Jullieth Suárez-Guevara

Hybrid energy storage: high voltage aqueous supercapacitors based on activated carbon–phosphotungstate hybrid materials

The use of hybrid electrodes prepared from phosphotungstic acid (H3PW12O40, PW12) and activated carbon (AC) allows the fabrication of highly durable aqueous supercapacitors operating at a superior voltage (1.6 V) thanks to the high overpotential of PW12 towards H2 generation. The combination of the double-layer capacitance plus the redox activity of the polyoxometalate clusters leads to an intrinsic increase in specific capacitance (from 185 F g−1 for AC to 254 F g−1 for AC–PW12) and a 60% increase in the operating voltage (compared to conventional AC supercapacitors with aqueous electrolytes, e.g. 1 M sulphuric acid). The hybrid energy storage mechanism and the increased operating voltage converge to yield improved specific energy and power. Moreover, the hybrid AC–PW12 electrode material showed an outstanding stability even after 30 000 cycles (0 to 1.6 V) with 98% retention of the initial capacitance, much superior to the stability of the parent supercapacitor based on plain AC under the same conditions.

A high voltage solid state symmetric supercapacitor based on graphene–polyoxometalate hybrid electrodes with a hydroquinone doped hybrid gel-electrolyte

In pursuit of high capacitance and high energy density storage devices, hybrid materials have quickly garnered well-deserved attention based on their power to merge complementary components and properties. Here, we report the fabrication of all-solid state symmetric supercapacitors (ASSSC) based on a double hybrid approach combining a hybrid electrode (reduced graphene oxide-phoshomolybdate, rGO-PMo12) and a hybrid electrolyte (hydroquinone doped gel-electrolyte). To begin with, a high-performance hybrid electrode based on H3PMo12O40 nanodots anchored onto rGO was prepared (rGO-PMo12). Later, an all-solid state symmetric cell based on these rGO-PMo12 electrodes, and making use of a polymer gel-electrolyte was assembled. This symmetric cell showed a significant improvement in cell performance. Indeed, it allowed for an extended potential window by 0.3 V that led to an energy density of 1.07 mW h cm-3. Finally, we combined these hybrid electrodes with a hybrid electrolyte incorporating an electroactive species. This is the first proof-of-design where a redox-active solid-state gel-electrolyte is applied to rGO-PMo12 hybrid supercapacitors to accomplish a significant enhancement in the capacitance. Strikingly, a further excellent increase in the device performance (energy density of 1.7 mW h cm-3) was realized with the hybrid electrode-hybrid electrolyte combination cell as compared to that of the conventional electrolyte cell. Thus, this unique symmetric device outclasses the high-voltage asymmetric counterparts under the same power and represents a noteworthy advance towards high energy density supercapacitors.

Copper@polypyrrole nanocables

A simple hydrothermal redox reaction between microcrystalline CuOHCl and pyrrole leads to the isolation of striking nanostructures formed by polypyrrole-coated copper nanocables. These multicomponent cables that feature single-crystalline face-centered cubic Cu cores (ca. 300 nm wide and up to 200 μm long) are smoothly coated by conducting polypyrrole, which in addition to its functionality, offers protection against oxidation of the metal core.