Biomass willow catkin-derived Co3O4/N-doped hollow hierarchical porous carbon microtubes as an effective tri-functional electrocatalyst

Oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions are extremely important electrochemical reactions for electrochemical energy conversion and storage. The development of highly efficient, low-cost, durable, and sustainable electrocatalysts is required for these three crucial electrochemical reactions. Herein, an effective tri-functional electrocatalyst, Co3O4 nanoparticle-modified N-doped hollow hierarchical porous carbon microtubes (Co3O4/ NCMTs), was successfully prepared via the pyrolysis of metal cobalt(II) complex willow catkin biomass under an argon-ammonia atmosphere. The obtained carbon materials inherit the original micron tubular structure of the willow catkin and form a hollow micro/mesoporous hierarchical construction. Ammonia can hugely elevate the content of doped nitrogen in the carbon skeleton. The doped N and Co3O4 nanoparticles contribute to form more active sites for the electrochemical reactions. When compared with the Pt/C catalyst, the Co3O4/NCMT-800 electrocatalyst with a positive onset potential (E-0 = 0.906 V) and half-wave potential (E-1/2 = 0.778 V) exhibit superior catalytic stability and tolerance to methanol in the ORR. The optimal Co3O4/NCMT-800 material exhibit high activity with a low overpotential of 0.35 V for the OER and 0.21 V for the HER to achieve a current density of 10 mA cm(-2). The enhanced OER and HER performance of the Co3O4/NCMTs contribute to improve the overall water splitting ability. The excellent tri-functional electrocatalytic activity can be ascribed to the doped N and Co3O4 nanoparticles loaded into the hollow hierarchical porous carbon microtubes that accelerate electron transport and enhance charge delocalization. Due to the abundant biomass precursor with a unique structure, the advanced non-noble metal-doped hollow porous carbon materials exhibit outstanding application prospects in the electrocatalysis field.