N and S dual-coordinated Fe single-atoms in hierarchically porous hollow nanocarbon for efficient oxygen reduction.

Fe-, and N-co-doped carbon (FeNC) electrocatalysts are promising alternatives to Pt-based catalysts for oxygen reduction reaction (ORR); however, simultaneously enhancing their intrinsic activity and exposure of Fe active sites remains challenging. Herein, we report S-modified Fe single-atom catalysts (SACs) anchored on N,S-co-doped hollow porous nanocarbon (Fe/NS-C) for ORR. The unique hollow structure and large surface area of the SACs are favorable for mass/electron transport and exposure of Fe single-atom active sites. The as-prepared Fe/NS-C electrocatalysts display a high-efficiency ORR activity with a half-wave potential of 0.893 V versus the reversible hydrogen electrode and exceed that of the benchmark commercial Pt/C catalyst as well as most reported transition-metal based SACs. Impressively, the Fe/NS-C-based Al-air battery (AAB) displays a high open circuit voltage of 1.48 V, a maximum power density of 140.16 mW cm-2, and satisfactory durability, outperforming commercial Pt/C-based AAB. Furthermore, Fe/NS-C exhibits considerable potential as a cathode catalyst for application in direct methanol fuel cells. Experimental and theoretical calculation results reveal that the excellent ORR performance of Fe/NS-C can be contributed to the highly active FeN3S sites and the unique hollow structure. This work provides new insights into the rational design and synthesis high-performance ORR electrocatalysts for energy conversion and storage devices. of employing ZIF-8 as precursors.

ZnS anchored on porous N, S-codoped carbon as superior oxygen reduction reaction electrocatalysts for Al-air batteries.

The development of non-precious based oxygen reduction reaction (ORR) catalysts with outstanding catalytic performance is desirable but still a grand challenge for practical Al-air battery. Herein, we report a vulcanization-assisted pyrolysis strategy for creating zeolitic imidazolate framework-derived catalysts with a N, S co-doped carbon support and highly exposed ZnS and Zn-Nx sites. The trithiocyanuric acid (TCA) is found not only to introduce S into the carbon derived from ZIF-8 and ZnS to adjust the electronic structure of carbon matrix during the pyrolysis, but also result in a shrinkage of carbon framework with a hierarchical porous structure. Such an architecture boosts abundant active sites exposed and accelerates remote mass transportation. As a result, the optimized 3.5ZnS/NSC-NaCl-900 delivers an impressive enhanced performance toward ORR in alkaline medium with a high half-wave potential of 0.905 V (vs. reversible hydrogen electrode), which is superior to most of non-precious metal-based catalysts. Density functional theory calculations unveil that the ZnS in 3.5ZnS/NSC-NaCl-900 can effectively lower the Gibbs energy barrier of crucial steps and therefore promotes the reaction kinetics. Furthermore, 3.5ZnS/NSC-NaCl-900 also displays greater power density and specific capacity than Pt/C in Al-air batteries.