Enhanced Long-Term Stability of a Photosensitizer with a Hydroxamic Acid Anchor in Dye-Sensitized Photocatalytic Hydrogen Generation

Climate change mitigation on a global scale will only be possible through the achievement of ambitious decarbonisation goals, requiring an energy transition that involves switching from fossil fuels to clean fuels such as hydrogen. The photocatalytic approach is one of the most studied methods for directly converting sunlight into hydrogen. In this work, we present the synthesis, characterization, and application of the PTZ1-HA dye, which was obtained by replacing the terminal conventional carboxylic anchoring moieties of a previously studied phenothiazine-based dye (PTZ1) with hydroxamic acid functionalities. The photoinduced performance of the two dyes as photosensitizers was compared in both dye-sensitized solar cells and dye-sensitized photocatalytic systems. PTZ1-HA-sensitized photocatalysts showed improved stability in hydrogen generation due to the introduction of the hydroxamic acid as an alternative anchor group, which was shown to slow down hydrolysis in aqueous media. Even though the light harvesting ability of PTZ1-HA was lower than that of PTZ1, the higher stability of PTZ1-HA-sensitized devices allowed for improved photocatalytic generation of H2 over prolonged periods. The superior long-term efficiency of the hydroxamic acid based dye is important in view of potential practical applications.