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.

Direct and efficient photocatalytic water splitting is critical for sustainable conversion and storage of renewable solar energy. Here, we propose a conceptual design of two-dimensional CN-based in-plane heterostructure to achieve fast spatial transfer of photoexcited electrons for realizing highly efficient and spontaneous overall water splitting. This unique plane heterostructural carbon ring (C)-CN nanosheet can synchronously expedite electron-hole pair separation and promote photoelectron transport through the local in-plane π-conjugated electric field, synergistically elongating the photocarrier diffusion length and lifetime by 10 times relative to those achieved with pristine g-CN. As a result, the in-plane (C)-CN heterostructure could efficiently split pure water under light irradiation with prominent H production rate up to 371 μmol g h and a notable quantum yield of 5% at 420 nm.

Understanding the initial nucleation mechanism of monodisperse nanocrystals (NCs) during synthesis process is an important prerequisite to control the desired sizes and to manipulate the properties of nanoscale materials. The acquisition of information for the small nanocluster nucleation process, however, still remains challenging. Here, using a continuous-flow in situ X-ray absorption fine structure (XAFS) spectroscopy for time-resolved studies, we have clarified the initial kinetic nucleation of Au clusters under the grain size of 1 nm for the classical Au NCs synthesis via the reduction of AuCl(4)(-) in aqueous solution. The in situ XAFS results present the experimental revelation of the formation of intermediate Cl(3)(-)Au-AuCl(3)(-) dimer and the subsequent higher complexes 'Au(n)Cl(n+x)' in the initial nucleation stage. We propose a kinetic three-step mechanism involving the initial nucleation, slow growth, and eventual coalescence for the Au NCs formation, which may be helpful for the synthesis of metallic nanomaterials.

There remains a pressing challenge in the efficient utilization of visible light in the photoelectrochemical applications of water splitting. Here, we design and fabricate pseudobrookite Fe 2 TiO 5 ultrathin layers grown on vertically aligned TiO 2 nanotube arrays that can enhance the conduction and utilization of photogenerated charge carriers. Our photoanodes are characterized by low onset potentials of B0.2 V, high photon-to-current efficiencies of 40-50% under 400-600 nm irradiation and total energy conversion efficiencies of B2.7%. The high performance of Fe 2 TiO 5 nanotube arrays can be attributed to the anisotropic charge carrier transportation and elongated charge carrier diffusion length (compared with those of conventional TiO 2 or Fe 2 O 3 photoanodes) based on electrochemical impedance analysis and first-principles calculations. The Fe 2 TiO 5 nanotube arrays may open up more opportunities in the design of efficient and low-cost photoanodes working in visible light for photoelectrochemical applications.

X-ray absorption fine structure (XAFS) and first-principles calculations were employed to study the structure and ferromagnetism origin of Zn0.97Mn0.03O thin film grown by metal organic chemical vapor deposition. The magnetization measurements indicate that this sample is ferromagnetic at room temperature. The Mn ions are located at the substitutional Zn sites as revealed by the Mn K-edge XAFS spectroscopy. Moreover, the O K-edge XAFS analysis indicated the existence of numerous Zn vacancies. Based on first-principles calculations, the authors propose that the Zn vacancy can induce the room-temperature ferromagnetism in Mn-doped ZnO.

Understanding the formation process in the controlled synthesis of nanocrystals will lead to the effective manipulation of the morphologies and properties of nanomaterials. Here, in-situ UV-vis and X-ray absorption spectroscopies are combined to monitor the tracks of the nucleation pathways in the solution synthesis of platinum nanocrystals. We find experimentally that the control over nucleation pathways through changing the strength of reductants can be efficiently used to manipulate the resultant nanocrystal shapes. The in-situ measurements show that two different nucleation events involving the formation of one-dimensional "Pt(n)Cl(x)" complexes from the polymerization of linear "Cl(3)Pt-PtCl(3)" dimers and spherical "Pt(n)(0)" clusters from the aggregation of Pt(0) atoms occur for the cases of weak and strong reductants; and the resultant morphologies are nanowires and nanospheres, respectively. This study provides a crucial insight into the correlation between the particle shapes and nucleation pathways of nanomaterials.

Infrared-to-visible upconversion emission intensities are investigated in Li+ and Er3+ codoped ZnO nanocrystals. Li+ ions doped in ZnO/Er3+ nanocrystals can greatly enhance the upconversion emission intensity of Er3+ ions. The extended X-ray absorption fine structure spectroscopy data show that both the Er−O bond length and coordination number of the Er−Er bond have been altered by introducing Li+ ions in the ZnO/Er3+ nanocrystals. The variation of Er−O bond length leads to the change in the local asymmetry around Er3+ ions. Meanwhile, the greater coordination number of the Er−Er bond causes stronger interaction between neighboring Er3+ ions and, hence, strengthens the reaction Er3+ (4F7/2) + Er3+ (4I11/2) → 2Er3+ (4F9/2). In this process, the 4F9/2 state is a metastable state that could be excited to the 2H9/2 state by absorbing one photon at high excitation power. Li+ ions also can reduce the OH groups in specimen, which is the other reason for enhancing the upconversion emission intensities.

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 CoO6−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.