Photoelectrode design principles for efficient photo-charging of solar redox flow batteries

Abstract

In connection with attempts to increase the Solar Redox Flow Battery (SRFB) viability, an investigation was done into the charge carrier transport mechanisms entailed at the photoelectrode interlayer interfaces. On the basis of a preliminary study, the investigation focused on the development of a suitable conducting layer at the electrolyte/electrode interface as well as the development and control of a hole extraction layer, based on the device electronic structure and energy levels matching. Research was conducted into the properties of various prospective materials that could improve charge carrier transport at the electrolyte/photoelectrode interface. Once the optimal configuration is determined, the photoelectrode and redox couples are prepared and characterized and the photocharging performance of the device is optimized. Furthermore, the control of the formation conditions of a hole extraction layer took place, in order to yield improved internal charge carrier separation and transport. Various hole transport layers were assessed in SRFB system in relation to the photo-charging performance. The described process resulted in the development of a conducting layer through the growth of well distributed islands, which led to a high solar-to-chemical conversion of 9.4%. Through the control of the formation conditions of the hole extraction layer, better spatial separation of the photogenerated charge carriers was achieved, leading to improved device performance. Despite the enhanced viability of each device in terms of efficiency, further research into the long-term stability is essential for its practical implementation. This mainly relates to electrolyte degradation to form solid precipitates and photocorrosion of the absorber semiconductor materials in acidic conditions.