Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Self-Charged Graphene Battery Harvests Electricity from Thermal Energy
  of the Environment   The energy of ionic thermal motion presents universally, which is as high as
4 kJ\bullet kg-1\bullet K-1 in aqueous solution, where thermal velocity of ions
is in the order of hundreds of meters per second at room temperature1,2.
Moreover, the thermal velocity of ions can be maintained by the external
environment, which means it is unlimited. However, little study has been
reported on converting the ionic thermal energy into electricity. Here we
present a graphene device with asymmetric electrodes configuration to capture
such ionic thermal energy and convert it into electricity. An output voltage
around 0.35 V was generated when the device was dipped into saturated CuCl2
solution, in which this value lasted over twenty days. A positive correlation
between the open-circuit voltage and the temperature, as well as the cation
concentration, was observed. Furthermore, we demonstrated that this finding is
of practical value by lighting a commercial light-emitting diode up with six of
such graphene devices connected in series. This finding provides a new way to
understand the behavior of graphene at molecular scale and represents a huge
breakthrough for the research of self-powered technology. Moreover, the finding
will benefit quite a few applications, such as artificial organs, clean
renewable energy and portable electronics.

10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci