Simultaneous doping of nitrogen and zinc on nickel selenide nanoparticles for enhanced electrocatalytic hydrogen evolution

Transition metal selenides are regarded as profound electrocatalytic materials owing to their unique crystal structure and electrochemical stability and interestingly several efforts are underway globally in order to boost their electrocatalytic efficacy further. Herein, we envisage the simultaneous doping of anion (N) and cation (Zn) into the crystal structure of nickel selenide nanoparticles (NiSe₂ NPs), in order to modulate their electronic properties, enhance the catalytic sites and subsequently to enhance the electrocatalytic hydrogen evolution reaction (HER) performance. Initially, Zn doped NiSe₂ with varying amount of Zn (as dopant) were synthesized in order to optimize the Zn loading, amongst which Zn_0.4Ni_0.6Se₂ NPs exhibited maximum electrocatalytic HER activity. After optimizing the Zn loading, N and Zn doped NiSe₂ NPs (N–Zn_0.4Ni_0.6Se₂ NPs) were synthesized via hydrothermal method and systematically characterized. Further, the synthesized material was employed as an electrocatalyst towards hydrogen evolution process in 0.5 M H₂SO₄. N–Zn_0.4Ni_0.6Se₂ NPs portrayed excellent electrocatalytic performance with a lower overpotential of 97 mV at 10 mA cm⁻² and a Tafel slope of 32.8 mV dec⁻¹, which demonstrates appreciatively best result among all synthesized materials. Furthermore, the hydrogen adsorption Gibb's free energy on the Ni sites of N and Zn codoped NiSe₂ has been calculated to be 0.49 eV using computational studies, which is lesser than the other prepared electrocatalysts. The theoretical investigations are well in agreement with the experimental observations and infer that simultaneous doping of N and Zn has resulted in enhanced electrocatalytic HER activity at N–Zn_0.4Ni_0.6Se₂ NPs. In addition, N–Zn_0.4Ni_0.6Se₂ shows excellent stability for 24 h under continuous electrolysis conditions in 0.5 M H₂SO₄ substantiating the robustness of the designed electrocatalyst.