Abstract
A novel redox electrolyte is proposed based on organo‐aqueous solvent and a polyoxometalate (POM) redox moiety. The presence of dimethyl sulfoxide (DMSO) plays multiple roles in this system. Firstly, it enhances the cathodic electrochemical stability window by shifting the H2 evolution to lower potentials with respect to pure aqueous systems; secondly, it improves the reversibility of the redox reaction of the PW12O40 3− anion at low potentials. The presence of DMSO suppresses the Al corrosion, thus enabling the use of this metal as the current collector. An activated carbon‐based supercapacitor is investigated in 1 M LiNO3/10 mM H3PW12O40 in a mixed DMSO/H2O solvent and compared with a POM‐free electrolyte. In the presence of POMs, the device achieves better stability under floating conditions at 1.8 V. At 1 kW kg−1, it delivers a specific energy of 8 Wh kg−1 vs. 4.5 Wh kg−1 delivered from the POM‐free device. The H2 evolution is further shifted by the POMs adsorbed on the activated carbon, which is one reason for the improved stability. The POM‐containing cell demonstrates a mitigated self‐discharge, owing to strong POMs adsorption into the carbon pores.
Highlights
LiNO3/10 mM H3PW12O40 in a mixed dimethyl sulfoxide (DMSO)/H2O solvent and compared with a POM-free electrolyte
The organic solvent can play a role in coordinating the polyoxometalate and as well as influencing the redox potential of the multistep reactions. Stimulated by these findings, we aim to study if the addition of an organic solvent to water can stabilize the POM moiety and, at the same time, enlarge the electrochemical stability window (ESW)
Carbon electrodes of electrolytes based on 1 M LiNO3 in different solvents: pure water, a mixture of water and 1,4dioxane (DO), and a mixture of water and DMSO in volume ratio
Summary
LiNO3/10 mM H3PW12O40 in a mixed DMSO/H2O solvent and compared with a POM-free electrolyte. 1. Introduction capacitor-type and the other one a pure battery-type.[4] Both strategies focus on solid-state electrode materials. Introduction capacitor-type and the other one a pure battery-type.[4] Both strategies focus on solid-state electrode materials Another intriguing method is the introduction of a faradaic material as a moiety dissolved in the electrolyte.[5,6,7,8] With this approach, the electrolyte contains an active faradaic material, which reacts at the surface of the capacitive-type electrode material, providing the additional capacity. The capacitivetype material is usually activated carbon, which can offer relatively high capacitance owing to its extremely high surface area (about 1500–2000 m2 g 1).[9] Electrolytes for supercapacitors can be mainly categorized in organic and aqueous-based
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