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It is commonly accepted that different structural parameters of electrode materials (i.e. SBET, Smicro, Vtot, Rt and ID/IG) have different effects on the electrochemical properties (i.e. specific capacitance, power density, energy density, and rate capability) in terms of the influencing magnitude and trend. It's therefore extremely desirable to establish a relatively unified structure–function relationship using a single performance indicator. This work luckily finds a defined/composite performance indicator (Smicro/SBET), which can uniformly influence the capacitor performances. Such analysis is based on the characterization of the as-assembled symmetric electrochemical double-layer capacitors using a series of samples as electrodes (obtained by a dual-activator strategy with C3N3Na3S3 and KOH as dual activators and egg yolk as precursor). All the electrochemical performances (the specific capacitance, rate capability, energy storage performance, etc.) have the same tendency with Smicro/SBET changes and the peak for all the performances can be obtained when the Smicro/SBET value is 53.53% in this research. Herein, Smicro/SBET is expected to be one composite performance indicator to reflect the structure–function relationship and in turn judge the whole performances of the materials through the relationship of Smicro/SBET and a single performance, thus greatly simplifying the screening of electrode materials for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

A series of sponge-like hierarchical porous carbons are prepared using semen cassiae as the precursor and potassium oxalate monohydrate as the activation agent. These sponge-like carbon materials have high surface areas, wide distributions of pore size, and the appropriate forms of nitrogen/oxygen derivatives. All these advantages in structures and surface states contribute to the outstanding performances of such materials as electrodes for high performance electric double-layer capacitors, which include high specific capacitance, high cycling stability, and high energy density. For example, the optimal sample exhibits a high specific capacitance of 401 F g−1, excellent cycling stability (94.5% retention after 10 000 cycles), high energy density (12.01 W h kg−1) and a high power density (10 200 W kg−1) in 1 M H2SO4 solution. [ABSTRACT FROM AUTHOR]

Besides a lack of low-cost electrode materials, the match between the electrode materials and electrolytes is one of the top issues to achieve high-rate electrochemical supercapacitors. Herein, we report an environmentally friendly strategy to prepare three-dimensionally interconnected carbon nanorings (TDICNs) from biomass waste, batata leaves and stalks (BLS). The microstructure of TDICNs matches well with acidic and alkaline electrolytes, making them exhibit high specific capacitances of 532.5 F g−1 (1 A g−1) and 264.0 F g−1 (30 A g−1), excellent capacitance retention (95.1% and 91.7% after 1000 cycles at 1 A g−1 and 10 000 cycles at 30 A g−1, respectively) and a high energy density of 25.8–11.9 W h kg−1 with a power density of 249.5–13 068.0 W kg−1 in 1 mol L−1 H2SO4 aqueous electrolyte. In 6 mol L−1 KOH electrolyte, they still exhibit high specific capacitances of 350.0 F g−1 (1 A g−1) and 246.9 F g−1 (30 A g−1), excellent cycling stability (95.06% and 91.1% of capacitance retention after 1000 (1 A g−1) and 10 000 (30 A g−1) cycles, respectively), a high energy density of 24.5 W h kg−1 and a power density of 12 918.0 W kg−1. [ABSTRACT FROM AUTHOR]

Substituting sustainable/cost-effective catalysts for scarce and costly metal ones is currently among the major targets of sustainable chemistry. Herein, we report the synthesis of N-, S-, and P-tridoped worst-weed-derived carbon nanorings (WWCNRs) that can serve as a metal-free and selective electrocatalyst for the oxygen reduction reaction (ORR). The WWCNRs are synthesized via activation-free polymerization of worst weed, Eclipta prostrata, and then removal of the metallic residues by using HCl. The WWCNRs exhibit good catalytic activity towards the 4 electron-transfer ORR with a low onset potential and high kinetic limiting current density, along with high selectivity (introducing CO, the sample loses only ＜7% of its original activity, in contrast to more than 30% loss of the original activity for 20 wt% Pt/C over 4000 s of the continuous ORR) and long durability (94% of the initial current still persists at the sample electrode compared with a 87% current retention at commercial Pt/C electrodes after 18 000 s). The present work highlights the smart transformation of organic-rich worst weed into value-added functional materials with great potential for applications such as fuel cells, lithium–air batteries, photocatalysis, and heterocatalysis. [ABSTRACT FROM AUTHOR]

The urgent need for sustainable energy development depends on the progress of green technologies, which have steered hot research areas into environmentally benign approaches via inexpensive precursors and abundant resources obtained directly from nature for energy devices such as fuel cells and supercapacitors. By using fermented rice as starting materials, we herein demonstrate a facile, green and scalable approach to synthesize porous N-doped carbon spheres characterised by high specific surface areas (2105.9 m2 g−1) and high porosity (1.14 cm3 g−1), which exhibit not only excellent electrocatalytic activity toward the four-electron oxygen reduction reaction with long-term stability for fuel cells, but also have excellent resistance to crossover effects and CO poisoning superior to that of the commercial Pt/C catalyst. Furthermore, the naturally derived porous N-doped carbon spheres, used as the active electrode materials, present superior performance for capacitors with a capacitance of 219 F g−1 at a high discharge current density of 15 A g−1 and good cycling stability for over 4400 cycles. This work shows a good example for taking advantage of the abundant resources provided by nature, and opening the door for the creation of functional materials with promising applications in high-performance renewable devices related to energy conversion and storage. [ABSTRACT FROM AUTHOR]

Correction for ‘Biomass-derived interconnected carbon nanoring electrochemical capacitors with high performance in both strongly acidic and alkaline electrolytes’ by Xianjun Wei et al., J. Mater. Chem. A, 2017, 5, 181–188. [ABSTRACT FROM AUTHOR]