MnO2 as ink material for the fabrication of supercapacitor electrodes

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material's configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Strategies for liquid-liquid extraction of oxide particles for applications in supercapacitor electrodes and thin films

Bottom-up and top-down liquid-liquid extraction methods have been developed for the transfer of colloidal metal oxide particles, synthesized in an aqueous phase, to organic phases. In such methods the agglomeration of the particles during the drying stage was avoided. Hexadecylamine was used as an extractor for MnO₂ particles in the bottom-up extraction to the 1-butanol phase and top-down extraction to the dichloromethane phase. The reduction of particle agglomeration facilitated the fabrication of MnO₂-carbon nanotube composite electrodes for electrochemical supercapacitors with enhanced mixing of the individual components and active mass as high as 35mgcm^-2. Electrochemical testing results showed superior performance of the composite MnO₂-carbon nanotube electrodes, prepared by the bottom-up strategy. The new strategies allowed the fabrication of advanced electrodes, which showed a capacitance of 5.48Fcm^-2 at a scan rate of 2mVs^-1, good capacitance retention at high scan rates and low resistance. In another conceptually new bottom-up strategy colloidal titania particles were modified during synthesis with 2,3,4-trihydroxybenzaldehyde, which allowed strong catecholate-type bonding to the Ti atoms on the particle surface. The Schiff base reaction with hexadecylamine at the liquid-liquid interface allowed for particle extraction. The extraction strategies developed in this investigation pave the way for agglomerate-free processing of advanced films, coatings and devices by colloidal methods.

Reconstruction of TiO2/MnO2-C nanotube/nanoflake core/shell arrays as high-performance supercapacitor electrodes

Construction of electrodes with fast reaction kinetics is of great importance for achieving advanced supercapacitors. Herein we report a facile combined synthetic strategy with atomic layer deposition (ALD) and electrodeposition to rationally fabricate nanotube/nanoflake core/shell arrays. ALD-TiO₂ nanotubes are used as the skeleton core for assembly of electrodeposited MnO₂-C nanoflake shells forming a core/shell structure. Highly porous architecture and good electrical conductivity are combined in this unique core/shell structure, resulting in fast ion/electron transfer. In tests of electrochemical performance, the TiO₂/MnO₂-C core/shell arrays are characterized as cathode for asymmetric supecapacitors and exhibit high specific capacitance (880 F g^-1 at 2.5 A g^-1), excellent rate properties (735 F g^-1 at 30 A g^-1) and good long-term cycling stability (94.3% capacitance retention after 20 000 cycles). The proposed electrode construction strategy is favorable for fabrication of other advanced supercapacitor electrodes.

One-pot hydrothermal synthesis of novel 3D starfish-like δ-MnO2 nanosheets on carbon fiber paper for high-performance supercapacitors

Novel 3D starfish-like δ-MnO₂ nanosheets with a hierarchical nanostructure supported on carbon fiber paper were synthesized through a facile hydrothermal method.

Controllable Fabrication of Amorphous Co-Ni Pyrophosphates for Tuning Electrochemical Performance in Supercapacitors

Incorporation of two transition metals offers an effective method to enhance the electrochemical performance in supercapacitors for transition metal compound based electrodes. However, such a configuration is seldom concerned in pyrophosphates. Here, amorphous phase Co-Ni pyrophosphates are fabricated as electrodes in supercapacitors. Through controllably adjusting the ratios of Co and Ni as well as the calcination temperature, the electrochemical performance can be tuned. An optimized amorphous Ni-Co pyrophosphate exhibits much higher specific capacitance than monometallic Ni and Co pyrophosphates and shows excellent cycling ability. When employing Ni-Co pyrophosphates as positive electrode and activated carbon as a negative electrode, the fabricated asymmetric supercapacitor cell exhibits favorable capacitance and cycling ability. This study provides facile methods to improve the transition metal pyrophosphate electrodes for efficient electrodes in electrochemical energy storage devices.