Generalized Synthesis of Ultrathin Cobalt-Based Nanosheets from Metallophthalocyanine-Modulated Self-Assemblies for Complementary Water Electrolysis

The development of effective approaches for preparing large-area, self-standing, ultrathin metal-based nanosheets, which have proved to be favorable for catalytic applications such as water electrolysis, is highly desirable but remains a great challenge. Reported herein is a simple and versatile strategy to synthesize ultrathin Co3 O4 and CoP NSs consisting of close-packed nanoparticles by pyrolyzing cobalt(II) phthalocyanine/graphene oxide (CoPc/GO) assemblies in air and subsequent topotactic phosphidation while preserving the graphene-like morphology. The strong π-π stacking interactions between CoPc and GO, and the inhibiting effect of the tetrapyrrole-derived macrocycle for grain growth during the catalytic carbon gasification contribute to the NSs forming. The resulting homologous Co3 O4 and CoP NSs display outstanding catalytic activity in alkaline media toward the oxygen evolution reaction and the hydrogen evolution reaction, respectively, ascribed to the richly exposed active sites, and the expedited electrolyte/ion transmission path. The integrated asymmetrical two-electrode configuration also presents a superior cell voltage of 1.63 V at 10 mA cm-2 for overall water splitting, accompanied with the excellent durability during long-term cycling. Further evidences validate that this strategy is appropriate to fabricate graphene-like ultrathin NSs of many other metal oxides, such as Fe2 O3 , NiO, MoO3 , and mixed-metal oxides, for various applications.