Energy band and interface engineering of ternary TNAs/g-C3N4/NCQDs photoanode with enhanced optical absorption and charge transfer for efficient photoelectrochemical water oxidation

Suitable energy band alignment and interface design of high-performance Ti-based photoanode is an effective way to address the easy compounding of photo-generated carriers, inferior light harvesting and poor oxygen evolution reaction (OER) kinetics. Hence then, the present work constructed a TiO2 nanotube arrays/g-C3N4/nitrogen-doped carbon quantum dots (TNAs/g-C3N4/NCQDs) composite system with enhanced optical absorption and charge transfer for efficient photoelectrochemical (PEC) water oxidation. As photosensitive components and light capture units, both g-C3N4 and NCQDs significantly increased light absorption of the composite photoanode. Continuous type-Ⅱ heterojunction formed in the composite photoanode through quantitative analysis of energy band positions. Based on the positive interfacial reaction, PEC water oxidation ability and bulk-phase charge separation efficiency were enhanced. Microstructure analysis combined with PEC measurements indicated that g-C3N4 and NCQDs enhanced near-UV-vis absorption, and OER kinetics of TNAs was boosted with reduced charge transfer resistance (Rct) at the photoanode/electrolyte solid-liquid interface. This well-matched energy level arrangement effectively inhibited the recombination of photo-generated charge carriers, while electrons and holes transfer to lower and higher energy levels across solid-solid interfaces with a formation of efficient and directional charge transfer channel. Photocurrent densities of the TNAs/g-C3N4/NCQDs under full light and visible-light-driven reached 4.7 mA cm−2 and 0.52 mA cm−2 at 1.23 V vs. RHE, which were 7.8 and 167 times of pristine system, respectively. This work concerned energy band and interface engineering of ternary Ti-based nanotube photoanodes, may provide fresh insights into creating multicomponent composite photoanodes for high-performance PEC water oxidation.