High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt

Abstract

The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).

High‐Performance Direct Methanol Fuel Cells with Precious‐Metal‐Free Cathode

“…The activity gap between the state‐of‐the‐art Pt/C (E‐TEK) and the Fe‐N‐rGO‐900°C catalyst, as reflected by a difference of half‐wave potential (Δ E 1/2 ) in RDE testing, has been substantially reduced to ≈60 mV (0.85 vs 0.79 V). The measured ORR activity in acidic media is comparable to that of advanced NPMCs 9. The Fe‐N‐rGO‐900 °C catalyst also demonstrates superior ORR activity in comparison to Fe‐N‐KJ‐900 °C and N‐rGO‐900 °C catalysts (Figure 5c).…”

“…On the other hand, high stability of the Fe‐N‐rGO‐900 °C catalyst is demonstrated in potential cycling tests (Figure 5d). The cycling was carried out within a potential range of 0.6 to 1.0 V in nitrogen‐saturated 0.5 m H 2 SO 4 at a scan rate of 50 mV s −1 9. No significant activity loss was observed in the ORR kinetic region of Fe‐N‐rGO‐900 °C catalyst even after 10 000 cycles, attesting to the high durability of the developed catalysts in acidic electrolyte.…”

“…In a search for high‐performance alternative NPMCs to Pt cathode over the last decade, significant progress has been made from new catalyst synthesis 6, 7, 8, 9, 10. Among the studied formulations, iron‐nitrogen‐carbon (Fe‐N‐C) catalysts are the most promising in terms of their activity and stability in more challenging acidic electrolytes 11, 12, 13, 14, 15.…”

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

“…We also demonstrated that FeN x C y moieties and Fe@N‐C species are moderately active toward PRR, proving their possible roles in both direct (major path) and indirect 4 e − ORR pathways. Since the synthesis of Fe‐N‐C catalysts with only FeN x C y moieties,10b, 15 only Fe@N‐C particles,10a or their combination3b,3d, 17 is now controllable, the understanding of the nature of active sites for PRR provided herein offers new insights for the rational design of advanced Fe‐N‐C catalysts with high selectivity and expectedly improved durability in polymer electrolyte fuel cells. …”

Surfactant-Template Preparation of Polyaniline Semi-Tubes for Oxygen Reduction

“…Very recently, a variety of N-doped carbon catalysts based on PANI have been constructed which showed superior electrocatalytic activities for the ORR [7][8][9][10][11][12]. The multi-technique characterization have suggested that the enviable performance should be ascribed to the formation of metal-N complexion structures as well as the carbon nanostructures such as thin graphene sheets and nanofibers [10][11][12].…”