High-Performing Unitized Regenerative Fuel Cell Using PGM-Free Bifunctional Catalysts from Waste-Derived Carbon

Notably, in single-cell operation, the prepared PGM-free catalystsNiNC, FeNC, and FeNiNCgenerated RTEs of 29%, 38%, and 35%, respectively, under corrosion-free alkaline electrolytes (0.5 M KOH); similar results were reported for benchmark commercial catalysts such as IrO₂, which displayed <i>ca</i>. 30% of RTE. Moreover, NiNC catalyst showed a half-wave potential of 0.74 V, an onset potential of 0.88 V, and an overpotential of 420 mV at 10 mA cm^–2.

In turn, the FeNC displayed a half-wave potential of 0.72 V, an onset potential of 0.90 V, and an overpotential of 510 mV at 10 mA cm^–2. Regarding the FeNiNC, this catalyst demonstrates a half-wave potential of 0.76 V, an onset potential of 0.86 V, and an overpotential of 380 mV at 10 mA cm^–2. These results are particularly noteworthy considering the significantly lower metal loadings in the produced PGM-free catalysts.

Besides, to evaluate their long-term performance, the single cell was submitted to several potential cycles within the potential window range for FC and WE modes, i.e., between 0.6 and 2.0 V. The noble Pt/C catalysts deactivated completely after the stress test, while the novel FeNiNC and NiNC catalysts, containing an ultralow loading of critical raw materials (CRMs), demonstrated an outstanding compromise between activity and stability, proving their potential to be integrated in UR-AEMFC.