Organic electrode materials hold substantial promise for sodium-ion batteries while suffering from poor electronic conductivity and high solubility in common organic electrolytes. Among various organic electrode materials, π-d conjugated coordination polymers (CCPs) are particularly noteworthy due to their exceptional chemical stability and conductivity, which arise from the hybridization between the d orbitals of metal ions and the π orbitals of organic ligands. Herein, we synthesized a variety of CCPs by utilizing 2,5-dihydroxy-1,4-benzoquinone (DHBQ) as a ligand, with M²⁺ (M = Ni, Co, and Mn) ions serving as metal centers. This approach enabled a thorough investigation into the impact of these metal sites on the electrochemical performance of the CCPs. Theoretical calculations demonstrated that Ni-DHBQ exhibits the smallest bandgap and the highest degree of π-d conjugation compared to its analogs, facilitating the transport of Na⁺ ions. Consequently, Ni-DHBQ delivers the highest capacity (157 mAh g⁻¹ at 0.1 A g⁻¹), enhanced rate ability (153.9 mAh g⁻¹ at 0.2 A g⁻¹), and remarkable cycling stability (capacity retention of 92.9% over 500 cycles at 1 A g⁻¹). Additionally, the reaction mechanism of Ni-DHBQ was comprehensively investigated using in situ x-ray diffraction, complemented by ex situ Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. The results suggest that π-conjugated quinone groups are responsible for the reversible accommodation of Na⁺ ions. This work underscores the significance of metal centers within CCPs, offering critical insights into the molecular-level design of CCPs with enhanced sodium-ion storage capabilities.

Based on the interference effect of surface self-oxidation peak on the oxygen evolution reaction (OER) performance, appropriate experimental strategies and data processing methods are crucial to correctly identify and address the oxidation peak in nickel-based materials to ensure data accuracy. Considering these facts that frequent OER performance misjudgment would confuse the readers, we revealed this reason and proposed the use of multi-potential step method to avoid non-steady-state currents caused by capacitive charging effects or intermediate oxidation. Additionally, combining electrochemical impedance spectroscopy (EIS) analysis, we discussed high-frequency response characteristics to further reveal the surface self-oxidation process. These research findings are crucial for accurately evaluating the actual performance of some special materials in electrochemical catalysis.

Covalent organic frameworks (COFs) after undergoing the superlithiation process promise high-capacity anodes while suffering from sluggish reaction kinetics and low electrochemical utilization of redox-active sites. Herein, integrating carbon nanotubes (CNTs) with imine-linked covalent organic frameworks (COFs) was rationally executed by in-situ Schiff-base condensation between 1,1′-biphenyl]-3,3′,5,5′-tetracarbaldehyde and 1,4-diaminobenzene in the presence of CNTs to produce core–shell heterostructured composites (CNT@COF). Accordingly, the redox-active shell of COF nanoparticles around one-dimensional conductive CNTs synergistically creates robust three-dimensional hybrid architectures with high specific surface area, thus promoting electron transport and affording abundant active functional groups accessible for electrochemical utilization throughout the whole electrode. Remarkably, upon the full activation with a superlithiation process, the as-fabricated CNT@COF anode achieves a specific capacity of 2324 mAh g⁻¹, which is the highest specific capacity among organic electrode materials reported so far. Meanwhile, the superior rate capability and excellent cycling stability are also obtained. The redox reaction mechanisms for the COF moiety were further revealed by Fourier-transform infrared spectroscopy in conjunction with X-ray photoelectron spectroscopy, involving the reversible redox reactions between lithium ions and C=N groups and gradual electrochemical activation of the unsaturated C=C bonds within COFs.