Polymer sphere lithography for solid oxide fuel cells: a route to functional, well-defined electrode structures

As a first step towards mechanistic studies of fuel cell electrodes with both well-defined and functionally representative structural features, two-dimensional anti-dot metal films with tunable features are prepared. The fabrication employs a facile, sacrificial templating method, known as polymer sphere lithography, and the resulting metal films are fully connected, yet fully porous. Using initial bead sizes in the range of 500 nm to 3.2 μm and oxygen plasma etching to remove from ¼ to ¾ of the original bead diameter, computed triple phase boundary densities in the porous films of 2,000 to 43,500 cm cm−2 are achieved. Image analysis shows the computed (theoretical) and experimental structural features to be in good agreement, demonstrating sufficient perfection in the films for electrochemical studies. Furthermore, thermal stability under hydrogen of thermally evaporated Ni films is excellent, with negligible change in triple phase boundary length as required for quantitative electrochemical measurements. Ultimately, these two-dimensional metallic networks may also serve as the platform for future fabrication of three-dimensional electrodes with truly optimized structural features.