Matthew Genovese

High capacitive performance of exfoliated biochar nanosheets from biomass waste corn cob

A high performance exfoliated biochar carbon with a layered nanosheet structure was prepared from a low cost agricultural residue (corn cob) via a novel synthesis strategy involving biomass pre-treatment, nitrogen pyrolysis, and a high temperature thermal–chemical flash exfoliation. The exfoliation strategy resulted in porous carbon nanosheets with BET specific surface area of 543.7 m2 g−1, far higher than the 7.9 m2 g−1 of the natural biochar produced without any pre- or post-treatment modifications. The exfoliated material also showed increased oxygen functionality in the form of electrochemically active quinone and pyrone surface groups. This combination of high specific surface area and highly active surface functional groups resulted in very promising capacitive performance, demonstrating a high capacitance of 221 F g−1, over 100 times greater than the natural biochar. The exfoliated biochar electrodes fabricated without any conductive or organic additives showed outstanding high rate capability retaining 78% of their low rate capacitance at a fast 40 A g−1 discharge. This combination of high capacitance and fast charge–discharge capability distinguishes this material from most other high surface area activated carbons; in fact, the electrochemical behaviour more closely resembles that of designer nanomaterials such as graphene and carbon nanotubes. The biochar electrodes were also extremely durable showing only a 3% reduction in capacitance after 5000 successive potential cycles. The exfoliation strategy developed here could provide a novel route for the low cost production of high performance energy storage materials from a variety of waste biomass feedstocks.

Polyoxometalate modified pine cone biochar carbon for supercapacitor electrodes

Pine cones were used as a biomass template for the synthesis of activated carbons with high specific surface area (up to 2450 m2 g−1) and a pore structure optimized for the adsorption of redox active polyoxometalate (POM) clusters. We have found that POM adsorption is highly favored within a carbon matrix possessing pore diameters in the 1–2 nm range. These large micropores are big enough to accommodate the large POM cluster, while still being small enough to effectively trap and hold the molecule. Pine cone activated carbon with this optimal pore arrangement demonstrated ultra-high loading of the PMo12O403− (PMo12) molecule resulting in carbon–POM hybrid materials consisting of over 55 wt% PMo12. This large POM loading imparted tremendous redox activity to the already large double layer capacity of the carbon substrate, leading to a high areal capacitance of 1.19 F cm−2 for the hybrid material, close to 2.5 times larger than for unmodified carbon. We have also demonstrated that a mixed molecular modifier combining multiple POM chemistries can be adsorbed onto the activated carbon substrate to create a more ideally capacitive charge storage profile. These results demonstrate a promising method for the design of high performance yet cost effective hybrid energy storage electrodes.

Polyoxometalates: Molecular Metal Oxide Clusters for Supercapacitors

Abstract The modification of conductive organic supports with polyoxometalate (POM) metal oxide clusters is a promising approach for the design of nanocomposite electrodes for energy storage. The fast and reversible electron-transfer processes of these POM molecules make them particularly well suited for supercapacitor (SC) applications. This chapter will provide a detailed overview of POM-based composite SC electrodes, including an evaluation of the most promising fabrication methods: (1) chemisorption to a carbon surface, (2) immobilization in a conductive polymer matrix, and (3) layer-by-layer self-assembly. Furthermore, the role of these POM composite materials in enhancing the performance of SC devices will also be reviewed, from pioneering work to the latest developments. This will include an analysis of how the tunability of POM redox properties can be leveraged to move from faradaic SC electrodes using only a single POM chemistry to pseudocapacitive electrodes incorporating multiple different POM molecules.