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首頁(yè)> 外文學(xué)位 >Reaction Current Phenomenon in Bifunctional Catalytic Metal-Semiconductor Nanostructures.
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Reaction Current Phenomenon in Bifunctional Catalytic Metal-Semiconductor Nanostructures.

機(jī)譯：雙功能催化金屬半導(dǎo)體納米結(jié)構(gòu)中的反應(yīng)電流現(xiàn)象。

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Energy transfer processes accompany every elementary step of catalytic chemical processes on material surface including molecular adsorption and dissociation on atoms, interactions between intermediates, and desorption of reaction products from the catalyst surface. Therefore, detailed understanding of these processes on the molecular level is of great fundamental and practical interest in energy-related applications of nanomaterials. Two main mechanisms of energy transfer from adsorbed particles to a surface are known: (i) adiabatic via excitation of quantized lattice vibrations (phonons) and (ii) non-adiabatic via electronic excitations (electron/hole pairs). Electronic excitations play a key role in nanocatalysis, and it was recently shown that they can be efficiently detected and studied using Schottky-type catalytic nanostructures in the form of measureable electrical currents (chemicurrents) in an external electrical circuit. These nanostructures typically contain an electrically continuous nanocathode layers made of a catalytic metal deposited on a semiconductor substrate.;The goal of this research is to study the direct observations of hot electron currents (chemicurrents) in catalytic Schottky structures, using a continuous mesh-like Pt nanofilm grown onto a mesoporous TiO2 substrate. Such devices showed qualitatively different and more diverse signal properties, compared to the earlier devices using smooth substrates, which could only be explained on the basis of bifunctionality. In particular, it was necessary to suggest that different stages of the reaction are occurring on both phases of the catalytic structure. Analysis of the signal behavior also led to discovery of a formerly unknown (very slow) mode of the oxyhydrogen reaction on the Pt/TiO2(por) system occurring at room temperature. This slow mode was producing surprisingly large stationary chemicurrents in the range 10--50 microA/cm2. Results of the chemicurrent measurements for the bifunctional Pt/TiO2(por) transducers were unusual in many regards. Addition of various H2 amounts to the initial 160 Torr O2 atmosphere over the sample led to well repeatable chemicurrents of both transient and steady-state characters, depending on a specific H2 addition procedure.;It is suggested that adsorption of hydrogen on Pt/TiO2 structures leads to dissociation of hydrogen molecules on Pt surface followed by "spillover" of hydrogen atoms from Pt toward TiO2 support. In contrast to oxygen, hydrogen manifests donor properties by giving electrons to the TiO2 conductance band and adsorbing as H+ ions. This effect is well illustrated with the I-V curves, showing highly conductive Ohmic characteristics of the samples in H2 atmosphere. Two versions of the spillover process leading eventually to H+ ion adsorption on TiO2 will be considered: H-atom and proton (pre-ionized H-atom) spillover.;This research work is a pioneering effort to challenge the direct utility of the non-adiabatic electronic processes in catalytic nanomaterial systems, paving the road toward novel energy conversion devices, solid-state chemical sensors and signal transducers.
機(jī)譯：能量轉(zhuǎn)移過(guò)程伴隨著材料表面催化化學(xué)過(guò)程的每個(gè)基本步驟，包括分子在原子上的吸附和解離，中間體之間的相互作用以及反應(yīng)產(chǎn)物從催化劑表面的解吸。因此，在分子水平上對(duì)這些過(guò)程的詳細(xì)理解在納米材料的能量相關(guān)應(yīng)用中具有重大的基礎(chǔ)和實(shí)踐意義。能量從吸附粒子轉(zhuǎn)移到表面的兩種主要機(jī)理是已知的：（i）通過(guò)量化晶格振動(dòng)（聲子）的激發(fā)絕熱，以及（ii）通過(guò)電子激發(fā)（電子/空穴對(duì)）的非絕熱。電子激發(fā)在納米催化中起關(guān)鍵作用，最近表明，可以使用外部電路中可測(cè)量的電流（化學(xué)電流）形式的肖特基型催化納米結(jié)構(gòu)有效地檢測(cè)和研究電子激發(fā)。這些納米結(jié)構(gòu)通常包含由沉積在半導(dǎo)體襯底上的催化金屬制成的電連續(xù)納米陰極層。 Pt納米膜生長(zhǎng)在介孔TiO2基底上。與較早的使用光滑襯底的設(shè)備相比，此類設(shè)備在質(zhì)量上顯示出不同且更加多樣化的信號(hào)特性，這只能基于雙功能性進(jìn)行解釋。特別地，有必要建議反應(yīng)的不同階段發(fā)生在催化結(jié)構(gòu)的兩個(gè)相上。對(duì)信號(hào)行為的分析還導(dǎo)致發(fā)現(xiàn)了以前在室溫下發(fā)生的Pt / TiO2（por）系統(tǒng)上的氫氧反應(yīng)的以前未知模式（非常慢）。這種慢速模式產(chǎn)生了令人驚訝的大靜態(tài)化學(xué)電流，范圍為10--50 microA / cm2。雙功能Pt / TiO2（por）換能器的化學(xué)電流測(cè)量結(jié)果在許多方面都不尋常。根據(jù)特定的H2添加程序，在樣品上最初的160 Torr O2氣氛中添加各種H2量會(huì)導(dǎo)致具有良好可重復(fù)性的瞬態(tài)和穩(wěn)態(tài)特性的化學(xué)流，這取決于特定的H2添加程序。;建議在Pt / TiO2結(jié)構(gòu)上吸附氫導(dǎo)致Pt表面上的氫分子解離，然后氫原子從Pt向TiO2載體“溢出”。與氧氣相反，氫通過(guò)將電子賦予TiO2電導(dǎo)帶并以H +離子的形式吸附而表現(xiàn)出供體性質(zhì)。 I-V曲線很好地說(shuō)明了這種效應(yīng)，顯示了H2氣氛中樣品的高導(dǎo)電歐姆特性。將考慮兩種形式的溢出過(guò)程，最終導(dǎo)致H +離子吸附在TiO2上：H原子和質(zhì)子（預(yù)電離的H原子）溢出。這項(xiàng)研究工作是一項(xiàng)開(kāi)拓性的工作，旨在挑戰(zhàn)非氫原子的直接用途。催化納米材料系統(tǒng)中的絕熱電子過(guò)程，為新型能量轉(zhuǎn)換設(shè)備，固態(tài)化學(xué)傳感器和信號(hào)傳感器鋪平了道路。

著錄項(xiàng)

  • 作者

    Hashemian, Mohammad Amin.;

  • 作者單位

    University of Illinois at Chicago.;

  • 授予單位 University of Illinois at Chicago.;
  • 學(xué)科 Materials science.;Nanotechnology.
  • 學(xué)位 Ph.D.
  • 年度 2015
  • 頁(yè)碼 180 p.
  • 總頁(yè)數(shù) 180
  • 原文格式 PDF
  • 正文語(yǔ)種 eng
  • 中圖分類 遙感技術(shù);
  • 關(guān)鍵詞

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