Porous ultrathin WO3 nanoflake arrays as highly efficient photoanode for water splitting

•Porous ultrathin WO3 nanoflake array was prepared by one-step hydrothermal method.•The morphologies of WO3 nanoarrays can be tuned by the dosage of (NH4)2C2O4.•WO3 arrays showed remarkable photocurrent of 1.80 mA cm−2 at 1.23 V vs RHE.•The reasons for the improvement of photoelectrochemical performance were discussed. To overcome the limitation of minority carrier diffusion length and high recombination of electron-hole pairs, porous ultrathin tungsten trioxide (WO3) nanoplate arrays with amorphous layer were prepared by one-step hydrothermal method without pre-seeded which possessed the highest photocurrent density of 1.80 mA cm−2 at 1.23 V vs RHE and 100 mV cathodic shift of onset potential with 0.20 g dosage of (NH4)2C2O4. The remarkable photoelectrochemical performance mainly benefits from enhanced red-shift light absorption, cathodic shifted onset potential, lowest recombination of photoelectron-hole pairs and abundant active surface areas. These results confirm that engineering the thickness and surface state of oxide semiconductor nanoplate arrays are the promising ways to improve the photoelectrochemical performance for solar water splitting.