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Flexible and binder-free multi-walled carbon nanotube (MWNT)-modified sponge-based nickel (Ni) is employed as the electrode material for methanol (CHOH) electrooxidation. The nano-spherical Ni is electrodeposited on the surface of the MWNTs which are assembled on the skeleton of a commercial sponge. The as-prepared MWNT-modified sponge-based Ni electrode (MSNi) is characterized by scanning electron microscopy, transmission electron microscope, and X-ray diffractometer. The catalytic activity of the MSNi electrode for CHOH electrooxidation is investigated by means of cyclic voltammetry, chronoamperometry, and electrochemical impedance spectra. The preparation process of the flexible MSNi electrode does not use any binder and it exhibits a unique three-dimensional (3D) network-porous structure. The MSNi exhibits a high electrocatalytic performance of 23 mA (cm mg) in 0.5 mol dm CHOH at 0.5 V. [ABSTRACT FROM AUTHOR]

Catalytic performance and NaBH 4 utilization are two crucial concerns in the electrooxidation of NaBH 4. To improve the inherent properties of regular performance and low fuel utilization of the transition metal Co and Ni, an efficient anode catalyst of ultra-thin CoNi nanosheets modified novel 3D self-supported reduced graphene oxide foam is prepared in this work. The alkaline condition borohydride oxidation reaction on the prepared catalyst is investigated in a typical three-electrode system. The prepared catalyst shows a high performance due to the large electrochemical active surface area, low activation energy (8.29 kJ·mol−1), and the small electrochemical impedance it embraced. Linear scan voltammetry recorded in a low concentration of NaBH 4 suggests that borohydride oxidation is a first-order reaction on the prepared catalyst. Based on the unique structure of the catalyst, which is useful to capture the hydrogen and perform further oxidation of hydrogen, higher utilization of NaBH 4 achieved on the catalyst. Besides, the prepared anode catalyst applied to a direct borohydride-hydrogen peroxide fuel cell (DBHPFC). The results of polarization curve and power density curves, as well as stability research, all indicate that the as-prepared catalyst is a highly efficient anode material for application in DBHPFC. Unlabelled Image • Novel 3D self-supported rGO foam skeleton was prepared by a simple template method. • The catalytic activity of CoNi-NS/rGO foam is higher than CoNi-NS/Ni foam electrode. • Self-supported rGO foam matrix improved the utilization efficiency of NaBH4. • CoNi-NS/rGO foam anode catalyst exhibited highest power density of 140 mW·cm−2. [ABSTRACT FROM AUTHOR]

Highlights • A gas foaming strategy is adopted to prepare the 3D hierarchical porous carbon. • NaHCO 3 is used as activator based on its multistep pyrolysis process. • The HPC shows high specific capacitance and outstanding stability. Abstract Inspired by people to make flour food, a one-pot, low-cost, green and environmental friendly gas foaming strategy is adopted here to prepare the three-dimensional hierarchical porous carbon (HPC) by introducing NaHCO 3 as foaming and activation agent. During the pyrolysis process, the CO 2 gas produced during the transforms from NaHCO 3 into Na 2 CO 3 will resulted in the producers of the macro-pores and meso-pores, meanwhile, the as-produced Na 2 CO 3 further reactor with the carbon intermediate at a high temperature, and finally result in forming a micro-pores porous structure. Such intimate structural interconnectivities provide three-dimensional continuous pathway for electron rapid transfer and the interconnected pores allow for the ion to penetrate and evenly contact the electrode material quickly. The electrochemical performance of HPC exhibits a high specific capacitance of 350 F g−1 at 1 A g−1 and outstanding electrochemical stability with capacitance retention up to 97% after 10,000 cycles. Moreover, the as-assembled symmetric supercapacitor exhibits an ultrahigh energy density of 27.4 Wh kg−1, much higher than most of carbon-based supercapacitors. These results demonstrate a straightforward environment friendly method to mass-produce economical, robust carbon materials as promising candidates for supercapacitor application. [ABSTRACT FROM AUTHOR]

• N-rich activated carbon was prepared from waste cotton. • The difference from the conventional KOH activation method is the addition of urea to the etching process. • The product exhibits better capacity, rate capability and lifetime in libs. • Larger surface area, suitable pore size, and high nitrogen content are key merits. With the advancement of battery technology, graphite as a negative electrode material for commercial lithium-ion batteries (LiBs) is reaching the limit of its capacity, and mesoporous carbon with a larger capacity is regarded as its best alternative. In this paper, waste cotton is used as the carbon source, and KOH and urea are used as pore formers and pore size regulators to prepare uniform mesoporous materials (N-PCC800) with a pore size distribution of 2–5 nm. Compared with the traditional KOH pore-making method, the addition of urea can adjust the pore size upward, thereby increasing the effective number of pores for Li+ insertion. While optimizing the structure, urea can also be used as an additional nitrogen source for the material to enrich the content of heteroatoms and defects, thereby increasing the amount of Li+ adsorbed by porous carbon. As an anode material, N-PCC800 exhibits a stable discharge capacity (1086 mAh g−1 at 100 mA g−1) far exceeding that of graphite. At a current density of 1000 mA g−1, there is still a capacity of 596 mAh g−1 remaining after 1000 cycles, indicating its advantages in rate performance and cycle performance. The optimized pore size and higher nitrogen content endow the carbon material with higher Li+ storage performance, and further kinetic analysis indicates that the increased capacity comes from the increased Li+ insertion. This work proposes a new pore size optimization scheme to obtain high-capacity mesoporous carbon, which provides an effective scheme for the reuse of waste cotton and cotton products and helps achieve the goal of carbon neutrality. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-rich biomass carbon (N-CHC) was prepared by urea etching method. • N-CHC exhibits excellent capacity and rate performance as a K+ half-cell anode. • Large specific surface area, lots of defects and heteroatoms are key advantages. • The hybrid capacitor composed of N-CHC and AC exhibits high energy and power density. Potassium ion hybrid capacitors have the advantages of high energy density, high power density, and low cost, and are expected to replace expensive lithium ion storage devices in large-scale applications. Here, an innovative nitrogen-rich biomass carbon (N-CHC) is prepared using urea as the etchant and hemp core as the raw material, which has a high specific surface area of 1185.3 m2 g−1 and nitrogen content of 8.56%. In addition, it shows a capacity of 442.4 mAh g−1 as a potassium ion half-cell anode at 30 mA g−1. Even under the high current test of 2000 mA g−1, N-CHC also shows excellent performance (175.0 mAh g−1). Further, the good rate performance is attributed to the large-scale capacitance control by analyzing reaction process kinetics. And the constant current intermittent titration technique (GITT) results show that N-CHC has a larger K+ diffusion coefficient than unetched biomass carbon. The maximum energy density of the full carbon-based hybrid capacitor composed of N-CHC anode and activated carbon cathode is 127.36 Wh kg−1, and the maximum power density is 2371 W kg−1. [ABSTRACT FROM AUTHOR]

• A PPy-rGO Janus-faced film is prepared through a facile and scalable method. • The PPy-rGO electrode reveals a ultra-high specific capacitances of 1380 mF cm−2. • The assembled PPy-rGO//PPy-rGO device delivers a high energy density of 31.95 Wh L−1. The flexible supercapacitors have attracted tremendous attention, but challenges still remain in seeking suitable electrode materials to enhance the energy density and other aspects. To this end, a unique Polypyrrole (PPy)-reduced graphene oxide (rGO) Janus-faced film is prepared through a facile and scalable method consisting of the deposition of graphene film on the surface of copper foil via a Cu||GO electrochemical cell followed by the self-assembly of PPy at the heterogeneous interface. Such a distinctive structure, in which the PPy layer acts as the source of high pseudo-capacitance, while the graphene layer is employed as the "high way" for rapid electron transport and as well as the strong π-π coupling effect between graphene and polymer nanosheets, endows the resultant electrode ultra-high specific capacitances (1380 mF cm−2 at 1 mA cm−2) and excellent rate capability (65.1% capacitance retention with the current density increases to 20 mA cm−2). Furthermore, the assembled PPy-rGO//PPy-rGO symmetric supercapacitors deliver a maximum energy density of 31.95 Wh L−1, remarkable cyclic stability (89.7% capacitance retention after 10,000 cycles) and superior mechanical property (82% capacitance retention after 8000 cycles under different bending conditions). [ABSTRACT FROM AUTHOR]