Tolerance of non-platinum group metals cathodes proton exchange membrane fuel cells to air contaminants

Abstract

The effects of major airborne contaminants (SO 2 , NO 2 and CO) on the spatial performance of Fe/N/C cathode membrane electrode assemblies were studied using a segmented cell system.The injection of 2-10 ppm SO 2 in air stream did not cause any performance decrease and redistribution of local currents due to the lack of stably adsorbed SO 2 molecules on Fe-N x sites, as confirmed by density functional theory (DFT) calculations. The introduction of 5-20 ppm of CO into the air stream also did not affect fuel cell performance. The exposure of Fe/N/C cathodes to 2 and 10 ppm NO 2 resulted in performance losses of 30 and 70-75 mV, respectively.DFT results showed that the adsorption energies of NO 2 and NO were greater than that of O 2 , which accounted for the observed voltage decrease and slight current redistribution. The cell performance partially recovered when the NO 2 injection was stopped. The long-term operation of the fuel cells resulted in cell performance degradation. XPS analyses of Fe/N/C electrodes revealed that the performance decrease was due to catalyst degradation and ionomer oxidation.The latter was accelerated in the presence of air contaminants. The details of the spatial performance and electrochemical impedance spectroscopy results are presented and discussed. stream [7,8,[10][11][12][13][14][15][16][17][18][19]. The effects of nitrogen-containing air contaminants (NO x , NH 3 ) were found to be moderate and recoverable [7,8,[10][11][12][13][14][15][16][20][21][22][23][24].However, there have been limited studies on the impact of air contaminants, such as CO, SO 2 , and NO x , on the performance of non-PGM catalysts. Impacts of CO on the ORR activity of Fe/N/C catalysts were reported in [25][26][27][28][29][30]. Common precursors for Fe/N/C, such as Fe-porphyrin and Fe-phthalocyanine, are well-known to have a higher affinity for CO than O 2 . Therefore, the Fe-N 4 /C and Fe-N 2 /C sites in catalysts were expected to strongly chemisorb CO. However, it was observed that steric factors of ligands in Fe-porphyrin complexes can reduce affinity to CO or even suppress any CO binding at atmospheric pressure [25,26]. Moreover, studies of Feporphyrin interactions with CO in aqueous solutions by in situ X-ray absorption showed the formation of CO-Fe-porphyrin adduct, which disappeared at a 0.6 V potential, released the CO molecules [27]. Recent studies have showed CO tolerance of iron-containing catalysts [28][29][30].In attempts to identify active sites on Fe/N/C catalysts, CNwas observed to have strong poisoning effects [31][32][33]. The authors indicated that CNbound at an axial position on the sites, inhibiting oxygen reduction and shifting the reaction pathway from 4-electron to 2-electron.Remarkably, catalytic activity was restored after rinsing a poisoned electrode in water [33]. SO 2 tolerance was reported for ORR catalysts wherein Fe was encapsulated in carbon nanotubes [34].Fe/N/C catalysts derived from poly-m-phenylenediamine were found to be insensitive to NO x , whereas oxygen reduction was su...

Progress in the Development of Fe‐Based PGM‐Free Electrocatalysts for the Oxygen Reduction Reaction

“…[70] Additionally, PGM-free ORR electrocatalysts have shown tolerance to anions ( , , ), aromatic compounds (benzene and toluene), urea, methanol and airborne contaminates (SO 2, NO 2 ). [11,71,72] A poisoning study by Zhang et al showed a 20 mV decrease in the RDE half-wave potential (E ½ ) for a Fe-N-C catalyst but no change in E ½ for a metal-free (C-N x ) catalyst upon exposure to CO. [73] By combining their experimental data with DFT studies Zhang et al…”

Gas- and Water-Phase PAHs Emitted from a Single Hydrogen-Oxygen PEM Fuel Cell

“…An H 2 -O 2 PEMFC has the main components of membrane-electrode assembly (MEA), gasdiffusion layer (GDL), and bipolar/end plate (Huang et al, 2006;Lai et al, 2012;Tenson and Baby, 2017). It is common that a PEM is symmetrically sandwiched by anode and cathode to prepare the MEA; moreover, the electrodes usually contain precious metal catalysts (e.g., Pt) (Huang et al, 2006;Lai et al, 2012), Pt-based alloys , or non-platinum group metals (Reshetenko, et al, 2016) supported by carbon materials (e.g., carbon black, fiber, and nanotube) which are also used for the fabrication of bipolar/end plates and GDLs (e.g., carbon paper or cloth) (Tran et al, 2015;Zeis, 2015;Lee and Lee, 2016).…”

Effect of Operating Conditions on PAHs Emission from a Single H2-O2 PEM Fuel Cell

“…The key components of a H 2 -O 2 PEMFC are membrane-electrode assembly (MEA), gas-diffusion layer (GDL), and bipolar/end plate (including carbon/epoxy composite bipolar plates (Huang et al, 2006;Lee and Lee, 2016). The MEA is usually consisted of a PEM (solid electrolyte) and two symmetrical electrodes (anode and cathode) which have precious metal catalysts (e.g., Pt) (Huang et al, 2006;Lai et al, 2012) and non-platinum group metals (Reshetenko, et al, 2016) supported by carbon materials (e.g., carbon black, fiber, and nanotube). Additionally, it is common that the bipolar/end plates and GDLs (e.g., carbon paper (CP) or carbon cloth (CC)) are made using carbon materials (Dicks, 2006;Wissler, 2006;Tran et al, 2015;Zeis, 2015).…”