Enhanced electrochemical ozone production via sp2 carbon content optimization in boron doped diamond electrodes using laser micromachining

Abstract

The role and bonding arrangement of deliberately added sp2 carbon in maximising the current efficiency, output and longevity of boron doped diamond (BDD) electrodes for electrochemical dissolved ozone generation is elucidated. We show, using a zero-gap cell (ZGC) arrangement, how systematically increasing sp2 carbon results in increased ozone concentration and current efficiency. sp2 carbon addition is made using nanosecond pulse laser micromachining which converts BDD to sp2 carbon. Two ZGC geometries are investigated which incorporate a Nafion membrane sandwiched between two BDD electrodes. Through-holes are integrated into either the membrane or the BDD, the latter using laser micromachining which also converts the hole walls to sp2 carbon. Increasing the number of through-holes (or changing hole geometry) increases the sp2 carbon content of the electrode (from 5-100%). For the planar electrode, the proportion of the surface which is laser micromachined controls the sp2 carbon content (from 4-100%). sp2 carbon content %’s are significantly higher than is possible using diamond growth. sp2 carbon contents >40% and >60% for the planar and perforated BDD electrodes, respectively, are found to be particularly effective, allowing electrode designs to be proposed for optimised ZGC ozone generation. Importantly, the sp2 carbon introduced via laser micromachining is shown to be extremely stable over 20 hr (anode potential ∼ 10 V) in contrast to glassy carbon, which corrodes within 10 mins. Whilst both are 100% sp2 carbon, the laser-machined surface is amorphous whereas the glassy carbon contains disorganised graphitic layers. This work also highlights the intriguing stability of amorphous sp2 carbon towards high oxidative potentials.

Topics & Concepts