"Atomic Topping" of MnOx on Al2O3 to Create Electron-Rich, Aperiodic, Lattice Oxygens that Resemble Noble Metals for Catalytic Oxidation.

Enhancing the catalytic oxidation activity of traditional transition-metal oxides to rival that of noble metals has been a prominent focus in the field of catalysis. However, existing synthesis strategies that focus on controlling the electronic states of metal centers have not yet fully succeeded in achieving this goal. Our current research reveals that manipulating the electronic states of oxygen centers can yield unexpected results. By creating electron-rich, aperiodic lattice oxygens through atomic topping of MnOx, we have produced a catalyst with performance that closely resembles supported Pt. Spherical aberration-corrected transmission electron microscopy and X-ray absorption spectra have confirmed that the atomic topping of the MnOx layer on Al2O3 can form an aperiodic arrangement oxide structure. Near-ambient pressure X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, reaction kinetics test, and theoretical calculations demonstrated that this structure significantly increases the electron density around the oxygen in MnOx, shifting the activation center for CO adsorption from Mn to O, thereby exhibiting catalytic activity and stability close to that of the precious metal Pt. This study presents a fresh perspective on designing efficient oxide catalysts by targeting electron-rich anionic centers, thereby deepening the understanding of how these centers can be altered to enhance catalytic efficiency in oxidation reactions.

Exsolution of Iron Oxide on LaFeO3 Perovskite: A Robust Heterostructured Support for Constructing Self-Adjustable Pt-Based Room-Temperature CO Oxidation Catalysts.

Constructing highly active and stable surface sites for O2 activation is essential to lower the barrier of Pt-based catalysts for CO oxidation. Although a few active Pt-metal oxide interfaces have been reported, questions about the stability of these sites under the long-term storage and operation remain unresolved. Here, based on developing a robust FeOx/LaFeO3 heterostructure as a support, we constructed stable Pt-support interfaces to achieve highly active CO oxidation at room temperature. Even after it is kept in the air for more than 6 months, the catalyst (without pretreatment) still maintains the high activity like a fresh one, which is superior to metal hydroxide-Pt interfaces, and meets the requirements of long-term storage for emergency use. In situ characterizations and systematic reaction results showed that CO oxidation occurs through an alternative mechanism, which is triggered by intrinsic reactants and self-adjusted to a more active interface in the reaction process. Theoretical calculations and 57Fe Mössbauer spectra revealed that abundant cation vacancies significantly increase the activity of surface oxygen species and should be responsible for this unique process. This work demonstrates an alternative concept to fabricate robust and highly active Pt-based catalysts for catalytic oxidation.

Edge/Defect-Rich, Metallic, and Oxygen-Heteroatom-Doped WS2 Superstructure with Superior Electrocatalytic Performance for Green Solar Energy Conversion.

Two-dimensional tungsten sulfide is widely applied in electrocatalysis. However, WS2 possesses catalytic active sites located at the layer edge and an inert surface for catalysis. Therefore, increasing the exposure of active sites at the edge and effectively activating the inert sites on the surface is an important challenge. Here, an edge/defect-rich and oxygen-heteroatom-doped WS2 (ED-O-WS2 ) superstructure was synthesized. The power-conversion efficiency (PCE) of dye-sensitized solar cells (DSCs) based on an ED-O-WS2 counter electrode reached 10.36 % (under 1 sun, AM 1.5, 100 mW cm-2 ) and 11.19 % (under 40 mW cm-2 ). These values are, to our knowledge, the highest reported efficiency for DSCs based on Pt-free counter electrodes in I3 - /I- electrolytes. Analysis of the micro/nano structure and the electrocatalytic mechanism indicate that ED-O-WS2 exhibits metallic properties in the electrolyte, and that abundant edges and defects as well as oxygen doping in ED-O-WS2 play an important role in improving the catalytic activity of WS2 . Moreover, ED-O-WS2 displays better catalytic reversibility for I3 - /I- electrolytes than Pt.

Band-Gap Tuning of Organic-Inorganic Hybrid Palladium Perovskite Materials for a Near-Infrared Optoelectronics Response.

Organic-inorganic hybrid material is a recent hot topic in the scientific community. The best band gap for the entire solar absorption spectrum is about 1.1 eV. However, the lead perovskite band gap is about 1.5 eV. Therefore, developing organic-inorganic hybrid material toward the broader light harvesting of the solar spectrum is extremely urgent. In this study, we prepare three kinds of organic-inorganic hybrid palladium perovskite materials, including (CH3NH3)2PdCl4, (CH3NH3)2PdCl4-x Br x , and CH3NH3PdI3, for an optoelectronic response. The absorption cut offs of (CH3NH3)2PdCl4, (CH3NH3)2PdCl4-x Br x , and CH3NH3PdI3 are approximately 600, 700, and 1000 nm, respectively. The band gaps of (CH3NH3)2PdCl4, (CH3NH3)2PdCl4-x Br x , and CH3NH3PdI3 are determined to be approximately 2.15, 1.87, and 1.25 eV, respectively. To the best of our knowledge, this is the first study that discusses adsorption properties and photoelectric behavior of organic-inorganic hybrid palladium perovskite materials. Interestingly, the photoelectric response of the devices based on CH3NH3PdI3 reaches 950 nm. The results will attract attention in the fields of optical recorders, optical memory, security, light capture, and light treatment.

Synthesis, Crystal Structure, UV-Vis Adsorption Properties, Photoelectric Behavior, and DFT Computational Study of All-Inorganic and Lead-Free Copper Halide Salt K2Cu2Cl6.

In this study, all-inorganic copper halide salt K2Cu2Cl6 single-crystal and thin films were prepared. The single-crystal diffraction data belonged to the monoclinic K2Cu2Cl6 (space group = P 2(1)/C, unit cell parameters of a = 4.0340 Å, b = 13.7987 Å, c = 8.7445 Å, α = 90.000, ß = 97.123, and γ = 90.000). As far as we know, this is the first study of the copper halide salt K2Cu2Cl6 for optoelectronic applications. The band gap of K2Cu2Cl6 is calculated to be approximately 1.85 eV. A low-cost photodetector based on the K2Cu2Cl6 thin film was efficient under different monochromatic light from 330 to 390 nm with different chopping frequencies (1.33-30 Hz). Density functional theory (DFT) computational results indicate that the valence bands (VBs) and conduction bands (CBs) are shifted up in energy using the orbital-dependent correction to the DFT energy. Partial density of states reveals that the VBs and narrow CBs are derived from the hybrid orbitals of Cu2+ 3d and Cl- p, respectively.

Tuning Ni-Foam into NiOOH/FeOOH Heterostructures toward Superior Water Oxidation Catalyst via Three-Step Strategy.

Splitting of water into hydrogen and oxygen has become a strategic research topic. In the two semi-reactions of water splitting, water oxidation is preferred to the four-electron-transfer process with a higher overpotential (η) and is the decisive step in water splitting. Therefore, efficient water oxidation catalysts must be developed. IrO x and RuO x catalysts are currently the most efficient catalysts in water oxidation. However, the limited reserve and high prices of precious metals, such as Ir and Ru, limit future large-scale industrial production of water oxidation catalysts. In this study, we tune inert Ni-foam into highly active NiOOH/FeOOH heterostructures as water oxidation catalysts via three-step strategy (surface acid-treating, electroplating, and electrooxidation). NiOOH/FeOOH heterostructures as water oxidation catalysts only require η of 257 mV to reach a current density of 10 mA cm-2, which is superior to that of IrO2/Ni-foam (280 mV). The high electrochemically active surface area (72.50 cm2) and roughness factor demonstrate abundant interfaces in NiOOH/FeOOH heterostructures, thus accelerating water oxidation activity. The small value (4.8 Ω cm2) of charge transfer resistance (R ct) indicate that fast electronic exchange occurs between NiOOH/FeOOH heterostructures catalyst and reaction of water oxidation. Hydrogen-to-oxygen volume ratios (approximately 2:1) indicate an almost overall water splitting by the double-electrode system. Faraday efficiency of H2 or O2 is close to 90% at 2:1 hydrogen-to-oxygen volume ratio. NiOOH/FeOOH heterostructures exhibit good stability. The results provide significance in fundamental research and practical applications in solar water splitting, artificial photoelectrochemical cells, and electrocatalysts.

Earth-abundant and environment friendly organic-inorganic hybrid tetrachloroferrate salt CH3NH3FeCl4: structure, adsorption properties and photoelectric behavior.

Organic-inorganic hybrid-based lead perovskites show inherent and unavoidable problems such as structural instability and toxicity. Therefore, developing low-cost and environment-friendly organic-inorganic hybrid materials is extremely urgent. In this study, we prepared earth-abundant and environment-friendly organic-inorganic hybrid tetrachloroferrate salt CH3NH3FeCl4 (MAFeCl4) for optoelectronic applications. The single crystal diffraction data are assigned to the orthorhombic MAFeCl4 (Pnma space group), with parameters a = 11.453 (5) Å, b = 7.332 (3) Å, c = 10.107 (5) Å, α = 90.000, ß = 90.000, and γ = 90.000. The band gap of MAFeCl4 is approximately 2.15 eV. Moreover, three-emission luminescence (398, 432 and 664 nm) was observed. To the best of our knowledge, this is the first study involving the investigation of the structure, adsorption properties and photoelectric behavior of MAFeCl4. A low cost photodetector based on the MAFeCl4 thin film is efficient under different monochromatic light from 330 nm to 410 nm with different chopping frequencies (1.33 Hz to 40 Hz). The photoelectric conversion efficiency based on FTO/TiO2/MAFeCl4/carbon electrode device reaches 0.054% (V oc = 319 mV, J sc = 0.375 mA cm-2, and fill factor = 0.45) under AM1.5, 100 mW cm-2 simulated illumination. Our findings will attract attention from the magnetic, piezoelectric and photoelectronic research fields.

Low defects, large area and high stability of all-inorganic lead halide perovskite CsPbBr3 thin films with micron-grains via heat-spraying process for self-driven photodetector.

All-inorganic lead halide perovskite CsPbBr3 has important applications in photoelectronic devices such as photodetectors, LEDs and photovoltaic devices. However, preparing high-quality CsPbBr3 thin films has proven to be challenging. In this study, we prepared all-inorganic lead halide perovskite CsPbBr3 thin films with micron-grains (MG-CsPbBr3-TF) via a heat-spraying process (HSP) using a CsPbBr3-saturated solution (CsPbBr3-SS), and the films exhibited large area, low defects and high stability. The grain size of MG-CsPbBr3-TF was about 1-5 microns. The micron-sized grains in MG-CsPbBr3-TF enabled the absorption cutoff edge to be extended from 537 to 545 nm. In addition, the presence of fewer boundaries in MG-CsPbBr3-TF reduced the defects in MG-CsPbBr3-TF (the blue shift of luminescence). The response wavelengths of a low-cost and self-driven (zero-biased) photodetector based on MG-CsPbBr3-TF were from 330 to 600 nm. CsPbBr3 thin films having a large area (10 cm × 10 cm) and micron-sized grains were also prepared by HSP and exhibited excellent stability (1944 h) in air (T = 298 K, 40% humidity). To the best of our knowledge, this is the first study of high-quality CsPbBr3 thin films prepared by HSP. The results are of great interest for both fundamental research and practical applications of CsPbBr3 in photodetectors, LEDs and photovoltaic devices.

From two-dimensional graphene oxide to three-dimensional honeycomb-like Ni3S2@graphene oxide composite: insight into structure and electrocatalytic properties.

Three-dimensional (3D) graphene composites have drawn increasing attention in energy storage/conversion applications due to their unique structures and properties. Herein, we synthesized 3D honeycomb-like Ni3S2@graphene oxide composite (3D honeycomb-like Ni3S2@GO) by a one-pot hydrothermal method. We found that positive charges of Ni2+ and negative charges of NO3- in Ni(NO3)2 induced a transformation of graphene oxide with smooth surface into graphene oxide with wrinkled surface (w-GO). The w-GO in the mixing solution of Ni(NO3)2/thioacetamide/H2O evolved into 3D honeycomb-like Ni3S2@GO in solvothermal process. The GO effectively inhibited the aggregation of Ni3S2 nanoparticles. Photoelectrochemical cells based on 3D Ni3S2@GO synthesized at 60 mM l-1 Ni(NO3)2 exhibited the best energy conversion efficiency. 3D Ni3S2@GO had smaller charge transfer resistance and larger exchange current density than pure Ni3S2 for iodine reduction reaction. The cyclic stability of 3D honeycomb-like Ni3S2@GO was good in the iodine electrolyte. Results are of great interest for fundamental research and practical applications of 3D GO and its composites in solar water-splitting, artificial photoelectrochemical cells, electrocatalysts and Li-S or Na-S batteries.