Ring-disk Electrode Technique Research Articles

Anodic Hydrogen Generation from Benzaldehyde on Au, Ag, and Cu: Rotating Ring-Disk Electrode Studies

Abstract Aldehydes are selectively oxidized to carboxylates on group 11 metals at low potentials (<0.4 V vs. RHE) in alkaline media. This process can occur by a pathway that generates H2 gas from the aldehyde, known as electro-oxidative dehydrogenation (EOD) or anodic hydrogen production. The EOD process occurs with transfer of only one electron per aldehyde, whereas typical oxidation with discharge of hydrogen to form water is a two-electron process. Here, we study the catalytic activity and selectivity toward H2 of Au, Ag, and Cu electrodes using benzaldehyde with rotating disk and ring-disk electrode (RDE/RRDE) techniques. The average number of electrons per benzaldehyde molecule obtained via H2 detection by RRDE agrees with that obtained via Koutecký-Levich analysis conducted at various rotation rates. We find that Au and Ag have much higher H2 and benzoate formation rates than Cu, but that Cu can perform the reaction at about 0.2 V lower overpotentials. On all three materials, benzaldehyde oxidation has high selectivity to anodic H2 (one-electron pathway) below ~0.5 V vs. RHE, but, with increasing potential, the selectivity shifts to H-oxidation forming water (two-electron pathway).

Suppression of Hydrogen Peroxide Formation on Pt Using WO3 as Anode Co-Catalysts

Polymer electrolyte fuel cells (PEFCs) are emerging as promising candidates for next-generation energy systems, particularly for hydrogen vehicles and clean energy applications, due to their advanced high-power density production and efficiency. However, the commercialization of PEFCs is hindered by issues related to fuel cell durability, primarily caused by the chemical degradation of proton exchange membranes (PEMs) due to reactive oxygen-related radical attacks, notably generated through the production of hydrogen peroxide (H2O2). Anode catalysts, such as carbon-supported platinum nanoparticles (Pt/C), play a vital role in facilitating the hydrogen oxidation reaction (HOR), which is accompanied by the undesired formation of H2O2 due to oxygen gas (O2) crossover from the cathode. As for the Pt surface, the structure is sensitive to H2O2 production. Hence, minimizing H2O2 generation while maintaining HOR activity by developing anode catalysts is necessary to suppress degradation. Tungsten oxide (WO3) has emerged as an interesting active material due to its stability in acidic solutions and its ability to increase the rate of hydrogen oxidation by facilitating hydrogen spill-over from the Pt surface to WO3 to generate hydrogen tungsten bronze (HxWO3). [1, 2] This process enhances the availability of hydrogen on the Pt surface by effectively transferring hydrogen atoms from Pt to WO3. With more active sites available on the Pt surface, there is a higher likelihood of hydrogen oxidation, reducing the formation of H2O2 as an intermediate product.This study aims to develop an anode catalyst by incorporating WO3 nanoparticles into the Pt/C to suppress H2O2 production during HOR, particularly in the presence of oxygen. The rotating ring-disk electrode (RRDE) technique was utilized to evaluate catalyst performance and detect H2O2 generation during HOR. HOR activity and H2O2 production rate measurements were conducted in H2-sat. and H2/air-sat. 0.1 M HClO4 electrolyte at different temperatures (25, 40, and 60 ℃). The electrochemical measurements demonstrated that both Pt/C and WO3-Pt/C catalysts exhibited enhanced H2O2 formation rates with increasing temperature. This observation underscores the significance of temperature as a modulator of catalytic performance and suggests the existence of temperature-dependent kinetic mechanisms governing H2O2 generation during HOR. Moreover, the comparative analysis between Pt/C and WO3-Pt/C catalysts reveals distinct temperature-dependent behaviors. While both catalysts exhibit temperature-enhanced H2O2 formation, the WO3-Pt/C catalyst demonstrated significantly reduced H2O2 production at 0 V vs reversible hydrogen electrode (RHE) approximately 40% at 60 ℃ as compared with Pt/C, and it exhibited high HOR mass activity and surface activity across a broad temperature range. This suppression is attributed to the synergistic effect between platinum and tungsten oxide species, which facilitates improved HOR kinetics and H2O2 selectivity.This study was supported in part by funds for the “R&D of novel anode catalyst” project in the “Collaborative industry-academia-government R&D project for solving common challenges toward dramatically expanded use of fuel cells” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors thank Prof. Hiroyuki Uchida (The University of Yamanashi) for his kind advice.

Alkali metal cations at work: Enhancing CO2 electroreduction to CO on ZnO nanorods

Oxide-derived zinc, an abundant and cost-effective electrode material alternative to gold and silver, has exhibited high activity for the electroreduction of CO2 to CO (CO2RR). However, the impact of cations on the CO2RR activity remains unexplored. In this study, we investigated the effect of three alkali metal cations (Cs+, K+, and Li+) on the CO2RR over a ZnO nanorod electrode, using a rotating ring disk electrode (RRDE) technique. Cyclic voltammetry of the Pt ring in the RRDE tip reveals a consistent trend in the buffering capacity of these cations (Cs+ > K+ > Li+), as evidenced by the availability of OH⁻ ions for CO electrooxidation and hydrogen oxidation reactions (HOR). Cs+ showed a pronounced effect on the activity of the CO2RR to CO since it can regulate OH⁻ concentration and maintain the local pH. This study addresses the ongoing debate concerning the effects of cations; interfacial electric field and buffering capacity; and elucidates the relationship among electrolyte/cation, local pH dynamics, and the CO2RR activity towards CO over the active oxide-derived Zn electrodes, all derived from the fast and facile RRDE technique.

Selectivity Study of Direct Seawater Electrolyzer Anode Catalysts Using the Rotating Ring-Disc Electrode Method

Seawater electrolysis suffers from many issues that must be resolved before the technology can be scaled. The corrosive hypochlorite formation at the anode can damage the electrode and other electrolyzer components. Furthermore, hypochlorite is unstable and can decay, particularly when exposed to heat and metal ions, which could lead to erroneously high oxygen evolution reaction (OER) selectivity calculations in catalyst benchmarking experiments, resulting in poor catalyst and electrolyzer component selection. In this study, we used the rotating ring-disc electrode (RRDE) technique for the characterization of IrO2, NiO, Co3O4, RuO2, Pt/C, and PtRu electrocatalysts at near-neutral pH (8.4) in 0.5 M NaCl. The RRDE can overcome the challenge posed by thermocatalytic hypochlorite decay. IrO2 and PtRu were also studied over a range of chloride concentrations from 0.1 to 1 M. Our findings reveal that elevated temperatures (313 and 333 K) are conducive to higher OER selectivity, as the OER faradaic efficiency (FE) on IrO2 increased by 23% at 1.22 V vs SHE when the temperature was increased from 293 to 333 K. Increasing the chloride concentration from 0.1 to 1 M increased the OER current density by 40% and 200% on IrO2 and PtRu, respectively, indicating a synergistic relationship.

Coordination Structure Modulation in Group-VIB Metal Doped Ag3PO4 Augments Active Site Density for Electrocatalytic Conversion of N2 to NH3.

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag3PO4 to enhance the active site density, accompanied by d-p orbital mixing at the active site/N2 interface. Doping induces compressive strain in the Ag3PO4 lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N2 adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N2H4, which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N2 to NH3 on Mo/Ag3PO4-10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR.

Improving the durability and anti-poisoning properties of platinum catalysts by carbon shell encapsulation: A promising approach for both cathode and anode catalysts for polymer electrolyte membrane fuel cells

Carbon shell encapsulation has emerged as an effective strategy for enhancing the durability of Pt-based electrocatalysts for polymer electrolyte membrane fuel cells (PEFCs). Here, a nitrogen-doped carbon shell-encapsulated Pt catalyst supported on Ketjen black (Pt@C/KB) was synthesized, and its catalytic performance was characterized. The oxygen reduction reaction (ORR) performance and anti-poisoning properties were investigated in 0.1 M HClO4 with and without H2SO4 or H3PO4 poisoning, using a rotating ring-disk electrode (RRDE) technique. Despite a decrease in the electrochemical surface area (ECSA), Pt@C/KB encapsulated by a thin graphene-like carbon shell (<1 nm thick) showed high selectivity for the four-electron reaction due to its superior anti-poisoning properties, as well as improved ORR activity and durability. The H2O2 yield of Pt@C/KB, the precursor of hydroxyl radicals, was decreased approximately one third compared to bare Pt catalyst and the gap was more pronounced in the low potential (E ≤ 0.1 V/RHE) where close to practical anode potential, suggesting that Pt@C/KB can be applied as a new anode catalyst. Applying carbon core-shell catalysts to both the cathode and anode is a prospectively effective approach for improving the cell performance by improving the ORR activity and anti-poisoning properties, as well as for extending the lifespan of PEFCs.

Selectivity Study of Anodic Seawater Electrolysis Catalysts Using the Rotating Ring-Disc Electrode Method

Seawater Electrolysis is an exciting alternative to freshwater electrolysis; however, it suffers from a multitude of issues that must be resolved before the technology can be scaled. Corrosive hypochlorite forms at the anode of seawater electrolysis and can damage catalysts and electrolyzer components. Hypochlorite is unstable and can decay, particularly when exposed to heat and metal ions, which can lead to erroneously high oxygen evolution reaction (OER) selectivity conclusions, resulting in poor catalyst and electrolyzer component selection. In this study, we use the rotating ring-disc electrode technique to characterize the selectivity of IrO2, NiO, Co3O4, RuO2, Pt and PtRu electrocatalysts in situ at near-neutral pH (8.4) with linear scan voltammetry (LSV), potentiostatic and galvanostatic experiments. Our findings reveal that elevated temperatures are conducive to higher OER selectivity. Furthermore, when we increased the chloride concentration in the electrolyte with an IrO2 catalyst, we observed that although the overall selectivity towards the OER reaction decreased, the OER current independently increased, indicating a synergistic relationship.

Electrocatalytic hydrogen peroxide generation using WO3 nanoparticle-decorated sodium niobate microcubes

The current work studies the electrocatalytic performance of NaNbO3 microcubes decorated with WO3 nanoparticles on Printex L6 at varying concentrations (1%, 3%, 5%, and 10% by weight) for H2O2 electrogeneration aiming for future use in electrochemical advanced oxidation processes for organic pollutant degradation·H2O2 electrogeneration was studied using oxygen reduction reaction (ORR) with the rotating ring-disk electrode (RRDE) technique. Electrochemical results revealed an improvement in H2O2 electrogeneration for the NaNbO3@WO3/C materials compared to that achieved with Printex L6 carbon. Notably, the 5% NaNbO3@WO3/C electrocatalyst exhibited a higher ring current for oxygen reduction reaction and promoted a 2.1-electron transfer, facilitating a higher rate of H2O2 electrogeneration through the 2-electron mechanism. Also, enhancing oxygen-containing functional groups has shown the capability to thoroughly adjust characteristics and enhance active sites, increasing H2O2 electrogeneration. These findings suggest that 5% NaNbO3@WO3/C electrocatalysts hold promise for in situ hydrogen peroxide electrogeneration.

Tuning the Interfacial Reaction Environment for CO2 Electroreduction to CO in Mildly Acidic Media.

A considerable carbon loss of CO2 electroreduction in neutral and alkaline media severely limits its industrial viability as a result of the homogeneous reaction of CO2 and OH- under interfacial alkalinity. Here, to mitigate homogeneous reactions, we conducted CO2 electroreduction in mildly acidic media. By modulating the interfacial reaction environment via multiple electrolyte effects, the parasitic hydrogen evolution reaction is suppressed, leading to a faradaic efficiency of over 80% for CO on the planar Au electrode. Using the rotating ring-disk electrode technique, the Au ring constitutes an in situ CO collector and pH sensor, enabling the recording of the Faradaic efficiency and monitoring of interfacial reaction environment while CO2 reduction takes place on the Au disk. The dominant branch of hydrogen evolution reaction switches from the proton reduction to the water reduction as the interfacial environment changes from acidic to alkaline. By comparison, CO2 reduction starts within the proton reduction region as the interfacial environment approaches near-neutral conditions. Thereafter, proton reduction decays, while CO2 reduction takes place, as the protons are increasingly consumed by the OH- electrogenerated from CO2 reduction. CO2 reduction reaches its maximum Faradaic efficiency just before water reduction initiates. Slowing the mass transport lowers the proton reduction current, while CO2 reduction is hardly influenced. In contrast, appropriate protic anion, e.g., HSO4- in our case, and weakly hydrated cations, e.g., K+, accelerate CO2 reduction, with the former providing extra proton flux but higher local pH, and the latter stabilizing the *CO2- intermediate.

The Durability of the Platinum/Polypyrrole Nanotubes' Catalysts in Oxygen Reduction Reaction

Platinum (Pt) catalysts supported on carbon-based materials are effective catalysts for fuel cells. However, the durability of the carbon supports in acidic media needs to be improved. Platinum/polypyrrole (PPy) nanotubes have emerged as promising catalysts for the oxygen reduction reaction (ORR) due to their high surface area and good electrocatalytic activity. Furthermore, the nitrogen atoms within the chemical structure of PPy nanotubes are expected to improve their durability.In this study, we investigated the performance and durability of Pt catalysts during ORR by decorating different carbon-based materials with Pt nanoparticles. The catalytic activity and durability were analyzed using the rotation ring-disk electrode (RRDE) technique. We also examined the influence of the different supports on the electrochemical degradation of the catalysts.Our results showed that Pt/PPy nanotubes exhibited high activity and durability in ORR reactions. We paid particular attention to the chemical changes of the catalysts' surfaces, including both the metal and support components, during the ex-situ electrochemical measurements. The surface of the catalysts was characterized using photoelectron X-ray spectroscopy (XPS), synchrotron radiation photoelectron spectroscopy (SRPES), and near-edge X-ray absorption fine structure (NEXAFS) analysis before and after electrochemical degradation. Based on our findings, we proposed degradation mechanisms of the Pt/PPy nanotubes catalysts.In addition, we tested the Pt/PPy nanotubes catalysts in fuel cells and observed their high performance. These findings suggest that Pt/PPy nanotubes catalysts can serve as durable and effective catalysts for ORR reactions, even under harsh conditions. Further research is needed to optimize the synthesis conditions and operating parameters of these catalysts to improve their performance and durability.

On the Degradation of Vanadium-Based Phosphate Framework Electrode Materials in Aqueous Environments

Na3V2(PO4)3 and Na3V2(PO4)2F3 are among the most studied and applied positive electrode materials in non-aqueous sodium-ion batteries due to their relatively high capacities and redox potentials. However, the stability of these materials in aqueous environments is relatively low limiting their applications in aqueous batteries or deionization cells. In this study, we provide a comprehensive analysis of Na3V2(PO4)3 and Na3V2(PO4)2F3 degradation in aqueous media using a number of techniques such as standard electrochemical methods, elemental analysis, powder X-ray diffractometry, and rotating ring-disc electrode. The latter allows for real time in situ/operando degradation analysis during electrochemical operation. The results show that Na3V2(PO4)3 suffers from chemical vanadium dissolution when immersed even in neutral pH electrolytes, whereas Na3V2(PO4)2F3 is significantly more stable. The results obtained by the rotating ring-disc electrode technique explicitly show that at pH ∼7 Na3V2(PO4)3 and Na3V2(PO4)2F3 generate most of the soluble V(V) species during the electrochemical charging process. Whereas in acidic pH, there is also additional electrochemically-induced generation of soluble V(IV) species during the discharging process. The overall results suggest that fluoride ions significantly increase the structural stability of phosphate materials in aqueous environments. Potentially, a careful electrolyte design with controlled proton and water activity could enable the use of Na3V2(PO4)2F3 in aqueous electrochemical devices.

Electrochemically Reduced Graphene Oxide Supported Palladium-Cobalt Alloy Nanoparticles as Highly Efficient Electrocatalyst for Oxygen Reduction Reaction

Pd-Co alloy nanoparticles were synthesized on electrochemically reduced graphene oxide (ErGO) for electrocatalytic oxygen reduction reaction (ORR) in alkaline media. The morphological structure, chemical composition, and crystallinity of the afforded ErGO/Pd-Co catalyst were examined by various techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. The Pd-Co alloy nanoparticles were evenly distributed on the ErGO sheet and had a narrow size distribution, with an average particle size of 4.25 nm. The ORR activity of the as-prepared ErGO/Pd-Co alloy catalyst was evaluated by cyclic voltammetry, linear sweep voltammetry, rotating disk electrode, and rotating ring disk electrode techniques in an alkaline electrolyte. The ErGO/Pd-Co catalyst exhibits a very high electrocatalytic activity in ORR with the mass activity more than 2.0 times of the commercial 20% Pt/C due to the synergistic catalytic effect of both ErGO and Pd-Co nanoparticles. Electrocatalytic kinetics investigation shows that, the ORR on the ErGO/Pd-Co catalyst proceeds through four electrons transferred mechanism with negligible amount of peroxide species. Moreover, the ErGO/Pd-Co shows an excellent methanol tolerance than the commercial 20% Pt/C.

Methanol assisted water electrooxidation on noble metal free perovskite: RRDE insight into the catalyst’s behaviour

In this work, we have hypothesized that noble metal-free perovskites are an essential class of oxygen evolution reaction (OER) catalysts in an alkaline medium and thus, they are a suitable candidate for the assisted water oxidation catalysts. Herein, we demonstrate that the origin of the methanol-assisted OER activity at near thermodynamic potential on perovskite electrode arises due to the involvement of additional hydroxyls as a result of dissociative chemisorption of methanol. When the perovskite electrode is screened for methanol electrooxidation reaction in 0.5 M KOH + 0.5 M methanol electrolyte, it delivers a two times higher current density. This imparts an 82 % increase in the evolution of oxygen gas moles with complete oxidation of methanol to carbon dioxide. Along with the electrochemical characterization to understand the electrocatalyst property, Rotating ring disk electrode (RRDE) technique is explored for the first time in literature to validate the catalyst’s involvement during OER. RRDE is effective in understanding the lattice oxygen behaviour and methanol-assisted water electrooxidation during OER. Our results suggest new insights and ideas towards the oxygen evolution reaction process and the mechanistic insight into the elevated OER due to assisted methanol electrooxidation.

Using a novel gas diffusion electrode based on Vulcan XC-72 carbon modified with Nb2O5 nanorods for enhancing H2O2 electrogeneration

The production of H2O2 through oxygen reduction reaction (ORR) from a 2-electron mechanism is an attractive alternative method because it allows the in-situ production of H2O2 at moderate temperature and atmospheric pressure. The present study investigates, for the first time, the modification of Vulcan XC-72 carbon with niobium oxide (Nb2O5) nanorods in different mass proportions (1%, 3%, 5%, and 10%) and their application as electrocatalysts in ORR through the 2-electron mechanism in alkaline media and in gas diffusion electrode for electrogeneration of H2O2 in acid media. The modified electrocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), contact angle measurements, and X-ray photoelectron spectroscopy (XPS), while the ORR assays were analyzed using the rotating ring-disk electrode (RRDE) technique. The modification of Vulcan XC-72 carbon with 1% Nb2O5 contributed to the enhancement of selectivity toward H2O2 electrogeneration in ORR with current efficiency of 40 % higher than bare Vulcan XC-72 carbon and a relatively more positive initial potential. The application of gas diffusion electrodes for H2O2 generation in acid medium using 1% Nb2O5-modified Vulcan XC-72 carbon yielded 645 mg L−1 of H2O2 in 120 min of experiment at −2.5 V vs. Ag/AgCl. The concentration of H2O2 electrogenerated via the application of the modified carbon material was 48 % higher compared to the concentration electrogenerated using the unmodified carbon material (444 mg L−1) under the same experimental conditions. In addition, the proposed electrocatalyst presented lower energy consumption and higher current efficiency compared to Vulcan XC-72 carbon. The results obtained can be attributed to the greater hydrophilicity of the surface of the proposed catalyst caused by the insertion of only 1% of Nb2O5 nanorods.

Sodium niobate microcubes decorated with ceria nanorods for hydrogen peroxide electrogeneration: An experimental and theoretical study

The present work investigates the catalytic activity of NaNbO3 microcubes decorated with CeO2 nanorods on carbon (1 %, 3 %, 5 %, and 10 % w/w) for H2O2 electrogeneration. The crystalline phases and the morphology of the materials were identified with scanning electron microscopy, transmission electron microscopy, X‐ray diffraction and X-ray Photoelectronic spectroscopy. Contact angle measurements were performed to characterize the hydrophilicity of each material. The H2O2 electrogeneration was assessed by oxygen reduction reaction using the rotating ring-disk electrode technique. Electrochemical characterization results shown an enhancement on the H2O2 electrogeneration by NaNbO3 @CeO2/C-based materials compared to what was obtained with pure Vulcan XC72. The 1 % NaNbO3 @CeO2/C electrocatalyst presented the lower starting potential for the ORR and a 2.3 electron transfer, favoring the 2-electron mechanism and providing a higher H2O2 electrogeneration rate. Also, the enhancement of oxygen-containing functional groups showed the potential to comprehensively tune properties and optimize active sites and, consequently, increases the H2O2 electrogeneration. Density functional theory calculations indicated that NaNbO3 and CeO2 surfaces have a similar low theoretical overpotential for this reaction and that CeO2 improves the catalyst facilitating the electron transfer. These results indicate that NaNbO3 @CeO2/C-based electrocatalysts are promising materials for in situ H2O2 electrogeneration.

GDE vs RDE: Impact of operation conditions on intrinsic catalytic parameters of FeNC catalyst for the oxygen reduction reaction

We present a comprehensive comparison of the catalytic evaluation of a FeNC catalyst using two different approaches, i.e., employing the rotating ring disk electrode (RRDE) technique and a gas diffusion electrode (GDE) setup. With both techniques, the FeNC catalyst is evaluated in acidic as well as in alkaline environment. The oxygen reduction reaction (ORR) is studied and parameters such as ORR kinetic activity, Tafel slope, and the apparent activation energy are determined at different applied temperatures/overpotentials. The obtained results offer clear evidence that in alkaline medium, the GDE offers reaction conditions with improved reactant mass transport enabling an evaluation of the FeNC catalyst closer to membrane electrode assembly (MEA) testing. As compared to the RRDE evaluation, the ORR rate is higher in the GDE setup and the potential range for extracting kinetics and activation energies is substantially improved. However, in acidic environment only minor differences between the two reaction environments (RRDE and GDE) are observed. The difference between alkaline and acidic conditions is rationalized based on the different reaction pathway in the two environments.

(Digital Presentation) Electrochemical Analysis of Oxygen Reduction in Phosphonium Ionic Liquids Based on Rotating Ring-Disk Electrode Method

Ionic liquids (ILs) have characteristic physicochemical properties such as high thermal stability, low volatility, low melting point, and flame resistance. Moreover, ILs exhibit also excellent electrochemical properties represented by a wide potential window.[1] Hence, they have a great potential for electrochemical applications such as electrolytes for batteries, capacitors, fuel-cells and so on. Phosphonium ILs have unique physical characters such as lower viscosity and higher ionic conductivity compared with corresponding structured ammonium ILs.[2] Recently, we have evaluated the diffusion coefficient and the solubility of oxygen molecules in phosphonium ILs and have clarified that such oxygen behaviors strongly depends on the chemical structure of cation rather than that of anions. In the present study, we demonstrated the proton effect for the ORR in phosphonium ILs using rotating ring disk electrode (RRDE) technique.[3] Tetraalkyl-phosphonium(PXXXY+ and bis(trifluoromethane sulfone) imide (TFSA-)) ILs were used for electrolytes.Cyclic voltammetry (CV) and convective voltammogram were performed using a three electrode cell at 25oC. The RRDE constructed a glassy carbon (GC) or platinum (Pt) disk, and Pt ring electrodes were used as the working electrodes. The ring current was measured at a potential of 1.0 V vs. Ag/Ag+ reference electrode, where the intermediate oxidation reaction enough attached to diffusion limit.In the non-protonic media, ORR currents were observed from –0.6 V on GC disk electrode and –0.5 V on Pt disk electrode respectively, which were corresponding to the one-electron reduction reaction in ORR. On the other hand, the on-set potential of ORR in protonic media was higher than that in non-protonic media on both electrodes. Such potential shifts were strongly appeared on the Pt disk electrode than that on the GC disk electrode. Moreover, the diffusion limiting current was observed on Pt disk electrode at higher potential region in protonic media, and the current increased with increasing H-TFSA content. Therefore, the limiting current originated from not the transport of oxygen molecules, but that of proton, while the ring current oppositely decreased with increasing H-TFSA content. The ring current originated from intermediate formed on Pt disk electrode was smaller than that on GC disk electrode. These results indicated that the number of electrons in ORR increased by the existence of proton, and the effect of proton was promoted on Pt surface better than the GC surface.[1] A. Khan, C. Zhao, ACS sustainable Chem. Eng. 4, 506 (2016)[2] K. Tsunashima, and M. Sugiya, Electrochemistry Communications, 9, 2353- 2358(2007)[3] M. Hildera, et al, Electrochimica Acta, 202, 100-109(2016).

The enhanced local CO concentration for efficient CO2 electrolysis towards C2 products on tandem active sites

Electrochemical reduction of CO2 to C2 products on Cu-based catalysts provides a promising approach for controlling the global carbon balance and restoring renewable surplus electricity. The enhanced CO2 adsorption and CO local concentration are beneficial for CO2 conversion and C2 intermediates formation, promoting the progress of CO2 utilization. Here, we report a bimetallic MOF-derived Co3O4-CuOx/C (M-CuCo/C) catalyst constructed with Co3O4 and CuOx sites wrapped in the carbon skeleton, achieving efficient CO2 activation and C2 generation under low overpotential. The optimized M-CuCo/C catalyst (Cu/Co ratio of 1:2) exhibits a total current density of 19.28 mA/cm2 at −1.05 (V vs. RHE), which is 8.60 times than that on MOF-derived CuOx/C (M-Cu/C). The highest C2 faradic efficiency (FE) reaches 79.2% (-0.75 V vs. RHE), accompany with a C2 production rate of 275.6 μmol/(g·h). The special nanorods-like morphology assembled by dual sites significantly increases electrochemical surface area and electron transmission rate during eCO2RR. The local CO intermediates under real-time electrochemical environment are monitored via rotation ring disk electrode (RRDE) techniques. Combined with in situ infrared measurements and DFT studies, it’s demonstrated that CO2 could be efficiently converted to CO under low overpotential on Co3O4 sites, forming local CO-enriched environment around neighboring CuOx sites and further accelerating the process of C2 formation.

Synthesis, characterization, and degradation study of Mn-based phosphate frameworks (Na3MnTi(PO4)3, Na3MnPO4CO3, Na4Mn3(PO4)2P2O7) as aqueous Na-ion battery positive electrodes

Aqueous electrolyte Na-ion batteries based on abundant materials offer one of the attractive alternatives to replace conventional Li-ion batteries in the field of stationary electricity storage. However, the search for and development of stable, low-cost and compatible positive electrode materials remains a significant challenge. Mn-based materials are deemed to be among the most suitable due to their abundance, environmental compatibility and suitable electrochemical properties. In this work, three different phosphate and mixed phosphate framework compounds Na3MnTi(PO4)3, Na3MnPO4CO3, and Na4Mn3(PO4)2P2O7 are successfully prepared and comprehensively characterized as potential aqueous Na-ion positive electrode materials using a wide range of methods such as impedance spectroscopy, cyclic voltammetry, galvanostatic charge/discharge cycling. The degradation of these materials is studied by rotating ring-disc electrode technique. The results clearly show that charge capacity loss observed in these materials is related to the electrochemical and electrochemically-induced chemical dissolution of manganese from the electrode. The results obtained using a combination of different methods also indicate that a significant part of Mn is electrochemically inactive or inaccessible in such Mn-based phosphate frameworks. The fraction of electrochemically inactive Mn also tends to increase during the electrochemical operation, limiting the performance of these materials as potential battery electrodes in aqueous electrolytes.

A new spin on electrochemistry in the undergraduate lab

Abstract The growing interest in electrochemistry over recent years has sparked an increase in the popularity of various electrochemical techniques, including more advanced methods, that have previously been overlooked in academia and industry. This makes comprehensive hands-on experience in electrochemistry a highly demanded addition to chemistry graduates. However, many students do not receive sufficient training in the theory and experimental design to confidently use and apply various electrochemical techniques throughout their undergraduate, and sometimes even in graduate studies. Here we summarize the theory and practical applications for both rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques. The different modes of operation of rotating ring disk voltammetry, methodologies of data analysis and interpretation as well as the scope of the information that can be extracted from the RDE/RRDE are discussed. Proposed modifications of the laboratory curriculum will allow students to examine and learn valuable information about the reactions on the surface of the electrode/liquid interface. This information will allow chemists to confidently use RDE and RRDE techniques for a wide range of research and development targets. Furthermore, incorporating these techniques into existing chemistry laboratories will help chemistry educators to enrich the undergraduate chemistry curriculum and improve students’ learning outcomes.