Proton exchange membrane (PEM) fuel cells are electrochemical devices that convert chemical energy to electrical energy. These devices are attractive alternative power sources due to their compact designs, high efficiencies, low emissions, and low noise but have issues with high cost and low durability. In this thesis, electrochemical and thin-film methods were used to understand the limitations of the electrocatalyst in PEM fuel cells and address the issues that limit PEM fuel cell commercialization. The electrochemical deposition of Pt from a novel plating solution was used to control the proximity of fuel cell electrocatalysts. We found that optimized pulse potential deposition parameters produced a large density of nanoparticles with narrow size distribution (1.36 +/- 0.36 nm) on amorphous carbon supports. This resulted in thin catalyst layers (< 8 microm thick) that contained 93 % less Pt that performed similar to and greater than commercial fuel cells.

In addition, pulse potential deposition was used to produce functioning PEM fuel cells by using the Nafion membrane as a template to selectively localize Pt in the three-phase reaction zone. The fuel cell performance of these devices had Pt loadings down to 11 microg cm--2 with a maximum power density of 213 mW cm--2. The catalyst layer was redesigned to improve conventional catalyst layer designs that limited MEA durability. A spin cast thin-film method was developed to produce smoother electrode surfaces that lead to lower resistance, isotropic conductivity, and increased contact area to the Nafion membrane. These fuel cells produced higher power and were resistant to electrode delamination. The catalyst activity and stability was improved by redesigning the support structure via constant potential electrolysis of 4-aminomethylpyridine on carbon electrodes.

The Pt nanoparticles that were electrodeposited on carbon electrodes functionalized with 4-aminomethylpyridine had improved size and dispersion compared to a non-functionalized support. The fuel cell performance was comparable to commercial MEA at low currents which contained only 25.5 microg cm--2 Pt less than 2% from the DOE 2020 target.