Carbon-supported single-atom catalysts (C-SACs) demonstrate great potential in various key electrochemical reactions. Nevertheless, the development of facile and economical strategies is highly appealing yet challenging given that the commonly used pyrolysis method has strict requirements on the structure and composition of precursors. Here, we demonstrate for the first time a facile and low-cost pyrolysis strategy assisted by molten salts at high temperature for preparing porous C-SACs with well-dispersed Co-N-4 sites directly from a Chlorella precursor. Based on the X-ray absorption fine structure results and aberration-corrected scanning transmission electron microscopy images, we show that single atom Co-N-4 moieties are anchored on a carbon matrix. A porous structure with a large specific surface area (2907 m(2) g(-1)) and atomically dispersed active sites of Co provide the as-prepared Co-N/C-SAC with excellent electrocatalytic activity and stability for the ORR. The electrochemical measurements show that the half-wave potential and limited current density of this material are 0.83 V vs. RHE and 5.5 mA cm(-2), respectively, which are comparable to those of commercial Pt/C. (C) 2020 Elsevier Inc. All rights reserved.