Biomass waste carbon materials have been emerging as high performance and low cost electrodes for energy storage such as supercapacitors. Addition of thin layers of redox active pseudocapacitive materials onto biomass activated carbon can leverage the strength of the electrochemical activity of the former and the high surface area as well as the low cost of the latter. In our study, several biomass carbon materials, including corncobs and pine cones, have been investigated as substrates for adsorption of electrochemically active and highly reversible polyoxometalates (POM) clusters. In this talk we will compare these two carbons to show the influential factors on the adsorption of POM clusters.

Among various chemical and structural properties of biomass activated carbons, 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 PMo₁₂O₄₀^3- (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 high 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 coating 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.