Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon-Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol

Electro-optical synergy has recently been targeted to improve the separation of hot carriers and thereby further improve the efficiency of plasmon-mediated chemical reactions (PMCRs). However, the electro-optical synergy in PMCRs needs to be more deeply understood, and its contribution to bond dissociation and product selectivity needs to be clarified. Herein, the electro-optical synergy in plasmon-mediated reduction of p-bromothiophenol (PBTP) was studied on a plasmonic nanostructured silver electrode using in situ Raman spectroscopy and theoretical calculations. It was found that the electro-optical synergy-induced enhancements in the cleavage of carbon-bromine bonds, reaction rate, and product selectivity (4,4'-biphenyl dithiol vs thiophenol) were largely affected by the applied bias, laser wavelength, and laser power. The theoretical simulation further clarified that the strong electro-optical synergy is attributed to the matching of energy band diagrams of the plasmonic silver with those of the adsorbed PBTP molecules. A deep understanding of the electro-optical synergy in PBTP reduction and the clarification of the mechanism will be highly beneficial for the development of other highly efficient PMCRs.

Accurate prediction of the optical properties of nanoalloys with both plasmonic and magnetic elements

The alloying process plays a pivotal role in the development of advanced multifunctional plasmonic materials within the realm of modern nanotechnology. However, accurate in silico predictions are only available for metal clusters of just a few nanometers, while the support of modelling is required to navigate the broad landscape of components, structures and stoichiometry of plasmonic nanoalloys regardless of their size. Here we report on the accurate calculation and conceptual understanding of the optical properties of metastable alloys of both plasmonic (Au) and magnetic (Co) elements obtained through a tailored laser synthesis procedure. The model is based on the density functional theory calculation of the dielectric function with the Hubbard-corrected local density approximation, the correction for intrinsic size effects and use of classical electrodynamics. This approach is built to manage critical aspects in modelling of real samples, as spin polarization effects due to magnetic elements, short-range order variability, and size heterogeneity. The method provides accurate results also for other magnetic-plasmonic (Au-Fe) and typical plasmonic (Au-Ag) nanoalloys, thus being available for the investigation of several other nanomaterials waiting for assessment and exploitation in fundamental sectors such as quantum optics, magneto-optics, magneto-plasmonics, metamaterials, chiral catalysis and plasmon-enhanced catalysis.

Photoassisted Strategy to Promote Glycerol Electrooxidation to Lactic Acid Coupled with Hydrogen Production

Electrocatalytic oxidation of glycerol (GLY; from a biodiesel byproduct) to lactic acid (LA; the key monomers for polylactic acid; PLA) is considered a sustainable approach for biomass waste upcycling and is coupled with cathodic hydrogen (H₂) production. However, current research still suffer from issues of low current density and low LA selectivity. Herein, we reported a photoassisted electrocatalytic strategy to achieve the selective oxidation of GLY to LA over a gold nanowire (Au NW) catalyst, attaining a high current density of 387 mA cm^-2 at 0.95 V vs RHE, together with a high LA selectivity of 80%, outperforming most of the reported works in the literature. We reveal that the light-assistance strategy plays a dual role, which can both accelerate the reaction rate through the photothermal effect and also promote the adsorption of the middle hydroxyl of GLY over Au NWs to realize the selective oxidation of GLY to LA. As a proof-of-concept, we realized the direct conversion of crude GLY that was extracted from cooking oil to attain LA and coupled it with H₂ production using the developed photoassisted electrooxidation process, revealing the potential of this strategy in practical applications.

Multi-Layered PtAu Nanoframes and Their Light-Enhanced Electrocatalytic Activity via Plasmonic Hot Spots

Here, the rational design of complex PtAu double nanoframes (DNFs) for plasmon-enhanced electrocatalytic activity toward the methanol oxidation reaction (MOR) is reported. The synthetic strategy for the DNFs consists of on-demand multiple synthetic chemical toolkits, including well-faceted Au growth, rim-on selective Pt deposition, and selective Au etching steps. DNFs are synthesized by utilizing Au truncated octahedrons (TOh) as a starting template. The outer octahedral (Oh) nanoframes (NFs) nest the inner TOh NFs, eventually forming DNFs with a tunable intra-nanogap distance. Residual Au adatoms on Pt skeletons act as light entrappers and produce plasmonic hot spots between inner and outer frames through localized surface plasmon resonance (LSPR) coupling, which promotes enhanced electrocatalytic activity for the MOR. Importantly, the correlation between the gap-induced hot carriers and electrocatalytic activity is evaluated. The highest catalytic activity is achieved when the gap is the narrowest. To further harness their light-trapping capability, hierarchically structured triple NFs (TNFs) are synthesized, wherein three NFs are entangled in a single entity with a high density of hot regions, exhibiting superior electrocatalytic activity toward the MOR with a sixfold larger current density under light irradiation compared to the dark conditions.

Killing Two Birds with One Stone: Upgrading Organic Compounds via Electrooxidation in Electricity-Input Mode and Electricity-Output Mode

The electrochemically oxidative upgrading reaction (OUR) of organic compounds has gained enormous interest over the past few years, owing to the advantages of fast reaction kinetics, high conversion efficiency and selectivity, etc., and it exhibits great potential in becoming a key element in coupling with electricity, synthesis, energy storage and transformation. On the one hand, the kinetically more favored OUR for value-added chemical generation can potentially substitute an oxygen evolution reaction (OER) and integrate with an efficient hydrogen evolution reaction (HER) or CO₂ electroreduction reaction (CO₂RR) in an electricity-input mode. On the other hand, an OUR-based cell or battery (e.g., fuel cell or Zinc-air battery) enables the cogeneration of value-added chemicals and electricity in the electricity-output mode. For both situations, multiple benefits are to be obtained. Although the OUR of organic compounds is an old and rich discipline currently enjoying a revival, unfortunately, this fascinating strategy and its integration with the HER or CO₂RR, and/or with electricity generation, are still in the laboratory stage. In this minireview, we summarize and highlight the latest progress and milestones of the OUR for the high-value-added chemical production and cogeneration of hydrogen, CO₂ conversion in an electrolyzer and/or electricity in a primary cell. We also emphasize catalyst design, mechanism identification and system configuration. Moreover, perspectives on OUR coupling with the HER or CO₂RR in an electrolyzer in the electricity-input mode, and/or the cogeneration of electricity in a primary cell in the electricity-output mode, are offered for the future development of this fascinating technology.

Recent Developments in Plasmonic Alloy Nanoparticles: Synthesis, Modelling, Properties and Applications

Despite the traditional plasmonic materials are counted on one hand, there are a lot of possible combinations leading to alloys with other elements of the periodic table, in particular those renowned for magnetic or catalytic properties. It is not a surprise, therefore, that nanoalloys are considered for their ability to open new perspectives in the panorama of plasmonics, representing a leading research sector nowadays. This is demonstrated by a long list of studies describing multiple applications of nanoalloys in photonics, photocatalysis, sensing and magneto-optics, where plasmons are combined with other physical and chemical phenomena. In some remarkable cases, the amplification of the conventional properties and even new effects emerged. However, this field is still in its infancy and several challenges must be overcome, starting with the synthesis (control of composition, crystalline order, size, processability, achievement of metastable phases and disordered compounds) as well as the modelling of the structure and properties (accuracy of results, reliability of structural predictions, description of disordered phases, evolution over time) of nanoalloys. To foster the research on plasmonic nanoalloys, here we provide an overview of the most recent results and developments in the field, organized according to synthetic strategies, modelling approaches, dominant properties and reported applications. Considering the several plasmonic nanoalloys under development as well as the large number of those still awaiting synthesis, modelling, properties assessment and technological exploitation, we expect a great impact on the forthcoming solutions for sustainability, ultrasensitive and accurate detection, information processing and many other fields.

CO2 and Formate Pathway of Methanol Electrooxidation at Rhodium Electrodes in Alkaline Media: An In Situ Electrochemical Attenuated Total Refection Surface-Enhanced Infrared Absorption Spectroscopy and Infrared Reflection Absorption Spectroscopy Investigation

Rh catalysts exhibit unexpected high activity for the methanol oxidation reaction (MOR) in alkaline conditions, making them potential anodic catalysts for direct methanol fuel cells (DMFCs). Nevertheless, the MOR mechanism on Rh electrodes has not been clarified thus far, which impedes the development of high-efficiency Rh-based MOR catalysts. To investigate it, a combination of in situ electrochemical techniques called attenuated total refection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and infrared reflection absorption spectroscopy (IRAS) is used. Cyclic voltammograms of MOR at Rh electrodes show considerable activity in alkaline media rather than acidic media, although the real-time ATR-SEIRA spectral results demonstrate that methanol can rarely self-decompose on Rh at open-circuit conditions. Meanwhile, in combination of ATR-SEIRAS and IRAS results, CO₂ and formate are thought to be MOR products, suggesting a dual-pathway mechanism ("CO₂ pathway" and "formate pathway"). Specifically, CO_ad species, which are the major intermediates in the CO₂ pathway, can produce at lower potentials and be oxidized into CO₂ at a potential of 0.5-0.75 V. Concurrently, the formate can be produced from 0.5 V and diffuse into the bulk electrolyte to become one of the MOR products, while the further electrochemical conversion of formate to CO₂ is essentially negligible. More directly, the apparent selectivity (r) of the CO₂ pathway is estimated to reach ca. 0.63 at 0.9 V, confirming the potential-dependent selectivity of MOR at Rh surfaces. This study might provide fresh insights into the design and fabrication of effective Rh-based catalysts for MOR.

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

Direct conversion of methane (CH₄) to C_1-2 liquid oxygenates is a captivating approach to lock carbons in transportable value-added chemicals, while reducing global warming. Existing approaches utilizing the transformation of CH₄ to liquid fuel via tandemized steam methane reforming and the Fischer-Tropsch synthesis are energy and capital intensive. Chemocatalytic partial oxidation of methane remains challenging due to the negligible electron affinity, poor C-H bond polarizability, and high activation energy barrier. Transition-metal and stoichiometric catalysts utilizing harsh oxidants and reaction conditions perform poorly with randomized product distribution. Paradoxically, the catalysts which are active enough to break C-H also promote overoxidation, resulting in CO₂ generation and reduced carbon balance. Developing catalysts which can break C-H bonds of methane to selectively make useful chemicals at mild conditions is vital to commercialization. Single atom catalysts (SACs) with specifically coordinated metal centers on active support have displayed intrigued reactivity and selectivity for methane oxidation. SACs can significantly reduce the activation energy due to induced electrostatic polarization of the C-H bond to facilitate the accelerated reaction rate at the low reaction temperature. The distinct metal-support interaction can stabilize the intermediate and prevent the overoxidation of the reaction products. The present review accounts for recent progress in the field of SACs for the selective oxidation of CH₄ to C_1-2 oxygenates. The chemical nature of catalytic sites, effects of metal-support interaction, and stabilization of intermediate species on catalysts to minimize overoxidation are thoroughly discussed with a forward-looking perspective to improve the catalytic performance.

Designer Gold-Framed Palladium Nanocubes for Plasmon-Enhanced Electrocatalytic Oxidation of Ethanol

Surface plasmon of coinage metal nanostructures has been employed as a powerful route in boosting the performances in heterogenous catalysis. Development of efficient plasmonic nanocatalysts with high catalytic performance and efficient light harvesting properties is of vital importance. Herein, we rationally designed and synthesized a plasmonic nanocatalyst composed of Au-framed Pd nanocubes by an Ag(I)-assisted seed-mediated growth method. In the synthesis, the incorporation of Ag(I) suppresses the reduction of Au on the {100} surface of cubic Pd seeds and leads to the formation of Au nanoframes on the Pd nanocubes. The unique Au-framed Pd nanocubes can integrate the superior electrocatalytic of Pd and the outstanding plasmonic properties of Au. Thus, these nanostructures were employed as plasmonic nanocatalysts for plasmon-enhanced electrocatalytic oxidation of ethanol with improved stability.

Coupling, lifetimes, and "strong coupling" maps for single molecules at plasmonic interfaces

The interaction between excited states of a molecule and excited states of a metal nanostructure (e.g., plasmons) leads to hybrid states with modified optical properties. When plasmon resonance is swept through molecular transition frequency, an avoided crossing may be observed, which is often regarded as a signature of strong coupling between plasmons and molecules. Such strong coupling is expected to be realized when 2|⟨U⟩|/ℏΓ > 1, where ⟨U⟩ and Γ are the molecule-plasmon coupling and the spectral width of the optical transition, respectively. Because both ⟨U⟩ and Γ strongly increase with decreasing distance between a molecule and a plasmonic structure, it is not obvious that this condition can be satisfied for any molecule-metal surface distance. In this work, we investigate the behavior of ⟨U⟩ and Γ for several geometries. Surprisingly, we find that if the only contributions to Γ are lifetime broadenings associated with the radiative and nonradiative relaxation of a single molecular vibronic transition, including effects on molecular radiative and nonradiative lifetimes induced by the metal, the criterion 2|⟨U⟩|/ℏΓ > 1 is easily satisfied by many configurations irrespective of the metal-molecule distance. This implies that the Rabi splitting can be observed in such structures if other sources of broadening are suppressed. Additionally, when the molecule-metal surface distance is varied keeping all other molecular and metal parameters constant, this behavior is mitigated due to the spectral shift associated with the same molecule-plasmon interaction, making the observation of Rabi splitting more challenging.

Plasmonic Photoelectrochemical Coupling Reactions of para-Aminobenzoic Acid on Nanostructured Gold Electrodes

Surface plasmon resonance (SPR) bridges photonics and photoelectrochemistry by providing an effective interaction between absorption and confinement of light to surface electrons of plasmonic metal nanostructures (PMNs). SPR enhances the Raman intensity enormously in surface-enhanced Raman spectroscopy (SERS) and leads to the plasmon-mediated chemical reaction on the surface of nanostructured metal electrodes. To observe variations in chemical reactivity and selectivity, we studied the SPR photoelectrochemical reactions of para-aminobenzoic acid (PABA) on nanostructured gold electrodes. The head-to-tail coupling product "4-[(4-imino-2,5-cyclohexadien-1-ylidene)amino]benzoic acid (ICBA)" and the head-to-head coupling product p,p'-azodibenzoate (ADBA) were obtained from PABA adsorbed on PMN-modified gold electrodes. In particular, under acidic and neutral conditions, ICBA was obtained as the main product, and ADBA was obtained as the minor product. At the same time, under basic conditions, ADBA was obtained as the major product, and ICBA was obtained as the minor product. We have also provided sufficient evidence for the oxidation of the tail-to-tail coupling reaction product that occurred in a nonaqueous medium rather than in an aqueous medium. The above finding was validated by the cyclic voltammetry, SERS, and theoretical calculation results of possible reaction intermediates, namely, 4-aminophenlylenediamine, 4-hydroxyphenlylenediamine, and benzidine. The theoretical adsorption model and experimental results indicated that PABA has been adsorbed as para-aminobenzoate on the gold cluster in a bidentate configuration. This work offers a new view toward the modulation of selective surface catalytic coupling reactions on PMN, which benefits the hot carrier transfer efficiency at photoelectrochemical interfaces.

Light in Electrochemistry

Electrochemistry represents an important analytical technique used to acquire and assess chemical information in detail, which can aid fundamental investigations in various fields, such as biological studies. For example, electrochemistry can be used as simple and cost-effective means for bio-marker tracing in applications, such as health monitoring and food security screening. In combination with light, powerful spatially-resolved applications in both the investigation and manipulation of biochemical reactions begin to unfold. In this article, we focus primarily on light-addressable electrochemistry based on semiconductor materials and light-readable electrochemistry enabled by electrochemiluminescence (ECL). In addition, the emergence of multiplexed and imaging applications will also be introduced.

Plasmon Induced Photocatalysts for Light-Driven Nanomotors

Micro/nanomachines (MNMs) correspond to human-made devices with motion in aqueous solutions. There are different routes for powering these devices. Light-driven MNMs are gaining increasing attention as fuel-free devices. On the other hand, Plasmonic nanoparticles (NPs) and their photocatalytic activity have shown great potential for photochemistry reactions. Here we review several photocatalyst nanosystems, with a special emphasis in Plasmon induced photocatalytic reactions, as a novel proposal to be explored by the MNMs community in order to extend the light-driven motion of MNMs harnessing the visible and near-infrared (NIR) light spectrum.

Platinum-Based Electrocatalysts for Direct Alcohol Fuel Cells: Enhanced Performances toward Alcohol Oxidation Reactions

In the past few decades, Pt-based electrocatalysts have attracted great interests due to their high catalytic performances toward the direct alcohol fuel cell (DAFC). However, the high cost, poor stability, and the scarcity of Pt have markedly hindered their large-scale utilization in commerce. Therefore, enhancing the activity and durability of Pt-based electrocatalysts, reducing the Pt amount and thus the cost of DAFC have become the keys for their practical applications. In this minireview, we summarized some basic concepts to evaluate the catalytic performances in electrocatalytic alcohol oxidation reaction (AOR) including electrochemical active surface area, activity and stability, the effective approaches for boosting the catalytic AOR performance involving size decrease, structure and morphology modulation, composition effect, catalyst supports, and assistance under other external energies. Furthermore, we also presented the remaining challenges of the Pt-based electrocatalysts to achieve the fabrication of a real DAFC.

Recent Advances in Noble Metal Catalysts for Hydrogen Production from Ammonia Borane

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.

High-efficiency methanol oxidation electrocatalysts realized by ultrathin PtRuM-O (M = Ni, Fe, Co) nanosheets

A general method for controlling the synthesis of a class of ultrathin PtRuM-O (M = Ni, Fe, Co) NSs is reported for the first time. By optimizing the metal ratio, the Pt₇RuNi₂-O NS catalyst is found to have the highest electrocatalytic activity (mass activity, 3.57 A mg_Pt^-1) for the MOR among PtRuM-O NSs and PtRu-O NSs, which is 10.5 times higher than that of commercial Pt/C (0.34 A mg_Pt^-1). And the Pt₇RuNi₂-O NSs also have better stability and CO anti-poisoning properties in the prepared materials. In addition, the ultrathin Pt₇RuNi₂-O NS catalyst also shows the highest performance among reported Pt-based catalysts for the MOR in acidic medium.