Query: Bulk electronic transport impacts on electron transfer at conducting polymer electrode– electrolyte interfaces.

Candidate papers:

abstract: Significance Spreading electrochemical technologies, such as energy, bioelectrochemical devices, and industrial electrochemical synthesis, require low cost large area electrodes. Conducting polymers possess a unique combination of properties compared with most of the inorganic electrodes: acid resistance, the absence of surface insulating oxide, low temperature and solution processability, a high natural abundance of their elements, molecular porosity. Conducting polymers are inhomogeneous conductors composed of ordered and disordered regions through which electronic transport takes place via percolation paths. We discovered that the density of percolation paths in the bulk of the material dictates the rate of electron transfer at the electrolyte polymer electrode interface. This reveals one of the key parameters of designs to achieve efficient electrochemical technologies based on polymer electrodes. Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio )electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4 ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors.
author_names: Kosala Wijeratne

Ujwala Ail

Robert E Brooke

Mikhail Yu Vagin

Xianjie Liu

Mats Fahlman

Xavier Crispin
title: Bulk electronic transport impacts on electron transfer at conducting polymer electrode electrolyte interfaces
venue: Proceedings of the National Academy of Sciences
year: 2018

abstract: Abstract Oxidation of ferrocene at a poly(3 octylthiophene) (POT) film electrode has been investigated by using cyclic voltammetry, rotating disc electrode voltammetry and electrochemical impedance spectroscopy. The POT film electrode was prepared by galvanostatic electropolymerization of 3 octylthiophene on a rotating Pt disc electrode. In the medium used, i.e. 0.1 M LiBF 4 propylene carbonate, the formal redox potentials of ferrocene and POT are 0.4 and 1.1 V vs. Ag|AgCl respectively. This makes it possible to study the oxidation of ferrocene at both undoped (semiconducting) POT and at doped (electronically conducting) POT. The voltammetric data show that the oxidation of ferrocene is kinetically controlled at undoped or lightly doped POT while ferrocene is oxidized at a diffusion limited rate at highly doped POT. Impedance data on the POT film electrode in solutions containing different concentrations of supporting electrolyte and ferrocene indicate that the ferrocene oxidation occurs in parallel with the doping process, resulting in a competition between ferrocene and doping ions for the available 'sites' at the polymer|solution interface. The kinetics of electron transfer at the polymer|solutio interface are discussed based on the Butler Volmer formulation of electrode kinetics.
author_names: Johan Bobacka

Maria Grzeszczuk

Ari Ivaska
title: Electron transfer at conducting polymer film electrodes mechanism and kinetics of ferrocene oxidation at poly(3 octylthiophene)
year: 1997

abstract: DOI: 10.1002/aenm.202000219 energy density Li metal batteries, and they can greatly improve safety by replacing the traditional flammable liquid electrolyte.[1 4] In recent years, the ion conductivity of SSEs has been greatly enhanced to a level comparable to that of liquid electrolytes,[2,5 7] which is critical for fast charging/discharging. To date, ion transport has primarily been characterized by macroscopic measurements such as electrochemical impedance spectroscopy (EIS) galvanostatic profiles of charging/ discharging, and nuclear magnetic resonance relaxometry.[8,9] These measurements essentially reflect an average of microscopic ion transport phenomena. Ion transport in SSEs can be far more complicated than in liquid electrolytes, where it is fundamentally isotropic and uniform. Furthermore, detailed microscopic transport characterization studies are currently lacking in this field.[10] Theoretical studies have proposed that ion transport can be governed by highly crystalline orientationdependent ionic hopping inside the ceramic lattice,[11,12] and some SSEs can even act as 1D[13 15] or 2D ion conductors.[16] The polycrystalline and glassy ceramic ion conductors often contain multiple phases with different crystalline structures and significant chemical nonuniformity; these phases thus complicate efforts to define ion transport properties. The bulk SSE may also have a significant volume fraction of disordered grain/particle boundaries versus interior regions of small sized grains.[17,18] All these factors can complicate our understanding of ion transport phenomena. In addition, ion transport can be further complicated by the formation of the solid electrolyte interphase (SEI) layer through chemical reaction of the SSE and electrode materials[19,20] and by the formation of the spacecharge layer by Li ion transfer across the interfaces.[21,22] To expose the details of ion conduction processes, it is necessary to use characterization methods that measure ion transport with nm scale spatial resolution to improve our understanding and tune the ion conduction in solid state batteries (SSBs) Currently, the two major directions inorganic ceramicbased and polymer based for developing SSEs pose challenges unique to the chosen approach. Inorganic ceramics SSEs have superior ion conductivity, comparable to liquid electrolyte, but they are also accompanied by chemical interaction Replacing the liquid electrolyte in lithium batteries with solid state ion conductor is promising for next generation energy storage that is safe and has high energy density. Here, nanometer resolution ionic and electronic transport imaging of Li3PS4 (LPS) a solid state electrolyte (SSE) is reported. This nm resolution is achieved by using a logarithm scale current amplifier that enhances the current sensitivity to the fA range. Large fluctuations of ion current one to two orders of magnitude on the LPS and on the LPS region of a polymer/LPS bulk hybrid SSE that must be mitigated to eliminate Li dendrite formation and growth, are found. This ion current fluctuation is understood in terms of highly anisotropic transport kinetic barriers along the different crystalline axes due to different grain orientations in the polycrystalline and glass ceramic materials. The results on the bulk hybrid SSE show a sharp transition of ionic and electronic transport at the LPS/polymer boundary and decreases in average ionic current with decreasing polyimine particle size and with extensive cycling. The results elucidate the mechanism of polyimine extension into interparticles to prevent Li dendrite growth. This work opens up novel characterization of charge transport, which relates to Li plating and stripping for solid state batteries.
author_names: Chunsheng Jiang

Nathan Arthur Dunlap

Yejing Li

Harvey L Guthrey

Ping Liu

Sehee Lee

Mowafak M Al-Jassim
title: Nonuniform Ionic and Electronic Transport of Ceramic and Polymer/Ceramic Hybrid Electrolyte by Nanometer Scale Operando Imaging for Solid State Battery
year: 2020

abstract: A double submerged impinging jet (DSIJ) cell has been built allowing an identical hydrodynamic regime to be established on both faces of a bipolar electrode consisting of either a Pt sheet or a free standing polypyrrole (PPy) membrane. Both electrode materials have been studied in this cell, in the presence of electrolytes containing redox couples. The experimental current potential characteristics and impedance diagrams relative to PPy may be analyzed as the result of two parallel paths of charge transport involving (i) convective diffusion of the redox species in solution, electron transfer at the polymer/electrolyte interface, and electron transport within the film and (ii) migration of nonelectroactive ions in solution, ion transfer at the polymer/electrolyte interface, and ion transport within the film. In the most favorable circumstance of a fast redox couple and a low ionic conductivity of the membrane, comparison between Pt and PPy explicitly shows an electrocatalytic effect of the latter.
author_names: Claude Deslouis

++ and Marco M Musiani

Bernard Tribollet
title: Free Standing Membranes for the Study of Electrochemical Reactions Occurring at Conducting Polymer/Electrolyte Interfaces
year: 1996

abstract: The kinetics of heterogeneous electron transfer across films of electronically conducting nickel 4,4',4',4' tetraaminophthalocyanine polymer (poly(NiTAPc) are reported. Poly(NiTAPc) which is formed by oxidative electropolymerization of NiTAPc, acts as an n doped electronic conductor between about 0.8 and 2.0 V vs. Ag/AgCl. Within this range it sustains diffusion limited charge transfer to one electron bulk solution reactants at their anticipated formal potentials. However, the rates of heterogeneous electron transfer to these species are diminished by a small, uniform amount that is exponentially dependent on film thickness. Results are interpreted in terms of a porous electrode model in which electron transfer occurs at the polymer solution interface, a large bulk capacitance arises from an interior pore volume that is inaccessible to diffusing reactants and a resistive element (suggested to be pores of electrolyte trapped between aggregrates of the polymer) is present which acts to reduce apparent values of ks,h. It is demonstrated that electronically conducting polymer films do not accelerate the rate of electron transfer to solution reactants but rather restore kinetics to their anticipated values by preventing suface involvement.
author_names: Haiqin Xi

Franklin A Schultz
title: Heterogeneous electron transfer at electrodes coated with electronically conducting nickel tetraaminophthalocyanine polymer films
year: 1993

abstract: Organic electronics based on organic semiconductors offer tremendous advantages compared to traditional inorganic counterparts such as low temperature processing, light weight, low manufacturing cost, high throughput and mechanical flexibility. Many key electronic processes in organic electronic devices, e.g. charge injection/extraction, charge recombination and exciton dissociation, occur at interfaces, significantly controlling performance and function. Understanding/modeling the interface energetics at organic electrode/organic organic heterojunctions is one of the crucial issues for organic electronic technologies to provide a route for improving device efficiency, which is the aim of the research presented in this thesis.Integer charge transfer (ICT) states pre existed in the dark and created as a consequence of Fermi level equilibrium at donor acceptor interface have a profound effect on open circuit voltage in organic bulk heterojunction photovoltaics. ICT state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed.Doping and insertion of interlayer are two established methods for enhancing charge injection/extraction properties at organic electrode interface. By studying the energy level alignment behavior at low to intermediate doping levels for molecule doped conjugated polymer/electrode interfaces, we deduce that two combined processes govern the interface energetics: (i) equilibration of the Fermi level due to oxidation (or reduction) of polymer sites at the interface as per the ICT model and (ii) a double dipole step induced by image charge from the dopant polymer charge transfer complex that causes a shift of the work function. Such behavior is expected to hold in general for low to intermediate level doped organic semiconductor systems. The unified model is further extended to be suitable for conjugated electrolyte/electrode interfaces, revealing the design rules for achieving the smallest charge injection/extraction barrier for both thin tunneling and thick charge transporting conjugated electrolyte interlayers.To probe into the energy level spatial extension at interfaces, we employ the original approach of building and characterizing multilayers composed of a well defined number of polymer monolayers with the Langmuir Shafer method to control polymer film uniformity and thicknesses, avoiding the problems associated with spin coating ultrathin films. The disordered/amorphous films feature smaller, and in fact negligible, energy level bending compared to the more well ordered films, in contradiction with existing models. It is found that that energy level bending depends on the ICT state distribution rather than the density of states of the neutral polymer chains in relation to the Fermi energy, thus taking into account the Coulomb energy associated with charging the polymer chain and transferring a charge across the interface. Based on this work, a general model for energy level bending in absence of significant doping of conjugated polymer films is proposed.Organic semiconductors are sensitive to ambient atmosphere that can influence the energetics. The degradation effects of common PCBM film induced by oxygen and water are found to be completely different. Upon exposure to oxygen, the work function is down shifted by 0.15 eV compared to the ICT curve of the pristine PCBM film, originating from the weak interaction between the fullerene part of PCBM and oxygen, and this can be reversed by thermal treatment in vacuum. The down shift in energetics will cause a loss in open circuit voltage at electrode interface, but aids free charge generation at donor acceptor interface. Upon exposure to water, there is irreversible extensive broadening and bleaching of the valence electronic structure features as well as a substantial decrease of work function and ionization potential, severely degrading the transport properties.Overall, the research results in this thesis thus give a deeper understanding of interface phenomena in organic electronics, especially regard to organic solar cells, aimed to further improve the device operation efficiency and lifetime.
author_names: Qinye Bao

Xianjie Liu

Slawomir Braun

Feng Gao

Mats Fahlman
title: Energetics at Doped Conjugated Polymer/Electrode Interfaces
year: 2015

abstract: Multiheme cytochromes, located on the bacterial cell surface, function as long distance 10 nm) electron conduits linking intracellular reactions to external surfaces. This extracellular electron transfer process, which allows microorganisms to gain energy by respiring solid redox active minerals, also facilitates the wiring of cells to electrodes. While recent studies suggested that a chiral induced spin selectivity effect is linked to efficient electron transmission through biomolecules, this phenomenon has not been investigated in the extracellular electron conduits. Using magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin dependent electrochemistry of the decaheme cytochromes MtrF and OmcA from the metal reducing bacterium Shewanella oneidensis MR 1, we show that electron transport through these extracellular conduits is spin selective. Our study has implications for understanding how spin dependent interactions and magnetic fields may control electron transport across biotic abiotic interfaces in both natural and biotechnological systems.
author_names: Suryakant Mishra

Sahand Pirbadian

Amitabha Mondal

Mohamed Y El-Naggar

Ron Naaman
title: Spin Dependent Electron Transport through Bacterial Cell Surface Multiheme Electron Conduits
year: 2019

abstract: Abstract Hierarchical CuNiO2 nanospheres composed of large number of spikes, which look like a dandelion flower like morphologies are grown on nickel foam via a facile and low cost hydrothermal technique. These CuNiO2 electrodes are used as an efficient electrode material for supercapacitor without using any binders or conducting polymer additives. The structural, composition and morphological behaviors of the CuNiO2 electrodes are characterized using X ray diffraction, X ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy methods. The CuNiO2 nanoarchitectures provide the abundant active sites, high conductivity and rapid charge transport, which resulting the low charge transfer resistance at the interface of electrode electrolyte. Cyclic voltammetry and galvanostatic charge discharge plateaus from the CuNiO2 electrode exhibit the Faradic battery type redox behavior, which is distinct form the profiles of carbon based materials. As a battery type electrode, the dandelion flower like CuNiO2 nanoarchitectures exhibits the outstanding electrochemical performances with a high specific capacity ~111.52 mA h g 1 at 2 A g 1) superb rate capability ~81.4% retains even at 10 A g 1) and excellent cycling life ~89.13% at 6 A g 1 over 3000 cycles) respectively. Therefore, with the above findings, CuNiO2 material has remarkable application potential in supercapacitors and could be effectively applied in other energy storage technologies.
author_names: Hyungmin Joo

Chandu V V Muralee Gopi

Rajangam Vinodh

Hee-Jee Kim

Sangaraju Sambasivam

Ihab M Obaidat
title: Facile synthesis of flexible and binder free dandelion flower like CuNiO2 nanostructures as advanced electrode material for high performance supercapacitors
year: 2019

abstract: Organic electronics based on organic semiconductors offer tremendous advantages compared to traditional inorganic counterparts such as low temperature processing, light weight, low manufacturing cost, high throughput and mechanical flexibility. Many key electronic processes in organic electronic devices, e.g. charge injection/extraction, charge recombination and exciton dissociation, occur at interfaces, significantly controlling performance and function. Understanding/modeling the interface energetics at organic electrode/organic organic heterojunctions is one of the crucial issues for organic electronic technologies to provide a route for improving device efficiency, which is the aim of the research presented in this thesis.Integer charge transfer (ICT) states pre existed in the dark and created as a consequence of Fermi level equilibrium at donor acceptor interface have a profound effect on open circuit voltage in organic bulk heterojunction photovoltaics. ICT state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed.Doping and insertion of interlayer are two established methods for enhancing charge injection/extraction properties at organic electrode interface. By studying the energy level alignment behavior at low to intermediate doping levels for molecule doped conjugated polymer/electrode interfaces, we deduce that two combined processes govern the interface energetics: (i) equilibration of the Fermi level due to oxidation (or reduction) of polymer sites at the interface as per the ICT model and (ii) a double dipole step induced by image charge from the dopant polymer charge transfer complex that causes a shift of the work function. Such behavior is expected to hold in general for low to intermediate level doped organic semiconductor systems. The unified model is further extended to be suitable for conjugated electrolyte/electrode interfaces, revealing the design rules for achieving the smallest charge injection/extraction barrier for both thin tunneling and thick charge transporting conjugated electrolyte interlayers.To probe into the energy level spatial extension at interfaces, we employ the original approach of building and characterizing multilayers composed of a well defined number of polymer monolayers with the Langmuir Shafer method to control polymer film uniformity and thicknesses, avoiding the problems associated with spin coating ultrathin films. The disordered/amorphous films feature smaller, and in fact negligible, energy level bending compared to the more well ordered films, in contradiction with existing models. It is found that that energy level bending depends on the ICT state distribution rather than the density of states of the neutral polymer chains in relation to the Fermi energy, thus taking into account the Coulomb energy associated with charging the polymer chain and transferring a charge across the interface. Based on this work, a general model for energy level bending in absence of significant doping of conjugated polymer films is proposed.Organic semiconductors are sensitive to ambient atmosphere that can influence the energetics. The degradation effects of common PCBM film induced by oxygen and water are found to be completely different. Upon exposure to oxygen, the work function is down shifted by 0.15 eV compared to the ICT curve of the pristine PCBM film, originating from the weak interaction between the fullerene part of PCBM and oxygen, and this can be reversed by thermal treatment in vacuum. The down shift in energetics will cause a loss in open circuit voltage at electrode interface, but aids free charge generation at donor acceptor interface. Upon exposure to water, there is irreversible extensive broadening and bleaching of the valence electronic structure features as well as a substantial decrease of work function and ionization potential, severely degrading the transport properties.Overall, the research results in this thesis thus give a deeper understanding of interface phenomena in organic electronics, especially regard to organic solar cells, aimed to further improve the device operation efficiency and lifetime.
author_names: Qinye Bao

Simone Fabiano

Mattias Andersson

Slawomir Braun

Zhengyi Sun

Xavier Crispin

Magnus Berggren

Xianjie Liu

Mats Fahlman
title: The energetics of the semiconducting polymer electrode interface for solution processed electronics
year: 2015

abstract: The thermoelectric transport properties of a metal ceramic interface based on Al and g Al2O3 are explored by employing the non equilibrium Green's function formalism (NEGF) coupled with density functional theory (DFT) However, to acquire the phonon thermal conductance, the parameterized ReaxFF potential is utilized for computing the intrinsic force constants of propagating phonons across the interface. Several interfacial electronic properties such as the charge transfer, the potential barrier, and the atomic orbital overlap are critically analyzed based on the DFT derived results of the electrostatic difference potential, the electron density difference, and the spin polarized density of states in the fully relaxed structure of the interface. Within the NEGF framework, both the electron and phonon transmission coefficients are estimated for the variations of bias voltage and temperature gradient across the interface. The strong orbital overlap and the scattering of electrons and phonons at the nanometer size interface suppress the lattice thermal conductivity significantly compared to the electron transport, which in turn enhances the thermoelectric performance of the Al/Al2O3 composite, in contrast to the bulk material of Al. Moreover, a steep rise of power factor induced by the increased transmission of charge carriers with temperature improves the energy conversion efficiency of the material. The present findings could pave the way for developing thermoelectric materials based on metal ceramic composites.
author_names: Pabitra Narayan Samanta

Jerzy Leszczynski
title: High temperature thermoelectric transport behavior of the Al/g Al2O3 interface: impact of electron and phonon scattering at nanoscale metal ceramic contacts.
venue: Physical chemistry chemical physics PCCP
year: 2018