Effect of plasma-assisted electrochemical treatment of the boron-doped synthetic diamond compact electrodes on the oxygen electroreduction kinetics

Abstract

The effect of plasma electrochemical activation of boron-doped diamond compact electrodes on the oxygen electroreduction reaction kinetics is studied. The conducting compact electrodes are prepared via graphite-to-diamond conversion in C–B growth system at high pressure and high temperature. The diamond compact electrode surface was modified in Na2SO4 aqueous solution by exposition to cathodic–anodic electrolytic plasma produced by the application of voltage pulses with amplitude up to 300 V. The cathodic–anodic plasma alone proved to produce but negligible catalytic effect with respect to the oxygen reduction reaction. However, on the cathodic reduction of thus treated electrode, it acquired significant electrocatalytical activity manifested itself in the predominant O2-to-H2O reduction by a four-electron pathway. At the same time, the cathodic treatment of the plasma-modified electrodes has no real impact on the rate constant of electron transfer in the “fast” [Ru(NH3)6]2+/3+ and [Fe(CN)6]4–/3– redox systems. The observed electrocatalytical effect with respect to the oxygen reduction reaction is assumed to be caused by the quinone groups formation at the boron-doped diamond electrode surface under the combined action of cathodic–anodic plasma and cathodic polarization, these groups being active centers for the four-electron oxygen reduction.