Oxygen reduction on stepped platinum surfaces in acidic media

Unifying the ORR and OER with surface oxygen and extracting their intrinsic activities on platinum

Common half-cell measurements deliver oxygen reduction activities linked to the chosen scan rate, limiting their value for fundamental and comparative studies on platinum. Here we show a deconvolution of the intrinsic kinetics from the effect of surface oxygen on platinum. We find an electronic effect of the surface oxygen, substantiate a Tafel slope of ~120 mV/decade, obtain an exchange current density of 13 ± 4 µA/cm2, and an activity of 7 mA/cm2 at 900 mV. Eventually, we broaden the scope of this analysis to the effects of surface rearrangement, alloying, and supported Pt nanoparticles, the latter providing insight into discrepancies between half-cell and fuel cell measurements. We find through computational methods that binding energies of intermediates would be weakened by the presence of highly coordinated oxygen atoms. Finally, we obtain a phenomenological rate equation for the oxygen reduction and evolution reaction, suggesting that both reactions follow a shared mechanism.

Cooperative Effect of Cations and Catalyst Structure in Tuning Alkaline Hydrogen Evolution on Pt Electrodes

The kinetics of hydrogen evolution reaction (HER) in alkaline media, a reaction central to alkaline water electrolyzers, is not accurately captured by traditional adsorption-based activity descriptors. As a result, the exact mechanism and the main driving force for the water reduction or HER rate remain hotly debated. Here, we perform extensive kinetic measurements on the pH- and cation-dependent HER rate on Pt single-crystal electrodes in alkaline conditions. We find that cations interacting with Pt step sites control the HER activity, while they interact only weakly with Pt(111) and Pt(100) terraces and, therefore, cations do not affect HER kinetics on terrace sites. This is reflected by divergent activity trends as a function of pH as well as cation concentration on stepped Pt surfaces vs Pt surfaces that do not feature steps, such as Pt(111). We show that HER activity can be optimized by rationally tuning these step-cation interactions via selective adatom deposition at the steps and by choosing an optimal electrolyte composition. Our work shows that the catalyst and the electrolyte must be tailored in conjunction to achieve the highest possible HER activity.

Enhanced oxygen reduction reaction on caffeine-modified platinum single-crystal electrodes

Enhancing the activity of the oxygen reduction reaction (ORR) is crucial for fuel cell development, and hydrophobic species are known to increase the ORR activity. This paper reports that caffeine enhanced the specific ORR activity of Pt(111) 11-fold compared to that without caffeine in a 0.1 M HClO4 aqueous solution. Moreover, caffeine increased the ORR activity of Pt(110) 2.5-fold; however, the activity of Pt(100) was unaffected. The infrared (IR) band of PtOH (blocking species of the ORR) decreased for all the surfaces. Caffeine was adsorbed with its molecular plane perpendicular to the Pt(111) and Pt(110) surfaces and tilted relative to the Pt(100) surface. Thus, the effects of caffeine on the ORR activity can be rationalized by a decrease in PtOH coverage and the difference in adsorption geometry of caffeine.

Site-specific reactivity of stepped Pt surfaces driven by stress release

Heterogeneous catalysts are widely used to promote chemical reactions. Although it is known that chemical reactions usually happen on catalyst surfaces, only specific surface sites have high catalytic activity. Thus, identifying active sites and maximizing their presence lies at the heart of catalysis research1-4, in which the classic model is to categorize active sites in terms of distinct surface motifs, such as terraces and steps1,5-10. However, such a simple categorization often leads to orders of magnitude errors in catalyst activity predictions and qualitative uncertainties of active sites7,8,11,12, thus limiting opportunities for catalyst design. Here, using stepped Pt(111) surfaces and the electrochemical oxygen reduction reaction (ORR) as examples, we demonstrate that the root cause of larger errors and uncertainties is a simplified categorization that overlooks atomic site-specific reactivity driven by surface stress release. Specifically, surface stress release at steps introduces inhomogeneous strain fields, with up to 5.5% compression, leading to distinct electronic structures and reactivity for terrace atoms with identical local coordination, and resulting in atomic site-specific enhancement of ORR activity. For the terrace atoms flanking both sides of the step edge, the enhancement is up to 50 times higher than that of the atoms in the middle of the terrace, which permits control of ORR reactivity by either varying terrace widths or controlling external stress. Thus, the discovery of the above synergy provides a new perspective for both fundamental understanding of catalytically active atomic sites and design principles of heterogeneous catalysts.

Surface-Dependent Hydrogen Evolution Activity of Copper Foil

Single-crystal planes are ideal platforms for catalytic research. In this work, rolled copper foils with predominantly (220) planes were used as the starting material. By using temperature gradient annealing, which caused grain recrystallization in the foils, they were transformed to those with (200) planes. In acidic solution, the overpotential of such a foil (10 mA cm^-2) was found to be 136 mV lower than that of a similar rolled copper foil. The calculation results show that hollow sites formed on the (200) plane have the highest hydrogen adsorption energy and are active centers for hydrogen evolution. Thus, this work clarifies the catalytic activity of specific sites on the copper surface and demonstrates the critical role of surface engineering in designing catalytic properties.

Colloidal Synthesis of Metal Nanocrystals: From Asymmetrical Growth to Symmetry Breaking

Nanocrystals offer a unique platform for tailoring the physicochemical properties of solid materials to enhance their performances in various applications. While most work on controlling their shapes revolves around symmetrical growth, the introduction of asymmetrical growth and thus symmetry breaking has also emerged as a powerful route to enrich metal nanocrystals with new shapes and complex morphologies as well as unprecedented properties and functionalities. The success of this route critically relies on our ability to lift the confinement on symmetry by the underlying unit cell of the crystal structure and/or the initial seed in a systematic manner. This Review aims to provide an account of recent progress in understanding and controlling asymmetrical growth and symmetry breaking in a colloidal synthesis of noble-metal nanocrystals. With a touch on both the nucleation and growth steps, we discuss a number of methods capable of generating seeds with diverse symmetry while achieving asymmetrical growth for mono-, bi-, and multimetallic systems. We then showcase a variety of symmetry-broken nanocrystals that have been reported, together with insights into their growth mechanisms. We also highlight their properties and applications and conclude with perspectives on future directions in developing this class of nanomaterials. It is hoped that the concepts and existing challenges outlined in this Review will drive further research into understanding and controlling the symmetry breaking process.

Adsorption Energy in Oxygen Electrocatalysis

Adsorption energy (AE) of reactive intermediate is currently the most important descriptor for electrochemical reactions (e.g., water electrolysis, hydrogen fuel cell, electrochemical nitrogen fixation, electrochemical carbon dioxide reduction, etc.), which can bridge the gap between catalyst's structure and activity. Tracing the history and evolution of AE can help to understand electrocatalysis and design optimal electrocatalysts. Focusing on oxygen electrocatalysis, this review aims to provide a comprehensive introduction on how AE is selected as the activity descriptor, the intrinsic and empirical relationships related to AE, how AE links the structure and electrocatalytic performance, the approaches to obtain AE, the strategies to improve catalytic activity by modulating AE, the extrinsic influences on AE from the environment, and the methods in circumventing linear scaling relations of AE. An outlook is provided at the end with emphasis on possible future investigation related to the obstacles existing between adsorption energy and electrocatalytic performance.

Ultrasmall, Coating-Free, Pyramidal Platinum Nanoparticles for High Stability Fuel Cell Oxygen Reduction

Ultrasmall (<5 nm diameter) noble metal nanoparticles with a high fraction of {111} surface domains are of fundamental and practical interest as electrocatalysts, especially in fuel cells; the nanomaterial surface structure dictates its catalytic properties, including kinetics and stability. However, the synthesis of size-controlled, pure Pt-shaped nanocatalysts has remained a formidable chemical challenge. There is an urgent need for an industrially scalable method for their production. Here, a one-step approach is presented for the preparation of single-crystal pyramidal nanocatalysts with a high fraction of {111} surface domains and a diameter below 4 nm. This is achieved by harnessing the shape-directing effect of citrate molecules, together with the strict control of oxidative etching while avoiding polymers, surfactants, and organic solvents. These catalysts exhibit significantly enhanced durability while, providing equivalent current and power densities to highly optimized commercial Pt/C catalysts at the beginning of life (BOL). This is even the case when they are tested in full polymer electrolyte membrane fuel cells (PEMFCs), as opposed to rotating disk experiments that artificially enhance electrode kinetics and minimize degradation. This demonstrates that the {111} surface domains in pyramidal Pt nanoparticles (as opposed to spherical Pt nanoparticles) can improve aggregation/corrosion resistance in realistic fuel cell conditions, leading to a significant improvement in membrane electrode assembly (MEA) stability and lifetime.

Elucidating the Correlation between ORR Polarization Curves and Kinetics at Metal-Electrolyte Interfaces

The metal-vacuum models used to analyze the thermodynamics of the oxygen reduction reaction (ORR) completely overlook the role of electrolytes in the electrochemical process and thus cannot reflect the actual kinetic process occurring at the metal-electrolyte interface. Therefore, based on the real experimental process, the current work elucidates the chemical interactions between the electrolyte and the chemical species for the ORR via a novel metal-electrolyte model for the first time by effectively elucidating the correlation between ORR kinetics and polarization curves. Our simulation model analysis comprises the study of all possible ORR mechanisms on different Pt surfaces (Pt(111), Pt(110), and Pt(100)) and PtNi alloys with different compositions (Pt₃Ni(111), Pt₂Ni₂(111), and PtNi₃(111)). The obtained results demonstrate that the hydrogenation of adsorbed oxygen to form adsorbed hydroxyl (R8), whose immense control weight is reflected by a coverage of adsorbed oxygen (θ_O*) of about 1, is the rate-determining step (RDS) in the four-electron-dominated ORR process. A direct correlation has been established by the great fitting of polarization curves from theoretical ORR kinetics obtained via both the metal-electrolyte model and experimental measurement. This study reveals that among the different Pt surfaces and PtNi alloys, Pt₃Ni(111) exhibits the highest ORR activity with the lowest free energy barrier of E_a (0.74 eV), the smallest value of |ΔG_O* - 2.46| (0.80 eV), the highest reaction rate r (9.98 × 10⁵ s^-1 per site), and a more positive half-wave potential U_1/2 (0.93 V). In contrast to previous model studies, this work provides a more accurate theoretical system for catalyst screening, which will help researchers to better understand the experimental phenomena and will be a guiding piece of work for catalyst design and development.

Electrocatalysis in Alkaline Media and Alkaline Membrane-Based Energy Technologies

Hydrogen energy-based electrochemical energy conversion technologies offer the promise of enabling a transition of the global energy landscape from fossil fuels to renewable energy. Here, we present a comprehensive review of the fundamentals of electrocatalysis in alkaline media and applications in alkaline-based energy technologies, particularly alkaline fuel cells and water electrolyzers. Anion exchange (alkaline) membrane fuel cells (AEMFCs) enable the use of nonprecious electrocatalysts for the sluggish oxygen reduction reaction (ORR), relative to proton exchange membrane fuel cells (PEMFCs), which require Pt-based electrocatalysts. However, the hydrogen oxidation reaction (HOR) kinetics is significantly slower in alkaline media than in acidic media. Understanding these phenomena requires applying theoretical and experimental methods to unravel molecular-level thermodynamics and kinetics of hydrogen and oxygen electrocatalysis and, particularly, the proton-coupled electron transfer (PCET) process that takes place in a proton-deficient alkaline media. Extensive electrochemical and spectroscopic studies, on single-crystal Pt and metal oxides, have contributed to the development of activity descriptors, as well as the identification of the nature of active sites, and the rate-determining steps of the HOR and ORR. Among these, the structure and reactivity of interfacial water serve as key potential and pH-dependent kinetic factors that are helping elucidate the origins of the HOR and ORR activity differences in acids and bases. Additionally, deliberately modulating and controlling catalyst-support interactions have provided valuable insights for enhancing catalyst accessibility and durability during operation. The design and synthesis of highly conductive and durable alkaline membranes/ionomers have enabled AEMFCs to reach initial performance metrics equal to or higher than those of PEMFCs. We emphasize the importance of using membrane electrode assemblies (MEAs) to integrate the often separately pursued/optimized electrocatalyst/support and membranes/ionomer components. Operando/in situ methods, at multiscales, and ab initio simulations provide a mechanistic understanding of electron, ion, and mass transport at catalyst/ionomer/membrane interfaces and the necessary guidance to achieve fuel cell operation in air over thousands of hours. We hope that this Review will serve as a roadmap for advancing the scientific understanding of the fundamental factors governing electrochemical energy conversion in alkaline media with the ultimate goal of achieving ultralow Pt or precious-metal-free high-performance and durable alkaline fuel cells and related technologies.

Engineering PtCu nanoparticles for a highly efficient methanol electro-oxidation reaction

Achieving a highly efficient and durable methanol electro-oxidation catalyst in acid media is critical for the practical utilization of direct methanol fuel cells (DMFCs) at the commercial scale. Herein, we report a facile and effective one-pot strategy for the synthesis of carbon-supported PtCu alloy nanoparticles (PtCu NPs) with a Pt-rich surface, small particle size and uniform dispersion. The as-prepared PtCu NPs with the optimal alloy composition (Pt₂Cu) exhibit a significantly improved electrochemical methanol oxidation reaction performance in terms of a high activity, superior CO tolerance and remarkable durability, in contrast to those of commercial Pt/C catalysts in acid media. Particularly, the Pt₂Cu/C catalyst exerts a 4.5 times enhancement in the mass activity and a larger I_f/I_b value compared to those of commercial Pt/C (Pt/C_comm). The enhanced catalytic activities can be ascribed to the high utilization of Pt and the high index facets of the surface. Also, the addition of Cu downshifts the d-band center of Pt and improves the CO tolerance during the methanol oxidation reaction process. This work provides an efficient strategy for designing desired Pt-based alloys for various catalytic reactions.

Recent Advances in Electrocatalysts for Proton Exchange Membrane Fuel Cells and Alkaline Membrane Fuel Cells

The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low-cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.

Prudent Practices in ex situ Durability Analysis Using Cyclic Voltammetry for Platinum-based Electrocatalysts

Platinum (Pt)-based electrocatalysts are at the vanguard of research initiatives to meet activity and durability targets for promoting large-scale adoption of fuel cell vehicles. Ex situ characterization of electrocatalyst activity and durability using cyclic voltammetry (CV) has a steep learning curve. Thus, many researchers who do not receive formal training in electrochemistry are left unsure how to proceed. Herein, we identify and compile prudent practices for reliable assessment of ECSA values with examples from our research on nanoscale catalytic films formed by the self-terminating electrodeposition of Pt. Starting with a conceptual framework to understand typical features in the CV of reversible redox couples, we present prudent practices in acquiring CV data aimed at nonelectrochemists. We then highlight specific features related to ECSA computation from Pt CV. Finally, we suggest safeguards that help avoid missteps and achieve repeatable results while conducting ex situ durability tests that extend over days.

Atomic Regulation of PGM Electrocatalysts for the Oxygen Reduction Reaction

With the increasing enthusiasm for the hydrogen economy and zero-emission fuel cell technologies, intensive efforts have been dedicated to the development of high-performance electrocatalytic materials for the cathodic oxygen reduction reaction (ORR). Some major fundamental breakthroughs have been made in the past few years. Therefore, reviewing the most recent development of platinum-group-metal (PGM) ORR electrocatalysts is of great significance to pushing it forward. It is known that the ORR on the fuel cell electrode is a heterogeneous reaction occurring at the solid/liquid interface, wherein the electron reduces the oxygen along with species in the electrolyte. Therefore, the ORR kinetic is in close correlation with the electronic density of states and wave function, which are dominated by the localized atomic structure including the atomic distance and coordination number (CN). In this review, the recent development in the regulation over the localized state on the catalyst surface is narrowed down to the following structural factors whereby the corresponding strategies include: the crystallographic facet engineering, phase engineering, strain engineering, and defect engineering. Although these strategies show distinctive features, they are not entirely independent, because they all correlate with the atomic local structure. This review will be mainly divided into four parts with critical analyses and comparisons of breakthroughs. Meanwhile, each part is described with some more specific techniques as a methodological guideline. It is hoped that the review will enhance an insightful understanding on PGM catalysts of ORR with a visionary outlook.

Nanoscale Chemical and Structural Analysis during In Situ Scanning/Transmission Electron Microscopy in Liquids

Liquid-cell scanning/transmission electron microscopy (S/TEM) has impacted our understanding of multiple areas of science, most notably nanostructure nucleation and growth and electrochemistry and corrosion. In the case of electrochemistry, the incorporation of electrodes requires the use of silicon nitride membranes to confine the liquid. The combined thickness of the liquid layer and the confining membranes prevents routine atomic-resolution characterization. Here, we show that by performing electrochemical water splitting in situ to generate a gas bubble, we can reduce the thickness of the liquid to a film approximately 30 nm thick that remains covering the sample. The reduced thickness of the liquid allows the acquisition of atomic-scale S/TEM images with chemical and valence analysis through electron energy loss spectroscopy (EELS) and structural analysis through selected area electron diffraction (SAED). This contrasts with a specimen cell entirely filled with liquid, where the broad plasmon peak from the liquid obscures the EELS signal from the sample and induces beam incoherence that impedes SAED analysis. The gas bubble generation is fully reversible, which allows alternating between a full cell and thin-film condition to obtain optimal experimental and analytical conditions, respectively. The methodology developed here can be applied to other scientific techniques, such as X-ray scattering, Raman spectroscopy, and X-ray photoelectron spectroscopy, allowing for a multi-modal, nanoscale understanding of solid-state samples in liquid media.

A Discreet Wearable IoT Sensor for Continuous Transdermal Alcohol Monitoring - Challenges and Opportunities

Non-invasive continuous alcohol (ethanol) monitoring has potential applications in both population research and in clinical management of acute alcohol intoxication or chronic alcoholism. Current wearable monitors based on transdermal alcohol content (TAC) sensing have limited accessibility and blood alcohol content (BAC) quantification accuracy. Here we describe the development of a self-contained discreet wearable transdermal alcohol (TAC) sensor in the form of a wristband or armband. This sensor can detect vapor-phase alcohol in perspiration from 0.09 ppm (equivalent to 0.09 mg/dL sweat alcohol concentration at 25 °C under Henry's Law equilibrium) to over 500 ppm at one-minute time resolution. Additionally, a digital sensor was employed to monitor the temperature and humidity levels inside the sensing chamber. Two male human subjects were recruited to conduct studies with alcohol consumption using calibrated prototype TAC sensors to validate the performance. Our preliminary data demonstrated that, under well-controlled conditions, this sensor can acquire TAC curves at low doses (1-2 standard drinks). Moreover, TAC data for different doses can be easily distinguished. However, substantial interpersonal and intrapersonal variabilities in measurement data were also observed in experiments with less controlled conditions. Our observations suggest that perspiration rate might be an important contributing factor to these variabilities. Further studies with sufficient sample sizes are required to validate and characterize the impact of different perspiration rates on TAC sensors, which may inform more reproducible and accurate sensor designs in the future.

In Situ Quantification of the Local Electrocatalytic Activity via Electrochemical Scanning Tunneling Microscopy

Identification of catalytically active sites at solid/liquid interfaces under reaction conditions is an essential task to improve the catalyst design for sustainable energy devices. Electrochemical scanning tunneling microscopy (EC-STM) combines the control of the surface reactions with imaging on a nanoscale. When performing EC-STM under reaction conditions, the recorded analytical signal shows higher fluctuations (noise) at active sites compared to non-active sites (noise-EC-STM or n-EC-STM). In the past, this approach has been proven as a valid tool to identify the location of active sites. In this work, the authors show that this method can be extended to obtain quantitative information of the local activity. For the platinum(111) surface under oxygen reduction reaction conditions, a linear relationship between the STM noise level and a measure of reactivity, the turn-over frequency is found. Since it is known that the most active sites for this system are located at concave sites, the method has been applied to quantify the activity at steps. The obtained activity enhancement factors appeared to be in good agreement with the literature. Thus, n-EC-STM is a powerful method not only to in situ identify the location of active sites but also to determine and compare local reactivity.

Challenges in applying highly active Pt-based nanostructured catalysts for oxygen reduction reactions to fuel cell vehicles

The past 30 years have seen progress in the development of Pt-based nanocatalysts for the oxygen reduction reaction, and some are now in production on a commercial basis and used for polymer electrolyte fuel cells (PEFCs) for automotives and other applications. Further improvements in catalytic activity are required for wider uptake of PEFCs, however. In laboratories, researchers have developed various catalysts that have much higher activities than commercial ones, and these state-of-the-art catalysts have potential to improve energy conversion efficiencies and reduce the usage of platinum in PEFCs. There are several technical issues that must be solved before they can be applied in fuel cell vehicles, which require a high power density and practical durability, as well as high efficiency. In this Review, the development history of Pt-based nanocatalysts and recent analytical studies are summarized to identify the origin of these technical issues. Promising strategies for overcoming those issues are also discussed.

Bridging the Gap in the Mechanistic Understanding of Electrocatalysis via In Situ Characterizations

Electrocatalysis offers a promising strategy to take advantage of the increasingly available and affordable renewable energy for the sustainable production of fuels and chemicals. Attaining this promise requires a molecular level insight of the electrical interface that can be used to tailor the selectivity of electrocatalysts. Addressing this selectivity challenge remains one of the most important areas in modern electrocatalytic research. In this Perspective, we focus on the use of in situ techniques to bridge the gap in the fundamental understanding of electrocatalytic processes. We begin with a brief discussion of traditional electrochemical techniques, ex situ measurements and in silico analysis. Subsequently, we discuss the utility and limitations of in situ methodologies, with a focus on vibrational spectroscopies. We then end by looking ahead toward promising new areas for the application of in situ techniques and improvements to current methods.

Probing the Irregular Lattice Strain-Induced Electronic Structure Variations on Late Transition Metals for Boosting the Electrocatalyst Activity

Owing to the simplicity in practice and continuous fine-tuning ability toward the binding strengths of adsorbates, the strain effect is intensively explored, especially focused on the modulation of catalytic activity in transition metal (TM) based electrocatalysts. Recently, more and more abnormal cases have been found that cannot be explained by the conventional simplified models. In this work, the strain effects in five late TMs, Fe, Co, Ni, Pd, and Pt are studied in-depth regarding the facet engineering, the surface atom density, and the d-band center. Interestingly, the irregular response of Fe lattice to the applied strain is identified, indicating the untapped potential of achieving the phase change by precise strain modulation. For the complicated high-index facets, the surface atom density has become the pivotal factor in determining the surface stability and electroactivity, which identifies the potential of high entropy alloys (HEA) in electrocatalysis. The work supplies insightful understanding and significant references for future research in subtle modulation of electroactivity based on the precise facet engineering in the more complex facets and morphologies.

Bimetallic PtAu electrocatalysts for the oxygen reduction reaction: challenges and opportunities

Highly active, durable oxygen reduction reaction (ORR) electrocatalysts have an essential role in promoting the continuous operation of advanced energy technologies such as fuel cells and metal-air batteries. Considering the scarce reserve of Pt and its unsatisfactory overall performance, there is an urgent demand for the development of new generation ORR electrocatalysts that are substantially better than the state-of-the-art supported Pt-based nanocatalysts, such as Pt/C. Among various nanostructures, bimetallic PtAu represents one unique alloy system where highly contradictory performance has been reported. While it is generally accepted that Au may contribute to stabilizing Pt, its role in modulating the intrinsic activity of Pt remains unclear. This perspective will discuss critical structural issues that affect the intrinsic ORR activities of bimetallic PtAu, with an eye on elucidating the origin of seemingly inconsistent experimental results from the literature. As a relatively new class of electrodes, we will also highlight the performance of dealloyed nanoporous gold (NPG) based electrocatalysts, which allow a unique combination of structural properties highly desired for this important reaction. Finally, we will put forward the challenges and opportunities for the incorporation of these advanced electrocatalysts into membrane electrode assemblies (MEA) for actual fuel cells.

Peptide Capping Agent Design for Gold (111) Facet by Molecular Simulation and Experimental Approaches

The stochastic tunneling-basin hopping method (STUN-BH) was utilized to obtain the most stable peptide S7 configuration (Ac-Ser-Ser-Phe-Pro-Gln-Pro-Asn-CONH2) adsorbed on Au(111) facet. After the most stable S7 configuration was found, molecular dynamics (MD) simulation was conducted to investigate the thermal stability between S7 and Au facet at 300 K in both vacuum and water environment. Moreover, further design sets of peptide sequences on Au(111) facet were used to compare with S7. All molecular simulations were carried out by the large-scale atomic/molecular massively parallel simulator (LAMMPS). The Amber99sb-ILDN force field was employed for modeling the interatomic interaction of peptides, and the TIP3P water was used for the water environment. The CHARMM-METAL force field was introduced to model the S7, PF8 (Ac-Pro-Phe-Ser-Pro-Phe-Ser-Pro-Phe-CONH2) and FS8 (Ac-Phe-Ser-Phe-Ser-Phe-Ser-Phe-Ser-CONH2) interactions with Au(111). The MD simulation results demonstrate that the morphology of Pro affects the adsorption stability of Phe. Therefore, we designed two sequences, PF8 and FS8, to confirm our simulation result through experiment. The present study also develops a novel low-temperature plasma synthesis method to evaluate the facet selecting performance of the designed peptide sequences of S7, PF8, and FS8. The experimental results suggest that the reduced Au atom seed is captured with the designed peptide sequences and slowing growing under room temperature for 72 hours. The experimental results are in the excellent agreement with the simulation finding that the Pro in the designed peptide sequences plays a critical role in the facet selection for Au atom stacking.

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

Understanding microscopic mechanism of multi-electron multi-proton transfer reactions at complexed systems is important for advancing electrochemistry-oriented science in the 21st century.