Disk Electrode Research Articles

Demonstration of Feasibility Using Ionic Liquid as Electrolyte for Electrochemical Deposition and Recovery of Silver from Silver Oxide

Silver oxide (Ag₂O) is soluble in the hydrophobic protic amide-type ionic liquid (IL), protonated-betaine bis((trifluoromethyl)sulfonyl)amide ([Hbet][TFSA]). Cyclic voltammetric behavior of Ag(I) showed a single redox couple, and NMR spectra implied that Ag⁺ might be coordinated with the [TFSA] anions in more extent than with the deprotonated [Hbet] ions (i.e. [bet]; a Zwitterion). By changing the scan rates and cycle numbers of potential scan utilized for the cyclic voltammetric electrodeposition, different particle sizes and distribution densities of silver nanoparticles (AgNPs) could be electrodeposited on glassy carbon disc electrode (GCE), which showed activities towards the electrochemical reduction of nitrate and oxidation of hydrazine, respectively, in alkaline solutions. The high faradic efficiencies (F.E.) of Ag electrodeposition using the contents of Ag₂O coin batteries as the Ag source implied that it may be possible to develop a process for recovering Ag from spent Ag₂O coin batteries based on the electrochemical system reported here.

Investigation of Iridium-Based OER Catalyst Layers in a GDE Half-Cell Setup: Opportunities and Challenges

To achieve widespread commercialization of proton exchange membrane (PEM) water electrolyzers, the optimization of iridium (Ir) utilization is crucial. Traditional full-cell-based approaches are time-consuming and labor-intensive. In this work, the feasibility of using a gas diffusion electrode (GDE) half-cell as an alternative to full-cell setups for accelerated investigation of Ir-oxide-containing anode catalyst layers (CLs) is scrutinized. Using CLs composed of Ir oxides of different intrinsic oxygen evolution reaction (OER) activity as a probe, we show that a GDE can successfully reveal the differences in the performance of the CLs. Comparison of the results obtained in the GDE to those from rotating disk electrode (RDE) and full-cell membrane electrode assembly (MEA) measurements indicate that GDE data can closely mimic both setups. However, essential discrepancies are observed between GDE and MEA, which are linked to differences in the catalyst layer | membrane interface and the presence of liquid electrolyte in the GDE setup. Our findings reveal that even though the direct comparison of the OER performance to full-cell measurements is still partially hampered, GDE half-cell setups can already be used for fundamental assessments and accelerated screening of electrocatalysts and CLs at relevant current densities up to 1.5 A cm−2.

REMnO3 (RE = Pr, Nd, Sm, Eu, Gd) perovskite as efficient catalysts for oxygen reduction reaction

Rare earth metal based perovskite emerges as important catalytic material for energy production and storage. These ABO3 type materials are now the focus of research in the field of oxygen reduction and evolution reactions. Here, in this work we evaluated the oxygen reduction properties of the synthesized one-dimensional REMnO3 (RE = Pr, Nd, Sm, Eu and Gd). The one-dimensional REMnO3 prepared by the hydrothermal synthesis route results in pure phase perovskite on calcinations. The perovskite was characterized with X-ray diffraction, Fourier transform-infrared (FT-IR), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The oxygen reduction reaction activities were investigated with the help of electrochemical workstation that consists of three-electrode system immersed in 0.1 mol/L KOH electrolyte solution saturated with oxygen. The Koutechy–Levich plot obtained from rotating ring disk electrode shows all the prepared catalysts follow 4e– processes during oxygen reduction. The effect of “A” site cation variation in REMnO3 on oxygen reduction reaction is discussed. SmMnO3 showed better onset potential for oxygen reduction reaction among the prepared rare earth perovskite. SmMnO3 having high RE:Mn ratio (A-site rich compositions) promotes oxygen reduction reaction (ORR) activity. All the perovskites showed good oxygen reduction property with high stability and methanol tolerance.

Lead and Nitrogen Co-Doped Multi-Walled Carbon Nanotube Electrocatalyst for Oxygen Reduction Reaction

The electrocatalysis of oxygen reduction reaction (ORR) on lead and nitrogen co-doped multi-walled carbon nanotube (Pb/N/MWCNT) composite catalyst has been investigated in the neutral, acidic and alkaline media. The mixture of lead phthalocyanine (PbPc) and MWCNTs was pyrolysed in nitrogen atmosphere to achieve co-doping of lead and nitrogen. The successful co-doping as well as formation of Pb nanoparticles were confirmed with the use of various physical and surface characterisation methods such as scanning and transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction analysis. This work brings forth the electrocatalytic effect of Pb and nitrogen co-doping of carbon by a detailed electrochemical analysis using rotating disk electrode (RDE) method. The Pb and nitrogen co-doped MWCNT material demonstrate a reasonable electrocatalytic ORR activity in acidic, neutral and alkaline media. The results indicate great potential of Pb to be employed in electrocatalyst design as co-doping agent to achieve superior cathode catalysts for microbial, proton and anion exchange membrane fuel cells.

Exploiting synergistic effects: Co3O4/g-C3N4 composite catalyst for enhanced oxygen evolution reaction

In this study, we explore the potential of Co3O4/g-C3N4 composite catalysts for improving the oxygen evolution reaction (OER) performance. By employing a rotating disk electrode in 0.1 mol L−1 KOH electrolyte, we systematically investigate the OER properties of various ratios of Co3O4/g-C3N4 catalysts. Our findings reveal that Co3O4/g-C3N4-0.2 catalyst outperforms pure g-C3N4, exhibiting significantly higher current density (10 mA cm−2) and lower overpotential (627 mV). Furthermore, Tafel slope analysis demonstrates enhanced reaction kinetics, with Co3O4/g-C3N4-0.2 catalyst displaying the smallest Tafel slope (54 mV dec−1). Electrochemical impedance spectroscopy (EIS) confirms the superior charge transfer efficiency of Co3O4/g-C3N4-0.2 catalyst compared to other ratios and pure g-C3N4. Impressively, stability tests demonstrate only 5.4% performance decay after 1000 CV cycles, highlighting the excellent stability of Co3O4/g-C3N4-0.2 catalyst. These findings underscore the remarkable potential of Co3O4/g-C3N4 composite catalysts in OER applications. The synergistic effects between Co3O4 and g-C3N4 contribute to enhanced electrocatalytic performance, making it a promising candidate for future OER advancements.

The role of applied potential on particle sizing precision in single-entity blocking electrochemistry

Blocking electrochemistry, a subfield of single-entity electrochemistry, enables in-situ sizing of redox-inactive particles. This method exploits the adsorptive impact of individual insulating particles on a microelectrode, which decreases the electrochemically active surface area of the electrode. Against the background of an electroactive redox reaction in solution, each individual impacting particle results in a discrete current drop, with the magnitude of the drop corresponding to the size of the blocking particle. One significant limitation of this technique is “edge effects”, resulting from the inhomogeneous flux of the redox species’ diffusion due to increased mass transport to the edge of the disk electrode surface. “Edge effects” cause increased errors in size detection, resulting in poor analytical precision. Here, we use computational simulations to demonstrate that inhomogeneous diffusional edge flux of quasi-reversible redox species is mitigated at lowered overpotentials. This phenomenon is further illustrated experimentally by lowering the applied potential such that the system is operating under a kinetically-controlled regime instead of a diffusion-limited regime, which mitigates edge effects and increases particle sizing precision significantly. In addition, we found this method to be generalizable, as the precision enhancement is not limited to geometrically spherical particles but also occurs for cubic particles. This work presents a simple, novel methodology for edge effect mitigation with general applicability across different particle types.

Multiple Bubble Removal Strategies to Promote Oxygen Evolution Reaction: Mechanistic Understandings from Orientation, Rotation, and Sonication Perspectives.

Bubble coverage of catalytically active sites is one of the well-known bottlenecks to the kinetics of the oxygen evolution reaction (OER). Herein, various bubble removal approaches (electrode orientation, rotating, and sonication) were considered for the OER performance evaluation of a state-of-the-art Ir-based electrocatalyst. Key parameters, such as catalyst mass loss, activity, overpotential, and charge- and mass-transfer mechanisms, were analyzed. First, it was suggested that a suitable orientation of the working electrode facilitates coalescence and sliding bubble effects on the catalyst surface, leading to better electrochemical performance than those of the traditional rotating disk electrode (RDE) configuration. Then, the convection and secondary Bjerknes force were explained as the responsible phenomena in improving the OER activity in the RDE and sonication methods. Finally, simultaneous implementation of the methods enhanced the catalyst mass activity up to 164% and provided fast charge-transfer kinetics and low double-layer capacitance, which eventually led to a 22% reduction in overpotential, while the catalyst loss slightly increased from 1.93 to 3.88%.

Surfactant‐modified electrode–electrolyte interface for steering CO2 electrolysis on Cu electrodes

AbstractCu‐based catalysts exhibit the unique ability to generate high‐order products from electrochemical CO2 reduction reaction (CO2RR). The performance of electrochemical systems is jointly influenced by the catalysts and local microenvironment of the electrode–electrolyte interface. Here, Cu nanowires as a model catalyst, in combination with cetyl trimethyl ammonium bromide (CTAB) as electrolyte additives, are designed to steer CO2RR. By using the Cu rotating disc electrode and in situ vibrational spectroscopy, it is revealed that the hydrophobic interface microenvironment is built, and the interaction of interfacial water and surface‐adsorbed CO is disrupted by CTAB, which dramatically improve formate selectivity (from 5% to 63%) with a high partial current density of formate (13‐fold increase) at −1.0 V vs. reversible hydrogen electrode. The understanding of the surfactant‐modified electrode–electrolyte interface established here offers a distinct perspective to control the microenvironment on promoting electrosynthesis performance.

A novel electrochemical method determining pKa and transport parameters of buffers using acid-base transport limitation response

Dissociation constant (logarithmic form, pKa) and diffusion coefficient (D) are two fundamental physical parameters for weak acids and bases (buffers). Their effortless determinations from one method are not available yet. Herein, we propose an innovative method to determine pKa and D values based on a brand-new principle of electrochemical acid-base transport limitation (eABTL). The significance of eABTL lies in its ability to relate inert buffers to electrode reactions, enabling the acquisition of electrochemical responses for inert species. Acid-base transport limiting current (jl) is the only variable that needs to be measured. The pKa and transport coefficient (m) are determined from the relationship of jl vs. solution pH and jl vs. buffer concentration, respectively. Three ways are available for D determinations by introducing the expressions of diffusion layer thickness. The method is demonstrated using rotating disc electrodes to implement hydrogen evolution reaction. The pKa, m and D values exhibit good repeatability in multiple determinations. A well-defined electrode geometry is necessary for accurate D determination. This method can be developed to a family of methods with the advantages for fast estimating practical parameter values of buffers.

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.

Fe–Pd nanoflakes decorated on leached graphite disks for both methanol and formic acid electrooxidation with excellent electrocatalytic performance

This paper introduces a unique and simple method for fabricating of inexpensive electrocatalysts for use in direct methanol fuel cells. The leached Fe1–Pd1 NFs/graphite (leached Fe1–Pd1/graphite) disk electrode was successfully obtained via uniform dispersion of Zn powder into the matrix of commercial graphite powder (98%), pressing under optimized pressure followed by the treatment in H2SO4 solution containing Fe+2 and Pd+2 cations, leading to the partial leaching out of Zn from graphite matrix, as well as partial electroless substitution of Fe–Pd nanoflakes with Zn metal. Based on the morphology studies, binary Fe–Pd nanoflakes with a large surface area uniformly dispersed on the leached graphite disk. The leached Fe–Pd/G disk showed the exceptional electrocatalytic activity toward methanol and formic acid oxidation without electrocatalyst poisoning being observed, in contrast to the leached Pd/graphite and leached Fe/graphite disks. This is due to the high surface area, and synergistic effect of Pd and Fe. The findings of this work may be used for the mass manufacture of graphite-based disks for commercial fuel cell applications using available graphite powders. The linear range of washed Fe1–Pd1/G electrocatalyst for measuring methanol was about 0.1–1.3 M, and its detection limit was calculated at about 0.03 M. Furthermore, the linear range of the nanocatalyst for measuring formic acid was about 0.02–0.1 M, and its detection limit was calculated at about 0.006 M.

Reduced Graphene Oxide-Supported Iron-Cobalt Alloys as High-Performance Catalysts for Oxygen Reduction Reaction.

Exploring non-precious metal-based catalysts for oxygen reduction reactions (ORR) as a substitute for precious metal catalysts has attracted great attention in recent times. In this paper, we report a general methodology for preparing nitrogen-doped reduced graphene oxide (N-rGO)-supported, FeCo alloy (FeCo@N-rGO)-based catalysts for ORR. The structure of the FeCo@N-rGO based catalysts is investigated using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and transition electron microscopy, etc. Results show that the FeCo alloy is supported by the rGO and carbon that derives from the organic ligand of Fe and Co ions. The eletrocatalytic performance is examined by cyclic voltammetry, linear scanning voltammetry, Tafel, electrochemical spectroscopy impedance, rotate disc electrode, and rotate ring disc electrode, etc. Results show that FeCo@N-rGO based catalysts exhibit an onset potential of 0.98 V (vs. RHE) and a half-wave potential of 0.93 V (vs. RHE). The excellent catalytic performance of FeCo@N-rGO is ascribed to its large surface area and the synergistic effect between FeCo alloy and N-rGO, which provides a large number of active sites and a sufficient surface area.

Effects of Catalyst Ink Storage on Polymer Electrolyte Fuel Cells

The shelf-life of catalyst ink for fabricating polymer electrolyte fuel cells (PEFCs) is relevant for large-scale manufacturing with unforeseen production stops. In this study, the storage effects on the physicochemical characteristics of catalyst ink (Pt/C, Nafion, 2-propanol, water) and subsequently manufactured catalyst layers are investigated. Sedimentation analysis showed that catalyst particles are not fully stabilized by charge interaction induced by Nafion. Acetone was found to be an oxidation product, even in freshly prepared ink with platinum catalyzing the reaction. Rotating disk electrode analysis revealed that the electrochemically active surface area is, overall, minimally increased by storage, and the selectivity towards water formation (4-electron pathway) is unharmed within the first 48 h of storage. MEAs prepared from stored ink reach almost the same current density level after conditioning via potential cycling. The open-circuit voltage (OCV) increases due to increased catalyst availability. Scanning electron microscopy and mercury intrusion porosimetry showed that with increasing acetone content, the pore structure becomes finer, with a higher specific surface area. Electrochemical impedance spectroscopy revealed that this results in a more hindered mass transfer but lowered charge transfer resistance. The MEA with the highest OCV and power output and the lowest overall cell resistance was fabricated from catalyst ink stored for a duration of four weeks.

Theoretical understanding of reaction and kinetics in the reduction of the bromate anion to bromine on a rotating disk electrode

The reduction of the bromate anion to bromine on a rotating disk electrode (RDE) at steady-state conditions is discussed. This model is based on a system of nonlinear equations. The most crucial aspect of this investigation is finding the analytical expression of the concentration of reagents by solving the coupled second-order nonlinear equation using hyperbolic function methods. The effects of the kinetic parameters on concentration and current are explored in the unitizing graph and tables. The analytical results are validated in numerical results using MATLAB software. The effects of the parameters such as diffusion layer thickness, rotation rate, rate constants and the ratio of concentration of bromate anion and volume of concentration of bromine ions on current are discussed.

Interaction of Catalysts for Unitized Regenerative Fuel Cells

Unitized regenerative fuel cells have emerged as promising energy conversion and storage systems for various applications. However, in order to optimize their efficiency, it is crucial to enhance the performance of the bifunctional catalyst. This study aims to provide deeper insights into the electrochemical behavior and performance of the bifunctional catalyst. Several electrocatalysts were prepared and evaluated using rotating disk electrode measurements. The focus was placed on investigating the interaction between Pt, Ir, and the support material, antimony doped tin oxide (ATO), and their impact on the oxygen evolution reaction and oxygen reduction reaction. Among the analyzed catalysts, Pt-black mixed with synthesized IrO2 supported on developed ATO exhibited the highest performance, considering the results from both the fuel cell and electrolyzer systems.

Where do ferrate ions form? A dual dynamic voltammetry study

One of the most effective methods to produce ferrate ions (FeO42–) is electrochemical synthesis. During the transpassive anodic dissolution of iron, the formation of ferrate ions and the evolution of oxygen occur simultaneously, and only the sum of the currents generated by the two processes can be observed in the voltammetric curves. Products of the above process have been investigated in 45% (m/m) aqueous NaOH solutions by using the dual dynamic voltammetry (DDV)&rotating ring-disk electrode (RRDE) method (i.e., applying dynamic potential programs to the disk and the ring electrodes of the RRDE disk electrode and the RRDE ring electrode simultaneously) combined with spectrophotometric measurements. Fedisk/Ptring and Ptdisk/Ptring RRDE tips were used in the voltammetric experiments. The electrode potential regions where ferrate ions and oxygen are forming could effectively be identified. The results imply that, under the applied experimental conditions, the oxygen evolved at the disk cannot be reduced at the ring. This can be explained by the fact that elemental oxygen practically does not dissolve in concentrated aqueous sodium hydroxide solutions due to the “salting-out effect”. By using the dual voltammetric method, it was also possible to determine the optimal potential range for the electrochemical production of ferrate ions in terms of charging efficiency. The latter quantity has an important impact on the economics of practical applications. The approach proposed in this study proved to be very promising for the simultaneous detection of different dissolution products.

Nitrogen-rich carbon nitride (C3N5) coupled with oxygen vacancy TiO2 arrays for efficient photocatalytic H2O2 production

Developing efficient and facilitated recycling photocatalysts for H2O2 formation is an ideal strategy for solar-to-chemical energy conversion. In this work, we synthesized ultrathin C3N5 nanosheets through the process of thermal polymerization and polyvinylpyrrolidone (PVP)-assisted solvent exfoliation. Subsequently, the obtained ultrathin C3N5 nanosheets were tightly attached to the surface of TiO2-x arrays, resulting in an enhanced photocatalytic H2O2 production rate. The density functional theory (DFT) calculations demonstrate that an internal electric field (IEF) is generated between the TiO2-x array and the ultrathin C3N5 due to the different work functions. The presence of IEF provides an additional driving force for carrier separation and transfer in the heterointerface. Benefitting from this unique strategy, the optimal heterojunction obtains the highest H2O2 formation rate (2.93 μmol/L/min), which is about 4.1 times than that of TiO2-x arrays. The rotating disk electrode (RDE) analysis manifests H2O2 formation through 2e--dominated oxygen reduction reaction (ORR). This research provides an innovative strategy for assembling a type-II heterojunction with a useful IEF for efficient photocatalytic H2O2 production.

Synergistic effect of two metal porphyrins in a polymer catalyst for oxygen electroreduction

This work considers the formation and catalytic properties of films of individual hydroxyphenyl porphyrin complexes with manganese (manganese(III) acetate 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (MnAc(4-OHPh)P)) and iron (iron(III) chloride 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (FeCl(4-OHPh)P)) and their composites. The films of individual metalloporphyrins and bimetallic composites were obtained by superoxide-assisted electrochemical deposition in dimethylsulfoxide solutions. The formation of the bimetallic (Mn + Fe) porphyrin composite was confirmed by spectral methods. An analysis of the atomic-force microscopy results showed that the composite films consisted of larger globules and were rougher than those of individual porphyrins. The electroactive surface areas of the individual porphyrin films and the composite were significantly different from each other. The mechanism and kinetics of the oxygen electroreduction reaction (ORR) on the films of individual porphyrins and bimetallic composite were evaluated using a rotating disk electrode. The kinetic current density of the Tafel slope and the position of the ORR current wave on the surface of the poly-(MnAc(4-OHPh)P + FeCl(4-OHPh)P) composite indicate smaller kinetic limitations and lower overvoltage on this material than on carbositall and films of individual porphyrins. The smaller kinetic limitations and better energy characteristics can be explained by the synergistic effect produced by the combined action of the Mn- and Fe- catalytically active centers during ORR on the composite film.

Differences in the electrochemical behavior of Vulcan XC-72 carbon black and glassy carbon after prolonged potential cycling

The electrochemical characteristics of a carbon carrier play an important role in catalyst investigations. The evolution of the electrochemical characteristics of Vulcan XC-72 carbon black and a glassy carbon disk electrode was studied under prolonged electrochemical action. The electrochemical action was performed by repeated application of a sawtooth periodic potential to the electrodes in the range from 0.05 to 1 V vs. RHE and back at a scan rate of 50 mV/s. The EDL charging current, the cyclic current–voltage curves, the equilibrium electrode potential, and the dissolved oxygen reduction current in potentiostatic mode at 0.05 V vs. RHE were recorded periodically. Carbon black was characterized by helium pycnometry, SEM, TEM, X-ray diffraction, and Raman spectroscopy. The currents on the carbon black were several orders of magnitude higher than those on the glassy carbon. The differences in the dynamics of electrochemical characteristics are discussed.

Salt-induced nanoporous gold electrodes: One-step scalable fabrication of high-performance flexible electrochemical sensors from gold nanoparticles

Here, a simple filtration method for the fabrication of salt-induced nanoporous gold electrodes (SINPGEs) from gold nanoparticles (AuNPs) is reported. This method employs sodium chloride (NaCl) to trigger the aggregation, room-temperature sintering and region-selective deposition of AuNPs on patterned polyvinylidene fluoride (PVDF) membranes during filtration, which enables the one-step scalable fabrication of flexible SINPGEs three-electrode arrays with high conductivity, good mechanical property, large surface area and extremely low cost. Moreover, compared with traditional gold disc electrodes, the nanoporous structure of SINPGEs was demonstrated to apparently improve the electrochemical responses of various electroactive species, e.g., dopamine (DA), uric acid (UA), ascorbic acid (AA) and hydrogen peroxide (H2O2), reflected by the apparent enlargement of redox currents. In addition, the passivation effect of chloride ions (Cl−) on the oxidation of H2O2 at SINPGEs can be greatly repressed by a simple electrochemical activation approach, producing a sensitive H2O2 sensor with a calibration range of 1.0–1000 μM in the presence of 0.1 M Cl−. The present work thus establishes a new approach to the scalable construction of gold electrode-based electrochemical sensors with high performance and low cost.