Improvement in the photoelectrochemical water-splitting performance using GaN nanowires with bundle structures

We report an approach for improving the photoelectrochemical water splitting (PEC-WS) performance using GaN-nanowire (NW) bundles (GNW-BDLs) as the photoanode material. The bundles were formed by dipping GaN NWs with an average length of 648.3 nm and diameter of 35.2 nm into acetone. The effect thereof was that the upper sections of several NWs were agglomerated via van der Waals bonding to form a bundle structure. The current density and applied bias photon-to-current efficiency of the GNW-BDL photoanode in a 0.5 M H 2 SO 4 electrolyte were measured to be 2.2 mA cm −2 and 1.9%, respectively, at 0.6 V vs. reversible hydrogen electrode. These values were increased by 314% and 317% compared with those (0.7 mA cm −2 and 0.6%) of the photoanode using pristine GaN NWs. In addition, the PEC-WS performance was observed at the potential of 0 V vs. Pt. This remarkable improvement is largely attributed to the reduction in the effect of the surface-trap states of GaN NWs on the migration of the photogenerated carriers to the electrolyte because of the formation of structures consisting of bundles of neighboring NWs. Improvement in the photoelectrochemical water splitting performance by reducing surface-trap states by forming bundle structures of GaN nanowires.