Electrode Measurements Research Articles

Improving the Performance of the ToGoFET Probe: Advances in Design, Fabrication, and Signal Processing.

We report recent improvements of the tip-on-gate of field-effect-transistor (ToGoFET) probe used for capacitive measurement. Probe structure, fabrication, and signal processing were modified. The inbuilt metal-oxide-semiconductor field-effect-transistor (MOSFET) was redesigned to ensure reliable probe operation. Fabrication was based on the standard complementary metal-oxide-semiconductor (CMOS) process, and trench formation and the channel definition were modified. Demodulation of the amplitude-modulated drain current was varied, enhancing the signal-to-noise ratio. The I-V characteristics of the inbuilt MOSFET reflect the design and fabrication modifications, and measurement of a buried electrode revealed improved ToGoFET imaging performance. The minimum measurable value was enhanced 20-fold.

Reaction mechanisms for electrolytic manganese dioxide in rechargeable aqueous zinc-ion batteries

This study reports the phase transformation behaviour associated with electrolytic manganese dioxide (EMD) utilized as the positive electrode active material for aqueous zinc-ion batteries. Electrochemical techniques, including galvanostatic charge–discharge and rotating ring-disk electrode measurements, and microstructural techniques, using X-ray powder diffraction, scanning electron microscopy, and transmission/scanning transmission electron microscopy, were utilized to characterize the positive electrode at different stages of discharge and charge of zinc-ion cells. The results indicate that, during discharge, a fraction of EMD undergoes a transformation to ZnMn2O4 (spinel-type) and Zn2+ is intercalated into the tunnels of the γ- and ε-MnO2 phases, forming ZnxMnO2 (tunnel-type). When a critical concentration of Mn3+ in the intercalated ZnxMnO2 species is reached, a disproportionation/dissolution reaction is triggered leading to the formation of soluble Mn2+ and hydroxide (OH–) ions; the latter precipitates as zinc hydroxide sulfate (ZHS, Zn4(OH)6(SO4)·5H2O) by combination with the ZnSO4/H2O electrolyte. During charge, Zn2+ is reversibly deintercalated from the intergrown tunneled phases (γ-/ε-ZnxMnO2), Mn2+ is redeposited as layered chalcophanite (ZnMn3O7·3H2O), and ZHS is decomposed by protons (H+) formed during the electrochemical deposition of chalcophanite.

Analysis of Decay of Photocatalytic Effect of Titanium Dioxide Electrode

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was appeared that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source and measured its electrochemical properties. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused the potential loss during the measurement. In this study, we have been trying to understand the mechanism affecting the potential degradation of the TiO2 electrode and the factors affecting that decay.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated Xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photopotential measurement, the potentials dropped to active direction as the electrodes were exposed to the light irradiation. But the potential values were ennobled rapidly after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the rebounded potential values (open circuit potential loss) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the electrode with second layer heat treatment temperature of 150 ºC was higher and longer compared to that of the electrode with 550 ºC one. Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS) analysis. The surfaces of the electrodes before and after the measurements of photopotential were compared and observed using the scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of decay mechanism of photocatalytic on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit potential decay in the TiO2 electrode will be presented to the upcoming ECS conference meeting.

Preparation of PEFC Electrocatalysts Using SnO2 Thin Layer Support

Pt/C is widely used as polymer electrolyte fuel cell (PEFC) electrocatalyst. However, under high potential at the cathode, Pt detachment and aggregation due to carbon corrosion can occur. Therefore, conventional Pt/C electrocatalysts have a difficulty in durability, for e.g. heavy-duty applications. Our research group has been preparing electrocatalysts with both high activity and high durability (1-3). However, their electrocatalytic activity has to be further improved. For this reason, we are further improving catalytic activity by alloying platinum with cobalt on such SnO2-based catalyst support. Cobalt is one of the relatively stable metals under the PEFC electrocatalyst condition, and PtxCoy alloy catalysts are known to be capable of exhibiting higher activity over Pt catalysts (4). In addition, the doping of SnO2 with 2 mol% Nb is expected to increase electronic conductivity of SnO2 (5,6). Experimental Sn0.98Nb0.02O2 thin layer was deposited on the GCB (denoted as Sn0.98Nb0.02O2/GCB) by the ammonia coprecipitation method. Pt(acac)2 and Co(acac)2 were applied to simultaneously impregnate Pt and Co to obtain Pt-Co alloy catalysts (acac method). The Pt : Co ratio was adjusted to prepare Pt3Co alloy to obtain Pt3Co/Sn0.98Nb0.02O2/GCB electrocatalyst. The preparation procedure is schematically described in Figure.1. Results and discussion In order to evaluate Pt and Co loadings, ICP analysis was performed. We then made half-cell tests to evaluate electrochemical activities of these electrocatalysts. Electrochemical surface area (ECSA) was measured by cyclic voltammetry (CV), and oxygen reduction reaction (ORR) activity was derived from kinetically controlled current density (ik ) in the rotating disk electrode (RDE) measurement. We prepared MEA (Membrane Electrode Assembly) using this electrocatalyst (Pt3Co/Sn0.98Nb0.02O2/GCB) on the cathode side. We then made full-cell tests to evaluate cell performance such as current-voltage characteristicsFrom the ICP results, we confirmed that we could impregnate both Pt and Co close to the designated ratio in the acac method. Microstructures and EDS maps are shown in Figure. 2, confirming that Pt and Co were uniformly supported on the SnO2 surface layer on GCB. Electrochemical results and detailed microstructural analysis will be reported and discussed. Acknowledgement Financial support from New Energy and Industrial Technology Development Organization (NEDO) is gratefully acknowledged (Contract No. 20001214-0). References S. Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1164 (2018).Y. Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1154 (2018). T. Yoshizumi, M. Nagamine, Z. Noda, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 92 (8), 479 (2019). T. Tada, Y. Yamamoto, K. Matsutani, K. Hayakawa, and T. Namai, ECS Trans., 16 (2), 215 (2008). F. Takasaki, S. Matsuie, Y. Takabatake, Z. Noda, A. Hayashi, Y. Shiratori, K. Ito, and K. Sasaki, J. Electrochem. Soc., 158, B1270 (2011). K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, and K. Ito, ECS Trans., 33 (1), 473 (2010). Figure 1

X-Ray Absorption Spectroscopy Studies of Ir-Oxide Based Oxygen Evolution Catalysts Revisited

Hydrogen plays a pivotal role in the future decarbonization of the energy sector [1], but its production in a sustainable way is crucial for it to have a positive environmental impact. Due to its high power density, quick start-up and response time as well as pressurized hydrogen delivery, polymer electrolyte membrane water electrolysis (PEMWE) is perfectly suited to facilitate H2 production from renewable electricity [2]. However, at large scale application, the use of scarce and expensive, Ir-based catalysts in PEM water electrolyser anodes limits the proliferation of this technology [3, 4]. For this reason, significant research activities are being conducted to better understand the oxygen evolution reaction (OER) mechanism on benchmark IrO2 based catalysts, as to further improve catalyst design and decrease the efficiency losses related to this reaction.When trying to elucidate a reaction mechanism, the use of operando and/or in situ techniques is often beneficial, and thus in last decades the OER mechanism on Ir-based materials has been extensively investigated through operando / in-situ X-ray absorption as well as X-ray photoelectron spectroscopy (XAS, XPS) [5-10]. Despite enormous efforts in this research area, there is still a lack of consensus regarding the Ir oxidation state under OER conditions and the nature of the OER-active sites. In line with this, in this study we employed operando XAS to investigate the Ir oxidation state in commercial IrO2 (Umicore®) catalyst under OER polarization curve conditions. These XAS measurements were performed both in transmission and fluorescence modes; for the former, electrodes with loadings ≈ 40 fold higher than those used in rotating disk electrode (RDE) measurements were required in order to achieve appropriate XAS data quality. In fluorescence mode, however, thinner electrodes with only four times higher loadings than in RDE could be investigated. Prior to the operando XAS measurement, the utilization of these IrO2 catalyst layers in the operando flow cell (FC) was assessed to ensure that the acquired spectroscopic data was representative of the processes occurring under real conditions. Achieving a good catalyst layer utilization was especially important in the case of the thick electrodes used in transmission XAS measurement, since their resistance is much higher compared to that in thin film RDE measurements. The so obtained results were additionally affected by beam damage of the Nafion ionomer used as the catalyst layer binder. All these factors can further lead to data misinterpretation. Regarding the beam damage, reducing the beam flux helped to prevent this effect and allowed us to obtain reliable results. Additionally, the use of thin catalyst layers in the operando FC and its combination of time-resolved XAS (so called “quickXAS”) in fluorescence mode led to novel insight on the effects of evolved O2 bubbles on the spectroscopic results and subsequent interpretation thereof.In summary, this contribution will provide an overview of common pitfalls and good practices encountered when conducting operando XAS studies of OER-electrocatalysts.

Asymmetric Li-Ion Diffusion Profiles during Lithium Plating and Stripping in Ionic Liquid Electrolytes

The electrochemical behavior of lithium metal in ionic-liquid based Li-electrolytes is typically characterized by an anodic peak due to the formation of an inhibition layer. In symmetric Li-Li cells, this shows up as a symmetric set of peaks in the current-cell voltage curves (Figure left), as here the current is limited by the slowest process, in this case the anodic dissolution side. Indeed, for 3-electrode measurements with a Li reference electrode and a lithium counter electrode with much larger surface area as the lithium working electrode, an asymmetric cathodic and anodic current-potential behavior is found (Figure right). Peculiar is that this behavior is reversible and thus not due to a single formation of an irreversible electrolyte decomposition layer, often referred to as a solid-electrolyte interphase or SEI layer even though the dense electronically isolating character and even ionic conductance of these decomposition layers are often doubtful. Our group has reported previously on the peculiar electrochemical behavior of ionic-liquid based electrolytes against lithium metal [1],[2]. We attributed the asymmetric behavior in the 3 electrode measurements to the formation of a temporary passivation layer on top of the usual SEI layer (dead lithium) which diffuses away when stopping the lithium dissolution, i.e., explaining the reversible behavior. As the focus of these papers was on the electrolyte material and cell performance, respectively, we did not go into more detail on the mechanism. In this paper, we will discuss the changes at the interface explaining the time dependent change in kinetics.[1] “Silica gel solid nanocomposite electrolytes with interfacial conductivity promotion exceeding the bulk Li-ion conductivity of the ionic liquid electrolyte filler” Xubin Chen, Brecht Put, Akihiko Sagara, Knut Gandrud, Mitsuhiro Murata, Julian A. Steele, Hiroki Yabe, Thomas Hantschel, Maarten Roeffaers, Morio Tomiyama, Hidekazu Arase, Yukihiro Kaneko, Mikinari Shimada, Maarten Mees and Philippe M. Vereecken, Science Advances, 6, 2, eaav3400 (2020). [2] “ High-Rate Performance Solid-State Lithium Batteries with Silica-Gel Solid Nanocomposite Electrolytes using Bis (fluorosulfonyl) imide-Based Ionic Liquid” Akihiko Sagara, Xubin Chen, Knut B Gandrud, Mitsuhiro Murata, Maarten Mees, Yukihiro Kaneko, Hidekazu Arase, Philippe M Vereecken, Journal Electrochemical Society 167 (7), 070549 (2020). Figure 1

Bimetallic Oxygen Evolution Electrocatalysts: Relationships of Structure, Activity and Stability

Acidic oxygen evolution reaction (OER) electrocatalysts that have high activity, extended durability, and lower costs are needed to further the development of proton-exchange membrane (PEM) electrolyzers. Within acidic OER catalysts, stability remains a critically important but significantly less studied factor relative to activity. Our work involves investigating relationships between structure, activity, and stability within bimetallic acidic OER electrocatalysts. Bimetallic catalysts that interact iridium or ruthenium with non-noble metals provide an approach to lower the amount of noble metal and increase the OER activity and stability. Non-noble metals have different electronegativities and atomic radii compared to iridium and ruthenium which alters the surface atomic and electronic structure and influences both OER activity and metal dissolution. Our prior work showed that the inclusion of nickel or cobalt within iridium-metal two-dimensional nanoframes resulted in differences in the surface structure that significantly changed the OER activity and electrochemical degradation.1,2 Bimetallic structures can undergo very different degradation processes compared to monometallic structures, as shown by our prior study.1 Our recent work has explored the effects of interacting non-noble metals within ruthenium oxide on the structure, OER activity and stability. Nanostructured bimetallic oxides were synthesized using solution-phase chemistry and through utilizing various temperature/atmosphere treatments. The synthesis and processing conditions significantly affected the resulting material’s structure and properties. The materials’ composition, morphology and structure are probed using energy dispersive X-ray spectroscopy, scanning electron microscopy, nitrogen physisorption, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Rotating disk electrode measurements are used to evaluate the electrochemical oxygen evolution activity and stability of the bimetallic oxides which were compared to baseline OER catalysts. Metal dissolution that occurs during accelerated durability testing is evaluated using inductively coupled mass spectroscopy measurements. Our recent efforts towards understanding the relationships between structure, activity, and stability within nanostructured bimetallic oxides/hydroxides will be presented. References Ying, Y.; Godínez-Salomón, J.F.; Moreno, A.; Lartundo-Rojas, L.; Meyer, B.; Damin, C.A.; Rhodes, C.P. Hydrous Cobalt-Iridium Oxide Two-Dimensional Nanoframes: Insights into Activity and Stability of Bimetallic Acidic Oxygen Evolution Electrocatalysts. Nanoscale Advances 2021, 3, 1976-1996. DOI: 10.1039/D0NA00912A Godínez-Salomón, F.; Albiter, L.; Alia, S.M.; Pivovar, B.S.; Camacho-Forero, L.E.; Balbuena, P.B.; Mendoza-Cruz, R.; Arellano-Jimenez, M.J.; Rhodes, C.P. Self-Supported Hydrous Iridium-Nickel Oxide Two-dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catalysis 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171

Compositionally Tuned Trimetallic Thiospinel Catalysts for Enhanced Electrosynthesis of Hydrogen Peroxide and Built-In Hydroxyl Radical Generation

On-site electrochemical production of hydrogen peroxide (H2O2), an oxidant and disinfectant with growing demand, could be realized through the selective two-electron oxygen reduction reaction (2e– ORR), but the widespread adoption of this method depends on robust and efficient electrocatalysts. Current catalysts have been limited by cost or toxicity and lack well-defined structures that can facilitate systematic tuning of activity and selectivity. Here, we demonstrate a series of CuCo2–xNixS4 (0 ≤ x ≤ 1.2) thiospinel catalysts for 2e– ORR with variable compositions that can be synthesized via hydrothermal conversion. Rotating ring disk electrode measurements show that these catalysts have high selectivity for 2e– ORR (>60%) and that their activity can be improved by increasing the nickel content without compromising selectivity. An acid treatment step is critical prior to employing the optimized CuCo0.8Ni1.2S4 catalyst for bulk electrosynthesis of H2O2 in 0.05 M H2SO4 solution. Various structural analyses, including synchrotron X-ray spectroscopy, confirm that the catalysts retain the spinel structure after acid treatment and H2O2 electrosynthesis. The acid treatment likely leaches the soluble copper species from the as-synthesized catalysts that would catalyze an electro-Fenton process to consume H2O2, generate hydroxyl radicals, and therefore prevent the accumulation of H2O2. This work demonstrates a general strategy for systematic tuning of metal compound catalysts for practical H2O2 electrosynthesis and facile generation of hydroxyl radicals.

Enhanced oxygen reduction and methanol oxidation reaction over self-assembled Pt-M (M = Co, Ni) nanoflowers

Herein, we introduce a facile approach to synthesize a unique class of Pt-M (M = Ni, Co) catalysts with a nanoflower structure for boosting both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). By controlling the surface-active agents, we modified the functional groups surrounding the Pt atoms, tuned the alloying of Pt and the transition metals Ni and Co, and prepared two different kinds of nanodendrites. Their successful synthesis depends on the selection and amount of surfactants (hexadecyltrimethylammonium bromide (CTAB), Polyvinylpyrrolidone (PVP)). Besides, by controlling reaction time, we also explored the forming procedures for Pt-Co globularia nanodendrite (Pt-Co GND) and Pt-Ni petalody nanodendrite (Pt-Ni PND). Our investigation highlights the importance of complex nanoarchitecture, which enables surface and interface modification to achieve excellent catalytic performance in fuel cell electrocatalysis. The characterization of the as-prepared catalysts reveals a high electrochemical surface area and mass activity (2041 mAmgPt-1and 950 mAmgPt-1 for Pt-Co GND and Pt-Ni PND, respectively, for ORR). Furthermore, Pt-Co GND showed a high MOR activity, with a mass activity value recorded at 1615 mAmgPt-1 which is far superior to that for Pt/C. Moreover, both catalysts retain high activity after accelerated durability tests (ADTs). The electron transfer number was calculated by performing the rotating ring-disk electrode (RRDE) measurements. Due to abundant active sites of Pt, both Pt-Co GND and Pt-Ni PND exhibit a 4e− pathway for ORR with electron transfer number of >3.95.

Design of a Marine Sediments Resistivity Measurement System Based on a Circular Permutation Electrode

Marine sediments are rich in mineral resources, organic resources, and microbial life. The study of marine sediments is of great significance for the development and utilization of marine resources and understanding the life process. Resistivity is the overall characteristic of the electrical conductivity of marine sediments. Measuring the resistivity of marine sediments is helpful to ascertain the marine geological structure, study the distribution of marine mineral resources, and evaluate the marine soil environment. Measuring the resistivity of marine sediments is of great significance to promote marine exploration. At present, the resistivity measurement device on the market can be directly used to measure soil and water on land, but if used to measure marine sediments, it will be disturbed by seawater temperature and pressure, resulting in large errors. In this paper, a high-precision pressure-maintaining transfer system of marine sediment resistivity measurement instrument based on circular permutation electrode is designed, which can measure the resistivity of marine sediment samples after pressure-maintaining transfer. At the same time, a new type of circular permutation electrode measurement method is proposed, which makes the resistivity value more accurate, reduces the length of the probe appropriately, and saves the cost. By measuring the resistivity of marine sediments, the type of sediments can be inverted, which provides a way of thinking about the promotion of the research and development and utilization of marine resources.

An Examination of the Catalyst Layer Contribution to the Disparity between the Nernst Potential and Open Circuit Potential in Proton Exchange Membrane Fuel Cells

The dependency of the Nernst potential in an operating proton exchange membrane fuel cell (PEMFC) on the temperature, inlet pressure and relative humidity (RH) is examined, highlighting the synergistic dependence of measured open circuit potential (OCP) on all three parameters. An alternative model of the Nernst equation is derived to more appropriately represent the PEMFC system where reactant concentration is instead considered as the activity. Ex situ gas diffusion electrode (GDE) measurements are used to examine the dependency of temperature, electrolyte concentration, catalyst surface area and composition on the measured OCP in the absence of H2 crossover. This is supported by single-cell OCP measurements, wherein RH was also investigated. This contribution provides clarity on the parameters that affect the practically measured OCP as well as highlighting further studies into the effects of catalyst particle surrounding environment on OCP as a promising way of improving PEMFC performance in the low current density regime.

Heat-Treated Electrolytic Manganese Dioxide as an Efficient Catalyst for Oxygen Reduction Reaction in Alkaline Electrolyte

We developed an oxygen depolarized cathode (ODC) catalyst that can be employed for industrial chlor-alkali electrolysis by improving the oxygen reduction reaction (ORR) activity of commercially available electrolytic manganese dioxide (EMD). The ORR activity of EMD was systematically investigated by rotating disc electrode (RDE) measurements for EMD samples having different particle sizes and heat-treated at different temperatures. We found that the ORR activity of EMD became comparable to commercially available platinized carbon (Pt/C) when EMD with a median diameter of 0.5 μm was heat-treated at 500 °C. From XPS analysis, the EMD heat-treated at 500 °C contains many surface oxygen vacancies that were advantageous for adsorption of oxygen molecules. The obtained EMD sample was assembled into an ODC electrode and its ORR performance was evaluated under chlor-alkali electrolysis conditions (32.5 wt% NaOH, 88 °C). The heat-treated EMD showed an overpotential of ∼0.1 V smaller (at a current density of −1.0 A cm−2) than the benchmark catalyst, i.e., Ag particles. The catalyst we developed is therefore a most promising candidates to replace precious metal catalysts, owing to industrially valuable features such as low cost, simple synthesis method, and high ORR activity.

A prototype device of microliter volume voltammetric pH sensor based on carbazole\u2013quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

As an alternate for the conventional glass-based pH sensor which is associated with problems like fragile nature, alkaline error, and potential drift, the development of a new redox-sensitive pH probe-modified electrode that could show potential, current-drift and surface-fouling free voltammetric pH sensing is a demanding research interest, recently. Herein, we report a substituted carbazole-quinone (Car-HQ) based new redox-active pH-sensitive probe that contains benzyl and bromo-substituents, immobilized multiwalled carbon nanotube modified glassy carbon (GCE/MWCNT@Car-HQ) and screen-printed three-in-one (SPE/MWCNT@Car-HQ) electrodes for selective, surface-fouling free pH sensor application. This new system showed a well-defined surface-confined redox peak at an apparent standard electrode potential, Eo′ = − 0.160 V versus Ag/AgCl with surface-excess value, Γ = 47 n mol cm−2 in pH 7 phosphate buffer solution. When tested with various electroactive chemicals and biochemicals such as cysteine, hydrazine, NADH, uric acid, and ascorbic acid, MWCNT@Car-HQ showed an unaltered redox-peak potential and current values without mediated oxidation/reduction behavior unlike the conventional hydroquinone, anthraquinone and other redox mediators based voltammetry sensors with serious electrocatalytic effects and in turn potential and current drifts. A strong π–π interaction, nitrogen-atom assisted surface orientation and C–C bond formation on the graphitic structure of MWCNT are the plausible reasons for stable and selective voltammetric pH sensing application of MWCNT@Car-HQ system. Using a programed/in-built three-in-one screen printed compatible potentiostat system, voltammetric pH sensing of 3 μL sample of urine, saliva, and orange juice samples with pH values comparable to that of milliliter volume-based pH-glass electrode measurements has been demonstrated.

Copper single-atoms embedded in 2D graphitic carbon nitride for the CO2 reduction

We report the study of two-dimensional graphitic carbon nitride (GCN) functionalized with copper single atoms as a catalyst for the reduction of CO2 (CO2RR). The correct GCN structure, as well as the adsorption sites and the coordination of the Cu atoms, was carefully determined by combining experimental techniques, such as X-ray diffraction, transmission electron microscopy, X-ray absorption, and X-ray photoemission spectroscopy, with DFT theoretical calculations. The CO2RR products in KHCO3 and phosphate buffer solutions were determined by rotating ring disk electrode measurements and confirmed by 1H-NMR and gas chromatography. Formate was the only liquid product obtained in bicarbonate solution, whereas only hydrogen was obtained in phosphate solution. Finally, we demonstrated that GCN is a promising substrate able to stabilize metal atoms, since the characterization of the Cu-GCN system after the electrochemical work did not show the aggregation of the copper atoms.

Carbonic anhydrase inhibitors suppress seizures in a rat model of birth asphyxia.

Seizures are common in neonates recovering from birth asphyxia but there is general consensus that current pharmacotherapy is suboptimal and that novel antiseizure drugs are needed. We recently showed in a rat model of birth asphyxia that seizures are triggered by the post-asphyxia recovery of brain pH. Here our aim was to investigate whether carbonic anhydrase inhibitors (CAIs), which induce systemic acidosis, block the post-asphyxia seizures. The CAIs acetazolamide (AZA), benzolamide (BZA), and ethoxzolamide (EZA) were administered intraperitoneally or intravenously to 11-day-old rats exposed to intermittent asphyxia (30min; three 7+3 min cycles of 9% and 5% O2 at 20% CO2 ). Electrode measurements of intracortical pH, Po2 , and local field potentials (LFPs) were made under urethane anesthesia. Convulsive seizures and blood acid-base parameters were examined in freely behaving animals. The three CAIs decreased brain pH by 0.14-0.17 pH units and suppressed electrographic post-asphyxia seizures. AZA, BZA, and EZA differ greatly in their lipid solubility (EZA > AZA > BZA) and pharmacokinetics. However, there were only minor differences in the delay (range 0.8-3.7min) from intraperitoneal application to their action on brain pH. The CAIs induced a modest post-asphyxia elevation of brain Po2 that had no effect on LFP activity. AZA was tested in freely behaving rats, in which it induced a respiratory acidosis and decreased the incidence of convulsive seizures from 9 of 20 to 2 of 17 animals. AZA, BZA, and EZA effectively block post-asphyxia seizures. Despite the differences in their pharmacokinetics, they had similar effects on brain pH, which indicates that their antiseizure mode of action was based on respiratory (hypercapnic) acidosis resulting from inhibition of blood-borne and extracellular vascular carbonic anhydrases. AZA has been used for several indications in neonates, suggesting that it can be safely repurposed for the treatment of neonatal seizures as an add-on to the current treatment regimen.

Elucidating Pt-Based Nanocomposite Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Gas Diffusion Electrode Measurements

Elucidating Pt-Based Nanocomposite Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Gas Diffusion Electrode Measurements

Characterization and Electrocatalytic Performance of Molasses Derived Co-Doped (P, N) and Tri-Doped (Si, P, N) Carbon for the ORR

There is a growing need to develop sustainable electrocatalysts to facilitate the reduction of molecular oxygen that occurs at the cathode in fuel cells, due to the excessive cost and limited availability of precious metal-based catalysts. This study reports the synthesis and characterization of phosphorus and nitrogen co-doped carbon (PNDC) and silicon, phosphorus, and nitrogen tri-doped carbon (SiPNDC) electrocatalysts derived from molasses. This robust microwave-assisted synthesis approach is used to develop a low cost and environmentally friendly carbon with high surface area for application in fuel cells. Co-doped PNDC as well as tri-doped SiPNDC showed Brunauer–Emmet–Teller (BET) surface areas of 437 and 426 m2 g−1, respectively, with well-developed porosity. However, examination of X-ray photoelectron spectroscopy (XPS) data revealed significant alteration in the doping elemental composition among both samples. The results obtained using rotating disk electrode (RDE) measurements show that tri-doped SiPNDC achieves much closer to a 4-electron process than co-doped PNDC. Detailed analysis of experimental results acquired from rotating ring disk electrode (RRDE) studies indicates that there is a negligible amount of peroxide formation during ORR, further confirming the direct-electron transfer pathway results obtained from RDE. Furthermore, SiPNDC shows stable oxygen reduction reaction (ORR) performance over 2500 cycles, making this material a promising electrocatalyst for fuel cell applications.

Impact of Nickel Ions on the Oxygen Reduction Reaction Kinetics of Pt and on Oxygen Diffusion through Ionomer Thin Films

The effects of dissolved nickel on the oxygen reduction reaction (ORR) kinetics and oxygen transport properties of perfluorosulfonic acid (PFSA) thin films were investigated using rotating disk electrode (RDE) measurements of ORR on a PFSA-coated platinum electrode. The electrochemical characterization in 0.1 M perchloric acid (HClO4) with and without added Ni2+ quantitatively measured the impact of ionic interactions between the Ni2+ cations and sulfonate (SO3 −) anions on oxygen transport through the PFSA thin film. Cyclic voltammetry (CV) curves in deaerated electrolyte showed that Ni2+ cations diffusing through the PFSA thin film interact with the Pt surface altering the hydrogen underpotential deposition and stripping processes and decreasing ORR kinetics. The RDE limiting current results point to reduced permeability of oxygen through PFSA-Ni2+ compared to PFSA-H+. The results indicate that transition metals leached from Pt alloy catalyst may be detrimental not only to the intrinsic ORR kinetics of the PEFC cathode catalyst through loss of the ORR-enhancing transition metal, but may also inhibit the diffusion of oxygen to the catalytic sites and poison the ORR.

Synthesis of Platinum Based Single-Atom Catalysts over Intermetallic Compounds for Hydrogen Evolution Reaction By Electrochemically Assisted Dissolution-Deposition

Platinum metal is not inert as it undergoes irreversible surface oxidation1. Platinum oxide (PtO) formation and corresponding reduction brings irreversibility on the surface due to famous place-exchange phenomena. Rise of this irreversibility during PtO reduction results in Pt dissolution2. Pt dissolution has been investigated upto an appreciable extent, in rigorous fuel cell conditions, which gives immense opportunity to restrain it by controlling accessible electrochemical operational parameters3. Advantageousness of modulated electrochemical dissolution of Pt, deployed as sacrificial electrode (S.E), renders ultra-low amount of simultaneous Pt electrodeposition through electrolyte on an anchoring substrate electrode (A.S.E). Thereby isolated atoms and subnanometric clusters becomes achievable over suitable A.S.E, utilizing altered rates of dissolution and deposition, by a four-electrode assembly (FEA). Presently, field of electrochemical energy conversion is evolving with highly active and stable electrocatalysts for Hydrogen Evolution Reaction (HER). One such pinnacle group of electrocatalysts emerged as metal-based single-atom catalysts (SACs) are quite efficient as well as stable for HER4. Current research work is focussed on using Pt dissolution phenomena to prepare SACs over certain stable substrates by using four-electrode assembly (FEA).Electrochemically assisted Dissolution-Deposition (EADD) by using FEA is utilized in present work to prepare Pt SACs supported by Intermetallic compounds. EADD being a novel, controlled and efficient synthesis technique has helped to evaluate the insitu Pt dissolution-deposition mechanism by Alternating Current Voltammetry. Authors also demonstrates that typical three-electrode assembly (TEA) used for Pt dissolution from Pt counter electrode is an uncontrolled method for Pt deposition over working electrode. In TEA, Open Circuit Potential (OCP) measurements of counter electrode conducted during cyclic voltammetry (CV) has helped to evaluate the scan rates experienced by Pt counter electrode. Finally, scan rates has given the insights about Pt dissolution and redeposition kinetics demonstrating the problems associated with TEA in context of dissolution-deposition synthesis. While using FEA the challenges experienced in TEA has also overcome. Synthesized Pt SACs tested for HER showed onset potential (η0) of 0mV and over potential at 10mA/cm2 (η10) of 50mV with a quite stable performance for 20h. Ultimately, EADD is summarized as a general, unique and effective surface synthesis technique in the domain of single atom catalysis availing immense opportunities for various other catalytic applications too.(1) H. ANGERSTEIN-KOZLOWSKA; B. E. CONWAY and W. B. A. SHARP. Faraday Trans. I, 1973. Langmuir 1973, 43, 9–36.(2) Gómez-Marín, A. M.; Clavilier, J.; Feliu, J. M. Sequential Pt(1 1 1) Oxide Formation in Perchloric Acid: An Electrochemical Study of Surface Species Inter-Conversion. J. Electroanal. Chem. 2013, 688, 360–370. https://doi.org/10.1016/j.jelechem.2012.07.016.(3) Topalov, A. A.; Cherevko, S.; Zeradjanin, A. R.; Meier, J. C.; Katsounaros, I.; Mayrhofer, K. J. J. Towards a Comprehensive Understanding of Platinum Dissolution in Acidic Media. Chem. Sci. 2014, 5 (2), 631–638. https://doi.org/10.1039/c3sc52411f.(4) Ji, S.; Chen, Y.; Wang, X.; Zhang, Z.; Wang, D.; Li, Y. Chemical Synthesis of Single Atomic Site Catalysts. Chem. Rev. 2020. https://doi.org/10.1021/acs.chemrev.9b00818. Figure 1

Gas Diffusion Electrode Half Cells – a Powerful Tool for Fuel Cell Electrocatalyst Evaluation in Relevant Conditions

In aqueous rotating disk electrode (RDE) measurements, advanced catalyst materials show tremendous performance improvements in comparison to commercial Pt/C catalysts towards oxygen reduction reaction (ORR). However, these promising improvements cannot (yet) be transferred to realistic membrane electrode assembly (MEA). [1] These discrepancies can be explained by non-ideal catalyst layer composition, leading to mass transport limitations of either oxygen (which is transported through the pores) or protons (via the ionomer) to the active centers of the catalyst material. Mass transport phenomena in real catalyst layers are still under debate and hold huge potential to significantly improve catalyst performance.However, mass transport in realistic fuel cell catalyst layers cannot be assessed with RDE experiments, as they are limited to low current densities and idealized catalyst layers on solid substrate. Therefore, MEA experiments are usually employed to evaluate those phenomena. Yet, those investigations are time consuming, expensive (large quantities of catalyst needed, extended test equipment) and do not allow segregated investigation of either cathode or anode catalyst layer. Furthermore, comparison of different MEA studies can be challenging due to varying operating conditions. Therefore, techniques combining the advantages of RDE, namely simplicity and comparability, with the realistic operating ranges of MEA are urgently required to retrieve the potential of catalyst layer optimization.In this presentation half-cells using gas diffusion electrodes (GDE) are proposed as a new powerful experimental tool to enable high mass transport catalyst screening in relevant potential ranges and realistic electrode structures.On the example of a Pt loading study we show, that current densities of up to 2 A/cm² can be achieved [2]. In contrary to other formerly used methods [3], it is thereby possible to overcome mass transport limitations at relevant fuel cell operating potentials. Additionally, we demonstrate good compliance with MEA experiments, proving the method´s suitability for catalyst evaluation in realistic fuel cell potential ranges.Besides activity, also stability of the electrocatalyst is affected significantly by the catalyst layer structure. We present here a novel method, where a GDE half-cell is coupled to an inductively coupled plasma mass spectrometer (ICP-MS) to gain deeper insights into dissolution of electrocatalysts in realistic electrode structures [4]. With this unique online tool, we could measure Pt dissolution in realistic catalyst layers for the first time reported in literature. We show, how mass transport of dissolved Pt species influences net Pt dissolution and how Pt dissolution can also be detected through Nafion membranes. Besides that, also the mobility of Pt-ions through Nafion membranes is further investigated. Literature [1] Ly, A., et al. J. Power Sources, 2020. 478: 228516[2] Ehelebe, K., et al., J. Electrochem. Soc., 2019. 166(16): F1259-F1268,[3] Inaba, M., et al., Energy Environm. Sci., 2018. 11(4): 988-994,[4] Ehelebe, K. et al. submitted Figure 1