bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Dendrite Growth through a Porous Separator during the Cycling of Lithium Batteries
Authors: Cannon Andrew , Ryan Emily
Published: May 2020

A complete understanding of dendrite growth under realistic conditions is an ongoing challenge in creating safe and efficient lithium batteries. While advancements have been made in dendrite suppression in isolated tests, the complex interaction between the components, i.e. the anode and the battery separator, of the battery system is still unclear. These components behave differently under charging and discharging and to realize their coupled effect, they must be studied together. Through computational modeling, the effect of both the separator and battery cycling are investigated at the anode-electrolyte interface. The model resolves the complex multiphysics of charge and discharge at the mesoscale, and considers both idealized and realistic porous separator microstructures.
(Invited) Dynamic Electrochemical Control of Oxide Thin Film Oxygen Stoichiometry with Application to Electrochemical Mechanical Actuation
Authors: Bishop Sean R. , Swallow Jessica G. , Maloney John M. , Tuller Harry L. , Van Vliet Krystyn J.
Published: May 2020

Dynamic chemical expansion (DCX) provides a direct method for probing defect induced dilation (chemical expansion) of thin films during voltage induced changes in defect concentration. The voltages, applied across electrochemical cells, pump oxygen in or out of the film leading, in turn, to measurable expansions on the nano-scale. In this work, both the current and mechanical displacement response to an electrochemical driving force are modeled in the time domain using previously derived defect equilibria and kinetics relationships previously established for the studied thin film Pr0.1Ce0.9O2-δ system. The response is also modeled in the frequency domain, by approximating the mechanical response as linear, resulting in an electrochemomechanical admittance spectroscopy interpretation of the system. The relationship between equivalent circuit parameters used to fit the admittance spectra and constants in the equation of motion are discussed.

Figure 1
(Invited) High-Rate Ammonia Synthesis at Tailored Interfaces
Authors: Manthiram Karthish
Published: May 2020

The Haber Bosch process has served as the dominant method of synthesizing ammonia over the last century. Ammonia produced through this route leads to a stoichiometric carbon dioxide footprint and also involves harsh conditions which limit modularity of the process. We are developing a continuous lithium-mediated approach through which nitrogen can be fixed at ambient conditions while eliminating the carbon dioxide footprint. We have elucidated the reaction network through which ammonia synthesis occurs in competition with hydrogen evolution. The coupling of kinetics and transport has a significant influence on the rates of ammonia synthesis, providing a means to improve selectivity of nitrogen fixation.
(Invited) Carbon-Based Single Ni Site Catalysts for Nitrogen Reduction Toward Electrochemical Ammonia Synthesis
Authors: Mukherjee Shreya , Wu Gang
Published: May 2020

Ammonia electrosynthesis using nitrogen and water has been attracting significant attention and can be easily used for distributed fertilizer production or fuel generation. However, electrochemically nitrogen reduction reaction (NRR) under ambient conditions is very challenging and largely dependent on active and selective catalysts. Herein, we report a new class of atomically dispersed Ni site catalyst, which exhibited the highest ammonia yield of 112 µg cm-2h-1 and a FE of 20 % in neutral electrolyte. The coordination of Ni sites with nitrogen was further verified by advanced X-ray absorption spectroscopy and electron microscopy, suggesting a coordination number close to 3. Density functional theory calculations provide insightful understanding on the possible structure of active sites and the relevant reaction pathway of the NRR on the single Ni site catalysts. Although we are not able to do the very expensive 15N2 isotope tests, extensive controls strongly suggest the atomically dispersed Ni-Nx-C coordination provides more intrinsically active sites than those in N-doped carbon for ammonia production throng the NRR, instead of possible environmental contamination. This work further supports that single metal sites catalyst with appropriate nitrogen coordination is very promising for the NRR and indeed improve the scaling relationship of transition metals.
(Invited) Reduced Graphene Oxides with Engineered Defects for Efficient Electrochemical Reduction of Dinitrogen to Ammonia in Wide pH Range
Authors: Sun Zhenyu
Published: May 2020

Electrochemical nitrogen fixation under mild conditions is highly demanded yet remains a grand challenge. Herein we report metal-free electrocatalysis of aqueous N2 reduction to produce NH3 over reduced graphene oxide (DrGO) with tuned defects. The defect sites in DrGO, consisting of unsaturated carbon [single vacancy (SV), double vacancy (DV), and –COOH], were examined, and showed an improved NH3 selectivity due to the strong binding of N2 instead of H. In addition to improved selectivity, the calculated free energies for N2 reduction reaction at DrGO-COOH and DrGO-DV sites suggest that the thermodynamic ovepotentials of these metal-free catalysts are comparable to the most efficient transition metal-based catalysts reported thus far. Our nonmetallic and dopant-free catalysts can convert N2 to NH3 at a faradaic efficiency of up to 22.0% at -0.116 V (versus the reversible hydrogen electrode vs. RHE) in 0.1 M HCl and 10.8% at -0.166 V (vs. RHE) in 0.1 M KOH, surpassing most earlier reported catalysts. An NH3 formation rate exceeding 7.3 μg·h-1 mg-1 was achieved at low overpotentials in both acidic and alkaline environments, comparable to the values shown by metal electrocatalysts under similar conditions.
Electrochemical Oxidation of Ammonia on Non-Noble Metals
Authors: Johnston Sam , Kemp Liam , Turay Bila , Simonov Alexandr N. , MacFarlane Douglas R. , Suryanto Bryan H R
Published: May 2020

The electrochemical oxidation of ammonia has been studied in detail due to its inherent utility as a fuel cell reactant 1 for the remediation of wastewater systems 2 for sensors 3 and as a hydrogen carrier.4 However, the bulk of the research conducted has been focused on the use of noble metal-based catalysts such as Pt, Pd, Rh and Ir due to their inherent activity towards the ammonia oxidation reaction (AOR).5,6 Electrochemically, the ammonia oxidation reaction on platinum is a complex multistep reaction which tends to be sluggish and suffers from poor faradaic efficiency, with a variety of products being formed. Another notable feature of noble based systems is the tendency to become poisoned, by strongly adsorbed ‘N’ species.5 These have been shown to build up over time resulting in electrode de-activation.

In nature, transition metals are found at the core of AOR enzymes such as ammonia monooxygenase which suggests that it is possible to perform this reaction with non-noble catalysts.7 With the issues surrounding noble-metal catalysts and following nature as an example, we have begun investigating the oxidation of ammonia with transition-metal based catalysts. To this end our investigations have revealed that it is possible to conduct electrochemical ammonia oxidation to NOx species with faradaic efficiencies of up to 100%, at appreciable rates with no evidence of catalytic poisoning (see fig. 1). This work represents a step forward in our understanding of the electrochemical AOR reaction and may serve as a foundation for future work in this field.

1. M. H. M. T. Assumpção et al., Int. J. Hydrogen Energy, 39, 5148–5152 (2014).

2. L. Marinčić and F. B. Leitz, J. Appl. Electrochem., 8, 333–345 (1978).

3. A. Galdikas et al., Sensors Actuators B Chem., 67, 76–83 (2000).

4. F. Vitse, M. Cooper, and G. G. Botte, J. Power Sources, 142, 18–26 (2005).

5. Z.-F. F. Li, Y. Wang, and G. G. Botte, Electrochim. Acta, 228, 351–360 (2017).

6. S. Johnston, B. H. R. Suryanto, and D. R. MacFarlane, Electrochim. Acta, 297, 778–783 (2019).

7. J. A. Zahn, D. M. Arciero, A. B. Hooper, and A. A. DiSpirito, FEBS Lett., 397, 35–38 (1996).

Fig. 1. (A) Chronoamperometry conducted in 1 M KOH + 0.1 M NH3 over a time of 48 hours and (B) associated yields of NOx.

Figure 1
Synthesis and Diversification of Azanucleosides By Anodic Oxidation
Authors: Chiba Kazuhiro , Okamoto Kazuhiro , Tsutsui Mizuki , Okada Yohei
Published: May 2020

Azanucleosides in which the 4'-oxygen atom is replaced with a nitrogen atom are attracting considerable attention due to their anticancer and antiviral activities and resistance to nucleases. However, traditional synthesis strategies require multiple steps and harsh conditions, limiting the structural and functional diversity of the product. Reactive intermediates can be generated by directly activating target C-H bonds on the substrate by electro-organic reactions. We have also developed various electrochemical synthesis methods. Here, we report a novel synthesis method of pharmacologically relevant azanucleosides, riboazanucleosides via site-specific anodic C-H activation.

The anodic oxidation reaction with a lithium perchlorate(LPC)–nitroethane medium activated N-acryloyl(Acr)-prolinol derivatives efficiently by decreasing the oxidation potential, possibly as a result of reduction of the Lewis acidity of Li+ by the nitroethane. When the activated prolinol substrate was coupled at the 5-position with nucleophiles, including nucleobases, the N-Acr group remained intact. The functionality of the prepared N-Acr-azanucleosides was readily increased by chemical modifications.

In addition, C-glycoside is also valuable analogue for naturally occurred O-, N-glycosides because of its stability in biological condition. Especially, C-azanucleoside was developed as transition-state analog of purine nucleoside phosphorylase (PNP), which showing therapeutic effect for leukemia. This gave incentive to establish efficient synthetic method for C-azanucleoside by anodic oxidation. As a result of examining many reaction conditions, a coupling reaction between electroauxiliary (4-methoxyphenylthio group)-tethered prolinol and non-protected 9-deazahypoxanthine was accomplished in the LPC–nitromthane medium (1.0 M). This method opens the way for the electrosynthesis of various C-azanucleoside.

Figure 1
Redox and Coordination Chemistry of Chalcogenophenes
Authors: Shida Naoki , Nishiyama Hiroki , Zheng Feng , Ye Shuyang , Seferos Dwight S. , Tomita Ikuyoshi , Inagi Shinsuke
Published: May 2020

Chalcogenophene is a five membered aromatic ring containing group 16 elements, and widely used for the design of small molecule or polymer based organic devices. In this work, we report a thorough discussions on the electrochemical redox chemistry of chalcogenophenes, with special emphasis on tellurophene (N. Shida, H. Nishiyama, F. Zheng, S. Ye, D. S. Seferos, I. Tomita, S. Inagi, Communications Chemistry, 2019, 2, 124.).

2,5-Diphenyl tellurophene (PT) was first chosen as a model molecule for this study (Figure). By employing spectroelectrochemstry, electroorganic synthesis and quantum simulations techniques, it was revealed that PT change their redox behavior in two different modes: one electron oxidation to generate radical cation in weakly coordinating electrolyte or two electron oxidation with coordination of anions and solvents onto tellurium in coordinating electrolyte. The strong interaction between anions (ClO4, BF4, PF6) or neutral donor (MeCN) with tellurium in oxidized tellurophenes became evident for the first time, which implies that the positive charge is not delocalized in the conjugated π-system as is usually expected for the conjugated molecules. By using analogous molecule with larger π-system, i.e., 2,5-(9,9-dimethylfluorene)tellurophene (FT), coordinated species and radical cation were generated simultaneously. These finding will lead further understanding of the fundamental redox chemistry of chalcogenophenes.

Figure 1
Designing Polymers for Electrochemical Energy Conversion & Storage
Authors: Huang Zhuojun
Published: May 2020

Rational design of the electrode-electrolyte interphase is essential to stabilize the electrodeposition of reactive metals like lithium, irrespective of the nature of electrolyte (liquid or solid-state). Thus, it is important to design an artificial interfacial layer that can accommodate the stress generated due to the volume changes during battery operation and at the same time maintain ionic continuity. In our work, we design novel materials based on dynamic ionic bond polymer networks that can be used as a coating on metal anode for enhancing the electrochemical stability. It was seen that polymers comprising of dynamic bonding groups are more effective in preventing the morphological instabilities compared to covalently bonded rigid polymers and crosslinked elastomers. The stabilization mechanism of the dynamic polymeric coatings is understood to arise from the spontaneous structural response of the polymer in response to the roughening electrode during electrodeposition. As the polymer coating is free to flow, if there is a ‘hotspot’ (uneven deposit) on the surface of the lithium metal, the dynamic polymer coating can rearrange and cover these regions resulting in increased overpotential, such that the successively Li+ ions deposit on the flatter regions resulting in a uniformity of deposition. In my talk, I will discuss the mechanics, microstructure, and 'self-healing properties' of these dynamic polymer networks and the relationship with their electrochemical functions.
Interfacing Electron Transfer-Competent Cells with Electrodes Using DNA
Authors: Furst Ariel L
Published: May 2020

Microbial fuel cells offer promising technology for clean energy by degrading components of wastewater while simultaneously generating power. However, challenges remain with the broad implementation of these systems, namely due to inconsistent interactions between microbes and electrode surfaces. A key challenge in the interaction of cells with inorganic surfaces is to maintain specificity in the placement of cells while facilitating electron transfer between them and the surface. DNA has the unique ability to both self-recognize and act as a molecular wire. By applying the inherent specificity of DNA hybridization, we have used DNA-modified electrodes to capture and quantify non-adherent cells, including the electron transfer-proficient organism Shewanella oneidensis. When immobilized on electrodes via DNA hybridization, Shewanella preserve their electron transfer capabilities prior to biofilm formation. We attribute this ability, at least in part, to the conductivity of DNA. Our DNA-based technique to interface cells with electrodes has significantly improved the ease of fabrication and generation of current from Shewanella-modified electrodes.
Insight into the Specific Adsorption Properties of Pristine Ionic Liquid: Temperature Dependent Flatband Potential Study
Authors: Patel Dipal B , Mukhopadhyay Indrajit , Chauhan Khushbu
Published: May 2020

Specific adsorption of ions of ionic liquids on an electrode plays an important role in controlling the mass and/or charge transport phenomena in electrochemical techniques. Insufficient experimental evidences put limit on wider acceptance and usage of ionic liquids in the field of energy devices. In the present study, two different photoelectrochemical cells (PECs) having configurations as (i) PbOx/Fe(CN)6
-4/-3/Pt and (ii) PbOx/[Bmim]Tf2N/Pt were utilized to provide the experimental pathway and to unveil the adsorption characteristics of ion-pairs of any ionic liquid. The photoresponse curves of PECs under chopped light illumination conditions were used to extract the flatband potential of PbOx film. The band edge positions and electron affinity of PbOx films were calculated with the help of Mott-Schottky plots. It is well known that the adsorption properties of electrolytes can be understood by calculating the point of zero charge (pHpzc). Hence, this parameter was calculated by analyzing the temperature dependent flatband potential which further unveiled the adsorption characteristics of ionic liquids. This study is an unexplored approach to get closer to the understanding of inherent properties of ionic liquids which can be of utmost interest to either basic or applied field researchers.
Dissolution Stability of Photoanodes and Co-Catalysts in Photoelectrochemical Water Splitting
Authors: Knöppel Julius , Kormányos Attila , Mayerhöfer Britta , Hofer André , Speck Florian Dominik , Bachmann Julien , Thiele Simon , Cherevko Serhiy
Published: May 2020

In the future energy scenario, production of hydrogen is a promising solution for the storage of renewables. Photoelectrochemical water splitting with integrated devices can be engaged for the production of hydrogen with the advantage of less space consumption and saving power lines to the production site. Current devices have already come close to the efficiency of an electrolyzer coupled to a solar cell [1]. However, to be profitable in commercial use several challenges have to be resolved. One of the most pressing issues is photostability of materials during operation. Even though photoelectrodes are able to reach lifetimes of several days in lab conditions, it is still a long way until real device lifespans of several years are possible.

While efforts in the field of photoelectrochemical water splitting are mainly focused on achieving higher activity, research on stability is still at the very beginning. Evaluation of photostability is typically done by rather short (only few hours) chronoamperometry measurements and post mortem analysis. One option to study degradation processes in-situ is to use on-line inductively coupled plasma mass spectrometry (on-line ICP-MS) which became available recently and revealed photocorrosion of WO3 [2] and BiVO4 [3].

In this study, we aim to achieve a better understanding of the key factors driving photocorrosion. It has already been shown, that WO3 exhibits significant differences in faradaic efficiency towards the oxygen evolution reaction (OER) in various electrolytes [4]. One reason behind this behavior might be degradation processes driven by the electrolyte. To study the effect of electrolytes on stability, dissolution of spray-coated WO3 films was investigated in four electrolytes (HClO4, H2SO4, HNO3 and CH3SO3H). Additionally, the influence of protective iridium co-catalyst layers on stability, synthesized in various thicknesses by atomic layer deposition (ALD) was explored.

1. Cheng, W.-H., et al., Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Letters, 2018. 3(8): p. 1795-1800.

2. Knöppel, J., et al., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochemistry Communications, 2018. 96: p. 53-56.

3. Zhang, S., et al., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements Under Photoelectrochemical Conditions. The Journal of Physical Chemistry C, 2019.

4. Reinhard, S., F. Rechberger, and M. Niederberger, Commercially Available WO 3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution. ChemPlusChem, 2016. 81: p. 935-940.
Spectroelectrochemistry of Explosive Aliphatic Nitro Compounds
Authors: Holubowitch Nicolas , Budimir Zachary , Crabtree Cameo
Published: May 2020

The spectroelectrochemical behavior of non-aromatic explosive compounds, namely two nitramines (RDX and HMX), a nitrate ester (PETN), and a plastic explosive composite (Semtex 1A) in acetonitrile is reported. The electrochemical behavior of these compounds using cyclic voltammetry is performed while monitoring the UV absorbance spectra of transient and product species in situ. In search of a low-cost solution-phase detection technique, we compare the spectroelectrochemistry of these compounds in the absence and presence of naturally dissolved oxygen (~2 mM in AcN), where the superoxide radical is co-electrogenerated during explosive analyte reduction. Free superoxide yields an intense UV signal in this medium (λmax = 250 nm) that the explosives attenuate to varying degrees. We deconvolute UV spectral data through time- and potential-resolved analyses coupled with electrochemical data. It is found that superoxide interacts with the explosives through unique, previously unreported ways, likely due to strongly polarized electrostatic potentials across the poly-nitro aliphatic molecules. Reaction mechanisms will be proposed and the findings expand the understanding of high-explosive solution chemistry and offer a route to novel signal transduction for (electro-)chemical sensors for energetic materials.

Figure 1. Spectroelectrochemistry of the control solution, aerated 0.1 M TBAPF6 in acetonitrile. (a) CV (ν = 50 mV s-1) in time and potential domains with the superoxide absorbance at 250 nm plotted for qualitative visualization; (b) time-resolved, full-spectrum UV data recorded during the CV.

Figure 1
Composite Ag/AgCl/KCl Screen-Printed Reference Electrode
Authors: Dawkins Rebecca Claire , Vepsalainen Mikko , Hart Judy Nancy
Published: May 2020

The drive for automation in multiple industries has generated unmet demand for low-cost, disposable sensors with short response times for routine electrochemical sensing. Glass ion selective electrodes containing a liquid electrolyte have remained the standard for decades, despite their fragile, bulky nature and regular maintenance requirements restricting their suitability for long-term in-situ monitoring. Advances in printing technologies have enabled solid thick film electrodes to emerge as a possible solution to these challenges.

Screen printing can be used to mass-produce units of simple, modifiable, and reproducible sensors using minimal materials, increasing portability and reducing fabrication costs. Traditional glass electrode materials are not suitable for printed fabrication, so new materials and designs are required to deliver reliable and robust printed sensors for a variety of industries. While electrochemical sensors can be used to monitor key aqueous environmental indicators, including pH, heavy metals, and oxidation-reduction potential, they often require a stable reference electrode to gain meaningful measurements. Many previous printed electrochemical sensors have relied on a pseudo-reference electrode containing no stabilising electrolyte, however any resultant potential variation can affect measurement accuracy in unknown solutions.

In this study, a new screen-printed "true" reference electrode was developed based on Ag/AgCl and a solid composite KCl electrolyte. The electrode lifetime was tested in a 0.1 M K2SO4 solution, and open circuit potential (OCP) stability was tested in H2SO4, KOH, alkali cations (Li+, K+, Na+), halogen anions (F-, Cl-, Br-, I-), KMnO4, H2O2, ascorbic acid, KCl, and standard pH buffers (pH 4, 7, 10). The initial stabilisation and water permeation was monitored via electrochemical impedance spectroscopy (EIS).

The observed electrode lifetime in 0.1 M K2SO4 was up to 39 days, with less than 5 mV deviation from the theoretical value (-45 mV vs SCE) and a shelf life of over 1 year. According to the EIS and OCP data, the electrode typically stabilised within 2 hours. In the stability tests, the electrode potential did not deviate more than 10 mV from the theoretical value in the presence of KOH, alkali cations, halogen anions, ascorbic acid, KCl, and standard pH buffers. The electrode was also stable in H2O2 at concentrations up to 0.1 M. On average, the electrode potential was 12 mV below the theoretical value in 10% H2SO4 and was significantly below the theoretical value in 0.1 M KMnO4.

The results of this study suggest that this screen-printed reference electrode is suitable for use in electroanalytical systems in most tested chemical environments. The relatively long lifetime and stability of the electrode allows it to be used in a variety of applications, including environmental monitoring, laboratory measurements, and industrial process monitoring, as part of a printed sensor system.
Simple Method for Preparing Customizable Pyrolyzed Photoresin Carbon Electrodes Using 3D Printing
Authors: Glasco Dalton L. , Knust Kyle N.
Published: May 2020

We report an accessible fabrication procedure to prepare customizable pyrolyzed photoresin electrodes (PPE) for electroanalytical applications. A stereolithography 3D printer was used to pattern carbon containing photoresin on a quartz substrate before being pyrolyzed to yield a carbon electrode with X and Y dimensions ranging from mm to a minimum feature size of approximately 200 µm as determined by optical microscopy. Stylus profilometery was used to determine PPEs have an approximate step height of 600 nm. Atomic force microscopy was employed to examine the surface roughness of PPEs, which were found to have a rms roughness of approximately 25 nm. Cyclic voltammetry with hexaammineruthenium chloride was performed to examine the electrochemical behavior of the PPEs, which was consistent with the Randles-Sevcik equation and commercial glassy carbon electrodes. Hydrodynamic voltammetry in a microfluidic device was also demonstrated.
Sustainable Hydrogen Production through Electrocatalytic Water Splitting with Manganese and Nickel-Based Catalysts
Authors: Yuan Hao
Published: May 2020

Solar-driven water splitting has potential for sustainable solar energy conversion and storage in the form of fuels. Its practical use requires highly effective yet non-expensive electrocatalysts synthesized from earth-abundant materials. Here we report a new electrocatalytic system with two electrocatalysts based on Mangnese and Nickel for effective electrocatalytic water splitting. We have developed a synthesis method for a manganese-based (MnOx) water oxidation catalytic films in situ fromaqueous media. This method involves two series of electrodepositions by cyclic voltammetry (CV) over different potential ranges to tune the oxidation state of the catalyst, followed by calcination to increase its crystallinity. The resulting film has a morphology of uniformly distributed fibrous nanoscale as well as stable and excellent catalytic performance toward water oxidation. The resulting onset potential is so low that a single AA alkaline battery can be used to power the water splitting process. For the hydrogen evolution reaction, we have developed an electrodeposition method to synthesize Ni/Ni(OH)2 electrocatalysts in situ on conductive surfaces. The new method uses two cycles of CV over a single potential range, producing a film with a large number of Ni(OH)2/Ni interfaces which significantly shifts performance towards that of platinum.The new method involves only two cycles of CV over a single potential range. The resulting catalytic film has a morphology of packed walnut-shaped particles. It has superior catalytic activity and good stability over long periods. To test the functionality of the entire catalytic system, we have connected the two electrocatalysts in tandem and the system has shown stable water splitting functionality with low overpotential.
Surface X-Ray Diffraction Studies of Single Crystal Electrochemistry
Authors: Lucas Christopher A. , Grunder Yvonne
Published: May 2020

The atomic structure on the metal side of the electrochemical interface depends on the applied electric potential and the nature of the adsorbing species in the electrolyte solution. In this poster we will present some recent results probing surface stress and surface relaxation effects in single crystal metal electrodes that are driven by potential changes. The principal method for probing changes in the atomic structure at the interface is surface x-ray diffraction employing the use of high intensity synchrotron radiation [1]. Measurements on Pt(hkl), Au(hkl) and Ag(hkl) electrodes enable a comprehensive study of the phenomena of surface reconstruction and surface relaxation. The measurements also give insight into the potential-dependent layering in the liquid side of the interface. Both the potential and the structure in the electrolyte layers at the interface alter the metal electronic structure so that the surface in the electrochemical environment is strongly modified from the ultra-high vacuum (UHV) counterpart. A methodology for linking experimental and theoretical approaches for a fundamental understanding of electrochemical reactions will be presented.

[1] Y. Gründer and C. A. Lucas, NanoEnergy, 29, 378-393 (2016).
Electrochemical Semiconductor Analysis By Square Wave Voltammetry
Authors: Miljkovic Bojan , Ruda Harry E
Published: May 2020

Studies in the past 20 years have utilized cyclic voltammetry (CV) for determining various electronic properties (e.g. density of states, electron carrier concentrations, trap state capacitances) of semiconducting titanium oxide films in photoelectrocatalytic systems such as dye-sensitized solar cells [1-4]. Though primarily used for redox sensing, this work presents square wave voltammetry (SWV) as an alternative to determining said properties. As an electrochemical characterization technique, SWV can provide significantly less background current and greater sensitivity than CV [5]. This is beneficial for the accurate measurement and calculation of electronic properties from electrochemical semiconductor current-voltage data. By varying the applied frequency as well as step and/or pulse sizes of the square wave, one can probe electronic processes of various time scales, in contrast to CV which only allows control of the potential scanning rate across the same potential window [5, 6]. This work presents a comparative study of electronic properties as determined by SWV versus CV for various semiconducting electrodes such as silicon, germanium, titanium oxide, and doped diamond films. This technique was also extended to semiconductor heterostructures - such as noble metal-decorated titanium oxide - for observation of intraband gap states and their contribution to the overall electronic properties of the electrode as determined by SWV.

[1] Liu, B. et. al., “Intrinsic intermediate gape states of TiO2 materials and their roles in charge carrier kinetics”, J. Photochem. and Photobio. C: Photochem. Rev., 39 (2019) 1-57

[2] Zare, M., Mortezaali, A., and Shafiekhani, A., “Photoelectrochemical determination of shallow and deep trap states of platinum-decorated TiO2 nanotube arrays for photocatalytic applications”, J. Phys. Chem. C, 120 (2016) 9017-9027

[3] Fabregat-Santiago, F. et al., “High carrier density and capacitance in TiO2 nanotube arrays induced by electrochemical doping”, J. Am. Chem. Soc., 130 (2008), 11312-11316

[4] Abayev, I. et al., “Properties of the electronic density of states in TiO2 nanoparticles surrounded with aqueous electrolyte”, J. Solid State Electrochem, 11 (2007) 647-653

[5] Mirceski, V. et al., ”Square-wave voltammetry: A review on the recent progress”, Electroanalysis, 25 (2013) 2411-2422

[6] Bard, A. J. and Faulkner, L. R., Electrochemical Methods: Fundamentals and Applications, 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2001.
Pt/Ga Microelectrode Localized Lithium Detection in Li-Ion Battery Electrolytes
Authors: Hatami Mojgan , sazzad Hossain Md , Schougaard Steen Brian
Published: May 2020

Local Li+ ion detection in the Lithium Ion Batteries (LIBs) is important as lithium ions are exchanging between cathode and anode material via the electrolyte during battery operation. Therefore, the goal here is to develop a technique to detect lithium ions transport within the electrolyte filled porous network of the cathode.

Scanning electrochemical microscopy (SECM) was chosen for Li+ detection in this study as a powerful tool for recoding the in situ electrochemical behavior of this chemical species.1,2 A Pt/Ga microelectrode was used as a probe for SECM. After preparing a cone shape Pt/Ga microelectrode and using anodic stripping voltammetry (ASV) or square wave voltammetry (SWV), a linear current response from 0.3-5 mM Li+ concentrations was obtained. The limit of detection was determined to 77 µM. These result firmly established Pt/Ga microelectrode as a reliable probe for determining the diffusion of Li+ ion from different locations of the LIB solid materials.

References:

(1) Polcari, D.; Dauphin-Ducharme, P.; Mauzeroll, J. Chemical reviews
2016, 116, 13234-13278.

(2) Barton, Z. J.; Rodríguez-López, J. n. Analytical chemistry
2014, 86, 10660-10667.

Figure 1
Autonomous Electrolyte Discovery for Batteries with Experimentally Informed Bayesian Optimization
Authors: Dave Adarsh , Mitchell Jared , Kandasamy Kirthevasan , Burke Sven , Paria Biswajit , Poczos Barnabas , Whitacre Jay F , Viswanathan Venkat
Published: May 2020

An autonomous battery electrolyte experimental platform capable of mixing multi-component electrolyte systems and characterizing the transport and electrochemical properties in a high-throughput manner is disclosed. A Bayesian optimization software package found novel electrolyte compositions through optimization of the high-dimensional electrolyte design space over key design objectives like electrochemical stability and conductivity.

Electrolyte optimization is difficult because 1) electrolyte evaluation is expensive and takes time, and 2) the space of possible electrolytes is expansive, formed by many possible choices for solvents (often in ternary blends), salts (often in binary mixtures), and trace additives. Bayesian optimization methods are well suited for the optimization of high-dimensional functions with costly evaluations, often producing an efficient design-of-experiments to converge on multi-objective optimal formulations in few experiments. To expedite the optimization over the expansive design space, theoretical predictions of electrolyte properties via the Advanced Electrolyte Model were utilized as “priors” in the statistical model.

Implementation of the novel experimental platform was carried out by two novel test stands developed to automate the mixing and characterization of electrolytes: Otto (for aqueous systems) and Clio (for aprotic/organic systems). The test stands characterized the ionic conductivity and electrochemical stability of electrolyte systems, featuring a four-electrode conductivity probe, pH meter, and a flow-through three-electrode cell and potentiostat. Clio also integrated electrochemically active electrodes for optimization of electrolyte/electrode systems. The active electrode systems used were common functional ceramic metal oxides.

A software orchestration and data layer linked the test-stands to human experimenters and machine-learning packages through a web-services architecture; all experiment data and meta-data is saved in a database. Additional out-of-the-loop characterization was conducted on cathodic systems to validate composition, structure, and oxidation state.

The aqueous design space consisted of aqueous blends of lithium and sodium salts, including nitrates, sulfates, and other commonly-used battery salts. High-concentration aqueous electrolyte candidates were discovered by optimizing of electrochemical voltage stability and conductivity, including low-cost, high-performing alternatives to known but costly aqueous electrolytes (e.g. LiTFSI). Clio’s design space includes blends of both aprotic organic solvents and solutes in additional to various compositions of electrochemically active electrodes. The test-stands are demonstrated to be significantly faster than common human experimentation techniques, converging on novel, optimized electrolyte mixtures in mere hours or days of experimentation.
Polypyrrole:Carboxymethyl Cellulose Composites As Efficient, Multifunctional Electrode Matrices for Lithium Battery Cathodes
Authors: Nguyen At Van , Kuss Christian
Published: May 2020

Even though the conventional electrode matrix PVDF/C-black is widely used in lithium batteries to provide adhesion and an electronically conducting matrix for active electrode materials, its performance as a binder is not sufficient for many high capacity materials, such as silicon and Lithium Nickel Manganese Cobalt Oxide. The problem is mainly attributed to the weak interactions between inert PVDF binder and non-polar carbon additives with active materials. As a result, PVDF/C cannot buffer volume changes of active materials during lithiation and delithiation that induce electrode cracking and side-reactions, leading to electrical-contact loss and capacity fading. To overcome these problems, several studies suggest the use of a multifunctional electrode matrix of conducting polymer composite PEDOT:PSS. However, the production cost of PEDOT:PSS prohibits its wide-scale application in battery technologies. In this research, we proposed a facile, scalable, low-cost in-situ polymerization method for an analogous polymer composite. We are demonstrating the fabrication of highly conductive, water-processable polypyrrole:carboxymethyl cellulose (PPy:CMC) composite as a new class of electrode matrix. The PPy:CMC (1:1 wt%) is formed at nano-level with a particle size of approximately 50 nm. The electrical conductivity of PPy:CMC (1:1 wt%) was found to be 144 mS/cm, which was smaller than that of pure PPy at approximately 1.73 S/cm, however was 10 times higher than that of ball-milled PPy:CMC (1:1 wt%) composite (mS/cm). This could be interpreted as the formation of a molecular-level composite, with ionic interactions between the positively charged polypyrrole and the negatively charged carboxyl groups on CMC. The presence of CMC in the composite structure also resulted in the ability to disperse the composite in water, which allows environmental friendly electrode processing. Thanks to the self-conductive feature of PPy:CMC composite, no additional conductive or binder additive is needed in the electrode. More importantly, we are targeting to reduce capacity degradation by improving adhesion between the conductive binder to active material particles. This study highlights how research into inactive materials can provide alternative inexpensive electrode matrices, widening the property space within which new active materials can be expected to operate.

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Spectroscopic Analysis of LixMnyFe1-YPO4 Cathodes Materials to Revel the Phase Transition Mechanism.
Authors: Savignac Laurence , Griffin John M. , Schougaard Steen Brian
Published: May 2020

Olivine-type mixed-metal phosphate cathodes have demonstrated their ability to efficiently store energy in a wide range of applications. Moreover, ultrafast charging rates (seconds order) are observed for the LiFePO4 system. Nonetheless, charge storage proceeds via a phase transition mechanisms where fully charged or discharged particles act as electronic insulators. Considering olivine as a model structure with its outstanding stability, a higher energy density material is achieved by the incorporation of high operating potential transition metals. The challenge here is to understand the exact Li+ transport mechanism engendered by the modified crystalline structure, as it impacts on the dynamics of de/lithiation process.

For the purpose of identifying the encountered phase transition mechanism is impacted by the nature of the redox active sites, a range of LixMnyFe1-yPO4 (0 ≤ y ≤ 0.9) has been delithiated by a chemical route resulting in materials at various state of charge. Powder X-ray diffraction (PXRD) and Rietveld refinement was used to describe the bulk crystalline structure. 6Li nuclear magnetic resonance (MAS NMR) and attenuated total reflectance infrared spectroscopy (ATR-IR) where employed to detect the Li+ and PO4 local environments, respectively. The information obtained by spectroscopic characterizations, e.g. local organization of transitions metals and their oxidations state, phosphate backbone distortion and presence of defects, provide an exhaustive image of the phases changes, including the crucially the Li+ transport mechanism in high energy density cathodes.

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Suppressing Electrochemical Instabilities of Li Metal Using Ionomer-Based Interfaces
Authors: Huang Zhuojun
Published: May 2020

A fundamental challenge shared across many energy storage devices, is the complexity of electrochemistry at the electrode-electrolyte interfaces that impacts the faradaic efficiency, operational rate capability and lifetime. Specifically, in energy-dense lithium metal batteries, the charging process results in morphological heterogeneity of the metal anode, leading to battery failure by short-circuit or capacity fade. Perhaps, a facile way of addressing these challenges is designing a polymer thin-film at the electrode-electrolyte interface. We envision that an ideal interface should be based on several design principles including: presence of Li+ ion conduction pathway; chemically inert, mechanically robust, adaptive to volume changes and solution-processable for large scale thin-film casting.

Here, we use free-radical polymerization technique to synthesize novel stimuli-responsive polymers which exhibit the aforementioned characteristics. Unlike, previous works where the electrode coating acts as a pure physical barrier, the designer polymers in this work possess multifunctional characteristics to suppress different electrochemical instabilities. Because of the viscoelastic and electroactive nature of the polymers, they respond to any morphological changes of the electrodes during electrodeposition, giving rise to an electrochemical shielding mechanism that modulates lithium ion migration pathway and prevents surface roughening.

This work takes advantage of contemporary characterizations techniques like NMR, voltammetry and rheology to mechanistically understand the role of polymer dynamics and ion content on the electrodeposition morphology. We show that systematic optimization of these parameters can significantly boost the coulombic efficiency of the battery. Remarkably, we found that these polymer coatings can enhance the lifetime of conventional high-voltage lithium metal battery by at least two-times.
Cathodically Deposited Birnessite As the Electrode Material
Authors: Pugolovkin Leonid V. , Levin Eduard E. , Arkharova Natalya A , Orekhov Anton , Presnov Denis E , Tsirlina Galina A.
Published: May 2020

Various manganese oxides are considered as rather active ORR catalysts and/or supercapacitor materials for operation in alkaline medium. However all these oxides are thermodynamically unstable at high pH and undergo more or less slow transformations to non-stoichiometric oxides containing alkali metal cations M (MxMnO2*nH2O, known also as birnessite mineral). We report a possibility to deposit birnessite thin layers by means of permanganate cathodic reduction. We consider ORR activities and reversible recharging data for birnessite deposited at various potentials with account for XRD information on birnessite cell disordering and microscopic data on the morphology of the deposits.

Deposition is complicated by formation of soluble Mn(V) and Mn(VI) species and their disproportionation. However fortunately these by-side reactions appear to be strongly inhibited by forming birnessite solid, and the resulting current efficiencies are high enough. We compare deposition efficiency and adhesion for Pt, Ni, and glassy carbon supports. The best adhesion is found for Ni support.

Deposits morphology strongly depends on deposition potential. Thin deposits formed at low overvoltage demonstrate homogeneously distributed pores, and only starting from sub-mkm thickness branched flakes appear, which are typical for natural birnessite morphology. Contrary, at higher overvoltage the deposits start to branch from the very beginning, and consist from thin flakes exclusively. This morphology is unfavorable for electrode behavior because of too high material resistance. Deposition transients allow to monitor the morphology. For flakes formation, oscillatons at deposition transients are observed, which can be associated with layer-by-layer growth.

The recharging of all birnessite materials is reversible, but the specific capacity strongly depends on deposition potential and deposit thickness. The best results (ca. 500 mkF/cm2 at scan rates up to 0.1 V/s) are found for thin deposits fabricated at low overvoltage. ORR mass activity is comparable with observed earlier for MnO2, which is believed to undergo slow transformation to birnessite in alkaline solutions. The important advantage of electrodeposited birnessite as compared to the majority of chemically synthesized manganese oxides is a possibility to operate in the absence of conducting binder.
Elucidation of Ionomer-Pt Interactions By Operando Vibrational Spectroscopy
Authors: Cruse Ryan , Doan Jonathan , Smith Sam Jackson , Smotkin Eugene S.
Published: May 2020

Operando vibrational spectroscopy of the membrane electrode assembly (MEA) of Pt catalyzed fuel cell cathodes elucidates potential dependent adsorptive properties of ionomers upon Pt surfaces. These include direct evidence of sulfonate group adsorption at fuel cell potentials of 700 mV. An increase in the ionomer state-of-hydration, from oxygen reduction at the cathode, transitions ion exchange sites from the sulfonic acid to the dissociated sulfonate form. C1 and C3V modes correlate to the sulfonic acid and sulfonate forms respectively. The gradual transition of the MEA spectra from C1 to C3V modes, from the fuel cell open circuit voltage to the short circuit current respectively, demonstrate the utility of vibrational group mode assignments in terms of exchange site local symmetry. Operando vibrational spectroscopy coupled with polarization modulated IR spectroscopy of Nafion coated Pt also confirms adsorption of the Nafion -CF3 group upon Pt. At the anode side of the operando spectroscopy cell, Stark tuning of CO stretching modes are observed and discussed. The absence of Stark tuning is evidence of metal based materials as non-catalytic surfaces.