In Situ and Continuous Decoding Hydrogen Generation in Solar Water-Splitting Cells

Photoelectrochemical (PEC) water splitting is gaining recognition as an effective method for producing green hydrogen. However, the absence of in situ, continuous decoding hydrogen generation tools hampers a detailed understanding of the physics and chemistry involved in hydrogen generation within PEC systems. In this article, we present a quantitative, spatiotemporally resolved optical sensor employing a fiber Bragg grating (FBG) to probe hydrogen formation and temperature characteristics in the PEC system. Demonstrating this principle, we observed hydrogen formation and temperature changes in a novel cappuccino cell using a BiVO₄/TiO₂ photoanode and a Cu₂O/CuO/TiO₂ photocathode. Our findings demonstrate that FBG sensors can probe dynamic hydrogen formation at 0.5 s temporal resolution; these sensors are capable of detecting hydrogen concentrations as low as 0.6 mM. We conducted in situ and continuous monitoring of hydrogen and temperature to ascertain various parameters: the rate of hydrogen production at the photocathode surface, the time to reach hydrogen saturation, the distribution of hydrogen and temperature, and the rate of hydrogen transfer in the electrolyte under both external bias and unbiased voltage conditions. These results contribute valuable insights into the design and optimization of PEC water-splitting devices, advancing the in situ comprehensive monitoring of PEC water-splitting processes.