Biomass-Derived Carbon Electrodes for High-Performance Supercapacitors.

Supercapacitors with the performance advantages of high-power density are emerging materials for energy storage/conversion systems that can combat climate change caused by CO2 emissions and are of importance with the development of electronic products and artificial intelligence. But rationally preparing high-performance electrode with high mass-loading quantity remains challenge. Herein, we have opted for chitosan as well-structured binding agent to combine with active carbon (SSP-900), a 3D hierarchical micro-meso-macro porous biochar previously obtained, to synthesize high mass-loading freestanding electrode. Especially, the freestanding material (C1000 G0.2 ), owning 0.2 g SSP-900 and suffering carbonization at 1000 °C exhibits high specific surface area of 389.3 cm2 g-1 , and self-doped N, O (2.75 %, 5.64 %). That awards C1000 G0.2 outstanding electrochemical properties, including high specific mass capacitance of 199.2 F g-1 , splendid specific area capacitance of 4.37 F cm-2 in 21.93 g cm-2 , which is more competitive than conventional freestanding materials. Symmetrical supercapacitor with mass loading of 12 mg is assembled and exhibits large specific capacitance of 65 F g-1 , high energy density of 32.5 Wh kg-1 under the power density of 90.4 W kg-1 , and capacitance stability of 98 % after 10,000 cycles. The distinguished electrochemical performance of freestanding electrodes supplies prospective application for storing/converting electrical energy from intermittent solar and wind.

Rice Hull-Derived Carbon for Supercapacitors: Towards Sustainable Silicon-Carbon Supercapacitors.

A simple and effective mixing carbonization-activation process was developed to prepare rice hull-derived porous Si-carbon materials. The morphologies and pore structures of the materials were controlled effectively without any loading or additions at various carbonization temperatures. The structures of the samples changed from large pores and thick walls after 800 ∘C carbonization to small pores and thin walls after 1000 ∘C carbonization. An additional alkali activation-carbonization process led to coral reef-like structures surrounded by squama in the sample that underwent 900 ∘C carbonization (Act-RH-900). This optimal material (Act-RH-900) had a large specific surface area (768 m2 g-1), relatively stable specific capacitance (150.8 F g-1), high energy density (31.9 Wh kg-1), and high-power density (309.2 w kg-1) at a current density of 0.5 A g-1 in 1 M KOH electrolyte, as well as a good rate performance and high stability (capacitance retention > 87.88% after 5000 cycles). The results indicated that Act-RH-900 is a promising candidate for capacitive applications. This work overcomes the restrictions imposed by the complex internal structure of biomass, implements a simple reaction environment, and broadens the potential applicability of biomass waste in the field of supercapacitors.