Combined current and temperature mapping in an air-cooled, open-cathode polymer electrolyte fuel cell under steady-state and dynamic conditions

Abstract

In situ diagnostic techniques provide a means of understanding the internal workings of fuel cells so that improved designs and operating regimes can be identified. Here, for the first time, a combined current density and temperature distributed measurement system is used to generate an electro-thermal performance map of an air-cooled, air-breathing polymer electrolyte fuel cell stack operating in an air / hydrogen cross-flow configuration. Analysis is performed in low-and high-current regimes and a complex relationship between localised current density, temperature and reactant supply is identified that describes the way in which the system enters limiting performance conditions. Spatiotemporal analysis was carried out to characterise transient operations in dead-ended anode / purge mode which revealed extensive current density and temperature gradients. KeywordsCurrent mapping; temperature mapping; air-breathing fuel cell; performance optimisation; spatiotemporal electro-thermal analysis. Current mapping was first introduced by Cleghorn and Derouin[1] and Brett et al. [2,3], using printed circuit board (PCB) technology to produce segmented current collector plates, along with Stumper et al.[4], using segmented membranes. This technique shows that significant current density gradients can be generated as a result of fuel and oxidant depletion. Other techniques have proven the value of localised current measurements, including segmented PCBs [1,3,5-9], segmented current collector plates [10-12], shunt resistors [13-15] and Hall effect sensors [16-21]. Measurements have also been performed at sub-millimetre resolution [22,23], investigating the gradients across the land and channel areas. Most studies highlighted uneven performance under high current density, uneven fuel consumptions [2,5,6,14], the crucial influence of the operating conditions [3,13,19], stoichiometric ratios [8,11,12,20], fuel orientations [6,13], water management [10], CO electro-oxidation [7] and CO poisoning [24,25] distribution.Temperature distribution has also been extensively studied, identifying areas of higher electrochemical activity, hot spot formation and fuel depletion. Thermocouples can provide a crude measure of temperature inside fuel cells [16,17,26,27] but have accuracy limited to ±1 o C and cannot provide high spatial resolution. Moreover, thermocouples need to be inserted inside the fuel cell, which often requires design modifications. In contrast, infrared thermal imaging can provide very high spatial and temperature resolution [28][29][30][31][32][33][34], yet it typically requires use of specially designed fuel cells with a window transparent to infrared radiation, or is otherwise confined to measurement of the outer surface of a cell or stack.(highlighted using neutron imaging [37,38]) and nitrogen accumulation (measured via off-gas analysis [37,42,43]).Meyer et al. [37] reported an increase of the overall temperature and ohmic resistance in dead-ended mode. Eventually, local current density could be much higher than the...

Nitrogen Blanketing and Hydrogen Starvation in Dead-Ended-Anode Polymer Electrolyte Fuel Cells Revealed by Hydro-Electro-Thermal Analysis

“…Initiated by Cleghorn et al 4 Combined temperature and current mapping studies allow the impact and interactions of these two parameters on the overall performance to be assessed [17,20,[31][32][33]. However, capturing the water content may provide insights on how the temperature and current density fluctuate, and therefore should ideally be measured at unison.…”

“…In air-cooled, open-cathode systems the temperature depends on the voltage and current density [67,78], air cooling flow rate [73,76], and heat transfer characteristics of the stack. In practice, the temperature management is normally performed using a single-point thermocouple inserted in the centre of the cell [18,29,75], or for development work using multiple microthermocouple measurements at various locations in the fuel cell [15,79,80].The authors have previously studied dead-ended operation, on a cell with dry fuel and air, using techniques such as mass spectrometry (revealing nitrogen 6 accumulation), thermal imaging and electrochemical impedance spectroscopy [29], as well as combined current and temperature mapping, revealing large gradients between the fuel inlet and exhaust [33].Here, we present the results obtained by applying the recently developed hydroelectro-thermal analysis [57] technique to an air-cooled, open-cathode fuel cell operated in dead-ended anode mode, to capture dynamic operation, combining current and temperature mapping with water mapping during dead-ended operation. …”

The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

“…Further details on the approach can be found in previously published work. [80] Neutron imaging facility The neutron beam is converted into a photonic field by the scintillator, whereby the intensity of evoked light is proportional to the intensity of the incoming neutron beam [56].…”

“…Here, we present the results obtained by applying a novel metrology approach to an air-cooled, open-cathode two-cell stack, operated without external humidification: the technique combines water visualisation using neutron imaging, with current and temperature mapping using a printed circuit board (PCB) sensor plate [80]. The effect and relationship between the key hydro-electro-thermal properties allows important new insight into this type of fuel cell to be achieved.…”

Development of a polymer electrolyte fuel cell dead-ended anode purge strategy for use with a nitrogen-containing hydrogen gas supply

“…3a) allows determination of a region of constant change between 0.18 A cm -2 and 0.36 A cm -2 which is defined as the area of interest for the remaining study. This coincides with the centre of the ohmic region and thus ensures avoidance of mass transport limitations which would negatively impact upon any deadended event [32,33]. Secondly, in dead-ended mode, the impact of changing the H2:N2 ratio on the mean cell voltage was investigated at a constant load of 0.36 A cm -2 ( Fig.…”