Impact of chloride surface treatment on nano-porous GaN structure for enhanced water-splitting efficiency

Photoelectrochemical devices equipped with semiconductor electrodes could be used for economically feasible hydrogen generation from water and sunlight energy. The bottleneck is in designing efficiently operating photoelectrodes, in particular with practical nano-architectures maximizing the extraction of the generated charge carriers for the water splitting reaction. In this work, using conventional electrochemical wet etching, we fabricated a nano-porous GaN structure and demonstrated its excellent functionality as a photoelectrode applicable for the water splitting. In particular, using a conventional analysis, we confirmed the water splitting efficiencies of 0.12% and 0.31%, comparing the planar and the nano-porous photoelectrode architectures, respectively. The major advantage of the porosity was in the increased fraction of the space charge region allowing for radically more efficient extraction of photo-generated charge carriers. The water splitting performance of the nano-porous electrodes was further improved by chloride treatment of the samples. This improvement was attributed to the surface chemical bonds reconstruction and/or electronic traps filling, resulting in additional ~20% water splitting efficiency improvement employing the nano-porous photoelectrode architecture. Altogether, we conclude that chloride treated nano-porous GaN photoelectrodes has a great potential for the use in the photoelectrochemical water splitting devices.