Nitrogen-doped carbon (CN x ) nanostructures are appealing metal-free electrocatalysts for some key electrochemical processes such as oxygen reduction reaction (ORR), due to their low cost, exceptional stability, and desirable selectivity. However, the precise configuration engineering of N-related active sites still remains a big challenge. Herein, we report a concept of monovacancy coupled pyridinic N (MV-c-PN) active site, which is designed and successfully fabricated by the pyrolysis of welldesigned precursor. This unique active site couples the features of pyridinic N and topological monovacancy defect, synergistically tuning the electronic properties of CN x moiety. This tuning induces stronger adsorption of oxygen-containing intermediates on the MV-c-PN sites and alters the ORR kinetics pathway. Additionally, the hierarchical porous nature of CN x nanostructure facilitates the penetration of electrolyte and the transportation of O 2 . Accordingly, the CN x nanomaterial with such MV-c-PN sites shows outstanding ORR activity in alkaline solution, surpassing most of the reported metal-free catalysts, with its intrinsic turnover frequency (TOF) 7.26 times higher than conventional pyridinic N. The assembled zinc-air battery reaches a maximum power density even 40.3% higher than that with the benchmark Pt/C. Our fine configuration engineering of CN x active sites provides a novel strategy for developing efficient carbon-based metal-free ORR catalysts.

A widely adopted strategy to enhance the electronic conductivity of lithium transition metal phosphates is to form a phosphate/C composite by introducing reagents (carbon sources) that can transform to carbon during calcination. In the present work, a systematic study combining X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, solid-state nuclear magnetic resonance, and electrochemical measurements was conducted to investigate how the electrostatic interaction between the functional groups (carboxyl, hydroxyl, etc.) of a carbon source and the building units of Li3V2(PO4)3 (Li+, VO2+, PO4 3–, etc.) in the original precursor affects the structure of a Li3V2(PO4)3–carbon interface in the final composite. It was demonstrated that the types and concentrations of electronegative functional groups in a carbon source play an important role in controlling not only the morphology of the product but also the composition, crystallinity and microstructure of the Li3V2(PO4)3–carbon interface and, in turn, the electrochemical behavior of the Li3V2(PO4)3/C composite. This study provides guidance on carbon–lithium transition metal phosphate interface design and control.

Combining XRD with 31P NMR, it is demonstrated that the Mg and Cl atoms of the new Mg and Cl co-doped Li3V2(PO4)3/C material occupy V and O sites in its structure, respectively.