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The challenges associated to oxygen reduction reaction (ORR) electrocatalysis are undoubtedly the most intricate impediments to solve regarding fuel cell vehicle (FCV) commercialization, mainly due to the complexity of this reaction and the scarcity of the required electrocatalysts. The synthesis of non-precious electrocatalysts with high intrinsic selectivity is indeed crucial in this field, but the methodology utilized to come to selectivity conclusions is undeniably equally important. In this work, we demonstrate how the higher required electrode loadings of a Fe-N-MWCNT catalyst in a rotating ring disc electrode (RRDE) prevent access to all of the peroxide produced by the catalyst during ORR. Via a spraying technique, much smaller amounts of the same catalyst were deposited on a flat boron-doped diamond (BDD) and their loading was determined meticulously by atomic force microscopy (AFM). These ultra-low loadings were investigated using scanning electrochemical microscopy (SECM), which revealed higher peroxide production and lower selectivity. This finding may have crucial implications for future ORR investigations in the laboratory, considering the harmful effect peroxide has on the catalyst.

Hydrogen evolution reaction (HER) activities of self-assembled monolayers (SAMs) of [Mo3S7(S2CNMe2)3] and several other MoSx molecular clusters are presented on planer Au electrode. Our study suggests that such Mo-S clusters are unstable under HER reaction conditions of a strongly acidic electrolyte. The [Mo3S7(S2CNEt2)3]I monolayer prepared from DMF showed greater stability among all the studied precursors. The X-ray photoelectron spectroscopy (XPS) analysis on a monolayer of [Mo3S7(S2CNMe2)3]I in THF assembled on Au/ITO suggested sulfur-rich composition with S:Mo ratio of 2.278. The Mo-S monolayer clusters resulting from [Mo3S7(S2CNMe2)3]I in THF showed a Tafel slope of 75.74 mV dec−1 and required a lower overpotential of 410 mV to reach a high HER catalytic current density of 100 mA cm−2 compared to the other studied precursors. Surface coverage of the Mo-S clusters on the Au surface was confirmed by cyclic voltammetry (CV) curves from K3Fe(CN)6 and anodization of Au surface. Further, the rotating ring-disk electrode (RRDE) measurements were performed for the monolayer of [Mo3S7(S2CNMe2)3]I prepared in THF to study its reaction kinetics. The HER catalytic activity of such monolayer Mo-S clusters can further be improved by controlling the sulfur vacancy.

The oxidation of Cu(II) complexes with tetra, penta and hexaglycine in borate buffer aqueous solution, by dissolved oxygen is strongly accelerated by sulfite. The formation of Cu(III) complexes with maximum absorbances at 250 nm (e = 9000 mol-1 L cm-1) and 365 nm (e = 7120 mol-1 L cm-1) was also characterized by using rotating ring-disk voltammetry, whose anodic and cathodic components were observed in voltammograms recorded in solutions containing Cu(II). Voltammograms, obtained at various rotation speeds, showed that the Cu(III) species electrochemically generated is not stable over the entire time window of the experiment and in solutions containing tetraglycine the overall limiting current is controlled by the kinetics of an equilibrium involving Cu(II) species.The calculated first order rate constant of the decomposition was 4.37x10-3 s-1. Electrochemical experiments carried out in Cu(II) solutions after the addition of relatively small amounts of sulfite demonstrated that the Cu(III) species formed in the chemical reaction is the same as the one collected at the ring electrode when Cu(II) is oxidized at the disk electrode in ring-disk voltammetry. The concentration of Cu(III) complexes is proportional to the amount of added sulfite and the results indicated that indirect analytical methods for sulfite may be developed by means of spectrophotometric or amperometric detection of the chemically generated product.

Abstract: The electrochemical reduction of oxygen has been investigated for a cobalt-amine complex pyrolysed at various temperatures. The activity of the corresponding cobalt-free materials has also been studied. The selectivity of the catalysts towards hydrogen peroxide production has been determined using Koutecky–Levich analysis and rotating ring disc electrochemical measurements. A combination of the rotating ring disc data and studies of the reduction of hydrogen peroxide have been used to investigate the reaction mechanism kinetics. The selectivity towards hydrogen peroxide passes through a minimum at a pyrolysis temperature of 700°C. The highest activity for oxygen reduction and yield for hydrogen peroxide formation was observed for the catalysts treated at higher temperatures. [Copyright &y& Elsevier]

The oxygen reduction reaction in sulphuric acid on commercial carbon supported platinum and ruthenium catalysts as well as on a home-made carbon supported ruthenium selenide catalysts (RuSe x /C) was investigated. The RuSe x /C catalysts were synthesised using similar procedures to those found in the literature. A dependency of H2O2 formation on the selenium content was found using the thin-film rotating ring disc electrode technique, namely that the H2O2 formation in the typical operation range of a Direct Methanol Fuel Cell (0.7–0.4 V) on Pt/C is below 1% and 1–4% on Ru/C and RuSe x /C catalysts. Finally for comparing the intrinsic activities of the catalysts the electrochemically active surface areas were determined in-situ by means of copper underpotential deposition. Our results indicate a comparable activity of the present RuSe x /C catalyst to commercial Pt/C if the activities are related to the electrochemical active areas. [ABSTRACT FROM AUTHOR]

Abstract: This study provides experimental evidence for proton and hydrogen formation caused by the anodic electropolymerization of cyclohexyl benzene (CHB), which is a popular electrolyte additive for overcharge protection of lithium-ion batteries (LIBs). It is found that considerable H2 evolution is observed in overcharged LiCoO2/graphite cells, especially when CHB is included as an electrolyte additive. In order to confirm the proton generation during the CHB oxidation, Pt/Pt-rotating ring disc electrode (RRDE) measurements are performed in 1M Li(C2F5SO2)2N ethylene carbonate/ethyl methyl carbonate (1/2, v/v) solutions with and without CHB. The cathodic ring current is intimately correlated to the anodic disc current, and the cathodic reaction at the ring is determined to be the reduction of the proton. The proton generation efficiency during the CHB oxidation is as high as 90%. Proton liberation is also observed during the anodic decomposition of the electrolyte solvents, although it occurs in a much less stoichiometric way compared with that during the CHB oxidation. [Copyright &y& Elsevier]

Abstract: Three types of spinel-based cathode powders, namely, LiMn2O4, Li1.07Mn1.93O4, and Li1.06Al0.2Mn1.74O4, are examined with rotating ring-disc collection experiments to measure manganese dissolution and capacity losses in lithium-ion cells. The cyclic voltammograms are similar at high scan rates for all three electrodes. Initially, all electrodes rapidly lose capacity during cycling. After about 25 cycles, the electrodes start to exhibit capacity retention, and the performance matches that of the best spinels. The cation-substituted spinel electrodes experience a moderate capacity loss of 0.2% per cycle over 200 cycles, which is half that suffered by a typical spinel electrode (LiMnO4). Manganese (Mn) dissolution from all the spinel-based samples is monitored in situ under various conditions. The ring cathodic currents for the cation-substituted spinel electrodes are similar to those for LiMn2O4, which shows that the Mn dissolution behaviour is the same for all spinel-based cathode powders. The ring currents reach maximum values at the end-of charge (EOC) and end-of discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from all spinel-based samples occurs during charge–discharge cycling, especially in a charged state at >4.0V and in a discharged state at <3.1V. In addition, lower ring cathodic currents are observed in the cation-substituted spinel cathodes and this indicates that the rate of dissolution of Mn has decreased in these materials. [Copyright &y& Elsevier]

The electrochemical behaviour of electrodeposited Co–Cu/Cu multilayers from citrate electrolytes was investigated using cyclic voltammetry and stripping techniques at a rotating ring disc electrode. Copper and cobalt–copper alloy sandwiches were deposited from an electrolyte containing 0.0125 M CuSO4, 0.250 M CoSO4 and 0.265 M trisodium citrate at two different pHs, 1.7 and 6.0. The Cu/Co–Cu/Cu sandwich is representative of a single layer in a Co–Cu/Cu multilayer deposit, which is known to exhibit unusual physical and magnetic properties. Results from cyclic voltammetry and detection of dissolving species at the ring showed that cobalt is stripped from a Cu/Co–Cu/Cu sandwich even when a copper layer as thick as 600 nm covers the Co–Cu alloy. Scanning electron microscopy showed that cobalt can dissolve from the deposit easily because the copper layer covering the Co–Cu alloy is porous. A separate series of experiments with Cu/Co–Ni–Cu/Cu sandwich showed that cobalt does not dissolve from these deposits because the addition of nickel stabilises cobalt in the Co–Ni–Cu alloy. [ABSTRACT FROM AUTHOR]

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) activities of self-assembled monolayers (SAMs) of [Mo3S7(S2CNMe2)3] and several other MoSx molecular clusters are presented on planer Au electrode. Our study suggests that such Mo-S clusters are unstable under HER reaction conditions of a strongly acidic electrolyte. The [Mo3S7(S2CNEt2)3]I monolayer prepared from DMF showed greater stability among all the studied precursors. The X-ray photoelectron spectroscopy (XPS) analysis on a monolayer of [Mo3S7(S2CNMe2)3]I in THF assembled on Au/ITO suggested sulfur-rich composition with S:Mo ratio of 2.278. The Mo-S monolayer clusters resulting from [Mo3S7(S2CNMe2)3]I in THF showed a Tafel slope of 75.74 mV dec−1 and required a lower overpotential of 410 mV to reach a high HER catalytic current density of 100 mA cm−2 compared to the other studied precursors. Surface coverage of the Mo-S clusters on the Au surface was confirmed by cyclic voltammetry (CV) curves from K3Fe(CN)6 and anodization of Au surface. Further, the rotating ring-disk electrode (RRDE) measurements were performed for the monolayer of [Mo3S7(S2CNMe2)3]I prepared in THF to study its reaction kinetics. The HER catalytic activity of such monolayer Mo-S clusters can further be improved by controlling the sulfur vacancy. [ABSTRACT FROM AUTHOR]