DOE Hydrogen and Fuel Cells Program FY 2014 Annual
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V.F.2 The Effect of Airborne Contaminants on Fuel Cell Performance and Durability Fiscal Year (FY) 2014 Objectives Jean St-Pierre (Primary Contact), Yunfeng Zhai, Quantify spatial variability of performance loss and Junjie Ge, Tatyana Reshetenko, Michael Angelo, identify principal poisoning mechanism for at least four Trent Molter1, Leonard Bonville1, Ugur Pasaogullari1, different contaminants. Xiaofeng Wang1, Jing Qi1, Ozan Ozdemir1, 1 1 Amman Uddin , Navvab Khajeh-Hosseini-Dalasm , Technical Barriers Jaehyung Park1, Selvarani Ganesan1, William Collins2, Silvia Wessel3, Tommy Cheng3 This project addresses the following technical Hawaii Natural Energy Institute barriers from the Fuel Cells section of the Fuel Cell 1680 East-West Road Technologies Office Multi-Year Research, Development, and Honolulu, HI 96822 Demonstration Plan: Phone: (808) 956-3909 Email: [email protected] (A) Durability (B) Cost DOE Managers Nancy Garland (C) Performance Phone: (202) 586-5673 Email: [email protected] Technical Targets Reg Tyler The following 2017 technical targets for automotive Phone: (720) 356-1805 Email: [email protected] applications, 80-kWe (net) integrated transportation fuel cell power systems operating on direct hydrogen, are considered: Technical Advisor • Durability: 5,000 hours in automotive drive cycle Tom Benjamin Phone: (630) 252-1632 • Cost: $30/kWe Email: [email protected] • Performance: 60% energy efficiency at 25% of rated Contract Number: DE-EE0000467 power The effects of specific airborne contaminants are studied Subcontractors 1 including a commercially relevant low-cathode-catalyst University of Connecticut, Storrs, CT loading and the resulting information will be used to impact 2 WPCSOL, East Windsor, CT 3 both preventive measures and recovery procedures: Ballard Power Systems, Burnaby, BC, Canada • Airborne contaminant tolerance limits to support the Project Start Date: April 1, 2010 development of filtering system component specifications Project End Date: March 31, 2015 and ensure negligible fuel cell performance losses • Fuel cell stack material, design, operation, or maintenance changes to recover performance losses Overall Objectives derived from contamination mechanisms • Identify and mitigate the adverse effects of airborne FY 2014 Accomplishments contaminants on fuel cell system performance and durability • Completed characterization database using ex situ • Provide contaminants and tolerance limits for filter and in situ diagnostic techniques for seven airborne specifications (preventive measure) contaminants and one foreign cation to support the development of contamination mechanisms and recovery • Identify fuel cell stack’s material, design, operation or procedures that diminish the contamination impact on maintenance changes to remove contaminant species and system durability and performance recover performance (recovery measure) • Assessed the effect of a decrease in cathode catalyst loading from 0.4 to a commercially relevant 0.1 mg Pt cm−2 on the steady-state cell voltage loss during contamination for seven airborne contaminants FY 2014 Annual Progress Report V–133 DOE Hydrogen and Fuel Cells Program V.F Fuel Cells / Impurities St-Pierre – Hawaii Natural Energy Institute • Developed a transient, one-dimensional, through for the case of foreign cations, present experimental methods the membrane/electrode assembly plane model for are insufficient to separate the different contributions to cell foreign cation contamination to isolate individual cell performance loss (thermodynamic, kinetic, ohmic, mass performance effects which are not experimentally transport) [2,6,7]. Mathematical modeling is a valuable accessible and advance the understanding of substitute approach. However, existing models either need contamination mechanisms improvement [8] or are incomplete. A separation factor more accurately represents ion exchange processes [9,10] and the • Evaluated and modeled the scavenging effect of product change in oxygen permeability in the ionomer due to the liquid water for two cases, contaminant dissolution presence of a foreign cation has not previously been tackled and contaminant dissolution followed by dissociation [11,12]. reactions, to determine effective contaminant concentrations within the cell and increase the accuracy of cell performance loss correlations APPROACH Impedance spectroscopy was first used to classify G G G G G airborne contaminant effects into different resistance losses to focus subsequent activities. As a second step, more INTRODUCTION detailed information was obtained using other diagnostics methods to unravel contamination mechanisms: rotating The composition of atmospheric air cannot be controlled ring/disc electrode, membrane conductivity cell, segmented and typically includes contaminants, volatile compounds, fuel cell for current/cell voltage distributions over the active as well as ions entrained by liquid water drops in the form area, and gas chromatography/mass spectrometry. Because of rain, mist, etc., especially near marine environments. many of these diagnostics methods are not applicable or are Proton exchange membrane fuel cells operated with ambient irrelevant to foreign ions partly due to their different state air are therefore susceptible to deleterious effects which (in a liquid rather than a gaseous state) and behavior (salt include decreased cell performance and durability [1,2]. precipitation within the fuel cell), other diagnostic methods Numerous air contaminants have not yet been tested in were employed including photography, scanning electron fuel cells and consequently their effects as well as recovery microscopy and energy dispersive X-ray spectroscopy. methods are unknown [2,3]. Furthermore, prevention is Mathematical modeling was also exploited as experimental difficult to achieve because tolerance limits are also missing data obtained with many in situ diagnostic methods are in most cases [2]. This increases the risk of failure for fuel subject to misinterpretations because the presence of foreign cell systems and thus jeopardizes their introduction into ions in the membrane and ionomer affects fuel cell resistance the market. losses that invalidate assumptions needed to separate Airborne contaminants and foreign ions have previously individual performance loss contributions. been selected using a cost-effective two-tiered approach The cathode catalyst loading impact was investigated combining qualitative and quantitative criteria [3]. under a single set of operating conditions. The scavenging Automotive fuel cells are used under a wide range of effect of liquid water was studied with an inactive fuel cell operating conditions resulting from changes in power to minimize the presence of side reactions. The contaminant demands (drive cycle). Temperature and current density was carried inside the fuel cell with a saturated and inert impact fuel cell contamination the most [4]. The effect of carrier gas whereas the water was transferred from the contaminant concentration is also particularly important. anode compartment by thermo-osmosis [13]. Water transfer Contaminant threshold concentrations for predetermined was facilitated by avoiding the use of a gas diffusion layer fuel cell performance losses were determined [5] to facilitate on the anode side. The amount of water transferred was the definition of air filtering system tolerances (prevention). measured by collection at the fuel cell outlet. Methanol and The effect of inlet reactant relative humidity is linked to the sulfur dioxide were used as model contaminants that either presence of liquid water within the cell which in turn may only dissolve in water or hydrolizes and reacts to form affect the effective contaminant concentration by dissolution a bisulfite ion. For methanol, outlet water samples were and entrainment in water drops. This scavenging effect has analyzed by cyclic voltammetry and total organic carbon. not previously been considered. Cell design parameters also For sulfur dioxide, outlet gas samples were analyzed by gas impact the severity of contamination. However, the effect chromatography. of catalyst loading, which is important for cost reduction, has only been determined for a few species [2]. It is likely that prevention will be insufficient to avert all contaminant RESULTS effects. Therefore, recovery procedures will also be needed, Table 1 summarizes key metrics obtained from the in and these are more easily devised by understanding the situ and ex situ diagnostic tests. Electrochemical catalyst origins of the contaminant effects (mechanisms). However areas and peroxide production currents indicate that the DOE Hydrogen and Fuel Cells Program V–134 FY 2014 Annual Progress Report St-Pierre – Hawaii Natural Energy Institute V.F Fuel Cells / Impurities TABLE 1. Summary of Ex Situ And In Situ Diagnostic Methods’ Results for Seven Airborne Contaminants and One Foreign Cation To Resolve Contamination Mechanisms Contaminant Kinetic Current Electrochemical H2O2 Current Membrane Dimensionless Local Current Contaminant (% loss in air at Catalyst Area (% gain in air Conductivity (maximum % loss and gain in air at 80°C) Conversion b 30°C and 0.9 V (% loss in N2 at at 30°C and 0.5 (% loss at 80°C and (% in air at 80°C) vs RHE) 30°C) V vs RHE)a 50% relative humidity) Contamination Phase Recovery Phase Acetonitrile 79-84 >76 850-1300 0 Step change followed by a cell Traveling current wave 20 to 45 for 0.55 to (16.9 mM) (16.9 mM) (16.9 mM) (100 ppm), potential triggered