New tetracobalt cluster compounds for electrocatalytic proton reduction: syntheses, structures, and reactivity

Reaction of Co2(CO)8 and 1,3-propanedithiol in a 1:1 molar ratio in toluene affords a novel tetracobalt complex, [(μ2-pdt)2(μ3-S)Co4(CO)6] (pdt = -SCH2CH2CH2S-, 1), which possesses some of the structural features of the active site of [FeFe]-hydrogenase. Carbonyl displacement reaction of complex 1 in the presence of mono- or diphosphine ligands leads to the formation of [(μ2-pdt)2(μ3-S)Co4(CO)5(PCy3)] (2) and [(μ2-pdt)2(μ3-S)Co4(CO)4(L)] [L = Ph2PCH=CHPPh2, 3; Ph2PCH2N(Ph)CH2PPh2, 4; Ph2PCH2N(iPr)CH2PPh2, 5]. Complexes 1-5 have been fully characterized by spectroscopy and single-crystal X-ray diffraction studies. Cyclic voltammetry has revealed that complexes 1-5 show a reversible first reduction wave and are active for electrocatalytic proton reduction in the presence of CF3COOH. Protonation reactions have been monitored by (31)P and (1)H NMR and infrared spectroscopies, which revealed the formation of different protonated species. The mono-reduced species of 1-5 have been spectroscopically characterized by EPR and spectro-electro-infrared techniques.

ZnGa(2-x)In(x)S4 (0 ≤ x ≤ 0.4) and Zn(1-2y)(CuGa)(y)Ga(1.7)In(0.3)S4 (0.1 ≤ y ≤ 0.2): optimize visible light photocatalytic H2 evolution by fine modulation of band structures

Band structure engineering is an efficient technique to develop desired semiconductor photocatalysts, which was usually carried out through isovalent or aliovalent ionic substitutions. Starting from a UV-activated catalyst ZnGa2S4, we successfully exploited good visible light photocatalysts for H2 evolution by In(3+)-to-Ga(3+) and (Cu(+)/Ga(3+))-to-Zn(2+) substitutions. First, the bandgap of ZnGa2-xInxS4 (0 ≤ x ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction band position. Second, Zn1-2y(CuGa)yGa1.7In0.3S4 (y = 0.1, 0.15, 0.2) provided a further and significant red-shift of the photon absorption to ∼500 nm by raising the valence band maximum and barely losing the overpotential to water reduction. Zn0.7Cu0.15Ga1.85In0.3S4 possessed the highest H2 evolution rate under pure visible light irradiation using S(2-) and SO3(2-) as sacrificial reagents (386 μmol/h/g for the noble-metal-free sample and 629 μmol/h/g for the one loaded with 0.5 wt % Ru), while the binary hosts ZnGa2S4 and ZnIn2S4 (synthesized using the same procedure) show 0 and 27.9 μmol/h/g, respectively. The optimal apparent quantum yield reached to 7.9% at 500 nm by tuning the composition to Zn0.6Cu0.2Ga1.9In0.3S4 (loaded with 0.5 wt % Ru).

n-type thermoelectric material Mg2Sn0.75Ge0.25 for high power generation

Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT, has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor (PF) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg2Sn-based material, Mg2Sn0.75Ge0.25, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg2Sn0.75Ge0.25 has an average ZT of 0.9 and PF of 52 μW⋅cm(-1)⋅K(-2) over the temperature range of 25-450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW⋅cm(-1)⋅K(-2) at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with Th = 400 °C and Tc = 50 °C to be of 10.5% and 6.6 W⋅cm(-2) under a temperature gradient of 150 °C⋅mm(-1), respectively.

Recent advances in the metabolic engineering of Corynebacterium glutamicum for the production of lactate and succinate from renewable resources

Recent increasing attention to environmental issues and the shortage of oil resources have spurred political and industrial interest in the development of environmental friendly and cost-effective processes for the production of bio-based chemicals from renewable resources. Thus, microbial production of commercially important chemicals is viewed as a desirable way to replace current petrochemical production. Corynebacterium glutamicum, a Gram-positive soil bacterium, is one of the most important industrial microorganisms as a platform for the production of various amino acids. Recent research has explored the use of C. glutamicum as a potential cell factory for producing organic acids such as lactate and succinate, both of which are commercially important bulk chemicals. Here, we summarize current understanding in this field and recent metabolic engineering efforts to develop C. glutamicum strains that efficiently produce l- and d-lactate, and succinate from renewable resources.