Opening of bottleneck pores for the improvement of nitrogen doped carbon electrocatalysts

A facile synthesis strategy to control the porosity of ionothermal nitrogen doped carbons is demonstrated. Adenine is used as cheap and biomass based precursor and a mixture of NaCl/ZnCl2 as combined solvent-porogen. Variation of the ratio between the two salt influences the pore structure over a wide range. The eutectic mixture leads to micro- and mesoporous material with high total pore volume (TPV) of 3.0 cm3 g−1 and very high surface area of 2900 m2 g−1 essentially rendering the product an ""all-surface-area"" nitrogen doped carbon. Increasing NaCl contents cause a continuous increase of the mesopore size and the formation of additional macropores resulting in a very high maximal TPV of 5.2 cm3 g−1, showing 2540 m2 g−1 specific surface area using 60 mol% NaCl. Interestingly, the electrocatalytic activity of the samples toward oxygen reduction is strongly affected by the detailed pore structure. The different-however, chemically equivalent-catalysts vary up to 70 mV in their half wave potentials (E 1/2).The sample with optimized pore system shows a high selectivity toward the favored four electron process and an outstanding E 1/2 of ≈880 mV versus reversible hydrogen electrode (RHE), which is one of the best values reported for nitrogen doped carbons so far.