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Metal‐Organic Frameworks (MOFs) hold great potential to be used as porous (photo)‐electrocatalytic platforms containing large concentration of immobilized molecular catalysts. Indeed, the use of MOFs in a photo‐electrochemical devices was recently demonstrated. However, so far there are no reports of MOFs used for photo‐electrochemical O2 reduction to H2O2. Herein, we utilize a Co‐porphyrin based MOF (Co‐MOF‐525), that produces H2O2 at high faradaic efficiency (95 %), both electrochemically and photo‐electrochemically. Electrochemical characterization show that the active catalytic site is a MOF‐tethered Co(I)‐porphyrin. Additionally, under light illumination, the MOF's intrinsic catalytic rate is significantly accelerated compared to dark electrolysis conditions. Thus, this work could open a path for future implementation of photoactive MOFs in solar fuel schemes. [ABSTRACT FROM AUTHOR]

Abstract Metal‐Organic Frameworks (MOFs) hold great potential to be used as porous (photo)‐electrocatalytic platforms containing large concentration of immobilized molecular catalysts. Indeed, the use of MOFs in a photo‐electrochemical devices was recently demonstrated. However, so far there are no reports of MOFs used for photo‐electrochemical O2 reduction to H2O2. Herein, we utilize a Co‐porphyrin based MOF (Co‐MOF‐525), that produces H2O2 at high faradaic efficiency (95 %), both electrochemically and photo‐electrochemically. Electrochemical characterization show that the active catalytic site is a MOF‐tethered Co(I)‐porphyrin. Additionally, under light illumination, the MOF's intrinsic catalytic rate is significantly accelerated compared to dark electrolysis conditions. Thus, this work could open a path for future implementation of photoactive MOFs in solar fuel schemes.

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Nitrogen-doped carbon with and without Fe additives is a promising alternative for commercial Pt/C catalysts for the oxygen reduction reaction (ORR) in proton and anion exchange membrane fuel cells. To understand the nature of the rate-determining steps (RDSs) of the ORR over newly developed catalysts, the analysis of the Tafel slopes of ORR voltammograms is beneficial for elucidating the number of electrons involved in the RDS. Conventionally, the Tafel slope is evaluated from the measured total current, which involves several different reaction pathways: the four-electron pathway from O2 to H2O described with a kinetic constant k1, the two-electron pathway from O2 to H2O2 with k2, and the two-electron pathway from H2O2 to H2O with k3. This method provides reasonable Tafel slopes as long as the measured ORR is selective to a particular reaction pathway, such as the four-electron pathway over a Pt/C catalyst; however, typical Fe/N/C and N/C catalysts have mixed reaction pathways and analyzing the Tafel slopes from the total current does not provide meaningful information. To address this, we propose a new methodology for analyzing Tafel slopes. In this study, the measured ORR currents were converted into inherent kinetic constants (k10, k20, and k30) using the Nabae model, which was previously developed by our group, and the Tafel plots for k10, k20, and k30 were analyzed to determine the Tafel slopes of each reaction pathway. Four ORR systems (Fe/N/C and N/C catalysts in acid and base) were analyzed using the proposed method, and the differences in the reaction mechanisms were successfully reflected in the determined parameters. [ABSTRACT FROM AUTHOR]

The effect of the support nature and the mass of platinum on the stability, electrochemical characteristics of monoplatinum catalysts, and the reaction path of electrochemical oxygen reduction in alkaline electrolyte is studied. Catalysts with the Pt mass content of 10, 20, 40, 60 wt % are synthesized by the polyol method on carbon nanotubes functionalized in NaOH and doped with nitrogen. The activity, the percentage of hydrogen peroxide formed, and the number of electrons participating in the oxygen reduction reaction are determined from the data obtained by the rotating ring-disk electrode method. For catalysts synthesized on the nitrogen-doped carbon nanotubes, the highest selectivity in the reaction of oxygen reduction to water is observed; the higher Pt surface area at the electrode, the greater is the selectivity, because the contribution of the support surface to the total oxygen reduction reaction decreased. Both the presence of hydrogen peroxide and a decrease in stability result from the decrease in the platinum content in the catalyst. [ABSTRACT FROM AUTHOR]

Understanding the origin of the active sites in the heteroatom-doped carbon material plays a vital role in designing novel electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. Besides heteroatoms, the defects in the carbon materials are believed to be the potential active sites for oxygen reduction. The simple peracetic acid oxidation of nitrogen-doped reduced graphene oxide improved the ORR activity with the positive shift in onset (60 mV) and half-wave potential (120 mV). The spectroscopic (X-ray diffraction, infrared, Raman, X-ray photoelectron) and thermogravimetric analysis of oxidized carbon materials demonstrate the formation of the carbonyl functional group. The theoretical models were developed with various structural motifs to analyze the active sites. Based on the experimental and theoretical results, the oxidation of nitrogen-doped carbon materials using peracetic acid generates edge epoxides, followed by acid hydrolysis to form vicinal diols. Subsequently, the diols undergo pinacol-pinacolone rearrangement in the acidic medium, resulting in cyclopentadiene adjacent to the seven-membered heptagon ring containing the amide group, known as topological defects. [ABSTRACT FROM AUTHOR]

Zn‐polyiodide redox flow battery is considered to be promising energy storage systems. However, the rate of the I3−(aq)/I−(aq) half redox reaction could be limited by a metastable iodine film in aqueous solutions. In this article, we found that the addition of Br− could inhibit the formation of an iodine film (I2‐F) and form soluble I2Br−(aq) during the electrooxidation of I−. I− was electrochemically oxidized to the soluble form I3−(aq). The depletion of I−(aq) and an increase of I3−(aq) would lead to the formation of I2 and form I2‐F. Then, under a steady state, I−(aq) was electrochemically oxidized to I3−(aq) via I2‐F. However, the reaction pathway for the electrooxidation of I− was significantly altered by the addition of Br−. I− was electrochemically oxidized to I3−(aq) and was further oxidized to I2Br−(aq) without the formation of I2‐F. Moreover, we estimated the stability constant of I2Br−(aq) and consequently the fractional diagrams of I2(aq), I3−(aq), and I2Br−(aq) existing in a solution with both I− and Br− during the electrooxidation of I−, providing the necessity of a highly concentrated Br− condition in the vicinity of an electrode to form I2Br−(aq) as the main iodine species through the electrooxidation of I−. [ABSTRACT FROM AUTHOR]

[Display omitted] • Heteroatoms in graphene-based materials modulate their electrochemical activity. • Supporting Ni on S,N-doped graphene decreases the HO 2 − route for ORR below 10% • Supporting Ni on doped graphene materials reduces HER overpotential ca. 0.50 V. • These Ni materials are promising electrocatalysts for alkaline PEM devices. In this work, Ni nanoparticles (NPs), with nominal metallic loading of 20 wt%, were deposited on graphene-based materials (GMs) doped with nitrogen and sulphur, in order to study their electrocatalytic activity towards the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline medium. Different chemical reducing agents were employed to synthesize the catalysts. Results indicate that the presence of heteroatoms in the GMs influences the activity of both the GMs and the Ni-based catalysts. Thus, best results were obtained for catalyst containing nitrogen and sulphur for the ORR which favours the direct four-electron pathway, whereas for the HER, the highest performance was observed for N -doped materials. [ABSTRACT FROM AUTHOR]

Knowledge of the degradation mechanisms inside lithium-ion batteries (LIBs) is critical in designing robust next-generation materials. While significant efforts have led to advances in characterization techniques and in our general understanding of the numerous decomposition reactions, the complex, multicomponent nature of batteries has hindered our progress towards developing a complete picture of these processes. In this work, we present a method for the detection of protons—one of the commonly proposed products of battery electrolyte decomposition at high potentials—using the rotating ring disk electrode (RRDE) method. Using the H2 oxidation reaction (HOR) as a model reaction, we first determine that protons generated at the disk electrode can be detected in organic carbonate-based electrolyte at the ring electrode with a ring collection efficiency close to the theoretical value. We then show that protons are indeed generated during the electrochemical decomposition of the battery electrolyte on Pt(111) at high potentials. Furthermore, quantitative detection of protons provided a valuable insight into the mechanism of oxidation for the electrolyte used. Overall, our work demonstrates the value of RRDE as a complementary method for studying potential-dependent electrolyte stability.

Powders of metals, oxides, and sulfides have been widely investigated as electrochemical catalysts to enhance the performance of energy devices such as fuel cells and metal-air batteries, and to establish efficient electrolysis processes. The author has been studying electrochemical catalysts with high activities and stabilities for oxygen electrochemical reactions utilized in metal-air batteries, water splitting, and electrowinning of zinc in cooperation with domestic researchers. Here, a method to modify electrodes with catalyst powders is explained in detail in addition to evaluation methods and compensations for reliable comparison. [ABSTRACT FROM AUTHOR]

Abstract: Alkaline membrane fuel cells (AMFCs) have started to become more attractive in recent years due to the development of polymeric membranes with good anionic conductivity and durability. However, few studies investigating the performance of H2/O2 fueled AMFCs and alkaline direct ethanol fuel cells (DEFCs) with membrane electrode assemblies (MEAs) fabricated with Pt‐group metal (PGM)‐free catalysts are available in the literature. In this paper, we synthesized and fully characterized a Fe−Co−N−C electrocatalyst for the oxygen reduction reaction (ORR) by a sacrificial method, using pyrrole as a unique and inexpensive precursor for N‐doped carbonaceous materials. Very good ORR activity and stability were obtained in alkaline conditions, most likely due to the presence of Co−Fe@C nanoparticles. We achieved a very high performance in an AMFC, 420 mW cm−2 at 60 °C, among the highest in the literature for PGM‐free catalysts, and a good performance in a passive DEFC, 28 mW cm−2 at room temperature. [ABSTRACT FROM AUTHOR]

Selectivity between chlorine evolution and oxygen evolution in aqueous media is a phenomenon of central importance in the chlor-alkali process, water treatment, and saline water splitting, which is an emerging technology for sustainable energy conversion. An apparent scaling between oxygen vs. chlorine evolution has been established, making it challenging to carry the two reactions out individually with 100% faradaic efficiency. To aid selectivity determination, we developed a new method to quickly measure chlorine evolution rates using a conventional RRDE setup. We showed that a Pt ring fixed at 0.95 V vs. RHE in pH 0.88 can selectively reduce the Cl 2 formed on the disk and this allows precise and flexible data acquisition. Using this method, we demonstrate that oxygen evolution and chlorine evolution on a glassy carbon supported IrO x catalyst proceed independently, and that the selectivity towards chlorine evolution (ε CER ) rapidly approaches 100% as [Cl − ] increases from 0 to 100 mM. Our results suggest that on IrO x , oxygen evolution is not suppressed or influenced by the presence of Cl − or by the chlorine evolution reaction taking place simultaneously on the surface. [ABSTRACT FROM AUTHOR]

Electro-peroxone process utilizes the in-situ generated H 2 O 2 by electro-reduction of O 2 to react with ozone molecule to produce hydroxyl radical, and achieves high efficiency in the wastewater treatment. However, detailed reaction mechanism in this process is still deficient. In this paper, a three-electrode system was adopted in the electro-peroxone process, and the origin of the synergy was revealed with the aid of the rotating ring disk electrodes. It was found that besides the main reaction between O 3 and H 2 O 2 , O 3 is also electro-reduced to O 3 − and then transformed into OH. Meanwhile, O 3 electro-reduction on the cathode can also possibly generate O 2 and promote H 2 O 2 production. Higher concentration of OH − near the cathode originated from O 2 and O 3 reduction may also react with O 3 to produce H 2 O 2 . These two pathways contributed to the higher amount of H 2 O 2 than the system with O 2 bubbling only, and ultimately contributed to produce more OH. All these reactions are synthetically responsible for the higher degradation rate of sodium oxalate in the electro-peroxone process than those in O 3 -electrolysis and ozonation processes, respectively. Though this system was quite different from normal electro-peroxone process, the conclusions are useful for understanding the practical reactions possibly happened on electrodes in the electro-peoxone process. [ABSTRACT FROM AUTHOR]

The kinetics of the oxygen reduction reaction (ORR) on the practical air cathode in a Lithium-air cell, which is conventionally composed of porous carbon with or without catalysts supported on it, was investigated. The mechanism and kinetics of the oxygen reduction reaction (ORR) was studied on a porous carbon electrode in an oxygen saturated solution of 0.1 M Lithium bis-trifluoromethanesulfonimide (LiTFSI) in Dimethoxyethane (DME) using cyclic voltammetery (CV) and the rotating ring-disk electrode (RRDE) technique. The oxygen reduction and evolution reactions were found to occur at similar potentials to those observed on a smooth, planar glassy carbon (GC) electrode. The effect of porosity and the resultant increase in surface area were readily observed in the increase in the transient time required for the intermediates to reach the ring and the much larger disk currents (compared to smooth, planar GC) recorded respectively. The RRDE data was analyzed using a kinetic model previously developed by us and the rate constants for the elementary reactions were calculated. The rates constant for the electrochemical reactions were found to be similar in magnitude to the rate constants calculated for smooth GC disks. The porosity of the electrode was found to decrease the rate of desorption of the intermediate and the product and delay their diffusion by shifting it from a Fickian regime in the electrolyte bulk to the Knudsen regime in the film pores. Thus, it is shown that the effect of the electrode porosity on the kinetics of the ORR is physical rather than electrochemical. [ABSTRACT FROM AUTHOR]

In the current work, heteroatom-doped graphene materials containing different atomic ratios of nitrogen and sulphur were employed as electrocatalysts for the oxygen reduction reaction (ORR) in acidic and alkaline media. To this end, the hydrothermal route and different chemical reducing agents were employed to synthesize the catalytic materials. The physicochemical characterization of the catalysts was performed by several techniques, such as X-ray diffraction, Raman spectroscopy and elemental analysis; meanwhile, the electrochemical performance of the materials toward the ORR was analyzed by linear sweep voltammetry (LSV), rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. The main results indicate that the ORR using heteroatom-doped graphene is a direct four-electron pathway, for which the catalytic activity is higher in alkaline than in acidic media. Indeed, a change of the reaction mechanism was observed with the insertion of N into the graphenic network, by the rate determining step changes from the first electrochemical step (formation of adsorbed OOH) on glassy carbon to the removal of adsorbed O (Oad) from the N-graphene surface. Moreover, the addition of sulphur atoms into the N-graphene structure increases the catalytic activity toward the ORR, as the desorption of Oad is accelerated. [ABSTRACT FROM AUTHOR]

A novel La 0.7 Sr 0.3 MnO 3 -CeO 2 (LSM-CeO 2 ) hybrid catalyst for oxygen reduction reaction (ORR) has been synthesized by a facile one-pot method. The flower-like CeO 2 with the diameter of about 3 μm is formed by the agglomeration of nanosheets with the thickness of about 40 nm. The LSM particles with the diameter of about 150 nm are well distributed on the flower-like CeO 2 , thus the interaction between LSM and CeO 2 is built. Therefore, the LSM-CeO 2 composite catalyst exhibits the much higher catalytic activity toward ORR with the direct four-electron transfer mechanism in alkaline solution than LSM or CeO 2 . Furthermore, the stability of LSM-CeO 2 is superior to that of Pt/C, and the current retention is 93% after 100000 s. The maximum power density of the aluminum-air battery using LSM-CeO 2 as the ORRC can reach 238 mW cm -2 , which is about 29% higher than that with LSM (184 mW cm -2 ). It indicates that LSM-CeO 2 composite material is a promising cathodic electrocatalyst for metal-air batteries. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is at the core of various applications, such as fuel cells, metal-air batteries and H 2 O 2 electro-generation. Depending on the targeted application, catalysts that follow a “direct four-electron (4e − )” pathway or “two-electron (2e − )” pathway are envisaged. We have systematically investigated the impact of the electrocatalyst loading on the rotating ring-disk electrode (RRDE), on their activity and selectivity towards ORR in alkaline medium (0.1 M and 1 M KOH). Four representative catalysts, including a noble metal catalyst (commercial 20 wt% Pt/C, ETEK), metal-free catalysts (Printex carbon black and graphene), and non-noble metal catalyst (Fe/N/C), were selected because they exhibit different behaviours for ORR following a “direct four-electron (4e − )” pathway, “two-electron (2e − )” pathway, or a “series 2e − + 2e − ” pathway. The results confirmed that the catalyst loading influences the activity and the selectivity of the catalysts, with lower loadings favoring the H 2 O 2 electrogeneration, and researchers should pay attention to it. Moreover, in order to make possible comparison between results coming from different research groups, we recommend reasonable loading ranges for each type of catalyst. [ABSTRACT FROM AUTHOR]

Anodic oxidation of copper in aqueous alkaline media is studied using the method of chronoamperometry on a rotating ring-disk electrode in a wide range of potentials. Partial currents of processes of anodic oxide formation, active copper dissolution, and chemical dissolution of Cu(I) oxide taking into account the possibility of its chemical growth are calculated. The current of chemical oxide dissolution is registered at all the studied potentials. In the cathodic range of potentials, anodic dissolution of copper is thermodynamically impossible, but, after the disk electrode polarization is switched off, oxide is formed via the chemical route. In the range of potentials where anodic copper dissolution is thermodynamically possible, the current of anodic oxide formation prevails over the currents of the other partial processes. The dependence of partial currents on time within the studied time interval (120 s) is not systematic, while their dependence on the disk polarization potential is very significant: the rate of oxide formation repeats the shape of the cyclic voltammogram, the rate of active copper dissolution through the oxide pores increases with potential, and the rate (and rate constant) of chemical dissolution of Cu(I) oxide are maximum at the potentials of its anodic formation. If the thermodynamic activity of the oxide layer does not reach unity within the anodic oxidation period, then the rate constant of chemical copper oxidation exceeds the rate constant of chemical oxide dissolution. The result is chemical oxidation of copper by traces of molecular oxygen in the solution. [ABSTRACT FROM AUTHOR]

A non-noble metal (NNM) catalyst for oxygen reduction reaction (ORR) was synthesized using Fe(II)-phthalocyanine as unique source of Fe, N, and C, and SBA-15 ordered mesoporous silica as templating agent, resulting in a material with an extremely high specific surface area and a high microporosity (around 50%). FESEM, FTIR and Raman analyses were performed to investigate the morphology and the physicochemical properties of the catalyst. The ORR activity and the methanol tolerance were tested in rotating disk electrode (RDE), and the selectivity towards a complete 4-electrons reduction was investigated by rotating ring disk electrode (RRDE) test and hydrogen peroxide reduction test in RDE, showing very promising results. Thus, the Fe-N-C catalyst was tested at the cathode of a DMFC after determination of the optimal electrode formulation regarding catalyst loading and Nafion ® content, showing a maximum power density of 20 mW cm −2 at 90 °C. A short term durability test to assess the behavior of both the Fe-N-C and the Pt/C catalysts was conducted on the DMFC, showing a better performance of the non-noble catalyst. Thus, the Fe-N-C catalyst is a potential good candidate to be used as catalytic material for DMFC cathode, in alternative to Pt. The performance in a H 2 /O 2 PEMFC was tested as well, showing a power density of 105 mW cm −2 at 60 °C. [ABSTRACT FROM AUTHOR]

Anodic oxidation of copper in alkaline media is presented in the form of a sum of concurrent partial processes. An approach to using the method of chronoamperometry on a rotating ring-disk electrode is developed for establishing the kinetics of partial processes of anodic copper oxidation taking into account the possibility of its chemical oxidation by traces of dissolved oxygen. The possibility of implementation of two different cases after switching off anodic disk electrode polarization is shown: prevailing chemical dissolution of oxide Cu(I) or chemical copper postoxidation with formation of this oxide. The conditions of realization of the first or second case are determined by the value of thermodynamic activity of the oxide phase reached at the moment of termination of anodic polarization of the disk electrode. [ABSTRACT FROM AUTHOR]

This work presents the oxygen reduction reaction (ORR) activity of three different plasma-synthesized cobalt oxides supported on carbon (CoO x /C) in 0.1 M KOH and 0.1 M K 2 CO 3 at 323 and 348 K. To evaluate the stability of the catalyst material, cyclic voltammograms (CVs) were recorded. To investigate the catalytic activity, a high-temperature rotating ring-disk electrode (RRDE) was used. Cobalt based catalyst materials seem to be a good alternative to costly platinum-based catalysts. This work shows the temperature dependent catalytic activity of plasma-treated cobalt acetate precursor material. This work showed that the increase of temperature to 323 K resulted in an increase in activity for ORR for the three catalyst materials, but a further temperature increase up to 348 K leads to a decrease in activity. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) layers were electrodeposited from an aqueous nitrate bath at 62 °C on copper substrates. At −0.9 V (vs. saturated calomel reference electrode), the growth rate is 600 nm min −1 . In the early stages of the deposition, the layers are porous. At longer deposition times, the surface becomes dense and rough. The wurtzite crystalline structure is confirmed by XRD measurements and the chemical composition of the ZnO surface was assessed by EDX and XPS. The oxygen reduction reaction (ORR) was investigated at room temperature in a 10 −3 M KOH solution with KCl as supporting electrolyte. The ORR onset potential is found to be much larger than that of platinum taken as reference electrocatalyst. Rotating ring-disk electrode experiments evidence a negligible production of hydrogen peroxide as intermediate product of the reaction. The latter follows thus a direct four-electron pathway at pH ∼11. [ABSTRACT FROM AUTHOR]

The electrocatalytic activities of Mn3O4/C composites are studied in lithium-oxygen (Li-O2) batteries as cathode catalysts. The Mn3O4/C composites are fabricated using ultrasonic spray pyrolysis (USP) with organic surfactants as the carbon sources. The physical and electrochemical performance of the composites is characterized by X-ray diffraction, scanning electronmicroscopy, particle size analysis, Brunauer-Emmett-Teller (BET) measurements, elemental analysis, galvanostatic charge-discharge methods and rotating ring-disk electrode (RRDE)measurements. The electrochemical tests demonstrate that the Mn3O4/C composite that is prepared using Trition X-114 (TX114) surfactant has higher activity as a bi-functional catalyst and delivers better oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performance in Li-O2 batteries because there is a larger surface area and particles are homogeneous with a meso/macro porous structure. The rate constant (kf) for the production of superoxide radical (O2-) and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) for M3O4/C and Super P electrodes are measured using RRDE experiments and analysis in the 0.1Mtetrabutylammonium hexafluorophosphate (TBAPF6)/PC electrolyte. The results show that TX114 has higher electrocatalytic activity for the first step of ORR to generate O2 - and produces a faster PC-electrolyte decomposition rate. [ABSTRACT FROM AUTHOR]

The dismutation of electrochemically generated soluble lithium superoxide with the formation of a lithium peroxide deposit on Au has been studied by addition of lithium ions and following the mass uptake detected by the electrochemical quartz crystal microbalance at the open-circuit potential and the surface morphology evolution by using atomic force microscopy. [ABSTRACT FROM AUTHOR]

The impact of Thalassospira sp., an iron-reducing bacterium isolated from marine corrosion product layers, on oxygen reduction reaction (ORR) has been investigated in the present study. ORR catalysis has been observed on a glassy carbon (GC) electrode when it is exposed to phosphate-buffered saline containing Thalassospira sp., and the adhesive biofilm consisting of bacterial cells and metabolites is believed to be responsible for the catalysis. A certain time of contact between the electrode and live cells is necessary for ORR catalysis, but the metabolic activity of cells after adhesion is not vital for the catalysis, and adsorbed compounds excreted by bacteria play a more important role. The ORR catalytic activity of Thalassospira sp. does not depend directly on bacterial surface coverage given the results of cyclic voltammetry and scanning electron microscopy. For the ORR kinetics analysis, the 4-electron pathway with H 2 O as the final product is achieved by the biofilm, which is different from the predominant 2-electron transformation on the bare GC electrode. [ABSTRACT FROM AUTHOR]

Designing highly active and cost-effective electrocatalysts is essential for accelerating commercialization of fuel cell technology. In this work, oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) are both investigated on monodisperse palladium nanoparticles (Pd NPs) supported on Vulcan XC72 as well as on two prepared carbon materials obtained from different biosources, namely grape stalk activated carbon (GSAC) and vine shoots activated carbon (VSAC). The electrocatalysts are characterized using TEM and XRD and their activity for ORR and BOR in alkaline media is studied using linear scan voltammetry with rotating ring-disk electrode. ORR and BOR onset potentials and number of exchanged electrons reveal significantly higher activity of the Pd NPs supported on biobased carbons compared to the one supported on Vulcan XC72. Pd/GSAC shows good activity towards direct 4-electron ORR, whereas Pd/VSAC electrocatalyst has improved performance for BOR. Namely, number of exchanged electrons in ORR at Pd/GSAC and Pd/VSAC was evaluated to be approximately 4 and 2, respectively. Conversely, number of exchanged electrons in BOR was found to be 2.0 and 5.6 for Pd/GSAC and Pd/VSAC, respectively. [ABSTRACT FROM AUTHOR]

The use of rotating ring-disk electrodes has become a general practice for evaluating the activity of the oxygen reduction reaction (ORR) performed with electrocatalysts. This technique typically employs simple equations based on the charge/mass balance to calculate the average number of electrons transferred and the percentage of peroxide production. However, the underlying mechanistic assumptions of this analysis and the uncertainty involved when considering the catalytic decomposition of HO2− have not been well elucidated. This work demonstrates through electrokinetic derivations that the conventional formalism presumes a stepwise ORR pathway and four reaction parameters in total are provided for indexing ORR activity. Furthermore, we provide a method of current density deconvolution to separate the individual reaction components and exemplify its use for Tafel analysis. Finally, we provide analytical solutions to the reaction parameters for the ORR when heterogeneous HO2− decomposition is involved. [ABSTRACT FROM AUTHOR]

A non-epitaxial growth method for the synthesis of Ag nanocubes by using Pt seed crystals was successfully developed. Tuning the amount of Pt seeds introduced into the reaction allowed for precise control over the size of the Ag nanocubes from 12 nm to 38 nm. Further experiments demonstrated the size-dependent properties of surface oxides and specific activities in terms of electrochemical surface areas for these Ag nanocubes to act as oxygen reduction catalysts in the KOH solution without and with methanol. [ABSTRACT FROM AUTHOR]

A simple and versatile method for the robust attachment of nanocatalytic assemblies on gold surface is developed. To this purpose, carbon disulfide is used to establish a stable linkage between Au (111) surface and magnetite (Fe 3 O 4 ) nanoparticles, functionalized with metalloporphyrins (Co or Fe) containing carboxylic acids as anchor groups. For comparison purposes the same systems were prepared with gold nanoparticles, which are known to strongly interact with sulfur derivatives. Surface modification is carried out in a one-pot procedure in ethanolic solutions. UV–vis spectra prove the functionalization of the nanoparticles by metalloporphyrins and AFM images reveal the density and size of modified nanoparticles attached to gold by CS 2 . The efficiency of the immobilization method is demonstrated by the electrochemical performance of the modified electrodes toward oxygen reduction reaction (ORR) in aqueous acidic medium. Koutecky-Levich plots and rotating ring-disk electrode experiments revealed distinct oxygen reduction mechanisms for the nanostructured Co or Fe porphyrin modified electrodes, with the transfer of two or four electrons to form hydrogen peroxide or water, respectively. The chemical nature, composition and size of nanoparticles clearly influence the ORR behavior. The largest magnetite nanoparticles (ca. 40 nm) exhibit the best catalytic response, either modified with iron or cobalt porphyrins. Additionally, electrodes with metalloporphyrin/Fe 3 O 4 nanocatalysts exhibit good stability under acidic conditions. Altogether the results highlight the potentialities of this simple and versatile surface modification for the design of electrocatalytic systems. [ABSTRACT FROM AUTHOR]

The electrocatalytic activities of the MnO2/C composites are examined in Li-O2 cells as the cathode catalysts. Hierarchically mesoporous carbon-supported manganese oxide (MnO2/C) composites are prepared using a combination of soft template and hydrothermal methods. The composites are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, small angle X-ray scattering, The Brunauer-Emmett-Teller (BET) measurements, galvanostatic charge-discharge methods, and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests indicate that the MnO2/C composites have excellent catalytic activity towards oxygen reduction reactions (ORRs) due to the larger surface area of ordered mesoporous carbon and higher catalytic activity of MnO2. The O2 solubility, diffusion rates of O2 and O2•- coefficients (DO2 and DO2-), the rate constant (kƒ) for producing O2•-, and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) of the MnO2/C material were measured by RRDE experiments in the 0.1 M TBAPF6/PC electrolyte. The values of kƒ and k for MnO2/C are 4.29 × 10-2 cm. s-1 and 2.6 s-1, respectively. The results indicate that the MnO2/C cathode catalyst has higher electrocatalytic activity for the first step of ORR to produce O2- and achieves a faster PC-electrolyte decomposition rate. [ABSTRACT FROM AUTHOR]