With a demonstrated high Faradaic efficiency of 95%, an all-vanadium (all-V) photoelectrochemical storage cell (PESC) has been deemed as a promising candidate for efficiently capturing and storing solar energy.(1, 2) In this work, we further enhanced photocurrent of the existing all-V PESC by 5X by utilizing forced convective transport of the reactants throughout the cell in a continuous flow reactor, such that diffusive transport is only required over a short length scale relative to the cell dimension. It has been found that the maximum solar storage performance of the all-V PESC device tends to be limited by ionic and reactant transport, since we already employed vanadium redox species with fast electrochemical kinetics. Zero-resistance ammetry (ZRA) and electrochemical impedance spectroscopy (EIS) were employed to study the photoelectrochemical response of this system during conversion and storage of solar energy under both illumination and dark. It was discovered that introduction of flow during photoelectrochemical conversion greatly enhanced the photocurrent by 5 times comparing to the static condition (Fig. 1). Furthermore, EIS results indicated that both charge transfer resistance and interfacial capacitance were greatly reduced with convective flow of vanadium redox. On the other hand, variation of flow rate, if above a certain threshold, didn’t have a noticeable impact on the photocurrent under the range we explored. To better understand the photoelectrochemical behavior of the system, a CFD-based numerical simulation was carried out to understand the influence of flow rate on the photocharging process as well as the reaction limiting factors during solar energy storage. 

Reference:

1.      D. Liu, W. Zi, S. D. Sajjad, C. Hsu, Y. Shen, M. Wei and F. Liu, ACS Catalysis, 5, 2632 (2015).

2.      Z. Wei, D. Liu, C. Hsu and F. Liu, Electrochemistry Communications (2014).