In recent times, microwave synthetic strategies have been considered as one of the facile methods for the development of efficient supercapacitor electrodes. Reduced graphene oxide containing cobalt oxide (rGO@Co3O4/CoO) hybrids were synthesized via single-step microwave irradiation in which the uniform Co3O4/CoO nanoparticles were attached in thin layers of rGO nanosheets. During short time of single-step microwave irradiation process, three kind of phenomena occurs as (i) reduction and exfoliation of graphite oxide into rGO nanosheets, (ii) decomposition of cobalt(II) acetate into Co3O4/CoO nanoparticles and (iii) rGO nanosheets covers the Co3O4/CoO nanoparticles. The BET surface area and pore diameter range of rGO@Co3O4/CoO hybrids were 133.2 m2g−1 and 5–45 nm, respectively, which shows the mesoporous structure formation of hybrids. Electrochemical evaluations of rGO@Co3O4/CoO hybrids as electrode materials for supercapacitor shows specific capacitance of 276.1 F g−1 (scan rate of 5 mV s−1) and long-term cycling stability as 82.37% capacitance retention after 10,000 cycles (scan rate of 60 mV s−1) in 0.1 M KOH electrolyte solution. The Co3O4/CoO nanoparticles with conducting scaffolds rGO structure will pave an encouraging alternative for electrode materials and suggesting good potential for supercapacitors applications.

Microwave-assisted thin reduced graphene oxide-cobalt oxide nanoparticles as hybrids for electrode materials in supercapacitor

Carbon-supported well-dispersed PdeNieP ternary catalyst targeted for ethanol oxidation reaction (EOR) in alkaline media is synthesized in a simple aqueous bath containing Pd(II) and Ni(II) salts with sodium hypophosphite as the reducing agent and the source for P and sodium citrate as the complexing agent. XRD analysis on the as-prepared PdeNieP/C reveals that Ni shrinks while P expands the Pd lattice structure, and XPS measurement suggests different electronic effects of the two alloying elements on Pd. Cyclic voltammetry and chronoamperometry indicate that the PdeNieP/C presents a remarkably higher electrocatalytic activity than the state-of-the-art Pd/C, PdeP/C and PdeNi/C catalysts. This may be ascribed to the unique electronic, geometric and bifunctional effects involved in this ternary nanoalloy. 2013 Elsevier B.V. All rights reserved.

Carbon Supported Pd-Ni-P Nanoalloy As An Efficient Catalyst for Ethanol Electro-Oxidation in Alkaline Media

Developing efficient electrocatalysts for selective nitrate contamination reduction into value-added ammonia is significant. Here, heterostructured Co/CoO nanosheet arrays (Co/CoO NSAs) exhibited excellent Faradaic efficiency (93.8%) and selectivity (91.2%) for nitrate electroreduction to ammonia, greatly outperforming Co NSAs. 15N isotope labeling experiments and 1H nuclear magnetic resonance (NMR) quantitative testing methods confirmed the origin of the produced ammonia. Electrochemical in situ Fourier transform infrared (FTIR) spectroscopy, online differential electrochemical mass spectrometry (DEMS) data and density functional theory (DFT) results revealed that the superior performances arose from the electron deficiency of Co induced by the rectifying Schottky contact in the Co/CoO heterostructures. The electron transfer from Co to CoO at the interface could not only suppress the competitive hydrogen evolution reaction, but also increase energy barriers for by-products, thus leading to high Faradaic efficiency and selectivity of ammonia.

Promoting selective electroreduction of nitrates to ammonia over electron-deficient Co modulated by rectifying Schottky contacts

Three-dimensional core–shell structured NiCo2O4@CoS/Ni-Foam electrocatalyst for oxygen evolution reaction and electrocatalytic oxidation of urea

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co3 O4 nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co3 O4 nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co3 O4 nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g-1 (2760 F g-1 ) at current density 2 A g-1 , which is greater than pristine Co3 O4 @NF (1045.8 C g-1 or 2324 F g-1 ). The rate capability with 5 nm NiO/Co3 O4 @NF nanocone structures is about 77% whereas Co3 O4 @NF retains 46 % of capability at 10 A g-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co3 O4 @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg-1 (4268 W kg-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

Dan Zhang

Papers

Room-temperature sulfurization for obtaining Co3O4/CoS core-shell nanosheets as supercapacitor electrodes

Hydroxamic acid pre-adsorption raises the efficiency of cosensitized solar cells

Synthesis of binder-free Co/CoO encapsulated in graphene as electrode material for electrochemical applications

Atomically dispersed antimony on N-doped carbon for highly efficient oxygen reduction reaction

Facile preparation of N-doped porous carbon and its CO2 gas adsorption performance