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Engineering nanocomposites with interfaces was already found to be an efficient method for designing water-splitting catalysts. In this study, a rationally designed 3D Ru/RuO 2 @N-rGO hierarchical porous heterocatalyst containing abundant interfaces was obtained via a hydrothermal-calcining strategy for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). In the synthesis process, polypyrrole helped the self-assembled GO to form a hybrid aerogel network, in situ reducing the Ru salt as reductant and doping graphene as N precursor. CO 2 , which was in situ produced via the reaction between Na 2 SO 4 and C, could partially or totally oxidize metal Ru to regulate the composition of Ru/RuO 2 nanoparticles. Benefiting from the large surface area and a high number of bifunctional active sites coupled interfaces, the as-obtained Ru/RuO 2 @N-rGO heterostructure catalyst revealed high HER/ OER activities in 1.0 M KOH and 0.5 M H 2 SO 4 solutions, respectively. The present work could provide a way to engineer Ru/RuO 2 nanoparticles in 3D electrocatalysts to boost HER/OER performances.