Ni2Mn-layered double oxide electrodes in organic electrolyte based supercapacitors.

The development of future mobility (e.g. electric vehicles) requires supercapacitors with high voltage and high energy density. Conventional active carbon-based supercapacitors have almost reached their limit of energy density which is still far below the desired performance. Advanced materials, particularly metal hydroxides/oxides with tailored structure are promising supercapacitor electrodes to push the limit of energy density. To date, research has largely focused on evaluation of these materials in aqueous electrolyte, while this may enable high specific capacitance, it results in low working voltage window and poor cycle stability. Herein, we report the development of Ni2Mn-layered double oxides (Ni2Mn-LDOs) as mixed metal oxide-based supercapacitor electrodes for use in an organic electrolyte. Ni2Mn-LDO obtained by calcination of [Ni0.66Mn0.33(OH)2](CO3)0.175·nH2O at 400 °C produced the best performing Ni2Mn-LDOs with high working voltage of 2.5 V and a specific capacitance of 44 F g-1 (at 1 A g-1). We believe the performance of the Ni2Mn-LDOs is related to its unique porous structure, high surface area and the homogeneous mixed metal oxide network. Ni2Mn-LDO outperforms both the single metal oxides (NiO, MnO2) and the equivalent physical mixture of the two oxides. We propose this performance boost arises from synergy between NiO and MnO x due to a more effective homogeneous network of NiO/MnO x domains in the Ni2Mn-LDO. This work clearly shows the advantage of an LDO over the single component metal oxides as well as the physical mixture of mixed metal oxides and highlights the possibilities of development of further mixed metal oxides-based supercapacitors in organic electrolyte using LDH precursors.

Water-soluble MoS3 nanoparticles for photocatalytic H2 evolution.

Polyvinylpyrrolidone (PVP)-modified MoS3 nanoparticles with unusual water solubility up to 1.0 mg mL(-1) were synthesized through a facile hydrothermal method in the presence of thioacetic acid. The amorphous nanoparticles wrapped by PVP have sizes of around 2.5 nm, which represent the smallest MoS3 clusters reported. The photocatalytic performance of the MoS3 nanoparticles was evaluated under visible light for H2 evolution using xanthene dyes as photosensitizers. The quantum efficiency of the optimized system for H2 evolution under green light irradiation (520 nm) is up to 36.2 %, which is comparable with those of other excellent photocatalytic systems involving earth-abundant catalysts. The excellent photocatalytic activity can be attributed to its good dispersion in water, amorphous nature and limited layers with abundant surface active sites, and possibly higher conduction band potential for proton reduction and larger indirect band gap for a longer lifetime of the excited electrons.

Porous carbon nitride nanosheets for enhanced photocatalytic activities.

Porous carbon nitride nanosheets (PCNs) have been prepared for the first time by a simple liquid exfoliation method via probe sonication. These mesoporous nanosheets of around 5 nm in thickness combine several advantages including high surface area, enhanced light absorption and excellent water dispersity. It can be used as a versatile support for co-catalyst loading for photocatalytic dye degradation and water reduction. With 3.8 wt% Co(3)O(4) loaded, PCNs can achieve more efficient photocatalytic degradation of Rhodamine B, compared with non-porous C(3)N(4) nanosheets (CNs), bulk porous C(3)N(4) (PCN) and bulk nonporous C(3)N(4) (CN). With 1.0 wt% Pt loaded, CNs and PCN exhibit 7-8 times enhancement in H2 evolution than CN. Remarkably, PCNs with both porous and nanosheet-like features achieve 26 times higher activity in H2 evolution than CN. These significant improvements in photocatalytic activities can be attributed to the high surface area as well as better electron mobility of the two-dimensional nanostructure.

Cadmium sulfide quantum dots supported on gallium and indium oxide for visible-light-driven hydrogen evolution from water.

In this work, CdS quantum dots (QDs) supported on Ga2O3 and In2O3 are applied for visible-light-driven H2 evolution from aqueous solutions that contain lactic acid. With Pt as the cocatalyst, the H2 evolution rates on CdS/Pt/Ga2O3 and CdS/Pt/In2O3 are as high as 995.8 and 1032.2 µmol h(-1), respectively, under visible light (λ>420 nm) with apparent quantum efficiencies of 43.6 and 45.3% obtained at 460 nm, respectively. These are much higher than those on Pt/CdS (108.09 µmol h(-1)), Pt/Ga2O3 (0.12 µmol h(-1)), and Pt/In2O3 (0.05 µmol h(-1)). The photocatalysts have been characterized thoroughly and their band structures and photocurrent responses have been measured. The band alignment between the CdS QDs and In2O3 can lead to interfacial charge separation, which cannot occur between the CdS QDs and Ga2O3. Among the various possible factors that contribute to the high H2 evolution rates on CdS/Pt/oxide, the surface properties of the metal oxides play important roles, which include (i) the anchoring of CdS QDs and Pt nanoparticles for favorable interactions and (ii) the efficient trapping of photogenerated electrons from the CdS QDs because of surface defects (such as oxygen defects) based on photoluminescence and photocurrent studies.

Noble-metal-free NiS/C3 N4 for efficient photocatalytic hydrogen evolution from water.

A NiS/C3 N4 photocatalyst containing earth-abundant elements only was constructed by means of a simple hydrothermal method. This photocatalyst shows efficient hydrogen evolution (48.2 µmol h(-1) ) under visible light when using triethanolamine as a sacrificial reagent. The optimal loading of 1.1 wt % NiS on C3 N4 as a cocatalyst can enhance the H2 production by about 250 times compared with the native C3 N4 . The highest apparent quantum efficiency of 1.9 % was recorded at 440 nm.

Nickel-thiolate complex catalyst assembled in one step in water for solar H2 production.

We report the use of a simple complex assembled from Ni(II) salt and 2-mecaptoethanol in one step in water as the efficient catalyst in a molecular hydrogen system which can be sensitized by a low-cost xanthene dye, Erythrosin B. An excellent quantum efficiency of 24.5% is attained at 460 nm. This simple system is expected to contribute toward the development of economical and environmentally benign solar hydrogen production systems.

Self-assembled dye-layered double hydroxide-Pt nanoparticles: a novel H2 evolution system with remarkably enhanced stability.

A novel photocatalytic hydrogen evolution system was constructed by using well-dispersed layered double hydroxide (LDH) to immobilize the photosensitizer (rose bengal, RB) and photocatalyst (Pt). The produced amount of H(2) from such a self-assembled RB-LDH-Pt system is a few times more than that from the Free system (without LDH). Moreover, RB-LDH-Pt can be reused for at least 6 times (still having 64% of the activity in the 6(th) run) by a simple method of centrifugation which makes this system more economical by recycling the expensive Pt. The total turnover number (TON) obtained after six runs for RB-LDH-Pt was calculated to be 304 based on Pt, which gave at least 13-fold enhancement compared with that from the Free system.