Synthesis of Co-NC-900 Catalyst

First, 2.0 g of montmorillonite (MMT) and 4.0 g of CoCl₂ is added to a 50-ml beaker filled with 30 ml deionized water, and stirred for 24 h to fully exchange the Co²⁺ ion and Na⁺ ion at room temperature. After centrifugation at 2500 rpm, the obtained solid is dried at 80 °C to yield the Co-modified montmorillonite (Co-MMT). Subsequently, 0.40 g of Co-MMT and 0.40 g of aniline (ANI) are added into a 50-ml beaker filled with 20 ml deionized water, and regulated at pH = 2 with 0.1 mol l^–1 HCl solution. Two grams of ammonium thiosulfate (APS) is further added into the above solution and stirred for 24 h to facilitate the polymerization of ANI at room temperature and form the precursor. The precursor is subsequently heat-treated at different temperatures (800, 900, and 1000 °C) for 2 h under Ar atmosphere. All produced samples were finally etched off in a 40 wt.% HF solution to prepare the Co-NC-X (X = 800, 900, or 1000) catalysts. The schematic illustration for preparation of Co-NC catalyst via using of Co-MMT flat template is indicated in Fig. 1. As a control, a similar method is performed to generate the NC-900 catalyst via directly using MMT flat template. Besides, the Co-PANI-900 was synthesized by direct polymerization of ANI monomers in the presence of the same Co²⁺ content without using of flat template.

Schematic illustration for synthesis of the Co-NC catalyst