Improvement of efficiency in graphene/gallium nitride nanowire on Silicon photoelectrode for overall water splitting

Highlights: • Pristine GaN NWs were grown on n-type Si (111) substrates using radio-frequency plasma-assisted MBE. • The graphene grown by CVD was coated on surface of GaN nanowires (Gr/GaN NWs). • The photoelectrochemical properties of these structures were investigated. • The saturated photocurrent density increased in Gr/GaN NWs than ref GaN NWs. • We reported the reason for this difference. - Abstract: Gallium nitride (GaN) nanowires are one of the most promising photoelectrode materials due to their high stability in acidic and basic electrolytes, and tunable band edge potentials. In this study, GaN nanowire arrays (GaN NWs) were prepared by molecular beam epitaxy (MBE); their large surface area enhanced the solar to hydrogen conversion efficiency. More significantly, graphene was grown by chemical vapor deposition (CVD), which enhanced the electron transfer between NWs for water splitting and protected the GaN NW surface. Structural characterizations of the prepared composite were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocurrent density of Gr/GaN NWs exhibited a two-fold increase over pristine GaN NWs and sustained water splitting up to 70 min. These improvements may accelerate possible applications for hydrogen generation with high solar to hydrogen conversion efficiency.