Fig. 3

HER electrocatalysis of Mo₂N-r, Mo–N, P–Mo–N and reference 20% Pt/C. a Polarization curves recorded on glassy carbon electrodes, the catalyst loading was 0.2 mg/cm². b The corresponding overpotentials of the samples under the current density (j) values of 10, 50, 100, and 150 mA/cm². Please note that every sample was tested 10 times and then the corresponding standard deviation value was used for the error bar. c The Tafel plots, derivate from the polarization curves. d The electrochemical impedance spectra (EIS) of Mo₂N-r, Mo–N, and P–Mo–N samples. e Durability test of the P–Mo–N catalyst, showing the results of initial and 10,000 cycles. f The current density vs time response results under three potentials of 145, 157, and 164 mV. 0.5M H₂SO₄ was used as the electrolyte, Ag/AgCl (saturated KCl) and a graphite rod were used as the reference and counter electrodes, respectively