Fuel cell system and fuel cell system diagnosis method

#This is a 371 national phase application of PCT/IB2011/003229 filed 16 Dec. 2011, claiming priority to Japanese Patent Application No. 2010-282983 filed 20 Dec. 2010, the contents of which are incorporated herein by reference.

#1. Field of the Invention

#The invention relates to a fuel cell system incorporating a steam generation system that has an evaporating portion for generating steam for fuel reforming from raw material water (water as a raw material), and relates to a fuel cell system diagnosis method.

#Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

#FIG. 1 is a block diagram conceptually illustrating the configuration of a fuel cell system of the first example embodiment of the invention;

#FIG. 2 is a graph illustrating how the value of each parameter changes in a state where the power generation of the fuel cell system of the first example embodiment is suspended;

#In example embodiments of the invention, a determination process is executed while feeding a cathode fluid (gas containing oxygen, such as air) to the cathodes in the fuel cell stack. At this time, the cathodes of the respective fuel cells of the stack are cooled by the cathode fluid and thus prevented from being heated excessively. In this case, further, it is considered that the oxygen concentration at the cathodes in the fuel cell stack increases and thus the electric potential of the cathodes increases to be closer to the standard electrode potential of oxygen (+1.229 Vvs.SHE), and thus the electric potential difference between the cathodes and the anodes increases, and therefore the open circuit voltage (OCV) of the fuel cell stack increases, making it easier to detect an increase in the open circuit voltage of the fuel cell stack.

#The block diagram of FIG. 1 schematically shows the configuration of a fuel cell system of the first example embodiment of the invention. The fuel cell system of the first example embodiment is provided with a stack 12 of fuel cells 1 each having an anode 10 to which an anode fluid (gas containing hydrogen) is fed through an anode fluid passage 73 and a cathode 11 to which a cathode fluid (a gas containing oxygen, such as air) is fed via a cathode fluid passage 70, an evaporating portion 2 that evaporates a raw material water (water as a raw material) which is in a liquid phase, which is fed via a water feed passage 8, and thereby generates steam which is in a gas phase, the water feed passage 8 that delivers the raw material water, which is pure water, to the evaporating portion 2 using a pump 80 (water deliverer), a reforming portion 3 that produces the anode fluid by performing steam-reforming on a fuel (e.g., manufactured gas, liquefied petroleum gas (LPG)) using the steam generated at the evaporating portion 2, a combustion portion 105 that heats the evaporating portion 2 and the reforming portion 3, the pump 80 (water deliverer) that is provided on the water feed passage 8 and delivers the raw material water to the evaporating portion 2, a heat exchanger 76 that performs heat-exchange between a high-temperature exhaust gas from the stack 12 and the water in a water storage, and a controller 100 that controls various devices including the pumps 80, 60, and 71. The anode-off gas discharged from the anodes 10 is delivered to the combustion portion 105 via a passage 103, while the cathode-off gas discharged from the cathodes 11 are delivered to the combustion portion 105 via a passage 104. The combustion portion 105 combusts the anode-off gas and the cathode-off gas to heat the evaporating portion 2 and the reforming portion 3. A combustion exhaust gas passage 75 is connected to the combustion portion 105, and the combustion exhaust gas, containing both the gas burned in the combustion at the combustion portion 105 and unburned gas, is released to the atmosphere via the combustion exhaust gas passage 75.

#The anodes 10 each have a catalyst for facilitating anode reactions, and the cathodes 11 each have a catalyst for facilitating cathode reactions. These catalysts may each be a transition-metal-based catalyst, preferably a noble-metal-based catalyst. The reforming portion 3 and the evaporating portion 2 are arranged adjacent or close to each other. Gaseous fuel is fed to the reforming portion 3 via the evaporating portion 2 using the pump 60 (fuel deliverer) at the fuel passage 6. The multiple fuel cells 1 constituting the stack 12 are electrically connected in series to obtain a high voltage. The cathode fluid (air) is fed to the cathodes 11 of the respective fuel cells 1 from the pump 71 (cathode pump) (cathode fluid deliverer) at the cathode fluid passage 70. The combustion portion 105 is provided to heat the evaporating portion 2 and the reforming portion 3. Thermal insulation wall 19 are provided to surround the reforming portion 3, the evaporating portion 2, the stack 12, the combustion portion 105, etc. to maintain their temperatures, whereby a power generator module 18 of which the temperature becomes high is formed.