Nanofiber Fuel Cell MEAs with a PtCo/C Cathode

Abstract

PtCo/C and Pt/C catalyst powders were incorporated into electrospun nanofiber and conventional sprayed cathode membraneelectrode-assemblies (MEAs) at a fixed electrode loading of 0.1 mg Pt /cm 2 . The binder for PtCo/C nanofiber cathodes and Pt/C nanofiber anodes was a mixture of Nafion and poly(acrylic acid) (PAA), whereas the sprayed electrode MEAs utilized a neat Nafion binder. The structure of electrospun fibers was analyzed by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), which showed that the fibers were ∼30% porous with a uniform distribution of catalyst and binder in the axial and radial fiber directions. The initial performance of nanofiber MEAs at 80°C was 20% better than the sprayed electrode MEA (a maximum power density of 1,045 mW/cm 2 vs. 869 mW/cm 2 ). The benefit of the nanofiber electrode morphology was most evident at end-of-test (after a metal dissolution accelerated stress test), where power densities dropped by only 8%, after 30,000 square wave voltage cycles (0.6 V to 0.95 V), as compared to a 35% drop in the maximum power for the sprayed electrode MEA. The use of a recovery protocol improved the initial performance of a nanofiber MEA by ∼13%, to 1,070 mW/cm 2 at 0.65 V, and increased the power after a metal dissolution stress test by 5-10% (e.g. 840 mW/cm 2 at 0.65 V after 30,000 voltage cycles). At rated power, the nanofiber MEA generated more than 1,000 mW/cm 2 at 99°C and a pressure of 250 kPa abs. The high performance and durability of PtCo/C nanofiber cathode MEAs is due to the combined effects of a highly active cathode catalyst and the unique nanofiber electrode morphology, where there is a uniform distribution of catalyst and binder (no agglomeration) and short transport pathways across the submicron diameter fibers (which lowers gas transfer resistance and facilitates water removal from the cathode).

Direct Integration of Strained‐Pt Catalysts into Proton‐Exchange‐Membrane Fuel Cells with Atomic Layer Deposition

“…Several state‐of‐the‐art catalytic systems have approached similar HCD performance (including credible but not printed results as compiled in Figure S18, Supporting Information). The strategies of Pt‐ionomer relative distribution tuning with carbon support modification [ 43,68,69 ] and agglomerate engineering [ 70 ] have shown promises in enhancing both LCD and HCD performance. Catalytic activity is less relevant to HCD than LCD as the activation energy barrier is significantly reduced by the overpotential applied at a lower voltage.…”

“…Estimates made according to H 2 –O 2 data are plotted in diamonds for the grain boundary porous platinum (GBP‐Pt @0.2 mg cm −2 ), [ 67 ] Pt‐alloy/Pt‐free dual‐catalysts (LP@PF‐2@0.035 mg cm −2 ), [ 31 ] and Pt on nitrogen‐modified Ketjenblack (Pt/N‐KB @0.11 mg cm −2 ). [ 43 ] Reported H 2 –air data and estimates according to reported H 2 –air data are plotted in circles for PtCo/C nanofiber (@0.1 mg cm −2 ), [ 70 ] PtCo on HSC‐e support (@0.06 mg cm −2 ), [ 69 ] Pt/Ketjenblack by polyol reduction (Pt/KB‐PO) (@0.06 mg cm −2 ), [ 68 ] and hard magnet core–shell L1 0 ‐CoPt/Pt (@0.1 mg cm −2 ). [ 6 ]…”

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

“…They compared electrospun nanofiber cathodes with Nafion/PVDF and Nafion/poly(acrylic acid) (PAA) binders with a slurry cathode with neat Nafion and Nafion/PVDF binder and found that the presence of the hydrophobic PVDF reduced carbon loss and increased the binder strength [ 181 ]. In an earlier investigation, the group studied PtCo/C and Pt/C catalyst powders integrated in electrospun nanofibrous mats in comparison with conventional sprayed cathode membranes, again using Nafion/PAA as a binder, and found a higher initial performance as well as a superior long-term stability for the electrospun cathodes [ 182 ]. Similarly, Khandavalli et al used PAA to reduce agglomerations of platinum on carbon catalyst particles in catalyst inks [ 183 ].…”

Pt utilization in proton exchange membrane fuel cells: structure impacting factors and mechanistic insights

“…0.2 mg Pt cm À2 , making PEMFCs approach the edge of commercial viability. [5][6][7][8][9][10][11][12] However, there is still a visible gap between the current status quo and the target. Taking both the cost to the consumer and the supply-demand relation in the precious metal market into account, a stretch target of 0.0625 g PGM kW À1 has been proposed for automobile PEMFCs.…”