Electrode Setup Research Articles

Analysis of Kinetic and Ohmic Resistances in PEM Water Electrolysis through Reference Electrode Measurements

We investigated a three electrode setup utilized in a temperature variation study to extract the activation energy for the half-cell reactions in PEM water electrolysis and the contributions of electronic resistances to ohmic resistance. The reference electrode configuration used in this investigation is an improved version of a setup previously introduced by our group. Enhancements have been made to minimize the influence of the reference electrode and improve the accuracy of electrochemical impedance spectroscopy.

Early detection of deep-seated smouldering fires in wood waste storage using ERT

Incidents of waste and biofuel fires are common at all stages of the waste recycling chain and have grave implications for business, employees, firefighters, society, and environment. An early detection of waste and biofuel fires in the smouldering stage could save precious lives, resources, and our environment. Existing fire detection methodologies e.g. handheld temperature sensors, IR cameras, gas sensors, and video and satellite-based monitoring techniques have inherent limitations to efficiently detect smouldering fires. An attempt was made to explore the potential of electrical resistivity tomography (ERT) as an alternate tool to address the problem. In the experiments an externally powered resistive wire was employed to initiate the smouldering fire inside the test material (wood pellets, wood shavings, wood fines). Time series of ERT that followed the initiation and development of smouldering were recorded using an automated monitoring instrument setup. The actual geometry of the experimental sample container and electrode setup was integrated in the 3D finite element method (FEM) model grid to perform inverse numerical modelling (inversion) and to develop resistivity tomographic images. The study shows a sharp increase in ratio of resistivity (R/Ro ≥ 50 %) in the test material in the region of smouldering hotspot and demonstrates the potential use of ERT technique for the detection of smouldering hotspots in silos and pile storage of organic material such as wood-based fuels, wood waste, coal, municipal solid waste (MSW), recyclables etc. More research is however required for enabling the use of this technique at the practical scale for different storage conditions.

Optimization and miniaturization of SE-ECL for potential-resolved, multi-color, multi-analyte detection

Electrochemiluminescence (ECL) is a bioanalytical technique with numerous advantages, including the potential for high temporal and spatial resolution, a high signal-to-noise ratio, a broad dynamic range, and rapid measurement capabilities. To reduce the complexity of a multi-electrode approach, we use a single-electrode electrochemiluminescence (SE-ECL) configuration to achieve the simultaneous emission and detection of multiple colors for applications that require multiplexed detection of several analytes. This method exploits intrinsic differences in the electric potential applied along single electrodes built into electrochemical cells, enabling the achievement of distinct colors through selective excitation of ECL luminophores. We present results on the optimization of SE-ECL intensity for different channel lengths and widths, with sum intensities being 5 times larger for 6 cm vs. 2 cm channels and linearly increasing with the width of the channels. Furthermore, we demonstrated for the first time that applying Alternating Current (AC) voltage within the single electrode setup for driving the ECL reactions has a dramatic effect on the emitted light intensity, with square waveforms resulting in higher intensities vs sine waveforms. Additionally, multiplexed multicolor SE-ECL on a 6.5 mm × 3.6 mm CMOS semiconductor image sensor was demonstrated for the first time, with the ability to simultaneously distinguish four different colors, leading to the ability to measure multiple analytes.

Parameter estimations from SARS-CoV-2 electrochemical interactions

Electrochemical pathogen sensing has gathered limelight for its effective and ultrafast detection capabilities. More recently, several electrochemical sensors were developed to counter the increasing testing requirement for the 2019 coronavirus disease (COVID-19) diagnosis. One such sensor developed was the Ultrafast COVID-19 (UFC-19) diagnostic sensor which could detect the SARS-CoV-2 spike protein in saliva samples. Although UFC-19 was established in literature to sense SARS-CoV-2 in saliva samples, the factors causing such an interaction or parameters to model such an interaction are yet to be studied in detail. In this work, an attempt has been made to electrochemically characterize the interactions at the interface by employing cyclic and linear sweep voltammetry on a rotating disk electrode setup. As a result, electrochemical parameters were calculated using chemical and electrochemical principles. The electrochemical surface area, electrode surface coverage, diffusion coefficient, reaction order with respect to SARS-CoV-2 whole virus, electron transfer coefficient have been estimated providing additional insights into the events occurring at the electrical double layer. The reaction order for the interaction was reckoned to be 0.7 confirming a non-elementary, multi-step process occurring at the interface. Theoretical and experimental calculations confirm higher hydroxide ion accumulation at the interface in the presence of SARS-CoV-2 whole virus. Results from this work lay the foundation for developing models for electrochemical SARS-CoV-2 interaction and possible extension toward other pathogenic viruses.

Adjusting the Operational Potential Window as a Tool for Prolonging the Durability of Carbon-Supported Pt-Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts.

A current trend in the investigation of state-of-the-art Pt-alloys as proton exchange membrane fuel cell (PEMFC) electrocatalysts is to study their long-term stability as a bottleneck for their full commercialization. Although many parameters have been appropriately addressed, there are still certain issues that must be considered. Here, the stability of an experimental Pt-Co/C electrocatalyst is investigated by high-temperature accelerated degradation tests (HT-ADTs) in a high-temperature disk electrode (HT-DE) setup, allowing the imitation of close-to-real operational conditions in terms of temperature (60 °C). Although the US Department of Energy (DoE) protocol has been chosen as the basis of the study (30,000 trapezoidal wave cycling steps between 0.6 and 0.95 VRHE with a 3 s hold time at both the lower potential limit (LPL) and the upper potential limit (UPL)), this works demonstrates that limiting both the LPL and UPL (from 0.6-0.95 to 0.7-0.85 VRHE) can dramatically reduce the degradation rate of state-of-the-art Pt-alloy electrocatalysts. This has been additionally confirmed with the use of an electrochemical flow cell coupled to inductively coupled plasma mass spectrometry (EFC-ICP-MS), which enables real-time monitoring of the dissolution mechanisms of Pt and Co. In line with the HT-DE methodology observations, a dramatic decrease in the total dissolution of Pt and Co has once again been observed upon narrowing the potential window to 0.7-0.85 VRHE rather than 0.6-0.95 VRHE. Additionally, the effect of the potential hold time at both LPL and UPL on metal dissolution has also been investigated. The findings demonstrate that the dissolution rate of both metals is proportional to the hold time at UPL regardless of the applied potential window, whereas the hold time at the LPL does not appear to be as detrimental to the stability of metals.

Achieving new insights on rational design and application of double perovskite Y2CrMnO6 nanostructures as potential materials for electrochemical hydrogen storage performance

Fossil fuel consumption and environmental concerns have long motivated the use of electric vehicles around the world. To meet the global energy demand, hydrogen has been proposed as a clean energy carrier with carbon-free combustion. There is, however, a great need for high-performance electrode materials in hydrogen storage applications in order to achieve the desired goals of long life and superior specific capacity. The purpose of our study is to investigate how novel double perovskite Y2CrMnO6 (YCMO) nanostructures can be used as highly active electrocatalysts in hydrogen storage activity by kinetics of redox and physisorption mechanisms. For the first time, spherical-shaped YCMO nanoparticles were fabricated via sol-gel auto-combustion using grape juice as fuel and complexing agent. A series of physic-chemical and electrochemical techniques was used to analyze the electrochemical performance of resultant YCMO samples based on their uniformity, size, and phase purity, including X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), Cyclic Voltammetry (CV), chronopotentiometry, electrochemical impedance spectroscopy (EIS), and Tafel polarization. At a constant current of 1 mA in a three electrode set-up, the 15th profile of hydrogen storage capacity of YCMO-15, synthesized with 15 mL of grape juice, reached a maximum value of 465 mAh g−1 at a constant current of 1 mA, which is higher than that of YCMO-5 (355 mAh g−1) and YCMO-10 (350 mAh g−1). The results presented here can also lead to a new plan for developing Cr–Mn-based double perovskite oxides with hydrogen storage properties.

Enhanced synergistic redox activity of SrCoS/PANI for hybrid energy storage and oxygen evolution reaction

Supercapacitors (SCs) and secondary batteries (SBs) are commonly utilized for energy storage, although each has some limitations: low energy density (Ed) and power density (Pd), respectively. To address these issues, a hybrid supercapacitor is a new emerging technique known as supercapattery, which combines both of these devices to optimum the Ed and Pd in a single setting. The hydrothermal method was adopted to synthesize a cost-effective, eco-friendly, and non-toxic SrCoS/PANI, a composite material for optimum results of supercapattery. Crystallinity and morphology study of synthesized nanocomposites strontium cobalt sulfide with Polyaniline (SrCoS/PANI) were examined using SEM and XRD techniques. Initially, the performance was tested using a three-electrode setup of nanocomposites (SrCoS/PANI) in 1 M KOH electrolyte. The effectiveness of a SrCoS/PANI-activated carbon two-electrode supercapattery was examined through cyclic CV, GCD, and EIS techniques. In the two electrodes setup, the device performs admirably with an astonishing specific capacity of 139.4 C g−1, a high Ed of 29.56 Wh kg−1, and a high Pd of 800 W kg−1 at 1.0 A g−1. The cyclic stability was tested by putting the device through 5000 charging and discharging cycles, which maintained 91.65% of its Specific capacity (Qs). A hybrid nanocomposite (SrCoS/PANI) device was accomplished, with exceptional electrochemical capabilities at a low price making them a fascinating active material with potential applications in supercapattery technology. The electrocatalytic performance of the synthesized nanostructure (NSs) was studied comprehensively with regard to an oxygen evolution reaction (OER).

Nitrogen-doped carbon nanostructures embedded with Fe-Co-Cr alloy based nanoparticles as robust electrocatalysts for Zn-air batteries

Two types of nitrogen-doped carbon nanomaterials embedded with novel transition metal-based medium entropy alloy nanoparticles are synthesized via a simple, scalable, and cost-effective single-step pyrolysis route, by varying the stoichiometric ratio of iron and cobalt. The samples predominantly have bamboo-shaped nanotube morphology with some globular structures. The globules are core-shell type nanoparticles, i.e., containing the metallic-alloy nanoparticles encapsulated by the graphitic shell and embedded within defective amorphous-type carbon matrix. The electrochemical studies using these samples are conducted in basic medium to explore their potential for Zn-air batteries. Electrochemical measurements are carried out in 1 M and 0.1 M KOH, respectively, on a rotating disk electrode setup. The sample with higher cobalt content performs better for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with regards to lower onset potential, lower Tafel slope and lower activation energy. However, the stability towards OER is better for the sample with higher iron content. The sample with higher cobalt content shows a better overall oxygen electrochemistry compared to the one with higher iron content, is at par with several state-of art electrocatalysts and is utilized for fabrication of a prototype Zn-air battery demonstrating its practical applicability.

Facile hydrothermally grown cobalt oxide (Co3O4) nanostructures and their electrochemical performances

Abstract In this study, pure cobalt oxide (Co3O4) nanoparticles were synthesized using a simple hydrothermal approach. The effect of the reducing agent and reaction temperatures of the prepared products were examined. Co3O4 is formed in the as-synthesized sample, at reaction temperature 190 °C was observed in the XRD pattern. The XPS survey scan spectrum showed the distinctive peaks of the Co and O elements and their valence states. FESEM and HRTEM revealed the particles as cubical in nature. Peak associated with the elements Co and O on the EDAX spectrum demonstrated the purity of the nanoparticles. Three electrode setups were used to measure the electrochemical properties of the synthesized nanoparticles. DTA curve corresponding exothermic peak at 225 °C and the crystallization of the final product was attributed for the third weight loss of 1.5 % in the temperature range of 280 °C to 450 °C. Formation of Co3O4 was confirmed by the observed XRD diffraction peaks at 2θ = 36.83°, 59.82°, and 65.30°, which correspond to h k l planes (311), (511) and (440), respectively. The high-resolution Co2p spectra showed two prominent spin-orbital peaks, 2p1/2 and 2p3/2, at 796.37 eV and 781.81 eV, respectively. The increase in temperature causes the particle size to grow ranges between 20 and 70 nm and the average particle size distribution in the TEM image is 42 nm. The integral area of the CV curve was measured during the CV measurement and as the as-prepared Co3O4 electrode displays specific capacitance values of 154, 126, 81, 65, and 49 Fg−1 at various scan rates of 10, 20, 50, 70, and 100 mVs−1, respectively.

Optimization of the Electrochemical Nature of Ni/Co MOF Assisted by Zn Metal Centres for Better Electrode Performance in Hybrid Devices

Owing to the exceptional porous coordination chemistry and expanded redox culture of mixed metal organic framework (MMOF) materials are now presenting a hot matter for their potential usage in battery-supercapacitor electrodes. Here, we synthesized Ni/Co-MOF and its based Zn x -(Ni/Co)y-MOF nanoparticles containing different transition metals ratio; x: y = 0.25:0.75, 0.50:0.50, and 0.75:0.25 by hydrothermal process and named as ZMOF1, ZMOF2 and ZMOF3. Their electrochemical profile was carried out by CV, GCD and EIS characterization in three electrode setup. Among the MOFs nanoparticles, partially Zn enriched ZMOF1 shows prominent specific capacity of 177.23 and 181.12 C g−1 in 1.0 and 3.0 M KOH electrolyte solution at current density of 0.3 A g−1 along with good rate capability performance. Meanwhile, it retains brilliant specific capacity ∼ 86% of its original value compared to other displayed by ZMOF2 and ZMOF3 (80% and 69%) after charging-discharging for 3000 cycles at j = 4.0 A g−1. Moreover, modified power law was utilized to estimate the battery-type charge storage worth of ZMOF1 from CV cycle (at 5 mV s−1) in 1.0 and 3.0 M electrolytes medium thereby found the contribution 91.58% and 94.32%, respectively. These features of ZMOF1 attributed to particle diverse morphology, enriched redox sites and admiring electrical conductivity.

One-Pot Synthesis of a Robust Crosslinker-Free Thermo-Reversible Conducting Hydrogel Electrode for Epidermal Electronics.

Traditional epidermal electrodes, typically made of silver/silver chloride (Ag/AgCl), have been widely used in various applications, including electrophysiological recordings and biosignal monitoring. However, they present limitations due to inherent material mismatches with the skin. This often results in high interface impedance, discomfort, and potential skin irritation, particularly during prolonged use or for individuals with sensitive skin. While various tissue-mimicking materials have been explored, their mechanical advantages often come at the expense of conductivity, resulting in low-quality recordings. We herein report the facile fabrication of conducting and stretchable hydrogels using a "one-pot" method. This approach involves the synthesis of a natural hydrogel, termed Golde, composed of abundant and eco-friendly components, including gelatin, chitosan, and glycerol. To enhance the conductivity of the hydrogel, various conducting materials, such as poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), thermally reduced graphene (TRG), and MXene, are introduced. The resulting conducting hydrogels exhibit remarkable robustness, do not require crosslinkers, and possess a unique thermo-reversible property, simplifying the fabrication process and ensuring enhanced long-term stability. Moreover, their fabrication is sustainable, as it employs environmentally friendly materials and processes while retaining their skin-friendly characteristics. The resulting hydrogel electrodes were tested for electrocardiogram (ECG) signal acquisition and outperformed commercial electrodes even when implemented in an all-flexible electrode setup simply using copper tape, owing to their inherent adhesiveness.

Membrane electrode assembly simulation of anion exchange membrane water electrolysis

Anion exchange membrane water electrolysis (AEMWE) offers a green hydrogen production method that eliminates the need for platinum group metals (PGM) as electrocatalysts. This study employs a COMSOL® 6.0 model to simulate a 1x1 cm2 Ni fibre − Raney® Ni || X37-50RT || NiFe2O4− SS316L fibre AEMWE membrane electrode assembly (MEA). The membrane is set at a thickness of 60μm, while the anodic and cathodic porous transport layers (PTL) are modelled with a thickness of 370μm, each having an average porosity of 0.70. The half−cell overpotentials are experimentally measured to validate the half−cell model in a three−electrode setup consisting of (working electrode) || AGAR-Ag/AgCl || Pt−wire (counter electrode). Two freshly prepared MEAs validated the (i) base case and (ii) sensitivity analysis models. The base case model validated the MEA results at 20 °C and 1 atm in 1M KOH electrolyte feed at 1.56 ml min−1 cm−2. The five parameters studied with the sensitivity analysis revealed the most influential parameters based on area-specific resistance (ASR) change in the following order (＋ and − indicate increase and decrease in ASR, respectively): KOH concentration (−97%), membrane thickness (＋ 9%), temperature (−4%), cathode feed type (<+0.5%), and KOH flow rate (>−0.5%).

ASSESSMENT OF INHIBITORS' PERFORMANCE ON CORROSION DEGRADATION OF CARBON STEEL IN FLOW ENVIRONMENTS USING ROTATING CYLINDER ELECTRODE (RCE)

This study investigates sweet corrosion mitigation methods focusing on the efficacy of inhibitors. Specifically, it examines the performance of two types of inhibitors: water-soluble and oil-soluble. Utilising a Rotating Cylinder Electrode (RCE) setup, turbulence is induced in saline solutions to assess the impact of inhibitors on the corrosion of carbon steel. Scanning Electron Microscopy (SEM) is employed to analyse corrosion degradation patterns and material damage mechanisms. Given the prevalent use of inhibitor injection in the oil sector, it is crucial to evaluate and compare the effectiveness of various inhibitors to recommend optimal options and further studies. The findings contribute to advancing corrosion mitigation strategies, providing insights into the performance of inhibitors in flow environments and aiding in the development of more effective corrosion control measures for carbon steel structures. The inhibitors under study are sourced from local oil company vendors. With a projected duration of six months and a total budget of KD 9850, this investigation aims to provide valuable insights into corrosion mitigation strategies

Temperature Distribution on Classical Two Needles IRE Setup Versus a Single Needle Prototype.

Irreversible Electroporation (IRE) is a non-thermal minimally invasive cancer therapy used in the treatment of liver tumors. However, the therapy entails an electrical current flux which can be high enough to cause a noticeable temperature increase. Therefore, the analysis of the heat distribution is important: during any IRE treatment, the target area is intended to be treated with non-thermal effects, where existing thermal effects should not damage nearby sensitive structures. This article aims to compare the established two parallel needles electrode setup, used by FDA-approved electroporation delivering devices, to a single needle, multiple electrode prototype design. Levels and distributions of the temperature at different distances from the applicators during an IRE liver treatment were investigated. The prototype results were collated with already published in-vivo data. All electrode configurations were analyzed numerically in COMSOL Multiphysics for different pulse protocols. The extension of coagulation necrosis predicted by the model matched available in-vivo data. While the maximum average temperature during pulsation was higher for the prototype (74 °C) than for the two-needle IRE setup (57 °C), the thickness of the coagulation necrosis around the conductive electrodes was in the same range for both configurations. However, the location differed completely: the necrosis engendered by the prototype was located inside the tumor, while the two-needle IRE setup created necrosis outside the tumor, potentially closer to sensitive structures. The results highlighted the importance of heat distribution analysis for the design of new IRE needles as well as for IRE treatment planning. Proper analysis ensures that the non-thermal effects are maximized while minimizing any potential thermal damage to surrounding sensitive structures.

Effect of Mechanical Pressure on Lifetime, Expansion, and Porosity of Silicon Dominant Anodes in Laboratory Lithium-Ion Cells

Silicon (Si) is a promising next-generation anode material for lithium-ion batteries due to its nearly ten times higher specific capacity of 3579 mAh/gSi 1. The high and economic availability of Si due to existing industrial infrastructure is another non-technical advantage.2 The main drawback of Si is its large volume expansion of nearly 300% during full lithiation causing SEI (re-) formation, electrochemical milling, and electrode instability leading to thickness changes resulting in the disruption of the electronic pathways and decoupling of particles.2 These problems still exist in partially lithiated µm-sized Si particles with lower volume expansion.2 In this work, we study the influence of compressive force on electrode stability in full cells composed of NCA3 cathodes and silicon-dominant anodes based on µm-sized particles.2 The different mechanical pressures were applied using spring-compressed 3.34 mAh Swagelok™ T-cells (A = 0.94 cm²) with metallic lithium reference electrodes. The investigated mechanical pressure ranges from 0.02 MPa as low pressure (LP) to 2.00 MPa, as high high pressure (HHP) to determine the optimal pressure for cyclic lifetime. Firstly, we introduce an experimental methodology to precisely adjust the common three-electrode SwagelokTM cell setup. Therefore, we take the compression from the single components into account, which were measured in a universal testing machine4 for the pressure range mentioned above. The cells were built with different mechanical pressures and cycled with C/2 until a SoH of 80% of the initial capacity was reached which was measured periodically in CheckUp tests. In the post-mortem analysis, Si anodes cycled at different mechanical pressures are prepared for scanning electron microscopy using a focused ion beam cross-section polisher. The images are then analyzed regarding electrochemical milling, thickness increase, and porosity decrease at 80% SoH by comparing them to the pristine state.The HHP cells with 2 MPa show a detrimental effect on lifetime during cell cycling as depicted in Figure 1 and with only 100 cycles nearly a halved lifetime compared to a normal pressure (NP) of 0.20 MPa. Moreover, the specific discharge capacity is significantly reduced for HHP or LP compressed cells compared to NP cells (see Figure 1b). The post-mortem analysis showed a dependency of the porosity and thickness of the aged Si anodes on the applied pressure. On the particle level, no electrochemical milling was observed due to the partial lithiation of the Si anodes. Vein-like microstructures were observed for the lithiated probes which might originate from different lithiation pathways of polycrystalline Si.5 Based on these experimental results, multilayer pouch cells with the same electrode setup and balancing are produced and cycled, and the expansion of the cells is measured operando in a compression test bench. Acknowledgments: S. F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany), under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank the research battery production team of iwb for the manufacturing of the electrodes

Towards Reliable Stability Measurements of OER Catalysts

Currently, significant efforts are taken to find the most active and stable electrochemical oxygen evolution reaction (OER) catalyst diverting from critical raw material. However, one also needs to consider new catalyst screening methods, especially with respect to stability investigations where rotating disk electrode (RDE) studies are not suitable.1 Recently, we introduced a gas diffusion electrode (GDE) setup as a new testing platform for OER catalysts.2 This methodology stems from fuel cell studies where carbon gas diffusion layer (GDL) is used as a transport layer to bring the reactant to the catalyst. Since carbon is not stable under the harsh OER conditions, water electrolyser uses titanium-based porous transport layers (PTLs). In the current work, we utilized the GDE setup to test the influence of the transport layer on the stability of a highly active Ir0.7Ru0.3Ox nanoparticle catalyst immobilized on homemade antimony-doped tin oxide (ATO) support. The test was conducted potentiostatically (@ 1.6 V vs RHE) for 2 h at 60 °C. The stability of the catalyst was then compared when deposited on GDL vs PTL. Rapid decline of the GDL-deposited catalyst activity was observed, while the PTL-deposited catalyst demonstrates a rather stable behavior (Fig. 1). We attribute this fast activity drop to the carbon oxidation of the GDL. Moreover, the activity at 30 °C of the PTL-deposited catalyst was compared to literature data on RDE setup [1]. In the RDE setup, a breakdown is observed after only 30 min when applying a constant current density. In contrast, PTL-deposited catalyst exhibits no activity loss during 2 h under similar conditions.[1] H. A. El-Sayed. Journal of The Electrochemical Society, 166 (8), F458-F464 (2019)[2] J. Schröder. JACS Au, 1, 247-251 (2021) Figure 1 . Potentiostatic stability transients at 1.6 V vs RHE of Ir0.7Ru0.3Ox/ATO deposited on C-based GDL (green full) and on Ti-based PTL at 60 °C (black full) and 30 °C (blue dashed). Figure 1

Operando and Dynamic XAS Studies of Metal-Support Interactions of Iridium-Based Catalysts for Oxygen Evolution Reaction (OER) in Proton Exchange Membrane Water Electrolysis (PEMWE)

Iridium (Ir) is an important electrocatalyst material for the oxygen evolution reaction (OER) in acidic media. However, high loadings of very costly and scarce Ir are needed to achieve sufficient performance in proton exchange membrane water electrolysis (PEMWE). [1] To establish a large-scale green hydrogen economy based on PEMWE in the near future, the Ir loading needs to be further reduced. In the last decades, promising Ir-based catalyst strategies has been developed to improve the OER activity by controlling the size of Ir nanoparticles (NPs) [2] and tuning the electronic interactions of the Ir NPs with the catalyst support material, referred to as strong metal support interaction (SMSI). The latter has frequently been observed for heterogeneous catalysts (e.g. Au NPs supported on titanium oxide [3]), while the SMSI for Ir-based OER electrocatalysts is poorly understood to date.This study focuses on operando and dynamic X-ray absorption spectroscopy (XAS) analysis of Ir NPs deposited on three support materials: graphitized carbon (C), titanium oxide (TiO2) and antimony-doped tin oxide (ATO). The surfactant-free Ir NPs with controlled size of around 1 nm were obtained by a colloidal approach in low-boiling point alcohols. [2, 4] Afterwards, the Ir NPs were homogeneously distributed on different support materials with similar loadings and particle sizes confirmed by TEM and XRD. Solute components from the aged catalyst materials (Ir and/or support material) in the electrolyte solution were determined by ICP-OES, while the solid catalyst powders were analysed by TGA and µ-XRF. Our first/initial electrochemical results by recording cyclic voltammetry (CV) profiles show that after the immobilization the Ir NPs obtained from the same batch are strongly oxidized on TiO2, while a metallic character of the Ir is still observed on the C and ATO. The OER mass activity of 120±8 A/gIr for Ir/C is 2-times higher than for Ir/TiO2 (60±6 A/gIr) and 1.2-times higher than for Ir/ATO (95±4 A/gIr) at 1.5 VRHE,iR-free and 25 °C obtained from rotating disc electrode (RDE) setup.Operando and dynamic Ir LIII edge XANES measurements during the cycling from 0.06 to different upper potentials (0.8, 1.0, 1.2, 1.4 and 1.6 VRHE) at 2 mV/s were performed in acidic media at the SuperXAS (X10DA) beamline, Switzerland. All measurements were carried out using a home-made spectro-electrochemical flow-cell. Principal component analysis (PCA) of Quick-XANES data confirmed the tendencies of the formation of irreversible Irz+ species on TiO2 even at low upper potentials, while ATO and C tend to retain the metallic character of the Ir NPs. From the PCA, two independent components were identified to describe the changes in the series of XANES data. The compositions of these components were then analyzed using linear combination fitting (LCF).For 60 wt.% Ir/C, the cycling up to 1.4 VRHE shows two components with 50:25:25 wt.% of Ir0:Ir3+:Ir4+ and 42:0:58 wt.% of Ir0:Ir3+:Ir4+ obtained from the PCA and LCF analysis. During the cycling, the ratios of these components change gradually. In spite of the strong hysteresis behavior, we observed that the ratio between both components reverses to the initial state. In other words, only the component with 42:0:58 wt.% of Ir0:Ir3+:Ir4+ is present at 1.4 VRHE, while the other component is dominant at lower anodic potential.In the same experiment, the analysis of our data for 60 wt% Ir/ATO using PCA indicates two independent components with 74:11:15 wt.% of Ir0:Ir3+:Ir4+ and 70:0:30 wt.% of Ir0:Ir3+:Ir4+. The cycling up to 1.4 VRHE shows similar behavior like 60 wt.% Ir/C.Although the same batch of colloidal Ir NPs were used for the immobilization, the PCA and LCF analysis for 60 wt.% Ir/TiO2 reveal two components with high content of Ir4+ species, more precisely 36:64 wt.% of Ir0:Ir4+ and 2:98 wt.% of Ir0:Ir4+. The cycling up to 1.4 VRHE shows mainly a reversible behavior due to high content of Ir4+ species on TiO2. With increasing anodic potential, the content of metallic Ir further decreases and the main component with almost only Ir4+ species is stable at 1.4 VRHE. In the backward direction, the reduction to metallic Ir takes place to small extent. Therefore, the component with 36:64 wt.% of Ir0:Ir4+ is mainly present at 0.06 VRHE.In summary, our PCA and LCF analysis of the operando and dynamic Quick-XANES data provide further insights into the electronic structure of Ir species and the mechanism of the complex metal-support interaction for Ir NPs immobilized on C, ATO and TiO2.

Regeneration Strategies for Ruthenium-Poisoned ORR Catalysts in Reformate PEM Fuel Cells

Reformate polymer electrolyte membrane (PEM) fuel cells have great potential to transform the global maritime transportation in a more environmentally friendly and CO2-neutral manner. Platinum (Pt)-ruthenium (Ru) alloy nanoparticles (NPs) supported on carbon (PtRu/C) are the most commonly used electrocatalyst material to accelerate the hydrogen oxidation reaction (HOR) of the reformate gas (H2/CO2/CO) at the anode [1]. The high CO tolerance of PtRu/C catalysts is based on the ensemble effect [2]. However, these materials suffer extremely from the Ru dissolution and Ruz+ crossover to the cathode, which are the main degradation processes in reformate PEM fuel cells. At the cathode, the Ruz+ species immediately redeposit on the Pt/C catalyst, resulting in a drastic decay of the entire performance of the reformate PEM fuel cell. Even if the Ru coverage on the Pt/C catalyst is less than 20 at. %, there is an 8-fold decrease in kinetics of the oxygen reduction reaction (ORR) [3]. Therefore, it is necessary to develop a regeneration protocols to mitigate the Ru poisoning at the cathode.In this study, we developed and tested different regeneration protocols to recover the Ru-poisoned ORR catalysts using a rotating disc electrode (RDE) set-up. To simulate the worst situation for poisoned ORR catalysts, commercially available Pt-Ru alloy NPs supported on carbon were used and characterized by TEM, XRD, XAS, and XPS. In general, our regeneration protocols can be classified into dynamic and steady-state conditions. All protocols included a pre-activation step by holding the potential at 1.4 VRHE for 5 minutes in 0.1 M HClO4. During the dynamic regeneration process, the potential was switched between 1.4 VRHE and 1.6 VRHE with a duration time of 10 s by 10 times using a pulse voltammetry technique. In contrast, the steady-state regeneration protocol consisted of only one pulse at 1.6 VRHE for 100 s. For the recovery procedure of the poisoned ORR catalysts, the experimental parameters were correlated with the changes in ORR performance and electrochemically active surface area (ECSA) via CO stripping as well as the loss of Ru content and particle structure established from μ-XRF, ICP-OES, and TEM.After the dynamic regeneration process, the ORR mass activity (MA) and specific activity (SA) of PtRu2/Vulcan increase initially from 0.07 ± 0.01 to 0.21 ± 0.02 A mgPt+Ru -1 and 62 ± 9 to 190 ± 16 μA cmPt+Ru -2 at 0.85 VRHE, iR-free, respectively. Hence, the dynamic regeneration protocol leads to an improvement of the MA by a factor of 2 and of the SA by 2.1 for PtRu2/Vulcan. In comparison, the steady-state regeneration experiment shows an enhancement by 2.2 (0.26 ± 0.03 A mgPt+Ru -1) for MA and by 3.5 (276 ± 16 μA cmPt+Ru -2) for SA, respectively. Therefore, the steady-state regeneration process is more effective compared to the dynamic regeneration protocol. Based on the µ-XRF data, we observed that the Ru content of the PtRu2/Vulcan decreases from 62 ± 2 at. % to either 5 ± 1 at. % or 8 ± 1 at. % after the steady-state or dynamic regeneration process. The loss of Ru from the particle surface can also be monitored by CO stripping, where the CO oxidation peak is shifted positively from 0.58 VRHE to 0.67 VRHE and 0.63 VRHE after steady-state and dynamic regeneration protocol, respectively. As the particle size of the PtRu2 NPs is around ~ 5.3 ± 1.2 nm, the ECSA is mainly unchanged after both regeneration protocols.Based on our results, the steady-state regeneration process with 1.6 VRHE for 100 s is more effective than the dynamic one with pulses from 1.4 to 1.6 VRHE each with 10 s by 10 times to recover the ORR activity of the PtRu2 alloy NPs. The proposed regeneration protocols can improve the performance and life-time of the reformate PEM fuel cell.

Development of IrO2 Nanosheet–Pt/C Composite as Reversal Tolerant Anode Catalysts for Polymer Electrolyte Fuel Cell

Introduction: During the start-up and shutdown cycles of a polymer electrolyte fuel cell (PEFC), certain areas of the anode flow channel may not receive sufficient hydrogen due to water blockage or sluggish diffusion. This can lead to hydrogen starvation, which in turn causes a shortage of protons during cell reaction. The result is an increase in anode potential, which triggers the carbon oxidation reaction (COR) and damages the catalyst layer.Promoting the oxygen evolution reaction (OER) to alleviate the COR is a promising strategy to develop reversal-tolerant anodes (RTAs). Incorporating OER-active materials, such as IrO2, as a co-catalyst is an effective way to mitigate the rise in anode potential and prevent COR [1].In this study, a novel OER-active material, iridium oxide nanosheet (IrO2(ns)), was used as the co-catalysts and combined with commercial Pt/C in three different ways; mixing Pt/C with normal- and small-sized IrO2 nanosheets (IrO2(ns)/Pt/C), and Pt/C mixed with carbon supported IrO2 nanosheet (Pt/C+IrO2(ns)/KB). The OER activity and tolerance to cell reversal conditions were characterized using a 3-electrode rotating disk electrode (RDE) setup. Experiment: IrO2(ns)(250 nm) colloid was synthesized following literature [2]. The resulting IrO2(ns)(250 nm) colloid was subjected to ultrasonication to obtain small-sized nanosheets (IrO2(ns)(100 nm)) [3]. Nanosheet-carbon composite (IrO2(ns)(100 nm)/KB) was prepared by mixing IrO2(ns)(100 nm) colloid and KB (Ketjen black EC-300J) and physically mixed with Pt/C. Commercially available IrO2 nanoparticles (c-IrO2) were purchased from Tokuriki Honten Co., Ltd. and added to Pt/C (c-IrO2-Pt/C) and used as a reference sample.The composite catalyst was prepared by mixing Pt/C with different IrO2 nanomaterials and will be denoted as IrO2(ns)(x mass%)-Pt/C or c-IrO2 (x mass%)-Pt/C depending on the source of the IrO2 material used. RDE studies were conducted using a 3-electrode half-cell setup with 0.1 M HClO4 as the electrolyte. The counter electrode was carbon fiber, and a reversible hydrogen electrode (RHE) was used as the reference electrode.Except for the OER activity, the electrodes for all measurement were prepared with a Pt loading of 8.0 μg/cm2. For hydrogen oxidation reaction (HOR) activity measurements, the electrolyte was purged with H2. For chronopotentiometry (CP) and electrochemically active Pt surface area (ECSA) measurement, the electrolyte was purged with N2. For OER activity measurements, the electrolyte was purged with N2, and the working electrode was prepared with a Pt loading of 17.3 μg/cm2. Except for ECSA measurement, all data were accumulated at an electrolyte temperature of 60oC. Results and Discussion: Figure 1 shows the OER activity (10 mV/s) of Pt/C and composite catalysts prepared with c-IrO2(5 mass%), IrO2(ns)(250 nm, 5 mass%), IrO2(ns)(100 nm, 5 mass%), IrO2(ns)(100 nm, 2.5 mass%) and IrO2(ns)(100 nm, 1 mass%). At 1.5 V vs. RHE, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C exhibited a 2-fold increase in OER activity compared to IrO2(ns)(250 nm, 5 mass%)-Pt/C and a 25 % increase compared to c-IrO2 (5 mass%)-Pt/C. All composite catalysts displayed significantly higher OER activity than the pristine Pt/C sample.To simulate the degradation behavior in the fuel cell anode, a series of CP tests were performed at 16, 48, 80, and 112 μA/cm2. The HOR mass activity was used as a quantitative factor to present the decay caused by cell reversal degradation. The HOR activity before and after CP was evaluated using linear sweep voltammetry (LSV) from -0.08 V to 0.5 V vs. RHE. The HOR mass activity at 20 mV vs. RHE was calculated based on the Koutecky-Levich equation. After CP, the Pt/C sample showed a decrease in HOR activity from 851 A/g to 621 A/g (72% retention). In contrast, IrO2(ns)(100 nm, 2.5 mass%)-Pt/C showed an initial HOR activity comparable to Pt/C (1420 A/g) and still retained a high HOR activity of 1400 A/g after CP (100% retention). The addition of IrO2(ns) as a co-catalyst effectively suppressed the carbon oxidation reaction under cell reversal conditions.

Every Step Counts: Importance of Final ALD Sequences for Oxygen Evolution Reaction Catalysts

In achieving the global dream of a sustainable future, the development of new and alternative methods to generate electricity are of high importance. Current renewable energy sources are mainly dependent on sun and wind, and are thus very unpredictable. To obtain an overall reliable energy supply, we need to be able to store clean energy for extended periods of time to compensate for unfavorable weather conditions or sudden surges in energy demand.One way to store energy is by generating H2-gas, which has a set of interesting advantages as an energy carrier molecule. It has a very high energy density, is multifunctional as feedstock or energy carrier and it is not a greenhouse gas in itself. The production efficiency of green H2, however, still needs to be optimized before it can be adapted on a global scale. Electrochemical water splitting is mainly hampered by the sluggish kinetics of the oxygen evolution half-reaction (OER) of the process. This involves a transfer of four electrons, each with its own intermediary product(s) requiring catalysis, resulting in a significant overpotential[1].Atomic layer deposition (ALD) could be an interesting technique in the research, development and possibly production of such OER catalytic materials. This technique is suited to deposit thin films in a controlled layer-by-layer way with dimension control up to the Angström level. In this development, transition metals could be interesting catalyst candidates due to their availability and pricing over tradition OER catalysts based on noble metals [2]. Both oxides and phosphate variants have been explored; the latter occasionally outperforming the former[3][4].Nickel has shown to be one of the more OER-active transition metals, and doping or combining it with iron seems to further increase its performance [5]. Inspired by these results, ALD was used in this work to deposit and finetune the properties of a Ni-Fe ternary phosphate for its use as an OER-catalyst material. This material was deposited by alternating ALD cycles of Ni- and Fe-phosphate (denoted here as NiPO and FePO) based on previous works of Rongé et al.[6] and Henderick et al.[7].Ni-Fe phosphates with varying composition and thickness were deposited on a solid nickel disc and tested in a rotating-disc electrode (RDE) set-up to quantify their electrochemical performance. Applying a coating with a selected composition of 4 NiPO to 1 FePO cycles improves the performance over a bare Ni-PVD substrate (Fig 1). A current density of 91 mA/cm2 at 0.685 V vs Hg/HgO is obtained for this material which is 75% higher than the uncoated nickel disk (51 mA/cm2) which indicates that the material has catalytic properties for the OER increasing the production of H2 at an identical overpotential. An additional observation was that the pulsing order of the two sub-processes within an ALD super-cycle has an important impact on the resulting layer’s performance. If the FePO sub-cycle is pulsed last, the current density increases further to approx. 150 mA/cm2 for a total increase of 200% compared to the uncoated performance.The results of this explorative work in the use of ALD for the development of OER catalytic materials indicate that it is a promising technique due to the precise control that can be exerted over both the thickness and composition of the material. Specifically the option to exert high control over the surface of the catalyst can be a big asset in researching catalytic materials.