Pits confined in ultrathin cerium(IV) oxide for studying catalytic centers in carbon monoxide oxidation

The Hydric Effect in Inorganic Nanomaterials for Nanoelectronics and Energy Applications

Protons, as one of the world's smallest ions, are able to trigger the charge effect without obvious lattice expansion inside inorganic materials, offering a unique and important test-bed for controlling their diverse functionalities. Arising from the high chemical reactivity of hydrogen (easily losing an electron) with various main group anions (easily accepting a proton), the hydric effect provides a convenient and environmentally benign route to bring about fascinating new physicochemical properties, as well as to create new inorganic structures based on the "old lattice" without dramatically destroying the pristine structure, covering most inorganic materials. Moreover, hydrogen atoms tend to bond with anions or to produce intrinsic defects, both of which are expected to inject extra electrons into lattice framework, promising advances in control of bandgap, spin behavior, and carrier concentration, which determine functionality for wide applications. In this review article, recently developed effective hydric strategies are highlighted, which include the conventional hydric reaction under high temperature or room temperature, proton irradiation or hydrogen plasma treatment, and gate-electrolyte-driven adsorption or doping. The diverse physicochemical properties brought by the hydric effect via modulation of the intrinsic electronic structure are also summarized, finding wide applications in nanoelectronics, energy applications, and catalysis.

CoOOH Nanosheets with High Mass Activity for Water Oxidation

Endowing transition-metal oxide electrocatalysts with high water oxidation activity is greatly desired for production of clean and sustainable chemical fuels. Here, we present an atomically thin cobalt oxyhydroxide (γ-CoOOH) nanosheet as an efficient electrocatalyst for water oxidation. The 1.4 nm thick γ-CoOOH nanosheet electrocatalyst can effectively oxidize water with extraordinarily large mass activities of 66.6 A g(-1), 20 times higher than that of γ-CoOOH bulk and 2.4 times higher than that of the benchmarking IrO2 electrocatalyst. Experimental characterizations and first-principles calculations provide solid evidence to the half-metallic nature of the as-prepared nanosheets with local structure distortion of the surface CoO(6-x) octahedron. This greatly enhances the electrophilicity of H2O and facilitates the interfacial electron transfer between Co ions and adsorbed -OOH species to form O2, resulting in the high electrocatalytic activity of layered CoOOH for water oxidation.

O vacancies on steps on the CeO2(111) surface

Cerium dioxide is a compound important for heterogeneous catalysis, energy technologies, biomedical applications, etc. One of its most remarkable properties is low O vacancy (Ovac) formation energy Ef. Nanostructuring of ceria was shown to decrease Ef and to make the oxide material more active in oxidative reactions. Here we investigate computationally formation of Ovac on CeO2(111) surfaces nanostructured by steps with experimentally observed structures. To facilitate the search for Ovac + 2Ce(3+) configurations that yield the lowest Ef values we proposed and employed an efficient computational scheme where DFT + U calculations were preceded by a pre-screening procedure based on the results of plain DFT calculations. Ef values on the steps were calculated to be up to 0.7 eV lower than on a regular CeO2(111) surface. Some energetically stable Ovac + 2Ce(3+) configurations were found to include subsurface Ce(3+) ions. The present results quantify to what extent the roughness of the CeO2(111) surface affects its reducibility.

Self-assembly fabrication of hollow mesoporous silica@Co-Al layered double hydroxide@graphene and application in toxic effluents elimination

Here, we propose a self-assembly process to prepare hierarchical HM-SiO2@Co-Al LDH@graphene, with the purpose of combining their outstanding performance. Hollow mesoporous silica was first synthesized as the core, using a novel sonochemical method, followed by a controlled shell coating process and chemical reduction. As a result of the electrostatic potential difference among HM-SiO2, Co-Al LDH, and graphene oxide, the HM-SiO2 spheres were coated by Co-Al LDH and graphene. Subsequently, the HM-SiO2@Co-Al LDH@graphene spheres were introduced into an epoxy resin (EP) matrix for investigation of their toxic effluents capture and elimination effectiveness during combustion. The amount of toxic CO and volatile organic compounds from the epoxy resin decomposition significantly suppressed after incorporating the HM-SiO2@Co-Al LDH@graphene hybrids, implying a reduced toxicity.

Monoatomic-thick graphitic carbon nitride dots on graphene sheets as an efficient catalyst in the oxygen reduction reaction

Atomically thick two-dimensional materials have been increasingly attracting research interest not only due to their promising applications in a range of functional devices but also to their theoretical value to unraveling the catalytic electron transfer process within a simplified scenario. In this work, the monoatomic-thick dot-sized graphitic carbon nitride (g-C3N4) has been synthesized and intimately contacted to the basal plane of the graphene sheet to form the monolayer g-C3N4 dots@graphene (MTCG). The electrocatalytic activity of the MTCG in the oxygen reduction reaction is found to rival that of the commercial Pt/C catalyst in terms of the catalytic current density and half-wave potential. The density functional theory calculations confirm the catalytic improvement of the MTCG originates from a higher efficiency for the reduction of OOH(-) than that of the g-C3N4 alone; therefore, the current work is expected to provide new insights in developing next-generation, highly efficient catalysts for the oxygen reduction reaction.

Ultrathin two-dimensional inorganic materials: new opportunities for solid state nanochemistry

CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

Controlling the physics and chemistry of binary and ternary praseodymium and cerium oxide systems

Binary and ternary PrO_xand CeO_xfilms grown on Si(111) are most versatile systems available in a variety of stoichiometries and surface structures.

Atomically-thin two-dimensional sheets for understanding active sites in catalysis

Atomically-thin two-dimensional sheets can serve as an ideal model to disclose the role of active sites in catalysis.

Surface chemical-modification for engineering the intrinsic physical properties of inorganic two-dimensional nanomaterials

This tutorial review summarizes the recent advances in engineering the intrinsic physical properties of inorganic two-dimensional nanomaterials by surface chemical modification.

Low overpotential in vacancy-rich ultrathin CoSe2 nanosheets for water oxidation

According to Yang Shao-Horn's principle, CoSe2 is a promising candidate as an efficient, affordable, and sustainable alternative electrocatalyst for the oxygen evolution reaction, owing to its well-suited electronic configuration of Co ions. However, the catalytic efficiency of pure CoSe2 is still far below what is expected, because of its poor active site exposure yield. Herein, we successfully overcome the disadvantage of insufficient active sites in bulk CoSe2 by reducing its thickness into the atomic scale rather than any additional modification (such as doping or hybridizing with graphene or noble metals). The positron annihilation spectrometry and XAFS spectra provide clear evidence that a large number of VCo″ vacancies formed in the ultrathin nanosheets. The first-principles calculations reveal that these VCo″ vacancies can serve as active sites to efficiently catalyze the oxygen evolution reaction, manifesting an OER overpotential as low as 0.32 V at 10 mA cm(-2) in pH 13 medium, which is superior to the values for its bulk counterparts as well as those for the most reported Co-based electrocatalysts. Considering the outstanding performance of the simple, unmodified ultrathin CoSe2 nanosheets as the only catalyst, further improvement of the catalytic activity is expected when various strategies of doping or hybridizing are used. These results not only demonstrate the potential of a notable, affordable, and earth-abundant water oxidation electrocatalyst based on ultrathin CoSe2 nanosheets but also open up a promising avenue into the exploration of excellent active and durable catalysts toward replacing noble metals for oxygen electrocatalysis.

Template-free and non-hydrothermal synthesis of CeO2nanosheets via a facile aqueous-phase precipitation route with catalytic oxidation properties

Petal and belt-like CeO₂nanosheets are synthesized using an aqueous phase precipitation method under template-free and non-hydrothermal conditions and exhibit excellent catalytic oxidation performance.