We present an overview of the electrochemical reduction of oxygen in water, focussing on carbon-based and modified carbon electrodes. This process is of importance for gas sensing, in fuel cells and in the electrosynthesis of hydrogen peroxide.
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"The electrochemical reduction of oxygen at modified electrodes has been recently reviewed. It is well documented in the literature that the oxygen reduction reaction on a modified electrode proceeds predominantly as a four-electron process producing H 2 O as the product     "
[Show abstract][Hide abstract] ABSTRACT: An amperometric oxygen sensor based on a polymeric nickel–salen (salen = N,N′-ethylenebis(salicylideneiminato)) film coated platinum electrode was developed. The sensor was constructed by electropolymerization of nickel–salen complex at platinum electrode in acetonitrile/tetrabutylammonium perchlorate by cyclic voltammetry. The voltammetric behavior of the sensor was investigated in 0.5 mol L−1 KCl solution in the absence and presence of molecular oxygen. Thus, with the addition of oxygen to the solution, the increase of cathodic peak current (at −0.25 V vs. saturated calomel electrode (SCE)) of the modified electrode was observed. This result shows that the nickel–salen film on electrode surface promotes the reduction of oxygen. The reaction can be brought about electrochemically, where the nickel(II) complex is first reduced to a nickel(I) complex at the electrode surface. The nickel(I) complex then undergoes a catalytic oxidation by the molecular oxygen in solution back to the nickel(II) complex, which can then be electrochemically re-reduced to produce an enhancement of the cathodic current. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the oxygen reduction. A plot of the cathodic current vs. the dissolved oxygen concentration for chronoamperometry (fixed potential = −0.25 V vs. SCE) at the sensor was linear in the 3.95–9.20 mg L−1 concentration range and the concentration limit was 0.17 mg L−1 O2. The proposed electrode is useful for the quality control and routine analysis of dissolved oxygen in commercial samples and environmental water. The results obtained for the levels of dissolved oxygen are in agreement with the results obtained with a commercial O2 sensor.
Full-text · Article · Dec 2012 · Sensors and Actuators B Chemical
"In a previous report  the electrochemical reduction of H 2 O 2 on carbon nanorod paste electrode (SCNRPE) prepared without the use of d-metallic catalysts has been reported. In that study, hydrogen peroxide was selected as one of model compounds since its detection is often needed, for example, in studying oxidative stress in bio-systems  , low temperature fuel cell processes,   and in the studies of corrosion processes  . Paste electrodes , as selected in this study, as working electrodes are useful because they (1) are simple to prepare and handle, (2) demonstrate reasonable reproducibility, (3) have a low "
[Show abstract][Hide abstract] ABSTRACT: Metallic impurity free solid carbon nanorod “Whiskers” (SCNR Whiskers), a derivative of carbon nanotubes, are explored in the fabrication of a Prussian Blue composite electrode and critically evaluated towards the mediated electroanalytical sensing of H2O2. The sensitivity and detection limits for H2O2 on the paste electrodes containing 20% (w/w) Prussian Blue, mineral oil, and carbon nanorod whiskers were explored and found to be 120 mA/(M cm2) and 4.1 μM, respectively, over the concentration range 0.01 to 0.10 mM. Charge transfer constant for the 20% Prussian Blue containing SCNR Whiskers paste electrode was calculated, for the reduction of Prussian Blue to Prussian White, to reveal a value of 1.8 ± 0.2 1/s ( α = 0.43 , N = 3 ). Surprisingly, our studies indicate that these metallic impurity-free SCNR Whiskers, in this configuration, behave electrochemically similar to that of an electrode constructed from graphite.
[Show abstract][Hide abstract] ABSTRACT: Uuriti hapniku elektrokeemilist redutseerumist kinoonidega modifitseeritud süsinikelektroodidel ning õhukestel kuld- ja plaatinakatetel, kasutades pöörleva ketaselektroodi ja pöörlev ketaselektrood rõngaga meetodeid. Määrati O2 redutseerumise kineetilised parameetrid kõigi uuritud elektroodide korral. Antrakinoon (AQ) ja fenantreenkinoon (PQ) seondati kovalentselt klaassüsinikelektroodide pinnale, kasutades diasooniumisoola redutseerumise meetodit. Hapniku redutseerumist kinoonidega modifitseeritud elektroodil katalüüsivad kinooni radikaalanioonid ja reaktsiooni lõppsaaduseks on vesinikperoksiid. Hapniku redutseerumise kineetilised parameetrid määrati AQ-ga modifitseeritud elektroodil erinevate kinooni pindkontsentratsioonide korral ning AQ-ga ja PQ-ga kovalentselt modifitseeritud booriga dopeeritud teemantelektroodil ja kõrgorienteeritud pürolüütilisest grafiidist elektroodil. PQ-ga modifitseeritud elektroodide elektrokatalüütiline aktiivsus oli oluliselt kõrgem kui AQ-ga modifitseeritud elektroodidel. See on tingitud peamiselt PQ positiivsemast redokspotentsiaalist, mis on kõige olulisem kinooni elektrokatalüütilist aktiivsust määrav parameeter O2 redutseerumisel. Uuriti hapniku redutseerumist vaakumaurustatud õhukestel Au ja Pt katetel nominaalse paksusega 0,25 kuni 20 nm. Läbistuselektronmikroskoopilised mõõtmised andsid tunnistust, et õhemad katted olid saarelise struktuuriga ja saarekese suurus vähenes metalli kattepaksuse kahanedes. Pöörleva ketaselektroodi meetodil läbi viidud O2 redutseerumise eksperiment näitas, et reaktsioonimehhanism õhukesekilelistel elektroodidel on sama, mis kompaktsetel metallelektroodidel. Au kilede eriaktiivsus vähesel määral langes kattepaksuse kahanedes nii 0,5 M H2SO4 kui ka 0,1 M KOH lahuses. Hapniku redutseerumist uuriti ka klaassüsinikule ja kuldalusele vaakumaurustatud õhukestel Pt kiledel 0,1 M HClO4 ja 0,05 M H2SO4 lahustes. Plaatina eriaktiivsus HClO4 lahuses mõnevõrra vähenes katte õhenedes ja selle põhjuseks võib olla hapnikkusisaldavate (vahe)ühendite tugevam adsorptsioon väiksematel Pt osakestel. H2SO4 lahuses ei sõltunud eriaktiivsus Pt kattepaksusest ja oli madalam kui HClO4-s, selle põhjuseks on pinna tsentrite blokeerimine adsorbeerunud sulfaatioonide poolt. Hapniku redutseerumine õhukesekilelistel plaatinaelektroodidel kulgeb peamiselt vee tekkeni. The electroreduction of oxygen on quinone-modified carbon electrodes and on thin gold and platinum films has been investigated, using the rotating disk electrode and rotating ring-disk electrode methods. The kinetic parameters for O2 reduction have been determined for all the electrodes studied. The covalent attachment of anthraquinone (AQ) and phenanthrenequinone (PQ) onto carbon electrodes was achieved by the electrochemical reduction of the corresponding quinone diazonium salt. The reduction of O2 on quinone-modified electrodes is catalysed by quinone radical anions and proceeds until the formation of peroxide. The kinetic parameters of oxygen reduction were determined for AQ-modified glassy carbon electrodes at various surface concentration of quinone and for boron-doped diamond and highly oriented pyrolytic graphite electrodes covalently modified with AQ and PQ. The electrocatalytic activity of PQ-modified electrodes was considerably higher than that of AQ-modified electrodes and this is primarily caused by more positive redox potential of PQ, which is the main factor that determines the electrocatalytic activity of quinone-modified electrodes towards O2 reduction. Thin Au and Pt films (nominal film thickness 0.25 to 20 nm) were prepared by vacuum-evaporation. The TEM measurements showed that the thinner films consist of separate metal clusters and the cluster size increases with metal loading. The rotating disk electrode studies revealed that O2 reduction mechanism on thin metal films is the same as on bulk metal electrodes. The specific activity of Au films only slightly decreased with decreasing film thickness in both 0.5 M H2SO4 and 0.1 M KOH solutions. The reduction of oxygen on thin Pt films on GC and Au substrates was studied in 0.1 M HClO4 and 0.05 M H2SO4 solutions. The specific activity of O2 reduction in HClO4 slightly decreased with decreasing film thickness; this was attributed to the stronger adsorption of surface oxygenated species that hinder the kinetics of O2 reduction. In H2SO4, the specific activity appeared to be independent of the Pt loading and was lower than in HClO4. This is due to the adsorbed sulfate ions, which block the sites for O2 adsorption and thereby reduce the O2 reduction activity. On thin Pt films, O2 is predominantly reduced to H2O.