Metal- and Oxide-Containing Carbons Made From Graphite Oxide

Lewis Research Center, Cleveland, Ohio

Carbon-based materials containing, variously, metals and metal oxides can be synthesized according to a method that involves reactions of metal chlorides with materials of general composition CO_x. In a typical material synthesized by the present method, the carbon is porous and serves as a substrate for the metal or metal oxide. Depending on the application, the metal or metal oxide could serve, for example, as a catalyst or as an electrode material in a gas sensor or electrochemical power cell. Alternatively, instead of serving as a substrate, the carbon could serve as a template for formation of a porous metal oxide (ceramic), from which the carbon is eventually removed.

A Carbon Material Is Partly Oxidized to obtain graphite oxide, which is treated with a metal chloride, then heated in a reducing, oxidizing, or inert environment to obtain one of three types of end products.

Aspects of a related older method were described in several previous articles in NASA Tech Briefs, including "Iron-Containing Carbon Materials Made From Graphite Fluoride" (LEW-16432), Vol. 22, No. 5 (May 1998), page 46 and "Modification of Carbon Fibers for Higher Young's Modulus" (LEW-15847) NASA Tech Briefs, Vol. 21, No. 4 (April 1997), page 56. The corrosiveness and toxicity of fluorine and the general difficulty and high cost of synthesizing graphite fluoride make the older method unattractive. Among the advantages of the present method are that in comparison with graphite fluoride, graphite oxide is safer and can be made more easily (under lower temperatures and otherwise milder conditions) and at lower cost.

Denoted loosely as graphite oxide (or sometimes as graphitic oxide or graphite acid), CO_x is a yellow-brown material that was first synthesized in 1859. In most of the known procedures for synthesizing CO_x, graphite is treated with oxidizing mixtures that contain concentrated acids and oxidizing materials. One such procedure, published in 1958, involves the treatment of graphite with an initially water-free mixture of concentrated sulfuric acid, sodium nitrate, and potassium permanganate. This procedure was used to prepare CO_x for use in initial experiments to demonstrate the present method of synthesizing carbon-based materials containing metals and oxides.

The figure illustrates a generic process for making a carbon-based material containing a metal or metal oxide according to the present method. The starting carbon material can be crystalline graphite, amorphous carbon, or graphitized carbon in fiber or powder form. The carbon material is treated as described above to obtain CO_x, which is then exposed to a metal chloride at a temperature between ambient and 200 °C. The metal chloride can be in the form of a solution, a pure liquid, a pure vapor, or a mixture of two or more of these forms. The resulting intermediate product, denoted "C(M,O,Cl)," consists of carbon filled with the metal, chlorine, and oxygen in various proportions.

Heating the C(M,O,Cl) in air at a temperature >300 °C causes oxidation and consequent removal of the carbon and chlorine, yielding a porous metal oxide. Heating the C(M,O,Cl) in a reducing environment yields porous carbon containing metal particles. Heating the C(M,O,Cl) in an inert atmosphere (e.g., N₂or Ar) at a temperature between 700 and 1,200 °C removes some or all of the chlorine, yielding a porous carbon containing a metal oxide.

This work was done by Ching-cheh Hung of Lewis Research Center. Inquiries concerning rights for the commercial use of this invention should be addressed to