Neutral pH Na2SO4/glycerol/PVA polymer hydrogel electrolyte prepared at room temperature for activated carbon supercapacitors

Neutral pH PVA/glycerol/Na₂SO₄ hydrogels were made by aging at room temperature, the effect of Na₂SO₄ concentration was evaluated, and the hydrogel with the best properties was tested as a neutral pH polymeric hydrogel electrolyte in a supercapacitor device with activated carbon electrodes. PVA/glycerol/Na₂SO₄ hydrogels were chemically and structurally studied using Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction. Hydrogel with 0.40 mol L⁻¹ of Na₂SO₄ has the most presence of hydrogen bonds and a lesser presence of crystalline regions in its polymeric matrix. By impedance spectroscopy, the ionic conductivity of the hydrogels was calculated. Hydrogel with 0.40 mol L⁻¹ of Na₂SO₄ has the highest value of ionic conductivity 17.4 mS cm⁻¹. This hydrogel was used as a polymer hydrogel electrolyte in a supercapacitor with Printex XE2B activated carbon electrodes by cyclic voltammetry and galvanostatic charge/discharge cycles. The supercapacitor device with 0.40 mol L⁻¹ Na₂SO₄ hydrogel reached a working potential window of 2.0 V in the cyclic voltammograms. Charge/discharge plots of the supercapacitor device with 0.40 mol L⁻¹ Na₂SO₄ hydrogel exhibit a triangle behavior at different current densities. Supercapacitor device with 0.40 mol L⁻¹ Na₂SO₄ hydrogel presents an equivalent series resistance of 14.7 ohms cm⁻², a specific capacitance of 54.7 F g⁻¹, and a specific energy of 7.6 Wh kg⁻¹ at 0.5 A g⁻¹. Obtained results were compared with a supercapacitor device with Na₂SO₄ 1.0 mol L⁻¹ and previously works.