Apparent Current Density Research Articles

Guidance for targeted degradation analysis of OER kinetics of low-loading iridium-based catalysts in PEM water electrolysis cells

This paper critically evaluates three methods for determining metrics of the oxygen evolution reaction (OER) describing the performance and stability of low-loading iridium-based anode catalyst layers (CLs) in proton exchange membrane water electrolysis (PEMWE) cells. The methods applied are OER mass activity, voltage breakdown analysis (VBA), and constant Tafel slope VBA (CT-VBA). They are used to assess the OER metrics as a function of anode CL configurations, potential cycling, and level of degradation. Therefore, various accelerated stress tests (ASTs) are carried out for a targeted degradation of different anode CLs based on Ir black or Ir oxide. It turns out that the OER mass activity method is robust, straightforward and an ideal method for e.g., in-house screening tasks. On the other hand, the VBA method is suitable for comparative analysis across laboratories by distinguishing between the three main overpotentials. The CT-VBA method, however, offers improved accuracy, as it accounts for mass transport overpotential at low current density, and is particularly suitable for determining apparent exchange current density values further used in modelling approaches. This benefit comes with a drawback, as commonly accepted reference Tafel slopes for respective catalyst type and PTL configurations would be required within the PEMWE community. This guidance therefore helps to choose the right method for determining OER metrics depending on the research question.

Interpreting the main effects on the efficiency and morphology for establishing a procedure of electrodepositing Zn from purified chloride SPL solutions

Potentiodynamic and galvanostatic experiments have been used to investigate the electrodeposition of Zn and to develop a reliable recovery method from a purified spent pickling liquor (SPL) of hot dip galvanization. The main bjective was to find the suitable conditions to deposit high-grade Zn from the purified ZnCl2–HCl–NaCl solution in a conventional electrowinning cell holding the stationary electrolyte. The effects of pH (1.5–4.5) in and Zn concentration (30–150 g/dm3) in the stationary electrolytes were studied first by the potentiodynamic method to reveal the major characteristics of the cathodic process and to give reference for further practical examinations by the galvanostatic technique. The electrowinning experiments pointed out the effects of these major parameters, beside other practical factors, like apparent current density (c.d.) and additional NaCl concentration. The long-term galvanostatic experiments proved that the current efficiency (c.e.) increases significantly as the pH and the Zn concentration are increased. A c.e. of ~ 99% can be reached with an electrolyte of pH ~ 5, Zn concentration ~ 50 g/dm3 applying a c.d. in the 300–600 A/m2 range. Increasing the Zn concentration could considerably improve also the deposit morphology. The addition of NaCl can practically improve the c.e. if the Zn concentration is at least around 50 g/dm3. In contrast, this improvement is largely off-set by the negative effects of strong H2 evolution at low (e.g. < 10 g/dm3) Zn concentrations. Extremely high Cl− ion concentrations, however, inhibit the cathodic reaction by stronger chloro-complex formation. In this case the intensive H+ reduction causes hydroxide precipitation.

Photoelectrochemical CO2 reduction in tandem photoelectrode cells: Interpretation of apparent photocurrents

Photoelectrochemical reactors harness solar energy to accelerate heterogeneous chemical reactions and reduce power consumption for a given reaction rate. The tandem photoelectrochemical cell design presented here employs a light penetrable TiO2 photoanode||Cu2O photocathode configuration that enables carbon dioxide turnover at limited cell voltages. During polarization tests, the tandem configuration demonstrated a photocurrent density of 0.2 mA/cm2 at a cell voltage of -2.6 V. That is 2-fold higher than the photocurrent density obtained with a solo photoanode (Cu||TiO2) and five orders of magnitude higher compared to the solo photocathode (Cu2O||Ni) design. Moreover, electrolysis under illumination (photoelectrolysis) showed a current density increase of 3.9 mA/cm2 with respect to electrolysis in the dark. However, this photocurrent density was merely apparent and was caused by light-triggered changes in the surface morphology and phase of Cu2O, which in turn affected the catalytic response. Moreover, the apparent partial ethylene photocurrent density and total partial current density during photoelectrolysis was 44 %, the highest among the detected products. That selectivity is attributed to the combined effect of Cu2O photoreduction and the associated local pH rise at the electrode-electrolyte interface.

VLF-EM data conversion into apparent resistivity using the Hilbert transform and its application for shallow fault investigation at Pinggirsari, Bandung Regency, Indonesia

This research presented the ability of the Hilbert transformation of The Very Low Frequency-Electromagnetic (VLF-EM) data to investigate the presence of faults. VLF-EM data was collected in the Pinggirsari village area, Arjasari District, Bandung Regency, West Java, Indonesia. Through the Hilbert transformation, the VLF-EM data was converted into apparent resistivity data and then inverted into a resistivity cross-section. For comparison, qualitative interpretation was also conducted using both the Fraser and the Karous-Hjelt filters. Interpretation results using both the Fraser and Karous-Hjelt filters indicate the presence of faults through tilt-angle curve peaks and apparent current density anomalies. The resistivity cross-section resulting from the Occam inversion of the apparent resistivity data, derived from the Hilbert transformation, accurately delineated fault positions. Resistivity changes around 700–800 m indicated fault proximity to a depth of approximately 150 m, with a good match to the geological map. Within a distance of 0–700 m, low resistivity values were associated with the Malabar tuff, while >700 m, higher resistivity values were associated with the Waringin-Bedil andesite. The Hilbert transform helps in clarifying VLF data interpretation for precise fault detection through resistivity parameters.

Critical performance comparisons between the high temperature and the low temperature proton exchange membrane fuel cells

Currently, there are only some general concepts about the performance difference between an LT-PEMFC (low temperature proton exchange membrane fuel cell) and an HT-PEMFC (high temperature proton exchange membrane fuel cell), i.e., no literature has been found to conduct direct comparisons between them. In this research, for the first time, according to the same level (low level, medium level or high level) under the same operating condition type (operating temperature or cathode air utilization rate), the tested I-V performance, EIS (electrochemical impedance spectroscopy), LSV (linear sweep voltammetry), and calculated ECSA (electrochemical surface area) are compared between LT-PEMFC and HT-PEMFC. Some mechanisms are further disclosed, for instance, the higher Pt loading in the catalyst layer of an HT-PEMFC and its elevated operating temperature do not result in improved performance, compared to that of the LT-PEMFC. This is attributed to the lower apparent exchange current density in the case of HT-PEMFC.

Advanced Method for Voltage Breakdown Analysis of PEM Water Electrolysis Cells with Low Iridium Loadings

Proton exchange membrane water electrolysis (PEMWE) is an established technology for hydrogen production. To meet the increasing demand and further reduce costs, there is a growing interest in reducing the iridium (Ir) loading. In recent works the complex interface between porous transport layer (PTL) and catalyst layer (CL) was identified as pivotal for PEMWE performance. In this study, this interface was systematically investigated for various Ir loadings and PTL types using a voltage breakdown analysis (VBA) method to differentiate between different sources for overpotential. As expected, the oxygen evolution reaction (OER) overpotential increases with decreasing Ir loading, but its extent depends on the CL/PTL interfacial contact area and the in-plane electrical conductivity of the CL. If the latter is low, this can be partly compensated by using a proper PTL counterpart. However, especially when using low Ir loadings, the VBA method results in inconclusive OER kinetic parameters such as the apparent exchange current density. Therefore, the constant Tafel slope voltage breakdown analysis (CT-VBA) method is proposed considering possible mass transport losses even at relatively small current densities within the Tafel fit regime. These findings provide insights to tackle challenges associated with reducing Ir loading.

Uniform Densification of Garnet Electrolyte for Solid-State Lithium Batteries.

Highly uniformly dense garnet type solid-state electrolyte plays a significant role in determining the performance of solid-state lithium batteries. Herein, a rational powder-covering sintering strategy is proposed and demonstrated, in which narrow-particle-size-distribution fine powder and uniform sintering temperature distribution are considered as very significant factors. It is suggested that powder materials with wider particle size distribution dramatically decrease the densified level of electrolytes. Slow temperature elevating rate and the overhead structure of bearing table are found to be beneficial to uniform densification. Moreover, the uniform densification process of sintering solid-state electrolyte is studied both microscopically and macroscopically, which can be divided into three phases according to the grain growing evolution and linear shrinkage patterns. The ionic conductivity of the as-prepared Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) garnet electrolyte is determined to be 0.73 mS cm-1 at 303 K with an activation energy of 0.37eV. The Li/LLZTO/Li symmetric cell exhibits a small interfacial impedance of 8.49 Ω cm2 and a high apparent critical current density of 2.15mA cm-2 and also can be cycled for 1000 h continuously without short-circuit. Such results indicate the good feasibility of as-proposed sintering strategy to prepare uniformly dense garnet type solid-state electrolytes for solid-state lithium batteries.

Effects of F− ions on the electrochemical and interface behavior of cathodes in zinc electrowinning

The increasing use of Zn metal in the energy and industrial sectors necessitates a higher level of research into the zinc electrowinning process. In this work, the effects of fluoride ions (F−) in zinc electrolyte on the cathodic kinetics and zinc product quality during zinc electrodeposition was systematically investigated via a series analysis. The results revealed that the addition of F− in the electrolyte showed a polarization effect, with an increase in the apparent cathodic exchange current density increased by 104 orders of magnitude, and a decrease in the zinc deposition overpotential by 46 mV at a concentration of 400 mg/L. However, F− also reduces the hydrogen evolution overvoltage, when the electrolyte contains 400 mg/L F−, the hydrogen evolution overvoltage on aluminum cathode and zinc cathode decreases by 121 mV and 97 mV, respectively. The promoted hydrogen evolution kinetics increases energy consumption and surface porosity. Additionally, F− ions corrode the Al2O3 oxide film on the cathode surface, accelerating the corrosion of the aluminum cathode plate. This results in increased adhesion of zinc deposition to the damaged aluminum substrate, making it difficult to peel off.

Impact of Pore Structure on Electrochemical Reduction of Carbon Dioxide in Iron- and Nitrogen-Doped Carbon Materials: Solid–Liquid Interface Versus Solid–Gas–Liquid Triple-Phase Boundary

The effect of porosity on the interface microenvironment and catalytic performance of carbon dioxide reduction reaction (CO2RR) is still unclear for iron- and nitrogen-doped carbon-based (Fe/N/C) materials, and previous studies mainly focus on aqueous electrode test conditions rather than a practical working environment. Herein, several Fe/N/C-based catalysts with very different pore structures were prepared and compared to understand how the surface area and micropores affect the CO2RR between aqueous electrode test and practical working conditions with a solid–gas–liquid triple-phase boundary. The apparent current density correlates positively to the surface area in both test conditions. The onset current density where hydrogen evolution reaction starts is irrelevant to the micropore fraction in the aqueous electrode test but correlates negatively to the micropore fraction in a practical working condition. The inconsistency is attributed to different reaction interfaces in both cases, resulting in different interface microenvironments in different pore size ranges. This work helps in designing porous electrocatalysts for CO2RR or beyond.

Revealing the potential of apparent critical current density of Li/garnet interface with capacity perturbation strategy

Apparent critical current density (jAca) of garnet all-solid-state lithium metal symmetric cells (ASSLSCs) is a fundamental parameter for designing all-solid-state lithium metal batteries. Nevertheless, how much the possible maximum apparent current density that a given ASSLSC system can endure and how to reveal this potential still require study. Herein, a capacity perturbation strategy aiming to better measure the possible maximum jAca is proposed for the first time. With garnet-based plane-surface structure ASSLSCs as an exemplification, the jAca is quite small when the capacity is dramatically large. Under a perturbed capacity of 0.001 mA h cm−2, the jAca is determined to be as high as 2.35 mA cm−2 at room temperature. This investigation demonstrates that the capacity perturbation strategy is a feasible strategy for measuring the possible maximum jAca of Li/ solid electrolyte interface, and hopefully provides good references to explore the critical current density of other types of electrochemical systems.

Electrochemical Oxygen Evolution Reaction on NixFe3-xO4 (0 ≤ x ≤ 1.0) in Alkaline Medium at 25ºC

Spinel ferrites (NixFe3-xO4; x = 0.25, 0.5, 0.75 and 1.0) have been prepared at 550ºC by egg white auto-combustion route using egg white at 550ºC and characterized by physicochemical (TGA, IR, XRD, and SEM) and electrochemical (CV and Tafel polarization) techniques. The presence of characteristic vibration peaks in FT-IR and reflection planes in XRD spectra confirmed the formation of spinel ferrites. The prepared oxides were transformed into oxide film on glassy carbon electrodes by coating oxide powder ink using the nafion solution and investigated their electrocatalytic performance for OER in an alkaline solution. The cyclic voltammograms of the oxide electrode did not show any redox peaks in oxygen overpotential regions. The iR-free Tafel polarization curves exhibited two Tafel slopes (b1 = 59–90 mV decade−1 and b2 = 92–124 mV decade−1) in lower and higher over potential regions, respectively. Ni-substitution in oxide matrix significantly improved the electrocatalytic activity for oxygen evolution reaction. Based on the current density for OER, the 0.75 mol Ni-substituted oxide electrode was found to be the most active electrode among the prepared oxides and showed the highest value of apparent current density (~9 mA cm−2 at 0.85 V) and lowest Tafel slope (59 mV decade−1). The OER on oxide electrodes occurred via the formation of chemisorbed intermediate on the active sites of the oxide electrode and follow the second-order mechanism.

Exchange current density of reversible solid oxide cell electrodes

Reversible solid oxide cells (r-SOCs) can be operated in either solid oxide fuel cell or solid oxide electrolysis cell mode. They are expected to become important in the support of renewable energy due to their high efficiency for both power generation and hydrogen generation. The exchange current density is one of the most important parameters in the quantification of electrode performance in solid oxide cells. In this study, four different fuel electrodes and two different air electrodes are fabricated using different materials and the microstructures are compared. The temperature, fuel humidification, and oxygen concentration at the air electrode are varied to obtain the apparent exchange current density for the different electrode materials. In contrast to ruthenium-and-gadolinia-doped ceria (Rh-GDC) as well as nickel-and-gadolinia-doped ceria (Ni-GDC) electrodes, significant differences in the apparent exchange current density were observed between electrolysis and fuel cell modes for the nickel-scandia-stabilized zirconia (Ni-ScSZ) cermet. Variation of gas concentration revealed that surface adsorption sites were almost completely vacant for all these electrodes. The apparent exchange current densities obtained in this study are useful as a parameter for simulation of the internal properties of r-SOCs.

Optimized Anticorrosion of Polypyrrole Coating by Inverted-Electrode Strategy: Experimental and Molecular Dynamics Investigations.

To improve the poor adhesion and the ensuing insufficient anticorrosion efficacy of electropolymerized polypyrrole (PPy) on copper surface, an inverted-electrode strategy was applied after the passivation procedure, for which the compact coating (PPy-I) was deposited on the substrate in a cathodic window. Morphological and physical characterizations revealed that PPy-I exerted satisfactory adhesion strength and suitable thickness and conductivity compared with the analogue prepared via the traditional protocol (PPy-T). Potentiodynamic polarization, electrochemical impedance spectroscopy and frequency modulation were employed to ascertain the propitious protection of PPy-I for copper in artificial seawater (ASW). Due to the dominant electroactivity, the PPy-I-coated sample possessed higher apparent current density and lower charge transfer resistance than its PPy-T-protected counterpart, which maintained the passivation of the substrate. Surface analysis also supported the viability of PPy-I for copper in ASW for a well-protected surface with inferior water wettability. Molecular dynamics simulations evidenced that PPy-I with the higher density retained efficient anticorrosion capacity on copper at elevated temperatures. Therein, the derived time-dependent spatial diffusion trajectories of ions were locally confined with low diffusion coefficients. Highly twisted pore passages and anodic protection behavior arising respectively from the tight coating architecture and electroactivity contributed to the adequate corrosion resistance of PPy-I-coated copper.

Single-atom Ir and Ru anchored on graphitic carbon nitride for efficient and stable electrocatalytic/photocatalytic hydrogen evolution

Renewable energy-powered water electrolysis and photocatalytic water splitting are two promising approaches to green hydrogen production. Electrocatalysts and photocatalysts are essential components determining the performance of water electrolyzers and photocatalytic reactors, respectively. Currently, there is a pressing need to develop efficient and stable electrocatalysts and photocatalysts for large-scale deployment of these devices to reach carbon neutrality. Herein, we report the synthesis of single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (Ir-g-CN and Ru-g-CN), which can be used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER). Remarkably, Ru-g-CN shows a high turnover frequency (TOF) of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming Ir-g-CN, commercial Pt/C benchmark and many other advanced HER catalysts reported recently. Moreover, Ru-g-CN can deliver an exceptionally high mass activity of 24.55 and 8.78 A mg−1 at η = 100 mV in acidic and alkaline solutions, meanwhile exhibiting a high apparent current density, which is favorable for practical applications. Additionally, both Ru-g-CN and Ir-g-CN show outstanding catalytic stability, continuously catalyzing the HER in acidic and alkaline conditions for 120 h with minimal degradation. Besides, when used for photocatalytic water splitting, Ru-g-CN can achieve a high hydrogen production rate of 489.7 mmol H2 gRu−1 h−1, and shows good photocatalytic stability. Our density functional theory (DFT) calculations demonstrate that loading Ir and Ru single-atoms on g-CN alters the electronic structure, resulting in a reduced bandgap and improved electrical conductivity, facilitating electron transfer during the catalysis. Moreover, the Gibbs free energy of hydrogen adsorption on Ru-g-CN and Ir-g-CN is also substantially lowered, enhancing HER performance.

Electronic effects on protective mechanism of electropolymerized coatings based on N-substituted aniline derivatives for mild steel in saline solution

Polyaniline (PANI), poly(N-methylaniline) (PNMA) and poly(N-formylanilide) (PNFA) coatings were fabricated over mild steel via chronoamperometric strategy in oxalate electrolyte. Scanning electron microscope (SEM), attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) evidenced the polymerization of monomers. Anticorrosive effects of PANI, PNMA and PNFA coatings for steel substrate were evaluated during long-term immersion in 3.5% NaCl solution by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and frequency modulation (EFM). Morphological variation for coated specimens before and after immersion in NaCl solution was also monitored by SEM and atomic force microscope (AFM). Differentiated protection capability were observed for three coatings following the sequence of PNFA > PNMA > PANI. Through electrochemical and interfacial analyses, electroactivity and physical barrier were ascertained as the critical factors, especially the former one, in the long-term protection capacity. Electroactivity was distinguished by the elevated apparent current density from non-destructive EFM measurements. Furthermore, electron-donation and -withdrawal effects of N-substituents played an essential role in coating electroactivity. In detail, N-substituents improved the anodic protection and physical barrier of PNMA and PNFA coatings. Particularly, formyl with electron-withdrawal effect reinforced the anodic protection and thus the superior the anticorrosion efficiency of PNFA for underlying steel.

Exchange Current Density of Solid Oxide Electrolysis Cell Electrodes

Introduction Numerical simulation is a powerful technique in evaluating solid oxide fuel cell (SOFC) performance. Such method enables to visualize SOFC performance e.g. in using new materials. It is also desirable to develop such method that visualizes internal phenomena in solid oxide electrolysis cell (SOEC). While various parameters are important in simulating phenomena in SOEC stacks, we focus on exchange current density (1,2). Here, exchange current density is experimentally measured and evaluated using single SOEC / SOFC reversible cells. Furthermore, the exchange current density for different electrode materials in both SOEC and SOFC operation modes is examined. Exchange current density is defined as the current exchanged at the electrode/electrolyte interfaces in both directions in equilibrium and thus , so that an identical value for a given electrode has to be obtained in both SOFC and SOEC modes. However, as such values are practically measured by applying certain current in opposite directions, apparent exchange current density measured could be somehow different due to various irreversible processes at the electrode/electrolyte interfaces. In this study, such apparent exchange current density values are obtained and discussed. Experimental In this study, we evaluated the exchange current densities of solid oxide cells with three types of fuel electrodes (A-1, 2, 3) and two types of air electrodes (B-1, 2). The exchange current densities were measured in the SOFC and SOEC modes using following materials: (A-1) Ni-ScSZ (NiO-ScSZ (ScSZ: 10mol%Sc2O3-1mol%CeO2-89mol%ZrO2)), (A-2) Rh-GDC (La0.1Sr0.9TiO3, Gd0.1Ce0.9O2, volume ratio 50:50 (LST-GDC), Rh 0.178 mg/cm2 supported on LST-GDC) co-impregnated material, and (A-3) Ni-GDC (Ni 0.167 mg/cm2 supported on LST-GDC) co-impregnated material for the fuel electrode; (B-1) LSCF/GDC ((La0.6 Sr0.4)(Co0.2 Fe0.8)O3/GDC), and (B-2) LSM ((La0.8Sr0.2)0.98MnO3) for the air electrode. The exchange current density was derived using the Butler-Volmer-type equation. The exchange current density obtained was fitted by the commonly used phenomenological formula of the exchange current density. We compared the obtained parameters and the dependencies on gas partial pressure. Results and Discussion Here, the differences in exchange current density at the fuel electrode are examined. Figure 1 shows the exchange current density as a function of humidity in the fuel, and fitted curves. The fitted curves of exchange current densities are almost similar in the SOFC and SOEC modes. However, the maximum value measured in the SOFC mode shown in Fig. 1 (b) was somehow higher than that measured in the SOEC mode shown in Fig. 1 (a). The difference in using the Ni-ScSZ fuel electrode was more remarkable than that using the Rh-GDC co-impregnated fuel electrode shown in Figs. 1 (c) and (d). It may be possible that the apparent exchange current density at the fuel electrode could include influences of irreversible processes, associated with steam electrolysis. The dependence of exchange current density on gas partial pressure (3) will be examined to discuss electrode processes in steam electrolysis. The exchange current density obtained in this study enables various simulations for SOECs, besides SOFCs. References T. Yonekura, Y. Tachikawa, T. Yoshizumi, Y. Shiratori, K. Ito, and K. Sasaki, ECS Trans., 35 (1), 1007-1014 (2011).K. Takino, Y. Tachikawa, K. Mori, S. M. Lyth, Y. Shiratori, S. Taniguchi, and K. Sasaki, Int. J. Hydrogen Energy, 45 (11), 6912-6925 (2020).T. Hosoi, T. Yonekura, K. Sunada, and K. Sasaki, J Electrochem Soc., 162 (1), F136-F152 (2015). Figure 1

Exchange Current Density of Solid Oxide Electrolysis Cell Electrodes

Solid oxide fuel cells (SOFCs) are expected to become widespread as an energy conversion technology that can directly produce electrical energy from fuel. Solid oxide electrolysis cells (SOECs) are essentially SOFCs operating in reverse to produce fuel from electricity. The exchange current density is one of the most important parameters to simulate SOEC/SOFC. In this study, experimental data was evaluated as apparent exchange current density and the effects of SOEC/SOFC operation and different electrode materials were discussed.

The Influence of Tin Addition on the Electrochemical Performance of IrO2 and Ir Black Oxygen Evolution Catalysts in Polymer Electrolyte Membrane Electrolysis

Polymer electrolyte membrane (PEM) electrolysis is widely considered a promising technology for energy storage and clean hydrogen production, due to the advantages it has over state-of-the-art alkaline water electrolysis.1 Typically, PEM electrolysers can operate at higher current densities than their alkaline counterparts, have a more robust design, and due to the zero-gap design, exhibit smaller Ohmic losses. Furthermore, PEM electrolysers can yield hydrogen at elevated pressures, eliminating the need for compression. Nevertheless, a series of challenges hinder the large-scale commercial implementation of PEM electrolysers. One of the most critical drawbacks is the need for noble metal electrocatalysts, especially at the anode of the cell, such as iridium or ruthenium, to catalyze the oxygen evolution reaction (OER) (1).2H2O → O2 + 4H+ + 4e- E° = 1.23 V vs NHE (1)These metals are used due to their high catalytic activity and long-term stability in the corrosive acidic environment of the PEM cells and their replacement by more available materials is difficult. Over the years, the main efforts of the scientific community towards solving this challenge were focused on increasing the noble metal dispersion, by using various high surface area catalyst supports, using core-shell catalysts, with the aim to minimize the amount of noble metal, modifying the morphology of the electrode, to improve mass transport limitations and electric contact between components and maximize noble metal utilization.2-4 Antimony-doped tin oxide has been reported as a stable OER catalyst support, offering sufficient electronic conductivity at the same, in order to minimize Ohmic losses.5 Furthermore, recent reports indicate that SnO2 does not only act as a catalyst support but takes part in catalysis.6 Building upon literature reports, we prepared a series of Sn/Ir OER catalysts by a two-step sodium borohydride reduction method, in which Sn nanoparticles were deposited over the surface of iridium black particles, decorating it. Catalysts with varying Sn content were incorporated in membrane electrode assemblies (MEAs) and their cell performance was evaluated in a single cell PEM electrolyser. We found that catalysts with up to 20 wt% tin content exhibited an improved cell performance compared to MEAs with similar iridium black loading. We modeled Ohmic, kinetic and mass transport overpotential contributions to experimentally acquired polarization curves and identified that the better cell performance arises mainly from the higher intrinsic catalytic activity, reflected by a higher apparent exchange current density of Sn/Ir OER catalysts compared to Ir black catalysts. The Sn/Ir MEAs also displayed lower mass transport overpotentials, which indicate improved transport in the catalyst layer. This can be due to a more porous structure and less agglomeration of iridium particles induced by the presence of tin over their surface.Interestingly, this performance improvement was only observed for iridium black catalysts. We prepared a series of IrO2-SnO2 catalysts by solution combustion synthesis method, which is known to yield high surface area disperse oxide materials. Comparing the performance of these catalysts to commercial iridium oxide catalysts in the PEM electrolysis cell, the MEAs with SnO2-containing catalysts displayed worse cell performance than MEAs with commercial iridium oxide. Modelling the overpotential contributions showed a lower apparent exchange current density, indicating a lower intrinsic catalytic activity of IrO2-SnO2 catalysts, as well as a higher Ohmic resistance, due to SnO2 addition. These observations indicate the importance of iridium oxidation state for harnessing the promotion effect of tin addition and give important insights into designing more efficient OER catalysts for PEM electrolysis cells.

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Groundwater Flow Monitoring via Joint Time-lapse Electrical Resistivity and Self Potential Data Tomography

Revealing the dynamics of groundwater movement in the vadose zone is crucial to groundwater management and artificial recharge development. In this study, the groundwater flow characterization of the pumping process is monitored by the time-lapse electrical resistivity tomography (ERT) and self-potential (SP)data tomography. The ERT data invert the resistivity distribution. Then, we combine the SP data and resistivity result to invert the apparent current density and estimate the permeability based on the Poisson equation. A total of 24 hours of time-lapse surveys are taken during the pumping and recharge of groundwater. The results show a significant increase in in resistivity and permeability during pumping water, which suggests groundwater drawdown. Similarly, significant decrease resistivity and permeability are observed during the recovery indicating groundwater recharge. These results have a significant agreement with the groundwater table monitoring result. Our experiment test suggests that combine ERT and SP data could provide a reliable way in groundwater or other hydrogeological surveys.