Abstract: Provided are a carbon dioxide decomposition step of generating magnetite that has a surface to which carbon adheres, a carbon separation step of generating carbon and iron chloride, a hydrogen production step of generating magnetite, hydrogen, and a hydrogen chloride gas, and a reducing agent regeneration step of generating the reducing agent used in the carbon dioxide decomposition step, in which the reducing agent is an oxygen-deficient iron oxide represented by Fe3O4-? (where, ? is 1 or more and less than 4) obtained by reducing magnetite while maintaining a magnetite crystal structure, an oxygen-completely deficient iron (?=4) obtained by completely reducing magnetite, an oxygen-deficient iron oxide obtained by reducing hematite or a used disposable warmer, or an oxygen-completely deficient iron obtained by completely reducing hematite or a used disposable warmer.

Abstract: There is provided a method for producing a carbon material, including a carbon generation step of causing carbon dioxide to react with a reducing agent to generate carbon, in which, as the reducing agent, an oxygen-deficient iron oxide represented by Fe3O4-? (where ? is 1 or more and less than 4), which is obtained by reducing magnetite while maintaining a crystal structure, or an oxygen-completely deficient iron (?=4) which is obtained by completely reducing magnetite is used.