Mechanistic insights into photocatalysis and over two days of stable H2 generation in electrocatalysis by a molecular cobalt catalyst immobilized on TiO2

To employ molecular water reduction catalysts (WRC) in a heterogeneous setup, a stable, macrocyclic CoIII–polypyridyl WRC containing two phosphonic acid groups was anchored on TiO2 to investigate photo- and electrocatalytic proton reduction. Photocatalytic investigations included kinetic studies of the electron transfer from the reduced photosensitizer to the WRC as well as H2-evolution measurements. Linear sweep voltammetry (LSV) performed on the immobilized WRC on a TiO2-coated FTO-glass electrode showed an onset potential of −0.6 V vs. SHE at pH = 5 for proton reduction, while operando UV/VIS confirmed the reduced CoI-species as the key catalytic intermediate. Finally, chronoamperometric investigations combined with XPS studies and ICP-MS studies of electrode and electrolyte revealed stable binding of the WRC on the electrode under catalytic conditions and constant H2-formation over the period of two days.