Lignin-derived electrospun carbon nanofiber mats with supercritically deposited Ag nanoparticles for oxygen reduction reaction in alkaline fuel cells

•Electrospun carbon nanofiber mats were prepared from a natural product of lignin.•The freestanding mats were flexible with BET specific surface area of ∼583 m2/g.•The mats were surface-deposited with Ag nanoparticles via the scCO2 method.•Novel electrocatalytic systems of Ag/ECNFs exhibited high activities towards ORR.

Ag nanoparticles (AgNPs) (11, 15, and 25 wt.%) were deposited on the surface of the freestanding and mechanically flexible mats consisting of lignin-derived electrospun carbon nanofibers (ECNFs) by the supercritical CO2 method followed by the thermal treated at 180 °C. The electrochemical activity of Ag/ECNFs electrocatalyst systems towards oxygen reduction reaction (ORR) was studied in 0.1 M KOH aqueous solution using the rotating disk/rotating ring disk electrode (RDE/RRDE) technique. The SEM, TEM, and XRD results indicated that, the spherical AgNPs were uniformly distributed on the ECNF surface with sizes in the range of 2-10 nm. The electrocatalytic results revealed that, all of the Ag/ECNFs systems exhibited high activity in ORR and demonstrated close-to-theoretical four-electron pathway. In particular, the mass activity of 15 wt.% Ag/ECNFs system was the highest (119 mA mg−1), exceeding that of HiSPEC 4100™ commercial Pt/C catalyst (98 mA mg−1). This study suggested that the lignin-derived ECNF mats surface-deposited with AgNPs would be promising as cost-effective and highly efficient electrocatalyst for ORR in alkaline fuel cells.

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