In-situ diagnostic tools for hydrogen transfer leak characterization in PEM fuel cell stacks part I: R&D applications

Abstract

h i g h l i g h t sIn-situ diagnostic tool to quantify hydrogen transfer leaks in PEM fuel cell stacks. Closed form relationship for the rate of hydrogen transfer leak. Requires hydrogen/nitrogen supply to anode/cathode with anode overpressure. Requires pressure, flow, temperature, humidity, and OCV measurements. Accurately estimates leak in each cell of a stack, suitable for R&D applications. a b s t r a c tThis paper describes a diagnostic tool for in-situ characterization of hydrogen transfer leak in individual cells of a Polymer Electrolyte Membrane (PEM) fuel cell stack, suitable for Research and Development (R&D) applications. The technique is based on supplying hydrogen and nitrogen to the anode and cathode of a PEM fuel cell stack while maintaining a prescribed anode overpressure. Under these conditions, hydrogen crosses over from the anode to the cathode, and the Open Circuit Voltage (OCV) represents the ratio of hydrogen partial pressure in the two electrodes. It is shown that by measuring temperature, pressure, flow, humidity, and individual OCVs, the proposed technique can accurately estimate the rate of hydrogen transfer leak in individual cells of a PEM fuel cell stack. This diagnostic tool is suitable for characterizing hydrogen transfer leaks during fuel cell R&D, as it only requires gasses and measurements that are readily available on fuel cell test stations, and does not need disassembling or modifying the fuel cell stack.

Voltammetric and galvanostatic methods for measuring hydrogen crossover in fuel cell

“…In this manner, all the hydrogen permeating through PEM is converted into a limiting hydrogen oxidation current (i.e., hydrogen crossover current), which is equivalent to the hydrogen crossover rate, and the key to the measurement is to isolate this component from the total current. Linear sweep voltammetry (LSV) is the most commonly used potential sweep technique in measuring hydrogen crossover (Brooker et al, 2012;Giner-Sanz et al, 2014;Huang et al, 2013;Hwang et al, 2018;Kocha et al, 2006;Niroumand et al, 2015;Wasterlain et al, 2011), but different scan rates always give rise to inconsistent results. Another electroanalytical method as a derivative of LSV is staircase voltammetry (also called as potential step method [PSM]), in which the potential sweep is a series of stair steps, and it has been employed in electrochemical measurements of hydrogen crossover (Schoemaker et al, 2014).…”

Real-time monitoring of proton exchange membrane fuel cell stack failure

“…Heterogeneous distributions of reactants within the FC stack can lead to uneven mass transport losses and the degradation of the membrane electrode assembly (MEA) through membrane thinning, while the localised build-up of water on the FC MEA results in droplet formation in the flow fields of the bipolar plates [22]. Water build-up can eventually lead to cell flooding and the formation of hotspots which can cause the formation of pin-holes, a major cause of FC failure [23].…”

“…Post-mortem open circuit voltage (OCV) monitoring has been used by several authors to identify failed cells within a stack, details of which have been used to characterise pinholes [22,23,32], whilst others have used segmented single cells to investigate differences in the current density in the presence of a pin-hole [13]. Commonly, small stacks of 5-18 cells are studied [33,34]; however, studies on automotive systems containing hundreds of cells are rarely reported.…”

Empirical membrane lifetime model for heavy duty fuel cell systems

“…The amount of hydrogen that leaksthrough the membrane at a given dP to the cathode was measured as voltage, which was correlated to a specific leak rate. The relationship between the leak rate from anode to cathode and the flow rates and pressures is described below [113].where L is the leak rate (cm 3 -H 2 min -1 ), P c is the pressure at cathode, P a is the pressure at anode, Q N is the nitrogen flow rate at cathode, Q w is the water flow rate at the cathode, Q H is the hydrogen flow rate at cathode exit, P w is the saturation vapor pressure of water, Q H = L is the steady state mass balance on H 2 .The following linear relationship between leak rates and pressure is assumed: …”

“…The amount of hydrogen that leaksthrough the membrane at a given dP to the cathode was measured as voltage, which was correlated to a specific leak rate. The relationship between the leak rate from anode to cathode and the flow rates and pressures is described below [113].…”