Ni(II) Complex Based on Imidazole Dicarboxylic Acid as a Promising Electrocatalyst for Hydrogen Evolution Reaction and H2O2-Sensing

Abstract

The determination of complex structure helps to explore its reaction mechanism and provides design strategies for guiding synthesis of high-performance hydrogen evolution reaction (HER) electrocatalysts. A new mononuclear Ni(II) complex, [Ni(p-MOPhH₂IDC)₂(H₂O)₂], was synthesized by the reaction of p-MOPhH₃IDC (2-(4-methoxyphenyl)-1 H-imidazole-4,5-dicarboxylic acid) and Ni(NO₃)₂·6H₂O under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV-vis spectroscopy. The structure analysis revealed that the nickel center was six-coordinated octahedron coordination geometry. The electrochemical properties of the Ni(II) complex-doped carbon paste electrode (Ni-CPE) were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.5 M H₂SO₄ electrolyte. The HER measurements show that the η₁₀^298K (overpotential, 10 mA cm^–2) of the Ni-CPE was positively shifted by 265 mv compared with the bare-CPE (without complex). The Tafel slope of the Ni-CPE was 187 mV dec^− 1. These indicated that the Ni-CPE was effective for HER electrocatalytic reaction. In addition, the electrochemical sensing performances of the Ni-CPE towards H₂O₂ were found to have a linear response from 0.5 µM to 4.0 mM with a detection limit of 0.036 µM. The above studies prove that the Ni(II) complex can be used as an effective bi-functional molecular electrocatalyst for HER and H₂O₂ sensing, and provide a new approach for designing efficient, non-precious metal electrochemical catalysts.

Graphical Abstract

A new mononuclear Ni(II) complex, [Ni(p-MOPhH₂IDC)₂(H₂O)₂], was synthesized under solvothermal conditions. The electrochemical properties of the Ni(II) complex-doped carbon paste electrode (Ni-CPE) were investigated. In the HER study, the Ni-CPE has more positive overpotentials (η₁₀^293K), smaller Tafel slopes and lower activation energies in the HER process compared to the bare-CPE, demonstrating that the Ni-CPE has effective electrocatalytic hydrogen evolution activity. Moreover, electrochemical sensing performance shows that Ni-CPE has good detection ability for H₂O₂ and exhibit good stability and anti-interference properties. Therefore, the Ni-CPE can be used as an effective bifunctional electrocatalyst.