Can polyoxometalates enhance the capacitance and energy density of activated carbon in organic electrolyte supercapacitors?

Abstract

Highlights: Tetraethylammonium phosphotungstate (TEAPW12) and activated carbon (AC) were used to prepare a hybrid electrode able to outperform AC in a high-voltage organic electrolyte supercapacitor cell.  The inorganic cluster undergoes multi-electron reactions integrated in the hybrid material, even in an aprotic organic electrolyte.  Volumetric capacitance increases by ~36% with polyoxometalates hybridization without sacrificing voltage window.  We are demonstrating for the first time the effective use of polyoxometalates in aprotic electrolyte supercapacitors.

Coherent Integration of Organic Gel Polymer Electrolyte and Ambipolar Polyoxometalate Hybrid Nanocomposite Electrode in a Compact High-Performance Supercapacitor

“…Figure 3b presents the SEM images of AC/TEAPMo12, from which we cannot see any aggregation of TEAPMo12. (The transmission electron microscopy images of AC and AC/TEAPMo12 are presented in Figure S2c,d) We expect the TEAPMo12 clusters to spread homogeneously on AC substrate as other keggin-type POMs do [11,12,30]. To study the distribution characteristics of TEAPMo12, we observe the samples under scanning transmission electron microscopy in the high angle annular dark field (HAADF-STEM).…”

“…It confirms that the TEAPMo12 clusters are dispersed homogeneously in nanoscale on AC substrate, agreeing with the speculation from XRD patterns. Indeed, the anchoring of TEAPMo12 clusters on AC would lead to a slight decrease in pore volume and surface area of the hybrid materials [11], and the bright dots make the contrast between pores and matrix less visible.…”

“…The b values at all the redox potentials are close to 1, which means the non-diffusion-controlled process dominates the charge storage. It might seem surprising for redox-active materials, but this phenomenon happens when the redox-active species are well-dispersed, such as POMs on 3D framework [31], AC/TEAPW12 hybrids [11]. The contribution of the non-diffusion-controlled process and the diffusion-controlled process to the capacitance in the whole potential is analyzed and presented in Supplementary Materials S4, Figure S4(b-f).…”

“…At any current densities, the volumetric capacitance of AC/TEAPMo12 gains more than 40 % improvement. The POMs clusters are mainly absorbed in pores and contribute little to the whole volume but a lot to the total weight [11]. Thus, the gravimetric capacitance improves only slightly, but the volumetric capacitance improves significantly.…”

“…On the other hand, POMs can carry out their fast reversible redox reaction when they are welldispersed. Thus, spreading or anchoring POMs on other materials, including activated carbon [11,12], reduced graphene oxide [13][14][15], carbon nanotubes [16,17], and a metalorganic framework [18] would be a solution. POMs-based hybrid materials have already shown their potential in supercapacitors to enhance capacitance and energy densities.…”