Non-precious Fe/N co-modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron-free N-doped carbon electrocatalysts, Fe/N-modified electrocatalysts show four-electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe-N complexes, however, the Fe-N structure remains unknown. We used o,m,p-phenylenediamine as nitrogen precursors to tailor the Fe-N structures in heterogeneous electrocatalysts which contain FeS and Fe3 C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half-wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe-N6 complexes (FeN6, [Fe(III)(porphyrin)(pyridine)2]). We expect the understanding of the FeN6 structure will pave the way towards new advanced Fe-N based electrocatalysts.

Incorporating heteroatoms into onion-like carbon (OLC, average size ∼5 nm) with a fullerene-like structure and investigating its peculiar properties are fascinating challenges. Here, we present straightforward fabrication of doped OLC samples with a high concentration of boron (0.63–4.57 at%) via a high-temperature thermal diffusion method. The highest proportion of substitutional boron of the boron species reaches 29%, which far exceeds most of the reported boron-doped carbon materials. The influence of boron on the fullerene-like layers and electronic properties of OLC is systematically investigated using Raman spectroscopy with different excitation energies (1.58–3.8 eV) and ultraviolet photoelectron spectroscopy (UPS). The as-prepared boron-doped OLC samples exhibit a perfect four-electron process for the oxygen reduction reaction (ORR), which is similar to commercial Pt/C. It is worth noting that the intrinsic relationship between the electronic properties and catalytic performance of doped samples is explored based on experimental studies instead of theoretical calculations. The results indicate that the lower work function, lower valence band edge and higher density of states (DOSs) of doped OLC are crucial to improve the catalytic performance. Our work can provide valuable information on the design of doped metal-free materials and give new evidence for enhanced ORR activity associated with heteroatom doping and electronic properties

Non-precious Fe/N co-modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron-free N-doped carbon electrocatalysts, Fe/N-modified electrocatalysts show four-electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe-N complexes, however, the Fe-N structure remains unknown. We used o,m,p-phenylenediamine as nitrogen precursors to tailor the Fe-N structures in heterogeneous electrocatalysts which contain FeS and Fe 3 C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half-wave potential. By combining advanced electron microscopy and Mçssbauer spectroscopy, we have identified the electrocatalytically active Fe-N 6 complexes (FeN 6 , [Fe III (porphyrin)(pyridine) 2 ]). We expect the understanding of the FeN 6 structure will pave the way towards new advanced Fe-N based electrocatalysts.