High-concentration ozone-water can be directly produced with a zero-gap electrolytic cell containing a freestanding perforated boron-doped diamond electrode. For the sake of improving current efficiency for electrochemical ozone-water production, optimization of the electrode configuration was performed. It was proven that the number of holes, hole size, and electrode thickness affect current efficiency. In particular, increasing the number of holes per unit area was the most effective method for improving current efficiency. In regard to hole size, 1 mm diameter was more appropriate than 1.5 mm diameter. Electrode thickness affected the current efficiency, and maximum values were found to be around 0.5-0.6 mm. Based on these results, an electrode optimal for electrochemical ozone-water production was prepared and achieved a maximum current efficiency of 47% in moderate conditions thus far. (c) 2007 The Electrochemical Society.