Mask-Patterned Wet Etching of Thin Titanium Liquid/Gas Diffusion Layers for a PEMEC

A liquid/gas diffusion layer (LGDL) is located between the catalyst layer and current collecting flow field in proton exchange membrane (PEM) devices. Typically composed of carbon-based materials for PEM fuel cells (PEMFCs), this is unsuitable for PEM water electrolyzers (PEMWEs) due to the high anodic potential of the oxygen electrode that occurs during electrolysis, which creates a highly corrosive environment. Titanium has received considerable attention as a promising material to replace carbon LGDLs due to its high corrosion resistance at high positive overpotential, even in highly acidic and humid conditions. In addition, titanium provides high thermal/electrical conductivities and excellent mechanical properties. Current titanium LGDLs may be woven mesh, foams, and sintered fiber felt. Woven mesh are difficult to machine, and do not have the pore size controlled due to limitations of the material and available fabrication methods. Titanium felt on the other hand is similar in random structure to carbon paper, where shaved fibers of metal are sintered together to form a non-ordered porous material. In addition, their extra thickness increases significant electrical conductive path and fluidic resistance. Because of these challenges with the LGDLs, a thin-film LGDL with well-controllable pore morphology  is  highly desired  in both PEMFCs and PEMWEs.

This presentation will highlight recent efforts to design and fabricate well-tunable and titanium thin film LGDLs using photolithography and etching techniques. The effect of mask size as well as different etchants on the etch rate  and pore size of titanium is investigated. After fabrication, both performance & efficiency as well as electrochemical impedance spectroscopy is performed on the metallic LGDLs in order to evaluate their effectiveness in the anode side of a PEMWE. Ex-situ analysis is also performed before and after testing in order to characterize the morphological features of the LGDLs post etching and post testing. From the results of the fabrication and testing, new methods for the fabrication of well-tunable thin film LGDLs and the effect of controlling their parameters on the performance and efficiency of PEMWEs will be detailed.