Synthesis of catalysts
Synthesis of Co1-SNC : 6 g melamine, 2 g L-Cysteine and 10 mg Cobalt chloride were first grounded into a homogeneous precursor by ZrO2 mortar ball. Subsequently, the fine powder mixture was undergone a two-stage pyrolysis and carbonization process at the Ar atmosphere (first stage: from 25°C to 580 °C, maintain at 580 °C for 2 h and then heated to 900 °C for 1.5 h). The heating rate of the whole process was 2 °C/min. After cooling down to room temperature, the product was leached at 80 °C in 0.5 M HCl for 24 h to remove the unstable species. Afterwards, the sample was heated at 700 °C again to eliminate the residual Cl-.
Synthesis of Co1-NC : The same method was used for the synthesis of Co1-NC (For Co1-NC, L-alanine was used instead of L-Cysteine. For detail: 6 g melamine, 2 g L-alanine and 10 mg Cobalt chloride was used).