(618ap) Applications of Anodized Aluminum Oxide At Mainstream Engineering Corporation

We are using anodized aluminum
oxide (AAO) for a variety of energy-related applications. Among these is as a
support for amorphous metal alloy hydrogen separation membranes. The ordered nanopore array found in AAO allows for the fabrication of a
membrane support with nanometer-scale surface roughness and a tunable, yet
uniform, porosity. This architecture not only enhances adhesion of the membrane
to the support but also facilitates the facile deposition of ultra-thin membranes without loss of
film cohesion. Other benefits are the scalability and tunability of the
electrochemical self-assembly mechanism used to fabricate AAO. A square foot of
the support is as easily fabricated as a square inch and the uniform diameters
of the pores within the array are easily tunable simply by adjusting the
applied voltage that drives the electrochemical oxidation reaction. The pores
are non-tortuous, channeling directly through the support which creates a
direct path for hydrogen diffusion. Additionally, the pore diameter can be
adjusted from 10 to 100s nm, thus avoiding the Knudsen diffusion limit. Though
mild anodization can be quite slow (2 ? 10 μm/hr),
we have developed a process to form high‐density pores using a hard
anodization technique which was recently discovered to form low‐density
pores under strict temperature/acid/voltage control at rates as high as 300 μm/h. Not only were the pores fabricated for this
study of high‐density, but the AAO template supports were also up to 1.6
mm thick (Figure 1). To the best of our knowledge, this is the thickest AAO
template ever fabricated (which only took 23 h of anodization), exceeding the
closest example in the literature by almost 20‐fold.

The membranes were fabricated as
continuous thin films of amorphous metal alloys (Figure 2) and were thin enough
to be surface reaction limited, exhibiting a linear increase in hydrogen flux
with ΔP_hydrogen. Sub-micron Pd-alloy
catalytic layers are currently being investigated to improve hydrogen
dissociation and reassociation rates.