Heteroatom-doped hierarchical porous carbon via molten-salt method for supercapacitors

Fundamental understanding of nitrogen in biomass electrocatalysts for oxygen reduction and zinc-air batteries

Exploring high-efficiency catalysts for oxygen reduction reactions (ORRs) is essential for the development of large-scale applications of fuel cell and metal-air batteries technology. The as-prepared Fe-NC-800 via polymerization-pyrolysis strategy exhibited superior ORR activity with onset potential of 1.030 V vs. reversible hydrogen electrode (RHE) and half-wave potential of 0.908 V vs. RHE, which is higher than that of the Pt/C catalyst and most of other Fe-based catalysts. The different d-band center values can be attributed to the influence of different N-doped carbon, leading to the adjustment in the ORR activity. In addition, Fe-NC-800-based Zn-air battery showed better electrochemical performance with a high discharge specific capacity of 806 mA h g-1 and a high-power density of 220 mW cm-2 than that of the Pt/C-based battery. Therefore, the biomass Fe-NC-800 catalyst may become a promising substitute for Pt/C catalysts in energy storage and conversion devices.

Dual-Salt-Induced Hierarchical Porous Structure in a Carbon Sheet for High Performance Supercapacitors

Porous carbon, one of the characteristic materials for electrochemical energy storage devices, has been paid wide-ranging attention. However, balancing the reconcilable mesopore volume with a large specific surface area (SSA) was still a challenge. Herein, a dual-salt-induced activation strategy was developed to obtain a porous carbon sheet with ultrahigh SSA (3082 m² g^-1), desirable mesopore volume (0.66 cm³ g^-1), nanosheet morphology, and high surface O (7.87%) and S (4.0%) content. Hence, as a supercapacitor electrode, the optimal sample possessed a high specific capacitance (351 F g^-1 at 1 A g^-1) and excellent rate performance (holding capacitance up to 72.2% at 50 A g^-1). Furthermore, the assembled zinc-ion hybrid supercapacitor also exhibited superior reversible capacity (142.7 mAh g^-1 at 0.2 A g^-1) and highly stable cycling (71.2 mAh g^-1 at 5 A g^-1 after 10,000 cycles with retention of 98.9%). This work was delivered a new possibility for the development of coal resources for the preparation of high performance porous carbon materials.

Oxygen-enriched lignin-derived porous carbon nanosheets promote Zn2+ storage

Carbon-based zinc-ion capacitors (ZICs) have sparked intense research enthusiasm because of large power density, good rate capability and cycling stability. However, there is still a long way to go before they achieve commercial applications. Herein, oxygen-enriched lignin-derived porous carbon nanosheets (OLCKs) were prepared by one-step carbonization-activation method, and more O-containing functional groups were generated on the surface of the porous carbon by post-surface functionalization strategy. The self-doped N can change the electron distribution of carbon skeleton and decrease energy barrier of chemical absorption of Zn²⁺/H⁺. Meanwhile, the carbonyl group can significantly enhance the wettability of OLCKs. Furthermore, the diffusion-controlled reactions mainly exist at high and low potential ranges in CV curves, which demonstrates the occurred Faradaic reaction. Consequently, the assembled aqueous ZICs based on OLCKs demonstrate a capacity of 121.7 mAh/g at 0.3 A/g, energy density of 94.3 Wh kg^-1 and good cyclic stability. Besides, the assembled Zn//PVA/LiCl/ZnCl₂(gel)//OLCK4 ZIC can also achieve energy density of 134.4 Wh kg^-1 at 0.1 A/g. This work provides a novel design strategy by incorporating abundant O and N-containing functional groups to enhance energy density.

Coal-based ultrathin N-doped carbon nanosheets synthesized by molten-salt method for high-performance lithium-ion batteries

Coal is a typical fossil fuel and it is also a natural carbon material, therefore, converting it to functional carbon materials is an effective way to enhance the economic advantages of coal. Here, ultrathin N-doped carbon nanosheets were prepared from low-cost coal via a handy and green molten-salt method, which shown excellent performance for lithium-ion batteries (LIBs). The formation mechanism of ultrathin nanosheets was studied in detail. The eutectic molten salts possess low melting points and become a strong polar solvent at the calcined temperature, making the acidified coal miscible with them in very homogeneously state. Therefore, they can play a gigantic role inin situpore-forming during the carbonization and induce the formation of ultrathin nanosheets due to the salt ions. Simultaneously, the ultrathin N-doped carbon nanosheets with rich defects and controllable surface area was smoothly prepared without any more complex process while revealing brilliant electrochemical performance due to rich ion diffusion pathways. It delivers reversible capacity of 727.0 mAh g^-1at 0.2 A g^-1after 150 cycles. Thus, the molten-salt method broadens the avenue to construct porous carbon materials with tailor-made morphologies. Equally important, this approach provides a step toward the sustainable materials design and chemical science in the future.