Tunable Photo-Electrochemistry of Patterned TiO₂/BDD Heterojunctions

Heterojunctions are especially attractive for photo-electrocatalytic applications if both high-performance photo and electrocatalysts are employed for their construction. Herein, a p–n heterojunction is synthesized using uniform patterns of p-type boron doped diamond (BDD) and an n-type anatase TiO₂ film. The exposure ratios of the BDD patterns are varied to tune the photo-electrocatalytic abilities of this heterojunction. A heterojunction with a BDD exposure ratio of 20% exhibits a photocurrent density of 0.63 mA cm⁻², which is 2.86-fold higher than that obtained on a BDD film and 1.91-fold higher than that obtained on a TiO₂ film coated on a BDD film. It completely degrades methyl orange within 4 h, following the application of a 2.5 V bias potential, while the degradation efficiency on the BDD film and the TiO₂ film is 56% and 45%, respectively. As confirmed by electron spin resonance spectroscopy, an accelerated production rate of •OH radicals is realized on this heterojunction. It originates from a synergistic effect between the BDD patterns that act as an ultra-microelectrode array with a TiO₂/BDD p–n heterojunction as well as facilitated charge separation in a lateral direction. This TiO₂/BDD patterned heterojunction is thus promising as a new photo-electrocatalyst for various catalytic applications.