For an efficient photoelectrocatalysis on bismuth oxychloride (BiOCl), it is highly desired to enhance the photogenerated charge separation and the photochemical stability. Herein, photoelectrocatalytic activities of BiOCl photoanodes for water oxidation to evolve O-2 and for methyl orange (MO) degradation have been greatly improved through firstly coupling with reduced graphene oxide (RGO) and then modifying with phosphoric acid. It is shown that the optimal amount of phosphate modified RGO/BiOCl nanocomposite photoanode exhibits 3.8-time and 8.4-time activity enhancement respectively for water oxidation and MO degradation, compared to the bare BiOCl. It is confirmed that the improved activities are attributed to enhanced charge separation and prolonged carrier lifetime of BiOCl after chemically coupling with RGO to collect electrons and modifying with phosphate groups to trap positive holes via the formed negative field on the surfaces, mainly based on electrochemical impedance spectra, time-resolved surface photovoltage responses, and produced hydroxyl radical amounts. Moreover, it is concluded that the phosphate groups are modified on BiOCl by replacing photochemically-unstable chloride ions, consequently leading to the enhanced stability. Expectedly, this positive strategy is also applicable to the visible-response BiOBr as an efficient photoanode. This work opens up a feasible route to efficiently improve the PEC performance of BiOX-based nanomaterials with high stability. (C) 2016 Elsevier B.V. All rights reserved.