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Surface Modification of Boron-Doped Diamond with Microcrystalline Copper Phthalocyanine: Oxygen Reduction Catalysis.

Gan P, Foord JS, Compton RG - ChemistryOpen (2015)

Bottom Line: Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution.A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD.Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide.

View Article: PubMed Central - PubMed

Affiliation: Chemistry Research Laboratory, University of Oxford Mansfield Road, Oxford, OX1 3TA, United Kingdom.

ABSTRACT
Surface modification of boron-doped diamond (BDD) with copper phthalocyanine was achieved using a simple and convenient dropcast deposition, giving rise to a microcrystalline structure. Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution. A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD. Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide. The lack of a further conversion of the peroxide was attributed to its rapid diffusion away from the triple phase boundary at which the reaction is expected to exclusively occur.

No MeSH data available.


Schematic diagram of the possible surface formation via dropcast modification.
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fig09: Schematic diagram of the possible surface formation via dropcast modification.

Mentions: The key to this apparent conundrum likely lies in the structure of the surface deposition. As illustrated in Figure 9, the dropcast modification of molecular compounds could result in the formation of a continuous film or an array of microcrystallites on the electrode surface. In the former case, hydrogen peroxide is expected to further react via Equation 3. However, the results above are suggestive of the case for the microcrystalline array, in which the charge transfer is thought to occur at the triple phase boundary formed between the copper phthalocyanine microcrystallite, the diamond, and the aqueous solution.24 At the junction of contact of the three phases, the catalyst, electrons, and reactants are all present in adequate proximity for the reaction to occur. The fact that the reduction of oxygen is an overall two-electron process probably has to do with the microcrystallites behaving in effect as a random array of “microelectrodes” (Figure 10), allowing the hydrogen peroxide formed in this instance to diffuse radially into the bulk phase at a rapid rate before it can undergo further conversion according to Equation 3. Indeed the presence of microcrystallites on the modified diamond surface has been evidenced earlier by SEM in Figure 3, and this supports our inference of a triple-boundary process.


Surface Modification of Boron-Doped Diamond with Microcrystalline Copper Phthalocyanine: Oxygen Reduction Catalysis.

Gan P, Foord JS, Compton RG - ChemistryOpen (2015)

Schematic diagram of the possible surface formation via dropcast modification.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608528&req=5

fig09: Schematic diagram of the possible surface formation via dropcast modification.
Mentions: The key to this apparent conundrum likely lies in the structure of the surface deposition. As illustrated in Figure 9, the dropcast modification of molecular compounds could result in the formation of a continuous film or an array of microcrystallites on the electrode surface. In the former case, hydrogen peroxide is expected to further react via Equation 3. However, the results above are suggestive of the case for the microcrystalline array, in which the charge transfer is thought to occur at the triple phase boundary formed between the copper phthalocyanine microcrystallite, the diamond, and the aqueous solution.24 At the junction of contact of the three phases, the catalyst, electrons, and reactants are all present in adequate proximity for the reaction to occur. The fact that the reduction of oxygen is an overall two-electron process probably has to do with the microcrystallites behaving in effect as a random array of “microelectrodes” (Figure 10), allowing the hydrogen peroxide formed in this instance to diffuse radially into the bulk phase at a rapid rate before it can undergo further conversion according to Equation 3. Indeed the presence of microcrystallites on the modified diamond surface has been evidenced earlier by SEM in Figure 3, and this supports our inference of a triple-boundary process.

Bottom Line: Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution.A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD.Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide.

View Article: PubMed Central - PubMed

Affiliation: Chemistry Research Laboratory, University of Oxford Mansfield Road, Oxford, OX1 3TA, United Kingdom.

ABSTRACT
Surface modification of boron-doped diamond (BDD) with copper phthalocyanine was achieved using a simple and convenient dropcast deposition, giving rise to a microcrystalline structure. Both unmodified and modified BDD electrodes of different surface terminations (namely hydrogen and oxygen) were compared via the electrochemical reduction of oxygen in aqueous solution. A significant lowering of the cathodic overpotential by about 500 mV was observed after modification of hydrogen-terminated (hydrophobic) diamond, while no voltammetric peak was seen on modified oxidised (hydrophilic) diamond, signifying greater interaction between copper phthalocyanine and the hydrogen-terminated BDD. Oxygen reduction was found to undergo a two-electron process on the modified hydrogen-terminated diamond, which was shown to be also active for the reduction of hydrogen peroxide. The lack of a further conversion of the peroxide was attributed to its rapid diffusion away from the triple phase boundary at which the reaction is expected to exclusively occur.

No MeSH data available.