Abstract: In an improved electrochemical fuel cell assembly, a reactant flow path extends substantially linearly across the electrochemically active area of an electrode. The electrode has an in-plane nonuniform structure in its electrochemically active area as the active area is traversed in the direction of the substantially linear reactant flow path. Embodiments in which the structure of the fuel cell electrode varies substantially symmetrically along the reactant flow path are particularly preferred in fuel cells in which the flow direction of a reactant is periodically reversed.

Abstract: Carbon-supported catalysts are frequently employed in the electrodes of solid polymer fuel cells in order to make efficient use of the catalyst therein. The catalyst utilization in the electrode and the fuel cell performance can be further improved by introducing acidic surface oxide groups on the carbon-supported catalyst. The introduction of acidic surface oxide groups on the carbon-supported catalyst can be accomplished by treating the carbon-supported catalyst with a suitable acid, such as nitric acid, before incorporating the carbon-supported catalyst in a fuel cell electrode. The present technique is particularly suitable for use in solid polymer fuel cell cathodes.

Abstract: The measuring range of a fuel cell based concentration sensor can be extended by decreasing the load across the fuel cell terminals and by increasing the amount of oxidant supplied to the fuel cell. In this way, such a sensor avoids saturation, for example, when measuring methanol concentrations from 0 M to over 4 M in liquid aqueous solution. Such a sensor is suitable for use in measuring fuel concentrations in the recirculating fuel stream of certain fuel cell stacks (for example, direct methanol fuel cell stacks).

Abstract: In a solid polymer fuel cell series, various circumstances can result in a fuel cell being driven into voltage reversal by other cells in the series stack. For instance, cell voltage reversal can occur if that cell receives an inadequate supply of fuel (for example, fuel starvation). In order to pass current during fuel starvation, reactions other than fuel oxidation may take place at the fuel cell anode, including water electrolysis and oxidation of anode components. The latter may result in significant degradation of the anode. Such fuel cells can be made more tolerant to cell reversal by promoting water electrolysis over anode component oxidation at the anode. This can be accomplished by enhancing the presence of water in the anode catalyst layer through modifications to the anode structure or anode composition near or in the catalyst layer.

Abstract: The activity of catalysts used in promoting the oxidation of certain oxidizable species in fluids can be enhanced via electrochemical methods, e.g., NEMCA. In particular, the activity of catalysts used in the selective oxidation of carbon monoxide can be enhanced. A purification system that exploits this effect is useful in purifying reformate supplied as fuel to a solid polymer electrolyte fuel cell stack. The purification system comprises an electrolytic cell with fluid diffusion electrodes. The activity of catalyst incorporated in the cell anode is enhanced.

Abstract: The electrocatalysts in certain fuel cell systems can be poisoned by impurities in the fuel stream directed to the fuel cell anodes. Introducing a variable concentration of oxygen into the impure fuel stream supplied to the fuel cells can reduce or prevent poisoning without excessive use of oxygen. The variation may be controlled based on the voltage of a carbon monoxide sensitive sensor cell incorporated in the system. Further, the variation in oxygen concentration may be periodic or pulsed. A variable air bleed method is particularly suitable for use in solid polymer fuel cell systems operating on fuel streams containing carbon monoxide.

Abstract: A method detects fluid leaks within a fuel cell assembly. The method comprises (a) introducing a first supply fluid to a first fluid passage within the fuel cell assembly, wherein the first supply fluid comprises a tracer; (b) introducing a second supply fluid to a second fluid passage within the fuel cell assembly, wherein in the absence of a leak in the first fluid passage, the second fluid passage is fluidly isolated from the first fluid passage; and (c) monitoring a second fluid exhaust stream exiting from the second fluid passage and detecting when a concentration of the tracer is present within the second fluid exhaust stream.

Abstract: A fuel cell fluid distribution layer, in one embodiment, comprises perforated graphite foil. The fluid distribution layer can have one or more reactant flow field channels formed in one or both major surfaces, one or more manifold openings, conductive filler on one or both major surfaces, conductive filler at least partially filling some or all perforations and/or an electrocatalyst one or both major surfaces.

Abstract: Application of two-dimensional materials (TDMs) that are exfoliated transition metal dichalcogenides in electrochemical fuel cells to remove contaminants that are harmful to the fuel cells; to effect proper transport and containment of various fluids in fuel cells to achieve proper and efficient operation; to protect various surfaces and materials commonly comprised in or used for fuel cells and critical to their operation; and to purify and lower the freezing point of cooling water used for the fuel cell stacks. Disclosed are methods whereby the TDM is used as a barrier to prevent unwanted crossover (between electrodes through a polymer electrolyte membrane or PEM) of chemical species; where the TDM is used to coat and/or encapsulate catalyst particles, carbon catalyst support, PEMs, and chemical or metal hydrides, to protect the same from unwanted exposure to chemical species; and where the TDM is used to purify and lower the freezing point of fuel cell stack cooling water.

Abstract: A method of detecting transfer leaks within a solid polymer electrolyte fuel cell stack comprises: supplying fuel or inert gas to the oxidant manifold(s) of the stack at a first pressure; supplying the other of fuel or inert gas to the fuel manifold(s) at a second pressure greater than or equal to the first pressure; optionally supplying fuel to the coolant manifold(s) at a third pressure; applying a potential difference across at least one of the fuel cell assemblies; and measuring the transfer current across the fuel cell assembly or assemblies. A corresponding apparatus detects transfer leaks within solid polymer electrolyte fuel cells stacks.

Abstract: An electrochemical fuel cell is operated with periodic reactant starvation at either or both electrodes. Periodic reactant starvation conditions cause a change in the potential of the starved electrode and may result in the removal of electrocatalyst poisons and in improved fuel cell performance. This technique may have other beneficial effects at the electrodes, including performance improvements due to water management effects or localized heating effects at the starved electrode. In a preferred method, while successive localized portions of a fuel cell electrode are periodically reactant starved, the remainder of the fuel cell electrode remains electrochemically active and saturated with reactant such that the fuel cell is able to continue to generate power.

Abstract: The present invention relates to improving the overall efficiency of a fuel cell system by reducing parasitic power consumption. A controller is programmed to decrease oxidant stoichiometry until oxidant starvation is detected or until oxidant stoichiometry is about one. When oxidant starvation is detected, the oxidant stoichiometry is increased until oxidant starvation is no longer detected. The fuel cell system employs a sensor for detecting an operational characteristic such as voltage output, or oxygen or hydrogen concentration in the cathode exhaust stream. The controller uses the operational characteristic to calculate oxidant stoichiometry or to determine when there is oxidant starvation at the cathode.

Abstract: In an improved electrochemical fuel cell assembly, a reactant flow path extends substantially linearly across the electrochemically active area of an electrode. The electrode has an in-plane nonuniform structure in its electrochemically active area as the active area is traversed in the direction of the substantially linear reactant flow path. Embodiments in which the structure of the fuel cell electrode varies substantially symmetrically along the reactant flow path are particularly preferred in fuel cells in which the flow direction of a reactant is periodically reversed.

Abstract: A fuel cell comprises a pair of separator plates and a pair of fluid distribution layers interposed between the separator plates. At least one of the fluid distribution layers comprises a sealing region and an electrically conductive, fluid permeable active region, and a polymeric material extending into each of the sealing region and the active region. An ion exchange membrane is interposed between at least a portion of the fluid distribution layers, and a quantity of electrocatalyst is interposed between at least a portion of each of the fluid distribution layers and at least a portion of the membrane, thereby defining the active region. Melt-bonding the thermoplastic and/or other polymeric material in the sealing region renders the at least one fluid distribution layer substantially fluid impermeable in a direction parallel to the major planar surfaces.

Abstract: An electrically conductive, substantially fluid impermeable fuel cell separator plate comprises a substantially planar major surface for facing a fluid permeable fuel cell electrode, a fluid inlet through which a fluid may be directed to the planar major surface, a fluid outlet through which fluid may be removed from the planar major surface, and at least one discrete fluid distribution feature, such as a channel, formed in the planar major surface. Within the thickness of the plate, the fluid distribution feature is fluidly isolated from the fluid inlet and the fluid outlet, such that in a fuel cell assembly the reactant fluid must pass through the adjacent fluid permeable electrode to travel between the discrete fluid distribution feature and each of the fluid inlet and the fluid outlet.

Abstract: A method of commencing operation of a fuel cell system which includes a fuel reformer is provided. During a start-up period, the same fuel which is used in the feedstock to the reformer is directed to at least a portion of the fuel cells in the system. These fuel cells provide output power by direct oxidation of the fuel, at least until the reformer is operational, producing a hydrogen-containing gas stream suitable for the fuel cells. Thus, useful output power can be obtained from the system without the delay typically associated with start-up of the reformer.

Abstract: Fluid diffusion layers with favorable mechanical and electrical properties are prepared for fuel cell electrodes by impregnating a porous carbonaceous web with a carbonizable polymer having pyrrolidone functionality and then carbonizing the pyrrolidone polymer. The polymer having pyrrolidone functionality is stabilized against vaporization by use of an oxidization step prior to carbonization. The fluid diffusion layers are particularly suitable for use as gas diffusion layers in solid polymer electrolyte fuel cells.

Abstract: A fuel cell comprises a pair of separator plates and a pair of fluid distribution layers interposed between the separator plates. At least one of the fluid distribution layers comprises a sealing region and an electrically conductive, fluid permeable active region, and a thermoplastic polymeric material extending into each of the sealing region and the active region. An ion exchange membrane is interposed between at least a portion of the fluid distribution layers, and a quantity of electrocatalyst is interposed between at least a portion of each of the fluid distribution layers and at least a portion of the membrane, thereby defining the active region. Melt-bonding the thermoplastic material in the sealing region renders the at least one fluid distribution layer substantially fluid impermeable in a direction parallel to the major planar surfaces.

Abstract: An improved fuel cell anode structure comprises a substrate and a first carbon-based component. The first carbon-based component exhibits little or no resistance to corrosion. When said anode structure is incorporated into a membrane electrode assembly, the membrane electrode assembly is tolerant to incidences of cell voltage reversal.

Abstract: A method of controlling the temperature within an electrochemical fuel cell stack comprises introducing a reactant fluid stream comprising both a heat transfer liquid and a reactant into a fuel cell assembly such that the reactant fluid stream contacts an electrode. The heat transfer liquid is other than water. Preferably, the method further comprises recirculating heat transfer liquid which is in the reactant exhaust stream, typically via a heat exchanger, and re-introducing it into the fuel cell assembly in the reactant fluid stream. The recirculated heat transfer liquid may be directed to a reservoir which in turn supplies heat transfer liquid to the reactant fluid stream as it is needed. In a further embodiment, the method may comprise using the heat transfer liquid to heat a fuel cell stack to a desired operating temperature rather than cooling the stack.