Electrochemical Investigation of Uranium Redox
|by Y. Shiokawa et
| For the leveling of output power fluctuations
of renewable energy sources, batteries for electricity power storage,
including the redox flow battery as a strong candidate, are investigated.
We have proposed the uranium redox flow battery on the basis of the
quite unique feature that the single element possesses two redox
couples with identical structures (UO2+/UO22+, U3+/U4+). Uranium
satisfies the necessary condition for the excellent active material
for the redox flow battery, i.e. the two battery reactions are reversible.
Since the energy efficiency of charge-discharge cycles depends on
the reversibility of the battery reactions, the uranium battery is
expected to be of higher charge-discharge performance at a large
current density even compared with the existing vanadium redox flow
Uranium battery requires an aprotic system because of the disproportionation
reaction of U(V) observed in protic media. The battery is
also effective to reuse the massive amount of depleted and
Our electrochemical investigation of uranium b-diketones, which
show relatively high solubilities in aprotic solvents, reveals
that (i) the large emf (>1V) is expected (Fig.2) and (ii)
their electrode reactions involve ligand dissociation reactions.
Since the latter feature prevent the high energy efficiency of
the battery, the development of new active materials without
the ligand dissociation are now underway.
Fig.1 Uranium redox flow battery for electricity power storage
Fig.2 Redox potentials for VI/V and IV/III of uranium complexes.
Emf larger than 1V is expected by using appropriate ligands.
| A new uranium complex, prepared for preventing the
ligand dissociation, shows a simple electrode reactions for both
positive and negative electrodes in a single solvents (Fig.3). Since
this complex seems to be an excellent material, further experiments
including charge and discharge of the battery are planned by using
the active materials.
Fig.3 Excellent reversibility of new uranium complexes for positive
and negative electrolytes
Neptunium battery had been already tested in an aqueous system,
where neptunium also possesses two reversible redox couples
like uranium. In the small scale experiments (Fig.4), the
reduction of emf is smaller than the vanadium cell (Fig.5)
and thus the higher energy efficiency is expected.
Fig.4 Non-flow cell of neptunium battery after discharge