Abstract
The exploration of noble metal-free catalysts with efficient electrochemical performance toward oxygen reduction reaction in the acid electrolyte is very important for the development of fuel cells technology. Novel pyrolyzed heteroatom-doped Fe/N/C catalysts have been regarded as the most efficient electrocatalytic materials for ORR due to their tunable electronic structure, and distinctive chemical and physical properties. Herein, nitrogen- and sulfur-doped (Fe/N/C and Fe/N/C-S) electrocatalysts were synthesized using ferric chloride hexahydrate as the Fe precursor, N-rich polymer as N precursor, and Ketjen Black EC-600 (KJ600) as the carbon supports. Among these electrocatalysts, the as prepared S and N-doped Fe/N/C-S reveals the paramount ORR activity with a positive half-wave potential value (E1/2) 0.82 at 0.80 V vs. RHE in 0.1 mol/L H2SO4 solution, which is comparable to the commercial Pt/C (Pt 20 wt%) electrocatalyst. The mass activity of the Fe/N/C-S catalyst can reach 45% (12.7 A g−1 at 0.8 V) and 70% (5.3 A g−1 at 0.95 V) of the Pt/C electrocatalyst in acidic and alkaline solutions. As result, ORR activity of PGM-free electrocatalysts measured by the rotating-ring disk electrode method increases in the following order: Fe/N/C<Fe/N/C-S, in both basic and acidic medium. This scientific work offers a facile approach to design and synthesizes efficient heteroatom-doped catalytic materials for electrochemical reactions in energy devices.
Highlights
The electrochemical oxygen reduction reaction is the most significant process at cathode in the polymer electrolyte membrane fuel cell (PEMFC) and anion-exchange membrane alkaline fuel cell (AEMFC)
The large-scale fuel cell applications are confined owing to high-cost, the fact they are poisoning to CO and methanol, have limited supply and long-term stability, low electrocatalytic selectivity, and due to the sluggish reaction kinetics of noble metal-doped (Pt, Pd, Ru, etc.) catalysts for ORR (Rauf et al, 2018; Wang Y. et al, 2018)
The XRD patterns showed broad and prominent peaks centering at the 2θ angles of 26.2◦ and 43◦, which were assigned to the graphitic carbon framework of (002) and (100) planes, respectively
Summary
The electrochemical oxygen reduction reaction is the most significant process at cathode in the polymer electrolyte membrane fuel cell (PEMFC) and anion-exchange membrane alkaline fuel cell (AEMFC). The heteroatom-doped Fe/N/C electrocatalysts had shown higher ORR performance in basic solution as compared to the acid solution, due to different reaction mechanisms under different pH values of electrolyte solution (Rauf et al, 2016; Gewirth et al, 2018).
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