Bio‐Inspired Leaf‐Mimicking Nanosheet/Nanotube Heterostructure as a Highly Efficient Oxygen Evolution Catalyst

Plant leaves represent a unique 2D/1D heterostructure for enhanced surface reaction and efficient mass transport. Inspired by plant leaves, a 2D/1D CoO x heterostructure is developed that is composed of ultrathin CoO x nanosheets further assembled into a nanotube structure. This bio‐inspired architecture allows a highly active Co 2+ electronic structure for an efficient oxygen evolution reaction (OER) at the atomic scale, ultrahigh surface area (371 m 2 g −1 ) for interfacial electrochemical reaction at the nanoscale, and enhanced transport of charge and electrolyte over CoO x nanotube building blocks at the microscale. Consequently, this CoO x nanosheet/nanotube heterostructure demonstrates a record‐high OER performance based on cobalt compounds reported so far, with an onset potential of ≈1.46 V versus reversible hydrogen electrode (RHE), a current density of 51.2 mA cm −2 at 1.65 V versus RHE, and a Tafel slope of 75 mV dec −1 . Using the CoO x nanosheet/nanotube catalyst and a Pt‐mesh, a full water splitting cell with a 1.5‐V battery is also demonstrated.