• Preparation of high activity CNFs/NiO via microwave conversion of alder wood. • First report on preparation of renewable CNFs/NiO for high-sensitivity detection of H 2 O 2 . • The sensitivity of CNFs/NiO electrode can reach 304.2 µA cm −2 mM −1 . • The catalytic mechanism analysis for high-sensitivity detection of H 2 O 2 by renewable CNFs/NiO. In the present study, carbon nanofibe (CNFs) with a highly defective structure were prepared via microwave pyrolysis of H 2 O 2 activated alder wood. The nickel oxide nanoparticles (NiO NPs) were anchored on the surface of the carbon nanofibers with the aid of microwave hydrothermal treatment. The electrochemical reactivity of the carbon nanofiber/nickel oxide electrode was evaluated for nonenzymatic H 2 O 2 detection and exhibited a fast response speed (within 1 s), high sensitivity (304.2 µA cm −2 mM −1 ), wide linear working range (0.1 µM to 3489.9 µM), low detection limit (0.57 µM), and good reproducibility, anti-interference and stability. For tap water, the prepared electrode was shown the recovery and RSD of H 2 O 2 between 94.7 and 98.9 % and 2.6–5.4 %, respectively as well the recovery and RSD of H 2 O 2 in river water samples reached 101.2–104 % and 2.8–4.7 %, respectively. The catalytic mechanism of hydrogen peroxide by using the prepared carbon nanofibers/nickel oxide was analyzed.