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