Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Tunable Low Density Palladium Nanowire Foams   Nanostructured palladium foams offer exciting potential for applications in
diverse fields such as catalyst, fuel cell, and particularly hydrogen storage
technologies. We have fabricated palladium nanowire foams using a cross-linking
and freeze-drying technique. These foams have a tunable density down to 0.1% of
the bulk, and a surface area to volume ratio of up to 1,540,000:1. They exhibit
highly attractive characteristics for hydrogen storage, in terms of loading
capacity, rate of absorption and heat of absorption. The hydrogen
absorption/desorption process is hysteretic in nature, accompanied by
substantial lattice expansion/contraction as the foam converts between Pd and
PdHx.

27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga