fig3

Figure 3. (A) Polarization curves of NFF, NiFe(OH)_x and RuO₂/NiFe(OH)_x electrocatalysts; (B) A comparison of the required overpotentials measured at 50 mA cm^-2 and 100 mA cm^-2 current densities; (C) The associated Tafel slopes; (D) Nyquist curves; (E) Linear changes of current densities versus the scanning rates; (F) Chronopotentiometry curve of RuO₂/NiFe(OH)_x at the constant current density of 200 mA cm^-2 for 100 h. (G) Comparison of the overpotential of RuO₂/NiFe(OH)_x at 100 mA cm^-2 with the recently published HER electrocatalysts. NFF: NiFe foams; HER: hydrogen evolution reaction; RHE: reversible hydrogen electrode.