Search

Abstract Currently, conventional dimethoxymethane synthesis methods are environmentally unfriendly. Here, we report a photo-redox catalysis system to generate dimethoxymethane using a silver and tungsten co-modified blue titanium dioxide catalyst (Ag.W-BTO) by coupling CO2 reduction and CH3OH oxidation under mild conditions. The Ag.W-BTO structure and its electron and hole transfer are comprehensively investigated by combining advanced characterizations and theoretical studies. Strikingly, Ag.W-BTO achieve a record photocatalytic activity of 5702.49 µmol g−1 with 92.08% dimethoxymethane selectivity in 9 h of ultraviolet-visible irradiation without sacrificial agents. Systematic isotope labeling experiments, in-situ diffuse reflectance infrared Fourier-transform analysis, and theoretical calculations reveal that the Ag and W species respectively catalyze CO2 conversion to *CH2O and CH3OH oxidation to *CH3O. Subsequently, an asymmetric carbon-oxygen coupling process between these two crucial intermediates produces dimethoxymethane. This work presents a CO2 photocatalytic reduction system for multi-carbon production to meet the objectives of sustainable economic development and carbon neutrality.

Abstract Anionic redox allows the direct formation of O─O bonds from lattice oxygens and provides higher catalytic in the oxygen evolution reaction (OER) than does the conventional metal ion mechanism. While previous theories have predicted and experiments have suggested the possible O─O bond, it has not yet been directly observed in the OER process. In this study, operando soft X‐ray absorption spectroscopy (sXAS) at the O K‐edge and the operando Raman spectra is performed on layered double CoFe hydroxides (LDHs) after intercalation with [Cr(C2O4)3]3−, and revealed a three‐step oxidation process, staring from Co2+ to Co3+, further to Co4+ (3d6L), and ultimately leading to the formation of O─O bonds and O2 evolution above a threshold voltage (1.4 V). In contrast, a gradual oxidation of Fe is observed in CoFe LDHs. The OER activity exhibits a significant enhancement, with the overpotential decreasing from 300 to 248 mV at 10 mA cm−2, following the intercalation of [Cr(C2O4)3]3− into CoFe LDHs, underscoring a crucial role of anionic redox in facilitating water splitting.

Highlights The acid etching Co-naphthalenedicarboxylic acid-based metal–organic frameworks (donated as AE-CoNDA) catalyst displayed an excellent oxygen evolution reaction (OER) activity for long-term stability. Integration of the AE-CoNDA cocatalyst into BiVO4 achieved a remarkable PEC-OER activity. The stretched Co-O bond length regulated the spin state transition at the Co active sites. The optimized high spin state of Co sites adjusted the orbitals hybridization of Co 3d and O 2p.

Abstract Ruthenium (Ru) is a promising electrocatalyst for the hydrogen evolution reaction (HER), despite suffering from low activity in non‐acidic conditions due to the high kinetic energy barrier of H2O dissociation. Herein, the synthesis of carbon nanosheet‐supported RuP/Ru heterostructures (RuP/Ru@CNS) from a natural polysaccharide is reported and demonstrates its behavior as an effective HER electrocatalyst in non‐acidic conditions. The RuP/Ru@CNS exhibits low overpotential (106 mV at 200 mA·cm−2) in alkaline electrolyte, exceeding most reported Ru‐based electrocatalysts. The electron shuttling between Ru atoms at the RuP/Ru interface results in a lowered energy barrier for H2O dissociation by electron‐deficient Ru atoms in the pure Ru phase, as well as optimized H* adsorption of electron‐gaining Ru atoms in the neighboring RuP. A low H* spillover energy barrier between Ru atoms at the RuP/Ru interface further boosts HER kinetics. This study demonstrates a sustainable method for the fabrication of efficient Ru‐based electrocatalysts and provides a more detailed understanding of interface effects in HER catalysis.

In this work, vanadium pentoxide (V2O5) and titanium-modified V2O5 thin films were synthesized using the sol-gel spin coating route. The effect of Ti-doping concentration on the electrochromic optical properties and atomic/electronic structures of V2O5 smart thin films is examined. As the doping concentration of Ti increases, the surface roughness of the films is reduced. The structure of the films is analyzed using X-ray diffraction (XRD) and Raman spectroscopy, while the electrochromic modulation of atomic and electronic structures is elucidated through Raman and X-ray absorption spectroscopy (XAS) conducted during lithiation and delithiation. The XRD patterns demonstrate that an increase in Ti concentration leads to a more amorphous structure of the films and a shift of the main diffraction peak to a lower angle, attributable to the enlarged spacing between the stacking layers resulting from the incorporation of Ti ions. Soft X-ray absorption spectroscopy (XAS) and in situ hard XAS of the V L-edge, the O K-edge, and the V K-edge revealed a reduction in the charge state of V and local atomic structural symmetry modification upon lithated coloration and delithiated bleaching process. The critical insights provided by in situ XAS provides reveal that a small amount of Ti has the ability to modify the interlayer distance and local atomic structure of V2O5, thereby improving its electrochromic switching rate and stability when utilized in smart windows.

Abstract Designing efficient catalyst for the oxygen evolution reaction (OER) is of importance for energy conversion devices. The anionic redox allows formation of O-O bonds and offers higher OER activity than the conventional metal sites. Here, we successfully prepare LiNiO2 with a dominant 3d 8 L configuration (L is a hole at O 2p) under high oxygen pressure, and achieve a double ligand holes 3d 8 L 2 under OER since one electron removal occurs at O 2p orbitals for NiIII oxides. LiNiO2 exhibits super-efficient OER activity among LiMO2, RMO3 (M = transition metal, R = rare earth) and other unary 3d catalysts. Multiple in situ/operando spectroscopies reveal NiIII→NiIV transition together with Li-removal during OER. Our theory indicates that NiIV (3d 8 L 2) leads to direct O-O coupling between lattice oxygen and *O intermediates accelerating the OER activity. These findings highlight a new way to design the lattice oxygen redox with enough ligand holes created in OER process.

Abstract The memory effect property, described as a reversible color persistence while the potential is withdrawn, is of particular importance to reaching zero‐energy consumption electrochromic devices. Nevertheless, often observed in organic materials, it is poorly studied in oxides. In this study, electrochromic tungsten oxide thin films are elaborated at different working pressures by radiofrequency magnetron sputtering. The influence of the deposition pressure on the electrochemical properties of WO3 films as well as on their memory effect is investigated. Three kinds of WO3 films can be distinguished: with irreversible blue coloration, with reversible coloration presenting a high memory effect, and with reversible coloration with a low memory effect. The origin of these discrepancies is studied through the composition, the local atomic environment, and the morphology of the WO3 thin films. An increase of transmittance at 550 nm as low as 15.8% in 48 h in air and 5.2% in 24 h in the electrolyte is recorded. This study highlights a better understanding of the memory effect property of electrochromic oxides for low‐consumption energy electrochromic devices, pointing out morphology as a key parameter.

Abstract Researchers are investigating innovative composite materials for renewable energy and energy storage systems. The major goals of this studies are i) to develop a low‐cost and stable trimetallic oxide catalyst and ii) to change the electrical environment of the active sites through site‐selective Mo substitution. The effect of Mo on NiCoMoO4 is elucidated using both in situ X‐ray absorption spectroscopy and X‐ray diffraction analysis. Also, density functional theory strategies show that NiCoMoO4 has extraordinary catalytic redox activity because of the high adsorption energy of the Mo atom on the active crystal plane. Further, it is demonstrated that hierarchical nanoflower structures of NiCoMoO4 on reduced graphene oxide can be employed as a powerful bifunctional electrocatalyst for oxygen reduction/evolution reactions in alkaline solutions, providing a small overpotential difference of 0.75 V. Also, Zn–air batteries based on the developed bifunctional electrocatalyst exhibit outstanding cycling stability and a high‐power density of 125.1 mW cm−2. This work encourages the use of Zn–air batteries in practical applications and provides an interesting concept for designing a bifunctional electrocatalyst.

The Zhang-Rice singlet is known for the superconductivity of high-temperature superconductors cuprate but is rarely studied for an electrochemical catalyst. Here, the authors use operando spectroscopic tools and observe Cu active site evolves into high-valent CuO4 geometry with Cu3+ active species, so-called Zhang-Rice singlet state, during oxygen evolution reaction.

Abstract Despite of suitable band structures for harvesting solar light and driving water redox reactions, polymeric carbon nitride (PCN) has suffered from poor charge transfer ability and sluggish surface reaction kinetics, which limit its photocatalytic activity for water splitting. Herein, atomically dispersed Zn-coordinated three-dimensional (3D) sponge-like PCN (Zn-PCN) is synthesized through a novel intermediate coordination strategy. Advanced characterizations and theoretical calculations well evidence that Zn single atoms are coordinated and stabilized on PCN in the form of Zn-N6 configuration featured with an electron-deficient state. Such an electronic configuration has been demonstrated contributive to promoted electron excitation, accelerated charge separation and transfer as well as reduced water redox barriers. Further benefited from the abundant surface active sites derived from the 3D porous structure, Zn-PCN realizes visible-light photocatalysis for overall water splitting with H2 and O2 simultaneously evolved at a stoichiometric ratio of 2:1. This work brings new insights into the design of novel single-atom photocatalysts by deepening the understanding of electronic configurations and reactive sites favorable to excellent photocatalysis for water splitting and related solar energy conversion reactions.

Improving fuel cell technologies based on Pt-based alloys is important for efficient fuel cells. Here, the authors report a hybrid PtCo alloy electrocatalyst for acidic oxygen reduction at high current densities and H2/air fuel cell power densities.

The sluggish water activation kinetics and instability of metal-organic frameworks for hydrogen evolution reaction limit their industrial applications. Here, authors construct a unique triangular active region to accelerate the crucial water activation and stabilize metal-organic frameworks.

In this work, the novel CuTa2O6 phase was successfully synthesized by the hydrothermal and followed by the calcination process. The X-ray diffraction pattern confirms the formation of different phases. At a low temperature, CuTa2O6 exhibits the orthorhombic phase, whereas, at a higher temperature, it underwent a phase transition to a cubic crystal structure. X-ray photoelectron spectroscopic results suggest the presence of all the elements (Cu, Ta, and O). The optical studies were carried out using a UV-Vis DRS spectrophotometer. FESEM images confirm the spherical-shaped particles for the sample annealed at a high temperature. The local atomic and electronic structures around Cu and the contribution of the Cu oxidation state in the CuTa2O6 system were determined by X-ray absorption spectroscopy. To investigate the effective usage of CuTa2O6 in treating wastewater, its photocatalytic activity was investigated by evaluating its use in the photodegradation of MO dye under visible light irradiation. Moreover, the prepared CuTa2O6 photocatalyst exhibits significant photocatalytic activity in the degradation of MO dye and shows excellent stability; it is therefore a promising material for potential use in a practical photocatalyst. The CuTa2O6 photocatalyst suggests an alternative avenue of research into effective photo-catalysts for solar hydrogen water splitting.

The successful separation of photoexcited charge carriers and their effective utilization are crucial for overcoming the slow kinetics of the four-electron process for photocatalytic oxygen evolution. Herein, a novel strategy utilizing urea as a source of N-doping on Ca _2 Nb _3 O _10 nanosheets is adopted, followed by the successful deposition of Co single atoms (Co-SAs) to achieve a synergistic effect. The presence of N-dopants and Co-SAs is validated via various experimental techniques. It is also observed that the presence of N-doping contributed towards the deposition of higher content of Co-SAs (0.21 wt%) in Ca _2 Nb _3 O _10− _x N _x -Co _SA nanosheets compared to 0.15 wt% for non-doped Ca _2 Nb _3 O _10 -Co _SA . The optimized Ca _2 Nb _3 O _10− _x N _x -Co _SA nanosheets exhibited an impressive photocatalytic O _2 evolution of ∼727.22 µ mol g ^−1 h ^−1 via the synergy of N-dopants and Co-SAs. As a result, the O _2 evolution response of Ca _2 Nb _3 O _10− _x N _x -Co _SA is 3.6 times higher than that of pristine Ca _2 Nb _3 O _10 nanosheets (201.26 µ mol g ^−1 h ^−1 ), 2.24 times better than Ca _2 Nb _3 O _10− _x N _x nanosheets (323.42 µ mol g ^−1 h ^−1 ), and 1.77 times higher compared to Ca _2 Nb _3 O _10 -Co _SA , (409.33 µ mol g ^−1 h ^−1 ), which clearly demonstrated the synergistic effect of N-dopants and Co-SAs in Ca _2 Nb _3 O _10− _x N _x -Co _SA nanosheets. Based on the findings of various characterization techniques, the co-presence of N-dopants and Co-SAs is observed to contribute towards better charge carrier separation, and utilization to achieve superior photocatalytic response. Thus, this study presents a novel approach for incorporating N-dopants and Co-SAs on Ca _2 Nb _3 O _10 nanosheets, which can be extended to a wide range of nanosheets produced by the soft chemical exfoliation method.

Abstract Electrochemical carbon dioxide (CO2) reduction (ECR) is a promising technology to produce valuable fuels and feedstocks from CO2. Despite large efforts to develop ECR catalysts, the investigation of the catalytic performance and electrochemical behavior of complex metal oxides, especially perovskite oxides, is rarely reported. Here, the inorganic perovskite oxide Ag‐doped (La0.8Sr0.2)0.95Ag0.05MnO3–δ (LSA0.05M) is reported as an efficient electrocatalyst for ECR to CO for the first time, which exhibits a Faradaic efficiency (FE) of 84.3%, a remarkable mass activity of 75 A g−1 (normalized to the mass of Ag), and stability of 130 h at a moderate overpotential of 0.79 V. The LSA0.05M catalyst experiences structure reconstruction during ECR, creating the in operando‐formed interface between the perovskite and the evolved Ag phase. The evolved Ag is uniformly distributed with a small particle size on the perovskite surface. Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite–Ag interface provides adsorption sites for CO2 and accelerates the desorption of the *CO intermediate to enhance ECR. This study presents a novel high‐performance perovskite catalyst for ECR and may inspire the future design of electrocatalysts via the in operando formation of metal–metal oxide interfaces.

Abstract Efficient ethanol oxidation reaction (EOR) is challenging due to the multiple reaction steps required to accomplish full oxidation to CO2 in fuel cells. High‐entropy materials with the adjustable composition and unique chemical structure provide a large configurational space for designing high‐performance electrocatalysts. Herein, a new class of structurally ordered PtRhFeNiCu high‐entropy intermetallics (HEIs) is developed as electrocatalyst, which exhibits excellent electrocatalytic activity and CO tolerance for EOR compared to high‐entropy alloys (HEAs) comprising of same elements. When the HEIs are used as anode catalysts to be assembled into a high‐temperature polybenzimidazole‐based direct ethanol fuel cell, the HEIs achieve a high power density of 47.50 mW/cm2, which is 2.97 times of Pt/C (16.0 mW/cm2). Online gas chromatography measurements show that the developed HEIs have a stronger C–C bond‐breaking ability than corresponding HEAs and Pt/C catalysts, which is further verified by density functional theory (DFT) calculations. Moreover, DFT results indicate that HEIs possess higher stability and electrochemical activity for EOR than HEAs. These results demonstrate that the HEIs could provide a new platform to develop high‐performance electrocatalysts for broader applications.

Abstract High dosage of expensive Pt to catalyze the sluggish oxygen reduction reaction (ORR) on the cathode severely impedes the commercialization of proton exchange membrane fuel cells. Therefore, it is urgent to cut down the Pt catalyst by efficiently improving the ORR activity while maintaining high durability. Herein, magic concave Pt–Zn nanocubes with high‐index faceted Pt skin (Pt78Zn22) are proposed for high‐efficiency catalysis toward proton exchange membrane fuel cells. These unique structural features endow the Pt‐skin Pt78Zn22/KB with a mass activity of 1.18 mA μgPt–1 and a specific activity of 3.64 mA cm–2 for the ORR at 0.9 V (vs RHE). Meanwhile, the H2–O2 fuel cell assembled by this catalyst delivers an ultrahigh peak power density of ≈1449 mW cm–2. Both experiments and theoretical calculations show that the electronic structure of the surface is adjusted, thereby shortening the length of the Pt–Pt bond and reducing the adsorption energy of OH*/O* on the Pt surface. This work demonstrates the synergistic effect of the oxidation‐resistant metal Zn and the construction of Pt‐rich surface engineering. Also, it guides the future development of catalysts for their practical applications in energy conversion technologies and beyond.

Abstract Controllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction (ORR) in fuel cells. However, the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge. In this study, we developed a facile and scalable method for fabricating highly efficient ORR electrocatalysts with sole atomic Fe–N4 species as the active site. Herein, the use of cost‐effective highly porous carbon as the support not only could avoid the aggregation of the atomic Fe species but also a feasible approach to reduce the catalyst cost. The obtained atomic Fe–N4 in activated carbon (aFe@AC) shows excellent ORR activity. Its half‐wave potential is 59 mV more negative but 47 mV more positive than that of the commercial Pt/C in acidic and alkaline electrolytes, respectively. The full cell performance test results show that the aFe@AC sample is a promising candidate for direct methanol fuel cells. This study provides a general method to prepare catalysts with a certain type of active site and definite numbers.

Understanding active-site geometry and structural evolution during electrocatalysis is important for further development. Here the authors use operando X-ray absorption spectroscopy combined with electrochemical impedance spectroscopy to investigate single atom catalysts derived from Vitamin B12.

Water oxidation catalysis may provide the electrons needed for sustainable fuel production, but catalysts often degrade under working conditions. Here, authors introduce soluble species into perovskites to exert positive ion leaching effects for enhancing perovskite stability and activity.

Determining catalyst electronic structures during electrochemical reactions is crucial to understand mechanisms. Here authors perform in operando soft X-ray spectroscopy on a cobalt oxide catalyst during O2 evolution and observe voltage and time-dependent valence state transitions.

Ion irradiation is an exceptionally effective approach to induce controlled surface modification/defects in semiconducting thin films. In this investigation, ion-irradiated Se–Te-based compounds exhibit electrical transport properties that greatly favor the transformation of waste heat into electricity. Enhancements of both the Seebeck coefficient (S) and the power factor (PF) of In2(Te0.98Se0.02)3 films under 120 MeV Ni9+ ion irradiation were examined. The maximum S value of the pristine film was about ~221 µVK−1. A significantly higher S value of about ~427 µVK−1 was obtained following irradiation at 1 × 1013 ions/cm2. The observed S values suggest the n-type conductivity of these films, in agreement with Hall measurements. Additionally, Ni ion irradiation increased the PF from ~1.23 to 4.91 µW/K2m, demonstrating that the irradiated films outperformed the pristine samples. This enhancement in the TE performance of the In2(Te0.98Se0.02)3 system is elucidated by irradiation-induced effects that are revealed by structural and morphological studies.

Bismuth vanadate (BiVO4) has attracted substantial attention on account of its usefulness in producing hydrogen by photoelectrochemical (PEC) water splitting. The exploitation of BiVO4 for this purpose is yet limited by severe charge recombination in the bulk of BiVO4, which is caused by the short diffusion length of the photoexcited charge carriers and inefficient charge separation. Enormous effort has been made to improve the photocurrent density and solar-to-hydrogen conversion efficiency of BiVO4. This study demonstrates that modulating the composition of the electrode and the electronic configuration of BiVO4 by decoration with silver nanoparticles (Ag NPs) is effective in not only enhancing the charge carrier concentration but also suppressing charge recombination in the solar water splitting process. Decoration with a small number of Ag NPs significantly enhances the photocurrent density of BiVO4 to an extent that increases with the concentration of the Ag NPs. At 0.5% Ag NPs, the photocurrent density approaches 4.1 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (RHE) under solar simulated light illumination; this value is much higher than the 2.3 mA cm−2 of pure BiVO4 under the same conditions. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of pure BiVO4 and its modification by decoration with Ag NPs. Analytical results indicate that increased distortion of the VO4 tetrahedra alters the V 3d–O 2p hybridized states. Additionally, as the Ag concentration increases, the oxygen vacancy defects that act as recombination centers in BiVO4 are reduced. In situ XAS, which is conducted under dark and solar illumination conditions, reveals that the significantly enhanced PEC performance is attributable to the synergy of modulated atomic/electronic structures and the localized surface plasmon resonance effect of the Ag nanoparticles.

Facile and reliable screening of efficient electrocatalysts is important for energy conversion technologies such as water splitting. Here, authors introduce A-site ionic electronegativity as a descriptor to understand the hydrogen-evolution activities of cobalt-based perovskites.

The MgO nanolayer effect on the microstructure and magnetic characterizations added into Fe/Pt stacked films directly deposited onto MgO (001) single-crystal substrates at the reduced temperature of 380 °C using electron-beam technology was investigated in this present work. The nanograin isolation and exchange decoupling for the FePt–MgO system is attributed to the magnetic FePt isolated grains that originate from MgO atoms with a spreading behavior mostly along grain boundaries owing to its weaker surface energy than that of a single Fe or Pt element. The grain and domain size decreased when the MgO nanolayer was applied due to the interpenetration of MgO and created a strain-energy variation at the MgO/FePt interface. Measuring angular-dependent coercivity indicates a general trend of a domain-wall motion, and changes to the rotation of the reverse-domain model occurred as the MgO nanolayers were added into FePt films. The intergrain interaction is confirmed by the Kelly–Henkel plot, which shows that there is strong intergrain exchange coupling (positive δM type) between neighboring grains in the continuous Fe/Pt stacked films without MgO nanolayers. In addition, a negative δM type occurred when the Fe/Pt stacked films were added into MgO nanolayers, showing that the MgO nanolayer can be applied to adjust the force of intergrain exchange coupling between the adjacent FePt nanograins, and the addition of MgO nanolayers change into magnetic decoupling; thus, there was a formed dipole interaction in our claimed FePt–MgO composite structure of stacked ultrathin films at a reduced temperature of 380 °C.

Direct formic acid fuel cell (DFAFC) has been considered as a promising energy conversion device for stationary and mobile applications. Advanced platinum (Pt) electrocatalysts for formic acid oxidation reaction (FAOR) are critical for DFAFC. However, the oxidation of formic acid on Pt catalysts often occurs via a dual pathway mechanism, which hinders the catalytic activity owing to the CO poisoning. Herein, we directly exfoliate bulk antimony to 2D antimonene (Sb) and in situ load Pt nanoparticles onto antimonene sheets with the assistance of ethylenediamine. According to the Bader charge analysis, the charge transfer from antimonene to Pt occurs, confirming the electronic interaction between Pt and Sb. Interestingly, antimonene, as a cocatalyst, alters the oxidation pathway for FAOR over Pt catalyst and makes FAOR follow the more efficient dehydrogenation pathway. The density functional theory (DFT) calculation demonstrates that antimonene can activate Pt to be a lower oxidative state and facilitate the oxidation of HCOOH into CO2 via a direct pathway, resulting in a weakened intermediate binding strength and better CO tolerance for FAOR. The specific activity of FAOR on Pt/Sb is 4.5 times, and the mass activity is 2.6 times higher than the conventional Pt/C.

A simple, efficient, and cost-effective extended graphite as a supporting platform further supported the MnO2 growth for the construction of hierarchical flower-like MnO2/extended graphite. MnO2/extended graphite exhibited an increase in sp2 carbon bonds in comparison with that of extended graphite. It can be expected to display better electrical conductivity and further promote electron/ion transport kinetics for boosting the electrochemical performance in supercapacitors and glucose sensing. In supercapacitors, MnO2/extended graphite delivered an areal capacitance value of 20.4 mF cm−2 at 0.25 mA cm−2 current densities and great cycling stability (capacitance retention of 83% after 1000 cycles). In glucose sensing, MnO2/extended graphite exhibited a good linear relationship in glucose concentration up to about 5 mM, sensitivity of 43 μA mM−1cm−2, and the limit of detection of 0.081 mM. It is further concluded that MnO2/extended graphite could be a good candidate for the future design of synergistic multifunctional materials in electrochemical techniques.

This study investigated the ultrathin Cu(002) capping nano-island effects on the magnetic characterizations and microstructure of epitaxial FePt(001) films directly fabricated on MgO(001) substrates at the relatively low temperature of 300 °C via electron-beam deposition. The enhancement of the coercivity is attributed to the lowered exchange coupling of FePt magnetic grains that begun from Cu atom behavior of spreading in many directions mainly along grain boundaries due to its lower surface energy than that of pure Fe or Pt. The measurement of angular-dependent coercivity shows a tendency of a domain-wall motion shift toward the rotation of the reverse-domain type upon the thickness of the Cu capping nano-island layer atop the FePt films. The intergranular interaction was clarified by the Kelly–Henkel plot, which indicated that there was strong exchange coupling (positive δM) between neighboring grains in the FePt continuous films without Cu capping nano-islands. On the other hand, a negative δM value was gained when the FePt films were capped with a Cu(002) single layer, indicating that the Cu capping layer can be used to control the strength of intergrain exchange coupling between the adjacent FePt grains and thicker Cu(002) capping nano-islands toward magnetic isolation; thus, there was an existence of dipole interaction in our designed Cu/FePt composite structure of stacked films.

The memory effect property, described as a reversible color persistence while the potential is withdrawn, is of particular importance to reaching zero-energy consumption electrochromic devices. Nevertheless, often observed in organic materials, it is poorly studied in oxides. In this study, electrochromic tungsten oxide thin films are elaborated at different working pressures by radiofrequency magnetron sputtering. The influence of the deposition pressure on the electrochemical properties of WO3 films as well as on their memory effect is investigated. Three kinds of WO3 films can be distinguished: with irreversible blue coloration, with reversible coloration presenting a high memory effect, and with reversible coloration with a low memory effect. The origin of these discrepancies is studied through the composition, the local atomic environment, and the morphology of the WO3 thin films. An increase of transmittance at 550 nm as low as 15.8% in 48 h in air and 5.2% in 24 h in the electrolyte is recorded. This study highlights a better understanding of the memory effect property of electrochromic oxides for low-consumption energy electrochromic devices, pointing out morphology as a key parameter. [ABSTRACT FROM AUTHOR]