Simultaneous photocatalytic reduction of water to H-2 and CO2 to CO was observed over Cu2O photocatalyst under both full arc and visible light irradiation (>420 nm). It was found that the photocatalytic reduction preference shifts from H-2 (water splitting) to CO (CO2 reduction) by controlling the exposed facets of Cu2O. More interestingly, the low index facets of Cu2O exhibit higher activity for CO2 photoreduction than high index facets, which is different from the widely-reported in which the facets with high Miller indices would show higher photoactivity. Improved CO conversion yield could be further achieved by coupling the Cu2O with RuOx to form a heterojunction which slows down fast charge recombination and relatively stabilises the Cu2O photocatalyst. The RuOx amount was also optimised to maximise the junction's photoactivity. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.