Rotating Ring Disk Electrode Research Articles

Electrochemical Reduction of O2 in Ca2+ -Containing DMSO: Role of Roughness and Single Crystal Structure.

In this study, the oxygen reduction reaction (ORR) in Ca2+‐containing dimethyl sulfoxide (DMSO) at well‐ordered and rough electrode surfaces is compared by using cyclic voltammetry, differential electrochemical mass spectrometry, rotating ring disk electrode, and atomic force microscopy measurements. Slightly soluble CaO2 is the main product during early ORR on gold electrodes; after completion of a monolayer of CaO and/or CaO2, which is formed in parallel and in competition to the peroxide, only superoxide is formed. When the monolayer is completely closed on smooth annealed Au, no further reduction occurs, whereas on rough Au a defect‐rich layer allows for continuous formation of superoxide. CaO2 formed either via two subsequent 1 e- transfer steps or by disproportionation of superoxide may be deposited on top of the CaO/CaO2 adsorbate layer. The slow dissolution of the peroxide particles is demonstrated by AFM. Whereas a smooth CaO/CaO2‐covered electrode shows severe deactivation and a CaO/CaO2‐covered rough electrode allows for diffusion‐limited superoxide formation, on single crystals peroxide formation is more pronounced. The reason is most likely the lack of nucleation sites for the blocking CaO/CaO2 layer. RRDE investigations showed sluggish reoxidation kinetics of the dissolved peroxide, which are most likely due to ion pairing with Ca2+. The apparent transfer coefficient is estimated by using variation of the electrode roughness, confirming the result of the usual Tafel analysis and indicating an equilibrated first 1 e- transfer.

The Relationships among Hydrogen Adsorption, CO Stripping, and Selectivity of CO2 Reduction on Pd Nanoparticles

The low formation overpotential and strong adsorption ability of CO on palladium surface sites constrain the lower potential limit and current density of the electrochemical reduction of CO2 (CO2ER) to formate on Pd although this reaction has been considered one of the most effective methods for CO2 recycling. Among various factors, the participation of adsorbed hydrogen atoms seems to be a key factor affecting the selectivity of CO2ER on Pd. This article discusses the relationship between the selectivity and hydrogen adsorption on the Pd nanoparticles/carbon (Pd/XC72) catalyst through two kinds of systems: gas diffusion electrode (GDE) and rotating ring disk electrode (RRDE). The main product of the CO2ER on Pd/XC72 is changed from formate to CO when both the terrace and step sites of Pd particles are under a low coverage of adsorbed H atoms. In addition, the progress of CO self-poisoning on the Pd/XC72 catalyst and the peak corresponding to the oxidation of COOH* on the Pt ring electrode are clearly observed by the electrochemical analysis methods. The high selectivity of CO generation from the CO2ER on the Pd/XC72 catalyst is attributed to the progressive adsorption of CO which inhibits the participation of Hads during the CO2ER.

Communication—A Rotating Ring Disk Study to Monitor the Concentration of 2M5S in Copper Low TEC Electrolytes

A leveller additive, 2-mercapto-5-benzimidazolesulfonic acid (2M5S), is characterized and monitored by cyclic voltammetry stripping (CVS) measurements using a rotating ring disk electrode (RRDE). The ring current gradually decreases with the increase of 2M5S concentration from 1 to 8 ppm. The relationship between the ring current and 2M5S concentration is used for determining the deterioration of the low thermal expansion coefficient (TEC) copper electrodeposition solution. The amount of 2M5S in the 20-hour-electrolyzed solution has been monitored then supplied. The copper pipe electrodeposited with the refreshed solution achieved low TEC, approximately the same as the copper pipe electrodeposited with the fresh solution.

Sustainable microwave-assisted hydrothermal synthesis of carbon-supported ZrO2 nanoparticles for H2O2 electrogeneration

This work proposes the use of a novel green and fast (<1h) route for the construction of electrocatalysts by microwave-assisted hydrothermal synthesis using carbon-supported metal oxide for H2O2 electrogeneration. Using ZrO2 supported on carbon black Printex L6 (PL6C) as a non-toxic model catalyst, the present study evaluated different synthesis conditions and their effects on ORR activity and selectivity via the application of the rotating ring-disk electrode (RRDE) and gas diffusion electrode (GDE) techniques. RRDE results showed that the optimized ZrO2/PL6C catalyst presented improvements in catalytic performance of 140 mV in the E1/2 for ORR and in selectivity for H2O2 production of 88.8% compared to the unmodified PL6C (78%). The improved electrocatalytic performance was attributed to the high dispersion of small ZrO2 nanoparticles (~7 nm) in direct contact with the carbon support which helped increase the ECSA values. GDE results showed that ZrO2/PL6C was responsible for doubling the kapp values of H2O2 production and for the reduction of energy consumption by about 150 kWh g−1 compared to the unmodified matrix. Key insights related to the construction of carbon-based metal oxide catalysts and the optimization of ORR are discussed further in the work aiming at providing useful contributions for future investigations and applications.

Metal-Organic Framework and Carbon Black supported MOFs as dynamic electrocatalyst for oxygen reduction reaction in an alkaline electrolyte

The Pt-based expensive catalysts and sluggish kinetics at cathode in oxygen reduction reaction (ORR) hinder the rapid commercialization of fuel cells. The quest for cheap, non-noble metal catalysts to replace Pt-based catalysts has thus become a critical issue in the field of fuel cells. The carbon black (CB) and CB supported catalyst have been explored with the ultimate goal of finding a substitute for Pt-based catalysts in fuel cells. In the present work, we synthesized Zn-based MOF (1), 1 selectivity gives H2O2 followed by two-electron pathways. However, sample 1 modification might be needed to enhance its selectivity for the generation of H2O. Two composites of MOFs with carbon black and 1 were prepared to increase the H2O yield, called 1⊃CB and 1⊃SCB. The electrochemical generation of H2O2 was analyzed by the rotating ring disk electrode (RRDE) using catalyst 1. Following the addition of CB, H2O2 yields decreased from above 93% (1) to 59% and 75% for 1⊃CB and 1⊃SCB, respectively. CB modified catalysts moved towards four-electron pathways due to the conductive nature of CB. Electrochemical Impedance Spectroscopy (EIS) has also been performed to study in detail the conductivity effect of CB and kinetic behavior of ORR in alkaline electrolyte. This research opens up a new path for ORR to advance non-precious metal catalysts based on MOFs. Synopsis: This paper describes how we synthesized carbon Black (CB) supported MOF: Zn-based MOF (1), 1 selectivity gives H2O2 (two-electron pathways). Two composites of MOFs (1⊃CB and 1⊃SCB) were prepared to increase the H2O yield. After addition of CB, H2O2 yields decreased from above 93% (1) to 75% (1⊃SCB) and 59% (1⊃CB).

The Enhancement of Selectivity and Activity for Two-Electron Oxygen Reduction Reaction by Tuned Oxygen Defects on Amorphous Hydroxide Catalysts

Amorphous catalysts, thanks to their unique coordinately unsaturated properties and abundant of defect sites, incline to possess higher activity and selectivity than their crystalline counterparts....

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

New insight into effect of potential on degradation of Fe-N-C catalyst for ORR

In recent years, Fe-N-C catalyst is particularly attractive due to its high oxygen reduction reaction (ORR) activity and low cost for proton exchange membrane fuel cells (PEMFCs). However, the durability problems still pose challenge to the application of Fe-N-C catalyst. Although considerable work has been done to investigate the degradation mechanisms of Fe-N-C catalyst, most of them are simply focused on the active-site decay, the carbon oxidation, and the demetalation problems. In fact, the 2e− pathway in the ORR process of Fe-N-C catalyst would result in the formation of H2O2, which is proved to be a key degradation source. In this paper, a new insight into the effect of potential on degradation of Fe-N-C catalyst was provided by quantifying the H2O2 intermediate. In this case, stability tests were conducted by the potential-static method in O2 saturated 0.1 mol/L HClO4. During the tests, H2O2 was quantified by rotating ring disk electrode (RRDE). The results show that compared with the loading voltage of 0.4 V, 0.8 V, and 1.0 V, the catalysts being kept at 0.6 V exhibit a highest H2O2 yield. It is found that it is the combined effect of electrochemical oxidation and chemical oxidation (by aggressive radicals like H2O2/radicals) that triggered the highest H2O2 release rate, with the latter as the major cause.

Revealing the electrocatalytic behaviour by a novel rotating ring-disc electrode (RRDE) subtraction method: A case-study on oxygen reduction using anthraquinone sulfonate

The state-of-the-art procedure for investigating homogenous and heterogeneous electrocatalysts is cyclic voltammetry (CV). However, this technique usually requires an inactive electrode material. One common problem arising e. g. in studying the oxygen reduction reaction (ORR) is the significant background contribution to the overall ORR current provided by many carbon-based and metal-based electrode materials. Furthermore, rotating ring-disc electrodes (RRDEs) made of common materials like glassy carbon/platinum (GC/Pt) can be affected by overlapping reduction potentials on the disc. Interference from overlapping reactions on the ring might also occur, particularly in connection with oxygen reduction and hydrogen peroxide oxidation in ORR studies.We present herein a novel subtraction method which allows a semi-quantitative description of homogeneous electrocatalysts and helps to overcome the overlapping problems described above using anthraquinone-2-sulfonate (AQS) as a “case study material” for the ORR.

Effects of Thiourea and Allyl Thioura on the Electrodeposition and Microstructures of Copper from Methanesulfonic Acid Baths

This work mainly focuses on the effects of two additives, thiourea (TU) and allyl thioura (ATU), on the electrodeposition behavior and microstructure development of copper deposits plated from the methane-sulfonic acid (MSA) bath. Three variables, including additive types, additive concentration, and current density, have been investigated in order to observe the variation in the crystallographic texture of Cu deposits. From the polarization behavior through the rotating ring disk electrode (RRDE) voltammograms and chronopotentiometric (CP) steady state electrode potential analyses, TU and ATU show the suppression ability of Cu deposition and the interaction strength between Cu2+ and ATU is weaker than that between Cu2+ and TU. The operating current density range of the preferential (111) Cu deposition becomes wider with the introduction of TU and ATU additives in the plating bath. The influences of TU and ATU on the nucleation and growth of Cu grains are significantly different, leading to the very different surface morphologies and surface roughness of resultant Cu films although both additives are of the similar molecular structures and show a suppression ability on Cu deposition.

Highly efficient electrochemical generation of H2O2 on N/O co-modified defective carbon

The electrochemical oxygen reduction reaction (ORR) via two-electron pathway is a sustainable way of producing hydrogen peroxide. Nanostructured carbon materials are proved to be effective catalysts for 2e− ORR. Herein, a series of mesoporous carbon with tunable nitrogen species and oxygen functional groups were synthesized by varying the added amount of dopamine hydrochloride as nitrogen and oxygen source. The modified catalysts exhibited higher content of pyrrolic-N and ether C–O groups which are confirmed by a series of characterization. Raman spectra and correlation analysis revealed that the increased proportion of defect sites in carbon materials are closely related to the introduced pyrrolic-N and ether C–O groups. And the rotating ring-disk electrode (RRDE) measurement carried out in 0.1 M KOH electrolyte showed the H2O2 selectivity increased with the content of defect sites. Among them, the optimized catalyst (NOC-6M) exhibited a selectivity of 95.2% and a potential of 0.71 V vs. RHE at −1 mA cm−2. Moreover, NOC-6M possessed the high H2O2 production rate of 548.8 mmol gcat−1 h−1 with faradaic efficiency of 92.4% in a two-chamber H-cell. Further mechanistic analysis revealed that the introduction of pyrrolic-N and ether C–O are likely to improve the binding energy of the defect sites toward ∗OOH intermediate, resulting in a more favorable 2e− ORR pathway for H2O2 production.

Mixed Diffusion‐Kinetic Control of H2O2 Oxidation at an Oxide‐Covered Platinum Electrode in Alkaline Electrolyte: Implications for Oxygen Electroreduction Studies with a Rotating Ring Disk Electrode

AbstractThe rotating ring disk electrode (RRDE) with a Pt ring is widely applied for oxygen reduction reaction (ORR) studies, and it is generally believed that oxidation of H2O2 at the Pt ring is controlled by diffusion. Indeed, H2O2 oxidation at bare platinum is a diffusion‐controlled reaction. However, when Pt ring is held at 1.2 VRHE, it is being covered with surface oxide, and H2O2 oxidation turns into a reaction under mixed diffusion‐kinetic control. We show that, for H2O2 oxidation at an oxide‐covered Pt ring in 0.1 M KOH, the ratio of the empirical ring current to corresponding ring current under pure diffusion control varies monotonically with rotation rate. At 1.2 VRHE, the ratio is equal to 79.9 % and 61.4 % at 400 rpm and 2500 rpm, respectively. We demonstrate that this deviation prevents the correct diagnosis of ORR mechanism and leads to overestimated electron transfer number values. To eliminate the error in RRDE measurements, we employed a procedure based on the Koutecký‐Levich method, which, to our best knowledge, has not been reported yet.

Design Platform for Sustainable Catalysis with Radicals: Electrochemical Activation of Cp2 TiCl2 for Catalysis Unveiled.

The combination of synthesis, rotating ring‐disk electrode (RRDE) and cyclic voltammetry (CV) measurements, and computational investigations with the aid of DFT methods shows how a thiourea, a squaramide, and a bissulfonamide as additives affect the EqCr equilibrium of Cp2TiCl2. We have, for the first time, provided quantitative data for the EqCr equilibrium and have determined the stoichiometry of adduct formation of [Cp2Ti(III)Cl2]−, [Cp2Ti(III)Cl] and [Cp2Ti(IV)Cl2] and the additives. By studying the structures of the complexes formed by DFT methods, we have established the Gibbs energies and enthalpies of complex formation as well as the adduct structures. The results not only demonstrate the correctness of our use of the EqCr equilibrium as predictor for sustainable catalysis. They are also a design platform for the development of novel additives in particular for enantioselective catalysis.

Elucidation of oxygen reduction reaction and nanostructure of platinum-loaded graphene mesosponge for polymer electrolyte fuel cell electrocatalyst

A graphene mesosponge (GMS), which has a sponge-like mesoporous framework, was applied to a catalyst support for polymer electrolyte fuel cell. Platinum loaded GMS (Pt/GMS) was prepared as electrocatalyst for oxygen reduction reaction (ORR) measurement and compared with platinum loaded Ketjen black (Pt/KB). ORR activity was evaluated by rotating ring disk electrode (RRDE) method to analyze hydrogen peroxide (H2O2) evolution behavior as an indicator of ionomer coverage on Pt. It was found that the ORR area specific activity of Pt/GMS was 1.2 times higher than that of Pt/KB with less H2O2 yield, mainly attributed to the lower ionomer coverage at Pt/GMS. It was also observed by transmission electron microtomography (3D-TEM) that Pt/GMS has a lot of pores between the sponge-like mesoporous framework with Pt nanoparticles therein. On the other hand, Pt/KB showed smoother agglomerate shapes with Pt nanoparticles inside the KB agglomerates mainly. Considering the frame-like mesoporous carbon network having hydrophobic basal nanosurface of the graphene of GMS and the aqueous electrolyte in this system, it is concluded that the ionomer can form self-aggregation with its hydrophobic domain inside, resulting in ineffective coverage of the ionomer on the nanostructure of GMS and the Pt nanoparticles in the GMS agglomerates.

High-Performance Organometallic Catalyst Based on Nickel Porphyrin/Carbon Fibre for the Oxygen Reduction Reaction

Development of efficient non-precious metals catalysts for the oxygen reduction reaction (ORR) has attracted considerable attention. A composite catalyst based on nickel- 5,10,15,20-tetra(p-thioanisole) porphyrin complex (Ni-TPT-P) and carbon fibres (CF) is here investigated for the ORR. The porphyrin is synthesised by a one-pot multi-step approach. Ultraviolet-visible (UV–vis) and fourier-transform infrared (FTIR) techniques are used to confirm the synthesis of the Ni-TPT-P complex. The metalloporphyrins (Ni-TPT-P) are non-covalently adsorbed on the CF via stacking interaction. The composite catalyst shows well-defined redox peaks attributed to the Ni2+/Ni3+ redox couple in O2-saturated 0.1 M KOH solution. The area under the reduction peak is used to calculate a surface coverage () of 2.43 × 1015 for the Ni2+/Ni3+ species on the catalyst surface area. The rotating ring disk electrode (RRDE) technique is used to assess the performance of the catalyst towards the ORR. Key performance indicators such as the onset potential, average number of electrons and yield are found to be, 0.82 V vs RHE, 3.6 electrons and 22.0% respectively.

Efficient Electrochemical Oxygen Reduction to Hydrogen Peroxide by Transition Metal-Doped Silicate Sr0.7Na0.3SiO3-δ.

Electrochemical oxygen reduction in a selective two-electron pathway is an efficient method for onsite production of H2O2. State of the art noble metal-based catalysts will be prohibitive for widespread applications, and hence earth-abundant oxide-based systems are most desired. Here we report transition metal (Mn, Fe, Ni, Cu)-doped silicates, Sr0.7Na0.3SiO3-δ, as potential electrocatalysts for oxygen reduction to H2O2 in alkaline conditions. These novel compounds are isostructural with the parent Sr0.7Na0.3SiO3-δ and crystallize in monoclinic structure with corner-shared SiO4 groups forming cyclic trimers. The presence of Na stabilizes O vacancies created on doping, and the transition metal ions provide catalytically active sites. Electrochemical parameters estimated from Tafel and Koutechy-Levich plots suggest a two-electron transfer mechanism, indicating peroxide formation. This is confirmed by the rotating ring disc electrode method, and peroxide selectivity and Faradaic efficiency are calculated to be in the range of 65-82% and 50-68%, respectively, in a potential window 0.3 to 0.6 V (vs RHE). Of all the dopants, Ni imparts the maximum selectivity and efficiency as well as highest rate of formation of H2O2 at 1.65 μmol s-1.

Electrochemical monitoring and mechanistic understanding of iodine film formation as a metastable intermediate during I3−/I− redox reaction in aqueous ZnI2 media

Zn-polyiodide redox flow batteries (RFBs) are a promising grid-scale electrical energy storage (EES) option because of their significant energy density, which is due to the high solubility of ZnI2 in water. In spite of the importance of the RFBs, a mechanistic understanding of both Zn2+/Zn and I3−/I− half redox reactions have not been fully achieved yet. The I3−/I− half redox reaction occurring on a cathode in this RFB is particularly complicated due to metastable iodine films, which only form on an electrode when an electrochemical potential is biased enough to drive the electro-oxidation of I−. Due to the thermodynamically unstable nature of iodine films in I−-rich aqueous solutions, the film is also difficult to characterize by ex-situ analyses, and its physicochemical properties are largely unknown.In this article, we report electrochemical in situ monitoring of the formation and dissolution of a metastable iodine film as an intermediate during I3−/I− redox reactions in an aqueous solution using a rotating ring disk electrode (RRDE). We suggested a reaction model for electro-oxidation of I− to I3− via iodine films and its electro-reduction to I− based on the mechanism proposed by Gileadi et al. Chronoamperograms (CAs) and cyclic voltammograms (CVs) associated with the I2/I− redox reaction involving only formation and dissolution of iodine films on a disk electrode were obtained using an RRDE. From the CAs and CVs, we successfully obtained trajectory information on the formation and dissolution of an iodine film during the I3−/I− redox reaction on a disk electrode under transient and potential-time variation conditions. In addition, we found evidence of a possible transition in the iodine film from an I−-conductor to an I−-semiconductor during formation based on the quantitatively monitored iodine formation curve as a function of time during electro-oxidation of I−.

Decorating vertically aligned MoS2 nanoflakes with silver nanoparticles for inducing a bifunctional electrocatalyst towards oxygen evolution and oxygen reduction reaction

Abstract Catalysts capable of improving the performance of oxygen evolution reaction (OER) and oxygen reduction reactions (ORR) are essential for the advancement of renewable energy technologies. Herein, Ag-decorated vertically aligned MoS2 nanoflakes are developed via magnetron co-sputtering and investigated as electrocatalyst towards OER and ORR. Due to the presence of silver, the catalyst shows more than 1.5 times an increase in the roughness-normalized rate of OER, featuring a very low Tafel slope (58.6 mv dec−1), thus suggesting that the catalyst surface favors the thermodynamics of hydroxyl radical (OH•) adsorption with the deprotonation steps being the rate-determining steps. The improved performance is attributed to the strong interactions between OOH intermediates and the Ag surface which reduces the activation energy. Rotating ring disk electrode (RRDE) analysis shows that the net disk currents on the Ag-MoS2 sample are two times higher at 0.65 V compared to MoS2, demonstrating the co-catalysis effect of silver doping. Based on the rate constant values, Ag-MoS2 proceeds through a mixed 4 electron and a 2 + 2 serial route reduction mechanism, in which the ionized hydrogen peroxide is formed as a mobile intermediate. The presence of silver decreases the electron transfer number and increases the peroxide yield due to the interplay of a 2 + 2 electron reduction pathway. A 2.5–6 times faster conversion rate of peroxide to OH- observed due to the presence of silver, indicating its effective cocatalyst nature. This strategy can help in designing a highly active bifunctional catalyst that has great potential as a viable alternative to precious-metal-based catalysts.

An adept approach to convert titanium carbide to titanium nitride and it’s composite with N-doped carbon nanotubes for efficient oxygen electroreduction kinetics

We report an in situ synthesis of titanium nitride (Ti3N2Tx) from its carbide (Ti3C2Tx) and concurrently composite formation with N-doped carbon nanotubes (N-CNTs). Unlike conventional wet-chemical method, a simple approach has been adopted for the synthesis of Ti3N2Tx and it’s composite with N-CNTs. The crystallographic study shows an obvious phase transformation from carbide to nitride. Importantly, an optimized composite electrocatalyst (Ti3N2@NCNT(20)-800) exhibits promising oxygen reduction ability under alkaline conditions with positive onset potential (Eonset) of 1.0 V versus reversible hydrogen electrode (RHE) and current density (JL) of 5.3 mA/cm2. The remarkable oxygen reduction reaction (ORR) properties mainly originate from the fascinating carbon-nitrogen exchange (Ti3C2Tx into Ti3N2Tx) in the MXene lattice along with N-doping in CNTs, which eventually lead to the formation of their composite and generating enough active centres for dioxygen adsorption followed by electroreduction. Moreover, the rotating ring disk electrode (RRDE) studies were carried to particularly detect peroxide (HO2−) formation and further to get an insight into ORR kinetics. Additionally, a robust performance of Ti3N2@NCNT(20)-800 electrocatalyst over Pt/C has been observed during the electrochemical cycling stability up to 10,000 (10 k) durable cycles. Thus, we believe that the present methodology provides an adept approach to convert carbide into nitride and further to extend it to synthesize the MXene based composite materials for energy conversion applications.

Bifunctional Pd‐CeO2 Nanorods/C Nanocatalyst with High Electrochemical Stability and Catalytic Activity for the ORR and EOR in Alkaline Media

AbstractThe catalytic activity and electrochemical stability of Pd‐CeO2‐NR/C (CeO2‐NR: cerium oxide nanorods) for the Oxygen Reduction Reaction (ORR) and the Ethanol Oxidation Reaction (EOR) is shown in alkaline media and compared to Pd/C. Evaluation of catalytic activity for the ORR in a Rotating Ring Disc Electrode (RRDE) set‐up, shows that Pd‐CeO2‐NR/C promotes the reaction with a percentage of hydrogen peroxide production (%H2O2) around 2–4 %, and an electron transfer number (n) close to 4. Tafel plots demonstrates higher mass and specific activities of Pd‐CeO2‐NR/C than Pd/C. Moreover, from cyclic voltammetry tests, Pd‐CeO2‐NR/C shows a higher mass catalytic activity (jm= 697 mA mg−1Pd) for the EOR at a more negative onset potential (Eonset= 0.29 V/RHE) than Pd/C. After Accelerated Degradation Tests (ADT), Pd‐CeO2‐NR/C retains ∼98 % of its Electrochemically Active Surface Area (ECSA), higher than ∼51 % of Pd/C. After ADT, the performance of Pd‐CeO2‐NR/C remains similar for the ORR, while it is significantly higher for the EOR, compared to Pd/C. Thus, the addition of CeO2‐NR enhances the electrocatalytic behavior and stability of Pd towards the ORR and the EOR.