Synthesis of Highly Active Fe-N-C Catalysts Via Non-Contact Pyrolysis of Gas-Phase Iron

INV-20028

 

Hydrogen fuel cell vehicles (FCVs), based on proton exchange membrane fuel cells (PEMFCs), were commercialized in 2014. The catalysts used for the oxygen reduction reaction (ORR) in PEMFCs are Pt-alloys. The cost of automotive fuel cell systems is still high due to the high loading of Pt on the PEMFC cathode. One of the strategies to address this issue is to replace Pt-alloys with earth-abundant, inexpensive materials (platinum group metal (PGM)-free). The leading PGM-free catalysts for the ORR in PEMFCs are single transition metal atoms (M=Mn, Fe or Co) embedded in a nitrogen-doped carbon matrix (M-N-C). 

However, the ORR activities of the type of M-N-C catalysts are still worse than that of Pt. Closing the activity gap between the M-N-C catalysts and Pt holds the key for replacing Pt with M-N-C in practical PEMFCs. By far, the synthesis strategies for M-N-C catalysts consist of combining sources of M, N, and C either in a single compound or in separate compounds and pyrolyzing the compound(s) typically in the 900 to 1100 °C temperature range. 

 

Northeastern researchers have developed a new synthesis approach (chemical vapor deposition) that is distinctly different from conventional ones. Specifically, the iron precursor anhydrous FeCl3 and the N-doped carbon (N-C) substrate are separately placed in two boats in a tube rather than mixing during the pyrolysis. Then the FeCl3 is evaporated at relatively low temperature at 750 ℃, and the gas phase FeCl3 incorporates into the N-C forming dense Fe-N4 sites. The formed Fe-N-C catalyst exhibits a record-high ORR activity in an H2-O2 PEMFC at 0.9 V. Multi-pronged characterizations show that the high activity can be ascribed to the ultrahigh density of Fe-N4 sites.

 

- The synthesized catalyst shows an unprecedented ORR activity in an H2-O2 PEMFC

- The synthesized catalyst has a Fe wt% of 4 wt%, which is four times higher than conventional ones (~ 1wt%)

- The surface deposition feature of this method forms enriched Fe-N4 sites on the surface and thus favors the PEMFC performance

- High scale-up production

 

- It can be used as the cathode catalyst in the PEMFC in hydrogen fuel cell vehicles

- It can be used as the cathode catalyst in the hydrogen fuel cells for stationary applications

- It can be used as the catalyst for CO2 reduction

- It can be used as the cathode catalyst in direct methanol fuel cell

- It can be used as the cathode catalyst in alkaline fuel cells

 

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