Chlorophyll-Based Organic Heterojunction on Ti₃ C₂ T_x MXene Nanosheets for Efficient Hydrogen Production

The Z-scheme process is a photoinduced electron-transfer pathway in natural oxygenic photosynthesis involving electron transport from photosystem II (PSII) to photosystem I (PSI). Inspired by the interesting Z-scheme process, herein a photocatalytic hydrogen evolution reaction (HER) employing chlorophyll (Chl) derivatives, Chl-1 and Chl-2, on the surface of Ti₃ C₂ T_x MXene with two-dimensional accordion-like morphology, forming Chl-1@Chl-2@Ti₃ C₂ T_x composite, is demonstrated. Due to the frontier molecular orbital energy alignments of Chl-1 and Chl-2, sublayer Chl-1 is a simulation of PSI, whereas upper layer Chl-2 is equivalent to PSII, and the resultant electron transport can take place from Chl-2 to Chl-1. Under the illumination of visible light (>420 nm), the HER performance of Chl-1@Chl-2@Ti₃ C₂ T_x photocatalyst was found to be as high as 143 μmol h^-1  g_cat ^-1 , which was substantially higher than that of photocatalysts of either Chl-1@Ti₃ C₂ T_x (20 μmol h^-1  g^-1 ) or Chl-2@Ti₃ C₂ T_x (15 μmol h^-1  g^-1 ).