Unbiased solar water splitting of GaN photoanodes with Au nanoparticles supported by plasmon-assisted hot-carrier transfer

•GaN thin films were grown by MOCVD for photoanodes.•Au NPs were decorated by annealing Au thin films at high temperature.•Photocurrent density of Au NP/GaN photoanode is 11.4% more compared to bare GaN.•STH conversion efficiency of Au NP/GaN photoanode is 1.14 times to bare GaN.•IPCE % of Au NP/GaN composite photoanode is almost 2 times of pristine GaN.