Hybrid Ni/NiO composite with N-doped activated carbon from waste cauliflower leaves: A sustainable bifunctional electrocatalyst for efficient water splitting

High-performance bifunctional electrocatalysts based on nickel/nickel oxide nanoparticles and nitrogen-doped activated carbon, derived from biomass waste (cauliflower leaves) were synthesized by a facile one-step process. The Ni and NiO compositions were controlled by varying the temperature during pyrolysis, which had significant effects on the crystallographic structure of the resulting hybrid and electrocatalytic properties. The Ni/NiO/N-doped activated carbon obtained at 500 °C shows modest Tafel slopes of 70 and 121 mV dec−1 along with overpotentials of 346 and 180 mV to drive a current density of 10 mA cm−2 for oxygen evolution and hydrogen evolution reactions in 0.1 M KOH electrolyte. In a two-electrode electrolyser the hybrid bifunctional electrocatalyst requires only 1.688 V to reach 10 mA cm−2 current density, confirming excellent rate capability and robust stability with variable current densities of 10–30 mA cm−2. The electrocatalytic performance of the NiOx-AC-500 || NiOx-AC-500 cell is comparable to that of recently reported electrolysers. The superior electrocatalytic performance of our electrocatalyst is due to synergies between Ni and NiO in a hierarchically porous N-doped carbon structure, rich in active sites and efficient charge transfer. This work offers a sustainable approach to develop eco-friendly bifunctional electrocatalysts for high-performance water splitting.