Collateral Advantages of a Gel Electrolyte for MnO2 Nanowire Capacitors: Higher Voltage and Reduced Volume

Recently we demonstrated that symmetric, all Au@δ-MnO2 core@shell nanowire capacitors can achieve cycle stability to 100 000 cycles and beyond in a poly­(methyl methacrylate) (PMMA) gel electrolyte. Here we examine the limits of the PMMA gel to confer this extraordinary stability, in terms of the accessible maximum voltage, V max, and the thickness of the PMMA gel electrolyte layer. Two conclusions are (1) the PMMA gel permits the V max to be increased by 50% from 1.2 V to 1.8 V, allowing the specific energy to be increased 5–6 fold, and (2) the PMMA gel layer thickness can be reduced from 180 μm (previously) to 2 μm while simultaneously utilizing two layers of nanowires and patterning nanowires in each layer at 5× higher density. For this nanowire “sandwich” architecture, a net increase in volumetric capacity of 600× up to 500 mF/cm3 can be achieved while retaining cycle stability to 100 000 cycles.