Enhancing oxygen reduction reaction performance through eco-friendly chitosan gel-assisted molten salt strategy: Small NiCo alloy nanoparticles decorated with high-loading single Fe-NX.

We developed an effective and eco-friendly strategy using chitosan gel-molten salt to achieve high loading (2.23 At. %) of single Fe-N X as assistive active sites. These sites were combined with small NiCo alloy NPs distributed on porous carbon aerogels to boost the ORR performance. The FeSAs-NiCo alloy@N-C sphere exhibits exceptional mass activity and specific activity of 3.705 A.mg−1 and 8.79 mA.cm−2 (ECSA) , respectively, at 0.85 V versus RHE. It has a superior onset potential of 1.08 V versus RHE, surpassing that of its nanoparticle Fe counterpart and NiCo alloy@N-C sphere. The significant improvement in ORR performance of the FeSAs-NiCo alloy@N-C sphere could be attributed to the positive effects of increased lattice strain due to the single atoms of Fe-N X hybridized with small NiCo alloy NPs. The chitosan gel-assisted molten salt strategy and assistive active sites of Fe-N X hybridized with NiCo alloy NPs regulate the electronic properties of the FeSAs-NiCo alloy@N-C sphere, both geometrically via lattice strain mismatch and electronically through shifting of the d-band center. This could influence the binding energies for oxygen and/or oxygen reduction intermediate adsorption/desorption. The additional improvement in the ORR performance of the FeSAs-NiCo alloy@N-C sphere also benefits from having a lower electrochemical activation energy. [Display omitted] • The coexistence of alloy nanoparticles with single atoms can enhance the performance of ORR, by tuning geometric and electronic properties. • An effective and eco-friendly chitosan gel assistive molten salt strategy was reported for designing high-loading single Fe–N X as assistive active sites that are further hybridized with small NiCo alloy NPs. • FeSAs-NiCo alloy@N-C sphere demonstrated exceptional mass activity (MA) and specific activity (SA) of 3.705 A mg-1 and 8.79 mA cm ECSA -2, respectively, at 0.85 V versus RHE. • Constructing single atom assistive active sites hybridizing with small NiCo alloy NPs can enhance dual functionality simultaneously for ORR activities. [ABSTRACT FROM AUTHOR]