Use of Hyperaccumulator to Enrich Metal Ions for Supercapacitor

Abstract

issues such as some complex processes and expensive equipment used in the experiments to achieve the uniform distribution of metal particles add to its difficulty in practical application.Biomass is a good resource for green chemical synthesis because it is renewable and eco-friendly. To better survive and procreate, many species have evolved subtle structures and specific functions to meet natural selection. If we use them properly, we could produce many outstanding materials. Scientists have already worked on this strategy, and many achievements have been published, some of which are about electrochemistry. [7] For example, Yan's group prepared heteroatom-doped porous carbon flakes via carbonized human hair and used them as supercapacitor electrode materials. [8] But most of the work so far just utilized the carbon element in the biomass, some of which explained the contribution of a small amount of nitrogen. [9] The combination of biomass and metal should be further explored. In our previous work, we synthesized 1D hierarchically porous carbon via carbonized and activated biomass, and used them as supercapacitor electrode materials. [10] But when we loaded metal element to the material, the electrochemical property was worse than before. Since then, we have been looking for new strategies to combine biomass and metal element.Hyperaccumulators are plants with extraordinary ability to absorb heavy metal from the environment, proposed by Brooks in 1977. [11] The plant has the following characteristics according to his report. The heavy metal content in the aboveground part is over 100 times than that of ordinary plants. It can keep normal growth in heavy metal-polluted environment, without being poisoned by heavy metal. Limitation of heavy metal mass fraction varies from the metal. Cd is 100 mg kg −1 ; Co, Cu, Ni, and Pb are 1 g kg −1 , while Mn and Zn are 10 g kg −1 . [12] Egeria densa belongs to the family Hydrocharitaceae, and it is a species of perennial submerged plants with vigorous growth. Submerged plants exhibit better performance on heavy metal ion enrichment because of the lack of cuticle and wax layer, which makes the direct absorption of gas, water, minerals, and heavy metal possible. Some research has already proved the enrichment phenomenon of E. densa on heavy metal. [13] Herein, we grew E. densa with cobalt ion solution to enrich metal ions in plant, and activated the metal-loaded biomass to obtain the composite of cobalt and biochar. Cobalt nanospheres are well distributed in carbon skeletons, and exhibit obvious pseudocapacitance. Interconnected macropores and 3D carbon skeletons reduce impedance, and the material performs well on specific capacitance and rate capability. We explored different Inspired by the capability of hyperaccumulators to enrich heavy metal ions, metal-loaded biomass is prepared, and the metal nanospheres are dispersed in hierarchical porous carbon skeletons uniformly after activation. The raw material comes from nature and is renewable and environmentally friendly. The s...

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