Fuel cell contaminants reformate

Fuel cell systems often include a reformer that converts hydrogen carbon fuel such as methane or methanol to a hydrogen-rich stream of gas. This stream is then fed to a fuel cell, which generates electric power. However, the reforming process also produces some unwanted trace species, such as CO, H2S, and NH3, which are considered poisonous to PEM fuel cells. Fuel cell contamination caused by these... 

Increasing the pressure in a MCFC system can also increase the likelihood of soot formation and decrease the extent of methane reforming. Both are undesirable. Furthermore, the effect of contaminants on the cell and their removal from a pressurized MCFC system have not been quantified. The increased pressure also will challenge the fuel cell seals (37). 

Natural gas is cleaned of its sulfur contaminants in a fuel cleanup device. Steam is added to the fuel stream prior to being fed to the internally reforming fuel cell. The fuel reacts electrochemically with the oxidant within the fuel cell to produce 3 MW of dc power. 

As an application of Pt nanowires in heterogeneous catalysis, we performed preferential oxidation (PROX) of CO as a test reaction [32]. The PROX reaction is useful for PEM fuel cells for the selective removal of contaminating CO from hydrogen gas, because CO works as a strong catalyst poison for Pt electrode catalysts (Figure 15.24). H2 produced in steam-reforming and the water-gas shift reaction needs further to be purified in the PROX reaction to selectively oxidize a few% CO towards inert CO2 in a H 2-rich atmosphere, to reduce the CO content to <10ppm. Under the PROX conditions, the facile oxidation of H2 to H2O may also occur, thus the catalyst selectivity for CO oxidation over H2 oxidation is an... 

The previously used flow sensor option in research fuel cells were the integrated circuit (IC)-type differential sensors, which were limited by their low tolerance for water contamination. This was a serious limitation in reforming-type fuel cell applications, because the presence of water is essential for the operation of the system, and no protection against water contamination was provided in the smaller and cheaper IC sensors. 

For all fuel cells, except those running on high-purity hydrogen, some form of fuel treatment is required. The main problem with fuel supplies intended for conventional combustion systems is the presence of minor contaminants containing ash-making chemicals and sulfur compounds. In fuel cell applications, the sulfur compounds form corrosive substances that poison the catalysts in the reformer stages and the fuel cell itself. 

PEM fuel cells use a solid proton-conducting polymer as the electrolyte at 50-125 °C. The cathode catalysts are based on Pt alone, but because of the required tolerance to CO a combination of Pt and Ru is preferred for the anode [8]. For low-temperature (80 °C) polymer membrane fuel cells (PEMFC) colloidal Pt/Ru catalysts are currently under broad investigation. These have also been proposed for use in the direct methanol fuel cells (DMFC) or in PEMFC, which are fed with CO-contaminated hydrogen produced in on-board methanol reformers. The ultimate dispersion state of the metals is essential for CO-tolerant PEMFC, and truly alloyed Pt/Ru colloid particles of less than 2-nm size seem to fulfill these requirements [4a,b,d,8a,c,66j. Alternatively, bimetallic Pt/Ru PEM catalysts have been developed for the same purpose, where nonalloyed Pt nanoparticles <2nm and Ru particles <1 nm are dispersed on the carbon support [8c]. From the results it can be concluded that a Pt/Ru interface is essential for the CO tolerance of the catalyst regardless of whether the precious metals are alloyed. For the manufacture of DMFC catalysts, in... 

Adapt catalytic gate field effect transistor (FET) sensors to resolve and detect carbon monoxide (CO) contamination levels from 1-100 ppm in reformer produced hydrogen (H2) fuel for (proton exchange membrane (PEM) fuel cells... 

Much knowledge on the effect of poisons has been generated in connection to reformer-based PEMFC systems. Both for transport as well as for stationary applications, the presence of CO, CO2, NH3 has to be taken into account besides N2 and H2O [100]. For reformer-based systems that are operated dynamically, that is, including many cold starts and load variations, CO concentrations exceed the 10 ppm level frequently [104]. The effect of CO is studied most extensively. For unalloyed platinum electrodes, CO concentrations as low as 10 ppm lead to a performance loss of 100 mV [105] at 70°C. When reformer-based systems are fueled with logistic fuels, such as diesel and kerosene, other contaminants than CO and CO2 are present in the reformate. Especially aromatics and unsaturated hydrocarbons can poison the fuel cell anode fast and irreversibly, even in concentrations so low that they are hardly detectable with state-of-the-art analytics. 

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