For organic redox flow batteries
(ORFBs), it is of significance
to clarify the influence mechanism of their electrode configuration
on the mass transfer inside electrodes and battery performance. A
novel three-dimensional (3D) numerical model for ORFBs is established
based on the Nernst–Planck and Butler–Volmer theories
and is verified by numerous experiments for both the charge and discharge
processes. ORFBs equipped with rectangular, trapezoidal, and sector
electrodes are investigated, in which the voltage, overpotentials,
uniformity factor, and the power efficiency of the discharge process
are presented. The results show that the sector electrode possesses
the best mass transfer and battery performance. The power-based efficiency
of the sector electrode is 1% higher than that of the trapezoidal
one. In addition, the opening angle of the sector electrode should
be as small as possible. The optimal aspect ratio of the rectangular
electrode is 60:107, and the optimal configuration of the trapezoidal
electrode is 30 mm top side length and 130 mm bottom side length.
The optimization of the porous electrode configuration is presented,
which can contribute to the commercial application of ORFBs.
How mass transfer performance limits the development of organic flow batteries, which are regarded as the emerging electrochemical energy storage technology, is unclear. Mass transfer behavior in the electrode is influenced by the flow fields, which is indispensable. A three-dimensional and steady numerical model of the organic flow battery is established and the results are verified by experimental data. The battery performance and mass transfer behaviors are analyzed under different flow field for the charge/discharge processes based on this model. Compared with other flow fields, the interdigital flow field can achieve the best charge-discharge performance, mainly due to the improvement distribution uniformity of active species. The average concentration of the interdigital flow field is 45.1% higher than that of the conventional flow field. The effects of the flow rates and initial concentration of electrolyte on the battery performance are investigated, and the results indicate that appropriate inlet flow rate can lead to the highest net discharge powers and power-based efficiency of the flow battery. Although increasing the initial concentration can improve the battery performance, the improvement is too slight when the concentration is high enough, which can lead to waste of the active species.
The high energy consumption during the regeneration process
is
an important issue that currently limits the application of ammonia
decarbonization technology. In this work, four solid metal oxides
are proposed to be added in ammonia-rich solutions during regeneration
for reducing energy consumption. The effects of the metal oxide type,
heat duty, and CO2 loading on CO2 regeneration
and NH3 escape are investigated. The results show that
WO3 enhances the desorption of CO2 regeneration
while inhibiting the escape of NH3 compared to other oxides.
The CO2 regeneration rate increased by 68.9%, and the ammonia
escape reduced by 36.3% with the addition of 4 wt % WO3 at 90 °C. Based on the CO2 loading rate and the
product characterization, a possible mechanism for the metal oxide
assisted ammonia regeneration process is analyzed, where WO3 can be used as an additive during the regeneration process of ammonia
decarbonization to reduce the activation energy of the regeneration
reaction and enhance CO2 desorption while suppressing NH3 escape.
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