Although the performance of the self-standing electrode has been enhanced for aqueous zinc-ion batteries (AZIBs), it is necessary to explore and analyse the deep modification mechanism (especially interface effects). Herein, density functional theory (DFT) calculations are applied to investigate the high-performance cathode based on the VO₂/carbon cloth composites with heterostructures interface (H-VO₂@CC). The adsorption energy comparisons and electron structure analyses verify that H-VO₂@CC has extra activated sites at the interface, enhanced electrical conductivity, and structural stability for achieving high-performance AZIBs due to the presence of built-in electric field at the interfaces. Accordingly, the designed self-standing H-VO₂@CC cathode delivers higher rate capacity, longer-life cyclability, and faster electronic/ion transmission kinetics benefiting from the synergistic effects. The risks of active material shedding and dissolution during the dis/charge process of two cathodes were evaluated via ex-situ ultraviolet–visible (UV–vis) spectrum and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) technique. Finally, this investigation also explores the charge storage mechanism of H-VO₂@CC through various ex-situ and in-situ characterization techniques. This finding can shed light on the significant potential of heterostructures interface engineering in practical applications and provide a valuable direction for the development of cathode materials for AZIBs and other metal-ion batteries.

Developing highly active iron-nitrogen-carbon catalysts for electrocatalytic oxygen reduction reactions (ORR) is pivotal to future energy technology. The penta-coordinated Fe-N-C with an augmented activity toward the oxygen reduction has been regarded as one of the promising candidates to replace platinum-based ORR catalysts. However, the lack of pertinent fundamental understanding hinders further optimizing the catalytic activity of such catalysts. Herein, through density functional theory (DFT) calculations, we systematically investigated the catalytic activity and ligand/metal coordination effects of 17 penta-coordinated Fe-N-C catalysts (labeled as FeNC-Xs, X denotes axial ligand). Our results not only show the theoretical overpotential of FeNC-Xs is lower than that of conventional tetra-coordinated Fe-N-C catalysts (labeled as FeNC), verifying the preeminent performance of FeNC-Xs, but also further indicate that the axial coordination effect of X ligands can decrease the orbital hybridization of Fe active center with ORR-relevant intermediates, sequentially accelerating the ORR. More importantly, we reveal that the catalytic activity of FeNC-Xs increases with a decreased electronegativity of X ligands, which can be utilized to describe the axial coordination effect for FeNC-Xs. These findings can deeply advance the understanding of penta-coordinated iron-nitrogen-carbon catalysts, which provide timely guidelines for designing optimum Fe-N-C based catalysts.

Designing highly efficient bifunctional electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) is extremely important for developing regenerative fuel cells and metal-air batteries. Single-atom catalysts (SACs) have gained considerable attention in recent years because of their maximum atom utilization efficiency and tunable coordination environments. Herein, through density functional theory (DFT) calculations, we systematically explored the ORR/OER performances of nitrogen-coordinated transition metal carbon materials (TM-N_x-C (TM = Mn, Fe, Co, Ni, Cu, Pd, and Pt; x = 3, 4)) through tailoring the coordination environment. Our results demonstrate that compared to conventional tetra-coordinated (TM-N₄-C) catalysts, the asymmetric tri-coordinated (TM-N₃-C) catalysts exhibit stronger adsorption capacity of catalytic intermediates. Among them, Ni-N₃-C possesses optimal adsorption energy and the lowest overpotential of 0.29 and 0.28 V for ORR and OER, respectively, making it a highly efficient bifunctional catalyst for oxygen catalysis. Furthermore, we find this enhanced effect stems from the additional orbital interaction between newly uncoordinated d-orbitals and p-orbitals of oxygenated species, which is evidently testified via the change of d-band center and integral crystal orbital Hamilton population (ICOHP). This work not only provides a potential bifunctional oxygen catalyst, but also enriches the knowledge of coordination engineering for tailoring the activity of SACs, which may pave the way to design and discover more promising bifunctional electrocatalysts for oxygen catalysis.

Although some experiments have shown that point defects in a cathode host material may enhance its performance for lithium-sulfur battery (LSB), the enhancement mechanism needs to be well investigated for the design of desired sulfur host. Herein, the first principle density functional theory (DFT) is adopted to investigate a high-performance sulfur host material based on oxygen-defective TiO₂ (D-TiO₂). The adsorption energy comparisons and Gibbs free energy analyses verify that D-TiO₂ has relatively better performances than defect-free TiO₂ in terms of anchoring effect and catalytic conversion of polysulfides. Meanwhile, D-TiO₂ is capable of absorbing the most soluble and diffusive long-chain polysulfides. The newly designed D-TiO₂ composited with three-dimensional graphene aerogel (D-TiO₂@Gr) has been shown to be an excellent sulfur host, maintaining a specific discharge capacity of 1,049.3 mAh·g^-1 after 100 cycles at 1C with a sulfur loading of 3.2 mg·cm^-2. Even with the sulfur mass loading increasing to 13.7 mg·cm^-2, an impressive stable cycling is obtained with an initial areal capacity of 14.6 mAh·cm^-2, confirming the effective enhancement of electrochemical performance by the oxygen defects. The DFT calculations shed lights on the enhancement mechanism of the oxygen defects and provide some guidance for designing advanced sulfur host materials.