Simultaneously increasing the activity and stability of the single-atom active sites of M–N–C catalysts is critical but remains a great challenge. Here, we report an Fe–N–C catalyst with nitrogen-coordinated iron clusters and closely surrounding Fe–N4 active sites for oxygen reduction reaction in acidic fuel cells. A strong electronic interaction is built between iron clusters and satellite Fe–N4 due to unblocked electron transfer pathways and very short interacting distances. The iron clusters optimize the adsorption strength of oxygen reduction intermediates on Fe–N4 and also shorten the bond amplitude of Fe–N4 with incoherent vibrations. As a result, both the activity and stability of Fe–N4 sites are increased by about 60% in terms of turnover frequency and demetalation resistance. This work shows the great potential of strong electronic interactions between multiphase metal species for improvements of single-atom catalysts.

The environmentally friendly synthesis of highly active Fe-N-C electrocatalysts for proton-exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is presented to fabricate Fe II -doped ZIF-8, which can be further pyrolyzed into Fe-N-C with 3wt% of Fe exclusively in Fe-N 4 active moieties.Significantly,this Fe-N-C derived acidic PEMFC exhibits an unprecedented current density of 1.65 Acm À2 at 0.6 Vand the highest power density of 1.14 Wcm À2 compared with previously reported NPMCs.T he excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe-N 4 active moieties on the small and uniform catalyst nanoparticles.Proton-exchange membrane fuel cells (PEMFCs) are ideal clean-energy systems that efficiently convert the chemical energy of hydrogen/oxygen into electricity through electrochemical reactions. [1] Theapplication of PEMFCs is,however, hindered by the scarcity and intolerable cost of the precious metal Pt, which is the most efficient catalyst so far for oxygen reduction reaction (ORR), and accounts for about 40 %ofthe fuel cell cost. [2] As anon-precious metal catalyst (NPMC), Fe-N-C decorated with Fe-N 4 active moieties has emerged as ap romising alternative to Pt for its high initial performance close to commercial Pt/C(20 %) in acidic PEMFCs. [3] The maximum power densities (P max )o ft hese Fe-N-C derived PEMFCs have reached above 0.9 Wcm À2 or even over 1Wcm À2 to date (the largest P max of 1.06 Wcm À2 was achieved at 2bar H 2 /O 2 @80 8 8Cin2 017). [4] Although the three-electrode system (half-cell) is efficient for afast judgement of the NPMC catalytic activity,PEMFC measurement is more valuable for comprehensively evaluating catalyst properties in the actual working condition. [5] The NPMC fuel cell performance is commonly determined by two factors.O ne is the mass transport property of the catalyst layer, which influences the utilization of the active sites and the polarization of the fuel cell; [6] theo ther is the catalyst parameters,i ncluding the composition and the dispersion density of active sites,a nd the catalyst morphology and size, Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

To develop efficient and durable acidic oxygen–reduction–reaction (ORR) catalysts based on all platinum group metals (PGMs) is crucial for large-scale application of proton-exchange membrane fuel cells (PEMFCs) but challenging. Here, we report a nitrogen coordination-induced strong metal–support interaction that can tune the surface atoms of ORR-inactive PGM clusters into efficient and durable active sites. Taking Rh as an example, the carbonization of Rh-overdoped zeolitic imidazolate framework-8 results in a large number of Rh clusters (with a little atomic Rh) in porous nitrogen-doped carbon. The cluster surface atoms coordinate with the nitrogen of the carbon support, forming much stronger metal–support interactions than that of common N-doped carbon-supported metal nanoparticles. The activity of surface-activated Rh clusters is close to that of Pt/C. The regulation rules for the surface active sites inherit most of the characteristics of the corresponding single-atom catalysts, but without their severe instability problem. This surface activation strategy has also shown applicable to other PGMs, thereby it is a promising way to alleviate the reliance of PEMFCs on platinum.