WO3 bilayer electrodes composed of WO3 top and bottom layers are designed for photoelectrochemical cells (PECs). The bottom layers are sputter-deposited at a high temperature (773K) that leads to large grains and suitable electrical pathways for carrier collection. The top layer is deposited at a low temperature (573K) and consists of small grains, which give rise to large electrochemical reaction sites. The bilayer electrodes give a significant enhancement in PEC performance compared with WO3 monolayer electrodes deposited at 573 or 773K, because of a combination of favourable effects.