Willow tree leaf-derived porous carbon-supported Co nanoparticles as enhanced oxygen reduction reaction electrocatalysts.

A willow tree leaf-derived porous carbon-supported Co nanoparticle composite (Co/LDPC) was proposed as a promising oxygen reduction reaction electrocatalyst under alkaline conditions. This material was fabricated through a sequential process involving activation, etching, soaking and heat treatment. Structural characterization revealed that Co/LDPC possesses an ultrahigh specific surface area of 1864.75 m2 g-1, attributed to KOH activation, urea etching and cobalt nanoparticle loading. The etching step effectively enhanced the surface defects and increased the nitrogen content via doping the N element into the carbon framework. Urea, which acts as a nitrogen source, is a superior etchant to glycine and melamine. Co nanoparticles were uniformly anchored on the carbon support surface through Co-N bonds, which served as catalytic sites. From electrochemical measurements, Co/LDPC exhibits an onset potential of 0.918 V, an effective 4-electron transfer pathway, a limiting current density close to that of commercial Pt/C (20%), a high electrochemically active surface area (855.4 cm2), a half-wave potential (E 1/2) of 0.811 V, good long-term stability and superior methanol tolerance in alkaline electrolytes for the ORR. This work opens up a low-cost and easily implementable way to transform fallen leaves into high-value functional materials.