Highly efficient electrocatalytic hydrogen generation in neutral water by a nanostructured cobalt catalyst derived in-situ from ionic liquid tagged cobalt terpyridine

Abstract

Electrocatalytic hydrogen production in a neutral aqueous medium is a promising, safe and economically viable technology to obtain clean and carbon-free fuel. Herein, we report the design and synthesis of ionic liquid (IL) tagged water soluble cobalt terpyridine (Co-ttpy-IL) and bis-terpyridine (Co-bisttpy-IL) complexes and their application towards electrocatalytic hydrogen generation in neutral water. The structure of Co-ttpy-IL complex was confirmed by single crystal XRD analysis. Initial electrochemical investigation on the prepared complexes by cyclic voltammetry (CV) revealed two sets of redox peaks corresponding to redox couples CoIII/CoII and CoII/CoI. Further, the electrocatalytic properties were investigated in organic medium with acetic acid acting as an external proton source, which revealed superior catalytic behaviour of the prepared complexes towards hydrogen evolution reaction (HER). Since, the complexes are water soluble, HER was performed by electrolysis at a fixed potential (−0.72 V vs RHE) for 10 h, during which evolution of H2 gas was observed. In the case of Co-ttpy-IL, deposition of certain electroactive nanostructured material on the electrode surface was observed after the electrolysis. This material was later identified as CoO nanoflakes, stabilized with the heteroatoms present in the ligand system and IL moiety. Interestingly, thus formed CoO/SPE demonstrated fascinating electrocatalytic activity towards HER, which produced hydrogen at −0.495 V (vs RHE) for 10 h without any loss in the activity (94% faradaic efficiency) in neutral water.