▎ 摘　　要

NOVELTY - Preparing graphene-coated cobalt-based Prussian blue nanocrystalline composite material comprises (a) adding 0.1-2 mol/l ligand solution to 0.1-10 g/l graphene oxide solution, stirring for 10-60 minutes, ultrasonically treating for 5-30 minutes to obtain mixture of ligand and graphene oxide, (b) adding 0.1-2 mol/l metal salt solution to mixture obtained in the step (a) and stirring for 12-36 hours to obtain mixture of graphene oxide and cobalt Prussian blue, (c) centrifuging mixture obtained in step (b) at 10000-20000 revolutions/minute for 10-30 minutes, freeze-drying solid obtained by centrifugation for 24-48 hours to obtain graphene oxide supported cobalt-based Prussian blue nanocrystal composite and (d) calcining graphene oxide supported cobalt-based Prussian blue nanocrystalline composite obtained in step (c) in an inert atmosphere. USE - The method is useful for preparing graphene-coated cobalt-based Prussian blue nanocrystalline composite material. ADVANTAGE - The method: has simple preparation method, low energy consumption in preparation process; utilizes easily available raw materials; improves the electron transfer efficiency and active site utilization of the composite material. The composite material has fast reaction speed, high nitrogen selectivity of 98.97%, good cycle stability and larger application prospect in the field of water treatment. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for preparing working electrode using graphene-coated cobalt-based Prussian blue nanocrystalline composite material comprising applying N-methylpyrrolidone solution of the graphene-coated cobalt-based Prussian blue nanocrystalline composite material, carbon black and polyvinylidene fluoride to length in mass-to-volume ratio of 5-10:0.5-1:50-100 (mg:mg:ml), where the working electrode is composed on the foamed nickel with width of 1-2 cm and width of 1-4 cm; and #use of working electrode in electrocatalytic treatment of sewage nitrate nitrogen reduction comprising using graphene-coated cobalt-based Prussian blue nanocrystalline composite material, platinum electrode as a counter electrode and silver chloride electrode as a reference electrode constitute a three-electrode system, placing three-electrode system in sewage containing nitrate nitrogen and sodium sulfate electrolyte of 0.05-0.1 mol/l to perform electrocatalytic reduction of nitrate nitrogen..