Highly efficient oxygen reduction on porous nitrogen-doped nanocarbons directly synthesized from cellulose nanocrystals and urea

• N-doped carbon nanosheets (NCN) were direct prepared by pyrolyzingcellulose/urea.
• NCN exhibited high SSA (∼1362.36 m2 g−1) and large pore volume (∼3.36 cm3 g−1).
• NCN exhibited superior ORR catalytic performancethan Pt/C in 0.1 M KOH.
• Urea is irreplaceableby NH3 and Fe catalyst is unnecessary for the synthesis.

This study displays an easy preparation of high-performance electrocatalyst from cellulose nanocrystals for oxygen reduction reaction (ORR) that occurs at cathode of fuel cells. Through a direct pyrolysis of cellulose nanocrystals and urea, porous nitrogen-doped carbon nanosheets (NCN) are successfully synthesized without involving any catalysts or post treatments. As-prepared NCN displays very high specific surface area (∼1362.36 m2 g−1), large pore volume (∼3.36 cm3 g−1) and high graphitic-/pyridinic-N proportion (∼80% in total N content). This metal-free material demonstrates a superior catalytic performance in terms of a comparable electrocatalytic activity, a better tolerance to the methanol crossover effect and an improved long-term durability toward ORR in the alkaline media when compared with the commercial Pt/C catalyst. Interestingly, the addition of FeCl3 catalyst to the reaction system does not benefit ORR activity of the resultant material; the replacement of urea by NH3 gas brings about much poorer material features of morphology, structure and catalytic activity. It is suggested that urea is irreplaceable during this catalyst-free synthesis of nitrogen-doped nanocarbons while cellulose nanocrystal is an unique choice for preparing high performance ORR electrocatalyst. The study herein contributes a very promising Pt-alternative cathode catalyst and also a facile and practical preparation of advanced carbon materials.

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