Ohmic Resistance Research Articles

Alkaline Water Electrolysis Beyond 3 A/cm2 Using Catalyst Coated Diaphragms

Alkaline water electrolysis using catalyst coated diaphragms (Zirfon UTP 500 and UTP 220) was conducted at current densities from 2 up to 3500 mA cm−2 at varying temperatures (20–75 °C) in 30 wt% KOH. The coatings were conducted using two different approaches, which were compared with each other: spray coating and stencil coating. Using platinum group free catalysts, which are either available commercially or easy to synthesize (Raney Ni; FeNi LDH), we reached 3.5 A cm−2 at less than 2.3 or 2.5 V, for Zirfon UTP 220 and 500, respectively. The improvements compared to conventional Ni felt were linked to a reduction in the kinetic overpotential due to better catalytic properties and an increase in active surface area. The internal resistance corrected potential at 1 A cm−2 was as low as 1.75 V (at 75 °C), showing that high current operation for industrial alkaline water electrolysers is possible, when ohmic resistances are adequately addressed. The catalyst coated diaphragms were stable under room temperature for at least 60 h, however, showed degradation at 75 °C over the course of up to 240 h. The catalyst layers degraded by fracturing followed by delamination to the porous transport layer, where they showed elongated stability.

Modeling electrolytic transport for systems with concentration gradients, Ohmic resistance and electrochemical reactions

ABSTRACT This paper describes a two-dimensional multi-component electrolytic transport model that calculates the electric field by applying electroneutrality as an upper bound. This approach avoids directly enforcing electroneutrality in mass transport calculations or using Poisson’s equation. The two coupled equations of this model were numerically solved for cases with no convection. The transport equation was solved using a modified Control Volume method and a Peclet number. The electric field equation was discretized using the finite difference method and solved using the Alternating Direction Implicit method. The model’s results were compared with free-diffusion liquid junction data. Comparisons were also made with one-dimensional transport models. The model was then used to simulate two-dimensional scenarios without prescribed current distributions. The simulations agreed with the comparison data. Hence, the model shows promise in its ability to simulate two-dimensional multi-component electrolytic transport with concentration gradients, Ohmic resistance, and electrochemical reactions.

Sulfonated Styrene-Grafted Polyvinylidene Fluoride Copolymers for Proton Exchange Membranes for AQDS/Bromine Redox Flow Batteries.

This study presents the preparation and electrochemical testing of sulfonated styrene-grafted poly(vinylidene fluoride) (pVDF) copolymers as proton exchange membranes (PEMs) for semi-organic redox flow batteries (RFBs) based on 9,10-anthraquinone-2,7-disulfonic acid (AQDS)/bromine. The copolymers are synthesized via a two-step procedure, involving i) atom transfer radical polymerization of styrene (Sty) for the grafting to the pVDF backbone and ii) the sulfonation of the polystyrene grafted side chains. Copolymers with different amounts of sulfonated styrene (SSty) in the side chains (i.e., degree of sulfonation (DS)) are obtained and used for the preparation of PEMs by solution casting. The PEMs are characterized to assess their thermal, mechanical, water absorption, and ion exchange properties, to evaluate the effect of DS on membrane properties, and to select the membrane with the best overall performance for application in single cell tests. Electrochemical testing reveals that the pVDF-g-(Sty26-co-SSty14) membrane exhibits low crossover of redox species, favorable ohmic resistance, and energy efficiency. Results from single cell tests, as compared with commercial benchmarks such as Nafion 115 and Aquivion E87-12s, highlight the potential of such copolymers as alternative membranes for RFBs.

Influence of Contact Pressure on Hydrogen Crossover and Polarization Behavior in AEM Water Electrolysis

Abstract Anion exchange membrane water electrolysis (AEMWE) holds the potential to become a key technology for future hydrogen production. In the present study, the influence of contact pressure on hydrogen crossover and polarization behavior is systematically investigated in a range from 0.5 MPa to 2.5 MPa in 0.5 MPa increments. The electrodes were prepared as catalyst-coated substrate (CCS), applying 3 mg cm−2 NiFe2O4 on the anode substrate and 0.5 mg cm−2 Pt on the cathode substrate. It is demonstrated that an elevated contact pressure results in a decreased high frequency resistance (RHF), while simultaneously leading to a significantly increased hydrogen content on the anode side. At 3 A cm−2 the ohmic resistance decreases by approx. 30 mΩ cm2 when increasing the contact pressure from 0.5 MPa to 2.5 MPa, whereas the anodic hydrogen content increased by approx. 1.5 vol.% respectively. Additionally, it can be observed that the selection of the gas diffusion layer (GDL) material has a strong effect on hydrogen crossover, while the influence on cell voltage is insignificant. Overall, these results show a promising starting point for further investigations on the interactions between cathode properties, cell compression and anodic gas contamination.

Quantitative Correction of Ohmic Effects on Square Wave Voltammetry for High-Concentration Soluble-Soluble Redox Reactions in Molten Salts

Molten salts are of particular interest for a variety of industrial applications. As such, accurate characterization of species’ concentrations within the molten salt media is critical to ensure a well-controlled unit operation. Although electroanalytical tools are properly suited for precise in situ monitoring in these systems, uncompensated ohmic resistance R Ω can lead to erroneous, technique-dependent results. Using numerical simulations applied to a model system, this work will first illustrate then quantify the extent to which R Ω attenuates square wave voltammograms. This approach allows for post-experiment correction that leads to converging results across voltammetric techniques and facilitates accurate predictions of species’ concentrations.

MnO2 Nanowire Thin Mesh With Enhanced Mass Transfer as Hydroxide Exchange Membrane Fuel Cell Cathode

AbstractHydroxide exchange membrane fuel cells (HEMFCs) are promising due to the potential use of nonprecious metal catalysts. However, the performance of HEMFCs based on nonprecious catalysts is still unsatisfactory, and one reason for this is hindered mass transfer in the catalyst layer. In this study, we employ a hydrothermal method to grow in situ a MnO2 nanowire thin mesh (NTM) catalytic layer on the gas diffusion electrode. The HEMFC prepared with MnO2 NTM cathode achieves a peak power density of 425 mW cm−2, surpassing the performance of the HEMFC prepared using the traditional powder catalyst spraying method by four times. High‐frequency resistance and limiting current tests indicate that the MnO2 NTM reduces ohmic resistance and improves mass transfer, thereby enhancing the HEMFC performance. Furthermore, the peak power density of the HEMFC is increased to 626 mW cm−2 by depositing additional active Co3O4 nanoparticles on the MnO2 NTM. These findings demonstrate that an interconnected and porous catalyst layer structure is beneficial for improving mass transfer properties, which in turn enhances HEMFC performance.

Effect of differently shaped spiral inductors on micro power integrated circuit

Abstract This paper investigates the impact of parasitic effects on the performance of on-chip planar spiral inductors for DC-DC converter applications, focusing on three geometries: square, hexagonal, and octagonal. Detailed electromagnetic simulations in MATLAB are employed to analyze the frequency-dependent behavior of key parasitic components, including ohmic resistance (Rs), substrate resistance (Rsub), oxide capacitance (Cox), and substrate capacitance (Csub) across a frequency range of 1 GHz to 10 GHz. The study reveals that the octagonal spiral inductor outperforms the others, demonstrating a 29% reduction in ohmic resistance at 1.5 GHz compared to the square geometry and achieving the highest substrate resistance, which helps reduce current leakage. Additionally, the octagonal inductor exhibits the lowest parasitic capacitance and a high-quality factor, peaking at 30 at 4.2 GHz. These results underscore the significant impact of inductor geometry on minimizing energy dissipation and electromagnetic interference, positioning the octagonal spiral inductor as a compelling choice for enhancing efficiency and miniaturization in DCDC converter designs.

Identifying electrochemical processes by distribution of relaxation times in proton exchange membrane electrolyzers

Distribution of relaxation time (DRT) is used to interpret electrochemical impedance spectroscopy (EIS) for proton exchange membrane (PEM) water electrolyzers, with an attempt to separate overlapped relaxation processes in Nyquist plots. By varying operating conditions and catalyst loadings, four main relaxation peaks arising from EIS can be identified and successfully separated from low to high frequencies as (P1) mass transport, (P2) oxygen evolution reaction kinetics, (P3) reaction kinetics (with faster time constant than P2), and (P4) ionic transport. The shape, height, and frequency of the DRT peaks change with different membrane electrode assembly (MEA) configurations. Electron microscopy reveals distinct features from the cross-sectioned MEAs which verify critical DRT results in that increasing the iridium (Ir)-anode loading from 0.2 mgIr/cm2 to 1.5 mgIr/cm2 reduces kinetic losses due to higher site-access; a thick and compacted anode, however, also triggers higher ohmic resistances from membrane/catalyst layer hydration and increases transport losses due to longer ionomer pathways. DRT provides higher resolution to EIS for deconvoluting processes with different relaxation times and the quantification of DRT peaks improves the accounting of total losses from each process.

Oxygen Concentration and Reaction Rate Profiles Analysis of Polymer Electrolyte Fuel Cell

Introduction A one-dimensional (1D) model of polymer electrolyte fuel cells (PEFCs) is especially suitable for performance diagnostics, design optimization, and material evaluation, due to its high computational efficiency. Uniform distributions of reactants are commonly assumed in 1D models, i.e., a single representative reactant concentration inside the gas channel is required. However, this concentration is strongly dependent on the flow field. Although plenty of 1D models with sufficient accuracy as 3D models have been reported, the effects of the flow field have not been sufficiently discussed in the literature. In this work, efforts have been put into developing a generalized theory suitable for various flow fields to quantitatively analyze the in-plane reaction rate profile, so that the flow-field-sensitive representative reactant concentration can be employed to further fill the gaps in the 1D models. Analytical model A series of a plug flow reactor (PFR) and a continuous stirred tank reactor (CSTR) was proposed to explain the unideal flow and the macromixing behaviors inside a gas channel coupled with a gas diffusion layer (GDL), as shown in Fig. 1(a).[1] The fraction of PFR’s space time to total space time was defined as the characterization factor γ, which should be the function of flow field shape and flow rate. Furthermore, under-rib oxygen concentration and current density profiles were taken into account by introducing the dimensionless moduli.[2] Especially, the under-rib convection can be evaluated by Péclet modulus Pe, by increasing which will improve the under-rib mass transfer and the effectiveness factor f. The in-plane profile of the ohmic resistance of the membrane was assumed uniform. The oxygen reduction reaction (ORR) was regarded as a surface reaction occurring on the interface of cathode catalyst layer (CCL) and GDL. The ORR rate was assumed to be proportional to oxygen partial pressure and independent of relative humidity (RH). Results and Discussion The characterization factors γ of different flow fields were determined according to the residence time distribution simulated by the computational fluid dynamics (CFD) model. The ORR rate constant at each electrical potential was obtained from the measured polarization curve of a parallel gas channel (PN0) with 0.35 mm channel depth, by employing the analytical model mentioned above. Fig. 1(c) shows the polarization curves of parallel channels with staggered 1-mm-long partially narrowed structures (PSN1) and PN0 with different channel depths. Compared to the PN0, the under-rib convection improves the oxygen mass transport and the cell performance, where f increases 17 % at 0.35 V in the case of the PSN1. On the other hand, increasing the channel depth restrains the oxygen diffusion and f decreases by 18 % at 0.35 V. The analytical model results show good agreement with experiment data, which indicates that the effects of the flow field can be summarized by the parameters γ and f.The analytical model provides the in-plane oxygen mole fraction and current density profiles. Fig. 2 shows the oxygen partial pressure distribution in a single gas channel calculated by the CFD model and analytical model. The mean oxygen partial pressure on the under-channel CCL-GDL interface calculated by the analytical model approximately equals the CFD result. By employing the ohmic resistance estimated according to the inlet conditions, although the current density is underestimated where RH is high, the integral mean of the in-plane current density offered by the analytical model has less than 5 % error compared to the CFD results, as shown in Fig. 3.The analytical model also gives an effective way to estimate the integral mean in-plane oxygen partial pressure. Fig. 4 demonstrates the relationships among integral mean, inlet, and outlet oxygen partial pressures. When the reaction rate constant and effectiveness factor are fixed, Fig. 4 also reveals the relationships between total and local current densities. If the parameters γ and f are determined, the integral mean of the oxygen partial pressure can be obtained when the outlet oxygen partial pressure or oxygen conversion is known. Conclusions The analytical model quantitatively demonstrates the effects of the flow field shape and provides a quick and effective way to estimate the reaction rate profile, based on the fixed in-plane ohmic resistance assumption. This model was verified by experiment and CFD model in case of the oxygen conversion less than 0.33 and can be applied to ORR kinetics determination and rapid performance prediction. Reference [1] Y. Ma et al., J. Electrochem. Soc., 170, 084506 (2023).[2] Y. Ma et al., ECS Meet. Abstr., MA2023-02, 1867 (2023). Figure 1

(Invited) Investigation of Co-Free Cathode Composited with Proton Conductors for Protonic Ceramic Fuel Cells with Yb-Doped BaZrO3 Electrolyte

Protonic ceramic fuel cells (PCFCs) are expected to gain significant advantage from the use of Co-free cathodes. This shift can lead to reduced manufacturing costs and enhance durability performance. In our previous study, the investigation compared the power generation characteristics of PCFCs with BaZr0.8Yb0.2O3-δ (BZYb) electrolytes utilizing cathodes composed of La0.6Sr0.4FeO3-δ (LSF) as a Co-free cathode material and La0.6Sr0.4CoO3-δ (LSC) or La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) as Co-containing cathode materials composited with BZYb. Consequently, the PCFC with an LSF-BZYb cathode exhibited lower performance compared to the PCFCs with LSC-BZYb and LSCF-BZYb cathodes due to the higher electrode polarization resistance.In this study, the challenges associated with achieving high-performance Co-free cathodes that can match the performance of Co-containing cathodes are presented, along with the mechanism to enhance performance. To improve performance, the use of La0.65Ca0.35FeO3-δ (LCaF), as a Co-free cathode, in addition to LSF, which has been reported to demonstrate high performance in SOFCs, was explored. Additionally, LCaF was composited with BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb), known for its higher proton conductivity and easier sinterability than BZYb.When comparing the power generation characteristics of PCFCs with LCaF-BZYb and LSF-BZYb cathodes, the PCFC with LCaF-BZYb cathode exhibited higher ohmic and electrode polarization resistances. These results were attributed to weak adhesion between the electrolyte and cathode, resulting in lower performance than the PCFC with LSF-BZYb cathode.Furthermore, when comparing the power generation characteristic of the PCFC with a composite cathode of LCaF and BCZYYb with the LCaF-BZYb cathode, the ohmic and electrode polarization resistances were significantly lower. This improvement was attributed to the advanced sintering of BCZYYb and the connected percolation of the proton-conducting network. Consequently, the performance of the PCFC with the LCaF-BCZYYb cathode surpassed that of the LCaF-BZYb cathode and was comparable to Co-containing cathodes such as LSC-BCZYYb cathode.In conclusion, for Co-free cathodes in PCFCs, it is crucial to composite them with proton conductors possessing better sinterability, such as BCZYYb, to achieve higher performance.Acknowledgements: This work is based on the results obtained from a project (JPNP20003) commissioned by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Investigation on Electrochemical Reaction for Anion Exchange Membrane Electrode Assembly-Based Electrolyzer

Although the use of fossil fuels is gradually decreasing every year, it still accounts for more than 80% of global energy consumption, and discriminatory use is causing a significant increase in atmospheric CO2 concentration and global warming. In order to control the indiscriminate use of fossil fuels that cause environmental problems, establishing an eco-friendly energy conversion system is essential. The water electrolysis using surplus power generated from renewable energy is recognized as a representative system that can produce high-purity hydrogen from water. On the other hand, CO2 electrolysis is also a promising energy conversion technology that can reduce atmospheric CO2 centration because it electrochemically converts CO2 into valuable carbon products. Both of the above systems are based on electrochemical reactions, which means they can operate under moderate conditions with zero pollutant emissions.In general, the composition of conventional energy conversion system includes an electrolyte layer, which has a large ohmic resistance and limitation of CO2 solubility, which reduces energy efficiency. To address the disadvantage of the conventional system, membrane electrode assembly (MEA)-based electrolyzer are receiving attention. The MEA consists of an electrode and a membrane with a polymer membrane capable of ion exchange between the anode and the cathode. These MEA-based electrolyzer has a zero-gap configuration, providing minimized ohmic resistance and improved energy efficiency. Among them, various studies are being actively conducted on applying an anion exchange membrane (AEM) to MEA-based electrolyzers. When using AEM, water electrolysis has the advantage of being able to use a non-noble metal catalyst, which can reduce costs, and CO2 electrolysis has the advantage of reducing the hydrogen evolution reaction (HER), which is a competing reaction.Herein, the electrode with a structure in which electrocatalyst is loaded on a porous transport layer (PTL) is fabricated by the facile electrodeposition method. The electrodeposition is possible to fabricate self-supported electrodes by modulating catalytic properties such as morphology, composition, and crystallinity by controlling various parameters. Additionally, ionomer and binder-free electrode structure prepared through electrodeposition contributes to improving catalytic performance by promoting electron transfer to the active site. Moreover, the as-prepared porous transfer electrodes (PTE) are used as cathode and anode in anion exchange MEA-based electrolyzer and exhibit reasonable single-cell performance, suggesting that PTEs prepared via electrodeposition are suitable for energy conversion systems such as water electrolysis and CO2 electrolysis.In the MEA configuration, three cathodes, anodes, and AEM were optimized. In the cathode part, the HER was optimized using catalysts such as NiMo, Pt, and PtRu, and the CO2 electrolysis was optimized using Au, Ag, Cu, and Pd. In the anode part, the oxygen evolution reaction (OER) was optimized using catalysts such as NiFe, IrO2. In the membrane part, optimization was performed by comparing the commercial membrane and the fabricated fluorine-containing poly(fluorene)-based AEM.

Improvement of Reversal-Tolerance By Ti4O7-C Supported Pt-Ir Composite Catalysts

ABSTRACTWhen hydrogen is depleted in PEFCs, the anode potential increases (cell reversal), which involves the oxidation of carbon (COR), resulting in the deactivation of the anode. The addition of the oxygen evolution (OER) catalysts has been reported to suppress the degradation1. Ioroi et al. have reported that the combination of Ti4O7 with Ir catalysts improved the reversal-tolerance2. Li et al. have recently reported that Pt-IrO2 catalyst supported on Ti4O7 exhibited excellent reversal-tolerance3. We have also independently found a similar combination to be effective using Ti4O7-C synthesized by the carbothermal process4 and reported that the composite catalysts (Pt and OER catalysts supported on Ti4O7-C) showed better reversal-tolerance than the physical mixture of Pt/Ti4O7-C and Ti4O7-supported OER catalysts5. In this study, the composite effect of Pt-Ir was studied in terms of the chemical state of iridium catalysts and the effect of Ti4O7-supported catalysts. The reversal-tolerance was evaluated on the hydrogen pump.Experimental Preparation of catalysts: 20 wt% Pt/Ti4O7-C (11 wt% C) was prepared as previously reported4. IrO2 catalysts Ti4O7-C or Pt/Ti4O7-C was impregnated in IrCl3 solution, and hydrothermally treated at 180°C. Afterwards, the sediment was washed and dried at 80°C. 3.8 - 5.7 wt% IrO2/Ti4O7-C and 18 wt% Pt-3.7 wt% IrO2/Ti4O7-C were used for the physical mixture catalysts (hereafter denoted as “catalyst name-M”) and the composite catalyst, respectively. Ir0 catalyst Pt/Ti4O7-C was dipped into IrCl3 aqueous solution, and NaBH4 solution was added. It was washed by ethanol and water and dried at 80°C. Electrochemical measurement: The MEA was composed of Nafion NRE211 as the electrolyte membrane, a commercial heat-treated c-Pt/CB as the cathode (0.5 mg-Pt/cm2), and the above-mentioned catalyst or the physical mixture catalyst as the anode (0.2 mg-Pt/cm2). A commercial c-Pt/CB was also used for a physical mixture catalyst. The Ir loadings were 0.036 - 0.047 mg/cm2 and are indicated in parentheses. The performance was firstly evaluated with IV curves, and then the hydrogen pump, CV and LSV were conducted by flowing H2 gas to the cathode under 80°C fully humidified condition. The cell reversal test was performed by switching the anode supply gas to N2 (RH 78%) while the hydrogen pump was carried out at 0.2 A/cm2, and it was kept it was kept for 10 minutes at a cutoff voltage of 2.7 V. After the test, the same check of the characteristics was conducted. The second test was repeated in the same manner, and the third test was performed until it reached the cutoff voltage.Results and Discussion Difference in Ir chemical states of composite catalysts: The difference between IrO2 and Ir0 catalysts was studied (Cat 1 and Cat2). Both catalysts exhibited similar behavior. It was inferred that the oxidized Ir on the surface functioned as the active species for both catalysts3. Since 41% of Ir was leached after the tests for Pt-IrO2/Ti4O7-C catalyst (Cat1), the catalyst calcined at 300°C was also tested. Though the amount of leached Ir by the tests was suppressed to 10%, the degradation behavior hardly changed. Effects of Ir catalysts for the physical mixture catalyst: To confirm the effect of Ti4O7-C-supported IrO2 catalyst for the physical mixture catalyst, the same loading of Ir black was added to Pt/Ti4O7-C (Cat4). It showed better reversal-tolerance than the catalyst with IrO2/Ti4O7-C (Cat3), which means that the reversal-tolerance was improved in the case that Ir was supported on Pt/Ti4O7-C. Differences between Pt/Ti 4 O 7 -C and c-Pt/CB for the physical mixture catalysts: For the physical mixture catalyst with IrO2/Ti4O7-C, c-Pt/CB was used (Cat5). c-Pt/CB showed better reversal-tolerance than the catalyst with Pt/Ti4O7-C. Even though the catalyst with c-Pt/CB held below 1.7 V during the second test, the performance on the hydrogen pump deteriorated, because the COR slowly occurred below 1.7 V2. On the other hand, Ti4O7-C supported Pt-based catalysts did not exhibit significant deterioration on the hydrogen pump while they were kept below 1.7 V, and the HOR activity decreased after the anode voltage increased over 1.7 V. We have confirmed that the Ti4O7-C was slightly oxidized above 1.7 V, however the increase in the ohmic resistance was not the main factor for the increase in the voltage.This work was supported by NEDO.(1) T. R. Ralph et al., Platinum Metals Rev. , 46, 117 (2002). (2) T. Ioroi et al., J. Power Sources, 450, 227656 (2020). (3) Z. Li et al., Energy Environ . Sci ., 17, 1580 (2024). (4) M. Chisaka et al., Chem. Comm. , 57, 12772 (2021). (5) H. Wakita et al., In s of Papers, The 91st ECSJ Annual Meeting, S9-1_3_06, Electrochemical Society of Japan, Nagoya (2024). Figure 1

Sr Doped LaScO3 Thin Film As Cathodic Functional Layers for Ni-Fe Metal Supported Protonic Ceramic Fuel Cell Using BaZr0.44Ce0.36Y0.2O3 Film

Metal support proton conducting fuel cells (MS-PCFCs) is expecting as highly efficient and reliable power generation devices. In this study, porous Ni-Fe alloy support PCFCs was studied using BaZr0.44Ce0.36Y0.2O3 (BZCY) film prepared by pulsed laser deposition (PLD) method. For increasing power density, the effects of the La(Sr)ScO3 (denoted LSSc) at the cathodic interlayer were studied. BZCY film was deposited on dense NiO-NiFe2O4 oxide support by PLD, followed LSSc is deposited as a cathode functional layer (CFL). Sm0.5Sr0.5CoO3 (SSC) was used for the cathode, and then NiO-NiFe2O4 was reduced to obtain the porous metal substrate. Humidified H2 and O2 were used for fuel and oxidant, respectively. Metal support BZCY cell was successfully prepared, and open circuit potential (OCV) and maximum power density were 0.99 V and 69 mW/cm2, respectively at 600 ºC. So reasonable power density was achieved on the Ni-Fe support BZCY film. The main potential drop is occurred by ohmic resistance. Effects of the cathodic functional layer were studied, and it was found that La(Sr)ScO3 film at the interlayer between BZCY and SSC was highly effective for increasing the power density of the cell by decreasing IR loss and overpotential. The optimization of LSSc film was performed and the optimum Sr amount was 15 wt % in LSSc film and the thickness was 200 nm. The power density of MS-PCFCs with LSSc15 CFL was 405 mW/cm2 and an open-circuit voltage (OCV) was ca.1.1 V at 600 ºC, as shown in Figure 1. Due to enhanced proton conductivity, interfacial resistance and cathodic overpotential were also decreased. Insertion of LSSc CFL is highly effective for improving the performance of MS-PCFCs.Acknowledgment; Part of this study was financially supported by New Energy and Industrial Technology Development Organization (NEDO, JPNP20003), JapanReference[1] H. Sumi, H. Shimada, K. Watanabe, Y. Yamaguchi, K. Nomura, Y. Mizutani, R. M. Matsuda, M. Masashi, K. Yashiro, T. Araki, Y. Okuyama, J. Power Sources 2023, 582, 233528[2] A,Y. Stroeva, and V. P. Gorelov. Russian Journal of Electrochemistry 2012, 48, 1079-1085 Figure 1

Evaluation of Extremely Stable Redox Active Materials and Porous Electrodes for Redox Flow Batteries Using Static Cells and Physics-Based Modeling

Aqueous Organic Redox Flow Batteries (AORFBs) have shown growing potential as a stationary energy storage technology used to alleviate the issue of intermittencyi for renewable energy sources. For systems with charge/discharge duration of 10 or more hours, the capital cost of a flow battery asymptotically approaches the cost of the electroactive material.ii While the field has made many new materialsiii and developed proper protocols for evaluating their decompositioniv, uncertainty in the fade rates of extremely stableiii materials remains comparable to the fade rates themselvesv, frustrating the evaluation of prospects of the material for commercialization. Additionally, evaluation of new materials in flow cells requires a significant amount of material synthesis, whereas evaluation methods requiring less material could accelerate the development of AORFBs.vi To reduce noise in measurements by removing pumping, splashing, and bubbling of solutions that occurs in flow cells, and to reduce the amount of required active material, we use static cells composed solely of porous electrodes sandwiched about a membrane, gaskets, and graphitic current collectors with no flow. With reduced material consumption, increased cycling rate, and less noise in capacity measurements, we more rapidly and more accurately determine the capacity fade rates for extremely stable materials for AORFBs (Figure 1) and test the limits for cycle-denominated fade rates. In addition, we discuss relevant reporting statistics for making fair comparisons between extremely stable materials.To evaluate overpotentials in the system due to kinetics, mass transfer, and Ohmic resistance, we model the system using Newman’s porous electrode modelvii to ensure the use of proper cycling protocols to access all of the capacity of the system.Figure 1: (left) An example of potentiostatic cycling of 0.1 M 2,6-DPPEAQ at pH 14 in a volumetrically unbalanced compositionally symmetric static cell with an applied voltage square wave of amplitude 0.20 V across the cell, held until the current drops to 1 mA/cm2. After cycling for a day while the electrolyte equilibrates, a capacity fade rate is evaluated from the slope of the natural log of discharge capacity vs time. (right) A whisker and box plot for capacity fade measurements from several potentiostatic symmetric cell cycling experiments in a flow cell from Ref [5], static cells with no attention to temperature fluctuations, and static cells where temperature fluctuations are kept within 1 degree Celsius.[i] J. Rugolo and M. J. Aziz, “Electricity storage for intermittent renewable sources.” Energy Environ. Sci., 2012, 5, 7151[ii] F. R. Brushett, M. J. Aziz, and K. E. Rodby. ACS Energy Lett. 2020, 5, 879−884[iii] David G. Kwabi, Yunlong Ji, and Michael J. Aziz, “Electrolyte Lifetime in Aqueous Organic Redox Flow Batteries: A Critical Review.” Chemical Reviews 2020 120 (14), 6467-6489[iv]M.A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”. J. Electrochem. Soc, 165 (7) A1466-A1477 (2018)[v] Eric M. Fell and Michael J. Aziz, “High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Battery Active Material.” 2023 J. Electrochem. Soc. 170 100507[vi] Cao, Y., Aspuru-Guzik, A. “Accelerating discovery in organic redox flow batteries.” Nat Comput Sci 4, 89–91 (2024)[vii] J. Newman and C. W. Tobias, J. Electrochem. Soc., 1962, 109, 1183 Figure 1

Multifunctional Calorimeter for Thermal Characterization of Pouch and Cylindrical Cell

Thermal management system (TMS) is crucial for the batteries to reject the heat generated during charging and discharging and maintain the proper working temperature. The design of cooling system requires accurate quantification of heat generation rate (HGR) of the cells. During actual operations, the HGR is further affected by various conditions such as temperature gradient and mechanical pressure. The inhomogeneous distribution of current density within the cell can cause a temperature gradient across the cell body. The volume changes taking place during charging and discharging can cause mechanical pressure to the adjacent cells or busbar in the battery pack. These conditions can affect the electrochemical-thermal behavior of the cells [1], [2]. In this work, a multifunctional calorimeter has been developed that enables accurate measurement of HGR under temperature gradient and mechanical pressure as testing conditions. Most of commercially available calorimeters generally have a large thermal time constant between the measuring points and the heat source of the cell while the developed one provides direct contact between the cell and the cooling plate and, a flexible fit to the dimensions, shape and format of the measured cells. In addition, it facilitates an accurate regulation of a constant reference temperature to create isothermal conditions (± 0.1 °C at continuous charging, ± 0.5 °C at pulse profile) and a tracking control that allows for determination of the entropy coefficient (EC, dUoc/dT) [3] for not only different formats of pouch cells but also cylindrical cells as shown in Figure (a).To study the temperature gradient effect, the cell is divided into three equal segments in the longitudinal direction, whose temperatures are separately controlled, creating uniform temperature (MMM, 25 °C) and high-low-high (HLH 28-18-28 °C) temperature conditions across the cell. The results At BOL have shown that the integrated total heat generation over the full discharge range (THG) is suppressed by the HLH when the high C-rates are applied. Further, two aging profiles are applied with the conditions of MMM and HLH. At MOL (400 cycles), the capacity fades of the MMM and HLH conditions are around 4% and 7%, respectively, as shown in Figure (b,1). Also, the HGR exhibits that HLH condition generates more heat than the MMM case after the cell is aged as shown in Figure (b,2).To study the pressure effect, the pressure conditions were set to be 30 kPa, 100 kPa, 170 kPa, 240 kPa and 310 kPa. The results have shown that while the discharge capacity of the cell is not significantly affected by the increase of compressive mechanical pressure, the HGR reduces as the pressure increases, especially at high C-rates, as shown in Figure (c). We further separately probe the reversible and irreversible heat generation heat source to root the cause of the decrease in HGR. The EC is measured at the five selected pressure conditions, and the trend and magnitude are found to be very similar at all SOC, which indicates that the reversible HGR is minimally affected by the increasing pressure. Then, the impedance measured by Electrochemical Impedance Spectroscopy (EIS) have shown a decreasing trend of Ohmic resistance and Charge Transfer resistance as the pressure increases, but not the SEI resistance. Consequently, the decrease in HGR as the compressive pressure increases is attributed to the decrease in Joule heating relating to the Ohmic resistance and Charge Transfer resistance, which is caused by the reduced contact resistance between the current collector and electrode and the decrease of ion transport distance in electrolyte.Furthermore, the accurate temperature regulation allows us to control a sinusoidal temperature profile and determine the EC using the Hybridized time-frequency method. The results show that temperature does not have a significant impact on the EC within 0-45 °C, as shown in Figure (d,1). At around 40% SOC, there is a transition point where the reversible HGR has been changed from exothermic to endothermic process if during continuous discharging. Moreover, the EC at different capacity fades (CF) has shown a gradual shift of the peak from B to B’ in the SOC direction, which might be related to the mechanism change during the aging, as shown in Figure (d,2).[1] Du, X., Hu, Y., Song, M., Choi, C., Choe, S. Y., Labaza, C., Gao, J., Koch, B. J., & Garrick, T. R. (2023). Journal of Power Sources, 587, 233688.[2] Du, X., Hu, Y., Choe, S. Y., Garrick, T. R., & Fernandez, M. A. (2023). Journal of Power Sources, 573, 233117.[3] Hu, Y., Choe, S. Y., & Garrick, T. R. (2020). Electrochimica Acta, 362. Figure 1

Performance and Durability of Metallic Aerogel Anode Catalyst in Pure-Water-Fed Hydroxide Exchange Membrane Electrolyzers

Hydrogen holds significance as a versatile energy carrier that can be used in various sectors. Recently, hydroxide exchange membrane electrolyzers (HEMELs) towards clean hydrogen production have gained intensive attention, due to the possibility to use low-cost platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers.1 Although a variety of PGM-free catalysts have shown promising activities towards the alkaline oxygen evolution reaction (OER), few of them delivered sufficient stability in the pure-water-fed HEMELs.2 In this work, metallic aerogel, featured with high porosity and amorphous metal oxide shells, was deployed as platform to study the structural-performance relationship in HEMELs. A poly(aryl piperidinium) membrane and ionomer with high hydroxide conductivity were integrated to study the evolution in the composition and structure of PGM-free anode catalysts.3 Owing to unique properties of the 3D metallic aerogel, the optimal aerogel anode outperformed the Ir-based anode in the KOH-fed HEMELs. A transition in the HEMEL performance with different anode catalyst was observed when shifting from alkaline electrolyte to pure water, implying a steering in the rate limiting steps in the different anode feedings. The limiting factor of pure-water-fed HEMEL was probed by deconvoluting the contributions from ohmic resistance, electrode kinetic, and mass transport. The optimal metallic aerogel anode showed no performance loss during the 580-hour stability test at an industrial electrolyzer-relevant current density of 1 A cm−2 in pure water feeding. The HEMEL performance was monitored, revealing the degradations of critical components in the membrane-electrode-assembly. The structural performance relationship in HEMEL was probed by linking the physical properties of the catalysts with HEMEL performance. The gained insight will shed light on the development of highly efficient PGM-free anode catalysts for viable pure-fed HEMELs.References R. Abbasi, B. P. Setzler, S. Lin, J. Wang, Y. Zhao, H. Xu, B. Pivovar, B. Tian, X. Chen, G. Wu and Y. Yan, Advanced Materials, 31, 1805876 (2019).M. Chatenet, B. G. Pollet, D. R. Dekel, F. Dionigi, J. Deseure, P. Millet, R. D. Braatz, M. Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn and H. Schäfer, Chemical Society Reviews, 51, 4583 (2022).J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. Ben Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu and Y. Yan, Nature Energy, 4, 392 (2019).

Dcir for in-Situ Analysis of Li-NMC Batteries

This research delves into the qualitative analysis of internal processes in lithium nickel manganese cobalt oxide (Li-NMC) batteries by utilizing direct current (DC) techniques throughout the battery's lifecycle. Expanding on the comparative approach between electrochemical impedance spectroscopy (EIS) and DC techniques highlighted by Martin Winter1, this study emphasizes the exclusive application of DC techniques for an in-situ understanding of battery behavior without the potentially performance-impacting application of EIS. By systematically measuring resistance changes, this work uncovers the effects of lithium coatings, electrode thickness variations, and the operation of anode-free batteries on the internal resistance profiles. The methodology provides a non-invasive insight into the electrochemical dynamics, enabling a deeper understanding of the material and design factors that influence battery efficiency and longevity. Utilizing the information imbedded within the electrochemical data the plating overpotential which translates into the ohmic resistance, a pattern is seen connect the ohmic resistance to that of cycle stability. Understanding the resistance helps to identify characteristics that have been previously hidden without intrusive testing. L. Stolz, M. Gaberšček, M. Winter and J. Kasnatscheew, Chemistry of Materials, 2022, 34, 10272-10278.

Investigating the Effect of Catalyst Configuration on the Performance of Silver-Based Membrane Electrode Assemblies for Electrochemical CO2 Reduction

As one of the most dominant greenhouse gases, CO2 plays a critical role in climate change. Electrochemical CO2 reduction (eCO2R) is a promising approach to mitigate this impact, as it is capable of converting the excess gas into valuable chemicals, especially concerning electrical energy storage from renewable sources at peak times. However, due to high overpotentials, the technology is still in a rather early stage of development and not yet feasible for economic implementation on industrial scale. One of these limitations results from the poor solubility of CO2 in water or commonly used aqueous electrolytes, leading to insufficient transport of the reactant gas to the cathode in classical H-cell setups. Therefore, gas diffusion electrodes (GDEs) are typically employed to reduce the according mass transport resistances [1]. Furthermore, ohmic resistances, among others caused by the electrolyte gaps in the system, contribute to overpotentials. To decrease these constraints, conducting CO2 reduction at membrane electrode assemblies (MEAs) is an interesting opportunity that has been gaining more and more attention in research throughout the past years. Exemplarily, fig. 1 shows that the elimination of only the catholyte compartment and thus implementation of an exchange MEA can already decrease the cell potential by more than 30 % at 2 kA m-2 in comparison to GDE [2] setup.Depending on the cathodic catalyst, there are various reaction routes of eCO2R, one of which aims to synthesize the target product carbon monoxide. This is possible e. g. at silver catalysts, providing high CO selectivity and hydrogen as the only byproduct [3]. The combination of these products, syngas, is an important feedstock for many chemical processes such as Fischer-Tropsch synthesis. Although the majority of studies regarding silver-based MEAs for eCO2R uses pure silver as a catalyst, the configuration of the material is varying: While we usually disperse a mix of powder and flakes to obtain our catalyst suspension, nanoparticles are more frequently used in literature [3-5]. Moreover, porous silver membranes [6, 7] or silver deposited from solutions such as AgNO3 [8] and various other structures have already been investigated. Anyways, when comparing the results yielded with the different configurations of silver (cf. fig. 1), it becomes clear that there is no obvious trend in which material generates the best performances. A closer look at the conditions of the corresponding experiments reveals that this is quite plausible, as there is, on the one hand, no uniform MEA manufacturing procedure: Not only are there deviations in the employed material form, but also the gas diffusion layer, ionomer and membrane as well as ink fabrication and processing. On the other hand, the electrochemical measurements are alternating between galvanostatic and potentiostatic methods with no constant active electrode area, let alone type of test cell or setup.Therefore, this study aims to investigate the influence of differing catalyst configuration used for MEAs while maintaining other parameters concerning manufacturing and characterization procedure. The base of all MEAs is a carbon-based gas diffusion layer of the same supplier and type. An anion exchange ionomer is chosen to enhance the mass transport of the reactants to the catalyst. Only the form of the catalyst, e. g. powder, nanoparticles or fixed structures, is varied. The catalyst and ionomer are attached to the gas diffusion layer which is then sandwiched with the membrane corresponding to the ionomer. Conducting galvanostatic step experiments in exchange MEA setup with a fixed type of anode, the performance of the resulting MEAs is evaluated. This way, important effects on parameters such as Faradaic efficiency for the target product and cell potential can be unraveled.Literature:[1] T. Burdyny, W. A. Smith, Energy Environ. Sci. 12 (5), 2019.[2] I. Moussallem et al., Chem. Eng. and Proc. 52 (2012).[3] Y. Hori et al., Chem. Lett. 14 (11), 1985.[4] Z. Liu et al., J. Electrochem. Soc. 165 (15), 2018.[5] R. B. Kutz et al., Energy Technol. 5 (6), 2017.[6] Y. C. Li et al., ACS Energy Lett. 1 (6), 2016.[7] G. O. Larrazábal et al., ACS Appl. Mater. Interfaces 11 (44), 2019.[8] W. H. Lee et al., J. Mater. Chem. 9 (29), 2021.[9] Y. Hori et al., Electrochim. Acta 48 (18), 2003. Figure 1

Simulation of Voltammetric Measurements of Uranium Electrodeposition in Molten LiCl-KCl Eutectic

The electrochemical behavior of uranium in high-temperature molten salts is central to the development of advanced nuclear reactors (e.g., molten salt reactors) and reprocessing technologies (e.g., pyroprocessing). Numerous studies have been performed on uranium in molten salts, especially LiCl-KCl eutectic. However, many studies rely on models, such as Berzins-Delahay model, which assume mass transfer by diffusion only and a pure deposit (i.e., unit activity for the reduced species).1 In many situations, these assumptions may not be appropriate for analyzing electrochemical data in molten salts and may introduce significant error in the estimation of properties, such as diffusion coefficients. For example, a foreign substrate, such as tungsten or molybdenum, is often used as the working electrode in electroreduction of uranium ions to metal in molten salts. Hence, nucleation effects and incomplete coverage of the WE can affect measurements, especially at dilute concentrations. Additionally, macro electrodes are often used in molten salts due to a lack of compatible insulating material for construction of microelectrodes. This results in large currents which can introduce significant ohmic losses despite the relatively low ohmic resistance of molten salts. Furthermore, additional effects, such as migration and natural convection, can significantly impact electrochemical measurements in molten salts containing a heavy analyte, such as uranium ions.To address these challenges, a model was developed specifically for electrodeposition in molten salts based on the Nernst-Plank equation, Nernst equation, adsorption isotherms, and activity models. The initial iteration of the model has been designed to account for the combined effects of diffusion, migration, ohmic resistance, deposition onto a foreign substrate, and activity of non-ideal solutions. The significance of each effect and combination of effects has been examined for linear sweep voltammetry at various uranium ion concentrations and scan rates. Furthermore, the model has been validated against uranium electrodeposition measurements on a tungsten WE in molten LiCl-KCl eutectic.1. T. Berzins and P. Delahay, J. Am. Chem. Soc., 75, 555–559 (1953) http://dx.doi.org/10.1021/ja01099a013.

Innovative Anode Design Incorporating Sub-Catalyst Layer for Proton Exchange Membrane Water Electrolyzers with Ultra-Low Iridium Loading

Proton exchange membrane water electrolyzers (PEMWE) have garnered increasing attention in recent years due to their capability to produce clean, high-purity hydrogen. The optimization of the catalyst layer structure within these systems is critical, particularly in reducing the loading of platinum-group metal (PGM) anode catalysts. Under conditions of ultralow iridium loading, ion and mass transport are severely impeded, which hampers the kinetic performance of oxygen evolution reaction (OER) catalysts.In this study, we propose an innovative membrane electrode assembly (MEA) design for PEMWE, wherein an ultra-thin sub-catalyst layer is constructed atop the conventional catalyst layer. This sub-catalyst layer, fabricated via spray coating with an ultra-low iridium loading of less than 0.05 mg/cm², possesses a high surface area and is engineered to enhance the interfacial contact area between the catalyst layer and the porous transport layer. The integration of this sub-catalyst layer markedly reduces both kinetic and ohmic resistances, thereby lowering the overall overpotential.Our findings demonstrate that this novel approach results in a significant increase in the current density of the electrolyzer by 400 mA/cm² and a reduction in high-frequency resistance (HFR) by 35 mΩ cm², when compared to the conventional MEA structure. This study highlights the potential of the proposed MEA design to improve the efficiency and performance of PEMWE systems, contributing to the advancement of clean hydrogen production technologies.