3D holey hierarchical nanoflowers assembled by cobalt phosphide embedded N-doped carbon nanosheets as bifunctional electrocatalyst for highly efficient overall water splitting.

With the increasing energy and environmental crisis, exploring convenient and general strategies for constructing of highly active, stable, and cost-effective bifunctional electrocatalysts for overall water splitting are exceedingly desirable yet still challenging. Herein, 3D hierarchical mesoporous cobalt phosphide embedded N-doped carbon nanoflowers (CoP@NCNFs) are successfully constructed with ultrathin nanosheets by phosphatingof the cobalt coordination polymer nanoflowers (CoCPNFs). By virtue of their unique architecture and particular composition, the obtained CoP@NCNFs reveal extraordinary performance with ultralow overpotentials and small Tafel slopes for both OER (291 mV at 10 mA cm; 75 mV dec) and HER (166 mV at 10 mA cm; 76 mV dec) in alkaline medium. In particular, CoP@NCNFs can act as both anode and cathode to perform overall water splitting, and the assembled device only needs a cell voltage as low as 1.59 V to achieve the current density of 10 mA cm. Simultaneously, the CoP@NCNFs also exhibit admirable durability (at least 15 h) throughout the water splitting process. These remarkable electrocatalytic performances could be attributed to the synergistic effect of highlyactive CoP NPs and conductive mesoporous N-doped carbon nanosheets, which effectively improved the surface contact between catalyst and electrolyte, mass diffusion, and stability.