Focusing on renewable energy, we developed an efficient and robust catalyst for overall water splitting (OWS). Using density functional theory (DFT) as the guide, a combination electrode with bifunctional activities based on Co-based carbonate hydroxides (CCHs) and pyrenely-graphdiyne nanowalls (Pyr-GDY-NWs) with three-dimensional structures was designed, and then a series of experiments were attempted to prepare the combination electrode CCH@Pyr-GDY-NWs. From the data of theory and experiment, we found that the combination electrode CCH@Pyr-GDY-NWs exhibits an outstanding catalytic activity towards OWS. The design approach reported herein could open up a new avenue for the construction of three-dimensional Pyr-GDY-NW-based electrodes with high catalytic activity.