Fig. 1

Comparison of Mn-Co spinel (MCS) catalyst and commercial Pt catalyst. a Rotating disk electrode (RDE) measurements in O₂-saturated KOH solution (1 mol L⁻¹) using 40 wt% Pt/C (Johnson Matthey, 50 μg_Pt cm⁻²) and 40 wt% MCS/C (72 μg_metal cm⁻²), respectively. Inset: Tafel plots. Scan rate = 5 mV s⁻¹. Rotation rate = 1600 rpm. See Supplementary Figs 1 and 2 for relevant electrochemical data. b, c Alkaline polymer electrolyte fuel cell (APEFC) tests with H₂ and O₂ at different relative humidities (RH). Anode catalyst: 60 wt% Pt-Ru/C (Johnson Matthey, 0.4 mg_metal cm⁻²). Cathode catalyst: 60 wt% Pt/C (Johnson Matthey, 0.4 mg_Pt cm⁻²) or 40 wt% MCS/C with an optimized loading of 0.58 mg_metal cm⁻². (See Supplementary Fig. 3 for results with different catalyst loading.) Alkaline polymer electrolyte: aQAPS-S₈ membrane (35 μm in thickness) and aQAPS-S₁₄ ionomer (20 wt% in electrode)⁴. See Supplementary Figs 4 and 5 for impedance measurements and iR-corrected plots. Operation temperature = 60 °C. Backpressure = 0.1 MPa. d Performance comparison: Kinetic current densities (j_k) at 0.85 V, calculated from the RDE data recorded in 1 mol L⁻¹ NaOH/H₂O and 1 mol L⁻¹ NaOD/D₂O (See Fig. S6 for relevant results of isotopic labeling experiments), and the peak power density (PPD) resulting from APEFC tests