The main technical challenge for the electrolytic production of hydrogen via water splitting lies in realizing a very stable material that effectively oxidizes water under low overpotential (eta). Of all materials, metal oxides hold the greatest promise due to their inherited chemical stability in aqueous solutions; however, electrolytic effectiveness in water oxidation reactions (OERs) is limited to precious metals. In this study, we designed metal oxide/metal oxide (MO/MO) nanoparticle heterointerfaces to offer more active sites and enhance the overall performance of the OER. To demonstrate this improvement, we synthesized and characterized CeO2/Co3O4, CeO2/CuO, and CeO2/NiO nanoparticles. In these structures, onset potential and photoactivity were significantly improved relative to a single MO. A cathodic shift of onset potential as high as similar to 0.4 or 0.3 V was recorded for CeO2/Co3O4 relative to CeO2 or Co3O4, respectively. This improvement was further investigated using density functional theory calculations, upon which adsorption preferability and reaction free energy at the CeO2/Co3O4 heterointerface were found to play significant roles in OER enhancement. (c) 2020 Published by Elsevier Inc.