Search query: ELECTRODE/ELECTROLYTE INTERFACES: STRUCTURE AND KINETICS OF CHARGE TRANSFER

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abstract: When a metal is partly immersed in an electrolyte, a potential is set up across the two phases, i.e. at the electrode/electrolyte interface. The phases may be solids (metals or alloys, semiconductors, insulators) liquids (ionic liquids, molten salts, neutral solutions) or gases (polar or non polar) The more common terminology in electrochemistry is that a double layer is set up at the interface. There are several reasons for a potential difference being set up across the interface of two phases, the most common one being the charge transfer occurring across the interface. During this process, a charge separation will occur because of electron transfer across the interface. Other reasons for the occurrence of potential differences are due to surface active groups in the ionizable media (liquid, solid, or gas) and orientation of permanent or induced dipoles. The double layer at the interface between two phases has electrical, compositional, and structural characteristics. The electrical and compositional characteristics deal with the excess charge densities on each phase and the structural one with the distribution of the constituents (ions, electrons, dipoles, and neutral molecules) in the two phases, including the interfacial region. For the purposes of understanding and analyzing the electrical, compositional, and structural aspects relevant to the electrochemical reactions that occur in fuel cells, a
author_names: S Srinivasan
title: ELECTRODE/ELECTROLYTE INTERFACES: STRUCTURE AND KINETICS OF CHARGE TRANSFER
year: 2006

abstract: Controlling interfacial electron transfer rates is fundamental to maximizing device efficiencies in electrochemical technologies including redox flow batteries, chemical sensors, bioelectronics, and photo electrochemical devices. Conductive polymer electrodes offer the possibility to control redox properties through synthesis and processing, if critical structure property relationships governing charge transfer are understood. In this work, we show that the rate and symmetry of electron transfer at conductive polymer electrodes are directly connected to the microstructure and the density of states (DOS) using the model system of poly(3 hexylthiophene) (P3HT) and ferrocene/ferrocenium (Fc/Fc+ as predicted by the Marcus Gerischer model. Experimentally, crystalline P3HT exhibits a sufficient overlap between the polymer DOS and the DOS of both Fc and Fc+ resulting in a reversible electron transfer. Conversely, the DOS of amorphous electrodeposited P3HT does not overlap with that of Fc+ inhibiting reductio.
author_names: Bharati Neelamraju

Melanie Rudolph

Erin L Ratcliff
title: Controlling the Kinetics of Charge Transfer at Conductive Polymer/Liquid Interfaces through Microstructure
year: 2018

abstract: Potential modulated attenuated total reflectance (PM ATR) spectroscopy is a spectroelectrochemical method that utilizes the potential modulation approach and a waveguide ATR geometry. This unique combination enables measurements of electron transfer (ET) kinetics of monolayer to submonolayer thin films on waveguide electrode surfaces. Selective probing of molecular subpopulations in a film can be achieved by choosing appropriate combinations of applied potential, wavelength, and polarization of light, which allows subpopulation structure to be correlated with ET kinetics. In this review, the basic theory of PM ATR is introduced, and examples illustrating characterization of the structure and ET kinetics of organic semiconductor monolayers on electrode surfaces are presented, demonstrating the capabilities and applications of the PM ATR technique.
author_names: Yilong Zheng

S Scott Saavedra
title: Characterization of Charge Transfer Kinetics at Organic/Electrode Interfaces Using Potential modulated Attenuated Total Reflectance (PM ATR) Spectroscopy.
venue: Analytical sciences the international journal of the Japan Society for Analytical Chemistry
year: 2017

abstract: The interface between two functional oxide materials governs the physical, chemical, and electronic interactions between the two phases. We investigate the charge transfer across the interface between two structurally related material classes, namely, perovskite and Ruddlesden Popper type oxides, choosing La0.8Sr0.2CoO3 d (LSC) and Nd2NiO4+d (NNO) as our model systems for the two classes, respectively. The interface of Nd2NiO4+d and La0.8Sr0.2CoO3 d is investigated using in situ photoemission spectroscopy techniques on epitaxial thin films. A detailed analysis of the electronic structure with X ray photoelectron spectroscopy and X ray absorption spectroscopy under an oxygen atmosphere and at elevated temperature reveals charge transfer from La0.8Sr0.2CoO3 d into Nd2NiO4+d. Through the use of electrical conductivity relaxation, it is demonstrated that such charge transfer from LSC into NNO is accompanied by a reduction in the kinetics of oxygen exchange on Nd2NiO4+d, contrary to expectation. Fermi level pi.
author_names: Christian Lenser

Qiyang Lu

Ethan J Crumlin

Hendrik Bluhm

Bilge Yildiz
title: Charge Transfer Across Oxide Interfaces Probed by in Situ X ray Photoelectron and Absorption Spectroscopy Techniques
year: 2018

abstract: The growing energy demand of the mankind has lead to the extensive use of fossil fuels. The burning of oil, coal and natural gas has increased the global temperature and atmospheric carbon dioxide percentage to a dangerously high level. Therefore, carbon neutral energy sources such as solar cells are needed. In order to design more effective solar cells, a deep understanding of the primary photochemical processes in the cells is needed. Ultrafast time resolved spectroscopy, especially transient absorption methods, are a very useful tool for investigating the reaction kinetics in order to optimize the solar cell performance. In this thesis, kinetics of the photoinduced processes at the interface of an organic monomolecular layer and a semiconductor are studied. Such structures may be used as the active material e.g. in dye sensitized solar cells. Two different types of organic semiconductor hybrids were prepared: fullerenes (C60) immobilized on colloidal semiconductor quantum dots (QDs) and zinc phthalocyanine (ZnPc) derivatives on nanostructured titanium dioxide (TiO2) and zinc oxide (ZnO) surfaces. The driving force of photocurrent generation in these systems is a photonic excitation leading to an electron transfer reaction across the organic semiconductor interface. The observed electron transfer rates vary from a few picoseconds in ZnPc monolayers on TiO2 to ca. 100 ps in QD fullerene systems. Phthalocyanine derivatives are very attractive sensitizing dyes for solar cell applications because of their excellent stability and strong absorption in the red part of the spectrum. A drawback with these compounds is their tendency towards aggregation. It reduces the solar cell efficiencies due to intra aggregate losses. There are two common methods for aggregation reduction: the use of molecular co adsorbates and substitution of the phthalocyanine core with bulky side groups. Both mechanisms were observed to lower the degree of aggregation in the ZnPc samples. The substitution method proved to be more efficient in terms of the lifetime of the charge separated state. To more realistically mimic a solar cell, a hole transporting material (HTM) was used. Its effect on the primary photoinduced reactions in the phthalocyanine semiconductor samples was studied. With the chosen HTM, spiro MeOTAD, the charge separation was observed to occur first at the phthalocyanine HTM interface, followed by electron injection into the semiconductor material. Complete solar cell samples were prepared in order to link the ultrafast spectroscopy results to actual solar cell performance. A correlation between the degree of aggregation and the produced photocurrent was confirmed. The less aggregated samples produce a higher photocurrent per number of absorbed photons. This study indentifies bottlenecks in modern hybrid organic semiconductor solar cell design and suggests solutions for improving the solar cell performance.
author_names: K Virkki
title: Photoinduced Charge Transfer Processes at Organic Semiconductor Interfaces
year: 2019

abstract: Abstract The combination of transition metal based cocatalysts with semiconductors is a promising route to improve the photoelectrochemical performance in solar water splitting. However, it is difficult to evaluate the catalytic ability for cocatalysts quantitatively. Herein, we use kelvin probe force microscopy technique, combining with Mott Schottky method, to investigate the cocatalysts from the point of surface potential and Femi level. Through synthesis the nickel/cobalt oxide nanoparticles and nanoporous bismuth vanadate (BiVO4) the result indicates the surface potential of NiCoO2 coated BiVO4 is lower than pristine BiVO4 and BiVO4 coated by NiO and CoO cocatalysts respectively. The lower surface potential means a more upward band bending structure at the interface of electrode and electrolyte, which can promote the separation of electron hole pairs and enhance the charge transfer kinetics. Thus, the NiCoO2/BiVO4 photoanode achieve a remarkable photocurrent density of 2.34 mA/cm2 for water oxidation, and the charge separation and oxidation kinetics efficiencies are 61.9% and 72.7% respectively. In all, our studies provide a new mechanistic insight into cocatalysts for solar energy conversion.
author_names: Lin Yang

Yuli Xiong

Peng Xiao

Yun-huai Zhang
title: Guiding charge transfer kinetics into cocatalyst for efficient solar water splitting
venue: Electrochimica Acta
year: 2019

abstract: Conductive polymer electrodes have exceptional promise for next generation bioelectronics and energy conversion devices due to inherent mechanical flexibility, printability, biocompatibility, and low cost. Conductive polymers uniquely exhibit hybrid electronic ionic transport properties that enable novel electrochemical device architectures, an advantage over inorganic counterparts. Yet critical structure property relationships to control the potential dependent rates of charge transfer at polymer/electrolyte interfaces remain poorly understood. Herein, we evaluate the kinetics of charge transfer between electrodeposited poly (3 hexylthiophene) films and a model redox active molecule, ferrocenedimethanol. We show that the kinetics directly follow the potential dependent occupancy of electronic states in the polymer. The rate increases then decreases with potential (both normal and inverted kinetic regimes) a phenomenon distinct from inorganic semiconductors. This insight can be invoked to design polymer electrodes with kinetic selectivity toward redox active species and help guide synthetic approaches for the design of alternative device architectures and approaches.Charge transfer at conductive polymer/liquid interfaces critically affects the performance of organic bioelectronics and energy conversion/storage devices. Here, the authors provide a mechanistic framework to describe charge transfer rates in the context of hybrid ionic electronic conductivity.
author_names: Melanie Rudolph

Erin L Ratcliff
title: Normal and inverted regimes of charge transfer controlled by density of states at polymer electrodes
venue: Nature Communications
year: 2017

abstract: The correlations between bulk/surface structure change and electrochemical kinetics of LiNi0.80Co0.15Al0.05O2 are systematically investigated at atomic level, including the initial charged, half charged, and over charged states. In the initial stage of charge, surface rearrangement occurs and an amorphous Li2CO3 layer forms on the surface, which can release stress and provide a stable interface. The Li2CO3 surface layer decomposes upon charging, resulting in decreased interface resistance for charge transfer. Meanwhile, the bulk structure goes through the two phase reaction region toward the solid solution region, which demonstrates higher electrical conductivity and faster Li ion mobility. Along with the charging process, more substantial surface rearrangement and the decomposed Li2CO3 layer lead to surface degradation. Together with the anisotropic volume change induced mechanical stress, microcracks stem from the surface and provide access for electrolyte penetration. All of these cause high kinetic barriers for Li ion extraction, as demonstrated by the high interface and charge transfer resistance and slow lithium diffusion in this region.
author_names: Hai Feng Li

Dongqing Liu

Lihan Zhang

Kun Qian

Ruiying Shi

Feiyu Kang

Baohua Li
title: Combination Effect of Bulk Structure Change and Surface Rearrangement on the Electrochemical Kinetics of LiNi0.80Co0.15Al0.05O2 During Initial Charging Processes.
venue: ACS applied materials interfaces
year: 2018

abstract: AbstractCdTe quantum dots (QDs) were anchored on NaTaO3 nanocubes with the aim into tuning the charge kinetics for spatial separation of the photogenerated electrons and holes by modifying the relative potential of the conduction band of CdTe QDs. In this work, CdTe QDs (particle size 2 3 nm) and NaTaO3 were synthesized via reflux and hydrothermal reaction. Thioglycolic acid (TGA) acted as both a stabilizer and linker molecules during the synthesis of CdTe QDs and NaTaO3/CdTe heterostructure. On accounts of density functional theory (DFT) predictions, electrons can transfer from NaTaO3 to CdTe due to the difference of the Fermi level between two semiconductors, which will establish a built in electric field at semiconductor interfaces, accelerating the charge separation kinetics between CdTe and NaTaO3. In response, electronic structure tunable CdTe QDs were surface engineered on NaTaO3 nanocubes to enhance the visible light (VL) harvesting capability. By carefully controlling the fine nature of CdTe QDs, photogenerated electrons in CdTe can be efficiently injected into the conduction band of NaTaO3, leading to spatial charge separation between CdTe and NaTaO3. This could be affirmed by applied bias photo to current efficiency (ABPE) incident photocurrent responses as well as electrochemical impedance curves. With well defined crystallinity, electronic structure, and interfacial contact between NaTaO3 and CdTe, the optimized photocatalytic activity toward hydrogen production over NaTaO3/CdTe heterostructure achieved an evolution rate of 56 mmol*g 1*h 1, which is far surpassed than that of pristine NaTaO3 and CdTe. Graphical abstract
author_names: Fang Wang

Dongle Liu

Xiaojing Wang

Yiguo Su
title: Band edge alignment for tuning interfacial charge transfer: a case study of NaTaO3 as photoelectron platform by anchoring CdTe quantum dots
venue: Journal of Nanoparticle Research
year: 2019

abstract: The rational design of high performance hetero structure photovoltaic devices requires full understanding of the photoinduced charge transfer mechanism and kinetics at the interface of heterojunctions. In this paper, p BiOBr/n Bi2S3 heterojunction have been designed and in situ fabricated by a facile ion exchange method between BiOBr and thioacetamide (TAA) The degree of transformation of BiOBr to Bi2S3 was controlled through the adjustment of exposure time of BiOBr/FTO substrate to thioacetamide (TAA) aqueous solution. The morphologies of BiOBr and BiOBr/Bi2S3 heterojunctions films were examined by X ray diffraction (XRD) scanning electron microscope (SEM) and high resolution transmission electron microscopy (HRTEM) The presence of Bi2S3 was further validated through energy dispersive X ray spectroscopy (EDS) Assisted by the surface photovoltage (SPV) and transient photovoltage (TPV) technique, the photoinduced charge transfer kinetics on BiOBr nanosheet and BiOBr/Bi2S3 interface were systematically
author_names: Huimin Jia

WeiWei He

Yong Xiang

Zhi Zheng
title: Surface photovoltage phase spectra for analysing the photoinduced charge transfer kinetics of novel BiOBr/Bi2S3 heterojunction films
year: 2017