NOVELTY - A carbon dioxide electrochemical reduction catalyst contains tin dioxide nanoflower.    USE - Carbon dioxide electrochemical reduction catalyst for lithium ion batteries.    ADVANTAGE - The carbon dioxide electrochemical reduction catalyst effectively inhibits hydrogen evolution reaction, and has increased contact area, increased catalytic activity, and improved Faradaic current efficiency. Preparation is easy, low cost, and enhances formic acid selectivity.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) synthesis of carbon dioxide electrochemical reduction catalyst which involves hydrothermal synthesis of stannous chloride, trisodium citrate, and sodium hydroxide solution in which volume ratio of mixed solution of stannous chloride and trisodium citrate with sodium hydroxide is 1:1-9:1 (2) application of carbon dioxide electrochemical reduction catalyst for carbon dioxide electrochemical reduction diffusion electrode comprising loaded 2-20 mg tin dioxide nanoflower carbon dioxide electrochemical reduction catalyst in which gas diffusion electrode has dimension of 1 cmx 1 cm-7 cmx 7 cm; and (3) preparation of gas diffusion electrode catalyst which involves dissolving tin dioxide nanoflower in isopropyl alcohol, adding 1-5 wt.% Nafion (RTM: Sulfonated tetrafluoroethylene based fluoropolymer-copolymer)-perfluorosulfonic acid resin solution or 1-30 wt.% PTFE, stirring to obtain mixed solution, applying to gas diffusion electrode, drying, mixing with tin dioxide nanoflower and carbon materials, adding 1-5 wt.% Nafion-perfluorosulfonic acid resin solution or 1-30 wt.% PTFE, stirring to obtain mixed solution, applying to gas diffusion electrode, and drying in which amount of isopropyl alcohol is 100-1000 mu l and carbon material is 100-500 mg.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph of cyclic voltammetry of carbon dioxide electrochemical reduction catalyst in carbon dioxide saturated 0.5 M potassium bicarbonate. (Drawing includes non-English language text).