Neutral pH Gel Electrolytes for VO·0.5HO-Based Energy Storage Devices.

Gel electrolytes are considered to be promising candidates for the use in supercapacitors. It is worthy to systematically evaluate the internal electrochemical mechanisms with a variety of cations (poly(vinyl alcohol) (PVA)-based Li, Na, and K) toward redox-type electrode. Herein, we describe a quasi-solid-state PVA-KCl gel electrolyte for VO·0.5HO-based redox-type capacitors, effectively avoiding electrochemical oxidation and structural breakdown of layered VO·0.5HO during 10 000 charge-discharge cycles (98% capacitance retention at 400 mV s). With the gel electrolyte, symmetric VO·0.5HO-reduced graphene oxide (VO·0.5HO-rGO) devices exhibited a volumetric capacitance of 136 mF cm, which was much higher than that of 68 mF cm for PVA-NaCl and 45 mF cm for PVA-LiCl. Additionally, hybrid full cells of activated carbon cloth//VO·0.5HO-rGO delivered an energy density of 102 μWh cm and a power density of 73.38 mW cm over a wide potential window of 2 V. The present study provides direct experimental evidence for the contribution of PVA-KCl gel electrolytes toward quick redox reactions for redox-type capacitors, which is also helpful for the development of neutral pH gel electrolytes for energy storage devices.