bluuebunny/crossref_metadata_2025 huggingface dataset:
Clarification of the Reaction Mechanism of the Photoassisted Anodic Oxidation of SiC in a Newly Developed Inverted Rotating Disk Electrode Cell Setup
Authors: Mairhofer Katharina , Larisegger Silvia , Fafilek Guenter
Published: September 2023

Due to the distinctive chemical and physical properties of silicon carbide (SiC), interest in the material as a substrate for semiconductor industry has risen significantly during the past two decades. As a wide bandgap semiconductor SiC is known to be highly chemically inert. Still, under specific conditions SiC takes part in a number of electrochemical reactions that lead to a rapid oxidation of the surface. The goal of this work is to understand the fundamental factors driving this process for n-type SiC crystals in aqueous electrolytes.

In alkaline solutions, the photoelectrochemical behaviour of n-type SiC is determined by two partial reactions (oxidation/dissolution)
1
:

(1a) SiC + 6h+ (hν) + 6OH- → SiO2 + CO + 3H2O

(1b) SiC + 8h+ (hν) + 8OH- → SiO2 + CO2 + 4H2O

(2) SiO2 + 2OH- → [Si(OH)2O2]2-

For the investigation of such photoassisted or photoelectrochemical reaction mechanisms involving mass transfer, we specifically developed a new inverted rotating disk electrode (IRDE) cell setup
2
that allows to control the most essential experimental parameters (i.e. potential, diffusion conditions and light intensity).

In this setup, rotation of the disk electrode is achieved by magnetic coupling between a driver magnet (i.e. a magnetic stirrer) and the follower magnet included in the sample holder. The cell allows a homogeneous illumination and removal of gaseous reaction products, while still providing leak tightness. The surface of the semiconductor electrode is illuminated with UV light (λ = 365 nm) from a high-power LED. The distance between light source and sample is minimized to achieve maximum surface illumination of the sample.

To investigate mass transport phenomena, electrolytes with relatively low solubility of SiO2 are preferable. Therefore, we used potassium hydroxide solutions in a concentration range where mass transport of hydroxide ions plays a major role.

Performing cyclic voltammetry in this newly developed IRDE cell allows to distinguish different reaction regimes that are either limited by mass transport, photon flux or hole transport. For low light intensities (either through a large distance between the sample and the LED or through low driving currents through the LED) the number of photon-induced holes is limiting. At low electrolyte concentrations, the transport of hydroxyl ions and the dissolution of the oxidation products determine the reaction rate. At low potentials, hole transport limits the overall current flow. Each of these reaction regimes was studied individually to conduct a potential reaction mechanism.

[1] D. H. van Dorp und J. J. Kelly, „Photoelectrochemistry of 4H–SiC in KOH solutions,“ Journal of Electroanalytical Chemistry, Bd. 599, Nr. 2, pp. 260-266, 2007.

[2] K. Mairhofer, P. Mayr, S. Radl, M. Nelhiebel, S. Larisegger, G. Fafilek, „An Inherently Leakage-Free Inverted Rotating Disk Electrode Setup“, 2022.

Figure 1
Endothermic Dehydrogenation-Driven Preventive Magnesiation of Sio by Magnesium Hydride for High-Performance Sio-Based Lithium Storage Materials
Authors: Youn Donghan , Kim Nam Gyu , Jeong Won Joon , Yu Mi , Kim Ji Young , Kim Hansu
Published: September 2023

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials because of their superior cycle performance. However, low initial Coulombic efficiency (ICE) of SiO derived from the irreversible electrochemical reaction of the amorphous SiO2 phase in SiO makes wide use of the SiO-based anode materials in lithium-ion batteries challenging. Magnesiation of SiO is one of the promising solutions to improve ICE of SiO-based anode materials. Here, we propose an endothermic dehydrogenation-driven magnesiation of SiO by employing MgH2 to improve both ICE and cycle performance. The resulting Si/Mg2SiO4 nanocomposite material showed much-improved ICE of 89.5% and long-term cycle performance for over 300 cycles compared to the homologue prepared by the magnesiation of SiO using Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry−differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH2 mitigates the rapid temperature rise during magnesiation of SiO, thereby inhibiting the increase of Si domain size in the resulting Si/Mg2SiO4 nanocomposite. Detailed material characterization and electrochemical analysis of Si/Mg2SiO4 nanocomposite materials will be discussed in this presentation.
Mixed Isomer Chromium-Chelates for High Concentration Aqueous Flow Battery Electrolytes
Authors: Davis Casey M. , Waters Scott E. , Robb Brian H. , Thurston Jonathan R. , Reber David , Marshak Michael P.
Published: September 2023

Redox flow batteries have attracted attention for their potential for large-scale energy storage, largely due to their ability to decouple power and energy. However, their limited energy density is often cited as a major drawback preventing adoption at scale. Therefore, there is interest in research into increasing the solubility of the active material in these electrolytes. One such method is active materials with multiple redox events. Promising materials are, however, often poorly soluble, and computational studies showed that increasing differences in redox potential between e.g., two redox events will decrease the energy efficiency of the cell.1 Here, two Cr-chelate structural isomer complexes, with redox potentials 100 mV apart are characterized and compared electrochemically. The two chromium complexes are combined in mixed-anion electrolytes to generate an electrolyte of 2 M active species, corresponding to a capacity of 53.6 Ah L−1, significantly higher than the individual isomers could achieve. At 100 mA cm−2 the cell achieved average Coulombic efficiencies of 99.6% and an equilibrium cell potential of 1.65 V at 50% State-of-Charge. Due to high viscosity of the electrolyte, the voltaic efficiency was only 67%. At a 1 M concentration, the equimolar mixed-anion electrolyte had a comparable current efficiency to the individual Cr-isomers (within 0.2%) but lowered voltaic efficiency (75.8% compared to 77.8% and 78.6%). The lowered voltaic efficiency is attributed to inefficiencies caused by non-concerted multiple redox events. The high cell voltage and increased combined electrolyte capacity demonstrate that employing chirality, chelate geometry, and structural isomers in a mixed-anion approach can significantly increase overall active material concentrations, but that there are consequences for cell performance when using multiple molecules with disparate reduction potentials in an electrolyte. This highlights that concerted transitions should be prioritized in order to capitalize on multi-electron redox species.

References:

(1) Neyhouse, B. J.; Fenton, A. M.; Brushett, F. R. Too Much of a Good Thing? Assessing Performance Tradeoffs of Two-Electron Compounds for Redox Flow Batteries. J. Electrochem. Soc.
2021, 168 (5), 050501. https://doi.org/10.1149/1945-7111/abeea3.
A Comparative Study on Physics-Informed Machine Learning for Battery Degradation Diagnostics
Authors: Navidi Sina , Thelen Adam , Li Tingkai , Hu Chao
Published: September 2023

Quantifying the extent of degradation in lithium-ion battery cells using non-destructive approaches can provide valuable insights into the cell’s state of health and remaining useful life. However, physics-based degradation diagnostic methods typically require collecting long-term aging data and are computationally expensive to deploy locally on a device. This work investigates combining physics-based modeling and machine learning to retain high diagnostic accuracy while mitigating the need to collect long-term degradation data. To transfer knowledge from a physics-based model to a machine learning model, we develop two new approaches: co-kriging and physics-informed neural networks. We aim to effectively diagnose cell health in the late aging stage without needing long-term degradation data. Using a small set of early-life experimental data collected from an aging experiment, we train a co-kriging machine learning model to learn the difference between the experimental data and a set of simulation data generated from a physics-based half-cell model. Additionally, we train a neural network model using a physics-informed loss function with a new term that penalizes discrepancies between neural network model prediction and physics-based model prediction. The trained models can then be used to diagnose cell capacity and three primary component-level degradation modes at a future time. The proposed methods and two existing physics-informed machine learning methods named data augmentation and delta learning are comprehensively evaluated using data from a long-term (4+ years) cycle aging experiment of 24 implantable-grade Li-ion cells cycled under two different temperatures and C-rates. Cross-validated results show that the proposed physics-informed machine learning models can significantly improve the estimation accuracy of cell capacity and three primary degradation modes compared to a purely data-driven approach. Furthermore, this work comprehensively analyzes the trends of the degradation modes and provides insight into the long-term performance of high-quality implantable-grade lithium-ion cells.
Degradation Diagnostics of Lithium-Ion Batteries Cycled Under Varying Conditions
Authors: Li Tingkai , Thelen Adam , Karan Naba , Liu Jinqiang , Tischer Chad , Hu Chao
Published: September 2023

Lithium-ion (Li-ion) battery cell degradation is a complex process driven primarily by how the cells are used. Stress factors like temperature, charging and discharging rates, and the depth of discharge all influence the rate and type of degradation modes cells experience. Understanding the possible degradation modes and their severity under a given usage profile can help to optimize cell design, manufacturing, and control. In addition, elucidating the relationship between different degradation modes and their effects on cell capacity fade can help improve battery lifetime modeling strategies. In this study, we examine non-intrusive degradation diagnostics based on differential voltage analysis (half-cell curve fitting) and confirm the existence of certain degradation modes and mechanisms by destructively analyzing specific cells from a newly generated battery aging dataset of 245 nickel-manganese-cobalt/graphite (NMC) cells cycled under varying rates and depths of discharge. The results help to establish the link between the various aging stress factors (charging and discharging rates and depth of discharge), the measurable voltage vs. capacity data, and the observed capacity fade trends. We also investigate the impact of dominant degradation modes on battery lifetime and combine the destructive analyses with cycle aging data to understand the relationship between the rate of early-life degradation and total cell lifetime.
Enhanced Performance of Recovered Cathode Materials with Fluorine Impurity in Hydrometallurgy Recycling
Authors: Zheng Yadong , Wang Yan
Published: September 2023

With the growing lithium-ion battery (LIB) industry since its initial inception in the late 20th century, battery recycling is seen as an end-of-pipe process to resolve environmental and economic issues generated by the accumulation of waste batteries. In recent years, an increasing attention has been paid to the hydrometallurgy recycling due to its high recovery efficiency, low energy cost, as well as large-scale production capability. In order to achieve a high-quality recovered material, many resources have been poured into this field trying to develop better design and control of synthesis process. The impurities introduced in the recycling process is an important factor which could have unintended impacts on the final cathode product in a variety of aspects. The presence of fluoride ions in hydrometallurgy recycling, as one possible anion impurity which is released from the LiPF6 in electrolyte, aroused our research interest. In this work, the influence of the fluorine impurity on the recovered LiNi0.6Co0.2Mn0.2O2 (“NCM622”) cathode material via hydrometallurgy method is systematically investigated. The results show that the addition of fluorine impurity in the hydrometallurgy process improves the electrochemical properties of the recovered cathode materials.

It is found that the fluorine impurity has lots of positive impacts on the synthesized cathode materials. First of all, the equilibrium of co-precipitation reaction is affected by the fluoride ions, resulting in the formation of holes in hydroxide precipitates. After sintering, cathode particles preserve a hollow structure which leads to an improved rate capability and cycle stability. In addition, surface oxygen sites of cathode materials are found to be substituted by impurity fluoride ions. As a result, an increased surface Ni2+ concentration contributes to a better cathode surface stability as well as a higher reversible capacity. The inclusion of fluoride (<1 at%) in cathode lattice is also beneficial to the bulk lithium-ion diffusion. Not only that, but the fluorine impurity has no clear detrimental effects on the particle morphology, crystal structure, transition metal composition, and element distribution of the cathode materials. Therefore, the electrochemical performance of synthesized cathodes has achieved different levels of improvement due to those positive influences from the fluorine impurity. Specifically, cathode with 0.2 at% impurity exhibits a discharge capacity of ~168 mAh/g with a remarkable retention of 98% at 1/3C after 100 cycles, about 8% higher than the capacity of virgin benchmark. Also, rate test outcomes of fluorine-affected samples are superior to that of virgin standard. In summary, the electrochemical properties of recovered cathode via hydrometallurgy process can be boosted by fluorine impurity. Unlike adverse impurities, fluoride’s positive role in hydro-recycling indicates that it is no need to strictly control them in pre-treatment steps.

Figure 1
(Best Student Presentation) The Synthesis of Zr-Doped Li3-Xin1-XZrxCl6 with Ultrahigh Ionic Conductivity for All Solid State Lithium-Ion Batteries
Authors: Fu Jinzhao , Wang Yan
Published: September 2023

All-solid-state lithium-ion batteries (ASSLBs) are an important milestone for the future of energy storage because of their capability of impressive energy density and outstanding safety. However, oxide and sulfide solid-state electrolytes (SSEs) suffer from either low ionic conductivity or poor chemical stability. In contrast, halide-based SSEs, are promising as candidate materials owing to high conductivity, good stability, and broad cathode compatibility. Element doping is an effective and common approach to further improve the electrochemical properties of SSEs. For this aspect, a serious of Li3-xIn1-xZrxCl6 were synthesised to explore the influences of zircounium dopant on Li3InCl6
. The synthesized Li2.75In0.75Zr0.25Cl6 exhibited Li ionic conductivity of 5.82 × 10–3 S·cm–1 at room temperature, which is the highest among reported halide SSEs. The ASSLB formed with Li2CoO2-Li2.75In0.75Zr0.25Cl6-Li/In delivers a high initial capacity of 129.3 mAh·g-1. Conclusively, this work provides an effective approach for the development of halide SSEs with improved stability and conductivity. The compelling results provide further possibilities and capabilities in future SSE research.
Stable Anodeless Solid-State Batteries Enabled by Carbon-Metal Based Artificial Interface
Authors: Park Haeseok , Lee Jiwhan , Ko Da Young , Kim Hansu
Published: September 2023

Anodeless system maximizes all-solid-state batteries’ advantages of energy density and stability. Sulfide-based solid electrolytes exhibit high ionic conductivity and processability, but the narrow electrochemical stability window causes electrolyte decomposition. A preferential strategy to suppress electrolyte decomposition is limiting contact area between lithium metal and electrolyte by the introduction of protective layer, such as carbon-metal layer, between the current collector and the sulfide-based electrolyte layer is one example. In this presentation, we report protective capability of carbon only layer and carbon-metal layer using various electrochemical and analytical characterization technics. Cross sectional images of charged, discharged state of these two anodeless systems demonstrate carbon-metal layer could regulate the site for lithium plating and spatially separate the solid state electrolyte and lithium deposited layer. From these results, we will discuss the key parameters for stable operation of Li metal free anode for all solid-state battery systems.
Cathode Development for All Solid-State Lithium-Sulfur Batteries
Authors: Lopez Gonzalez Daniela , Neburchilov Vladimir , Tsay Ken , Gyenge Elod
Published: September 2023

With higher demand for alternative energy sources that are cleaner and more sustainable, research has shifted towards various lithium metal-based batteries with higher capacities than lithium-ion (LIBS). The study of lithium-sulfur energy storage systems has been heavily influenced due to the high gravimetric capacity of sulfur (1672 mA h g−1) and its abundance in the Earth’s crust. To increase the safety of lithium-sulfur batteries, solid state systems have been developed. These systems are also advantageous as the polysulfide shuttle effect normally seen in organic liquid electrolytes (OLEs) is eliminated, decreasing degradation due the irreversible reactions. Some of the most successful electrolytes found for lithium-sulfur all solid-state batteries (ASSLSBs) are ceramic based electrolytes. These electrolytes have high ionic conductivities (ranging 10-3-10-4 S cm-1) and do not pose any safety risks. However, one of the biggest bottlenecks of ASSLSBs is the utilization and accessibility of sulfur during cycling.

To ensure these attributes are met, carbon materials have been used as supports; additionally, carbon also aids in electron transport due sulfur’s low electrical conductivity (10 -15 S m-1).

Sulfur is typically dispersed or deposited on these carbon supports in different approaches before a full cathode composition is developed. Varying synthesis methods of sulfur deposition onto reduced graphene oxide are studied to determine which synthesis method provides the most accessibility for sulfur utilization. Utilization and accessibility will be analyzed through cyclic voltammetry, galvanostatic charge and discharge and impedance measurements to obtain characteristic voltammograms, specific capacity curves and Nyquist plots. Cells are assembled in PEEK Split cells using ceramic based electrolyte and lithium metal for the development of a noble ASSLSB.
Nitrile-Containing Spiro-Twisted Benzoxazines for All-Solid-State Polymer Electrolytes in Lithium-Ion Batteries
Authors: Chen Tzu-Li , Lee Jen-Yu , Wu Tsung-Yu , Wu Nae-Lih (Nick) , Jeng Ru-Jong
Published: September 2023

In this study, we developed new cross-linkable benzoxazine molecules comprising a spiro-twisted core and benzyl cyanide or benzonitrile groups to prepare semi-interpenetrating polymer network (s-IPN) electrolytes. The features of spiro-twisted core and cross-linking network derived from the cured benzoxazines play a crucial role in creating a high free volume and inhibiting the crystallinity. In addition, the incorporation of the nitrile group onto the crosslinked spiro-twisted molecular chains by covalent bonding would certainly enhance the miscibility of SPE membranes with lithium salts while maintaining good mechanical properties. On the other hand, the -CN groups would have more space for rotation and vibration to improve lithium migration owing to the presence of a high fractional free volume of spiro-twisted matrix. Along blending with poly (ethylene oxide) (PEO) electrolytes, a new type of CN-containing semi-interpenetrating polymer networks for solid polymer electrolytes (SPEs) has been achieved.
Characterizing Mg2+ Conduction in Metal-Organic Frameworks
Authors: Wang Yang , Luo Tongtong , Elander Brooke , Mu Yu , Wang Dunwei , Mohanty Udayan , Bao Junwei Lucas
Published: September 2023

Next generation solid-state materials for fast ion conduction have the potential to revolutionize battery technology. Metal-organic frameworks (MOF) are a promising material for achieving this goal. Given their structural diversity and complexity, design of efficient MOF-based ion conductors can be accelerated by detailed understanding and quantitative prediction of ion conductivity. To this end, the chemical behavior and transport properties of an Mg(TFSI)2/DME electrolyte system inside Mg-MOF-74 were studied by a combination of computational and experimental methods.The dominant minimum energy pathway (MEP) for Mg2+ conduction inside Mg-MOF-74 was found to be “solvent hopping” mechanism, with an energy barrier of 4.4 kcal/mol.

However, due to the polycrystalline nature of solid-state materials, specifically MOF-74 in our case, grain boundary effects need to be taken into consideration, which is complicated by challenges in grain boundary characterization, as well as modeling of ensemble transport properties. To address these issues, we developed an approach for modeling ion transport at grain boundaries and predicting their contribution to conductivity. In particular, Mg2+ conduction in Mg-MOF-74 thin film was studied as a representative system. Using computational techniques and guided by experimental data, we investigated the structural details of MOF grain boundary interfaces to determine accessible Mg2+ transport pathways. Computed transport kinetics were input into a simplified model of the MOF nanocrystal, which combined ion transport in bulk structure and at grain boundaries. The model was able to predict Mg2+ conductivity in MOF-74 thin film within chemical accuracy (<1 kcal/mol difference for apparent activation energy), validating our approach. The results indicate that Mg2+ conduction in MOF-74 is inhibited due to strong Mg2+ binding at grain boundaries. Only favorable alignments of the grain boundary interface allow for fast Mg2+ transport through MOF and contribute notably to ion conductivity. The relative scarcity (~0.1% frequency) of these favorable alignments results in a reduction of conductivity by 2-3 orders of magnitude, illustrating the large impact of the grain boundary contribution. Grain boundary structure and its interaction with ions are critical for a molecular-level understanding of solid-state ion transport and quantitative prediction of conductivity.

Our work provides a computation-aided synergistic platform for quantifying the role of grain boundaries in mediating ion transport, which can serve as a complementary characterization tool for the solid-state ion conductor community and providing insights for MOFs’ application in Mg battery area.
(Keynote) The Piezoelectric Effect and Ionic Liquids
Authors: Blanchard Gary J
Published: September 2023

We have studied the response of room temperature ionic liquids to surface charge and had found the establishment of a free charge density gradient, ρf
, in these materials that persists for ca. 50 μm (e-1
depth). We have also applied mechanical force to room temperature ionic liquids with the resulting development of a potential across the ionic liquid when contained in a vessel. These two effects are manifestations the converse and direct piezoelectric effects, respectively. For the converse piezoelectric effect, the induced gradient is seen to be ca. 100 μC/cm3/μm and for the direct piezoelectric effect, the relationship between force applied and potential developed is ca. 16 mV/N. We will discuss the observation of the direct piezoelectric effect in the liquid phase and its possible utility.
(Keynote) Aerogel-Derived Nickel-Iron Oxide Catalysts for Oxygen Evolution Reaction in Alkaline Media
Authors: Osmieri Luigi , Yu Haoran , Myers Deborah J. , Cullen David A. , Zelenay Piotr
Published: September 2023

Low-temperature alkaline water electrolyzers, both liquid alkaline and—more recently—anion exchange membrane (AEM) ones, represent an attractive path towards large-scale generation of green hydrogen, possibly without relying on precious metals, otherwise required by the competing proton exchange membrane (PEM) electrolyzer technology. Of the two alkaline systems, the AEM electrolyzer offers an additional benefit of not needing highly concentrated alkaline solutions and, upon further development, possibly not requiring any electrolyte at all. The ultimate success of the AEM technology will depend though on progress in the development of several key materials: alkaline exchange membranes, electrode ionomers, and platinum group metal-free (PGM-free) electrocatalysts for the anode and the cathode. It will also depend on successful integration of the developed materials into a complete device, aiming especially at well-performing catalyst/membrane and catalyst/ionomer interfaces that are free of significant charge and mass transport losses.

The focus of this work has been on NiFe oxide electrocatalysts for oxygen evolution reaction (OER) for alkaline media in low temperature electrolyzers. The catalysts have been derived from aerogels heat-treated at different temperatures. Depending on the synthesis temperature the catalysts have shown dissimilar OER activities and morphologies, required different activation procedures and incurred diverse structural changes during testing. In addition to extensive performance evaluation in a three-electrode electrochemical cell and a small electrolyzer, the catalysts have undergone wide-ranging physicochemical characterization with the purpose of identifying causes of the differences in their activity and performance durability. Characterization involved among others high-resolution scanning microscopic techniques and electron and X-ray spectroscopy methods (e.g., EELS, XPS, EXAFS/XANES).

Of special interest in this research has been the development and optimization of catalyst activation approaches, both in-situ (in an operating cell) and ex-situ. The effect of ionomer type on catalyst performance and overall performance of NiFe catalysts in electrolyzer-type electrodes has been studied, too, and will be summarized in this presentation.

Acknowledgement

This work has been performed as part of catalyst development efforts in Electrocatalysis Consortium (ElectroCat), funded by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) via Hydrogen and Fuel Cell Technologies Office (HFTO).
(Keynote) Electrochemical CO2 Reduction on NiNC Single Metal Atom Catalysts Under Alkaline to Acidic pH Conditions
Authors: Strasser Peter
Published: September 2023

The science and technology of the direct electrochemical CO2 reduction reaction on both model electrodes in liquid-electrolyte H-cells and Gas Diffusion Electrodes (GDEs) in flow electrolyzers offer as many formidable challenges as intriguing opportunities. Controlling the selectivity (faradaic efficiency), while maximizing the energy efficiency by lowering the kinetic overpotentials remains key to turn this complex reaction into a practical process embedded in a process chain.

In this talk, I will highlight some of our recent advances in the design and characterization of NiNC single site electrocatalysts for the electrochemical reduction of CO2 to CO and CO2/CO mixed feeds into value-added fuels and chemicals in H-cell and Gas Diffusion Electrode (GDE) single cell electrolyzers. Further focus will be placed on the diagnosis of carbonate transport processes during electrolyzer cell operation using the experimentally accessible carbon crossover coefficient, CCC. Performance and its limitations of cell operation in alkaline and acid conditions will be contrasted and discussed.
Reaction Environment Impacts Charge Transfer but Not Chemical Reaction Steps in Hydrogen Evolution Catalysis
Authors: Tang Bryan , Bisbey Ryan , Lodaya Kunal , Lun Toh Wei , Surendranath Yogesh
Published: September 2023

Heterogeneous electrocatalysis involves elementary chemical and charge transfer reaction steps, with the kinetics of each step contributing to the overpotential requirement at a given reaction rate. Typical experiments report on the aggregate rate-overpotential profile with no information about the relative contributions from charge transfer and chemical steps. For the hydrogen evolution reaction (HER), the applied overpotential can be partitioned into a charge transfer overpotential, the overpotential necessary to drive proton-coupled electron transfer (PCET) to and from the surface, and a chemical overpotential, corresponding to a change in surface H activity. Reaction conditions can affect either or both the charge transfer and chemical components. Herein, we employ a Pd membrane double cell to spatially separate the charge transfer and chemical reactions steps of HER catalysis, enabling quantification of the chemical and charge transfer overpotential. We further analyze how each depend on pH, and the introduction of HER poisons and promoters. We find that for a given rate of H2 release, the chemical overpotential is constant across diverse reaction environments whereas the charge transfer overpotential is strongly sensitive to reaction conditions. These findings suggest that reaction condition dependent-HER efficiencies are driven predominantly by changes to the kinetics of charge transfer rather than the chemical reactivity of surface H.
Redox Polymer-Regulated Hysteresis in Ion Current Rectification through AAO Membranes and Single Nanopipettes
Authors: Yang Ruoyu , Kamila Swagatika , Baram Dipak , Wang Gangli
Published: September 2023

Nanopore technology has promising potential in fields such as high-density energy conversion, stochastic chemical sensing, logic operation and neuromorphic computing, separation and fundamental nanoelectrochemistry due to its rich ion transport features and easy fabrication. Understanding the ion transport dynamics at the solid-liquid interface is essential for further technological advancements. Ion current rectification (ICR) and its time-dependent hysteresis have been found to arise from the asymmetric nanointerfaces (geometry, together with surface charges in polarity and density). While various nanostructures can be fabricated and surface charges can be modified, active controls in ICR and hysteresis during transport applications are lacking. Here, we report actively controlled transport hysteresis in ion current rectification though PEDOT-modified single nanopipettes and anodic aluminum oxide (AAO) membranes. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) provides high conductivity and chemical stability, low operating voltages, and enhanced performances in hydrophilicity, processability, and flexibility. The PEDOT:PSS aqueous dispersion is crosslinked inside a nanopipette or assembled onto one side of the AAO surface. Oxidation and reduction reversibly switch the PEDOT between the positive and neutral form, and thus modulate the space charge in nanopores or across the AAO membranes, correspondingly, the ion transport behaviors. The amplitude and polarity of ICR and the scale of hysteresis through a nanopore or AAO membrane have been altered by oxidizing/reducing the PEDOT substrate by adjusting the external electrical field. In contrast, the surface charge varying on pH, ionic strength, and electrolyte type is commonly adopted in ion transport studies but cannot be externally regulated in real-time. Interestingly, negative differential resistance (NDR) is also found in the PEDOT-modified nanopores in simple KCl systems without external pressure differential or concentration gradients. The NDR peak position and magnitude can be easily adjusted by controlling the redox states of the PEDOT fillings.

Figure 1
Role of Electrolyte-Adsorbates Interaction in Determining CO2 Reduction Reaction Pathways
Authors: Morinaga Asuka , Itoine Ryota , Kondo Yasuyuki , Yamada Yuki , Katayama Yu
Published: September 2023

Electrochemical CO2 reduction reaction (CO2RR) is a promising strategy to convert atmospheric CO2 into valuable fuels and chemicals. Although the optimization of the catalyst-adsorbates interaction via tuning the binding energies of electrocatalysts has been extensively studied, activity and product selectivity remain a challenge. Recently, there has been a growing recognition that cations in electrolytes influence the activity of surface electrocatalytic reactions.1 A recent density functional theory study suggested that partially desolvated metal cations stabilize CO2RR intermediates via electrostatic interactions.2 Therefore, an experimental understanding of how the cations (and surrounding water molecules) control the intermediates present on the surface and govern the reaction pathway is critical to establish further insights into the design of electrolytes for CO2RR.

In this talk, the role of alkali metal cations and water molecules on the CO2RR is revealed by tracking the surface-bound intermediates using operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). We will also integrate the operando surface analysis with final product selectivity, further strengthening the understanding of the reaction mechanism. It will also be demonstrated that the holistic information about the electrolyte-adsorbates interaction can provide additional knobs to tune the energetics of key reaction intermediates, leading to further improvements in electrocatalytic activity for the CO2RR.

[Reference]

1 Ringe, S. et al., Energy Environ. Sci.
2019, 12, 3001–3014.

2 Monteiro, MCO. et al., Nat. Catal.
2021, 4, 654–662.
Impact of Catalyst Morphology on the Adsorption and Electrocatalytic Hydrogenation of Benzaldehyde
Authors: Padavala Sri Krishna Murthy , Geng Xin , Luo Long , Stoerzinger Kelsey A
Published: September 2023

Biomass represents an untapped resource for achieving a circular carbon economy. Current processes for converting biomass are limited to centralized processing facilities. Electrochemical approaches are inherently modular and enable decentralized upgrading of pyrolysis oil to value-added chemicals and fuels (products). A primary component of the aqueous phase of such feedstocks are carbonyl functionalities, where benzaldehyde (BZ) represents a model compound. Selective reduction of BZ to benzyl alcohol (BnOH) can be used to understand the catalytic upgrading of pyrolysis oil to value-added products. Electrocatalytic hydrogenation (ECH) of BZ can be carried out at mild temperatures and pressure with the hydrogen required for BZ reduction coming from the protons in the solution. However, these protons can also combine in the hydrogen evolution reaction (HER) in a competitive process. Among the noble and base metals studied in the literature, palladium (Pd) is very active and has demonstrated a high faradaic efficiency (FE) for ECH of BZ relative to HER. Palladium also forms a thermodynamically stable hydride under these conditions. However, prior work has shown that BZ inhibits the formation of palladium hydride under reaction conditions, whereas the presence of weaker adsorbing organics does not. Together, these observations raise interesting questions whether ECH occurs via a proton coupled electron transfer (PCET) pathway or via addition of H from the catalyst surface directly (Langmuir-Hinshelwood, LH pathway). The specific aims of this work investigate the effect of catalyst morphology on the surface coverage of intermediates like H and adsorbed BZ, the relative rates of PCET and LH pathways, and their competition with HER and hydride formation. For this, we investigate high surface area Pd nanoparticle electrocatalysts and a gel network (Pd Gel) of them rich with grain boundaries and strain via cyclic voltammetry. Adsorption isotherms on these Pd catalysts show changes in hydride formation and the relative affinity of H and BZ on the Pd surface. We further study the reaction rate orders and FE as a function of applied potential to better understand the contributions of PCET and LH pathways. These findings point to catalyst morphology as a further handle to manipulate activity and FE for ECH of BZ. Furthermore, these findings will enhance the mechanistic understanding of BZ ECH kinetics and will contribute to improving the overall efficacy of biomass conversion to biofuels.
The effect of strong electric fields in acetonitrile-water mixtures
Authors: Sourpis Anastasios , Forero-Marinez Nancy , Schmid Friederike
Published: September 2023

Electrolyte-free electrolysis fuel cells are central to a sustainable future

with clean water. With growing industrial development, for example, toxic heavy

metals, radioactive ions, and inorganic compounds are increasingly discharged into

the environment and our sources of drinking water. In novel cutting-edge developed

electrolysis fuel cells [1] the case of electrolyte-free electrolysis has been observed for

mixtures of water and acetonitrile. These high modular flow cells of electro organic

synthesis are very promising for the production of fine chemicals and pharmaceutically

active agents. The purpose of this study is to qualitatively and quantitatively evaluate

the effect of electric fields on electrolysis cells. Especially in the case of acetonitrile

and water mixtures, we have focused on understanding by atomistic simulations the

existence of the electrical conductance and how this can be described on larger scales.

References

[1] Highly Modular Flow Cell for Electroorganic Synthesis Christoph Gütz, Andreas

Stenglein, and Siegfried R. Waldvogel Organic Process Research Development 2017 21

(5), 771-778 DOI: 10.1021/acs.oprd.7b00123
(Digital Presentation) Operando x-Ray Emission/Absorption Spectroscopy to Characterize Electronic Structure Changes of Transition Metals in Lithium-Ion Batteries
Authors: Krishnan Abiram , Lee Dong-Chan , Read Ethan , Ahsan Sumaiyatul , Slagle Ian , Alamgir Faisal M.
Published: September 2023

Demand for high-performance rechargeable batteries has driven the development of novel electrodes with high reversibility and energy density. Tracking the change in electronic and local structure is crucial to investigate and improve the stability and performance of these batteries. Advanced characterization techniques allow the user to monitor electronic and local atomic structure changes to better understand the role and behavior of different elements during cycling of electrode material for rechargeable batteries.

X-ray Absorption and Emission Spectroscopy allow us to explore such changes in 3d transition metal elements through the process of generation and quenching of core holes in the sample. Operando measurements enable real-time monitoring of electronic structure changes in electrode materials which enable us to capture phenomena which are only kinetically accessible.

In this study, the change in electronic structure of transition metals present in electrode materials is explored as a function of lithium removal through XES Kβ1,3feature along with K-edge XAFS using a lab-scale instrument. The choice of electrodes explored in this study considers the degree of oxidation, structure, and mechanism for ion storage. Change in peak and edge positions of Kβ1,3and K-edge feature is utilized to monitor oxidation/spin changes in electrode materials during charge/discharge. Further the magnetic behavior for ex-situ samples prepared by electrochemical delithiation of LCO in the range of 2-10% delithiation is investigated using Kα and Kβ fluorescence (spin sensitive) followed by K-edge XAFS for Cobalt and Oxygen.

Figure 1
Field Deployable Sensor Arrays with Molecular Selectivity for Soil Health
Authors: Zhao Yaoli , Ranade Gayatri , Tidwell Michael , Neste Charles Van , Thundat Thomas
Published: September 2023

Monitoring soil health is very important in agriculture. Soil health can be monitored by the sensing the metabolomic activities of microbiota as increased concentrations in CO2, CH4, N2O, vapors in the soil. A vapor sensor based on microfabricated cantilever array is an ideal sensor platform for field deployable miniature sensors. Many such platforms, such as cantilever arrays, have been demonstrated as sensitive sensors for chemical and biological detection. In fact, the array-based sensor platform satisfies almost all of the requirements of an ideal high-performance sensor, such as its very high sensitivity, miniature size, array based multi-analyte detection, and low power consumption. However, poor molecular selectivity, especially for small molecules at trace level, as well as the lack of reproducibility, pose formidable challenges in translating this highly sensitive sensor platform into a practical reality. Traditionally, selectivity in chemical and biological sensing is achieved by using immobilized receptors or chemical interfaces on sensor surfaces. While poor selectivity in small molecule detection using reversible receptors is due to the lack of uniqueness of receptor-analyte interaction, nonuniformity in the immobilized receptor graft density is the reason for unacceptable rates of reproducibility in these sensors. We have used a multi-modal, multi-physics approach in overcoming these challenges. Multi-modal data when analyzed using deep learning techniques, show enhanced selectivity, sensitivity, and reliability. In order to operate these sensors in a field-scale study, a long range through-the-soil (TTS) wireless power transfer method is developed. Energy from an adjacent solar panel array is distributed wirelessly via conduction currents that propagate outward along and through the soil. Power transfer within a 0.25-ha (0.6acre) area is demonstrated using an average input power of 6W.This research is supported by NSF-SitS Award Nos. 2226614 and 2226612
Tailoring Geometry of Large-Area Hexagonal Close-Packed Plasmonic Nano-Array Structures for Biosensing
Authors: Wang Anyang , Hang Yingjie , Tan Weirui , Wang Anyang
Published: September 2023

Generally, a large area of plasmonic nanoarray patterns are employed for biosensing. Electromagnetic (EM) field and Quality-factor (Q-factor, the ratio of the resonance wavelength over its bandwidth) of plasmonic patterns, are important to the sensitivity of plasmon-enhanced biosensors, for example, fluorescence and surface enhanced Rama spectroscopy (SERS) biosensors. Hexagonal close-packed plasmonic nanostructures arranged in nano-disk, nano-ring, nano-disk/ring patterns are prevailing configurations using batch processes (e.g., anodic aluminum oxide (AAO)). Different patterns due to size/geometry difference can have different Q-factors. However, the geometry effect on Q-factor in such configurations is not clear. Therefore, we adopted Finite-difference time-domain (FDTD) simulation to numerically study how EM field and Q-factor are modulated by geometric design of large-area hexagonal close-packed gold disk/ring structures. The simulation results provide guidelines to increase Q-factor to improve the sensitivity of plasmon-enhanced biosensors.
Reversible Intercalation of Protons in Tungsten Oxide Films for Multi-Transduction Sensor Applications
Authors: Schwellberger Barbosa Martin , da Silva Ranilson Angelo , Orlandi Marcelo O.
Published: September 2023

Tungsten oxide films under electrochemical bias, can form tungsten oxide bronzes (MxWO3 with M being small cations such as H+ or Li+) featuring high electronic conductivity and change in coloration to deep blue1. This doping process occurs through the reduction of W6+, as described by the following equation:

WO3 + x H+ + xe- -> HxWO3

The bronze phase can also be formed through exposure of tungsten oxide to H2 at high temperatures (> 200 oC) or in presence of catalysts2, as described by the following equation:

WO3 + x/2 H2 -> HxWO3

Because of the significant changes in both optical and electrical proprieties of the films, electrochemical control of proton doping can be used as a strategy for the development of ion-gated transistors3,4, hydrogen sensors and smart windows5.

In this work, we report the use of thin films prepared by sol-gel synthesis using polyperoxotungstic acid (PPTA) as a precursor. We used three different types of substrates (conductive transparent fluorine-doped tin oxide (FTO) glass, Si/SiO2 patterned with Au source-drain electrodes and Interdigitated electrodes patterned on transparent glass) to study the changes of color and conductivity following the formation of the bronze in both electrochemical and dry environments. In electrochemical environment, we show that gating by ionic liquid in transistor configuration can be used to propose an iontronic sensor to detect H2 and H2O6. In dry environment, we show that simultaneous monitoring of visible light transmittance and electrical conductivity can be used a double transducer for H2 sensors6.

1 M. S. Whittingham, in Solid State Ionics, 2004, vol. 168, pp. 255–263.

2 C. C. Chan, W. C. Hsu, C. C. Chang and C. S. Hsu, Sensors and Actuators, B: Chemical, 2011, 157, 504–509.

3 M. Barbosa, X. Meng, F. Soavi, C. Santato and M. O. Orlandi, J Mater Chem C Mater, 2018, 6, 1980–1987.

4 G. V. de Oliveira Silva, A. Subramanian, X. Meng, S. Zhang, M. S. Barbosa, B. Baloukas, D. Chartrand, J. C. Gonzáles, M. O. Orlandi, F. Soavi, F. Cicoira and C. Santato, J Phys D Appl Phys,

5 G. Cai, J. Wang and P. S. Lee, Acc Chem Res, 2016, 49, 1469–1476.

6 M. S. Barbosa, R. A. da Silva, C. Santato and M. O. Orlandi, Journal of Vacuum Science & Technology A, 2022, 40, 013202.
Surfactant-Assisted Synthesis of Bismuth Oxychloride Nanoflowers for Electrochemical Sensing of Heavy Metal Ions
Authors: Fratto Edward S. , Li Cuilei , Yang Zhengyang , Joens Mary , von Boecklin Matthew , Gu Zhiyong
Published: September 2023

Heavy metal ion contamination of drinking water is a significant, invisible threat to public health which requires active and decentralized monitoring with high sensitivity, accuracy and reliability. The government and regulatory agencies actively survey and maintain established limits on heavy metal contamination, but generally prioritizing localized hotspots in high-risk communities. Their characterization techniques are typically expensive and inaccessible to the public, requiring specialized training and extended sample shipping times, with a purview restricted to public infrastructure. As plumbing systems corrode and contaminants leach into drinking water systems, independent means of oversight are becoming increasingly vital in effectively identifying and mitigating toxic exposure. In this work we propose the development and application of a high surface area bismuth oxychloride nanoflower for the electrochemical detection of zinc and lead ions in drinking water. The flower structure was synthesized via hydrolysis of bismuth chloride salt in a micellar environment of sodium dodecyl sulfate, followed by aqueous chemical reduction and transformation to metallic bismuth. The size and uniformity of the synthesized nanoflower was characterized with scanning electron microscopy (SEM), and the composition and microstructure were investigated using energy dispersive x-ray spectroscopy (EDS) analysis and x-ray diffraction (XRD). The nanoflowers were deposited onto a glassy carbon electrode and coated with a protective Nafion layer, prior to cyclic voltammetry analysis of analyte ion reactivity, achieving detection of lead and zinc ions in buffer and practical drinking water samples. These results indicate the viability of bismuth-based nanoflower structures for portable, accessible detection of heavy metal ions, with enhanced sensitivity.