Bis(2‐Pyridylmethyl)‐1,2‐ Thiobenzene Metal Complexes as Efficient Electrocatalyst and Photocatalyst for Hydrogen Production

ABSTRACT S,S′‐bis(2‐pyridylmethyl)‐1,2‐thiobenzene (bptb) ligand, KSCN and its cobalt and nickel metal salts formed two new complexes, [Co II (bptb)(SCN) 2 ] and [Ni II (bptb)(SCN) 2 ], respectively. They were all efficient catalysts that can reduce protons or water to hydrogen by electrocatalysis or photocatalysis. The complexes [Co II (bptb)(SCN) 2 ] and [Ni II (bptb)(SCN) 2 ], adopting a square pyramidal coordination structure, exhibited efficient activity in electrocatalytic proton reduction with acetic acid (AcOH) as the proton source in N,N′‐Dimethylformamide (DMF) solution, providing 108.4 and 292.3 (mol H 2 /mol catalyst/h) for hydrogen evolution at an overpotential of 400 mV, respectively. In neutral buffer solution (pH 7.0), the complexes [Co II (bptb)(SCN) 2 ] and [Ni II (bptb)(SCN) 2 ] exhibit excellent hydrogen evolution activity, showing turnover frequencies of 993.7 and 1484.9 mol H 2 (mol catalyst) −1 h −1 with an applied overpotential of 837.6 mV, respectively. Under blue light irradiation, the photolysis of aqueous solutions (pH 4.5) containing complexes [Co II (bptb)(SCN) 2 ] and [Ni II (bptb)(SCN) 2 ] with CdS as the photosensitizer and ascorbic acid (H 2 A) as the electron donor, exhibited remarkable photocatalytic hydrogen evolution activity, achieving turnover numbers (TON) of 16,710.2, and 17,926.1, respectively. The corresponding average apparent quantum yields (AQYs) were 17.8% and 18.7%. Notably, the examined metal cobalt and nickel complexes exhibited highly efficient hydrogen evolution reaction (HER) activity, and their catalytic activity following the nickel complex was superior to that of the cobalt complex in both electrochemical and photochemical conditions.