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

•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.