Photocatalytic methane oxidation over a TiO2/SiNWs p-n junction catalyst at room temperature.

Rapid recombination of charge carriers in semiconductors is a main drawback for photocatalytic oxidative coupling of methane (OCM) reactions. Herein, we propose a novel catalyst by developing a p-n junction titania-silicon nanowires (TiO2/SiNWs) heterostructure. The structure is fabricated by atomic layer deposition of TiO2 on p-type SiNWs. The TiO2/SiNWs heterostructure exhibited an outstanding OCM performance under simulated solar light irradiation compared to the single components. This enhanced efficiency was attributed to the intrinsic electrical field formed between n-type TiO2 and p-type SiNWs, which forces generated charge carriers to move in opposite directions and suppresses charge recombination. Besides, surface morphology and optical properties of the the p-n TiO2/SiNWs catalyst are also beneficial for the photocatalytic activity. It is expected that the results of this study will provide massive guidance in synthesizing an efficient photocatalyst for CH4 conversion under mild conditions.

Mathematical modeling of dark fermentative hydrogen and soluble by-products generations from water hyacinth.

The production of hydrogen and soluble metabolite products from water hyacinth via dark fermentation was modeled. The model was built on the assumption that the substrate exists in two forms (i.e., soluble and particulate) and undergoes two stages (i.e., hydrolysis and acidogenesis) in the dark fermentation process. The modified Michaelis-Menten and surface-limiting models were applied to describe the hydrolysis of soluble and particulate forms, respectively. Meanwhile, the acidogenesis stage was modeled based on the multi-substrate-single-biomass model. The effects of temperature, pH, and substrate concentration were integrated into the model to increase flexibility. As a result, the model prediction agreed with the experimental and literature data of water hyacinth-fed dark fermentation, with high coefficient of determination values of 0.92 - 0.97 for hydrogen and total soluble metabolite products. These results indicate that the proposed model could be further applied to dark fermentation's downstream and hybrid processes using water hyacinth and other substrates.

Designed Synthesis of Three-Dimensional Covalent Organic Frameworks: A Mini Review.

Covalent organic frameworks are porous crystals of polymers with two categories based on their covalent linkages: layered structures with two dimensions and networks with three-dimensional structures. Three-dimensional covalent organic frameworks are porous, have large surface areas, and have highly ordered structures. Since covalent bonds are responsible for the formation of three-dimensional covalent organic frameworks, their synthesis has been a challenge and different structures are generated during the synthesis. Moreover, initially, their topologies have been limited to dia, ctn, and bor which are formed by the condensation of triangular or linear units with tetrahedral units. There are very few building units available for their synthesis. Finally, the future perspective of 3D COFs has been designated for the future development of three-dimensional covalent organic frameworks.

Anion Exchange Membranes for Fuel Cell Application: A Review.

The fuel cell industry is the most promising industry in terms of the advancement of clean and safe technologies for sustainable energy generation. The polymer electrolyte membrane fuel cell is divided into two parts: anion exchange membrane fuel cells (AEMFCs) and proton exchange membrane fuel cells (PEMFCs). In the case of PEMFCs, high-power density was secured and research and development for commercialization have made significant progress. However, there are technical limitations and high-cost issues for the use of precious metal catalysts including Pt, the durability of catalysts, bipolar plates, and membranes, and the use of hydrogen to ensure system stability. On the contrary, AEMFCs have been used as low-platinum or non-platinum catalysts and have a low activation energy of oxygen reduction reaction, so many studies have been conducted to find alternatives to overcome the problems of PEMFCs in the last decade. At the core of ensuring the power density of AEMFCs is the anion exchange membrane (AEM) which is less durable and less conductive than the cation exchange membrane. AEMFCs are a promising technology that can solve the high-cost problem of PEMFCs that have reached technological saturation and overcome technical limitations. This review focuses on the various aspects of AEMs for AEMFCs application.

Co-production of hydrogen and electricity from macroalgae by simultaneous dark fermentation and microbial fuel cell.

In this study, a hybrid process of dark fermentation (DF) and microbial fuel cell (MFC), sDFMFC, was investigated for simultaneous H2 and electricity production from Saccharina japonica in a single reactor. The sDFMFC exhibited a considerably enhanced energy recovery owing to simultaneous H2/carboxylic acids (CAs) production by DF and electricity production by MFC consuming CAs. The co-production of H2 and electricity was confirmed by a time course of CAs concentration in sDFMFC. An excellent energy recovery of 17.3% was obtained from S. japonica with H2 yield of 110 mL/g-VS and maximum power density of 1.82 W/m2. The sDFMFC showed a diverse microbial community for a desirable microbial conversion of organic substrates. The results indicate that sDFMFC can be a promising single reactor process to produce H2 and electricity from various biomass feedstock with considerable cost savings while ensuring the strength of the individual DF and MFC process.

Hydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell.

Hydrogen production from Saccharina Japonica by simultaneous dark fermentation (DF) and microbial electrolysis cell (MEC), called sDFMEC, was studied. In the novel sDFMEC process, substrates were converted to H2 and volatile fatty acids (VFAs) by DF in the bulk phase, and VFAs are simultaneously oxidized by the exoelectrogens in the microbial film on anode electrode with further production of H2 at the cathode. The sDFMEC process was compared with DF and a combined process of DF and MEC in series (DF-MEC) in terms of H2 production. The overall H2 production from S. Japonica in sDFMEC process was higher (438.7 ± 13.3 mL/g-TS), than DF (54.6 ± 0.8 mL/g-TS) and DF-MEC (403.5 ± 7.9 mL/g-TS) process, respectively, which is approximately 3-times higher than those reported in the literature.