Hierarchical porous carbon spheres derived from larch sawdust via spray pyrolysis and soft-templating method for supercapacitors

N-doped CNTs wrapped sulfur-loaded hierarchical porous carbon cathode for Li-sulfur battery studies

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage devices due to their low cost and high energy density (2600 W h kg-1). However, the practical applicability of Li-S batteries is hindered by the insulating nature of sulfur cathodes, and the high solubility of polysulfides (Li2Sx, 3 < x ≤ 8) which are formed during the electrochemical process. Integrating sulfur into the carbon host is an effective way to enhance the conductivity of the electrode which hampers the shuttling effect of the polysulfides. Here in this study, hierarchical porous carbon structures (HPC) are prepared from spent coffee waste (SCW) by the KOH activation process and are encapsulated with sulfur (SHPC) which increases the interaction between sulfur and carbon and enhances both the electronic and ionic conductivities. Further wrapping of SHPC with N-doped multi-walled carbon nanotubes (NCNTs) gives a SHPC-NCNT composite, which alleviates the shuttling of polysulfides by trapping them and ensures the required conductivity to the sulfur cathode during the Li+ reactions. When studied as a cathode material for Li-S batteries, the prepared cathode showed 664 and 532 mA h g-1 specific capacities after 150 cycles at 0.2C and 0.5C, respectively. The stable cyclability and rate capability properties of SPHCNCNT suggest that the prepared sulfur composite is suitable as a cathode material for Li+ energy storage applications.

Reuse of Lignin to Synthesize High Surface Area Carbon Nanoparticles for Supercapacitors Using a Continuous and Single-Step Aerosol Method

There is a growing demand for the synthesis of high surface area carbons, also known as carbon nanoparticles (CNPs). Existing synthesis methods for high surface area carbons have limited environmental benignity and economic viability due to the requirement of multistep and batch processes and harsh activating and/or templating chemicals. Herein, we demonstrate the synthesis of high surface area CNPs from lignin, a waste byproduct, through a single-step, continuous gas phase aerosol technique without the use of activating or templating chemicals. This continuous approach requires significantly less time for synthesis: on the order of seconds in comparison to hours for conventional methods. Properties of carbon materials synthesized from lignin are controlled by temperature and residence time, and the role of these parameters inside the aerosol reactor on carbon nanoparticle size, morphology, molecular structure, and surface area is systematically investigated. Furthermore, the as-obtained carbon nanoparticles are tested for specific capacitance, and the best-performing material (surface area 925 m2/g) exhibited a specific capacitance of 247 F/g at 0.5 A/g with excellent capacity retainment of over 98% after 10,000 cycles. This is a clear demonstration of their superior performance compared with supercapacitors synthesized earlier from lignin. Overall, the simple (single-step, continuous, and rapid) operation and the avoidance of the use of activating/templating chemicals make the aerosol technique a promising candidate for the scalable and sustainable synthesis of CNPs from lignin.

Influence of Potassium-Based Activation on Adsorptive Properties of Carbon Spheres Modified with Iron(III) Citrate

Composites synthesized from iron(III) citrate and carbon spheres, and activated with potassium compounds were prepared and then characterized using XRD, SEM, and low-temperature nitrogen adsorption methods. The adsorption properties of the composites toward carbon dioxide were assessed using CO2 uptake measurement, as well as by measuring their selectivity toward carbon dioxide, given their further application as photocatalysts for the reduction of this gas. The effect of changing preparation conditions on the structural and adsorption properties of the material was assessed. The potential strength of such material is a synergistic effect between the high adsorption capacity related to the microporosity of carbon spheres combined with the catalytic properties of iron particles.