Membrane electrode assembly durability is explored for polymer electrolyte membrane electrolyzers, focusing on catalyst (iridium, Ir) degradation at low loading and dynamic operation. Low catalyst loading and high cell potential are critical to observing durability losses over reasonably short experiments, regardless of test profile. While small losses are seen during steady operation, cycling greatly accelerates performance decreases. Ir dissolution mechanistically drives performance loss, thinning the anode catalyst layer and resulting in increasing kinetic losses during extended operation. While morphological changes to the catalyst layer are found, increasing polarization resistance suggests that degradation at the catalyst/ionomer/membrane interface may also contribute. Electrolyzer operation with model wind and solar profiles results in less severe performance losses compared to triangleand square-wave potential cycling due to the lower cycling frequency of the renewable profiles. However, in both cases kinetics dominated the loss, indicating that higher cycling rates accelerate loss and can be used to project the impact of intermittency on device lifetime. These results suggest that performance losses impact electrolyzers' abilities to operate with low catalyst loading and intermittent inputs, and that a combination of component development and system controls are needed to limit potential and performance loss.

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this work, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factor over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in ∼5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO 2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support.

For the first time, a new generation of innovative non-platinum group metal catalysts based on iron and aminoantipyrine as precursor (Fe-AAPyr) has been utilized in a membraneless single-chamber microbial fuel cell (SCMFC) running on wastewater. Fe-AAPyr was used as an oxygen reduction catalyst in a passive gas-diffusion cathode and implemented in SCMFC design. This catalyst demonstrated better performance than platinum (Pt) during screening in “clean” conditions (PBS), and no degradation in performance during the operation in wastewater. The maximum power density generated by the SCMFC with Fe-AAPyr was 167 ± 6 μW cm−2 and remained stable over 16 days, while SCMFC with Pt decreased to 113 ± 4 μW cm−2 by day 13, achieving similar values of an activated carbon based cathode. The presence of S2− and showed insignificant decrease of ORR activity for the Fe-AAPyr. The reported results clearly demonstrate that Fe-AAPyr can be utilized in MFCs under the harsh conditions of wastewater.

Non-Pt-group metal (non-PGM) materials based on transition metal-nitrogen-carbon (M-N-C) and derived from iron salt and aminoantipyrine (Fe-AAPyr) of mebendazole (Fe-MBZ) were studied for the first time as cathode catalysts in double-chamber microbial fuel cells (DCMFCs). The pH value of the cathode chamber was varied from 6 to 11 to elucidate the activity of those catalysts in acidic to basic conditions. The Fe-AAPyr- and Fe-MBZ-based cathodes were compared to a Pt-based cathode used as a baseline. Pt cathodes performed better at pH 6-7.5 and had similar performances at pH 9 and a substantially lower performance at pH 11 at which Fe-AAPyr and Fe-MBZ demonstrated their best electrocatalytic activity. The power density achieved with Pt constantly decreased from 94-99 μW cm(-2) at pH 6 to 55-57 μW cm(-2) at pH 11. In contrast, the power densities of DCMFs using Fe-AAPyr and Fe-MBZ were 61-68 μW cm(-2) at pH 6, decreased to 51-58 μW cm(-2) at pH 7.5, increased to 65-75 μW cm(-2) at pH 9, and the highest power density was achieved at pH 11 (68-80 μW cm(-2) ). Non-PGM cathode catalysts can be manufactured at the fraction of the cost of the Pt-based ones. The higher performance and lower cost indicates that non-PGM catalysts may be a viable materials choice in large-scale microbial fuel cells.

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This work studies the morphology of platinum group metal-free (PGM-free) ironnitrogen-carbon (Fe-N-C) catalyst layers for the oxygen reduction reaction (ORR) and compares catalytic performance via polarization curves. Three different nitrogen-rich organic precursors are used to prepare the catalysts. Using scanning electron microscopy (SEM) and focused ion beam (FIB) tomography, the porosity, Euler number (pore connectivity), overall roughness, solid phase size and pore size are calculated for catalyst surfaces and volumes. Catalytic activity is determined using membrane electrode assembly (MEA) testing. It is found that the dominant factor in MEA performance is transport limitations. Through the 2D and 3D metrics it is concluded that pore connectivity has the biggest effect on transport performance.

In commercial electrolysis, the cost of electricity input drives the cost of hydrogen production. Therefore, electrolysis is typically run at high catalyst loading and constant power input over long periods of time. Lowering water-splitting hydrogen production costs to a level comparable to steam methane reformation requires: coupling electrolysis with low-cost power input (wind, solar) to reduce feedstock costs; and dropping catalyst loading to reduce the capital cost at lower capacity.[1,2] While minimal durability loss is seen in commercial electrolyzers, catalyst losses can be masked by high loading (several mg cm‒2). At low loading, however, these losses become more apparent.[3] In this study, electrolyzer durability was evaluated at low iridium-anode loading (0.1‒0.5 mg cm‒2) and with different power inputs (potentials, intermittency). Higher loading tended to delay the onset of durability losses; in contrast, a loading of 0.1 mg cmelec ‒2 resulted in incremental but immediate loss when exposed to high potential. Increasing the upper potential limit appeared to increase iridium dissolution and migration and resulted in higher performance losses. This trend was expected and iridium dissolution is anticipated to be a primary factor in electrolyzer loss at low loading.[4] Introducing cycling (square/triangle wave), however, significantly increased the rate of performance decay and was less expected from half-cell tests and even though less time was spent at elevated potential.[3] Changing the rate of potential increase (saw tooth profiles) confirmed that rapid input increases accelerated loss and may be due to localized potential spikes occurring within the catalyst layer. A variety of system control-based mitigation strategies have been evaluated for lessening durability losses when handling intermittent power sources. Several iridium catalyst types (oxides, surface areas) have been tested in half- and single-cells. Catalyst development efforts often focus on metallic- or hydroxide-based iridium structures, due to higher activity in ex-situ tests. These performance advantages, however, largely disappear in single-cell tests and may be due to surface/near-surface oxidation during conditioning protocols. Metallic/hydroxide durability losses further tend to be larger in both half- and single-cells and may be related to the kinetics of iridium metal/hydroxide/oxide dissolution. In single-cell testing, we have focused on how loading, test parameters, and catalyst type affect proton exchange membrane-based electrolyzer durability. These tests have significant implications on lowering the cost of electrolysis-based hydrogen production and on coupling electrolysis with renewable power inputs. [1] H2 at Scale: Deeply Decarbonizing our Energy System. Presented at Annual Merit Review, U.S. Department of Energy; Washington, DC, June 6−10, 2016. https://www.hydrogen.energy.gov/pdfs/review16/2016_amr_h2_at_scale.pdf. [2] Denholm, P.; O’Connell, M.; Brinkman, G.; Jorgenson, J. Overgeneration from Solar Energy in California: A Field Guide to the Duck Chart; Vol. NREL/TP-6A20-65023; National Renewable Energy Laboratory: Golden, CO, 2015. Available at the following: http://www.nrel.gov/docs/fy16osti/65023.pdf. [3] Alia, S. M.; Rasimick, B.; Ngo, C.; Neyerlin, K. C.; Kocha, S. S.; Pylypenko, S.; Xu, H.; Pivovar, B. S. J. Electrochem. Soc. 2016, 163, F3105−F3112. [4] Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J. P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Cat. Today 2016, 262, 170.

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...