The construction of a planar electrochemical cell with two interdigitated electrodes, with a finger spacing of 25-100 mu m and 200-50 pairs of fingers and gaps, respectively, is described. The working electrode consists of n-type semiconducting titanium dioxide (anatase). Under UV light, photocurrents are produced. No reduction in the photocurrent due to iR drop was observed, even in electrolytes of low ionic strength. This makes the device an interesting candidate for photoelectrocatalytic purification of drinking water. An example is shown in the degradation of the azo-dye AO7 (acid orange 7). k(photoelectrocatalysis) on a device with 50 finger pairs was 3.29 x 10(-6)/s and the corresponding kinetic parameter, p = kFV/i(photo) (rate constant normalized to unit volume and photocurrent), was 404 M-1. (C) 2011 Elsevier Ltd. All rights reserved.