LAUSR

Abstract A boron-doped diamond (BDD) electrode with a large specific surface area was fabricated by formation of a hierarchical nanostructure. A BDD thin film was deposited on a silicon pillar array substrate fabricated using photolithography to obtain a BDD pillar array (BDD-PA). The BDD-PA was subjected to a two-step thermal treatment to form dense pores on the surface (P-BDD-PA). The P-BDD-PA was then treated by reactive ion etching (RIE) to form nanowhiskers on the surface (P-BDDW-PA). The combination of these structures (pillar array, pores and nanowhiskers) enabled enhanced double-layer capacitance (ca. 2800 μF cm − 2 ) based on the enlarged specific surface area without narrowing of the potential window (ca. 3 V) in an aqueous electrolyte. The combination of the two-step thermal treatment and RIE treatment should be an effective post-treatment method for enhancement of the capacitance of porous BDD materials consisting of micrometer-sized structures without significant increase of the time constant.