Synthesis and electrochemical properties of a nickel(II) thiacalix[4]arene-based electrocatalyst for the hydrogen evolution reaction

Thiacalix[4]arene with four sulfur-bridging atoms and four hydroxy coordinating groups in the lower rim is a promising candidate for powerful electrocatalytic hydrogen production. However, there are only a few examples reported in the literature where conjugated thiacalix[4]arene is used as a pre-catalyst for the hydrogen evolution reaction. The present work evaluates the electrocatalytic performance of a nickel(II) coordination complex based on generic thiacalix[4]arene. The coordination complex is characterized by cyclic voltammetry, where two reduction peaks are observed at -0.57 and -1.33 V for the two redox couples Ni2+/Ni+ and Ni+/Ni, respectively. The proton reduction occurs at the second peak potential with a slight shift at about -1.0 V, with increasing peak currents directly related to the number of acetic acid equivalents. The maximum peak current was observed to be at about 67 mu A for 20 equiv. of acetic acid.