The article first studied the influence of different channel structures (semi-circular channel, rectangular channel, and triangular channel) on the performance of all vanadium flow batteries. The research results on charging and discharging voltage indicate that when SOC changes from 0.1 to 0.9, VRFB completes the charging process. The semi-circular channel requires the lowest charging voltage, while the triangular channel consumes the highest charging voltage. When the SOC changes from 0.9 to 0.1, the VRFB discharges externally, and the semi-circular channel releases the highest discharge voltage, while the triangular channel provides the lowest discharge voltage. The voltage performance of traditional rectangular channels is between semi-circular and triangular channels, indicating that the new semi-circular channel design can greatly improve the charging and discharging performance of traditional VRFB.

The variation curve of overpotential with SOC under different channel designs indicates that the semi-circular channel VRFB has the smallest overpotential, while the rectangular and triangular channels are much worse. As the discharge progresses, the overpotential of VRFB first decreases and then increases. The advantage of semi-circular flow channels is more significant at SOC=0.1.
The influence of channel shape on the polarization curve indicates that an increase in current density leads to a decrease in discharge voltage. The semi-circular channel design generates the highest voltage at the same current density, indicating that the semi-circular design has the smallest polarization loss and the least obvious polarization phenomenon. The lower overpotential in all vanadium flow batteries means lower polarization loss, which leads to higher voltage. Therefore, the semi-circular channel design can promote the transmission of multiple species, reduce voltage loss, and improve the performance of VRFB.

The concentration value and distribution of vanadium ions in porous electrodes are crucial for evaluating the performance of VRFB. Therefore, by studying the concentration distribution of V2+ions, it is clear that the average concentration gradually decreases from left to right, indicating that a semi-circular flow channel is more conducive to the transfer of active ions to the electrode. Moreover, the concentration distribution of the semi-circular design is more uniform than that of rectangular and triangular channels.
Through the study of the average concentration of V2+ions in three channels under the condition of SOC=0.2 on different cutting planes, it was found that regardless of the 1L/4, 1L/2, or 3L/4 cutting planes of the electrode, the average concentration of V2+is highest in the semi-circular channel. The concentration value of the semi-circular design is 10.6% higher than that of the rectangular channel on the 3/4L cutting plane, and 15.5% higher than that of the triangular channel. Therefore, the semi-circular design can significantly improve the performance of VRFB based on rectangular channels.

The study also explored the uniformity factor of V2+ions during discharge in different channels, and it can be seen that the concentration uniformity decreases continuously with the discharge of VRFB. The uniformity factor of semi-circular channels is higher than that of rectangular and triangular designs, and is more pronounced at the end of discharge. The uniformity coefficient of the semi-circular channel is 9% higher than that of the rectangular channel and 15.4% higher than that of the triangular channel, indicating that the semi-circular channel is more conducive to mass transfer.

The experiment also investigated the influence of different flow channel structures on battery performance under different flow rates. From the results, it can be seen that VRFB with semi-circular channels can achieve optimal performance in all three channel designs, regardless of SOC=0.2 or SOC=0.8, and the semi-circular channels show more obvious advantages under low flow rate conditions.

The difference in mass transfer and fluid dynamics behavior may be the main reason for the different voltage characteristics of VRFB under different channel designs. Therefore, studying the Reynolds number can serve as a performance indicator for evaluating mass transfer behavior. From the results, it can be seen that high flow velocity leads to high Reynolds numbers, and VRFBs with semi-circular flow channels can achieve the maximum Reynolds number, indicating a better synergistic effect between fluid dynamics and mass transfer, resulting in better battery performance of VRFBs. Due to the significantly higher Reynolds number in the semi-circular design compared to the traditional rectangular design, the semi-circular flow channel can enhance the mass transfer performance of VRFB and promote electrochemical reactions in the electrode.
The study also explored the variation of concentration uniformity factors in three flow channels with flow rate during the discharge process. The results show that under the same flow rate, the concentration uniformity factor of the semi-circular channel is the highest, and the triangular design is the lowest. The higher the concentration uniformity factor, the better the mass transfer behavior, which can lead to better battery performance. Therefore, the application of high flow and the use of semi-circular channels are effective measures to improve the performance of VRFB.

In summary, the semi-circular flow channel design is superior to the traditional rectangular and triangular flow channel designs, and can have the best effect on improving the performance of liquid flow batteries. Therefore, it can be considered in future liquid flow battery flow channel designs.