Studies of energy dissipation pathways in the water formation reaction using metal-oxide-semiconductor nanostructures

Katalytisch-chemische Reaktionen sind komplexe Prozesse, die eine Vielzahl von Schritten, wie molekulare Adsorption und Dissoziation auf einer Oberfläche, die Wechselwirkungen zwischen intermediären Produkten und die Desorption der Produkte von der Oberfläche in die Gasphase umfassen. Erhebliche Anstrengungen, unter Verwendung verschiedener experimenteller und theoretischer Methoden, wurden unternommen, um ein detailliertes mikroskopisches Verständnis der Dynamik dieser Prozesse zu erlangen. Doch noch wenig ist bekannt über die Wege der Energieübertragung im Zuge von Gas-Oberflächen-Wechselwirkungen. Insbesondere sind elektronische Anregungen als Energie Verlustkanal infolge von chemischen Oberflächenreaktionen von Interesse. Ein vielversprechender, Ansatz, um Energietransfers zu studieren, stellt die Verwendung von Metall-Halbleiter- (MS), Metall-Oxid-Halbleiter- (MOS), und Metall-Isolator-Metall-Nanostrukturen (MIM) dar. Diese Bauteile ermöglichen den direkten Nachweis von elektronischen Anregungen durch den nicht-adiabatischen Transfer von chemischer Energie als elektrischen Strom – den makroskopischen Chemostrom. Bis heute sind die bedeutendsten Fortschritte bei der Untersuchung von Chemoströmen infolge von Reaktionen zwischen atomaren Spezies an Metallen gemacht worden. Die wichtigsten Ergebnisse dieser Untersuchungen wurden an anderer Stelle überprüft. Wechselwirkungen molekularer Gase mit Metalloberflächen wurden hingegen weniger studiert – wie die Zahl der Veröffentlichungen zeigt, die über einen induzierten elektrischen Strom durch Oxidation von Wasserstoff oder Kohlenmonoxid auf der Oberfläche eines Platinkatalysators berichten. Es ist jedoch noch nicht klar, welche Reaktionsschritte für die Erzeugung dieses Stroms verantwortlich sind. Der Beitrag thermischer Effekte zur Erzeugung von Chemoströmen ist ebenfalls noch nicht vollständig verstanden.Catalytic chemical reactions are complex processes, which include a variety of steps such as molecular adsorption and dissociation on a surface, interactions between intermediates, and desorption of products from the surface to the gas phase. Considerable effort has been made to achieve a detailed microscopic understanding of the dynamics of these processes using different experimental and theoretical methods, nevertheless still little is known about the routes of energy transfer accompanying gas-surface interactions. In particular, the role of electronic excitations for the energy dissipation in surface chemical reactions is a subject of debate. Resolving this issue is of particular interest for the understanding of the surface chemical reactions. Recently, an easy to implement approach to study energy transfer processes accompanying exothermic gas-surface interactions with the use of metal-semiconductor (MS), metal-oxide-semiconductor (MOS), and metal-insulator-metal (MIM) nanostructures has been demonstrated. These devices allow direct detection of electronic excitation induced by the the non-adiabatic dissipation of chemical energy as a macroscopic electric current, called chemicurrent. To date, the most significant progress has been made in the study of chemicurrents induced in the course of reactions between atomic species on metals. Main results of these studies are reviewed elsewhere. At the same time, interactions of molecular gases with metal surfaces are less studied. For instance, the number of publications reported observation of an electric current induced by oxidation of hydrogen or carbon monoxide on the surface of platinum catalysts. However, it is not clear yet which reaction steps are responsible for the generation of this current. The contribution of thermal effects in the generation of the chemicurrent is also not fully understood. The goal of this work is to study processes of an electric charge generation and transfer, induced by adsorption of oxygen and hydrogen molecules, and reactions between them on a polycrystalline surface of platinum with the use of the Pt/SiO2-n-Si MOS nanostructures. In particular, it aims to find answers to the following questions: (1) Is there any electronic excitation, accompanying steps of the water formation on platinum, which can be detected using MOS nanostructures? (2) What is the mechanism of this chemicurrent creation? (3) How big is the impact of thermal effects, due to the surface chemical reaction, on the process of the chemicurrent detection using MOS nanostructures

Single Particle Plasmonics for Materials Science and Single Particle Catalysis

Single particle nanoplasmonic sensing and spectroscopy is a powerful and at the same time relatively easy-to-implement research method that allows monitoring of changes in the structure and properties of metal nanoparticles in real time and with only few restrictions in terms of surrounding medium, temperature and pressure. Consequently, it has been successfully used in materials science applications to, for instance, reveal the impact of size and shape of single metal nanoparticles on the thermodynamics of metal hydride formation and decomposition. In this Perspective, we review and discuss the research efforts that have spurred key advances in the development of single particle nanoplasmonic sensing and spectroscopy as a research tool in materials science. On this background we then assess the prospects and challenges toward its application in single particle catalysis, with the aim to enable operando studies of the relationship between metal nanoparticle structure or oxidation state and catalytic performance

Hot electron-driven electrocatalytic hydrogen evolution reaction on metal–semiconductor nanodiode electrodes

© 2019, The Author(s). Hot electrons generated on metal catalysts influence atomic and molecular processes, leading to hot electron-driven catalytic reactions. Here, we show the acceleration of electrocatalytic hydrogen evolution caused by internal injection of hot electrons on Pt/Si metal–semiconductor electrodes. When a forward bias voltage is applied to the Pt/Si contact, hot electrons are injected. The excess energy of these electrons allows them to reach the Pt/electrolyte interface and reduce the adsorbed hydrogen ions to form H 2 (2H + + 2e − →H 2 ). We show that the onset potential of the hydrogen evolution reaction shifts positively by 160 mV while the cathodic current exhibits an 8-fold increase in the presence of hot electrons. The effect disappears when the thickness of the Pt film exceeds the mean free path of the hot electrons. The concept of a hot electron-driven reaction can lead to the development of a novel mechanism for controlling reactivity at liquid–solid interface

The nature of hot electrons generated by exothermic catalytic reactions

We review recent progress in studies of the nature of hot electrons generated in metal nanoparticles and thin films on oxide supports and their role in heterogeneous catalysis. We show that the creation of hot electrons and their transport across the metal-oxide interface is an inherent component of energy dissipation accompanying catalytic and photocatalytic surface reactions. The intensity of hot electron flow is well correlated with turnover rates of corresponding reactions. We also show that controlling the flow of hot electrons crossing the interface can lead to the control of chemical reaction rates. Finally, we discuss perspectives of hot-electron-mediated surface chemistry that promise the capability to drive catalytic reactions with enhanced efficiency and selectivity through electron-mediated, non-thermal processes. © 2015 Elsevier Ltd. All rights reserved18101sciescopu

Nonadiabatic chemical-to-electrical energy conversion in heterojunction nanostructures

Nonadiabatic energy dissipation by electron subsystem of nanostructured solids unveil interesting opportunities for the solid-state energy conversion and sensor applications. We found that planar Pt/GaP and Pd/GaP Schottky structures with nanometer thickness metallization demonstrates a nonadiabatic channel for the conversion into electricity the energy of a catalytic hydrogen-to-water oxidation process on the metal layer surface. The observed above thermal current greatly complements the usual thermionic emission current and its magnitude is linearly proportional to the rate of formation and desorption of product water molecules from the nanostructure surface. The possibilities of utilizing the nonadiabatic functionality in chemical-to-electrical energy conversion devices are discussed

Charge Transfer during the Aluminum-Water Reaction Studied with Schottky Nanodiode Sensors

© 2019 American Chemical Society.The aluminum-water reaction is a promising source for hydrogen production. However, experimental studies of this reaction are difficult because of the highly concentrated alkaline solution used to activate the surface of aluminum. Here, we show that the reaction kinetics can be monitored in real time by a Schottky diode sensor, consisting of an ultrathin aluminum film deposited on a semiconductor substrate. Charge resulting from the corrosion of the aluminum film causes an electrical signal in the sensor, which is proportional to the rate of the chemical process. We discuss the possible mechanisms for the reaction-induced charge generation and transfer, as well as the use of Schottky diode based sensors for operando studies of the aluminum-water reaction and similar reactions on metals in concentrated alkaline solutions11sciescopu

Hot electron generation on metal catalysts under surface reaction: Principles, devices, and application

Understanding the fundamental mechanisms for charge transfer in supported catalysts is of great importance for heterogeneous catalysis. Several experimental and theoretical results suggest that charge flow through metal-support interfaces leads to the catalytic enhancement that is often observed in mixed catalysts. Therefore, it is crucial to directly probe this charge flow in metal-support catalysts during catalytic reactions. In this review, we consider the main aspects of research studying the processes that create and allow interfacial transfer of highly excited (hot) charge carriers in supported catalysts, and discuss the effect of this charge transfer on catalytic activity. We show a close connection between the phenomena of hot electron creation and chemical energy dissipation that accompanies catalytic reactions at both the gas/solid and liquid/solid interfaces. The intensity of hot electron flow is well correlated with the turnover rates of corresponding reactions, which opens up the possibility for developing new operando methodologies for studying chemical processes on catalytic surfaces. (C) 2018 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserve

Hot-Electron-Mediated Surface Chemistry: Toward Electronic Control of Catalytic Activity

Conspectus Energy dissipation at surfaces and interfaces is mediated by excitation of elementary processes, including phonons and electronic excitation, once external energy is deposited to the surface during exothermic chemical processes. Nonadiabatic electronic excitation in exothermic catalytic reactions results in the flow of energetic electrons with an energy of 1-3 eV when chemical energy is converted to electron flow on a short (femtosecond) time scale before atomic vibration adiabatically dissipates the energy (in picoseconds). These energetic electrons that are not in thermal equilibrium with the metal atoms are called hot electrons. The detection of hot electron flow under atomic or molecular processes and understanding its role in chemical reactions have been major topics in surface chemistry. Recent studies have demonstrated electronic excitation produced during atomic or molecular processes on surfaces, and the influence of hot electrons on atomic and molecular processes.We outline research efforts aimed at identification of the intrinsic relation between the flow of hot electrons and catalytic reactions. We show various strategies for detection and use of hot electrons generated by the energy dissipation processes in surface chemical reactions and photon absorption. A Schottky barrier localized at the metal-oxide interface of either catalytic nanodiodes or hybrid nanocatalysts allows hot electrons to irreversibly transport through the interface. We show that the chemicurrent, composed of hot electrons excited by the surface reaction of CO oxidation or hydrogen oxidation, correlates well with the turnover rate measured separately by gas chromatography. Furthermore, we show that hot electron flows generated on a gold thin film by photon absorption (or internal photoemission) can be amplified by localized surface plasmon resonance. The influence of hot charge carriers on the chemistry at the metal-oxide interface are discussed for the cases of Au, Ag, and Pt nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts. © 2015 American Chemical Society137391sciescopu

Liquid-phase catalytic reactor combined with measurement of hot electron flux and chemiluminescence

Understanding the role of electronically nonadiabatic interactions during chemical reactions on metal surfaces in liquid media is of great importance for a variety of applications including catalysis, electrochemistry, and environmental science. Here, we report the design of an experimental apparatus for detection of the highly excited (hot) electrons created as a result of nonadiabatic energy transfer during the catalytic decomposition of hydrogen peroxide on thin-film metal-semiconductor nanodiodes. The apparatus enables the measurement of hot electron flows and related phenomena (e.g., surface chemiluminescence) as well as the corresponding reaction rates at different temperatures. The products of the chemical reaction can be characterized in the gaseous phase by means of gas chromatography. The combined measurement of hot electron flux, catalytic activity, and light emission can lead to a fundamental understanding of the elementary processes occurring during the heterogeneous catalytic reaction. © 2016 Author(s)3