Proton exchange membrane fuel cells convert hydrogen and oxygen into electricity without emissions. The high cost and low durability of Pt-based electrocatalysts for the oxygen reduction reaction hinder their wide application, and the development of non-precious metal electrocatalysts is limited by their low performance.
Here we design a hybrid electrocatalyst that consists of atomically dispersed Pt and Fe single atoms and Pt–Fe alloy nanoparticles. Its Pt mass activity is 3.7 times higher than that of commercial Pt/C in a fuel cell.
More importantly, the fuel cell with a low Pt loading in the cathode (0.015 mgPt cm−2) shows an excellent durability, with a 97% activity retention after 100,000 cycles and no noticeable current drop at 0.6 V for over 200 hours.
These results highlight the importance of the synergistic effects among active sites in hybrid electrocatalysts and provide an alternative way to design more active and durable low-Pt electrocatalysts for electrochemical devices.
Proton exchange membrane fuel cells (PEMFCs) as a promising clean energy conversion technology have gained considerable attention. However, the high cost and low durability of Pt-based nanocatalysts for the cathodic oxygen reduction reaction (ORR) hinder the wide adoption of this technology1,2.
According to the ultimate cost target of US$30 kW−1 for the fuel cell stack3, the Pt loading in the catalyst layers must be below 0.125 mg cm−2 (ref. 4). However, as the Pt loading decreases, the oxygen transfer resistance increases because of the limited accessible active sites, which results in a lower durability4.
Thus, the ambition to develop low-Pt-loading cathodes poses great challenges in the areas of Pt utilization and the intrinsic durability of Pt-based electrocatalysts.
Despite great efforts in the development of advanced Pt-based catalysts to improve the Pt utilization and mass activity (MA) towards ORR5,6, high activities and/or durability measured in liquid cells have rarely been realized in fuel cells.
However, carbon-based Pt-group-metal-free ORR electrocatalysts that consist of highly dispersed transition metal single atoms in nitrogen-coordinated carbon surfaces (Me–N–C) are promising candidates to replace Pt (ref. 7).
Unfortunately, the poor durability of Me–N–C has limited their practical applications8. Some early studies9,10 applied Me–N–C as a support for Pt-based electrocatalyst with the aim to improve the stability of the latter.
Recently, Liu and co-workers reported a hybrid catalyst with an ultralow Pt loading (2–3 wt%) that consisted of Pt–Co alloy nanoparticles supported on Co–N–C with an excellent ORR activity (1.77 A mgPt−1 at 0.9 ViR-free, without pressure correction)11.
This result indicates that even small amounts of Pt introduction could contribute to a high activity enhancement of the hybrid electrocatalyst.
Despite the excellent Pt MA of this hybrid ORR catalyst, it still suffered notable activity losses during potential cycling (83% after 30,000 cycles between 0.6 and 0.95 V) and potential hold (45% after 22 hours at 0.75 V) (ref. 11).
Jaouen and co-workers12 found that the stability of Fe–N–C could be improved by adding a small amount of Pt (1–2 wt%), although the activity did not change.
Here we report a hybrid electrocatalyst (denoted as Pt-Fe-N-C) that consists of Pt–Fe alloy nanoparticles on highly dispersed Pt and Fe single atoms in a nitrogen-doped carbon support.
The multiple types of active sites result not only in a 3.7 times higher Pt MA, but also in an excellent durability. The performance loss is negligible even after 100,000 potential cycles, and no current drop is observed at 0.6 V in a fuel cell test with an ultralow Pt loading (0.015 mgPt cm−2) in the cathode.
Atomically dispersed Pt and Fe sites and Pt–Fe nanoparticles for durable proton exchange membrane fuel cells, June 2, 2022
