In-plane Conductivity Research Articles

Robust Porous TiN Layer for Improved Oxygen Evolution Reaction Performance.

The poor reversibility and slow reaction kinetics of catalytic materials seriously hinder the industrialization process of proton exchange membrane (PEM) water electrolysis. It is necessary to develop high-performance and low-cost electrocatalysts to reduce the loss of reaction kinetics. In this study, a novel catalyst support featured with porous surface structure and good electronic conductivity was successfully prepared by surface modification via a thermal nitriding method under ammonia atmosphere. The morphology and composition characterization-confirmed that a TiN layer with granular porous structure and internal pore-like defects was established on the Ti sheet. Meanwhile, the conductivity measurements showed that the in-plane electronic conductivity of the as-developed material increased significantly to 120.8 S cm−1. After IrOx was loaded on the prepared TiN-Ti support, better dispersion of the active phase IrOx, lower ohmic resistance, and faster charge transfer resistance were verified, and accordingly, more accessible catalytic active sites on the catalytic interface were developed as revealed by the electrochemical characterizations. Compared with the IrOx/Ti, the as-obtained IrOx/TiN-Ti catalyst demonstrated remarkable electrocatalytic activity (η10 mA cm−2 = 302 mV) and superior stability (overpotential degradation rate: 0.067 mV h−1) probably due to the enhanced mass adsorption and transport, good dispersion of the supported active phase IrOx, increased electronic conductivity and improved corrosion resistance provided by the TiN-Ti support.

Constructing three-dimensional conductive network in composite bipolar plates by sacrificial materials for improvement of proton exchange membrane fuel cell performance

The poor conductivity of traditional polymer-based composite bipolar plates (BP) greatly hinders its wide application in proton exchange membrane fuel cell (PEMFC). Three-dimensional conductive network in composite BP can significantly improve its performance. In this work, we propose a simple strategy to prepare an epoxy resin-based composite BP by sacrificial materials, forming a three-dimensional graphite structure (3D-graphite). Specifically, graphite and NH4HCO3 are mixed and pressed at room temperature, and heated at 90 °C to obtain 3D-graphite skeleton. Then, the 3D-graphite skeleton is impregnated by epoxy resin to obtain 3D-graphite/epoxy composites. The construction of 3D-graphite conductive network can greatly improve the electrical conductivity of composite BP. The highest in-plane conductivity is 212.64 S/cm, and area specific resistance is 4.50 mΩ cm2. The thermal conductivity can reach 16.01 W/mK, superior to the randomly distributed graphite/epoxy composite BP. Compared with the traditional mixed graphite/epoxy composite BP, 3D-graphite/epoxy composite BP can significantly improve the performance of PEMFC and its maximum power density (853.42 mW/cm2) is increased by 317.52%. In addition, 3D-graphite/epoxy composite BP has good corrosion resistance and hydrophobicity. This work develops a new paradigm for preparing highly performance polymer-based composite bipolar plates for PEMFC.

(Digital Presentation) Development of Composite Graphite Plate with Multiple Functional Layers for Pemfc

Composite graphite plates (CGPs) have attracted interest due to competitive benefits such as cheaper cost, lower density, and excellent corrosion resistance. Their mechanical and electrical qualities, on the other hand, are insufficient to meet the PEMFC's standards. In this study, a structural design of CGPs with different functional layers is proposed. In order to attain higher electrical conductivity and air tightness, the surface layer was molded graphite plate with resin infiltration treatment, and the middle layer was a carbon fiber fabric (CFF) as a reinforcing functional layer. The results show that the surface layer prepared from flake graphite (FGL) have a density of 2.1 g/cm3, while the surface layer made by expanded graphite (EGL) have a density of about 1.7 g/cm3 with higher porosity. As a result, the CGPs prepared by using FGL as the surface layer has higher airtightness and structural strength. The CFFs must be oxidized to promote the effective bonding with resin, and the addition of carbon nanotubes (CNTs) can effectively improve the interfacial bonding and reduce the area specific resistance (ASR). At a resin content of 20 wt.% with 2 wt.% CNTs in resin, a CGPs with multilayer construction possess a thickness of 0.4 mm, an in-plane conductivity of 446 S/cm, an ASR of 6.4 mΩ·cm2, a flexural strength of 72 MPa, and a Helium permeability of around 4.4*10-6 std cm3/cm2·s. In addition, the graphite particle size has a significant effect on the electrical conductivity, and the analysis on the cross-sectional morphology of the surface layer indicated that this is primarily due to the anisotropic properties of graphite, with larger particle tends to be more orderly distributed after compression resulting in higher in-plane conductivity.

Manipulation of Anode Nanostructure and Composition By Glancing Angle Deposition for Thin-Film Solid Oxide Fuel Cells

Co-sputtering is a simple yet effective technique for fabricating a thin film of composite materials and different compositions by adjusting the electrical power of each sputtering target. However, practical issues arise when depositing cermet materials such as Ni-YSZ and Ni-GDC because of the contrasting characteristics of metal and ceramic sputtering targets. For example, the surface binding energy of GDC is significantly higher than that of Ni, resulting in a considerably lower sputtering yield of GDC. The difference in sputtering yield is further exacerbated by the low power density limit of the GDC target, which is set by its unfavorable material properties such as brittleness and low thermal conductivity. In contrast, due to its magnetic property, Ni requires sufficiently high sputtering power during magnetron sputtering.This work combines co-sputtering with advanced sputtering techniques such as glancing angle deposition (GLAD) and oblique angle deposition (OAD) to fabricate otherwise unobtainable Ni-GDC anode microstructure with various compositions. Reduced flux capture area of Ni caused by the high incident angle of GLAD allowed control of thin-film compositions, and optimal composition was determined based on fuel cell performance and electrochemical impedance spectroscopy (EIS) analysis. A sufficient amount of GDC was necessary to expand the triple-phase boundary (TPB) and suppress the thermal agglomeration of highly mobile Ni.The effect of electrode nanostructure on fuel cell performance was also investigated. The ballistic shadowing effect during OAD was utilized to produce thin-film electrodes with various porosities. With the increase of the deposition angle, the porosity increased, whereas the in-plane electrical conductivity decreased due to the reduced density. The columnar structure was also manipulated by managing the substrate position through azimuthal rotation. As a result, various columnar structures such as vertical posts, slanted posts, and zig-zag were fabricated, and the optimal microstructure was determined via electrochemical examinations.

Effect of micro-cracks on the in-plane electronic conductivity of proton exchange membrane fuel cell catalyst layers based on lattice Boltzmann method

Micro-cracks commonly occur on the catalyst layers (CLs) during the manufacturing of catalyst coated membranes (CCMs). However, the crack shape parameters effect on CLs in-plane (IP) electronic conductivity λs is not clear. In this work, the relationship between crack parameters and the λs is obtained based on the two-dimensional (2D) multiple-relaxation time (MRT) lattice Boltzmann method (LBM). The LBM numerical model is validated by the normalized λs experiment applied on three different home-made cracked CLs, and the parameter study focus on crack width, length, quantity and phase angle are carried out. The results show that the decrease of λs has different sensitivity |k| to the parameters above. The crack width has little effect on λs decrease, and the |kw| is 0.038. However, crack arm length and quantity show more significant impact, which |kl| and |kN| are 0.753 and 0.725, respectively. The CLs with different crack propagation directions show significant anisotropy on λs, and a 53.53% decrease in λs is observed between 0° and 90° crack phase angle change. To manufacture a high electronic conductivity CL, crack initiation and migration mitigation are highly encouraged.

Multifunctionality of Li2 SrNb2 O7 : Memristivity, Tunable Rectification, Ferroelasticity, and Ferroelectricity.

Layered Li2 SrNb2 O7 , an inorganic oxide in its bulk single-crystalline form, is experimentally demonstrated to exhibit multiple structural facets such as ferroelasticity, ferroelectricity, and antiferroelectricity. The transition from a room temperature (RT) centrosymmetric structure to a low-temperature out-of-plane ferroelectric and in-plane antiferroelectric structure and the low-temperature (LT) ferroelectric domain configuration are unveiled in TEM, piezoresponse force microscopy, and polarization loop studies. Li2 SrNb2 O7 also exhibits highly tunable ferroelasticity and excellent Li+ in-plane conduction, which leads to a giant in-plane memristor behavior and an in-plane electronic conductivity increase by three orders of magnitude by electric poling at room RT). The accumulation of Li+ vacancies at the crystal-electrode interface is visualized using insitu optical microscopy. The Li-ionic biased state shows a clear in-plane rectification effect combined with a significant relaxation upon time at RT. Relaxation can be fully suppressed at LTs such as 200K, and utilizing an electric field cooling, a stable rectification can be achieved at 200K. The results shed light on the selective control of multifunctionalities such as ferroelasticity, ferroelectricity, and ionic-migration-mediated effects (a memristor effect and rectification) in a single-phase bulk material utilizing, for example, different directions, temperatures, frequencies, and magnitudes of electric field.

(Digital Presentation) Development of Composite Graphite Plate with Multiple Functional Layers for Pemfc

The bipolar plate is an important component of the proton exchange membrane fuel cell (PEMFC) and composite graphite bipolar plates (CGBPs) have attracted interest due to competitive benefits. However, their mechanical and electrical qualities are insufficient to meet the PEMFC's standards. In this study, a structural design of CGBPs with different functional layers was proposed. The surface layer was molded graphite plate with resin infiltration treatment, and the middle layer was a carbon fiber fabric (CFF) as a reinforcing functional layer. The results showed that the surface layer prepared from flake graphite possessed denser structure, leading to higher airtightness and structural strength. The addition of carbon nanotube or graphene nanoplate could enhance the combination between CFF and resin observably, making CGBPs possessed an in-plane conductivity of 446 S/cm, an area specific resistance of 6.4 mΩ·cm2, a flexural strength of 72 MPa, and a Helium permeability of around 4.4×10-6 std cm3/cm2·s.

Anisotropic ionic transport properties in solid PEO based electrolytes

Solid polymer electrolytes (SPE) based on dry poly(ethylene oxide) (PEO) are interesting candidates to develop solid-state lithium (Li) batteries thanks to their stability toward Li metal anode, mechanical properties and flexibility, as well as ionic conductivity high enough for a battery application at temperatures higher than the PEO melting temperatures. To optimize the ionic conductivity, one strategy is to favor in-plane conductivity thanks to its typical higher value in PEO homopolymer electrolyte compared to the through-plane one. Thus, there is the need to understand the in-plane ionic transport properties (ionic conductivity, transference number, and diffusion coefficient) of SPEs depending on their nature and architecture. Indeed, ionic transport in PEO based SPE is due to a complex interplay between different local mechanisms involving the interaction between the PEO chain segments and both cations and anions. The separation of the cationic and anionic mechanisms is thus necessary to distinguish their contributions on the ionic transport anisotropies. Here, we report on the determination by electrochemical methodologies of the cationic and anionic in-plane ionic conductivities, transference numbers and restricted diffusion coefficients for a series of SPEs made of PEO homopolymers (linear), composite (PEO with the addition of nanocellulose), binary (PS-PEO-PS) and single-ion (PSTFSI-PEO-PSTFSI) conducting triblock copolymer electrolytes. The methodology to get each parameter is presented and discussed while COMSOL simulations permit to take into account the geometries of the in-plane cell (positions of the electrodes and SPE dimension). In addition, an analytical model is presented to fit the experimental data of the in-plane cell relaxation (diffusion regime) with a simple equation to determine the in-plane ambipolar diffusion coefficient. We observed that the in-plane anionic transport in SPEs is strongly hindered by the presence of structural blocks leading to an overall in-plane conductivity lower than the through-plane one.

Vibro-acoustic characteristics of multifunctional carbon fiber reinforced panel

This paper deals with the assessment of vibro-acoustic properties of a multifunctional carbon fiber reinforced panel manufactured by bulk infusion, a modified resin film infusion process. The components of the epoxy resin were chosen to contrast the electrical insulating property and poor flame resistance of the epoxy resins impregnating carbon woven fabric. To confer electrical conductivity to the resin a percentage of 0.5 wt% of Multi-Wall Carbon Nanotubes (MWCNTs) was dispersed in the resin, whereas to increase flame resistance a percentage of 5 wt% of Glycidil Polyhedral Oligomeric Silsesquioxanes (GPOSS) was solubilized in the epoxy mixture. Furthermore, as hardener agents, a mixture of 4,4’-DiaminoDiphenyl Sulfone (DDS) (53.4 wt%) and Bis(3-Aminophenyl) Methyl Phosphine Oxide (BAMPO) (46.7 wt%) was used. The values of the electrical conductivity were found satisfactory enough, being 4.02 × 10−2 S/m for the multifunctional resin and 1.39 × 104 S/m for the in-plane conductivity of the panel, whereas the Limiting Oxygen Index (LOI) value of the multifunctional resin was found to increase from 27% to 36%. Considering these promising results, an experimental assessment of the vibro-acoustic properties of the manufactured multifunctional panel was also performed. The panel was tested mainly to evaluate its low-frequency vibration damping and sound insulation characteristics. The manufactured panel demonstrated an improved efficiency if compared to a baseline configuration, presenting almost the double modal damping and a gain of 10 dB on the global noise reduction.

Understanding the in-plane electron transport in low noble metal proton exchange membrane water electrolyser

Reducing noble metal loading in membrane electrode assembly (MEA) can lower the cost of proton exchange membrane (PEM) water electrolyser, but it always leads to performance decline. In-plane conductivity of catalyst layer is mentioned very critical to the cell performance, and it is necessary to fully understand the role of planar electron transportation of catalyst layer. Herein, a bilayer cathode which consists of catalyst layer and planar electron conductive layer is developed to investigate the role of in-plane electron transportation. The additional planar electron conductive layer can significantly improve the performance of the cathode under low noble metal loading. The ohmic polarization as well as the active overpotential are reduced. The results highlight the benefit of bilayer structure and provide a method for enhancing the performance even though the catalyst layer is less homogeneous. Moreover, it can be also used to guide the design of cost-effective anode.

Nanostructured La0.75Sr0.25Cr0.5Mn0.5O3-Ce0.8Sm0.2O2 Heterointerfaces as All-Ceramic Functional Layers for Solid Oxide Fuel Cell Applications.

The use of nanostructured interfaces and advanced functional materials opens up a new playground in the field of solid oxide fuel cells. In this work, we present two all-ceramic thin-film heterostructures based on samarium-doped ceria and lanthanum strontium chromite manganite as promising functional layers for electrode application. The films were fabricated by pulsed laser deposition as bilayers or self-assembled intermixed nanocomposites. The microstructural characterization confirmed the formation of dense, well-differentiated, phases and highlighted the presence of strong cation intermixing in the case of the nanocomposite. The electrochemical properties—solid/gas reactivity and in-plane conductivity—are strongly improved for both heterostructures with respect to the single-phase constituents under anodic conditions (up to fivefold decrease of area-specific resistance and 3 orders of magnitude increase of in-plane conductivity with respect to reference single-phase materials). A remarkable electrochemical activity was also observed for the nanocomposite under an oxidizing atmosphere, with no significant decrease in performance after 400 h of thermal aging. This work shows how the implementation of nanostructuring strategies not only can be used to tune the properties of functional films but also results in a synergistic enhancement of the electrochemical performance, surpassing the parent materials and opening the field for the fabrication of high-performance nanostructured functional layers for application in solid oxide fuel cells and symmetric systems.

Ultra-thin corrugated metamaterial film as large-area transmission dynode

Large-area transmission dynodes were fabricated by depositing an ultra-thin continuous film on a silicon wafer with a 3-dimensional pattern. After removing the silicon, a corrugated membrane with enhanced mechanical properties was formed. Mechanical metamaterials, such as this corrugated membrane, are engineered to improve its strength and robustness, which allows it to span a larger surface in comparison to flat membranes while the film thickness remains constant. The ultra-thin film consists of three layers (Al2O3/TiN/Al2O3) and is deposited by atomic layer deposition (ALD). The encapsulated TiN layer provides in-plane conductivity, which is needed to sustain secondary electron emission. Two types of corrugated membranes were fabricated: a hexagonal honeycomb and an octagonal pattern. The latter was designed to match the square pitch of a CMOS pixel chip. The transmission secondary electron yield was determined with a collector-based method using a scanning electron microscope. The highest transmission electron yield was measured on a membrane with an octagonal pattern. A yield of 2.15 was achieved for 3.15 keV incident electrons for an Al2O3/TiN/Al2O3 tri-layer film with layer thicknesses of 10/5/15 nm. The variation in yield across the surface of the corrugated membrane was determined by constructing a yield map. The active surface for transmission secondary electron emission is near 100%, i.e. a primary electron generates transmission secondary electrons regardless of the point of impact on the corrugated membrane.

Origin of oscillatory structures in the magnetothermal conductivity of the putative Kitaev magnet α-RuCl3

The layered honeycomb magnet α-RuCl3 has been suggested to exhibit a field-induced quantum spin liquid state, in which the reported large thermal Hall effect close to the half-quantized value still remains a subject of debate. Recently, oscillatory structures of the magnetothermal conductivity were reported and interpreted as quantum oscillations of charge-neutral particles. To investigate the origin of these oscillatory structures, we performed a comprehensive measurement of the in-plane magnetothermal conductivity κ(H) down to low temperature (100 mK), as well as magnetization M, for single crystals grown by two different techniques: Bridgman and chemical vapor transport. The results show a series of dips in κ(H) and peaks in the field derivative of M located at the same fields independent of the growth method. We argue that these structures originate from the field-induced phase transitions rather than from quantum oscillations. The positions of several of these features are temperature-dependent and connected to the magnetic phase transitions in zero field: the main transition at 7 K and weaker additional transitions, which likely arise from secondary phases at 10 K and 13 K. In contrast to what is expected for quantum oscillations, the magnitude of the structure in κ(H) is smaller for the higher conductivity crystal and decreases rapidly upon cooling below 1 K.

Effect of Electron–Phonon Interaction and Ionized Impurity Scattering on the Room-Temperature Thermoelectric Properties of Bulk MoSe2

We study the thermoelectric properties of bulk $MoSe_2$ within relaxation time approximation including electron-phonon and ionized impurity interactions using first-principles calculations at room temperatures. The anisotropy of this two-dimensional layered metal dichalcogenide is studied by calculations of electron mobility in the cross-plane and the in-plane directions. We show that the cross-plane mobility is two orders of magnitude smaller than the in-plane one. The inclusion of van der Waals interactions further lowers the carrier mobility in the cross-plane direction but minimally affects the in-plane one. The results for in-plane electrical mobility and conductivity are in close agreement with experimentally reported values indicating the accuracy of the calculations. The Seebeck coefficient calculations show that this coefficient is primarily dictated by the band structure. The details of relaxation times and inclusion of van der Waals interactions only slightly change the Seebeck coefficient. The in-plane thermoelectric power factor reaches a maximum value of 20 $\mu Wcm^{-1}K^{-2}$ at a carrier concentration of $1.5x10^{20}$ $cm^{-3}$ at 300K.

Mechanism of photo-ionic stoichiometry changes in SrTiO3

The impact of UV light (λ = 365 nm) on defect chemistry and composition of undoped SrTiO3 single crystals was investigated by means of impedance spectroscopy. In-plane conductivity measurements between 280 and 450 °C in air reveal a drastic increase of the bulk conductivity upon UV illumination. The measured time dependence of this increase is in accordance with oxygen chemical diffusion in SrTiO3. The corresponding photo-induced change in defect concentrations is caused by oxygen being pumped from the gas phase into the oxide under UV irradiation. This affects the entire SrTiO3 crystal rather than only the thin UV absorption zone and leads to very high oxygen chemical potentials with nominal oxygen pressures up to 106 bar. After switching the UV light off, the resulting conductivity increase relaxes extremely slowly due to slow surface exchange kinetics. A mechanistic model is introduced to explain the impact of UV light on the oxygen chemical potential as well as on the oxygen vacancy and hole/electron concentrations in semiconducting oxides, here SrTiO3. This model is based on the formation of oxygen quasi-chemical potentials in the illuminated region. It is discussed how the interplay of four kinetic parameters causes the observed time-dependent stoichiometry and thus conductivity changes.

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories

Rainer Waser – A Pioneer of Fundamentals of Resistive Switching Memories

How Electrochemical Impedance Spectroscopy Helps Drive Innovation in Fully Hydrocarbon, Reinforced Polymer Electrolyte Membranes

The realm of hydrocarbon-based polymer electrolyte membranes (PEMs) has undergone substantial changes over the past decade. A new era has emerged, based upon strong, fundamental R&D emphasizing both improved performance across a wider range of operating conditions, and greater combined chemical-mechanical stability, when integrated into a state-of-the-art fuel cell. The groundwork has been laid for commercialization of highly promising, fluorine-free technologies which simultaneously outperform previous generation materials, and address weaknesses historically attributed to all hydrocarbon-based membranes. Hydrocarbons address critical issues with perfluorinated sulfonic acid (PFSA) materials. Reduced gas crossover allows longer component lifetimes, operational window for system pressures, and reduced hydrogen venting. Higher temperature tolerances allow system operation or excursions to ≥ 100 °C, which affords a myriad of potential benefits such as reduction in heat exchanger volume, improved system water management, and increased catalyst activity due to mitigated activation losses. Furthermore, higher operating temperatures go hand-in-hand with greater pollution tolerance, and hence reduced hydrogen purity requirements.The award-winning hydrocarbon-based PEM, Pemion®, produced by Ionomr Innovations, is nested at the center of these exciting developments. Mechanically reinforced composite membranes are produced at scale utilizing advanced roll-to-roll manufacturing techniques, affording a hydrocarbon-based PEM that, for the first time, exhibits performance parallel to or greater than incumbent perfluorinated sulfonic acid (PFSA)-based PEMs. These developments, however, would not be possible without powerful characterization methods such as electrochemical impedance spectroscopy (EIS). Assessments of a membrane’s in-plane and through-plane proton conductivity are used to derive valuable insight to its constituents, the ion-conducting ionomer and chemically-inert mechanical reinforcement, as well as their interrelation. The anisotropic nature of the composite membranes is probed via comparison of in-plane and through-plane conductivity. The sensitivity of through-plane conductivity measurements to experimental parameters such as cell pressure are probed, and a new cell design is realized to reduce measurement error. These data help identify favorable and unfavorable material processing and manufacturing techniques, and their implications to in-situ fuel cell performance. The net consequence of these findings is establishing EIS as a core component of an iterative material design and production process for output of consistent, high-performance PEMs.

A Path to Significant Reduction of the Interfacial Contact Resistance of Sintered Titanium Porous Transport Layers in Advanced Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWEs) are a leading industry solution to large scale production of green hydrogen, and as a form of energy storage [5]. The PEMWEs have the advantages of having greater energy efficiency, higher product purity, and are environmentally friendly. Within the construction of a PEMWE stack, there are many catalysts coated membranes (CCMs) sandwiched between anode porous transport layers (PTLs) and cathode Gas Diffusion Layers. The PTL is constructed of sintered titanium powder or fibers. The Ti-PTL is on the anode side of a PEMWE cell where the water diffuses towards the CCM. The anode half-cell reaction or oxygen evolution reaction (OER) occurs on this side of the cell. This is important as the PTL is in contact with the bipolar plate (BPP) and the anode catalyst layer [9].A key aspect plaguing the PEMWEs is the highly oxidative and corrosive environment that is typically observed on the anode side. This significantly affects the interfacial contact resistance (ICR) of the components as the corrosion can cause the ohmic resistance of the PTL to increase. In order to combat the corrosion in the PTLs, in this work we use two thin film deposition methods, Physical Vapor Deposition (PVD) and Vacuum Sputtering, to deposit protective metal layers on top of the state-of-the-art Ti PTLs [2]. The explored metal coatings of interest are Platinum (Pt) and Gold (Au) [9]. For the purposes of these experiments, Au and Pt coatings with various thicknesses are deposited on Ti-PTLs by using either PVD or vacuum spattering method. As deposited thin films are characterized by scanning electron microscopy (SEM), digital optical microscopy, and inductively coupled plasma (ICP) analysis. Also, the in-plane conductivity and the ICR of all samples of interest are measured before and after the electrochemical tests by using the 4-probe method and in-house build setup for ICR measurements. The optimal deposition parameters for fabrication of thin, continuous and smooth Pt and Au protective coatings that result in minimum ICR and improved in-plane conductivity of the PTLs of interest are identified, and the results will be reported at the ECS 241 meeting.

(Invited) Design, Performance Characterization, and Durability of an Iridium-Based OER Catalyst for PEM Water Electrolysis

One of the building blocks to transition to a fully renewable energy supply is the utilization of hydrogen as a replacement of fossil fuels and as a chemical energy storage/carrier medium. This requires the economical and sustainable generation of hydrogen by water electrolysis, whereby proton exchange membrane (PEM) water electrolyzers would enable much higher power densities compared to conventional electrolyzers based on liquid alkaline electrolytes [1]. However, one of the short-comings of PEM water electrolyzers (PEMWEs) is the need for expensive and resource-limited iridium based catalysts for the oxygen evolution reaction (OER), so that the large-scale global deployment of PEMWEs would require a substantial reduction of the iridium loading from currently ~1-2 mgIr/cm2 elelctrode to below ~0.05 mgIr/cm2 elelctrode [2].In this contribution, we will discuss the technical challenge to reduce the iridium loading using currently employed iridium catalysts, which is related to the high iridium packing density in the electrode (in units of gIr/cm3 electrode), so that for iridium loadings below ~0.4 mgIr/cm2 the electrode becomes too thin to allow for a homogenous electrode with sufficient in-plane electrical conductivity [3]. We will then present a catalyst concept that results in much lower iridium packing densities and that thus enables lower iridium loadings [4]. While such a catalyst exhibits a lower electrical conductivity than a currently employed benchmark catalyst, this drawback can be mitigated by utilizing porous transport layers at the anode that have a highly conductive coating [4]. The long-term stability of this novel type of iridium based OER catalyst will be examined in a 30 cm2 active area short-stack over ~3700 h; comparing the evolution of the OER mass activity and of the high frequency resistance corrected cell voltage with that of a benchmark catalyst that is evaluated in the same short-stack, which allows for mechanistic insights into the observed degradation rates [5].

Operando Tracking of Ionic and Electronic Percolation in Electrodes for Energy Storage Application Using AC-in Plane Impedance

Achieving efficient electronic and ionic electrode percolation is one of the most important parameters to improve batteries and supercapacitors power performance. Various electrical and electrochemical techniques (Cyclic voltammetry, Electrochemical Impedance Spectroscopy, EQCM, SECM, in-situ XRD, etc) can be used to assess the electronic and ionic transport properties in these electrodes. However, there are only few studies and techniques on tracking the change in resistance of an electrode during electrochemical polarization [1, 2, 3], which plays a key-role on its electrochemical performance.In this study, we propose a new method to achieve operando resistance measurement under alternative current (AC), that we’ll call in-plane impedance measurement, under bias potential. In these experiments, the electrodes are deposited onto an insulating substrate so that, differently from conventional electrochemical impedance spectroscopy experiments, here the electrode in-plane conductivity is measured. Moreover, this method allows for distinguishing the ionic part of the in-plane electrode impedance from the electronic part that appears at high and low frequencies, respectively.In this work, in-plane electronic and ionic transport properties of porous carbon (YP50F) and MXene (Ti3C2) electrode are studied while being fully charged or. During polarization, both the ionic and electronic percolation change with the applied potential for both electrode, that could be associated with electrode volume and conductivity change under potential and/or because of some doping caused by ionic specific electrosorption. This operando in-plane impedance measurement method furthers the fundamental understanding of ionic and electronic transport properties and may turn out to be effective tool to improve the electrochemical performances of capacitive, pseudocapacitive, or battery-like electrodes.