Lignin-derived bimetallic platinum group metal-free oxygen reduction reaction electrocatalysts for acid and alkaline fuel cells

Metal-nitrogen-carbons (M-N-Cs) as a reliable substitution for platinum-group-metals (PGMs) for oxygen reduction reaction (ORR) are emerging candidates to rationalize the technology of fuel cells. The development of M-N-Cs can further be economized by consuming waste biomass as an inexpensive carbon source for the electrocatalyst support. Herein, we report the simple fabrication and in-depth characterization of electrocatalysts using lignin-derived activated char. The activated char (LAC) was functionalized with metal phthalocyanine (FePc and MnPc) via atmosphere-controlled pyrolysis to produce monometallic M-N-Cs (L_Mn and L_Fe) and bimetallic M1-M2-N-Cs (L_FeMn) electrocatalysts. Raman spectroscopy and transmission electron microscopy (TEM) revealed a defect-rich architecture. XPS confirmed the coexistence of various nitrogen-containing active moieties. L_Fe and L_FeMn demonstrated appreciable ORR in both acidic and alkaline conditions whereas L_FeMn helped in restricting the peroxide yield, particularly in alkaline media. L_Fe and L_FeMn demonstrated remarkable onset potential (Eonset) of -0.942 V (vs RHE) with an E1/2 of 0.874 V (vs RHE) in 0.1 M KOH. In acid, L_FeMn had an Eonset of 0.817 V (vs RHE) and an E1/2 of -0.76 V (vs RHE). Finally, the L_FeMn as a cathode electrocatalyst was integrated and tested in PEMFC and AEMFC. AEMFC demonstrated optimistic performance with a peak power density of 261 mW cm-2 at the current density of -577 mA cm-2.

Automated summary

Metal-nitrogen-carbons (M-N-Cs) are reliable substitutes for platinum-group-metals (PGMs) for oxygen reduction reaction (ORR), and can be economically produced by utilizing waste biomass as a low-cost carbon source. In this study, electrocatalysts derived from lignin-derived activated char were fabricated and characterized. The results showed that the metal phthalocyanine-functionalized activated char exhibited defect-rich architecture and various nitrogen-containing active moieties, leading to appreciable ORR activity in both acidic and alkaline conditions. Moreover, the integrated L_FeMn cathode electrocatalyst demonstrated promising performance in both PEMFC and AEMFC, with a peak power density of 261 mW cm-2 at -577 mA cm-2.