Influence of Ga-halogen bond formation at the interface of nanoporous GaN photoelectrodes for enhanced photoelectrochemical water splitting efficiency

The photoelectrochemical devices with morphologically tuned photoelectrodes assist in addressing the existing sustainable energy challenges by generating hydrogen energy from sunlight and water. In the present work, morphologically tuned nanoporous GaN photoelectrodes are successfully fabricated via a low-damage electrochemical wet etching. Also, a facile halogen treatment is used to replace Ga-O bonds with Ga-halogen bonds at the nanopore region. The influence of halogen treatment on the nanoporous GaN photoelectrodes is investigated in comparison with planar and nanoporous GaN photoelectrode. From the conventional analysis, a maximum 4-fold improvement in the applied bias photon-to-current efficiency is obtained for the Br treated nanoporous GaN photoelectrode (0.43%) compared to planar GaN (0.11%). Based on the result of X-ray and ultraviolet photoemission spectroscopy along with density functional theory calculations, the superior performance owing to the modification in the space charge region and reconstruction of the Ga-halogen bonds enables more efficient extraction of photogenerated charge carriers. In addition, it is confirmed that the halogen treatment assists in suitably tuning the band bending and electronic characteristics for enhanced photoelectrochemical water splitting performance. Altogether, we concluded that the halogen treatment has great potential for the development of photoelectrochemical water splitting devices.