Influence of boron concentration on growth characteristic and electro-catalytic performance of boron-doped diamond electrodes prepared by direct current plasma chemical vapor deposition

A series of boron-doped diamond (BDD) electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) with different compositions of CH ₄ /H ₂ /B(OCH ₃ ) ₃ gas mixture. A maximum growth rate of 0.65 mg cm ^-2 h ^-1 was obtained with CH ₄ /H ₂ /B(OCH ₃ ) ₃ radio of 4/190/10 and this growth condition was also a turning point for discharge plasma stability which arose from the addition of B(OCH ₃ ) ₃ that changed electron energy distribution and influenced the plasma reaction. The surface coating structure and electro-catalytic performance of the BDD electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Hall test, and electrochemical measurement and electro-catalytic oxidation in phenol solution. It is suggested that the boron doping level and the thermal stress in the films are the main factors affecting the electro-catalytic characteristics of the electrodes. Low boron doping level with CH ₄ /H ₂ /B(OCH ₃ ) ₃ ratio of 4/199/1 decreased the films electrical conductivity and its electro-catalytic activity. When the carrier concentration in the films reached around 10 ²⁰ cm ^-3 with CH ₄ /H ₂ /B(OCH ₃ ) ₃ ratio over a range of 4/195/5-4/185/15, the thermal stress in the films was the key reason that influenced the electro-catalytic activity of the electrodes for its effect on diamond lattice expansion. Therefore, the BDD electrode with modest CH ₄ /H ₂ /B(OCH ₃ ) ₃ ratio of 4/190/10 possessed the best phenol removal efficiency.