Seed layer-free hydrothermal synthesis of porous tungsten trioxide nanoflake arrays for photoelectrochemical water splitting.

The simple preparation of efficient nano-photoanodes has been a key issue in the development of photoelectrochemical water splitting. In this work, a convenient and seed layer-free hydrothermal approach has been developed to synthesize vertically aligned porous WO 3 nanoflakes on a fluorine-doped tin oxide conductive glass substrate. The morphology of WO 3 nanoflakes could be manipulated by changing the annealing time, which further affected the performance of WO 3 nanoflakes as photoanodes. Under optimum conditions, the obtained photoanode can lead to a high photocurrent density of 2.34 mA cm -2 at 1.4 V vs. Ag/AgCl under one sun irradiation (100 mW cm -2 ) and an incident photon to current conversion efficiency of 60% at 300 nm. The excellent photoelectrochemical performance can be mainly attributed to the larger active surface area, single crystal structure with an optimum thickness and the exposed highly active facets.