Anchoring MWCNTs to 3D honeycomb ZnO/GaN heterostructures to enhancing photoelectrochemical water oxidation

Abstract

Gallium nitride (GaN) is one of the ubiquitously known photoanode for photoelectrochemical water splitting (PEC-WS) due to its tunable band gap and favorable band edge positions. However, the unavoidable surface defects in GaN induces surface Fermi level pinning and surface band bending which severely reduces its PEC conversion efficiency. Constructing heterostructure is the key to approaching better charge separation efficiency and light harvesting ability for PEC-WS. Considering this, we have fabricated ternary heterostructure of GaN/ZnO/MWCNTs photoanode by combining metal organic chemical vapour deposition (MOCVD), hydrothermal and ‘dip and dry’ methods. FE-SEM results showed the formation of 3D hierarchical honeycomb structure of ZnO on GaN thin film surface when MWCNTs are added into hydrothermal reaction. We investigate the advantage of ZnO honeycomb structure in enhancing the solar PEC-WS performance of GaN photoanode. The synergy of incorporating MWCNTs has resulted into improvement in surface morphology, electron transportation and light harvesting capability. The as obtained ternary heterostructure exhibits photocurrent (Jph) of 3.02 mA/cm2 at 0 V versus Pt electrode under 1-sun light illumination which is about 2.58 times higher than that of pristine GaN photoanodes (Jph = 1.14 mA/cm2).