Publications by authors named "Petar M Radjenovic"

19 Publications

  • Page 1 of 1

Adsorption-Induced Active Vanadium Species Facilitate Excellent Performance in Low-Temperature Catalytic NO Abatement.

J Am Chem Soc 2021 Jul 30;143(27):10454-10461. Epub 2021 Jun 30.

Center for Excellence in Regional Atmospheric Environment and Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, People's Republic of China.

Vanadia-based catalysts have been widely used for catalyzing various reactions, including their long-standing application in the deNO process. It has been commonly considered that various vanadium species dispersed on supports with a large surface area act as the catalytically active sites. However, the role of crystalline VO in selective catalytic reduction of NO with NH (NH-SCR) remains unclear. In this study, a catalyst with low vanadia loading was synthesized, in which crystalline VO was deposited on a TiO support that had been pretreated at a high temperature. Surprisingly, the catalyst, which had a large amount of crystalline VO, showed excellent low-temperature NH-SCR activity. For the first time, crystalline VO on low-vanadium-loading catalysts was found to be transformed to polymeric vanadyl species by the adsorption of NH. The generated active polymeric vanadyl species played a crucial role in NH-SCR, leading to remarkably enhanced catalytic performance at low temperatures. This new finding provides a fundamental understanding of the metal oxide-catalyzed chemical reaction and has important implications for the development and commercial applications of NH-SCR catalysts.
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http://dx.doi.org/10.1021/jacs.1c05354DOI Listing
July 2021

Plasmonic Core-Shell Nanoparticle Enhanced Spectroscopies for Surface Analysis.

Anal Chem 2021 05 22;93(17):6573-6582. Epub 2021 Apr 22.

State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

Probing the properties and components of reactive surfaces is crucial for illustrating reaction mechanisms. However, common surface analysis techniques are restricted to in situ acquisition of surface information at the molecular scale in the human environment and industrial catalysis processes. Plasmonic spectroscopies are promising tools to solve this problem. This Feature is intended to introduce the plasmonic core-shell nanoparticle enhanced spectroscopies for qualitatively and quantitatively analyzing surface trace species. Four different working modalities are designed for meeting varied needs, involving in situ surface species detection, catalytic process monitoring, labeled sensing, and dual mode analysis. These newly developed plasmonic spectroscopies show great potential not only in fundamental research but also in practical applications.
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http://dx.doi.org/10.1021/acs.analchem.1c00233DOI Listing
May 2021

Probing Interfacial Electronic Effects on Single-Molecule Adsorption Geometry and Electron Transport at Atomically Flat Surfaces.

Angew Chem Int Ed Engl 2021 Jul 1;60(28):15452-15458. Epub 2021 Jun 1.

State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, iChEM, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.

Clarifying interfacial electronic effects on molecular adsorption is significant in many chemical and biochemical processes. Here, we used STM breaking junction and shell-isolated nanoparticle-enhanced Raman spectroscopy to probe electron transport and adsorption geometries of 4,4'-bipyridine (4,4'-BPY) at Au(111). Modifying the surface with 1-butyl-3-methylimidazolium cation-containing ionic liquids (ILs) decreases surface electron density and stabilizes a vertical orientation of pyridine through nitrogen atom σ-bond interactions, resulting in uniform adsorption configurations for forming molecular junctions. Modulation from vertical, tilted, to flat, is achieved on adding water to ILs, leading to a new peak ascribed to CC stretching of adsorbed pyridyl ring and 316 % modulation of single-molecule conductance. The dihedral angle between adsorbed pyridyl ring and surface decreases with increasing surface electronic density, enhancing electron donation from surface to pyridyl ring.
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http://dx.doi.org/10.1002/anie.202102587DOI Listing
July 2021

Plasmonic Core-Shell Nanomaterials and their Applications in Spectroscopies.

Adv Mater 2021 Apr 2:e2005900. Epub 2021 Apr 2.

College of Energy, State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Materials, Xiamen University, Xiamen, 361005, China.

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.
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http://dx.doi.org/10.1002/adma.202005900DOI Listing
April 2021

In Situ Surface-Enhanced Raman Spectroscopy Characterization of Electrocatalysis with Different Nanostructures.

Annu Rev Phys Chem 2021 Apr 20;72:331-351. Epub 2021 Jan 20.

State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, iChEM, College of Energy, Xiamen University, Xiamen 361005, China; email:

As energy demands increase, electrocatalysis serves as a vital tool in energy conversion. Elucidating electrocatalytic mechanisms using in situ spectroscopic characterization techniques can provide experimental guidance for preparing high-efficiency electrocatalysts. Surface-enhanced Raman spectroscopy (SERS) can provide rich spectral information for ultratrace surface species and is extremely well suited to studying their activity. To improve the material and morphological universalities, researchers have employed different kinds of nanostructures that have played important roles in the development of SERS technologies. Different strategies, such as so-called borrowing enhancement from shell-isolated modes and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)-satellite structures, have been proposed to obtain highly effective Raman enhancement, and these methods make it possible to apply SERS to various electrocatalytic systems. Here, we discuss the development of SERS technology, focusing on its applications in different electrocatalytic reactions (such as oxygen reduction reactions) and at different nanostructure surfaces, and give a brief outlook on its development.
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http://dx.doi.org/10.1146/annurev-physchem-090519-034645DOI Listing
April 2021

Spectroscopic Verification of Adsorbed Hydroxy Intermediates in the Bifunctional Mechanism of the Hydrogen Oxidation Reaction.

Angew Chem Int Ed Engl 2021 Mar 29;60(11):5708-5711. Epub 2021 Jan 29.

State Key Laboratory of Physical Chemistry of Solid Surfaces,iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen, 361005, China.

Elucidating hydrogen oxidation reaction (HOR) mechanisms in alkaline conditions is vital for understanding and improving the efficiency of anion-exchange-membrane fuel cells. However, uncertainty remains around the alkaline HOR mechanism owing to a lack of direct in situ evidence of intermediates. In this study, in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and DFT were used to study HOR processes on PtNi alloy and Pt surfaces, respectively. Spectroscopic evidence indicates that adsorbed hydroxy species (OH ) were directly involved in HOR processes in alkaline conditions on the PtNi alloy surface. However, OH species were not observed on the Pt surface during the HOR. We show that Ni doping promoted hydroxy adsorption on the platinum-alloy catalytic surface, improving the HOR activity. DFT calculations also suggest that the free energy was decreased by hydroxy adsorption. Consequently, tuning OH adsorption by designing bifunctional catalysts is an efficient method for promoting HOR activity.
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http://dx.doi.org/10.1002/anie.202015571DOI Listing
March 2021

Polarization- and Wavelength-Dependent Shell-Isolated-Nanoparticle-Enhanced Sum-Frequency Generation with High Sensitivity.

Phys Rev Lett 2020 Jul;125(4):047401

State Key Laboratory of Physical Chemistry of Solid Surfaces, MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

Sum-frequency generation (SFG) spectroscopy is a highly versatile tool for surface analysis. Improving the SFG intensity per molecule is important for observing low concentrations of surface species and intermediates in dynamic systems. Herein, Shell-Isolated-Nanoparticle-Enhanced SFG (SHINE-SFG) was used to probe a model substrate. The model substrate, p-mercaptobenzonitrile adsorbed on a Au film with SHINs deposited on top, provided an enhancement factor of up to 10^{5}. Through wavelength- and polarization-dependent SHINE-SFG spectroscopy, the majority of the signal enhancement was found to come from both plasmon enhanced emission and chemical enhancement mechanisms. A new enhancement regime, i.e., the nonlinear coupling of SHINE-SFG with difference frequency generation, was also identified. This novel mechanism provides insight into the enhancement of nonlinear coherent spectroscopies and a possible strategy for the rational design of enhancing substrates utilizing coupling processes.
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http://dx.doi.org/10.1103/PhysRevLett.125.047401DOI Listing
July 2020

Real-time detection of single-molecule reaction by plasmon-enhanced spectroscopy.

Sci Adv 2020 Jun 10;6(24):eaba6012. Epub 2020 Jun 10.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Materials, College of Energy, Department of Physics, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.

Determining structural transformations of single molecules (SMs) is an important fundamental scientific endeavor. Optical spectroscopies are the dominant tools used to unravel the physical and chemical features of individual molecules and have substantially contributed to surface science and biotechnology. In particular, Raman spectroscopy can identify reaction intermediates and reveal underlying reaction mechanisms; however, SM Raman experiments are subject to intrinsically weak signal intensities and considerable signal attenuation within the spectral dispersion systems of the spectrometer. Here, to monitor the structural transformation of an SM on the millisecond time scale, a plasmonic nanocavity substrate has been used to enable Raman vibrational and fluorescence spectral signals to be simultaneously collected and correlated, which thus allows a detection of photo-induced bond cleavage between the xanthene and phenyl group of a single rhodamine B isothiocyanate molecule in real time. This technique provides a novel method for investigating light-matter interactions and chemical reactions at the SM level.
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http://dx.doi.org/10.1126/sciadv.aba6012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286666PMC
June 2020

Probing Electric Field Distributions in the Double Layer of a Single-Crystal Electrode with Angstrom Spatial Resolution using Raman Spectroscopy.

J Am Chem Soc 2020 Jul 23;142(27):11698-11702. Epub 2020 Jun 23.

State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

The electrical double layer (EDL) is the extremely important interfacial region involved in many electrochemical reactions, and it is the subject of significant study in electrochemistry and surface science. However, the direct measurement of interfacial electric fields in the EDL is challenging. In this work, both electrochemical resonant Raman spectroscopy and theoretical calculations were used to study electric field distributions in the EDL of an atomically flat single-crystal Au(111) electrode with self-assembled monolayer molecular films. This was achieved using a series of redox-active molecules containing the 4,4'-bipyridinium moiety as a Raman marker that were located at different precisely controlled distances away from the electrode surface. It was found that the electric field and the dipole moment of the probe molecule both directly affected its Raman signal intensity, which in turn could be used to map the electric field distribution at the interface. Also, by variation of the electrolyte anion concentration, the Raman intensity was found to decrease when the electric field strength increased. Moreover, the distance between adjacent Raman markers was ∼2.1 Å. Thus, angstrom-level spatial resolution in the mapping of electric field distributions at the electrode-electrolyte interface was realized. These results directly evidence the EDL structure, bridging the gap between the theoretical and experimental understandings of the interface.
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http://dx.doi.org/10.1021/jacs.0c05162DOI Listing
July 2020

Shell-Isolated Nanoparticle-Enhanced Luminescence of Metallic Nanoclusters.

Anal Chem 2020 05 28;92(10):7146-7153. Epub 2020 Apr 28.

College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Energy, Department of Physics, Xiamen University, Xiamen 361005, China.

Metallic nanoclusters (NCs) have molecular-like structures and unique physical and chemical properties, making them an interesting new class of luminescent nanomaterials with various applications in chemical sensing, bioimaging, optoelectronics, light-emitting diodes (LEDs), etc. However, weak photoluminescence (PL) limits the practical applications of NCs. Herein, an effective and facile strategy of enhancing the PL of NCs was developed using Ag shell-isolated nanoparticle (Ag SHIN)-enhanced luminescence platforms with tuned SHINs shell thicknesses. 3D-FDTD theoretical calculations along with femtosecond transient absorption and fluorescence decay measurements were performed to elucidate the enhancement mechanisms. Maximum enhancements of up to 231-fold for the [AuAg(C≡CBu)] cluster and 126-fold for DNA-templated Ag NCs (DNA-Ag NCs) were achieved. We evidenced a novel and versatile method of achieving large PL enhancements with NCs with potential for practical biosensing applications for identifying target DNA in ultrasensitive surface analysis.
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http://dx.doi.org/10.1021/acs.analchem.0c00600DOI Listing
May 2020

Raman study of the photoinduced behavior of dye molecules on TiO() single crystal surfaces.

Chem Sci 2020 Apr 17;11(25):6431-6435. Epub 2020 Apr 17.

Department of Physics, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, College of Materials, Xiamen University Xiamen 361005 China

In dye-sensitized solar cells (DSSCs), the TiO/dye interface significantly affects photovoltaic performance. However, the adsorption and photoinduced behavior of dye molecules on the TiO substrate remains unclear. Herein, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to study the adsorption and photoinduced behavior of dye (N719) molecules on different TiO() surfaces. On TiO(001) and TiO(110) surfaces, the SHINERS and mass spectrometry results indicate S[double bond, length as m-dash]C bond cleavage in the anchoring groups of adsorbed N719, whereas negligible bond cleavage occurs on the TiO(111) surface. Furthermore, DFT calculations show the stability of the S[double bond, length as m-dash]C anchoring group on three TiO() surfaces in the order TiO(001) < TiO(110) < TiO(111), which correlated well with the observed photocatalytic activities. This work reveals the photoactivity of different TiO() surface structures and can help with the rational design of DSSCs. Thus, this strategy can be applied to real-time probing of photoinduced processes on semiconductor single crystal surfaces.
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http://dx.doi.org/10.1039/d0sc00588fDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159273PMC
April 2020

[email protected] Core-Shell Heterostructure as SERS Platform to Reveal the Hydrogen Evolution Active Sites of Single-Layer MoS.

J Am Chem Soc 2020 Apr 3;142(15):7161-7167. Epub 2020 Apr 3.

Department of Chemistry, City University of Hong Kong, Hong Kong, China.

Understanding the reaction mechanism for the catalytic process is essential to the rational design and synthesis of highly efficient catalysts. MoS has been reported to be an efficient catalyst toward the electrochemical hydrogen evolution reaction (HER), but it still lacks direct experimental evidence to reveal the mechanism for MoS-catalyzed electrochemical HER process at the atomic level. In this work, we develop a wet-chemical synthetic method to prepare the single-layer MoS-coated polyhedral Ag core-shell heterostructure ([email protected]) with tunable sizes as efficient catalysts for the electrochemical HER. The [email protected] core-shell heterostructures are used as ideal platforms for the real-time surface-enhanced Raman spectroscopy (SERS) study owing to the strong electromagnetic field generated in the plasmonic Ag core. The in situ SERS results provide solid Raman spectroscopic evidence proving the S-H bonding formation on the MoS surface during the HER process, suggesting that the S atom of MoS is the catalytic active site for the electrochemical HER. It paves the way on the design and synthesis of heterostructures for exploring their catalytic mechanism at atomic level based on the in situ SERS measurement.
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http://dx.doi.org/10.1021/jacs.0c01649DOI Listing
April 2020

Rapid and low-cost quantitative detection of creatinine in human urine with a portable Raman spectrometer.

Biosens Bioelectron 2020 Apr 31;154:112067. Epub 2020 Jan 31.

Department of Physics, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen, 361005, China. Electronic address:

The creatinine concentration of human urine is closely related to human kidney health and its rapid, quantitative, and low-cost detection has always been demanded. Herein, a surface-enhanced Raman spectroscopic (SERS) method for rapid and cost-effective quantification of creatinine concentrations in human urine was developed. A Au nanoparticle solution (Au sol) was used as a SERS substrate and the influence of different agglomerating salts on its sensitivity toward detecting creatinine concentrations was studied and optimized, as well as the effect of both the salt and Au sol concentrations. The variation in creatinine spectra over time on different substrates was also examined, demonstrating reproducible quantitative analysis of creatinine concentrations in solution. By adjusting the pH, a simple liquid-liquid solvent extraction procedure, which extracted creatinine from human urine, was used to increase the SERS detection selectivity toward creatinine in complex matrices. The quantitative results were compared to those obtained with a clinically validated enzymatic "creatinine kit (CK)." The limit of detection (LOD) for the SERS technique was 1.45 mg L, compared with 3.4 mg L for the CK method. Furthermore, cross-comparing the results from the two methods, the average difference was 5.84% and the whole SERS detection process could be completed within 2 min compared with 11 min for the CK, indicating the practicality of the quantitative SERS technique. This novel quantitative technique shows promises as a high-throughput platform for relevant clinical and forensic analysis.
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http://dx.doi.org/10.1016/j.bios.2020.112067DOI Listing
April 2020

Core-Shell Nanostructure-Enhanced Raman Spectroscopy for Surface Catalysis.

Acc Chem Res 2020 Apr 7;53(4):729-739. Epub 2020 Feb 7.

College of Materials, Fujian Key Laboratory of Advanced Materials, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

ConspectusThe rational design of highly efficient catalysts relies on understanding their structure-activity relationships and reaction mechanisms at a molecular level. Such an understanding can be obtained by in situ monitoring of dynamic reaction processes using surface-sensitive techniques. Surface-enhanced Raman spectroscopy (SERS) can provide rich structural information with ultrahigh surface sensitivity, even down to the single-molecule level, which makes it a promising tool for the in situ study of catalysis. However, only a few metals (like Au, Ag, and Cu) with particular nanostructures can generate strong SERS effects. Thus, it is almost impossible to employ SERS to study transition metals (like Pt, Pd, Ru, etc.) and other nonmetal materials that are usually used in catalysis (material limitation). Furthermore, SERS is also unable to study model single crystals with atomically flat surface structures or practical nanocatalysts (morphology limitation). These limitations have significantly hindered the applications of SERS in catalysis over the past four decades since its discovery, preventing SERS from becoming a widely used technique in catalysis. In this Account, we summarize the extensive efforts done by our group since the 1980s, particularly in the past decade, to overcome the material and morphology limitations in SERS. Particular attention has been paid to the work using core-shell nanostructures as SERS substrates, because they provide high Raman enhancement and are highly versatile for application on different catalytic materials. Different SERS methodologies for catalysis developed by our group, including the "borrowing" strategy, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), and SHINERS-satellite strategy, are discussed in this account, with an emphasis on their principles and applications. These methodologies have successfully overcome the long-standing limitations of traditional SERS, enabling in situ tracking of catalysis at model single-crystal surfaces and practical nanocatalysts that can hardly be studied by SERS. Using these methodologies, we systematically studied a series of fundamentally important reactions, such as oxygen reduction reaction, hydrogen evolution reaction, electrooxidation, CO oxidation, and selective hydrogenation. As such, direct spectroscopic evidence of key intermediates that can hardly be detected by other traditional techniques was obtained. Combined with density functional theory and other in situ techniques, the reaction mechanisms and structure-activity relationships of these catalytic reactions were revealed at a molecular level. Furthermore, the future of SERS in catalysis has also been proposed in this work, which we believe should be focused on the in situ dynamic studies at the single-molecule, or even single-atom, level using techniques with ultrahigh sensitivity or spatial resolution, for example, single-molecule SERS or tip-enhanced Raman spectroscopy. In summary, core-shell nanostructure-enhanced Raman spectroscopies are shown to greatly boost the application of SERS in catalysis, from model systems like single-crystal surfaces to practical nanocatalysts, liquid-solid interfaces to gas-solid interfaces, and electrocatalysis to heterogeneous catalysis to photocatalysis. Thus, we believe this Account would attract increasing attention to SERS in catalysis and opens new avenues for catalytic studies.
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http://dx.doi.org/10.1021/acs.accounts.9b00545DOI Listing
April 2020

Strong coupling between magnetic resonance and propagating surface plasmons at visible light frequencies.

J Chem Phys 2020 Jan;152(1):014702

Department of Physics, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Jiujiang Research Institute, Xiamen University, Xiamen 361005, China.

Light-matter interactions in nanostructures have shown great potential in physics, chemistry, surface science, materials science, and nanophotonics. Herein, for the first time, the feasibility of strong coupling between plasmon-induced magnetic resonant and propagating surface plasmonic modes at visible light frequencies is theoretically demonstrated. Taking advantage of the strong coupling between these modes allowed for a narrow-linewidth hybrid mode with a huge electromagnetic field enhancement to be acquired. This work can serve as a promising guide for designing a platform with strong coupling based on magnetic resonance at visible and even ultraviolet light frequencies and also offers an avenue for further exploration of strong light-matter interactions at the nanoscale.
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http://dx.doi.org/10.1063/1.5133942DOI Listing
January 2020

In situ Spectroscopic Insight into the Origin of the Enhanced Performance of Bimetallic Nanocatalysts towards the Oxygen Reduction Reaction (ORR).

Angew Chem Int Ed Engl 2019 Nov 4;58(45):16062-16066. Epub 2019 Oct 4.

MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, College of Materials, Xiamen University, Xiamen, 361005, China.

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel-cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real-time observation of catalytic processes.
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http://dx.doi.org/10.1002/anie.201908907DOI Listing
November 2019

Elucidating Molecule-Plasmon Interactions in Nanocavities with 2 nm Spatial Resolution and at the Single-Molecule Level.

Angew Chem Int Ed Engl 2019 Aug 2;58(35):12133-12137. Epub 2019 Aug 2.

MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, State Key Laboratory of Physical Chemistry of Solid, Surfaces,iChEM, College of Chemistry and Chemical Engineering, College of Materials, Xiamen University, Xiamen, 361005, China.

The fundamental understanding of the subtle interactions between molecules and plasmons is of great significance for the development of plasmon-enhanced spectroscopy (PES) techniques with ultrahigh sensitivity. However, this information has been elusive due to the complex mechanisms and difficulty in reliably constructing and precisely controlling interactions in well-defined plasmonic systems. Herein, the interactions in plasmonic nanocavities of film-coupled metallic nanocubes (NCs) are investigated. Through engineering the spacer layer, molecule-plasmon interactions were precisely controlled and resolved within 2 nm. Efficient energy exchange interactions between the NCs and the surface within the 1-2 nm range are demonstrated. Additionally, optical dressed molecular excited states with a huge Lamb shift of ≈7 meV at the single-molecule (SM) level were observed. This work provides a basis for understanding the underlying molecule-plasmon interaction, paving the way for fully manipulating light-matter interactions at the nanoscale.
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http://dx.doi.org/10.1002/anie.201906517DOI Listing
August 2019

Evaluating chemical bonding in dioxides for the development of metal-oxygen batteries: vibrational spectroscopic trends of dioxygenyls, dioxygen, superoxides and peroxides.

Phys Chem Chem Phys 2019 Jan;21(3):1552-1563

Stephenson Institute for Renewable Energy, Department of Chemistry, University of Liverpool, L69 7ZF, UK.

Dioxides (dioxygenyl (O2+), dioxygen (O2), superoxide (O2˙-) and peroxide (O22-)) are of immense biological, chemical and environmental importance. The ability to accurately detect and measure the changing strength of their chemical bonding and coordination in situ or operando is extremely beneficial in order to evaluate their chemical properties, this has been particularly important recently in the field of metal-oxygen batteries, where understanding the reactivity of the O2˙- intermediate is crucial in the development of more stable electrolytes. Meta-analysis of the collated vibrational Raman and IR spectral bands of numerous (>200) dioxygen species was used to interpret the effect that the immediate chemical environment has on the O-O bond. Subsequently, the dioxide vibrational spectral bands were empirically related directly with the bond electron density and other fundamental bond properties, with surprisingly high accuracy, allowing each property to be estimated, simply, from experimental spectroscopic observations. Important chemical information about the strength of secondary interactions between reduced oxygen species and its chemical environment can be also elucidated which provides a convenient method for determining the attractive strength an ion exerts over neighbouring counter ions.
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http://dx.doi.org/10.1039/c8cp04652bDOI Listing
January 2019

Time-resolved SERS study of the oxygen reduction reaction in ionic liquid electrolytes for non-aqueous lithium-oxygen cells.

Faraday Discuss 2018 01 29;206:379-392. Epub 2017 Sep 29.

Stephenson Institute for Renewable Energy, Department of Chemistry, University of Liverpool, L69 7ZF, UK.

Superoxide (O˙) is the key intermediate formed during oxygen reduction in non-aqueous electrolytes. One significant obstacle towards the realisation of a practical lithium-oxygen (Li-O) battery is electrolyte instability in the presence of radical oxides, principally superoxide. Here we use the Raman active bands of O˙ as a diagnostic molecule for probing the influence of the electrolyte on reaction processes and intermediaries at the electrode surface. In situ surface enhanced Raman studies of the interface at a roughened Au electrode with controlled and dynamic surface potentials were performed in two ionic liquids with differing properties: 1-butyl-1-methyl-azepenium bis(trifluoromethanesulfonyl)imide (AzeTFSI), which has a large/soft cation, and triethylsulfonium bis(trifluoromethanesulfonyl)imide (TESTFSI), which has a relatively small/hard and e accepting cation. The counter-cation and potential were seen to significantly influence the radical nature, or Lewis basicity of O˙. The analysis of peak intensities and Stark shifts in O˙ related spectral bands allowed for key information on its character and electrolyte interactions to be elucidated. Time-resolved studies of dynamic surface potentials permitted real time observation of the flux and reorientation of ions at the electrode/electrolyte interface.
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http://dx.doi.org/10.1039/c7fd00170cDOI Listing
January 2018
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