Nickel-Embedded Carbon Nanostructures as Noble Metal-Free Catalysts for the Hydrogen Evolution Reaction

Abstract

We demonstrate the electrocatalytic activity of “nitrogen (N)-doped porous carbon matrix embedded with nickel nanoparticles” for efficient hydrogen evolution reaction (HER) in alkaline medium. Three samples were synthesized via pyrolysis of a fixed amount (500 mg) of Ni(acac)₂, along with three different amounts of nitrogen precursor melamine (100, 250, and 500 mg) separately. The varying nitrogen concentrations of the surrounding carbon layers on the Ni nanoparticles enhance the surface area and porosity, exposing extensive active sites for catalytic reactions. The transition metal-based catalysts are crucial for long-term sustainability due to their combined edge (effectiveness and inexpensiveness) over traditional catalysts. Thus, by employing the protective carbon layer on the transition metal nanoparticles, we fabricated a catalyst that exhibits outstanding performance, with a low overpotential of 45.6 mV at 10 mA cm^–2 in 1 M KOH and maintains it for 24 h (durability), highlighting its exceptional catalytic efficacy and stability. The pores in carbon nanostructures facilitate the ionic moieties to move to active sites inside the pores. As the pore size variation influences the movement of charge or diffusion, this is reflected in the magnitude of impedance (|Z|_imp). Consequently, the enhanced number of active sites along with the larger pore sizes resulting from optimum amounts of nitrogen doping enables the sample with minimal |Z|_imp and an enhanced HER performance. The present study demonstrates the way to design a sustainable, extremely effective, and inexpensive HER electrocatalyst.