Fig. 3: Electrocatalytic performance.

a ORR polarization curves of the PD-PZFCNC-HEI, PZFCNC-HEA, and commercial 20 wt% Pt/C catalysts in O₂-saturated 0.1 M HClO₄ solution at 1600 rpm; b Mass activities at 0.9 V vs. reversible hydrogen electrode; c Polarization curves of PD-PZFCNC-HEI at different rotation rates; d Charge transfer number of PD-PZFCNC-HEI. e Normalized chronoamperometric curves of the PD-PZFCNC-HEI and Pt/C catalysts tested at a constant potential of 0.7 V; Polarization curves of f PD-PZFCNC-HEI and g Pt/C after AST between 0.6 and 0.95 V at different cycle numbers; h Mass activity before and after AST; The I–V polarization curves and power density of the H₂–O₂ fuel cell of the (i) PD-PZFCNC-HEI and j Pt/C sample with the cathode Pt loading of 0.05 mg_Pt cm⁻² before and after AST. k Long-term stability of the H₂-Air fuel cell with PZ-PZFCNC-HEI as the cathode at a current density of 500 mA cm⁻².