Single-atom catalysts (SACs) have attracted great attention due to their high atom-utilization and catalytic efficiency. However, a universal synthetic route is still lacking, which restricts the SAC-related investigation and application. Here, we report a simple and cost-effective method to fabricate transition metal SACs through ion exchange and annealing procedures. Benefiting from the "egg-box" structure property of alginate, the metal ion can be effectively anchored into the organic center. Using CuCl2 as a representative transition metal ion, the Cu SAC structure was synthesized and identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy. Through optimizing CuCl2 concentration, the obtained Cu SAC exhibited a good oxygen reduction reaction activity, whose onset potential, half wave potential, and limiting current density are all comparable to those of 20 wt % Pt/C. Cu-N4 was identified as the responsible catalytic site. More importantly, other transition metal SACs can be easily synthesized via altering metallic solution, which proves the universality of our proposed method. This work may be valuable for the cost-effective and universal SAC synthetic method development.
Keywords: alginate hydrogel; impregnation; oxygen reduction reaction; single-atom catalysts; transition metal.