An amphiphilic carbon nanofibre membrane electrode (ca. 50 nm fibre diameter, 50-100 m membrane t... more An amphiphilic carbon nanofibre membrane electrode (ca. 50 nm fibre diameter, 50-100 m membrane thickness) is employed as an active working electrode and separator between an aqueous electrolyte phase (with reference and counter electrode) and an immiscible organic acetonitrile phase (containing only the redox active material). Potential control is achieved with a reference and counter electrode located in the aqueous electrolyte phase, but the electrolysis is conducted in the organic acetonitrile phase in the absence of intentionally added supporting electrolyte. For the one-electron oxidation of n-butylferrocene coupled to perchlorate anion transfer from aqueous to organic phase effective electrolysis is demonstrated with an apparent mass transfer coefficient of m = 4 × 10 −5 m s −1 and electrolysis of typically 1 mg n-butylferrocene in a 100 L volume. For the two-electron reduction of tetraethylethylenetetracarboxylate the apparent mass transfer coefficient m = 4 × 10 −6 m s −1 is lower due to a less extended triple phase boundary reaction zone in the carbon nanofibre membrane. Nevertheless, effective electrolysis of up to 6 mg tetraethyl-ethylenetetracarboxylate in a 100 L volume is demonstrated. Deuterated products are formed in the presence of D 2 O electrolyte media. The triple phase boundary dominated mechanism and future microreactor design improvements are discussed.
A microfluidic double channel device was employed to study reactions at a flowing liquidjliquid i... more A microfluidic double channel device was employed to study reactions at a flowing liquidjliquid interface in contact with a gold electrode. The rectangular flow cell was calibrated for both single phase liquid flow and biphasic liquidjliquid flow for the case of the immiscible N-octyl-2-pyrrolidone (NOP)jaqueous electrolyte system. The influence of flow direction and speed and liquid viscosity on the position of the phase boundary was examined. The RuðNH 3 Þ 3þ=2þ 6 redox system was employed in aqueous solution to calibrate the flow cell in the absence and in the presence of the organic NOP phase. A significant ''undercutting'' of the organic phase into the aqueous phase was observed in particular for shorter gold band electrodes. The triple phase boundary reaction zone was visualized with a colour reaction based on the oxidation of N-benzylaniline. An approximate expression can be given to predict the mass transport controlled limiting currents even under two-phase flow conditions. Next, n-butylferrocene in NOP (without intentionally added electrolyte) was employed as the organic redox system with 0.1 M NaClO 4 as the adjacent aqueous electrolyte phase. Under these conditions the electrochemical reaction only proceeded at the organic liquidjaqueous liquidjsolid electrode triple phase boundary reaction zone and significant currents were observed. In contrast to the processes at conventional liquidjelectrode interfaces, these currents decreased with an increasing flow rate. The level of conversion at the triple phase boundary reaction zone can be further enhanced (i) at sufficiently slow flow rates and (ii) at larger electrodes. Bulk electrosynthetic processes are feasible, but the reactor design has to be further improved.
2-Bromomethyl-9,10-anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 200... more 2-Bromomethyl-9,10-anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 2000, Cabot Corp., with sulphonamide groups, ca. 9 to 18 nm diameter) with a coverage of ca. 250 anthraquinone molecules per particle (ca. 180 2 per anthraquinone). The resulting hydrophobic carbon particles are dispersed in ethanol and coated onto glassy carbon electrodes. Electrochemical experiments are reported demonstrating the effect of surface coverage, scan rate, and pH. A linear shift in reversible potential of ca. 59 mV per pH unit from pH 2 to 12 is observed consistent with the reversible 2-electron 2-proton reduction of anthraquinone. High density of anthraquinone in carbon nanoparticle aggregates causes buffer capacity effects. Binding of hydrophobic tetraphenylborate anions into carbon nanoparticle aggregate pores is demonstrated. Applications in buffer characterisation and pH-sensing are discussed.
This report describes exploratory experimental findings for electrochemical processes in nonpolar... more This report describes exploratory experimental findings for electrochemical processes in nonpolar solvents (hexane, toluene, and dichloroethane). Conventional 3 mm diameter glassy-carbon-disk electrodes are used in contact with a crystalline salt electrolyte (ammonium nitrate) immersed in nonpolar solvents. The insoluble salt is employed as a "surface thin film electrolyte", with humidity causing electrical connection from the working electrode to the SCE counterreference electrode. The organic solvents are employed without intentionally added electrolyte. Humidity in the nonpolar solvents is shown to be essential for the processes to work. The oxidation of decamethylferrocene is demonstrated as a test organometallic redox system. The electrochemical reduction of Au(III) in toluene (solubilized with tetraoctylammonium bromide, TOABr) is employed to demonstrate and visualize the reaction zone around salt crystal|working electrode contact points. Gold nanowire bundle formation is observed, presumably due to an ordered interfacial surfactant microphase at salt|electrode contact points. The triple phase boundary nature of these processes is discussed, and future applications are suggested.
An amphiphilic carbon nanofibre membrane electrode (ca. 50 nm fibre diameter, 50-100 m membrane t... more An amphiphilic carbon nanofibre membrane electrode (ca. 50 nm fibre diameter, 50-100 m membrane thickness) is employed as an active working electrode and separator between an aqueous electrolyte phase (with reference and counter electrode) and an immiscible organic acetonitrile phase (containing only the redox active material). Potential control is achieved with a reference and counter electrode located in the aqueous electrolyte phase, but the electrolysis is conducted in the organic acetonitrile phase in the absence of intentionally added supporting electrolyte. For the one-electron oxidation of n-butylferrocene coupled to perchlorate anion transfer from aqueous to organic phase effective electrolysis is demonstrated with an apparent mass transfer coefficient of m = 4 × 10 −5 m s −1 and electrolysis of typically 1 mg n-butylferrocene in a 100 L volume. For the two-electron reduction of tetraethylethylenetetracarboxylate the apparent mass transfer coefficient m = 4 × 10 −6 m s −1 is lower due to a less extended triple phase boundary reaction zone in the carbon nanofibre membrane. Nevertheless, effective electrolysis of up to 6 mg tetraethyl-ethylenetetracarboxylate in a 100 L volume is demonstrated. Deuterated products are formed in the presence of D 2 O electrolyte media. The triple phase boundary dominated mechanism and future microreactor design improvements are discussed.
A microfluidic double channel device was employed to study reactions at a flowing liquidjliquid i... more A microfluidic double channel device was employed to study reactions at a flowing liquidjliquid interface in contact with a gold electrode. The rectangular flow cell was calibrated for both single phase liquid flow and biphasic liquidjliquid flow for the case of the immiscible N-octyl-2-pyrrolidone (NOP)jaqueous electrolyte system. The influence of flow direction and speed and liquid viscosity on the position of the phase boundary was examined. The RuðNH 3 Þ 3þ=2þ 6 redox system was employed in aqueous solution to calibrate the flow cell in the absence and in the presence of the organic NOP phase. A significant ''undercutting'' of the organic phase into the aqueous phase was observed in particular for shorter gold band electrodes. The triple phase boundary reaction zone was visualized with a colour reaction based on the oxidation of N-benzylaniline. An approximate expression can be given to predict the mass transport controlled limiting currents even under two-phase flow conditions. Next, n-butylferrocene in NOP (without intentionally added electrolyte) was employed as the organic redox system with 0.1 M NaClO 4 as the adjacent aqueous electrolyte phase. Under these conditions the electrochemical reaction only proceeded at the organic liquidjaqueous liquidjsolid electrode triple phase boundary reaction zone and significant currents were observed. In contrast to the processes at conventional liquidjelectrode interfaces, these currents decreased with an increasing flow rate. The level of conversion at the triple phase boundary reaction zone can be further enhanced (i) at sufficiently slow flow rates and (ii) at larger electrodes. Bulk electrosynthetic processes are feasible, but the reactor design has to be further improved.
2-Bromomethyl-9,10-anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 200... more 2-Bromomethyl-9,10-anthraquinone is covalently bound to carbon nanoparticle surfaces (Emperor 2000, Cabot Corp., with sulphonamide groups, ca. 9 to 18 nm diameter) with a coverage of ca. 250 anthraquinone molecules per particle (ca. 180 2 per anthraquinone). The resulting hydrophobic carbon particles are dispersed in ethanol and coated onto glassy carbon electrodes. Electrochemical experiments are reported demonstrating the effect of surface coverage, scan rate, and pH. A linear shift in reversible potential of ca. 59 mV per pH unit from pH 2 to 12 is observed consistent with the reversible 2-electron 2-proton reduction of anthraquinone. High density of anthraquinone in carbon nanoparticle aggregates causes buffer capacity effects. Binding of hydrophobic tetraphenylborate anions into carbon nanoparticle aggregate pores is demonstrated. Applications in buffer characterisation and pH-sensing are discussed.
This report describes exploratory experimental findings for electrochemical processes in nonpolar... more This report describes exploratory experimental findings for electrochemical processes in nonpolar solvents (hexane, toluene, and dichloroethane). Conventional 3 mm diameter glassy-carbon-disk electrodes are used in contact with a crystalline salt electrolyte (ammonium nitrate) immersed in nonpolar solvents. The insoluble salt is employed as a "surface thin film electrolyte", with humidity causing electrical connection from the working electrode to the SCE counterreference electrode. The organic solvents are employed without intentionally added electrolyte. Humidity in the nonpolar solvents is shown to be essential for the processes to work. The oxidation of decamethylferrocene is demonstrated as a test organometallic redox system. The electrochemical reduction of Au(III) in toluene (solubilized with tetraoctylammonium bromide, TOABr) is employed to demonstrate and visualize the reaction zone around salt crystal|working electrode contact points. Gold nanowire bundle formation is observed, presumably due to an ordered interfacial surfactant microphase at salt|electrode contact points. The triple phase boundary nature of these processes is discussed, and future applications are suggested.
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