Fig. 4. Power and durability performance of N-G-CNT with the addition of KB in PEM fuel cells.

(A) Polarization curves of N-G-CNT with loadings: 2, 0.5, or 0.15 mg cm⁻² plus KB (2 mg cm⁻²) for each cathode. The weight ratio of (N-G-CNT/KB)/Nafion = 1/1. (B) Cell polarization and power density as the function of gravimetric current for the N-G-CNT/KB (0.5/2 mg cm⁻²) with the weight ratio of (N-G-CNT/KB)/Nafion = 1/1. (C) Durability of the metal-free N-G-CNT in a PEM fuel cell measured at 0.5 V compared with a Fe/N/C catalyst (see the Supplementary Materials for preparation details). Catalyst loading of N-G-CNT/KB (0.5 mg cm⁻²) and Fe/N/C (0.5 and 2 mg cm⁻²). Test condition: H₂/O₂: 80°C, 100% relative humidity, 2-bar back pressure.