Abstract
Alternative green binders processable in water are being investigated for the development of more efficient and sustainable supercapacitors. However, their electrochemical performances have fallen within or below the average of commercially available devices. Herein, an optimised gelled mixture of graphene oxide (GO) and starch, a biopolymer belonging to the family of polysaccharides, is proposed. The molecular interactions between the two components enhance electrodes structure and morphology, as well as their thermal stability. GO, thanks to its reduction that is initially triggered by reactions with starch and further progressed by thermal treatment, actively contributes to the charge storage process of the supercapacitors. The optimised electrodes can deliver a specific capacitance up to 173.8 F g−1 while providing good rate capabilities and long-term stability over 17,000 cycles. These are among the best electrochemical performances achieved by environmentally friendly supercapacitors using a biomaterial as a binder.
Highlights
Alternative green binders processable in water are being investigated for the development of more efficient and sustainable supercapacitors
The starting point of the degradation is not clear in graphene oxide (GO)-StC, it can be estimated being in a range between 250 and 300 °C with a kinetic that is slower with respect of the electrode material fabricated without GO (StC). These results provide for a reciprocal beneficial effect of the interactions between GO and Starch, with a boost of GO reduction and an improvement of the thermal stability of the binder
A further optimisation of the binder was achieved after a thermal treatment of the electrodes, where the reduction of GO sheets fully unlocked their capabilities to actively contribute to electrochemical performances
Summary
GO-StC electrodes were fabricated by a conventional method consisting of three main steps. All slurries were prepared so that the mass ratio of the components is fixed as AC:CB:GO-St = 85:5:10 by using essentially the same method and are termed GO-StC-I, GO-StC-II, GO-StC-III, GO-StC-IV, GO-StC-V, depending on the initial composition of the GO-St-gel (GO amount corresponding to the 2.5, 3.3, 5, 6.7, 7.5 wt%, respectively). With the binder consisting of St only (StC) and of GO only (GO-C), were manufactured by a similar method. Slurry composition of different GO-StC and reference electrodes are summarised in Supplementary Table 1. It is crucial to note that the physicochemical characterisation was focused on the GO-StC-III electrode (containing 5 wt% GO) that provided optimised electrochemical properties.
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