Herein,a cross-linked porous Ta3N5 film was prepared via a simple solution combustion route followed by a high-temperature nitridation process for photoelectrochemical(PEC)water oxidation.Meanwhile,the metal cations(Mg2+and Zr4+)were incorporated into the porous Ta3N5 to enhance the PEC performance.The porous Mg/Zr co-doped Ta3N5 photoanode yielded a photocurrent density of 1.40 mA cm-2 at 1.23 V vs RHE,which is 5.6 times higher than that of the dense Ta3N5 photoanode.The enhanced performance should be ascribed to the synergistic effect of porous structure and cation doping,which can enlarge the electrochemical active surface area and accelerate the charge transfer by introducing ON substitution defects.Subsequently,Co(OH)2 cocatalyst was loaded on the Mg/Zr-Ta3N5 photoanode to negatively shift the onset potential to 0.45 V vs RHE and further improve the photocurrent density to 3.5 mA cm-2 at 1.23 V vs.RHE,with a maximum half-cell solar to hydrogen efficiency of 0.45％.The present study provides a new strategy to design efficient Ta3N5 photoelectrodes via the simultaneous control of the morphology and composition.