Design of NiCo₂O₄ nanoparticles decorated N, S co-doped reduced graphene oxide composites for electrochemical simultaneous detection of trace multiple heavy metal ions and hydrogen evolution reaction

It is an enormous challenge to explore multifunctional electrocatalysts for simultaneous detection of Cd(II), Cu(II), Hg(II) and hydrogen evolution reaction (HER). In this work, NiCo₂O₄ decorated N, S co-doped reduced graphene oxide composites (NCO/N, S-rGO) are synthesized via hydrothermal followed calcination process. The synergetic effect, oxygen vacancies and hybridization of NCO/N, S-rGO improve its excellent electrocatalytic performance for simultaneous and individual detection of Cd(II), Cu(II), Hg(II) and HER activity. When NCO/N, S-rGO is acted as heavy metal ions (HMIs) electrochemical sensors, it exhibits the high sensitivity and low detection limit for Cd(II) with 2.38 μA μM⁻¹ and 123 nM, Cu(II) with 10.90 μA μM⁻¹ and 14.4 nM, as well as Hg(II) with 5.41 μA μM⁻¹ and 67 nM. NCO/N, S-rGO has outstanding stability and anti-interference performance and has been successfully implemented in the actual water environment. Furthermore, NCO/N, S-rGO also exhibits HER activity with overpotential and Tafel slope of 107 mV and 71.35 mV dec^-1, respectively. The electrochemical detection and HER activity mechanism of NCO/N, S-rGO are further investigated and demonstrated that the synergetic effect of NCO/N, S-rGO can improve its electronic microstructure and promote electrocatalytic performance. This work not only provides a simple method for the preparation of multifunctional electrocatalysts, but also enhances the comprehension of HMIs detection and HER mechanism.