We report a sparse Ni/NiOx core-shell nanoparticle coating on an n-GaN photoanode that yields a high photocurrent by engineering junction energetics. A conventional thin film coating of high work function NiOx induces a large band bending that helps generate high photovoltage. However, the high work function causes a Fermi level downshift and compromises photopotential. The discrete core-shell nanoparticle coating balances these two effects. The Ni core creates localized large band bending to produce a high photovoltage. Meanwhile, the reduced coating surface area decreases Fermi level downshift. The resulting higher photopotential together with the catalytic NiOx shell enables a photo current 50% higher than NiOx thin film coating and multiple times higher than Ni nano particle or film coating. The localized large band bending also forms a potential well to deplete holes from semiconductor, thereby providing full surface protection against corrosion. This core-shell nanoparticle coating demonstrates a new junction energetics engineering paradigm useful for photoelectrode optimization. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.