides are deemed to be practical and promising water oxidation electrocatalysts because of their low cost, intrinsically admirable electroconductivity and predominant durability. However, most electrocatalysts still suffer from the challenge of an increase in the loading of active materials without sacrificing the geometry area. In this work, a CoFe2O4@Ni3S2/NF composite was achieved through a series of hydrothermal and annealing processes by means of constructing a vertically stacked bilayer heterostructure CoFe2O4@Ni3S2 on a 3D porous nickel foam (NF). The structure and morphology of the as-synthesized catalyst have been characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. The as-obtained CoFe2O4@Ni3S2/NF electrode, which possesses a vertically stacked bilayer nanosheet heterostructure, displays an improved OER performance and cyclic stability and shows an early onset potential with a low overpotential (231 mV at 10 mA cm−2) in a 1.0 M KOH solution. In addition, CoFe2O4@Ni3S2/NF demonstrates dependable durability and delivers outstanding current density of ∼15 mA cm−2 without activity degradation for 20 h. This approach provides a new insight into developing earth-abundant, low-cost and high-efficiency OER electrocatalysts.

Cobaltite oxides, like Ba(La)CoO3, are very promising candidates as cathode materials for solid oxide fuel cells and electrolysers (SOFCs and SOECs). Lattice distortions have been shown as a promising approach to improve cathodic properties. To investigate this possible approach, biaxial strain is induced on model systems, i.e. through the epitaxial growth of barium lanthanum cobaltite on single crystalline substrates. The influence of strain on the oxidation state of cobalt is probed through energy electron loss spectroscopy. XRD measurements indicate that films with biaxial compressive strain exhibit a larger unit cell volume. Electron energy-loss spectroscopy (EELS) shows that biaxial compressive strain induces a higher Co2+/Co3+ ratio, probably enabled through the larger ionic radius of Co2+. Electrical conductivity relaxation measurements reveal that the activation energy for the surface exchange is decreased with the increasing amount of Co2+. This strongly indicates the connection between the unit cell volume, the oxidation state of cobalt, and the surface exchange kinetics of Ba(La)CoO3. An improved understanding of the fundamental kinetics in cathode materials for SOFCs is important for further materials development.

In this study, quasi-spherical copper cobaltite (CCO) with diameters in the range of 18.63 to 23.19 nm was produced by solvothermal method using ethylene glycol as solvent. XRD analysis revealed that all samples have spinel structure. Addition of CTAB effectively lowered the particle size to about 18.63 nm, successfully hindering growth in solution. Consequently, these particles exhibited excellent electrocatalytic OER activity in alkaline medium. The onset overpotential and overpotential at 10 mA/cm2 were about 210 and 360 mV, respectively. This performance is attributed to the low particle size of the particles that could expose more active sites for effective ion and electron transfer processes during OER

The temperature dependences of the specific heat capacities of nanosized samples of lanthanum magnesium cobaltite cuprate manganite LaMgCoCuMnO6 and lanthanum magnesium nickelite cuprate manganite LaMgNiCuMnO6 are studied via calorimetry in the temperature range of 298.15–673 K. Curve $$C_{p}^{ \circ }$$(T) shows that LaMgCoCuMnO6 and LaMgNiCuMnO6 undergo second-order phase transitions at 398 and 523 K, respectively. The standard specific heat capacities of the above compounds are calculated with independent means based on characteristic Debye temperatures determined via the Koref and Nernst–Lindemann equations. Their values agree satisfactorily with experimental data. The temperature dependences of functions S°(T), H°(T) – H°(298.15), and Фхх(T) are calculated.

Nickel cobaltite has become a popular energy storage material in recent years for high performance energy storage devices because of its low lost, high electronic conductivity, high electrochemical activity and environmental benignity. Nickel cobaltite (NCO)/porous graphene nanosheets network (PG) composites were synthesized via the two-steps hydrothermal method to enhance electrochemical properties in this study. The NCO/PG composite electrode demonstrated high specific capacitance of 3965 F g-1 at the current density of 1 A g-1 compared with the value of NCO that capacitance is 644 F g-1, and it maintained the 72% of the original capacitance after 3,000 charge-discharge cycles. It showed the maximum energy density of 46.3 Wh kg-1 and maximum power density of 1450 W kg-1. The NCO/GO composite has high potential as a psudocapacitance material for energy storage devices.

Oxygen vacancy (OV) manufacturing is an effective way to boost the efficiency of a catalyst; therefore, the development of OV-rich catalysts has attracted substantial research interest. Herein, the authors report the engineering of highly efficient NiCo2O4 nanostructures (OV–NCO) with plentiful oxygen vacancies. The presence of OV was confirmed by X-ray photoelectron microscopy (XPS) and electron spin resonance spectroscopy (ESR). Impedance analysis confirmed that oxygen vacancy manufacturing in the NCO lattice meaningfully promotes the interfacial electron transferability. As a result, OV–NCO could deliver improved electrocatalysis significantly. Furthermore, OV–NCO was used to fabricate a highly efficient and dependable nonenzymatic electrochemical H2O2 detector that achieved excellent sensing performance owing to the oxygen vacancy richness, high specific surface area and synergistic effects of OV–NCO. The sensor not only exhibited a wide linear response (26–6.6 mM) with a nanomolar limit of detection (9 nM) but also a high selectivity for H2O2. The practicability of this resultant sensor was verified by real-time monitoring of H2O2 release from RAW 264.7 cells, confirming the potential application of this biosensor in clinical analysis.

The spinel nanostructured nickel cobaltite (NiCo2O4) with different morphologies has been successfully synthesized via facile surfactant assisted hydrothermal route. Tri-ethanolamine ethoxylate (TEA-ethoxylate) and PEG-600 were used as surfactants. The synthesized samples were characterized using various physicochemical techniques and were further used for fabrication of electrode for supercapacitor application. The effect of reaction temperature and surfactant on typical morphology of product and their electrochemical properties has been explored. The morphological features of as-synthesized samples were studied by Field emission scanning electron microscopy (FESEM). The surface area, pore volume and pore diameter were estimated by BET-BJH surface area analysis. The dandelion-like morphology of nickel cobaltite showed the highest surface area (58.76 m2 g−1) with uniform porosity. This morphology provides numerous electrochemical active sites for high electrochemical performance and resulted into the high specific capacitance (479 Fg−1 at scan rate 5 mVs−1) with high energy density (21.3 Whkg−1) and power density (150 Wkg−1).

This dissertation is dedicated to the growth and investigation of La1-xSrx(Mn1-yCoy)zO3 (x = 0.20 ± 0.02; z = 1.15) (LSMCO) films. LSMCO films were grown by the pulsed-injection metalorganic chemical vapor deposition method (PI-MOCVD) at a deposition temperature of 750 oC. The structural, electrical, and magnetic properties were measured for thin LSMCO films exhibiting manganese nonstoichiometry and difference in cobalt content ranging from 0 to 0.17. LSMCO films grown on LaAlO3 substrates were epitaxial, while nanostructured films formed on sapphire-R and Al2O3 substrates. Structural studies have revealed that epitaxial LSMCO films are characterized by tensile and compressive stresses depending on the cobalt content. Meanwhile, only tensile stresses were found in nanostructured LSMCO films. The performed electrical measurements showed that the phase transition temperature determined for epitaxial and nanostructured LSMCO films decreases with increasing cobalt content in the film. The influence of cobalt on the magnetoresistive properties of both epitaxial and nanostructured LSMCO films has also been evaluated, as it is relevant for the application of magnetic sensor design. The results of structural, electrical and magnetic studies showed that the chemical composition determines the properties of LSMCO films, so the properties of LSMO (La1-xSrxMnzO3) and LSMCO were compared. Structural, electrical, and magnetic studies for the LSMO and LSMCO films revealed that changes in epitaxial films were Mn-dependent, whereas changes in nanostructured films were related to cobalt content. A hybrid prototype sensor composed of a three-layered graphene and LSMCO film was also developed during this work to measure the magnetic field at room temperature over a wide magnetic field range (0.1–20 T).

[EN] Bi2Ca2−xNaxCo2Oy materials with x = 0 ≤ x ≤ 0.125, have been prepared either by sintering through the classical ceramic method, or textured using the laser floating zone technique. XRD results have shown that Bi2Ca2Co2Oy phase is the major one, independently of the Na content, in both kind of samples. SEM studies have shown a drastic microstructural modification between sintered and laser-textured materials. Na-doping increases density and grain sizes in sintered materials, while it enhances grain alignment in laser-grown materials. Moreover, it decreases secondary phase content in all cases. Electrical resistivity is also drastically reduced through texturing, when compared to the sintered samples, and Na-doping further decreases it. The lowest values determined in the laser-textured samples (26 mΩ cm at 650 °C) are around 40% lower than the best in sintered materials. On the other hand, S has been only slightly affected for Na-doping or processing method for all samples. Consequently, the highest power factor at 650 °C (0.18 mW/K2 m) has been obtained in laser-grown 0.075Na-doped samples, which is around 20 and 70% higher than the measured in undoped laser-textured samples, and sintered ones, respectively., [ES] Se han preparado materiales de composición Bi2Ca2-xNaxCo2Oy, con x = 0 ≤ x ≤ 0,125, por el método de estado sólido, además de texturarlos mediante la técnica de zona flotante inducida por láser. Los resultados de XRD han mostrado que la fase Bi2Ca2Co2Oy aparece como la mayoriraria, independientemente del contenido de Na, en ambos tipos de muestras. Los estudios SEM han encontrado una drástica modificación microestructural entre materiales sinterizados y texturados. El dopado con Na aumenta la densidad y el tamaño de grano en materiales sinterizados, mientras que mejora la orientación de los granos en materiales texturados. Además, disminuye el contenido de fases secundarias en todos los casos. La resistividad eléctrica disminuye drásticamente con el texturado, en comparación con las muestras sinterizadas, mientras que el dopado con Na la disminuye aún más. Los valores más bajos determinados en muestras texturadas (26 mΩ cm a 650 °C) son alrededor del 40% menor que los mejores datos publicados en materiales sinterizados. Por otro lado, S solo se ha visto afectado levemente, tanto por el dopado como por el método de procesado. En consecuencia, el máximo factor de potencia a 650 °C (0,18 mW/K2 m) se ha obtenido en muestras dopadas con 0,075 Na y texturadas, que es alrededor de un 20 a un 70% superior al medido en muestras texturadas sin dopar y sinterizadas, respectivamente., This study was carried out within the scope of Cukurova University Scientific Research Projects Unit FBA-2020-13007. The authors wish to thank the Spanish MINECO-FEDER (MAT2017-82183-C3-1-R), and Gobierno de Aragón (Research Group T 54-20 R) for funding. The authors wish to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza.

The effect of K substitution for Ca in Bi2Ca2-xKxCo2Oy (x = 0.0, 0.05, 0.075, 0.10, and 0.125) thermoelectric ceramics, produced via laser floating zone (LFZ) method, have been systematically investigated. XRD patterns are quite similar for all samples and main peaks in the patterns correspond to reflection planes of the thermoelectric phase together with small amount of secondary phases. SEM micrographs revealed well oriented grains along the growth direction, and the presence of three different contrasts, associated through EDS to different phases, namely, black (Co oxide), white (Bi poor phase) and grey (Bi2Ca2Co1.7Oy TE phase). It was also seen that the amount of secondary phases diminishes with K-increase. The room-temperature resistivity values sharply decrease from 0.75 mΩ.m for the undoped sample to 0.44 mΩ.m for the 0.05 K-doped one, increasing for higher doping. Seebeck coefficient also decreases from 190 μV K−1 in the pristine sample, to 160 μV K−1 in all the K-doped ones, at 390 K. Thermal conductivity increases with temperature up to around 250 K, decreasing at higher temperatures. Thermal conductivity at 390 K decreases from 1.1 W K−1 m−1 in the pristine sample to lower values by K-doping, reaching the minimum, 0.9 W K−1 m−1, in the 0.125 K-doped one. As a result, the highest ZT value of has been determined in 0.05 K-doped sample, around 0.021 at 390 K., This study was carried out within the scope of Cukurova University Scientific Research Projects Unit FBA-202114163, FBA-2020-12784, FBA-2022-14414. The authors wish to thank the Spanish MINECO-FEDER (MAT2017-82183-C3-1-R), and Gobierno de Aragón (Research Group T54-20R) for funding.

In this work, Bi2Ca2-xNaxCo2Oy with x = 0.0, 0.05, 0.10, and 0.125 thermoelectric ceramic materials have been produced by the classical solid-state route, followed by texturing through the laser floating zone (LFZ) method. All specimens showed similar XRD patterns, with the main peaks corresponding to the (00l) plane reflections of the thermoelectric Bi2Ca2Co2Oy phase, independently of Na substitution. In addition, small amount of Co-free Ca4Bi6O13 secondary phase has been identified. SEM micrographs showed that annealing procedure after the texturing process allows obtaining higher proportion of thermoelectric phase, decreasing the number and amount of secondary phases. Electrical resistivity is very similar for all samples at room temperature, about 0.62 mΩ m. However, below 50 K, Na-substitution decreases resistivity when compared to the undoped one, reaching values around 9.41, 6.48, 5.00, and 2.07 mΩ m for x = 0, 0.05, 0.1, and 0.125 samples at 50 K, respectively. Seebeck coefficient values at room temperature decrease from 180 to 145 μV/K, for the pure and 0.125Na doped samples, respectively. Thermal conductivity tends to linearly increase with temperature up to around 200 K, decreasing for higher ones. Thermal conductivity values are slightly higher in undoped samples (1.2 W/K m), when compared to the Na-substituted ones (1.10–1.30 W/K m) at room temperature. Finally, the highest ZT value is around 0.018 at 400 K for the 0.10Na doped samples., This study was carried out within the scope of Cukurova University Scientific Research Projects Unit FBA-2020-13007. A. Sotelo and M. A. Madre wish to thank the Spanish MINECO-FEDER (MAT2017-82183-C3-1-R), and Gobierno de Aragón (Research Group T54-20R) for funding.

The solid-state compatibility between calcium-doped lanthanum niobate and three perovskite cathode materials was investigated using two X-ray microbeam techniques, micro X-ray fluorescence and micro X-ray absorption spectroscopy. The cathode powders (lanthanum strontium ferrite, either cobalt or copper-doped, and lanthanum strontium cobaltite) in contact with the dense electrolyte pellet were annealed at 1150 degrees C for 12-144 h to simulate the effect of thermal stresses due to fabrication and long-term operation. As a result, several interdiffusion phenomena were then observed on the bilayer cross-sections: in particular, the chemical state and coordination environment of calcium, iron, niobium and lanthanum were probed with space-resolved X-ray absorption spectroscopy. The ab initio modeling of the near-edge X-ray absorption spectra reveal that the cation interdiffusion is facilitated by the structural flexibility of the perovskite structure, which is able to accommodate a variety of foreign cations in different oxidation states. Limited stability at high-temperatures was found for all candidate perovskite compositions in contact with lanthanum niobate. (C) 2021 Elsevier Ltd. All rights reserved.

We present results of soft X-ray absorption spectroscopy studies of nonstoichiometric Tb1 ‒ yBa1 +yCo2 –xO5.5 – δ cobaltites and EuBaCo2O5.5 cobaltite powders subjected to mechanical impact (milling in a ball mill). It was established that in octahedra of Tb1 – yBa1 + yCo2 – xO5.5 – δ cobaltates Co3+ ions are in the high spin state. In EuBaCo2O5.5 powder after milling in a ball mill, a surface area (5–10 nm) of particles was found to be decomposed into Co3O4, BaCO3, and EuCoO3 phase components. A knowledge of the low-spin state of Co3+ ions in EuCoO3 and Co3O4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo2O5.5 sample (subjected to ball milling) near its surface, which is inaccessible to standard X-ray phase analysis.

Structural and magnetic behavior of a series of new cobaltite Y1-xYbxBaCo4O7 (0 ≤ x ≤ 0.5), prepared using the conventional solid state reaction method have been investigated. Increasing Yb...

Communicated by Corresponding Member Fedor P. Korshunov A comprehensive study of the crystal structure, magnetic and elastic properties of layered cobaltite Sr 0,8 Y 0,2 CoO 2,65 with a perovskite-type structure was carried out. It is established that the magnetic ordering in this composition is accompanied by a structural transition. The Neel temperature (T N ) is 375 K. The unit cell volume at TN increases as a result of the orbital ordering in the CoO 5 pyramids connected by the vertices in the anion-deficient layers. The main magnetic structure is an antiferromagnetic G-type structure with a small ferromagnetic component. The non-collinear magnetic structure is stabilized by the ferromagnetic bonds between the cobalt ions in the CoO 5 pyramids. Co 3+ ions in the both layers are in the mixed low-spin (LS)/high-spin (HS) state. The temperature dependence of the electrical resistivity has a semiconductor character. The large resistivity value and small magnetoresistance indicate a good stability of the semiconductor antiferromagnetic state of this composition.

In-situ investigations of structural transitions during the thermal-oxidative event of mixed-metal spinel oxide precursors, the so-called nickel- (NCO) and zinc-containing (ZCO) cobaltite spinel precursors, were investigated to understand the formations of the derived NiCo2O4 and ZnCo2O4 spinel oxides, respectively. In-situ XRD investigation revealed that emerged temperatures for spinel oxide phase were between 325 and 400 °C, depending on the cationic substituent. It indicated that the emerged temperature correlated with the absolute octahedral site preference energy (OSPE) of those cations that participated in the development of the spinel framework. Moreover, the incorporated nickel and zinc in the precursors was beneficial for inhibiting the occurrence of the undesired CoO phase. Time-resolved X-ray absorption spectroscopic (TRXAS) data suggested the local structure rearrangement of nickel and zinc throughout the calcination process, which differed from the behavior of single-metal cobalt system. The essential information reported herein provides a benefit to control the cationic distribution within spinel materials, leading to the tunable physical and chemical properties.

We studied structural and magnetic phase transitions under applied pressure for the doped cobaltite ${\mathrm{La}}_{0.75}{\mathrm{Ba}}_{0.25}{\mathrm{CoO}}_{2.9}$. Neutron and x-ray diffraction experiments established the coexistence of rhombohedral and cubic phases in the sample. The magnetic state at 2 K is best described as a long-range ordered antiferromagnet (AFM) with small ferromagnetic (FM) clusters. With application of pressure, the rhombohedral phase gradually transforms into a cubic one. At room temperature and the highest applied pressure of 16 GPa, the cubic phase accounts for 70% of the sample volume. Quantum mechanical modeling confirmed the experimental findings and provided more insights into the structural and magnetic phase transitions at pressures exceeding 16 GPa. While the cubic crystal structure was preserved above 10 GPa, the AFM to FM phase transition was found at around 16 GPa. Further increase of the pressure resulted in suppression of magnetic order above 45 GPa. Using density functional theory (DFT)$+\mathrm{U}$ calculations, we were able to relate macroscopic magnetic properties induced by pressure with corresponding spin-state transitions in Co ions.

In this paper, we report insights into the local atomic and electronic structure of ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ epitaxial thin films and its correlation with electrical, optical, and magnetic properties. We grew structurally well-defined ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ epitaxial thin films with controlled properties on $\mathrm{Mg}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}(001)$ substrates using pulsed laser deposition. Films grown at low temperatures ($l400{\phantom{\rule{0.28em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$) exhibit a ferrimagnetic and metallic behavior, while those grown at high temperatures are nonmagnetic semiconductors. The electronic structure and cation local atomic coordination of the respective films were investigated using a combination of resonant photoemission spectroscopy, x-ray absorption spectroscopy, and ab initio calculations. Our results unambiguously reveal that the ${\mathrm{Ni}}^{3+}$ valence state promoted at low growth temperature introduces delocalized $\mathrm{Ni}\phantom{\rule{0.28em}{0ex}}3d$-derived states at the Fermi level (${E}_{F}$), responsible for the metallic state in ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$, while the $\mathrm{Co}\phantom{\rule{0.28em}{0ex}}3d$-related state is more localized at higher binding energy. In the semiconducting films, the valence state of Ni is lowered and $\ensuremath{\sim}+2$. Further structural and defect chemistry studies indicate that the formation of oxygen vacancies and secondary CoO phases at high growth temperature are responsible for the ${\mathrm{Ni}}^{2+}$ valence state in ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$. The $\mathrm{Ni}\phantom{\rule{0.28em}{0ex}}3d$-related state becomes localized away from ${E}_{F}$, opening a band gap for a semiconducting state. The band gap of the semiconducting ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ is estimated to be $l0.8\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, which is much smaller than the quoted values in the literature ranging from 1.1 to 2.58 eV. Despite the small band gap, its optical transition is $d\text{\ensuremath{-}}d$ dipole forbidden, and therefore, the semiconducting ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ still shows reasonable transparency in the infrared-visible light region. The present insights into the role of ${\mathrm{Ni}}^{3+}$ in determining the electronic structure and defect chemistry of ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ provide important guidance for use of ${\mathrm{NiCo}}_{2}{\mathrm{O}}_{4}$ in electrocatalysis and opto-electronics.

For electrochemical supercapacitors, nickel cobaltite (NiCo2O4) has emerged as a new energy storage material. The electrocapacitive performance of metal oxides is significantly influenced by their morphology and electrical characteristics. The synthesis route can modulate the morphological structure, while their energy band gaps and defects can vary the electrical properties. In addition to modifying the energy band gap, doping can improve crystal stability and refine grain size, providing much-needed surface area for high specific capacitance. This study evaluates the electrochemical performance of aluminum-doped Ni1−xAlxCo2O4 (0 ≤ x ≤ 0.8) compounds. The Ni1−xAlxCo2O4 samples were synthesized through a hydrothermal method by varying the Al to Ni molar ratio. The physical, morphological, and electrochemical properties of Ni1−xAlxCo2O4 are observed to vary with Al3+ content. A morphological change from urchin-like spheres to nanoplate-like structures with a concomitant increase in the surface area, reaching up to 189 m2/g for x = 0.8, was observed with increasing Al3+ content in Ni1−xAlxCo2O4. The electrochemical performance of Ni1−xAlxCo2O4 as an electrode was assessed in a 3M KOH solution. The high specific capacitance of 512 F/g at a 2 mV/s scan rate, 268 F/g at a current density of 0.5 A/g, and energy density of 12.4 Wh/kg was observed for the x = 0.0 sample, which was reduced upon further Al3+ substitution. The as-synthesized Ni1−xAlxCo2O4 electrode exhibited a maximum energy density of 12.4 W h kg−1 with an outstanding high-power density of approximately 6316.6 W h kg−1 for x = 0.0 and an energy density of 8.7 W h kg−1 with an outstanding high-power density of approximately 6670.9 W h kg−1 for x = 0.6. The capacitance retention of 97% and 108.52% and the Coulombic efficiency of 100% and 99.24% were observed for x = 0.0 and x = 0.8, respectively. First-principles density functional theory (DFT) calculations show that the band-gap energy of Ni1−xAlxCo2O4 remained largely invariant with the Al3+ substitution for low Al3+ content. Although the capacitance performance is reduced upon Al3+ doping, overall, the Al3+ doped Ni1−xAlxCo2O4 displayed good energy, powder density, and retention performance. Thus, Al3+ could be a cost-effective alternative in replacing Ni with the performance trade off.

This paper covers a successful growth of nickel cobaltite oxide (NiCo2O4) thin films deposited on glass substrates at 450 °C and treated at 500 °C in air. The prepared samples were investigated by various spectroscopy techniques. First, X-ray diffractogram revealed that all films crystallized in cubic spinel structure with an intense and sharp diffraction peak corresponding to (311) plane. Raman spectra contain four peaks located at about 188, 477, 527 and 670 cm−1 originated from the F2g, Eg, F2g and A1g vibrational modes of NiCo2O4 spinel material, respectively. Second, the optical measurements by depicting the presence of two band gap energies are observed at 1.49 eV and 2.77 eV for annealed sample, respectively. Photoluminescence measurements showed broad peaks in the range of 720–780 nm identified mainly due to defect states. Moreover, the electro-pyroelectric study of these films has been carried out and discussed. Finally, the photocatalytic activity of prepared NiCo2O4 thin film was evaluated for degradation of MB dye which demonstrated 96% degradation rate after 120 min under visible illumination for annealed samples and a mechanism of degradation is indeed proposed.