Insight into Impacts of π-π Assembly on Phthalocyanine Based Heterogeneous Molecular Electrocatalysis.

Electrochemical CO2 reduction (CO2R) to feedstocks competes with the hydrogen evolution reaction (HER). Cobalt phthalocyanine (CoPc) immobilized onto carbon driven by π-π interaction represents a classical type of heterogeneous molecular catalyst for CO2R. However, the impacts of π conjugation on the electrocatalysis have not been clarified. Herein, the electrochemical properties of CoPc were investigated by comparison of its analogue to 2,3-naphthalocyanine cobalt (NapCo) having extended π conjugation. It is found that CoPc is redox-active on carbon to provide low oxidized Co sites for improving the CO2R activity and selectivity, while NapCo on carbon turned out to be redox-inert leading to lower performance. In addition, the redox-mediated mechanism for CO2R on CoPc tends to operate with increasing electrolyte alkalinity, which further enhances the reaction selectivity. We speculated that moderate π conjugation allows the redox-mediated mechanism on CoPc, which is critical to promote CO2R performance while depressing the competing HER.

Insight into Multiphase Interlayer Molecular Packing and Stepwise Phase Transition in 4-(Phenylazo)benzoate Anion-Intercalated Layered Zinc Hydroxide.

The properties of layered intercalation hybrids are closely related to interlayer molecular packing. To develop functional intercalation hybrids, it is essential to gain deep insights into interlayer molecular packing. This work reports a new comprehensive insight into the controllable multiphase interlayer molecular packing in 4-(phenylazo)benzoate anion-intercalated layered zinc hydroxide (LZH-4-PAB intercalation hybrids). The new insight breaks up the general understanding that the interlayer molecular packing of anions is usually single-phase, lacking diversity and controllability. Furthermore, it uncovers an interesting stepwise rather than the generally expected continuous phase transition of the interlayer molecular packing. The intercalated 4-PAB anions initially organize into the horizontal monolayer packing (θ = 0°, Phase I), which stepwise transforms to the tilted interdigitated antiparallel bilayer packing (θ ≈ 50°, Phase II) along with an increased intercalation loading and eventually to the vertical interdigitated antiparallel bilayer packing (θ = 90°, Phase III). The LZH-4-PAB hybrids exhibited a greatly enhanced interlayer molecular packing-dependent UV-vis absorption. This study provides helpful guidance for developing property-tailored intercalation hybrids. It may attract new interest in more layered intercalation hybrids. New and rich intercalation chemistry might be discovered in more functional intercalation hybrids beyond the 4-PAB anion-intercalated layered zinc hydroxide.

Resolving nanostructure and chemistry of solid-electrolyte interphase on lithium anodes by depth-sensitive plasmon-enhanced Raman spectroscopy.

The solid-electrolyte interphase (SEI) plays crucial roles for the reversible operation of lithium metal batteries. However, fundamental understanding of the mechanisms of SEI formation and evolution is still limited. Herein, we develop a depth-sensitive plasmon-enhanced Raman spectroscopy (DS-PERS) method to enable in-situ and nondestructive characterization of the nanostructure and chemistry of SEI, based on synergistic enhancements of localized surface plasmons from nanostructured Cu, shell-isolated Au nanoparticles and Li deposits at different depths. We monitor the sequential formation of SEI in both ether-based and carbonate-based dual-salt electrolytes on a Cu current collector and then on freshly deposited Li, with dramatic chemical reconstruction. The molecular-level insights from the DS-PERS study unravel the profound influences of Li in modifying SEI formation and in turn the roles of SEI in regulating the Li-ion desolvation and the subsequent Li deposition at SEI-coupled interfaces. Last, we develop a cycling protocol that promotes a favorable direct SEI formation route, which significantly enhances the performance of anode-free Li metal batteries.

Real-time tracking of colloidal stability based on collision behaviors probed by surface-enhanced Raman spectroscopy.

HYPOTHESIS: The dynamic behaviors of colloidal particles have already been considered as one of the key issues in their practical application, such as aggregation and dispersion. However, it is still remained significant challenge in developing the real time techniques to capture their dynamic tracks. The nano/subnanometer scale gap generated during the colloidal collisions served as the critical location for amplifying the Raman signal, so called as gap ("hot spots") based surface enhanced Raman spectroscopy (SERS). The alternating reversible "spike" of SERS intensity and irreversible step in baseline intensity are contributed to the preferred stability and the aggregation of colloid respectively. EXPERIMENTS: A facile approach is developed to track colloidal stability in real-time based on collisions and SERS. The effects of particle concentration, the dispersion medium, and solution pH on colloidal stability are systematically investigated, and the SERS intensity of a simulated single-like "hot spot" was calculated by combining a SEM position with SERS mapping technology to estimate the intensity of single-particle collision. FINDINGS: The colloidal particles exhibited higher stability in the solution with lower particle concentration, higher viscosity and neutral medium. The SERS intensity of single-particle collision was estimated to be about 2.06 × 10-7 counts, and the average number of collisions for the 0.13 mmol/dm3 SiO2@Ag solution was about 1.11 × 108 times/spike in the "spikes" with SERS intensity of 23.0 cps. It is believed that the SERS based strategy would be developed as a promising tool for obtaining the deeper insight into the nature of collisions in the colloidal science.

Construction of a HPLC-SERS hyphenated system for continuous separation and detection based on paper substrates.

The achievement of high-throughput separation and high-sensitivity detection of complex samples has been one of the most challenging issues in the field of analytical science. The application of a single technology alone could not satisfy the above requirements. The combination of technologies with the capability of high-efficiency separation and high-sensitivity structural-recognition is highly desired to meet the technical requirements. Herein, an automatic high-performance liquid chromatography (HPLC)-surface enhanced Raman spectroscopy (SERS) hyphenated system using paper substrates as the "interface" was constructed to achieve efficient separation and real-time detection. A homogeneous Au nanoparticle was printed on the hydrophobic filter paper with the inkjet technology. The prepared substrates served as a linkage for the continuous realization of HPLC and SERS functions. The complex system was separated by HPLC, and the effluents were loaded onto automatically and continuously replaceable paper substrates for real time SERS measurements. The continuous rapid separation and real-time detection of various two-component mixtures were achieved with the separation efficiency and detection sensitivity of each technology. The results demonstrated that the HPLC-SERS hyphenated system exhibited the complementary capability of the on-line separation and continuous structural identification of illegal additives in real samples. The detection sensitivity was increased by an order of magnitude to reach 10-5 mol dm-3, and the efficiency and accuracy for the separation and identification on the multi-components samples were higher than those of the individual HPLC or SERS technology. It is believed that the continuous paper substrate-based HPLC-SERS hyphenated system would be developed as a promising technique for the separation and identification of multi-components mixtures with high throughput.

Real-time visualization of the Suzuki reaction using surface enhanced Raman spectroscopy and a moveable magnetic nanoparticle film.

Utilizing a moveable Fe3O4@Au film, an operando SERS strategy was developed successfully for visualizing Suzuki reaction processes. The feasibility and generality were verified by using the reaction of 3-bromopyridine and phenylboronic acid as a probe.

Real-Time Monitoring of Surface Effects on the Oxygen Reduction Reaction Mechanism for Aprotic Na-O2 Batteries.

Discharging of aprotic sodium-oxygen (Na-O2) batteries is driven by the cathodic oxygen reduction reaction in the presence of sodium cations (Na+-ORR). However, the mechanism of aprotic Na+-ORR remains ambiguous and is system dependent. In-situ electrochemical Raman spectroscopy has been employed to study the aprotic Na+-ORR processes at three atomically ordered Au(hkl) single-crystal surfaces for the first time, and the structure-intermediates/mechanism relationship has been identified at a molecular level. Direct spectroscopic evidence of superoxide on Au(110) and peroxide on Au(100) and Au(111) as intermediates/products has been obtained. Combining these experimental results with theoretical simulation has revealed that the surface effect of Au(hkl) electrodes on aprotic Na+-ORR activity is mainly caused by the different adsorption of Na+ and O2. This work enhances our understanding of aprotic Na+-ORR on Au(hkl) surfaces and provides further guidance for the design of improved Na-O2 batteries.

Plasmonic Core-Shell Nanomaterials and their Applications in Spectroscopies.

Plasmonic core-shell nanostructures have attracted considerable attention in the scientific community recently due to their highly tunable optical properties. Plasmon-enhanced spectroscopies are one of the main applications of plasmonic nanomaterials. When excited by an incident laser of suitable wavelength, strong and highly localized electromagnetic (EM) fields are generated around plasmonic nanomaterials, which can significantly boost excitation and/or radiation processes that amplify Raman, fluorescence, or nonlinear signals and improve spectroscopic sensitivity. Herein, recent developments in plasmon-enhanced spectroscopies utilizing core-shell nanostructures are reviewed, including shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), plasmon-enhanced fluorescence spectroscopy, and plasmon-enhanced nonlinear spectroscopy.

Reducing Energy Disorder of Hole Transport Layer by Charge Transfer Complex for High Performance p-i-n Perovskite Solar Cells.

Solution-processed organic semiconductor charge-transport layers (OS-CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p-i-n planar perovskite solar cells (pero-SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge-transport ability of OS-CTLs. Here, a charge-transfer complex (CTC) strategy to reduce the energy disorder in the OS-CTLs by doping an organic semiconductor, 4,4'-(4,8-bis(5-(trimethylsilyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BDT-Si), in a commercial hole-transport layer (HTL), poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron-deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi-Fermi level splitting in the device. As a result, the p-i-n planar pero-SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero-SCs.

Surface-enhanced Raman spectroscopic investigation on adsorption kinetic of carbon monoxide at the solid-gas interface.

A molecular-level understanding of CO adsorption behavior would be greatly beneficial to resolving the problem of CO poisoning in fuel cells and medical science. Herein, an efficient borrowing strategy based on surface enhanced Raman scattering (SERS) has been developed to investigate the adsorption behavior of CO at the gas-solid interface. A composite SERS substrate with high uniformity was fabricated by electrochemical deposition of optimal Pt over-layers onto an Au nanoparticle film. The results indicated that the linearly bonded mode follows the Langmuir adsorption curve (type I), while the multiply bonded did not. It took a longer time for the C-OM vibration to reach the adsorption equilibrium than that of C-OL. The variation tendency toward the Pt-COL frequency was in opposition to that of C-OL, caused by the chemical and dipole-dipole coupling effects. The increase in dynamic coupling effects of the CO molecules caused a blue shift in νCO and a red shift of the Pt-CO band, while its shielding effect on SERS intensity cannot be ignored. Additionally, higher pressure is more conducive for linear adsorption to achieve saturation. Density functional theory calculations were employed to explore the adsorption mechanisms. It should also be noted that the substrate with good recycling performance greatly expands its practical application value. The present study suggested that the SERS-based borrowing strategy shows sufficient even valuable capacity to investigate gas adsorption kinetics behavior.

The moveable "hot spots" effect in an Au nanoparticles-Au plate coupled system.

Surface-enhanced Raman spectroscopy (SERS) is mainly contributed by "hot spots". Due to the huge electromagnetic enhancement, "hot spots" have wide applications in surface analysis and surface catalysis. The in-depth research on the "hot spots" effect is conducive to understanding SERS enhancement mechanisms and designing substrates with high enhancement. At present, the investigation on the "hot spots" effect is mainly based on theoretical simulation and simple experimental models. However, little attention has been paid to the SERS substrates with practical applications. The main reason is that it is difficult to construct a suitable coupled model with great uniformity and sensitivity, which led to the lack of comparability of SERS intensities from different spots or substrates. In this work, Au nanoparticle mono-/bi-layer films coupled with Au single-crystal plate systems were constructed to investigate the distribution and transformation of "hot spots" dependent on the excitation wavelength by a single or dual probe-modified strategy, in which one or two types of molecules with distinct characteristic peaks were modified in different enhanced gaps. The results demonstrated that the wavelength that drove the transformation of the coupling mode from the "particle-particle" mode to the "particle-surface" mode was around 638 nm in the Au nanoparticle monolayer film (Au MLF) covered Au plate system. As the second naked Au MLF was transferred onto the first Au MLF, "hot spots" were transferred to the "particle-particle" gap between the upper and lower Au MLFs with a 638 nm laser as the excitation line. This work offers a novel avenue to investigate the "hot spots" effect in the complex multidimensional nanostructures, which is beneficial for the development of theoretical research and practical applications of SERS.

Surface enhanced Raman spectroscopic studies on the adsorption behaviour of nitric oxide on a Ru covered Au nanoparticle film.

Nitric oxide (NO) is very interesting because of its effects on air pollution and especially biological systems. The adsorption behavior of NO molecules has fundamental importance with great technical challenges due to complex processes and species identification. Herein, the NO adsorption behavior on a Ru surface has been investigated using well-designed surface enhanced Raman spectroscopy (SERS) substrates. A Au nanoparticle monolayer film on ITO was employed as the electrode and Ru layers were electrochemically deposited. The internal SERS effect from the Au nanoparticles with high sensitivity and the metallic surfaces of Ru with practical application were integrated into a composite Au/Ru substrate. The molecular adsorption and dissociation of NO were observed simultaneously by SERS. A competitive relationship between adsorption and dissociation was observed at higher NO pressure, and the 3-fold and 2-fold bridge and top adsorption configurations appeared on the surface and were associated with different ν NO vibrational frequencies. The results indicated that 3-fold bridge sites are preferred for dissociation over other structures. The dissociation of NO produced adsorbed atomic nitrogen and oxygen species to form Ru-N and Ru-O bonds, respectively. The dissociation process, especially for linear NO, was site dependent and blocked at higher pressure or coverage. Due to the change in adsorption energy and coverage, a conversion of the adsorption configuration from bridge to top was observed in the initial stage of NO adsorption, and this was followed by a mixture of bridge and top configurations of NO and dissociated species. A two-step dissociation mechanism and the steps of NO adsorption were proposed. The present study suggested that the SERS technique with appropriate attractive metal overlayers provided a significant and possibly even a valuable approach to explore adsorption behavior and kinetics at gas-solid interfaces.

A study on 85Kr measurement with an internal gas proportional counter.

A measurement method of 85Kr using an internal gas proportional counter (IGPC) is presented in this study. The operation conditions of the IGPC were determined and optimized, including the operating voltage, pressure, sample volume, interference from other gas components such as nitrogen or air, and mitigation of the memory effect. The IGPC was calibrated using certified standards, and the detection efficiency was approximately 58% for typical samples. A lower limit of detection of approximately 0.11 MBq/m3(Kr) was achieved after counting for 5 h with 1 mL pure Kr, corresponding to the atmospheric activity concentration of 0.18 Bq/m3 (air). It was shown that the IGPC could be used effectively for measuring 85Kr.

Reconfiguration of interfacial energy band structure for high-performance inverted structure perovskite solar cells.

Charged defects at the surface of the organic-inorganic perovskite active layer are detrimental to solar cells due to exacerbated charge carrier recombination. Here we show that charged surface defects can be benign after passivation and further exploited for reconfiguration of interfacial energy band structure. Based on the electrostatic interaction between oppositely charged ions, Lewis-acid-featured fullerene skeleton after iodide ionization (PCBB-3N-3I) not only efficiently passivates positively charged surface defects but also assembles on top of the perovskite active layer with preferred orientation. Consequently, PCBB-3N-3I with a strong molecular electric dipole forms a dipole interlayer to reconfigure interfacial energy band structure, leading to enhanced built-in potential and charge collection. As a result, inverted structure planar heterojunction perovskite solar cells exhibit the promising power conversion efficiency of 21.1% and robust ambient stability. This work opens up a new window to boost perovskite solar cells via rational exploitation of charged defects beyond passivation.

Oxygen-Assisted Cathodic Deposition of Zeolitic Imidazolate Frameworks with Controlled Thickness.

Processing metal-organic frameworks (MOFs) as films with controllable thickness on a substrate is increasingly crucial for many applications to realize function integration and performance optimization. Herein, we report a facile cathodic deposition process that enables the large-area preparation of uniform films of zeolitic imidazolate frameworks (ZIF-8, ZIF-71, and ZIF-67) with highly tunable thickness ranging from approximately 24 nm to hundreds of nanometers. Importantly, this oxygen-reduction-triggered cathodic deposition does not lead to the plating of reduced metals (Zn and Co). It is also operable cost-effectively in the absence of supporting electrolyte and facilitates the construction of well-defined sub-micrometer-sized heterogeneous structures within ZIF films.

Ligand-Controlled Copper(I)-Catalyzed Cross-Coupling of Secondary and Primary Alcohols to α-Alkylated Ketones, Pyridines, and Quinolines.

One hexanuclear Cu(I) cluster of 4,6-dimethylpyrimidine-2-thiolate efficiently catalyzes the dehydrogenative cross-coupling of secondary and primary alcohols to α-alkylated ketones with high selectivity. This transformation proceeds through a one-pot sequence of dehydrogenation of alcohols, condensation of aldehydes and ketones, hydrogenation of the resulting α,ß-unsaturated ketones, and dehydrogenation of the α-alkylated alcohols to generate α-alkylated ketones. This catalytic system also displays high activity for the annulation reaction of secondary alcohols with γ-amino- and 2-aminobenzyl alcohols to yield pyridines and quinolines, respectively.

Surface-enhanced Raman spectroscopic identification in fingerprints based on adhesive Au nanofilm.

The visualization and acquisition of information on substances within fingerprints have attracted considerable interest owing to their practical application in forensic science. There are still some challenges in the transfer and imaging of fingerprints and the extraction of residues. Here, a facile approach was successfully developed for transferring and recovering the pattern of fingerprints, which is based on surface-enhanced Raman spectroscopy (SERS) and an adhesive Au nanofilm (ANF). The reproducibility of SERS effects and the adhesive quality of the ANF enabled the transfer, recovery of the pattern and extraction of chemical residues from living/latent fingerprints. The results demonstrated that the pattern of living fingerprints, including ridges, furrows and sweat pores, was recovered on the basis of SERS mapping of the vibrational band of amino acids from endogenous protein substances. The dye rhodamine 6G (R6G) was employed as a developing agent to enhance the visualization of fingerprints by SERS mapping of the band at 1360 cm-1. Moreover, exogenous residues, such as cotinine (COT) and methylene blue (MB), were also detected by SERS. Their distribution in fingerprints was also determined, although it was not associated with the pattern of fingerprints. This indicated that the extraction process based on the adhesive ANF could be applied to transfer fingerprints from a crime scene to the laboratory for precise identification via structural information on chemical residues and the pattern image of fingerprints. It is anticipated that the adhesive ANF when combined with an ultrahigh-sensitivity SERS technique could be developed as a promising tool for the visualization of fingerprints and monitoring of trace chemical residues for crime tracking in forensic science.

Observing the dynamic "hot spots" on two-dimensional Au nanoparticles monolayer film.

Interparticle spacing was controlled by evaporating water on 2D Au nanoparticles arrays. Relationships among SERS effect, SPR catalysis, and gap distance were experimentally and theoretically studied.

PtPb/PtNi Intermetallic Core/Atomic Layer Shell Octahedra for Efficient Oxygen Reduction Electrocatalysis.

Although explosive studies on pursuing high-performance Pt-based nanomaterials for fuel cell reactions have been carried out, the combined controls of surface composition, exposed facet, and interior structure of the catalyst remains a formidable challenge. We demonstrate herein a facile chemical approach to realize a new class of intermetallic Pt-Pb-Ni octahedra for the first time. Those nanostructures with unique intermetallic core, active surface composition, and the exposed facet enhance oxygen reduction electrocatalysis with the optimized PtPb1.12Ni0.14 octahedra exhibiting superior specific and mass activities (5.16 mA/cm2 and 1.92 A/mgPt) for oxygen reduction reaction (ORR) that are ∼20 and ∼11 times higher than the commercial Pt/C, respectively. Moreover, the PtPb1.12Ni0.14 octahedra can endure at least 15 000 cycles with negligible activity decay, showing a new class of Pt-based electrocatalysts with enhanced performance for fuel cells and beyond.

Precise tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis.

Comprising abundant interfaces, multicomponent heterostructures can integrate distinct building blocks into single entities and yield exceptional functionalities enabled by the synergistic components. Here we report an efficient approach to construct one-dimensional metal/sulfide heterostructures by directly sulfuring highly composition-segregated platinum-nickel nanowires. The heterostructures possess a high density of interfaces between platinum-nickel and nickel sulfide components, which cooperate synergistically towards alkaline hydrogen evolution reaction. The platinum-nickel/nickel sulfide heterostructures can deliver a current density of 37.2 mA cm-2 at an overpotential of 70 mV, which is 9.7 times higher than that of commercial Pt/C. The heterostructures also offer enhanced stability revealed by long-term chronopotentiometry measurements. The present work highlights a potentially powerful interface-engineering strategy for designing multicomponent heterostructures with advanced performance in hydrogen evolution reaction and beyond.