Coprecipitation Temperature Effects of Morphology-Controlled Nickel Hexacyanoferrate on the Electrochemical Performance in Aqueous Sodium-Ion Batteries.

Coprecipitation effortlessly fabricated nickel hexacyanoferrate (NiHCF) with outstanding rate capability and stability for aqueous batteries. Citrate-aided coprecipitation decelerated the crystallization, assembling cubic-shaped powder based on separation between nucleation and growth. This study revealed that coprecipitation temperature determined the electrochemical performance.

Facile synthesis of Mn-doped NiCoO nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode.

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo2O4) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo2O4 NPs show an excellent specific capacity of 417 C g-1 at a scan rate of 10 mV s-1 and 204.

Efficient Charge Storage in Dual-Redox Electrochemical Capacitors through Reversible Counterion-Induced Solid Complexation.

The performance of redox-enhanced electrochemical capacitors (redox ECs) is substantially improved when oxidized catholyte (bromide) and reduced anolyte (viologen) are retained within the porous electrodes through reversible counterion-induced solid complexation. Investigation of the mechanism illustrates design principles and identifies pentyl viologen/bromide (PV/Br) as a new high-performance electrolyte. The symmetric PV/Br redox EC produces a specific energy of 48.

Evidence of Porphyrin-Like Structures in Natural Melanin Pigments Using Electrochemical Fingerprinting.

Eumelanins are extended heterogeneous biopolymers composed of molecular subunits with ambiguous macromolecular topology. Here, an electrochemical fingerprinting technique is described, which suggests that natural eumelanin pigments contain indole-based tetramers that are arranged into porphyrin-like domains. Spectroscopy and density functional theory calculations suggest that sodium ions undergo occupancy-dependent stepwise insertion into the core of porphyrin-like tetramers in natural eumelanins at discrete potentials.

High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte.

We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx-/I- couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx-/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.

Design of aqueous redox-enhanced electrochemical capacitors with high specific energies and slow self-discharge.

Electrochemical double-layer capacitors exhibit high power and long cycle life but have low specific energy compared with batteries, limiting applications. Redox-enhanced capacitors increase specific energy by using redox-active electrolytes that are oxidized at the positive electrode and reduced at the negative electrode during charging. Here we report characteristics of several redox electrolytes to illustrate operational/self-discharge mechanisms and the design rules for high performance.

Catechol-mediated reversible binding of multivalent cations in eumelanin half-cells.

Electrochemical storage systems that utilize divalent cations such as Mg2+ can improve the volumetric charge storage capacities compared to those that use monovalent ions. Here, a cathode based on naturally derived melanin pigments is used in secondary Mg2+ batteries. Redox active catechol groups in melanins permit efficient and reversible exchange of divalent Mg2+ cations to preserve charge storage capacity in biopolymer cathodes for more than 500 cycles.

Biologically derived melanin electrodes in aqueous sodium-ion energy storage devices.

Biodegradable electronics represents an attractive and emerging paradigm in medical devices by harnessing simultaneous advantages afforded by electronically active systems and obviating issues with chronic implants. Integrating practical energy sources that are compatible with the envisioned operation of transient devices is an unmet challenge for biodegradable electronics. Although high-performance energy storage systems offer a feasible solution, toxic materials and electrolytes present regulatory hurdles for use in temporary medical devices.

Self-deployable current sources fabricated from edible materials.

Flexible biodegradable electronics have the potential to serve as the centerpiece for temporary electronically active medical implants. Biodegradable electronics may exhibit many advantages over traditional chronic implants. Two important long-term goals for biodegradable electronics are (1) supplying sufficient power and (2) reducing the invasiveness of device deployment.

Electrochemically active nitrogen-enriched nanocarbons with well-defined morphology synthesized by pyrolysis of self-assembled block copolymer.

Novel nanoporous nitrogen-enriched carbon materials were prepared through a simple carbonization procedure of well-defined block copolymer precursors containing the source of carbon, i.e., polyacrylonitrile (PAN), and a sacrificial block, i.