The development of low-cost and high-effi ciency electrocatalysts for the water-splitting reaction to produce oxygen and

hydrogen from alkaline electrolytes remains a major challenge, especially from the perspective of realizing fast and effi cient

oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, and it is important to improve the performance

of these reactions through rational catalyst design. In this study, Co-based heterostructures composed of cobalt (Co)

and molybdenum carbide (Mo 2 C) nanoparticles with micro-fl ower-like structures were intentionally designed as precursors

for OER and HER electrocatalysts. In particular, during polymerization, nanoparticle (metal precursor) ions and dopamine

aggregates combined to grow into nano-fl akes and retained their structure after carbonization, forming micro-fl ower-like

structures characterized by high specifi c surface area and porosity. The catalysts with hierarchical heterostructures constructed

using this unique structure showed activities similar to those of the commercially available IrO 2 and Pt/C catalysts, reaching

current densities of 10 mA/cm 2 for OER and HER in 0.1 M KOH and exhibiting good durability. Therefore, our results

present new concepts for the structuring and fabricating catalysts to realize effi cient OER and HER kinetics, and we expect

that they will be utilized in the energy conversion fi eld.