Enhanced photo-carrier transportation at semiconductor/electrolyte interface of TiO2 photoanode by oxygen vacancy engineering

Abstract

The practicality of photoanodes for photoelectrochemical (PEC) water splitting was severely hampered by poor bulk photo-carrier separation and slow surface reaction kinetics. Here, we report an oxygen vacancy-enriched TiO2 photoanode modified by a highly crystalline TiO2 layer with enhanced bulk photo-carrier separation and surface reaction kinetics through stepwise gas diffusion at elevated temperatures. Experimental studies reveal that the reduction treatment introduces oxygen vacancy to TiO2, thereby increasing the charge carrier concentration and shifting the Fermi level to conduction band. The oxidation treatment affects the oxygen vacancy distribution of TiO2 surface which forms a suitable Fermi energy difference with the bulk, thus accelerating the carriers’ drift near to semiconductor/electrolyte interface. The as-obtained TiO2 photoanode exhibits an enhanced photocurrent density of 2.26 mA cm−2 at +1.23 V vs. RHE which is 2.75 times higher than that of the pristine TiO2. Hence, the present work illustrates the great potential of oxygen vacancy engineering via simple gas annealing treatment for Fermi level manipulation that can be further explored to other metal oxide semiconductors to design highly efficient oxygen vacancy enriched crystalline PEC photoelectrodes and provides novel insights into contact interfaces between semiconductors and electrolytes in PEC water splitting.