N-Doped porous carbons obtained from chitosan and spent coffee as electrocatalysts with tuneable oxygen reduction reaction selectivity for H2O2 generation

Abstract

Nitrogen-containing porous carbons prepared by the pyrolysis of adequate biopolymer-based precursors have shown potential in several electrochemical energy-related applications. However, it is still of crucial interest to find the optimal precursors and process conditions which would allow the preparation of carbons with adequate porous structure as well as suitable nitrogen content and distribution of functional groups. In the present work we suggested a straightforward approach to prepare N-doped porous carbons by direct pyrolysis under nitrogen of chitosan : coffee blends of different compositions and using KOH for simultaneous surface activation. The synthetized carbon materials were tested for the electrochemical oxygen reduction to hydrogen peroxide (H₂O₂). A higher fraction of chitosan in the precursor led to a decrease in meso- and nano-porosity of the formed porous carbons, while their activity towards H₂O₂ generation increased. The nitrogen species derived from chitosan seem to play a very important role. Out of the synthesized catalysts the one with the largest content of pyridinic nitrogen sites exhibited the highest faradaic efficiency. The faradaic efficiencies and current densities of the synthesized materials were comparable with the ones of other commercially available carbons obtained from less renewable precursors.