The conventional gaseous diffusion fuel cell utilizes an anode half reaction employing hydrogen or a mixture of hydrogen, carbon dioxide and carbon monoxide formed from fossil fuel by reforming with steam. The cathodes are usually operated using oxygen from the air. At the temperatures and pressures utilized in the state-of-the-art fuel cells, the rate of reaction of the oxygen at the cathode is low and requires the use of expensive catalysts. Even with the use of catalysts, the performance of these fuel cells may be less than desired. Problems associated with catalyst decay, as well as capital investment required in maintaining large amounts of precious metal catalyst in the fuel cells, would be desirably avoided. It has been proposed to utilize some cathode reactions other than the direct reduction of oxygen. One approach has been the use of nitric acid as the cathode reactant with external regeneration of the nitric acid from the NO and H.sub.2 O formed in the cathode reaction. While this approach has promise, the nitric acid is utilized as a liquid and the well-developed technology associated with gaseous diffusion electrodes cannot be utilized. Also, the regeneration of the nitric acid from the nitric oxide and water is a difficult reaction requiring gas-liquid contact which causes a substantial amount of foaming and other processing problems.
According to this invention, we have found that a conventional gaseous diffusion, acid electrolyte fuel cell electrode can be operated using NO.sub.2, either alone or in conjunction with oxygen, as the oxidizing agent in a manner which permits the attainment of higher power levels without the use of catalysts at the cathode. In addition, the regeneration of the NO.sub.2 from the NO is a gas-gas contact reaction which can be conveniently carried out in an external regenerator.
Accordingly, it is an object of this invention to provide a fuel cell cathode operating with NO.sub.2 as the oxidizing agent.
It is another object of this invention to provide a fuel cell cathode operating with nitric oxide and oxygen as an oxidizing agent.
It is another object of this invention to provide a method for operating a gaseous diffusion fuel cell electrode using oxides of nitrogen as the oxidizing agent with recycling of the oxides of nitrogen from external regeneration.
USPTO Backgrounds
USPTO Backgrounds