Electrocatalytic reduction of molecular oxygen at electrodes coated with a new cobalt(II)–platinum(II) bimetallic porphyrin

Cobalt(II) inserts into 5-(4-pyridyl)-10,15,20-(3,4-dimethoxyphenyl)porphyrin (1) by reaction of the porphyrin with the cobalt(II) acetate salt in refluxing N,N′-dimethylformamide solutions. When the porphyrin and the cobalt porphyrin are reacted with PtCl₂(DMSO)₂ in dichloromethane at ambient temperatures the platinum complex coordinates to the peripheral pyridyl group of the porphyrin. Roughened EPG electrodes coated with the cobalt(II)–platinum(II) bimetallic porphyrin, complex (4), show a 500?mV shift in the reduction of molecular oxygen in acidic media when compared to the bare electrode. Oxidation of the bimetallic porphyrin coated electrodes at 1.20?V versus saturated calomel electrode (SCE) results in an additional shift of ca 100?mV for the reduction of molecular oxygen when compared to the bimetallic porphyrin coated electrode prior to oxidation. In addition the oxidized surface shows the ability to reduce approximately 50% of the oxygen to water and the other 50% to hydrogen peroxide according to rotating disk electrode measurements.     

Temperature dependence of oxygen reduction activity at Pt-Fe, Pt-Co, and Pt-Ni alloy electrodes

Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Pt(54)Fe(46), Pt(68)Co(32), and Pt(63)Ni(37) electrodes in 0.1 M HClO(4) solution at 20 to 90 degrees C were investigated by using a channel flow double electrode method. In the temperature range of 20-50 degrees C, the apparent rate constants k(app) for ORR at these electrodes were found to be 2.4-4.0 times larger than that at a pure Pt electrode, whereas their apparent activation energies of 41 kJ mol(-1) at -0.525 V vs E degrees (0.760 V vs RHE at 30 degrees C) were comparable to that at the Pt electrode. H(2)O(2) yield was ca. 1.0% at Pt(54)Fe(46) and ca. 0.16% at Pt(68)Co(32) and Pt(63)Ni(37) between 0.3 and 1.0 V vs RHE. The k(app) values at the alloy electrodes decreased with elevating temperature above 60 degrees C, and settled to almost the same values at the Pt electrode. The H(2)O(2) production was not detected at the alloy electrodes once heated at the high temperature in the solution, probably due to the thickening of the Pt skin-layer by a considerable dissolution of nonprecious metal components (Fe, Co, Ni) from the alloys.     

Electrochemistry, spectroelectrochemistry, chloride binding, and O2 catalytic reactions of free-base porphyrin-cobalt corrole dyads

Three face-to-face linked porphyrin-corrole dyads were investigated as to their electrochemistry, spectroelectrochemistry, and chloride-binding properties in dichloromethane or benzonitrile. The same three compounds were also investigated as to their ability to catalyze the electroreduction of dioxygen in aqueous 1 M HClO4 or HCl when adsorbed on a graphite electrode. The characterized compounds are represented as (PCY)H2Co, where P = a porphyrin dianion; C = a corrole trianion; and Y = a biphenylenyl, 9,9-dimethylxanthenyl, or anthracenyl spacer, which links the two macrocycles in a face-to-face arrangement. An axial binding of one or two Cl- ligands to the cobalt center of the corrole is observed for singly and doubly oxidized (PCY)H2Co, with the exact stoichiometry of the reaction depending upon the spacer size and the concentration of Cl- added to solution. No Cl- binding occurs for the neutral or reduced forms of the dyad, which contrasts with what is seen for the monocorrole, (Me4Ph5Cor)Co, where a single Cl- ligand is added to the Co(III) corrole in PhCN. The Co(III) form of the corrole in (PCY)H2Co also appears to be the catalytically active species in the electroreduction of dioxygen, which occurs at potentials associated with the Co(IV)/Co(III) reaction, that is, 0.35 V in 1 M HClO4 as compared to 0.31-0.42 V for the same three dyads in PhCN and 0.1 M TBAP. The potential for the catalytic electroreduction of O2 in HCl shifts negatively by 60 to 70 mV as compared to E(1/2) values in 1 M HClO4, consistent with the binding of Cl- to the Co(IV) form of the corrole and its rapid dissociation after electroreduction to Co(III) at the electrode surface.     

Molecular Oxygen Reduction Electrocatalyzed by meso-Substituted Cobalt Corroles Coated on Edge-Plane Pyrolytic Graphite Electrodes in Acidic Media

Five meso-substituted cobalt(III) corroles were examined as to their catalytic activity for the electoreduction of O(2) when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO(4). The investigated compounds are represented as (TpRPCor)Co(PPh(3)), where TpRPCor is the trianion of a para-substituted triphenylcorrole and R = OMe, Me, H, F, or Cl. Three electrochemical techniques, cyclic voltammetry, linear sweep voltammetry with a rotating disk electrode (RDE), and voltammetry at a rotating ring disk electrode (RRDE), were utilized to evaluate the catalytic activity of the corroles in the reduction of O(2). Cobalt corroles containing electron-withdrawing substituents were shown to be better catalysts than those having electron-donating groups on the three meso-phenyl rings of the triarylcorroles.     

The synthesis, self-assembly and electrocatalytic property of a novel disulphide derivatised cobalt(II) deuteroporphyrin

A novel disulphide derivatised deuteroporphyrin 2,7,12,18-tetramethyl-13,17-(propionylaminoethyldithioethyl amino-formy-lethyl) -29,34-bis-(methoxyformyl)porphyrin(PDTEP,3) and its cobalt(Ⅱ) complex(Co(II)PDTEP,4) were conveniently synthesized. The disulphide functional group of 4 allowed its stable immobilization on gold electrodes.The modified electrode was characterized by IR and confirmed electrochemically and showed good stability and catalytic activity toward the electro-catalyzed reduction of hydrogen peroxide.     

Simultaneous electrochemical determination of uric acid and ascorbic acid on a glassy carbon electrode modified with cobalt(II) tetrakisphenylporphyrin.

A cobalt(II) tetrakisphenylporphyrin (Co(II)TPP) film modified glassy carbon electrode (Co(II)TPP-GCE) was prepared by just coating Co(II)TPP solution on the surface of the electrode. It can be used for the simultaneous determination of ascorbic acid and uric acid. The anodic peaks of AA and UA can be separated well. Owing to the strongly hydrophobic property of porphyrin, the modified electrode has good stability and long life. The linear range for UA and AA were 2.0 x 10(-6)-1.0 x 10(-4) M and 9.0 x 10(-6)-2.0 x 10(-3) M with detection limits of 5.0 x 10(-7) and 5.0 x 10(-6) M, respectively. Furthermore, metalloporphyrins of other kinds were also used to construct modified electrodes. Their performances were inferior compared with that of the Co(II)TPP modified electrode.     

Temperature dependence of oxygen reduction activity at Nafion-coated bulk Pt and Pt/carbon black catalysts

Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Nafion-coated film electrodes of bulk-Pt and Pt nanoparticles dispersed on carbon black (Pt/CB) were investigated in 0.1 M HClO(4) solution at 30 to 110 degrees C by using a channel flow double electrode method. We have found that the apparent rate constants k(app) (per real Pt active surface area) for the ORR at bulk-Pt (with and without Nafion-coating) and Nafion-coated Pt/CB (19.3 and 46.7 wt % Pt, d(Pt) = 2.6 to 2.7 nm) thin-film electrodes were in beautiful agreement with each other in the operation conditions of polymer electrolyte fuel cells (PEFCs), i.e., 30-110 degrees C and ca. 0.7 to 0.8 V vs RHE. The H(2)O(2) yield was 0.6-1.0% at 0.7-0.8 V on all Nafion-coated Pt/CB and bulk-Pt and irrespective of Pt-loading level and temperature. Nafion coating was pointed out to be a major factor for the H(2)O(2) formation on Pt catalysts modifying the surface property, because H(2)O(2) production was not detected at the bulk-Pt electrode without Nafion coating.     

Adsorption of formaldehyde on Pt(111) and Pt(100) electrodes: cyclic voltammetry and scanning tunneling microscopy

The adsorption of formaldehyde (HCHO) on Pt(111) and Pt(100) electrodes was examined by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in 0.1 M HClO(4). The extent of HCHO adsorption at both Pt electrodes was evaluated by comparing the CVs, particularly for the hydrogen adsorption and desorption between 0.05 and 0.4 V, obtained in 0.1 M HClO(4) with and without HCHO. The adsorption of HCHO on these Pt electrodes was significant only when [HCHO] >/= 10 mM. Adsorbed organic intermediate species acted as poisons, blocking Pt surfaces and causing delays in the oxidation of HCHO. Compared to Pt(111), Pt(100) was more prone to poisoning, as indicated by a 200 mV positive shift of the onset of HCHO oxidation. However, Pt(100) exhibited an activity 3 times higher than that of Pt(111), as indicated by the difference in peak current density of HCHO oxidation. Molecular resolution STM revealed highly ordered structures of Pt(111)-( radical7 x radical7)R19.1 degrees and Pt(100)-( radical2 x radical2) in the potential region between 0.1 and 0.3 V. Voltammetric measurements further showed that the organic poisons produced by HCHO adsorption behaved differently from the intentionally dosed CO admolecules, which supports the assumption for the formation of HCO or COH adspecies, rather than CO, as the poison. On both Pt electrodes, HCHO oxidation commenced preferentially at step sites at the onset potential of this reaction, but it occurred uniformly at the peak potentials.     

Electroprecipitation of Ag(II)/Ag(III) tetraphenylsulfonate porphyrin and electrocatalytic behavior of the films

The electrochemical precipitation on glassy carbon and gold electrodes of Ag(II) tetraphenylsulfonate porphyrin (Ag(II)TPPS) from aqueous HClO₄ solutions, is reported. Electrochemical quartz crystal microbalance (EQCM) results indicate the possible formation of an Ag(II)–Ag(III) porphyrin dimer species. This species is oxidized and reduced in two consecutive steps: oxidation at +0.31 and +0.36 V (vs. SCE) and reduction at +0.11 and +0.07 V. The films show catalytic behavior toward O₂ reduction in 10⁻² M HClO₄ at relatively low potentials (E<−0.1 V) but catalyze NO reduction at relatively high-reduction potentials (E<0.4 V). The electrochemical results seem to indicate that the catalytic cycle in the case of NO involves formation of Ag(II)TPPS–Ag(II)TPPS(NO)⁺ and its electroreduction to regenerate Ag(II)TPPS–Ag(III)TPPS and NO-reduction products.     

Clarification of the oxidation state of cobalt corroles in heterogeneous and homogeneous catalytic reduction of dioxygen

Co(III) corroles were investigated as efficient catalysts for the reduction of dioxygen in the presence of perchloric acid in both heterogeneous and homogeneous systems. The investigated compounds are (5,10,15-tris(pentafluorophenyl)corrole)cobalt (TPFCor)Co, (10-pentafluorophenyl-5,15-dimesitylcorrole)cobalt (F 5PhMes 2Cor)Co, and (5,10,15-trismesitylcorrole)cobalt (Mes 3Cor)Co, all of which contain bulky substituents at the three meso positions of the corrole macrocycle. Cyclic voltammetry and rotating ring-disk electrode voltammetry were used to examine the catalytic activity of the compounds when adsorbed on the surface of a graphite electrode in the presence of 1.0 M perchloric acid, and this data is compared to results for the homogeneous catalytic reduction of O 2 in benzonitrile containing 10 (-2) M HClO 4. The corroles were also investigated as to their redox properties in nonaqueous media. A reversible one-electron oxidation occurs at E 1/2 values between 0.42 and 0.89 V versus SCE depending upon the solvent and number of fluorine substituents on the compounds, and this is followed by a second reversible one-electron abstraction at E 1/2 = 0.86 to 1.18 V in CH 2Cl 2, THF, or PhCN. Two reductions of each corrole are also observed in the three solvents. A linear relationship is observed between E 1/2 for oxidation or reduction and the number of electron-withdrawing fluorine groups on the compounds, and the magnitude of the substituent effect is compared to what is observed in the case of tetraphenylporphyrins containing meso -substituted C 6F 5 substituents. The electrochemically generated forms of the corrole can exist with Co(I), Co(II), or Co(IV) central metal ions, and the site of the electron-transfer in each oxidation or reduction of the initial Co(III) complex was examined by UV-vis spectroelectrochemistry. ESR characterization was also used to characterize singly oxidized (F 5PhMes 2Cor)Co, which is unambiguously assigned as a Co(III) radical cation rather than the expected Co(IV) corrole with an unoxidized macrocyclic ring.     

Pt（111）电极上O2与OHad的吸脱附及氧还原反应动力学

研究了Pt（111）电极在0．1mol／LHClO4溶液中O2吸附与OHad脱附及氧还原反应的动力学．研究发现OHad的可逆吸脱附速率很快;在氧还原的动力学或动力学与传质混合控制区,恒电位下氧还原的电流随反应时间缓慢衰减,在转速较大,扫速较慢的情形下正向扫描过程中氧还原的电流总是明显低于逆向扫描的电流;Pt／0．1mol／LHClO4从无O2切换到O2饱和时,其开路电位迅速从0．9V增加到1．0V．结果表明,Pt（111）电极上O2解离生成OHad速率很快,ORR过程中OHad会在表面缓慢积累,氧还原反应的动力学主要由反应 OHad＋H^＋＋e→←H2O的平衡热力学决定．     

Synthesis, characterisation and speciation studies of heterobimetallic pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni, Zn). Crystal structure of a novel heterobimetallic 3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like coordination polymer

The reaction of cis-[Pt(NH3)2(3-pyhaH)2]2+ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH3)2(4-pyhaH)2]2+ (4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetallic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH3)2(mu-3-pyha)M(mu-3-pyha)].SO4.xH2O}n and {cis-[Pt(NH3)2(mu-4-pyha)M(mu-4-pyha)].SO4.xH2O}n respectively. The crystal and molecular structure of one of these, {cis-[Pt(NH3)2(mu-3-pyha)Cu(mu-3-pyha)]SO4.8H2O}n 3a, has been determined and was found to be a novel heterobimetallic wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating units of Pt(II) and Cu(II) ions in slightly distorted square-planar N4 and O4 coordination environments respectively and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the SO4(2-) counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing pyridinehydroxamic acids as bridging scaffolds.     

Electrochemical Properties of a Porphyrin-Cobalt (II) Adsorbed on Silica-Titania-Phosphate Composite Surface Prepared by the Sol-Gel Method

SiO(2)/TiO(2)/phosphate was obtained by the sol-gel processing method, having the following characteristics: specific surface area S(BET)=800 m(2) g(-1), Ti=14.8 wt% and P=1.5 wt%, and ion exchange capacity of 0.58 mmol g(-1). The tetrakis(1-methyl-4-pyridyl) porphyrin ion, H(2)TmPyP(4+), was immobilized on the matrix surface by an ion exchange reaction and then metallated in situ with Co(II), resulting in SiO(2)/TiO(2)/phosphate/CoTmPyP material. The amount of CoTmPyP incorporated to the matrix was 35.0 μmol g(-1). Cyclic voltammetry studies and rotating disk electrode experiments using a carbon paste electrode made with the material were carried out. The immobilized complex catalyzed O(2) reduction to H(2)O at -0.22 V in 1 mol L(-1) KCl solution at pH 6.8. The cathodic current intensities plotted against O(2) concentrations, between 1 and 11 ppm, showed a linear correlation. Copyright 2000 Academic Press.     

Iodometric determination of peroxydiphosphate in the presence of copper(II) or iron(II) as catalyst

Peroxydiphosphate can be determined iodometrically in the presence of a large excess of potassium iodide with copper(II) or iron(II) as catalyst through the operation of the Cu(II)/Cu(I) or Fe(II)/Fe(III) cycle. The method is applicable in HClO(4), H(2)SO(4), HCl and CH(3)COOH acid media in the range 0.1-1.0M studied. Nickel, manganese(II), cobalt(II), silver, chloride and phosphate are without effect.     

Study of redox behavior of Cd(II) and interaction of Cd(II) with proline in the aqueous medium using cyclic voltammetry

The redox behavior of Cd(II) and the interaction of Cd(II) with cyclic amino acid, proline, have been studied in 0.1 M KCl, 0.1 M NaClO₄ and acetate buffer of different pH. The CVs were recorded at glassy carbon electrode within the potential window 200 and ?1500 mV. The reference and counter electrode used were Ag/AgCl and Pt wire, respectively. The cyclic voltammograms show one pair of cathodic and anodic peaks for the Cd(II)/Cd(0) system indicating the involvement of two electron transfer processes. The peak potential shift and charge transfer rate constant (k_f) values strongly support the interaction between metal and ligand. The higher value of peak current ratio and peak potential separation (ΔE) indicate that the systems are quasireversible. The effect of supporting electrolyte and concentration of electro active species on the interaction were also studied.     

Cobalt(III) corroles as electrocatalysts for the reduction of dioxygen: reactivity of a monocorrole, biscorroles, and porphyrin-corrole dyads

Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me(4)Ph(5)Cor)Co, one a face-to-face biscorrole linked by an anthracene (A), biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or dibenzothiophene (S) bridge, (BCY)Co(2) (with Y = A, B, X, O or S), and one a face-to-face bismacrocyclic complex, (PCY)Co(2), containing a Co(II) porphyrin and a Co(III) corrole also linked by one of the above rigid spacers (Y = A, B, X, or O). Cyclic voltammetry and rotating ring-disk electrode voltammetry were both used to examine the catalytic activity of the cobalt complexes in acid media. The mixed valent Co(II)/Co(III) complexes, (PCY)Co(2), and the biscorrole complexes, (BCY)Co(2), which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O(2) to H(2)O in aqueous acidic electrolyte when adsorbed on a graphite electrode, with the most efficient process being observed in the case of the complexes having an anthracene spacer. A relatively small amount of hydrogen peroxide was detected at the ring electrode in the vicinity of E(1/2) which was located at 0.47 V vs SCE for (PCA)Co(2) and 0.39 V vs SCE for (BCA)Co(2). The cobalt(III) monocorrole (Me(4)Ph(5)Cor)Co also catalyzes the electroreduction of dioxygen at E(1/2) = 0.38 V with the final products being an approximate 50% mixture of H(2)O(2) and H(2)O.     

In situ scanning tunneling microscopy of 1,6-hexanedithiol, 1,9-nonanedithiol, 1,2-benzenedithiol, and 1,3-benzenedithiol adsorbed on pt(111) electrodes

Cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) were used to examine four dithiol molecules, including 1,6-hexanedithiol, 1,9-nonanedithiol, 1,2-benzenedithiol, and 1,3-benzenedithiol, adsorbed on well-ordered Pt(111) electrodes in 0.1 M HClO(4). The open-circuit potential (OCP) of Pt(111) electrodes decreased substantially from 0.95 to 0.3 V (versus reversible hydrogen electrode) upon the adsorption of dithol molecules, which indicates that these adsorbates injected electrons into the Pt electrode. For all dithiol molecules, ordered adlattices of p(2 x 2) and (square root 3 x square root 3)R30 degrees were formed when the dosing concentration was lower than 150 microM and the potential of Pt(111) was more negative than 0.5 V. Raising the potential of Pt(111) from 0.1 to 0.4 V or more positive values could transform p(2 x 2) to (square root 3 x square root 3)R30 degrees before it turned disarray. The insensitivity of the structure of dithiol adlayers with their chemical structures was explained by upright molecular orientation with the formation of one Pt-S bond per dithiol molecule. This molecular orientation was independent of the coverage of dithiol molecules, as nucleation seeds produced at the beginning of adsorption were also constructed with p(2 x 2). The triangular-shaped STM molecular resolution suggested 3-fold binding of sulfur headgroup on Pt(111). All dithiols were adsorbed so strongly on Pt(111) electrodes that switching the potential negatively to the onset of hydrogen evolution in 0.1 M HClO(4) or water reduction in 1 M KOH could not displace dithiol admolecules.     

Designed nanostructured pt film for electrocatalytic activities by underpotential deposition combined chemical replacement techniques

Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost.     

Electropolymerization of iron tetra(<Emphasis Type="Italic">o</Emphasis>-aminophenyl)porphyrin from aqueous solution and the electrocatalytic behavior of modified electrode

Stable electroactive iron tetra(o-aminophenyl)porphyrin (FeTAPP) films are prepared by electropolymerization from aqueous solution by cycling the electrode potential between −0.4 and 1.0 V vs Ag/AgCl at 0.1 V s⁻¹. The cyclic voltammetric response indicates that polymerization takes place after the oxidation of amino groups, and the films could be produced on glassy carbon (GC) and gold electrodes. The film growth of poly(FeTAPP) was monitored by using cyclic voltammetry and electrochemical quartz crystal microbalance. The cyclic voltammetric features of Fe(III)/Fe(II) redox couple in the film resembles that of surface confined redox species. The electrochemical response of the modified electrode was found to be dependent on the pH of the contacting solution with a negative shift of 57 mV/pH. The electrocatalytic behavior of poly(FeTAPP) film-modified electrode was investigated towards reduction of hydrogen peroxide, molecular oxygen, and chloroacetic acids (mono-, di-, and tri-). The reduction of hydrogen peroxide, molecular oxygen, and dichloroacetic acid occurred at less negative potential on poly(FeTAPP) film compared to bare GC electrode. Particularly, the overpotential of hydrogen peroxide was reduced substantially. The O₂ reduction proceeds through direct four-electron reduction mechanism.     

An in vitro characterisation comparing carbon paste and Pt microelectrodes for real-time detection of brain tissue oxygen

In vitro characterisation results for O(2) reduction at Pt-based microelectrodes are presented and compared with those for carbon-paste electrodes (CPEs). Cyclic voltammetry indicates a potential of -650 mV vs. SCE is required for cathodic reduction at both electrode types, and calibration experiments at this potential revealed a significantly higher sensitivity for Pt (-0.091 ± 0.006 μAmm(-2)μM(-1) vs. -0.048 ± 0.002 μAmm(-2)μM(-1) for CPEs). Since Pt electrodes are readily poisoned through contact with biological samples selected surface coated polymers (polyphenylenediamine (PPD), polymethyl methacrylate (PMMA) and Rhoplex(?)) were examined in biocompatibility studies performed in protein, lipid and brain tissue solutions. While small and comparable decreases in sensitivity were observed for bare Pt, Pt-Rhoplex and PMMA there was minimal change at the Pt-PPD modified electrode for each 24h treatment, including an extended 3 day exposure to brain tissue. The polymers themselves had no effect on the O(2) response characteristics. Further characterisation studies at the Pt-based microelectrodes confirmed interference free signals, no effect of pH and ion changes, and a comparable detection limit (0.08 ± 0.01 μM) and response time (<1 s) to CPEs. Although a significant temperature effect (ca. 3% change in signal for each 1 °C) was observed it is predicted that this will not be important for in vivo brain tissue O(2) measurements due to brain temperature homeostasis. These results suggest that amperometric Pt electrodes have the potential to be used reliably as an alternative to CPEs to monitor brain tissue O(2) over extended periods in freely-moving animals.