Plasmonic-Enhanced Oxygen Reduction Reaction of Silver/Graphene Electrocatalysts

Electrogenerated chemiluminescence imaging of plasmon-induced electrochemical reactions at single nanocatalysts

This study explores plasmon-induced electrochemical reactions on single nanoparticles using electrogenerated chemiluminescence microscopy (ECLM). Under laser irradiation, real-time screening showed lower plasmon-induced reaction efficiency for bimetallic Au@Pt nanoparticles compared to monometallic Au nanoparticles. ECLM offers a high-throughput imaging and precise quantitative approach for analyzing photo-electrochemical conversion at single nanoparticle level, valuable for both theoretical exploration and optimization of plasmonic nanocatalysts.

Hot or Not? Reassessing Mechanisms of Photocurrent Generation in Plasmon-Enhanced Electrocatalysis

It is now widely accepted that certain effects arising from localised surface plasmon resonance, such as enhanced electromagnetic fields, hot carriers, and thermal effects, can facilitate electrocatalytic processes. This newly emerging field of research is commonly referred to as plasmon-enhanced electrocatalysis (PEEC) and is attracting increasing interest from the research community, particularly regarding harnessing the high energy of hot carriers. However, this has led to a lack of critical analysis in the literature, where the participation of hot carriers is routinely claimed due to their perceived desirability, while the contribution of other effects is often not sufficiently investigated. As a result, correctly differentiating between the possible mechanisms at play has become a key point of contention. In this review, we specifically focus on the mechanisms behind photocurrents observed in PEEC and critically evaluate the possibility of alternative sources of current enhancement in the reported PEEC systems. Furthermore, we present guidelines for the best experimental practices and methods to distinguish between the various enhancement mechanisms in PEEC.

Unveiling the Solvent Effect in Plasmon Enhanced Electrochemistry via the Nanoparticle-Impact Technique

Plasmon-enhanced electrochemistry (PEEC) has been observed to facilitate energy conversion systems by converting light energy to chemical energy. However, comprehensively understanding the PEEC mechanism remains challenging due to the predominant use of ensemble-based methodologies on macroscopic electrodes, which fails to measure electron-transfer kinetics due to constraints from mass transport and the averaging effect. In this study, we have employed nanoparticle impact electrochemistry (NIE), a newly developed electroanalytical technique capable of measuring electrochemical dynamics at a single-nanoparticle level under optimal mass transport conditions, along with microscopic electron-transfer theory for data interpretation. By investigating the plasmon enhanced hydrogen evolution reaction (HER) at individual silver nanoparticles (AgNPs), we have clearly revealed the previously unknown influence of solvent effects within the PEEC mechanism. This finding suggests an additional approach to optimize plasmon-assisted electrocatalysis and electrosynthesis systems.

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.

One-step pyrolysis synthesis of ternary (P,S,N)-doped graphene as an efficient metal-free electrocatalyst for the oxygen reduction reaction

Graphene-based materials have been regarded recently as a promising substance for electrochemical energy conversion and storage devices owing to their unique structure and extraordinary properties. Herein, an enormously facile one-step pyrolysis approach is reported for the fabrication of ternary (P,S,N)-doped graphene, which is further investigated as an efficient metal-free electrocatalyst for the oxygen reduction reaction (ORR). Furthermore, optimized ternary-doped graphene can deliver excellent ORR catalytic activity that favors the four-electron ORR process and outstanding long-term durability (90.54% current retention after 20000 s which is far superior to that of commercial Pt/C) owing to the preferable synergetic coupling effect between P, S and N. Density functional theory (DFT) calculations were performed to reveal the synergetic coupling effect between doping elements in the ORR process. This work provides an extremely simple one-step pyrolysis method for the synthesis of P,S,N-doped graphene for electrochemical energy conversion and storage devices.

Directing Energy Flow in Core-Shell Nanostructures for Efficient Plasmon-Enhanced Electrocatalysis

Conjugating plasmonic metals with catalytically active materials with controlled configurations can harness their light energy harvesting ability in catalysis. Herein, we present a well-defined core-shell nanostructure composed of an octahedral Au nanocrystal core and a PdPt alloy shell as a bifunctional energy conversion platform for plasmon-enhanced electrocatalysis. The prepared Au@PdPt core-shell nanostructures exhibited significant enhancements in electrocatalytic activity for methanol oxidation and oxygen reduction reactions under visible-light irradiation. Our experimental and computational studies revealed that the electronic hybridization of Pd and Pt allows the alloy material to have a large imaginary dielectric function, which can efficiently induce the shell-biased distribution of plasmon energy upon illumination and, hence, its relaxation at the catalytically active region to promote electrocatalysis.

Synthesis of Platinum Nanocrystals Dispersed on Nitrogen-Doped Hierarchically Porous Carbon with Enhanced Oxygen Reduction Reaction Activity and Durability

Platinum-based catalysts are widely used for efficient catalysis of the acidic oxygen reduction reaction (ORR). However, the agglomeration and leaching of metallic Pt nanoparticles limit the catalytic activity and durability of the catalysts and restrict their large-scale commercialization. Therefore, this study aimed to achieve a uniform distribution and strong anchoring of Pt nanoparticles on a carbon support and improve the ORR activity and durability of proton-exchange membrane fuel cells. Herein, we report on the facile one-pot synthesis of a novel ORR catalyst using metal-nitrogen-carbon (M-N-C) bonding, which is formed in situ during the ion exchange and pyrolysis processes. An ion-exchange resin was used as the carbon source containing R-N⁺(CH₃)₃ groups, which coordinate with PtCl₆^2- to form nanosized Pt clusters confined within the macroporous framework. After pyrolysis, strong M-N-C bonds were formed, thereby preventing the leaching and aggregation of Pt nanoparticles. The as-synthesized Pt supported on the N-doped hierarchically porous carbon catalyst (Pt/NHPC-800) showed high specific activity (0.3 mA cm^-2) and mass activity (0.165 A mg_Pt^-1), which are approximately 2.7 and 1.5 times higher than those of commercial Pt/C, respectively. The electrochemical surface area of Pt/NHPC-800 remained unchanged (~1% loss) after an accelerated durability test of 10,000 cycles. The mass activity loss after ADT of Pt/NHPC-800 was 18%, which is considerably lower than that of commercial Pt/C (43%). Thus, a novel ORR catalyst with highly accessible and homogeneously dispersed Pt-N-C sites, high activity, and durability was successfully prepared via one-pot synthesis. This facile and scalable synthesis strategy for high-efficiency catalysts guides the further synthesis of commercially available ORR catalysts.

Hydrothermally Grown Dual-Phase Heterogeneous Electrocatalysts for Highly Efficient Rechargeable Metal-Air Batteries with Long-Term Stability

Metal-air batteries as alternatives to the existing lithium-ion battery are becoming increasingly attractive sources of power due to their high energy-cost competitiveness and inherent safety; however, their low oxygen evolution and reduction reaction (OER/ORR) performance and poor operational stability must be overcome prior to commercialization. Herein, it is demonstrated that a novel class of hydrothermally grown dual-phase heterogeneous electrocatalysts, in which silver-manganese (AgMn) heterometal nanoparticles are anchored on top of 2D nanosheet-like nickel vanadium oxide (NiV₂ O₆ ), allows an enlarged surface area and efficient charge transfer/redistribution, resulting in a bifunctional OER/ORR superior to those of conventional Pt/C or RuO₂ . The dual-phase NiV₂ O₆ /AgMn catalysts on the air cathode of a zinc-air battery lead to a stable discharge-charge voltage gap of 0.83 V at 50 mA cm^-2 , with a specific capacity of 660 mAh g^-1 and life cycle stabilities of more than 146 h at 10 mA cm^-2 and 11 h at 50 mA cm^-2 . The proposed new class of dual-phase NiV₂ O₆ /AgMn catalysts are successfully applied as pouch-type zinc-air batteries with long-term stability over 33.9 h at 10 mA cm^-2 .

Hot Carrier Lifetimes and Electrochemical Water Dissociation Enhanced by Nickel Doping of a Plasmonic Electrocatalyst

Hot carriers generated by localized surface plasmon resonance (LSPR) excitation of plasmonic metal nanoparticles are known to enhance electrocatalytic reactions. However, the participation of plasmonically generated carriers in interfacial electrochemical reactions is often limited by fast relaxation of these carriers. Herein, we address this challenge by tuning the electronic structure of a plasmonic electrocatalyst. Specifically, we design an electrocatalyst for alkaline hydrogen evolution reaction (HER) that consists of nanoparticles of a ternary Cu-Pt-Ni ternary alloy. The CuPt alloy has both plasmonic attributes and electrocatalytic HER activity. Ni doping contributes an electron-deficient 3d band and fully filled 4s band, which promotes water adsorption and prolongs the lifetimes of excited carriers generated by plasmonic excitation. As an outcome, the Cu-Pt-Ni nanoparticles exhibit boosted activity for electrochemical water dissociation and HER under LSPR excitation.

Electrocatalytic oxygen reduction activity of AgCoCu oxides on reduced graphene oxide in alkaline media

Silver-based electrocatalysts as promising substitutes for platinum materials for cathodic oxygen electroreduction have been extensively researched. Electrocatalytic enhancement of the Ag nanoarchitectonics can be obtained via support structures and amalgamating Ag with one or two additional metals. The work presented here deals with a facile microwave-assisted synthesis to produce bimetallic Ag-Cu and Ag-Co (1:1) oxide nanoparticles (NPs) and trimetallic AgCuCo (0.6:1.5:1.5, 2:1:1, and 6:1:1) oxide NPs supported on a reduced graphene oxide (rGO) matrix. Morphology, composition, and functional groups were methodically analysed using various microscopic and spectroscopic techniques. The as-prepared electrocatalysts were employed as cathode substrates for the oxygen reduction reaction (ORR) in alkaline medium. Varying the Ag fraction in copper cobalt oxide has a significant influence on the ORR activity. At a ratio of 2:1:1, AgCuCo oxide NPs on rGO displayed the best values for onset potential, half-wave potential, and limiting current density (J _k) of 0.94 V vs RHE, 0.78 V, and 3.6 mA·cm^-2, respectively, with an electrochemical active surface area of 66.92 m²·g^-1 and a mass activity of 40.55 mA·mg^-1. The optimum electrocatalyst shows considerable electrochemical stability over 10,000 cycles in 0.1 M KOH solution.

Strain Modified Oxygen Evolution Reaction Performance in Epitaxial, Freestanding, and Van Der Waals Manganite Thin Films

In perovskite complex oxides, the strain has been established as a promising approach for tuning the oxygen evolution reaction (OER) performance by the manipulated electronic structure and interaction/coupling. In this study, we have employed rigid epitaxial, flexible freestanding, and van der Waals La_2/3Sr_1/3MnO₃ (LSMO) to investigate the strain effects on OER, which are different in stress strength and range via lattice mismatch and curvature change. It was found that the OER performances as a function of strain exhibited volcano and monotonous trends in rigid and flexible LSMO, respectively. The findings suggest that distinguished oxygen activation energy in varied lattice fields also plays a crucial role in the epitaxial LSMO in contrast to the pure strain effect in the flexible LSMO. Our results not only fundamentally clarify the effort of strain but also technologically provide an effective route to engineer the electronic structure for modified OER performance by perovskite complex oxides.

Combination of Plasmon-Mediated Photochemistry and Seed-Mediated Methods for Synthesis of Bicomponent Nanocrystals

Plasmon resonances of metal nanocrystals resulted from free electrons oscillating around nanocrystals, leading to a strong electromagnetic field around them. Because these oscillating electrons possess higher energy than the original ones, also known as hot electrons, these were widely used as photocatalysts for various reactions. Also, the strength and distribution of the electromagnetic field around the nanocrystals strongly depended on their morphology and excited irradiation, which led to the reaction environment around nanocrystals being controllable. Here, we integrated the seed-mediated and plasmon-mediated photochemistry methods for fabricating bimetallic and semiconductor-metal nanocrystals with controllable morphologies and compositions of the nanocrystals, resulting from the highly anisotropic reaction environment around the nanocrystals. The highly anisotropic reaction environment around the template nanocrystal was caused by the distribution of electromagnetic fields around it and its exposure area in the reaction solution. This new synthesis method should enable the fabrication of various multicomponent nanocrystals with desirable functions for potential applications, such as photocatalysts, chemical sensors, biosensors, biomedicines, etc.

Plasmonically enhanced electrochemistry boosted by nonaqueous solvent

Plasmon excitation of metal electrodes is known to enhance important energy related electrochemical transformations in aqueous media. However, the low solubility of nonpolar gases and molecular reagents involved in many energy conversion reactions limits the number of products formed per unit time in aqueous media. In this Communication, we use linear sweep voltammetry to measure how electrochemical H2O reduction in a nonaqueous solvent, acetonitrile, is enhanced by excitation of a plasmonic electrode. Plasmonically excited electrochemically roughened Au electrodes are found to produce photopotentials as large as 175 mV, which can be harnessed to lower the applied electrical bias required to drive the formation of H2. As the solvent polarity increases, by an increase in the concentration of H2O, the measured photopotential rapidly drops off to ∼50 mV. We propose a mechanism by which an increase in the H2O concentration increasingly stabilizes the photocharged plasmonic electrode, lowering the photopotential available to assist in the electrochemical reaction. Our study demonstrates that solvent polarity is an essential experimental parameter to optimize plasmonic enhancement in electrochemistry.

Asymmetric Activation of the Nitro Group over a Ag/Graphene Heterointerface to Boost Highly Selective Electrocatalytic Reduction of Nitrobenzene

The electrocatalytic reduction of nitrobenzene to aniline normally faces high overpotential and poor selectivity because of its six-electron redox nature. Herein, a Ag nanoparticles/laser-induced-graphene (LIG) heterointerface was fabricated on polyimide films and employed as an electrode material for an efficient nitrobenzene reduction reaction (NBRR) via a one-step laser direct writing technology. The first-principles calculations reveal that Ag/LIG shows the lowest activation barriers for the NBRR, which could be attributed to the optimum adsorption of the H atom realized by the appropriate interaction between Ag/LIG heterointerfaces and nitrobenzene. As a result, the overpotential of the NBRR is reduced by 217 mV after silver loading, and Ag/LIG shows a high aniline selectivity of 93%. Furthermore, an electrochemical reduction of nitrobenzene in tandem with an electrochemical oxidative polymerization of aniline was designed to serve as an alternative method to remove nitrobenzene from the aqueous solution. This strategy highlights the significance of heterointerfaces for efficient electrocatalysts, which may stimulate the development of novel electrocatalysts to boost the electrocatalytic activity.

Laser-Accelerated Mass Transport in Oxygen Reduction Via a Graphene-Supported Silver-Iron Oxide Heterojunction

Mass-transport acceleration is essential toward enhanced electrocatalytic performance yet rarely recognized under irradiation, because light is usually reported to improve charge transfer. We studied laser-enhanced mass transport through the heterojunction between Ag and semiconductor Fe₂O₃ situated on graphene for oxygen reduction reaction. Because of the decreased mass-transport resistance by 59% under 405 nm laser irradiation, the current density can be enhanced by 180%, which is also supported by a theoretical calculation. This laser-enhanced mass transport was attributed to local photothermal heating and the near-field local enhancement. Easier desorption of OH^- species occurring between the Fe and Ag centers under the laser accelerates the mass-transport centers.

Theoretically Revealed and Experimentally Demonstrated Synergistic Electronic Interaction of CoFe Dual-Metal Sites on N-doped Carbon for Boosting Both Oxygen Reduction and Evolution Reactions

Heteronuclear double-atom catalysts, unlike single atom catalysts, may change the charge density of active metal sites by introducing another metal single atom, thereby modifying the adsorption energies of reaction intermediates and increasing the catalytic activities. First, density functional theory calculations are used to figure out the best combination by modeling two transition-metal atoms from Fe, Co, and Ni onto N-doped graphene. Generally, Fe and Co sites are highly active for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. The combination of Co and Fe to form CoFe-N-C not only further improves the Fe's ORR and Co's OER activities but also greatly enhances the Co site's ORR and Fe site's OER activities. Then, we synthesize the CoFe-N-C by a two-step pyrolysis process and find that the CoFe-N-C exhibits exceptional ORR and OER electrocatalytic activities in alkaline media, significantly superior to Fe-N-C and Co-N-C and even commercial catalysts.

Template-free construction of hollow mesoporous carbon spheres from a covalent triazine framework for enhanced oxygen electroreduction

The construction of hollow mesoporous carbon nanospheres (HMCS) avoiding the use of traditional soft/hard templates is highly desired for nanoscience yet challenging. Herein, we report a simple and straightforward template-free strategy for preparing nitrogen, sulfur dual-doped HMCSs (N/S-HMCSs) as oxygen reduction reaction (ORR) electrocatalysts. The unique hollow spherical and mesoporous structure was in-situ formed via a thermally initiated hollowing pathway from an elaborately engineered covalent triazine framework. Regulation of pyrolysis temperatures contributed to precisely tailoring of the shell thickness of HMCSs. The resulting N/S-HMCS₉₀₀ (pyrolyzed at 900 °C) possessed high N and S contents, large specific surface areas, rich and uniform mesopores distribution. Consequently, as a metal-free ORR electrocatalyst, N/S-HMCS₉₀₀ exhibits a high half-wave potential, excellent methanol tolerance and great long-term durability. Additionally, density functional theory calculations demonstrate that N, S-dual dopant can create extra active sites with higher catalytic activity than the isolated N-dopant. This strategy provides new insights into the construction of hollow and mesoporous multi-heteroatom-doped carbon materials with tunable nanoarchitecture for various electrochemical applications.

N, S, P-Codoped Graphene-Supported Ag-MnFe2O4 Heterojunction Nanoparticles as Bifunctional Oxygen Electrocatalyst with High Efficiency

Due to slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharging and charging processes, it is essential to rationally design and synthesize non-precious metal bifunctional electrocatalysts with good performance for metal-air batteries. Herein, Ag-MnFe2O4 heterojunction nanoparticles supported on N, S, P-codoped graphene (NSPG) are developed with enhanced ORR and OER bifunctional electrocatalytic activities and stability. In contrast, S, P-doped graphene (SPG) and N, P-doped graphene (NPG) show less stabilization for the heterojunction particles. For example, under alkaline conditions, the ORR half-wave potential of Ag-MnFe2O4/NSPG can reach 0.831 V, and the over potential for OER is 0.56 V at the current density 10 mA·cm−2. Furthermore, Ag-MnFe2O4/NSPG shows better methanol resistance and durability than Pt/C catalysts.

Enhanced Electrochemistry of Single Plasmonic Nanoparticles

The structure-function relationship of plasmon enhanced electrochemistry (PEEC) is of great importance for the design of efficient PEEC catalyst, but is rarely investigated at single nanoparticle level for the lack of efficient nanoscale methodology. Herein, we report the utilization of nanoparticle impact electrochemistry to allow single nanoparticle PEEC, where the effect of incident light on the plasmonic Ag/Au nanoparticles for accelerating Co-MOFNs catalyzed hydrogen evolution reaction (HER) is systematically explored. It is found that the plasmon excited hot carrier injection can lower the reaction activation energy, resulting in a much promoted reaction probability and the integral charge generated from individual collisions. Besides, a plasmonic nanoparticle filtering method is established to effectively distinguish different plasmonic nanoparticles. This work provides a unique view in understanding the intrinsic physicochemical properties for PEEC at the nano-confined domains.

Localized surface plasmon resonance for enhanced electrocatalysis

Electrocatalysis plays a vital role in energy conversion and storage in modern society. Localized surface plasmon resonance (LSPR) is a highly attractive approach to enhance the electrocatalytic activity and selectivity with solar energy. LSPR excitation can induce the transfer of hot electrons and holes, electromagnetic field enhancement, lattice heating, resonant energy transfer and scattering, in turn boosting a variety of electrocatalytic reactions. Although the LSPR-mediated electrocatalysis has been investigated, the underlying mechanism has not been well explained. Moreover, the efficiency is strongly dependent on the structure and composition of plasmonic metals. In this review, the currently proposed mechanisms for plasmon-mediated electrocatalysis are introduced and the preparation methods to design supported plasmonic nanostructures and related electrodes are summarized. In addition, we focus on the characterization strategies used for verifying and differentiating LSPR mechanisms involved at the electrochemical interface. Following that are highlights of representative examples of direct plasmonic metal-driven and indirect plasmon-enhanced electrocatalytic reactions. Finally, this review concludes with a discussion on the remaining challenges and future opportunities for coupling LSPR with electrocatalysis.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Binary Surfactant-Mediated Tunable Nanotip Growth on Gold Nanoparticles and Applications in Photothermal Catalysis

Plasmonic nanostructures with sharp tips are widely used for optical signal enhancement because of their strong light-confining abilities. These structures have a wide range of potential applications, for example, in sensing, bioimaging, and surface-enhanced Raman scattering. Au nanoparticles, which are important plasmonic materials with high photothermal conversion efficiencies in the visible to near-infrared region, have contributed greatly to the development of photothermal catalysis. However, the existing methods for synthesizing nanostructures with tips need the assistance of poly(vinylpyrrolidone), thiols, or biomolecules. This greatly hinders signal detection because of stubborn residues. Here, we propose an efficient binary surfactant-mediated method for controlling nanotip growth on Au nanoparticle surfaces. This avoids the effects of surfactants and can be used with other Au nanostructures. The Au architecture tip growth process can be controlled well by adjusting the ratio of hexadecyltrimethylammonium bromide to hexadecyltrimethylammonium chloride. This is due to the different levels of attraction between Br^-/Cl^- and Au³⁺ ions. The surface-enhanced Raman scattering and catalytic abilities of the synthesized nanoparticles with tips were evaluated by electromagnetic simulation and photothermal catalysis experiments (with 4-nitrothiophenol). The results show good potential for use in surface-enhanced Raman scattering applications. This method provides a new strategy for designing plasmonic photothermal nanostructures for chemical and biological applications.

Strained Ultralong Silver Nanowires for Enhanced Electrocatalytic Oxygen Reduction Reaction in Alkaline Medium

Many noble metals are efficient catalysts for oxygen reduction reaction (ORR), including silver (Ag). Among all these noble metals, Ag is the most affordable because of its relative abundance. Surface energy has been proven to play a crucial role in the catalytic process, and straining is an effective operation to raise the surface energy over electrocatalysts. In this work, sonication was utilized to induce strain in Ag nanowires (NWs) through lattice deformation. A 0.18 J/m² improvement of the surface energy around the stacking faults area has been calculated via density functional theory. The diffusion-limiting current density was evaluated and increases by >20% (from -4.98 to -6.00 mA/cm²) after sonication straining. Meanwhile, the onset potential remains almost constant (i.e., 0.95 V vs RHE). The results show that induction of strain has a strong impact on the diffusion-limiting current density and significantly improves the ORR catalytic performance of Ag NWs.

Recent Advances in Plasmonic Nanostructures for Enhanced Photocatalysis and Electrocatalysis

Plasmonic nanomaterials coupled with catalytically active surfaces can provide unique opportunities for various catalysis applications, where surface plasmons produced upon proper light excitation can be adopted to drive and/or facilitate various chemical reactions. A brief introduction to the localized surface plasmon resonance and recent design and fabrication of highly efficient plasmonic nanostructures, including plasmonic metal nanostructures and metal/semiconductor heterostructures is given. Taking advantage of these plasmonic nanostructures, the following highlights summarize recent advances in plasmon-driven photochemical reactions (coupling reactions, O₂ dissociation and oxidation reactions, H₂ dissociation and hydrogenation reactions, N₂ fixation and NH₃ decomposition, and CO₂ reduction) and plasmon-enhanced electrocatalytic reactions (hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, alcohol oxidation reaction, and CO₂ reduction). Theoretical and experimental approaches for understanding the underlying mechanism of surface plasmon are discussed. A proper discussion and perspective of the remaining challenges and future opportunities for plasmonic nanomaterials and plasmon-related chemistry in the field of energy conversion and storage is given in conclusion.

Plasmon-Driven Electrochemical Methanol Oxidation on Gold Nanohole Electrodes

Direct methanol oxidation is expected to play a central role in low-polluting future power sources. However, the sluggish and complex electro-oxidation of methanol is one of the limiting factors for any practical application. To solve this issue, the use of plasmonic is considered as a promising way to accelerate the methanol oxidation reaction. In this study, we report on a novel approach for achieving enhanced methanol oxidation currents. Perforated gold thin film anodes were decorated with Pt/Ru via electrochemical deposition and investigated for their ability for plasmon-enhanced electrocatalytic methanol oxidation in alkaline media. The novel methanol oxidation anode (AuNHs/PtRu), combining the strong light absorption properties of a gold nanoholes array-based electrode (AuNHs) with surface-anchored bimetallic Pt/Ru nanostructures, known for their high activity toward methanol oxidation, proved to be highly efficient in converting methanol via the hot holes generated in the plasmonic electrode. Without light illumination, AuNHs/PtRu displayed a maximal current density of 13.7 mA/cm² at -0.11 V vs Ag/AgCl. Enhancement to 17.2 mA/cm² was achieved under 980 nm laser light illumination at a power density of 2 W/cm². The thermal effect was negligible in this system, underlining a dominant plasmon process. Fast generation and injection of charge carriers were also evidenced by the abrupt change in the current density upon laser irradiation. The good stability of the interface over several cycles makes this system interesting for methanol electro-oxidation.

Plasmon of Au nanorods activates metal-organic frameworks for both the hydrogen evolution reaction and oxygen evolution reaction

Electrocatalytic water splitting holds great promise for renewable energy conversion and storage systems. However, it usually suffers from sluggish kinetics, which greatly hinders its real application. Here, we demonstrate the utilization of the localized surface plasmon resonance (LSPR) of Au nanorods (AuNRs) to significantly improve the electroactivity of both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at Co-MOF nanosheets (Co-MOFNs) under different polarizations. Theoretical calculations suggest that the HER enhancement can be largely attributed to the injection of hot electrons from plasmonic AuNRs to Co-MOFN catalysts, which upraises the Fermi level of Co-MOFNs, increasing their reductive activity towards the HER. Regarding the promotion of the OER, it is indicated that the formed holes in Co-MOFNs should majorly locate on the surface oxygen atoms, which may also serve as active positions working jointly with neighboring Co atoms in oxidizing OH-. The plasmon enhanced HER and OER electrocatalysis could also be observed over AuNR/Ni-MOFN and AuNR/NiCo-MOFN catalysts, suggesting the generality of this strategy. This study highlights the possibility of accelerating both the HER and OER efficiency by AuNR plasmonic excitation and provides a new route towards the design of more efficient water splitting systems with the assistance of light energy.

Design-controlled synthesis of IrO2 sub-monolayers on Au nanoflowers: marrying plasmonic and electrocatalytic properties

We develop herein plasmonic-catalytic Au-IrO₂ nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO₂ shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO₂ layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO₂, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au-IrO₂ nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO₂ and to the activation of Ir-O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

In Situ ATR-SEIRAS of Carbon Dioxide Reduction at a Plasmonic Silver Cathode

Illumination of a voltage-biased plasmonic Ag cathode during CO2 reduction results in a suppression of the H2 evolution reaction while enhancing CO2 reduction. This effect has been shown to be photonic rather than thermal, but the exact plasmonic mechanism is unknown. Here, we conduct an in situ ATR-SEIRAS (attenuated total reflectance-surface-enhanced infrared absorption spectroscopy) study of a sputtered thin film Ag cathode on a Ge ATR crystal in CO2-saturated 0.1 M KHCO3 over a range of potentials under both dark and illuminated (365 nm, 125 mW cm-2) conditions to elucidate the nature of this plasmonic enhancement. We find that the onset potential of CO2 reduction to adsorbed CO on the Ag surface is -0.25 VRHE and is identical in the light and the dark. As the production of gaseous CO is detected in the light near this onset potential but is not observed in the dark until -0.5 VRHE, we conclude that the light must be assisting the desorption of CO from the surface. Furthermore, the HCO3- wavenumber and peak area increase immediately upon illumination, precluding a thermal effect. We propose that the enhanced local electric field that results from the localized surface plasmon resonance (LSPR) is strengthening the HCO3- bond, further increasing the local pH. This would account for the decrease in H2 formation and increase the CO2 reduction products in the light.

Proton exchange membrane with plasmon-active surface for enhancement of fuel cell effectivity

The action of fuel cells with proton-exchanged membranes (PEMs) requires the implementation of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) on the opposite sides of the PEMs. Recently, based on several models of electrochemical reactions a significant decrease in the thermodynamic activation barrier of both reactions under plasmon assistance was reported. In this work, we propose the design of a PEM fuel cell with a plasmon-active catalytic surface providing plasmonic triggering and enhancement of fuel cell efficiency. In particular, we deposited bimetallic (Au@Pt) nanostructures on the PEM surface and integrated them into the fuel cell design. Plasmon excitation occurs on the Au nanostructures under light illumination at the corresponding NIR wavelength, while the Pt shell is responsible for the introduction of catalytic sites. Light illumination results in a significant enhancement of the electric current produced by the fuel cell. In particular, the electric current increased several times. Control experiments indicated that the observed enhancement takes place only when the light wavelength is in compliance with the plasmon absorption band and the contribution from thermal effects is negligible. The present approach for the introduction of plasmon assistance into the design of advanced fuel cells makes them suitable for increasing the fuel cell efficiency under sunlight.

Important Considerations in Plasmon-Enhanced Electrochemical Conversion at Voltage-Biased Electrodes

In this perspective we compare plasmon-enhanced electrochemical conversion (PEEC) with photoelectrochemistry (PEC). PEEC is the oxidation or reduction of a reactant at the illuminated surface of a plasmonic metal (or other conductive material) while a potential bias is applied. PEC uses solar light to generate photoexcited electron-hole pairs to drive an electrochemical reaction at a biased or unbiased semiconductor photoelectrode. The mechanism of photoexcitation of charge carriers is different between PEEC and PEC. Here we explore how this difference affects the response of PEEC and PEC systems to changes in light, temperature, and surface morphology of the photoelectrode.

Enhancement in the rate of nitrate degradation on Au- and Ag-decorated TiO2 photocatalysts

The solar-driven reduction of nitrate to nitrogen has been studied in the presence of a formate hole scavenger, over a series of Au- and Ag-decorated TiO₂ catalysts.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

Nanowire Genome: A Magic Toolbox for 1D Nanostructures

1D nanomaterials with high aspect ratio, i.e., nanowires and nanotubes, have inspired considerable research interest thanks to the fact that exotic physical and chemical properties emerge as their diameters approach or fall into certain length scales, such as the wavelength of light, the mean free path of phonons, the exciton Bohr radius, the critical size of magnetic domains, and the exciton diffusion length. On the basis of their components, aspect ratio, and properties, there may be imperceptible connections among hundreds of nanowires prepared by different strategies. Inspired by the heredity system in life, a new concept termed the "nanowire genome" is introduced here to clarify the relationships between hundreds of nanowires reported previously. As such, this approach will not only improve the tools incorporating the prior nanowires but also help to precisely synthesize new nanowires and even assist in the prediction on the properties of nanowires. Although the road from start-ups to maturity is long and fraught with challenges, the genetical syntheses of more than 200 kinds of nanostructures stemming from three mother nanowires (Te, Ag, and Cu) are summarized here to demonstrate the nanowire genome as a versatile toolbox. A summary and outlook on future challenges in this field are also presented.

Electrochemical Fabrication of rGO-embedded Ag-TiO2 Nanoring/Nanotube Arrays for Plasmonic Solar Water Splitting

Effective utilization of hot electrons generated from the decay of surface plasmon resonance in metal nanoparticles is conductive to improve solar water splitting efficiency. Herein, Ag nanoparticles and reduced graphene oxide (rGO) co-decorated hierarchical TiO2 nanoring/nanotube arrays (TiO2 R/T) were facilely fabricated by using two-step electrochemical anodization, electrodeposition, and photoreduction methods. Comparative studies were conducted to elucidate the effects of rGO and Ag on the morphology, photoresponse, charge transfer, and photoelectric properties of TiO2. Firstly, scanning electron microscope images confirm that the Ag nanoparticles adhered on TiO2 R/T and TiO2 R/T-rGO have similar diameter of 20 nm except for TiO2 R-rGO/T. Then, the UV-Vis DRS and scatter spectra reveal that the optical property of the Ag-TiO2 R/T-rGO ternary composite is enhanced, ascribing to the visible light absorption of plasmonic Ag nanoparticles and the weakening effect of rGO on light scattering. Meanwhile, intensity-modulated photocurrent spectroscopy and photoluminescence spectra demonstrate that rGO can promote the hot electrons transfer from Ag nanoparticles to Ti substrate, reducing the photogenerated electron-hole recombination. Finally, Ag-TiO2 R/T-rGO photoanode exhibits high photocurrent density (0.98 mA cm-2) and photovoltage (0.90 V), and the stable H2 evolution rate of 413 μL h-1 cm-2 within 1.5 h under AM 1.5 which exceeds by 1.30 times than that of pristine TiO2 R/T. In line with the above results, this work provides a reliable route synergizing rGO with plasmonic metal nanoparticles for photocatalysis, in which, rGO presents a broad absorption spectrum and effective photogenerated electrons transfer.

Plasmonic nanoparticle simulations and inverse design using machine learning

Collective oscillation of quasi-free electrons on the surface of metallic plasmonic nanoparticles (NPs) in the ultraviolet to near-infrared (NIR) region induces a strong electromagnetic enhancement around the NPs, which leads to numerous important applications. These interesting far- and near-field optical characteristics of the plasmonic NPs can be typically obtained from numerical simulations for theoretical guidance of NP design. However, traditional numerical simulations encounter irreconcilable conflicts between the accuracy and speed due to the high demand of computing power. In this work, we utilized the machine learning method, specifically the deep neural network (DNN), to establish mapping between the far-field spectra/near-field distribution and dimensional parameters of three types of plasmonic NPs including nanospheres, nanorods, and dimers. After the training process, both the forward prediction of far-field optical properties and the inverse prediction of on-demand dimensional parameters of NPs can be accomplished accurately and efficiently with the DNN. More importantly, we have achieved for the first time ultrafast and accurate prediction of two-dimensional on-resonance electromagnetic enhancement distributions around NPs by greatly reducing the amount of electromagnetic data via screening and resampling methods. These near-field predictions can be realized typically in less than 10-2 seconds on a laptop, which is 6 orders faster than typical numerical simulations implemented on a server. Therefore, we demonstrate that the DNN is an ultrafast, highly efficient, and computing resource-saving tool to investigate the far- and near-field optical properties of plasmonic NPs, especially for a number of important nano-optical applications such as surface-enhanced Raman spectroscopy, photocatalysis, solar cells, and metamaterials.