Development of robust catalysts for electrochemical water splitting is a critical topic for the energy conversion field. Herein, a precise electrochemical reconstruction of IrTe 2 hollow nanoshuttles (HNSs) is performed for oxygen and hydrogen evolution reactions (OER and HER), the two half reactions of water splitting. It is determined that the reconstruction of IrTe 2 HNSs can be regulated by adjusting the potential during electrochemical dealloying, in which mild and high potentials lead to the formation of IrTe 2 HNSs with metal Ir shell (D-IrTe 2 HNSs) and IrO x surface (DO-IrTe 2 HNSs), respectively. Detailed analyses reveal that such electrochemical reconstruction has produced abundant defects in D-IrTe 2 and DO-IrTe 2 HNSs. As a result of this, D-IrTe 2 HNSs present a very low HER overpotential of 54 mV at a current density of 10 mA cm −2 in 1.0 m KOH. Moreover, the turnover frequency of DO-IrTe 2 HNSs is 0.36 O 2 s −1 at an OER overpotential of 250 mV in 0.5 m H 2 SO 4 , outperforming the most of reported Ir-based catalysts. Furthermore, the D-IrTe 2 ||DO-IrTe 2 couple exhibits promising activity for the overall water splitting in both 1.0 m KOH and 0.5 m H 2 SO 4. This study promotes the fundamental research for the design of efficient catalysts via surface engineering.
Inorganic CsPbX3 perovskite nanocrystals (NCs) have exhibited great optical properties, such as tunable emission wavelength, narrow emission line-widths, and high photoluminescent quantum yields. However, the unstable crystal structure of perovskite CsPbX3 NCs lead to a deterioration in optical performance. In this work, it is demonstrated that inorganic perovskite NCs, including CsPbCl3 and CsPbBr3‑x Cl x NCs with excellent photoluminescence quantum yield and optical stability can be improved via anion exchange reaction treated with a new halide precursor consisting of copper halide– (CuX2−) oleylamine (OLA) complexes. Unlike traditional perovskite synthesized processes for better crystalline structures operated at high temperatures, this work offers an economical method operable at the room temperatures. The treated CsPbX3 perovskite nanocrystals were characterized by in situ photoluminescence (PL) spectra and in situ X-ray diffraction (XRD). Cu2+ ions were only absorbed on the surface of perovskite NCs confirmed by the X-ray absorption spectroscopy (XAS) analysis. Density functional theory calculation explained that the origin of high stability and good crystallinity for treated perovskite NCs stemmed from adsorption of CuCl2 on perovskite’s surface to passivate defect sites during the recrystallization process.
Efforts have been made to elucidate the origin of d(0) magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO.
This work presents the O K-and Ti L 3,2-edge x-ray absorption near-edge structure ͑XANES͒ spectra of Pb x Sr 1−x TiO 3 ͑P x STO͒ and Ba x Sr 1−x TiO 3 ͑B x STO͒ compounds with various Pb and Ba concentrations. The result provides direct evidence that the Pb-O bonding strongly affects O 2p-Ti 3d hybridization in the TiO 6 octahedron of P x STO. In contrast, the Ba-O bonding does not substantially affect O 2p-Ti 3d hybridization in B x STO. The Ti L 3-edge XANES spectra show the splitting of the e g band for P x STO with x տ 0.5, which provides an evidence of Pb-induced tetragonal distortion in the TiO 6 octahedron. In contrast, e g band splitting is absent in B x STO.
catalyst surface to form the final product, which seriously hinders the progress of the reaction. [3,4] Although researchers have made significant progress in the design of catalysts, a large cell voltage is still needed to drive this process. Therefore, it is still highly desirable to design high-efficiency water-splitting electrocatalysts. Recently, ruthenium (Ru) has attracted special attention for water-splitting catalysis since its inherently excellent activity and far lower price than platinum (Pt) and iridium (Ir). [5-9] To date, various strategies have been applied to enhance the activity of the Ru-based catalysts, including turning the crystal phase, doping electrocatalysts with hetero atoms, alloying Ru with the transition metals, and so on forth. [7,10,11] In principle, since the electrocatalysis is usually carried out on the surface of a catalyst, controlling the surface structure of the catalyst is a more straightforward way to improve the catalytic performance. The high-index crystal facets have more coordination unsaturated atoms and more active sites, which is believed to be more active. [12-14] Nevertheless, there were fewer reports on controlling the Ru-based catalysts with high-index facets. To this end, the fine control of Ru-based catalysts is of great significance in both practical application and fundamental research. Shape control has realized huge success for developing efficient Pd/Ptbased nanocatalysts, but the control of Ru-based nanocrystals remains a formidable challenge due to the inherent anisotropy in hexagonal closedpacked nanocrystals. Herein, a class of unique RuCo nanoscrews (NSs) for water electrosplitting is successfully synthesized with rough surfaces and the exposure of steps and edges. Those high-index faceted RuCo NSs show superior performance for overall water electrosplitting, where a low cell voltage of 1.524 V (@ 10 mA cm −2) and excellent stability for more than 20 h (@ 10 mA cm −2) for overall water electrosplitting in 1 m KOH is achieved. The enhanced performance of RuCo NSs is due to the optimization of the binding energy with the intermediate species and the reduced energy barrier of water dissociation. Density functional theory calculations reveal that the RuCo NS structure intrinsically endows various ridges and edges, which create low coordinated Ru-and Co-sites. These active Ru-and Co-sites present high efficiencies in electronic exchange and transfer between adsorbing O species and nearby lattice sites, guaranteeing the high H 2 Osplitting activities. This present work opens up a new strategy for creating high-performance electrocatalysts for water splitting.
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