Electroreduction of a CoII coordination complex producing a metal-organic film with high performance toward electrocatalytic hydrogen evolution

This paper describes the synthesis and structural characterization of a novel, cheap and simple Co-II complex (Co-II(L)(2)Cl-2) based on the 1,3,5-trisubstituted-pyrazoline ligand along with the electrochemical production of metal-organic electroactive films derived from this new complex. These systems were applied as electrocatalysts for hydrogen production (ACN/ACA or ACN/TFA medium) where both materials presented high performance toward hydrogen evolution. Compared to the Co-II complex, the electroactive films exhibited significant electroactivity toward hydrogen evolution, presenting a remarkable TOF for H-2 production (312900 s(-1), corrected by Faraday efficiency) in the presence of TFA. In addition, the generated metal-organic film showed high stability toward the electrocatalytic hydrogen production, supporting at least 1000 cycles at 20 mV s(-1) in the large potential range investigated, as well as good performance and stability in the presence of 0.5 M H2SO4. Relevant insights into the mechanistic details and the role played by the Co-II complex and the films during the catalytic hydrogen production are also discussed in light of the structural features and electrochemical experiments.