Water splitting has been intensively investigated as a promising solution to resolve the future environmental and energy crises. The oxygen evolution reaction (OER) of the photo- and electric field induced water splitting limits the development of other reactions, including hydrogen evolution reaction (HER). Fe, Ni and NiFe (hydro) oxide-based catalysts are generally acknowledged among the best candidates of OER catalysts for water splitting. Herein, we developed a one-pot simple hydrothermal process to assemble NiFe2O4 nanoparticles onto the alpha-Ni(OH)(2) nanosheets. The first formed NiFe2O4 under high temperature and pressure environment induces and assists the alpha-Ni(OH)(2) formation without any further additives, because the distance between the neighboring Ni atoms in the cubic NiFe2O4 is similar to that in the alpha-Ni(OH)(2) {003} facets. We have synthesized a series of NiFe2O4/alpha-Ni(OH)(2) compounds and find that the overpotential decreases with the increase of Ni(OH)(2) content while the OER kinetics stays unchanged, suggesting that Ni(OH)(2) plays a major role in overpotential while NiFe2O4 mainly affects the OER kinetics. The obtained NiFe2O4/alpha-Ni(OH)(2) compounds is also found to be a promising co-catalyst for the photocatalytic water oxidation. In fact, it is even more active than the noble PtOx with acceptable stability for the oxygen generation. (C) 2016 Elsevier B.V. All rights reserved.