| AVS 55th International Symposium & Exhibition | |
| Energy Science and Technology Focus Topic | Wednesday Sessions |
| Session EN+AS+EM+TF-WeM |
| Session: | Electrochemical Storage |
| Presenter: | M. Gasda, Rensselaer Polytechnic Institute |
| Authors: | M. Gasda, Rensselaer Polytechnic Institute R. Teki, Rensselaer Polytechnic Institute T.-M. Lu, Rensselaer Polytechnic Institute N. Koratkar, Rensselaer Polytechnic Institute G. Eisman, Rensselaer Polytechnic Institute D. Gall, Rensselaer Polytechnic Institute |
| Correspondent: | Click to Email |
Platinum catalyst layers were deposited by magnetron sputtering from a variable deposition angle α onto gas diffusion layer (GDL) substrates and were tested as cathode electrodes in polymer electrolyte membrane (PEM) fuel cells. Layers deposited at normal incidence (α = 0°) are continuous, and approximately replicate the rough surface morphology of the underlying GDL. In contrast, glancing angle deposition (GLAD) with α = 85° and continuously rotating substrates yields highly porous layers consisting of vertical Pt nanorods. At 0.40 mg/cm2 total Pt loading, the rods are 100-500 nm long and ~300 nm wide, separated by 20-100 nm wide voids. The dramatic difference in microstructure is due to atomic shadowing during GLAD that causes Pt flux from highly oblique angles to preferentially deposit on surface protrusions, leading to nucleation and columnar growth on substrate mounds while surface depressions remain uncoated. Fuel cell testing at 70°C using Nafion 1135 membranes, Teflon-bonded Pt-black electrodes (TBPBE) at the anode, and atmospheric pressure hydrogen and air reactants shows a monotonic increase in performance of GLAD cathodes from 0.05 to 0.40 mg/cm2 total Pt loading. Nanorod cells exhibit approximately 2x higher mass activity than continuous layers at 0.50V (corrected for iR, shorting, and gas crossover); for example, GLAD and continuous layers with approximately the same Pt loading (0.18 and 0.25 mg/cm2, respectively) show 1.7 and 0.8 A/mg. In contrast, at low current density of 0.10 A/cm2, the continuous layers (0.70 V with 0.25 mg/cm2 Pt) outperform GLAD cells even with relatively high Pt loadings (0.65 V with 0.40 mg/cm2 Pt). The GLAD cells’ higher mass-specific performance at high current densities is due to their high porosity which facilitates reactant transport, while the low-current performance of the continuous layer is attributed to a higher active Pt surface area. The sputter-deposited electrodes exhibit a higher platinum utilization in comparison to TBPBE reference cathodes, with GLAD cells (1.7 A/mg) performing better than TBPBE (0.75 A/mg) at high current densities (0.50 V), while continuous layers (0.07 A/mg) outperform TBPBE (0.035 A/mg) at 0.80 V. These results indicate the promise of nanoengineering to boost catalyst utilization in PEM fuel cells.