A Standardizable Laboratory‑Scale Device for the Harmonization of Photoelectrochemical Experimental Procedures in Solar Redox Flow Cells

The solar redox flow cell (SRFC) is an emerging photoelectrochemical (PEC) technology capable of solar energy collection, storage, and conversion to dispatchable electricity and heat. Research efforts within this field have explored various semiconductor‐based photoelectrodes and redox‐active species, achieving notable efficiency and stability milestones. Nevertheless, the lack of standardized devices and testing protocols continues to hinder reliable benchmarking and comparison of SRFC performance across studies. This work initiates the discussion around the harmonization of experimental procedures for SRFCs. To achieve this goal, a simple, compact, and small device is proposed (UniFlow Cell), carefully designed to minimize design‐related efficiency losses; be compatible with long‐term operation using different materials; and perform measurements in dark/light illumination conditions, and under two‐/three‐electrode configurations. Characterization techniques such as J‐E characteristics, chronoamperometry, and photoelectrochemical immittance triplets are proposed to optimize key operational parameters. A long‐term stability test was performed as a test model, where a thin‐film hematite photoelectrode continuously photocharged a ferrocyanide/anthraquinone flow cell chemistry. A photocurrent density of ca . 0.45 mA·cm −2 was sustained over 1000 h of continuous operation at 0.45 V. This result demonstrates the applicability and long‐term operational robustness of the proposed device, positioning this work as a reference for new researchers.