Photocatalytic hydrogen evolution with porphyrin based metal-organic frameworks

Simulated sunlight driven overall water splitting has been carried out using porphyrin-based PCN-222 metal-organic frameworks having none or Zn, Fe, Mn and Co metal ion at the porphyrin linker. Influence of the transition metal on the photocatalytic water splitting reaction was systematically studied filling the existing gap. Under simulated sunlight irradiation, PCN-222(Zn) shows the highest H2 evolution reaction (HER) efficiency, reaching almost 1.5 mmol of H2 per gram of photocatalyst by using MeOH which corresponds to the HER rate of 65.8 μmol g1 h1 that is higher than some examples of porphyrinic MOFs with Pt. In addition to this, as the valence band (VB) levels of PCN-222(M) gets more positive than that of water oxidation potential, O2 evolution was detected ia quasi-stoichiometric ratio respect to H2. To gain insights into the mechanism of the H2 and O2 evolution, transient absorption (TA) spectroscopy measurements have been carried out, providing a strong evidence of the generation of a charge seperated state and that the positive holes are able to oxidize H2O in the microsecond time.