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.

Developing efficient oxygen reduction reaction (ORR) catalyst is essential for the practical application of Zn-air batteries (ZABs). In this contribution, we develop a novel zeolitic imidazolate framework (ZIF)-mediated strategy to anchor Co species on N-doped carbon nanorods for efficient ORR. Featuring ultrahigh N-doping (10.29 at.%), monodisperse Co nanocrystal decoration, and well-dispersed Co-N_x functionalization, the obtained Co-decorated N-doped carbon nanorods (Co@NCNR) exhibit a decent ORR performance comparable to commercial Pt/C in alkaline media. Aqueous ZABs have been assembled using Co@NCNR as the cathode catalyst. The assembled ZABs manifest high initial open-circuit voltage as well as high energy density. In addition, the Co@NCNR also demonstrates ideal ORR performance in quasi-solid-state ZABs.

Exploring efficient, cost-effective, and durable electrocatalysts for electrochemical oxygen evolution reaction (OER) is pivotal for the large-scale application of water electrolysis. Recent advance has demonstrated that the activity of electrocatalysts exhibits a strong dependence on the surface electronic structure. Herein, a series of ultrathin metal silicate hydroxide nanosheets (UMSHNs) M₃Si₂O₅(OH)₄ (M = Fe, Co, and Ni) synthesized without surfactant are introduced as highly active OER electrocatalysts. Cobalt silicate hydroxide nanosheets show an optimal OER activity with overpotentials of 287 and 358 mV at 1 and 10 mA cm⁻², respectively. Combining experimental and theoretical studies, it is found that the OER activity of UMSHNs is dominated by the metal–oxygen covalency (MOC). High OER activity can be achieved by having a moderate MOC as reflected by a σ^*-orbital (e_g) filling near unity and moderate [3d]/[2p] ratio. Moreover, the UMSHNs exhibit favorable chemical stability under oxidation potential. This contribution provides a scientific guidance for further development of active metal silicate hydroxide catalysts.

The unsatisfactory conductivity and large volume variation severely handicap the application of SnO₂ in sodium-ion batteries (SIBs). Herein, we design unique three-layer structured SnO₂@C@TiO₂ hollow spheres to tackle the above-mentioned issues. The hollow cavity affords empty space to accommodate the volume variation of SnO₂, while the C and TiO₂ protecting shells strengthen the structural integrity and enhances the electrical conductivity. As a result, the three-layer structured SnO₂@C@TiO₂ hollow spheres demonstrate enhanced Na storage performances. The SnO₂@C@TiO₂ manifests a reversible capacity two times to that of pristine SnO₂ hollow spheres. In addition, Ex situ XRD reveals highly reversible alloying and conversion reactions in SnO₂@C@TiO₂ hollow spheres. This study suggests the introduction of a hollow cavity and robust protecting shells is a promising strategy for constructing SIB anode materials.

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.