Hard carbon (HC) is widely regarded as one of the most promising anode materials for commercial sodium-ion batteries due to its excellent electrochemical performance and cost-effectiveness. Although organic polymers offer compositional homogeneity and structural tunability as HC precursors, their high raw material costs and uncontrollable carbonization processes limit large-scale applications. Here, we introduce a liquid-phase carbonization strategy to recycle waste polyethylene terephthalate (PET) into porous micro/nanostructured HC enriched with intrinsic carbon defects (LHC-3, LHC = liquid-phase-prepared hard carbon). These carbon defects and the morphological structures were modulated by bubbles generated from the decomposition of PET in the presence of N,N’-dimethylformamide and zinc acetate. The synergistic effects between intrinsic carbon defects and micro/nanostructure endow LHC-3 anode with high specific capacity (355 mAh·g⁻¹ at 0.1 A·g⁻¹), superfast charging capability (132.6 mAh·g⁻¹ input within 13 s of charging), and ultralong cycling stability (100,000 stable cycles at 50 A·g⁻¹). The sodium storage mechanism of LHC-3 anode was investigated by ex-situ Raman spectroscopy, X-ray photoelectron spectroscopy, and ion diffusion kinetics analysis. Theoretical calculations indicate that intrinsic carbon defects with non-zero curvature structure in LHC-3 enhance its ability to accommodate more Na⁺. These findings are expected to have broader applications in energy storage and waste management.

Using simple methods to obtain efficient catalysts has been a long-standing goal for researchers. In this work, the employment of a one-pot pyrolysis reaction to achieve molecular confinement, has led to the preparation of ruthenium (Ru)-based nanoclusters in a carbon matrix. A unique feature of the synthetic approach employed is that solvent and substrates were calcined together. As solvent evaporates, during calcination, the substrates form a dense solid which has the effect of limiting the aggregation of Ru centers during the carbonization process. The catalyst prepared in this simple manner showed an impressively high activity with respect to the hydrogen/oxygen evolution reaction (HER/OER). The Ru nanoclusters (Ru NCs), as the hydrogen evolution reaction (HER) catalysts, require ultralow overpotentials of 5 mV and 5.1 mV at –10 mA·cm^–2 in 1.0 M KOH, and 0.5 M H₂SO₄, respectively. Furthermore, the catalyst prepared by the one-pot method has higher crystallinity, a higher Ru content and an ultrafine cluster size, which contributes to its exceptional electrochemical performance. Meanwhile, the RuO_X nanoclusters (RuO_X NCs), obtained by oxidizing the aforementioned Ru NCs, exhibited good oxygen evolution reaction (OER) performance with an overpotential of 266 mV at 10 mA·cm^–2. When applied to overall water splitting, Ru/RuO_X nanoclusters as the cathode and anode catalysts can reach 10 mA·cm^–2 at cell voltages of only 1.49 V in 1 M KOH.