Drastically improved photooxidation efficiencies, when compared to bulk WO3, are obtained with nanocrystalline WO3 films (see Figure) deposited from a colloidal solution of tungstic acid. Saturation of the photocurrent, which occurs even for moderate potential differences, indicates a completely different mechanism of charge separation. The electrodes should be highly effective for photoelectrolysis of water by sunlight. [GRAPHICS]