FeS as a promising cathode catalyst for direct borohydride fuel cells

Highlights: • A new FeS-PPy-BP catalyst was synthesized. • FeS-PPy-BP had high ORR activity and good catalytic stability. • DBFC using FeS-PPy-BP as cathode achieved high power density. • FeS-PPy-BP is promising cathode catalyst for DBFC. The sluggish oxygen reduction reaction (ORR) in cathode is the bottleneck of polymer electrolyte membrane fuel cell. Discovery of ORR catalysts with high activity and low cost is the key solution for the cell development. In this work, we synthesized a novel polypyrrole modified carbon supported FeS (FeS-PPy-BP) through two-step reaction and used it as cathode catalyst in direct borohydride fuel cell (DBFC). The catalyst had an onset ORR potential of 0.89 V (vs. reversible hydrogen electrode (RHE)), little lower than the onset potential of commercial Pt/C. The ORR on the FeS-PPy-BP was mainly through 4-electron process with a low yield of H₂O₂ (below 5%). The FeS-PPy-BP exhibited a good catalytic stability. The half-wave potential shift of the FeS-PPy-BP after 5000 cycles was 31 mV while that of the Pt/C was 42 mV. The DBFCs using the FeS-PPy-BP as cathode catalyst achieved a maximum power density of 140.5 and 78.8 mW cm⁻² at 60 and 30 °C, respectively. The outstanding electrochemical properties and the cell performances strongly support the FeS-PPy-BP as a promising cathode catalyst for DBFC.