The Fe–N–C material represents an attractive oxygen reduction reaction electrocatalyst, and the FeN₄ moiety has been identified as a very competitive catalytic active site. Fine tuning of the coordination structure of FeN₄ has an essential impact on the catalytic performance. Herein, we construct a sulfur-modified Fe–N–C catalyst with controllable local coordination environment, where the Fe is coordinated with four in-plane N and an axial external S. The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN₄ active site. The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons. With the above characteristics, the adsorption and desorption of the reactants at FeN₄ active sites are optimized, thus promoting the oxygen reduction reaction activity. This work explores the key point in electronic configuration and coordination environment tuning of FeN₄ through S doping and provides new insight into the construction of M–N–C-based oxygen reduction reaction catalysts.

Trivalent titanium doped titania/carbon (TiO_2–x/C) composite microspheres have been prepared by a facile aerosol method (ultrasonic spray pyrolysis) using titanium (Ⅳ) bis(ammonium lactato)dihydroxide (TiBALDH) as the sole precursor. The obtained TiO_2–x/C microspheres have particle sizes in the range of 400–1, 000 nm. When evaluated as anode material for sodium-ion batteries (SIBs), they provide a high reversible capacity of 286 mA·h·g^–1 with good cycling performance. A capacity of 249 mA·h·g^–1 can be achieved after 180 cycles at 50 mA·g^–1, which is more than three times higher than that of white TiO₂ microspheres (77 mA·h·g^–1). The superior sodium storage performance of these TiO_2–x/C composite microspheres can be attributed to the simultaneous introduction of Ti³⁺ and oxygen vacancies, ultrafine grain size, as well as the conductive carbon matrix. This study provides a facile and effective approach for the production of TiO_2–x/C nanocomposites with superior sodium storage performance.