Fundamental Research on Increasing Output Power Density of Phosphoric Acid Fuel Cel

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Unstable performance of phosphoric acid fuel cells was found at high output power operation. Purposes of this research are to explicate these phenomena and to develop new methods for increasing the output power density. Main rsults are as follows,(1) Unstable phenomena occur early in operation of high output power density when a strong wet-proofed catalyst layr of a cathode is used. It is neccessary to penetrate phosphoric acid into the catalyst layr before operation.(2) In order to accelerate the penetration of the acid, five methods are tested such as vacuum impregnation, super-sonic penetration, alcohol-added penetration, electric capillary penetration and condenced acid penetration. Former two methods using external mechanical force are not so effective, whereas the latter three methods related to capillary force are effective and practical.(3) Unstable phenomena have features of propagation of oxgen dissipated electrode area. Diagnostic tests for acid penetration are possible by using oxgen poor gas.(4) Periodic change of acid concentration assuming load change or start-stop operation affect cell performance decay.