Electrochemical and photochemical hydrogen generation by a water soluble cobalt(II) complex of 2,2-bipyridine

A molecular catalyst based on a cobalt(II) complex, [(bpy)2Co(SCN)(Cl)] 1, has been prepared by the reaction of 2,2-bipyridine (bpy), CoCl2·6H2O, and KSCN. The complex has been investigated for both electrocatalytic hydrogen generation and photocatalytic hydrogen generation from purely aqueous solution. Under photoirradiation with blue light (λmax = 469 nm), with [Ru(bpy)3]Cl2 as a coupled photosensitizer and ascorbic acid (H2A) as a sacrificial electron donor in pH 5.0 aqueous solution, complex 1 possesses good activity with an initial turnover rate of 2.7 × 103 mol of H2 per mole of catalyst for the first 3 h of photolysis. This activity can be sustained for at least 10 h with a turnover number of 1.2 × 104 mol of H2 per mole of catalyst. Additionally, complex 1 electrocatalyzes hydrogen generation from neutral water (pH 7.0) with a turnover frequency of 809 mol of hydrogen per mole of catalyst per hour at an overpotential of 837.6 mV.