This paper reports experimental studies using the photoelectrocatalytic effect to eliminate a fundamental limit of photocatalysis - the recombination of photo-excited electrons and holes. The fabricated reactor has a planar reaction chamber (10 x 10 x 0.1 mm(3)), formed by a blank indium tin oxide glass slide, an epoxy spacer and a BiVO4-coated indium tin oxide glass substrate. A blue light-emitting diode panel (emission area 10 x 10 mm(2)) is mounted on the cover for uniform illumination of the reaction chamber. In the experiment, positive and negative bias potentials were applied across the reaction chamber to suppress the electron/hole recombination and to select either the hole-driven or electron-driven oxidation pathway. The negative bias always exhibits higher performance. It is observed that under -1.8 V the degradation rate is independent of the residence time, showing that the accompanying electrolysis can solve the oxygen deficiency problem. The synergistic effect of photocatalysis and electrocatalysis is observed to reach its maximum under the bias potential of +/- 1.5 V. The photoelectrocatalytic microreactor shows high stability and may be scaled up for high-performance water purification.