Tuning the extent of porosity and composition of N-doped carbon materials by NaNO3 and its effect on electrochemical activity

Abstract A facile one-pot method using NaNO 3 as etching agent in a molten salt medium is developed to tune the porous structure and composition of N-doped carbon materials derived from biomass at high temperatures. SEM and TEM analyses reveal that by increasing the amount of NaNO 3 , the structures of the obtained carbons become more open and graphene-like layers are formed. N 2 adsorption/desorption isotherms show that the hierarchical porous structure could be efficiently tuned by adjusting the amount of NaNO 3 in the salt mixture. It is observed that the specific surface area of the as-prepared N-doped carbon using NaNO 3 can reach 1430.1 m 2 g −1 , a much higher value than that of the sample prepared in the absence of NaNO 3 . The micropore ratio decreases with increased amount of NaNO 3 , from 49.42% to 9.98%. Whilst the surface composition of the obtained carbon materials is affected by NaNO 3 . The N content increases and O decreases respectively, by increasing the amount of NaNO 3 . Analysis on the N 1 s high resolution reveals that the sum of pyridinic-N and graphitic-N increased, whereas the sum of pyridinic-N oxide and NO x decreases from NC-0 to NC-0.75. It is also found that the changes of the porous structure and the oxygen-containing groups from NC-0 to NC-0.75 led to changes in hydrophilicity. When the as-prepared carbon materials are used as catalysts for the oxygen reduction reaction, high catalytic activity values are obtained, sample NC-0.5 shows the best performance due to the porous structure and doping effect of N atoms. More importantly, it is concluded that producing N-doped carbon materials from soybean dregs in molten salt medium using NaNO 3 as etching agent could provide a promising approach for the synthesis of opened N-doped carbons of controlled porous structures and large specific surface areas based on biomass precursors.