  Liquid electricity generator and hydrovoltaic technology have received
numerous attentions, which can be divided into horizontal movement generator
and vertical movement generator. The horizontal movement generator is limited
for powering the integrated and miniaturized energy chip as the current output
direction is depending on the moving direction of the water droplet, which
means a sustainable and continuous direct-current (DC) electricity output can
be hardly achieved because of the film of limited length. On the other hand,
the existing vertical movement generators include triboelectricity or humidity
gradient-based liquid electricity generator, where the liquid or water resource
must be sustainably supplied to ensure continuous current output. Herein, we
have designed an integratable vertical generator by sandwiching water droplets
with semiconductor and metal, such as graphene or aluminum. This generator,
named as polarized liquid molecular generator (PLMG), directly converts the
lateral kinetic energy of water droplet into vertical DC electricity with an
output voltage of up to ~1.0 V from the dynamic water-semiconductor interface.
The fundamental discovery of PLMG is related to the non-symmetric structure of
liquid molecules, such as water and alcohols, which can be polarized under the
guidance of built-in field caused by the Fermi level difference between metal
and semiconductor, while the symmetric liquid molecules cannot produce any
electricity on the opposite. Integratable PLMG with a large output power of ~90
nW and voltage of ~2.7 V has been demonstrated, meanwhile its small internal
resistance of ~250 kilohm takes a huge advantage in resistance matching with
the impedance of electron components. The PLMG shows potential application
value in the Internet of Things (IoTs) after proper miniaturization and
integration.
