La and CrCo-doped SrTiO_3 as an H_2 evolution photocatalyst for construction of a Z-scheme overall water splitting system

The photocatalytic activity of a semiconductor‐based photocatalyst largely depends on the semiconductor’s intrinsic crystal and electronic properties.We have prepared two types of La and Cr co‐doped SrTiO3photocatalysts(SrTiO3(La,Cr))using the polymerized complex method(PCM)and sol‐gel hydrothermal method(SHM).Under?>420‐nm visible light irradiation,only the Pt‐loaded SrTiO3(La,Cr)prepared by the SHM showed efficient photocatalytic activities for both H2evolution in the presence of an I?sacrificial reagent and for Z‐scheme overall water splitting when it was coupled with the Pt‐loaded WO3in the presence of I?and IO3?as the shuttle redox mediator.The superior photocatalytic activity of SrTiO3(La,Cr)prepared by the SHM has been ascribed to its more negative conduction‐band position,higher carrier concentration,and higher carrier mobility,demonstrating that the design and synthesis of an H2‐evolution photocatalyst with appropriate electronic properties is crucial for achieving Z‐scheme overall water splitting.

Water oxidation sites located at the interface of Pt/SrTiO_(3) for photocatalytic overall water splitting

When a proton reduction cocatalyst is loaded on an n-type semiconductor for photocatalytic overall water splitting(POWS),the location of water oxidation sites is generally considered at the surface of the semiconductor due to upward band-bending of n-type semiconductor which may ease the transfer of the photogenerated holes to the surface.However,this is not the case for Pt/SrTiO_(3),a model semiconductor based photocatalyst for POWS.It was found that the photogenerated holes are more readily accumulated at the interface between Pt cocatalyst and SrTiO_(3) photocatalyst as probed by photo-oxidative deposition of PbO_(2),indicating that the water oxidation sites are located at the interface between Pt and SrTiO_(3).Electron paramagnetic resonance and scanning transmission electron microscope studies suggest that the interfacial oxygen atoms between Pt and SrTiO_(3) in Pt/SrTiO_(3) after POWS are more readily lost to form oxygen vacancies upon vacuum heat treatment,regardless of Pt loading by photodeposition or impregnation methods,which may serve as additional support for the location of the active sites for water oxidation at the interface.Density functional theory calculations also suggest that the oxygen evolution reaction more readily occurs at the interfacial sites with the lowest overpotential.These experimental and theoretical studies reveal that the more active sites for water oxidation are located at the interface between Pt and SrTiO_(3),rather than on the surface of SrTiO_(3).Hence,the tailor design and control of the interfacial properties are extremely important for the achievement or improvement of the POWS on cocatalyst loaded semiconductor photocatalyst.

One dimensional nickel phosphide polymorphic heterostructure as carbon-free functional support loading single-atom iridium for promoted electrocatalytic water oxidation

Although conducting materials such as carbon nanotube and carbon fiber paper(CFP)have been extensively employed as support of electrocatalytic active sites,most of them are of poor catalytic functionality by themselves and undesirable stability during strong acid/alkaline environments or oxidation process.Here we report a novel one-dimensional(1D)nickel phosphide polymorphic heterostructure(denoted as NPPH)to work as one effective carbon-free functional support for loading of single-atom Ir water oxidation electrocatalyst.Specifically,the NPPH composed of both Ni12P5and Ni2P phases is not only active for robust alkaline water oxidation but also is of good stability and hydrophilicity for favorable loading of single-atom dispersed iridium.The NPPH supported single-atom Ir electrocatalyst(Ir/NPPH)is found to exhibit remarkably superior water oxidation activity with respect to the NPPH itself or CFP supported single-atom Ir catalyst(Ir/CFP),demonstrating the synergetic promotion effect between NPPH and single-atom Ir catalyst.Furthermore,the NPPH supported single-atom Ir catalyst can bear alkaline water oxidation for over 120 h at current density of 50 mA cm^(-2).The NPPH developed here is expected as functional support to composite with other water oxidation catalysts,as may be an alternative strategy of developing highly efficient carbon-free electrocatalysts.

Shape impact of nanostructured ceria on the dispersion of Pd species

The shape impact of nanostructured ceria on the dispersion of Pd species was investigated by analyzing the atomic configuration and the bonding environment of Pd species over spherical and cubic ceria particles,using STEM and XPS.Amorphous Pd particles of about 2.0 nm,with a substantial amount of tiny Pd species,dispersed on spherical ceria,primarily due to the enriched surface oxygen vacancies that bonded the Pd species tightly.While faceted Pd particles of about 2.9 nm located on cubic ceria with distinct interfaces where Pd atoms embedded into the ceria lattice.The crystalline Pd particles on ceria cubes were highly active and stable for methane combustion that occurred on the metal surface via a facile PdO/Pd redox cycle;while the amorphous Pd particles on spherical ceria particles were featured by a significantly higher activity and stability towards CO oxidation,where the Pd-ceria interface served as the active sites.

Perpendicular intergrowth ZSM-5 plates with shortened 10-MR pores

ZSM-5 plates with a perpendicular intergrowth structure was synthesized by using a simple amine as the structure directing agent under hydrothermal conditions,in which the mother plate and the perpendicularly standing plates oriented along the(010)and(100)planes of MFI crystals,respectively.During the crystallization process,the mother plate was initially formed on the surface of the amorphous solid gel,while a set of parallel plates perpendicularly grew on its surface,via a homogeneous nucleation mechanism.The mother plate and the perpendicular plates had a similar thickness of 100-200 nm and were characterized by considerably shortened straight and zigzag 10 member ring pores,respectively.This unique intergrowth structure greatly facilitated the diffusion of the reactive molecules in HZSM-5 crystals during methanol conversion to hydrocarbons.

Chemoselective transfer hydrogenation to nitroarenes mediated by oxygen-implanted MoS_2

We present an efficient approach for the chemoselective synthesis of arylamines from nitroarenes and formate over an oxygen-implanted MoS2 catalyst（O-MoS2）.O-MoS2 was prepared by incomplete sul idation and reduction of an ammonium molybdate precursor.A number of Mo-O bonds were implanted in the as-synthesized ultrathin O-MoS2 nanosheets.As a consequence of the different coordination geometries of O（Mo O2） and S（MoS2）,and lengths of the Mo-O and Mo-S bonds,the implanted Mo-O bonds induced obvious defects and more coordinatively unsaturated（CUS） Mo sites in O-MoS2,as confirmed by X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,high resolution transmission electron microscopy,and extended X-ray absorption fine structure characterization of various MoS2-based materials.O-MoS2 with abundant CUS Mo sites was found to efficiently catalyze the chemoselective reduction of nitroarenes to arylamines.

Co NP/NC hollow nanoparticles derived from yolk-shell structured ZIFs@polydopamine as bifunctional electrocatalysts for water oxidation and oxygen reduction reactions

The pyrolysis under inert atmosphere has been widely used for the synthesis of metal containing heteroatoms doped carbon materials, versatile catalysts for various reactions. However, it is difficult to prevent metal nanoparticles aggregation during pyrolysis process. Herein, we reported the efficient synthesis of nitrogen doped carbon hollow nanospheres with cobalt nanoparticles （Co NP, ca. 10nm in size） distributed uniformly in the shell via pyrolysis of yolk-shell structured Zn-Co-ZIFs@polydopamine （PDA）. PDA acted as both protection layer and carbon source, which successfully prevented the aggregation of cobalt nanoparticles during high-temperature pyrolysis process. The Co NP and N containing carbon （Co NP/NC） hollow nanospheres were active for both oxygen evolution reaction （OER） and oxygen reduction reaction （ORR）, affording overpotential of 430 mV at 10 mA/cm2 for OER in 1 M KOH and comparable half-wave potential to that of Pt/C （0.80V vs RHE） for ORR in 0.1 M KOH. The superior performance of carbon hollow nanospheres for both OER and ORR was mainly attributed to its small metal nanoparticles, N-doping and hollow nanostructure. The protection and confinement effect that originated from PDA coating strategy could be extended to the synthesis of other hollow structured carbon materials, especially the ones with small metal nanoparticles.

The role of water in methane adsorption and diffusion within nanoporous silica investigated by hyperpolarized 129Xe and 1H PFG NMR spectroscopy

Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance （NMR） studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized （HP） 129Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ~H pulsed field gradient （PFG） NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.