Hydrogen production from sewage sludge solubilized in hot-compressed water using photocatalyst under light irradiation

Photocatalytic hydrogen production from a digested sewage sludge solubilized in hot-compressed water (573K) was investigated in order to develop a low-cost sacrifice agent for CdS-based photocatalysts from biomass. H₂ evolution occurred over a LaMnO₃/CdS composite photocatalyst under Xe lamp irradiation from water containing the solubilized sewage sludge and the amount of evolved H₂ reached more than $\text{30}\text{mmol}\text{/}\text{g}$-catalyst for a $\text{200}\text{h}$-reaction; on the other hand, no H₂ was formed in the absence of the solubilized sewage sludge. The H₂ evolution rate was comparable to that when typical Na₂S–Na₂SO₃ sacrifice agents were used, suggesting the applicability of a biomass-derived sacrifice agent for photocatalysis. Organic compounds, such as methanol and formic acid, contained in the solubilized sewage sludge are responsible for the H₂ evolution observed.     

A new route to prepare macroporous bioactive sol–gel glasses with high mechanical strength

This paper reports a new method to obtain macroporous bioactive glasses by sol–gel and pore former technologies. The in vitro tests showed that the samples had good apatite-forming ability. Noticeably, these bioglasses exhibit high specific surface areas and excellent mechanical performances. The compressive strength is as high as 34.4±5.7 MPa. This method may be a useful approach for preparation of scaffolds for tissue engineering.     

Parallel interaction influence of single-stage photovoltaic grid-connected/hydrogen production multi-inverter system based on modal analysis

In order to study the harmonic resonance characteristics of single-stage photovoltaic (PV) grid-connected/hydrogen production multi-inverter system, the modal analysis method was used to systematically analyze and discuss the resonance problem. First, a three-phase single-stage photovoltaic grid-connected/hydrogen production system simulation model was established, and hydrogen production from water electrolysis was used as a local load. Secondly, this paper applied a modal analysis method that could determine the system resonance frequency, resonance center and the participation degree of each component by constructing the multi-inverter system node admittance matrix. Finally, the Thevenin equivalent model of multi-inverter system was established based on the modal analysis method. The influence of the number of inverters on the resonance characteristics of the system was studied. Compared with the frequency response analysis of the transfer function, the simulation results verify the correctness and effectiveness of the modal analysis method.     

High conductivity and surface area of Ti0.7W0.3O2 mesoporous nanostructures support for Pt toward enhanced methanol oxidation in DMFCs

For the first time, a novel Pt catalyst supported on mesoporous Ti_0.7W_0.3O₂ nanoparticles, which exhibited superior advantages such as high conductivity (0.022 S/cm), large specific surface area (201.481 m²/g) and homogeneous morphology with 9 nm spherical-like particles, was prepared successfully via the rapid microwave-assisted polyol route. It is found that uniform 3 nm spherical-like Pt nano-forms were adhered homogeneous on the surface of Ti_0.7W_0.3O₂. Intriguingly, the electrochemical surface area of Pt catalyst supported on mesoporous Ti_0.7W_0.3O₂ was found to be around 90.05 m²/gPt, which is profoundly higher than ECSA value obtained from Pt/C (E-TEK) catalyst. Furthermore, as for methanol oxidation reaction measurement, the I_f/I_b ratio of the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst was found to be approximately 2.33, which 2.5-folds higher than that of the commercial Pt/C (E-TEK) catalyst. Importantly, the chronoamperometry data also revealed that the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst possessed the higher durability than the commercial 20 wt % Pt/C (E-TEK) catalyst. In addition, the successful synthesis of the 20 wt % Pt/Ti_0.7W_0.3O₂ catalyst not only offers an attractive catalyst for fuel cell using methanol but also opens application potentials for solar cells, as well as biosensors.     

In-situ modified titanium suboxides with polyaniline/graphene as anode to enhance biovoltage production of microbial fuel cell

Microbial fuel cell (MFC) has been the focus of much investigation in the search for harvesting electricity from various organic matters. The electrode material plays a key role in boosting MFC performance. Most studies, however, in the field of MFC electrode material has only focused on carbonaceous materials. The finding indicates that titanium suboxides (Ti₄O₇, TS) can provide a new alternative for achieving better performance. Polyaniline (PANI) together with graphene is chosen to in-situ modify TS (TSGP). The MFC reactor with TSGP anode achieves the highest voltage with 980 mV, and produces a peak power density of 2073 mW/m², which is 2.9 and 12.7 times those with the carbon cloth control. The rather intriguing result could be due to the fact that TSGP has the high conductivity and large electrochemical active surface area, greatly improving the charge transfer efficiency and the bacterial biofilm loading. This study has gone some way towards exploring the conducting ceramics materials in MFC.     

Investment screening model for spatial deployment of power-to-gas plants on a national scale – A Danish case

When transitioning to a 100% renewable energy system storing electricity becomes a focal point, as the resource flexibility is lost and the design of the energy system needs to provide flexibility and balancing options to integrate intermittent renewable resources. Using technologies such as power-to-gas offers an opportunity to store electricity in chemical form, which can be used as a long-term storage option. This paper develops a spatial modelling method by using a GIS tool to investigate potential generation sites for power-to-gas plants. The method determines the location of the plants by carbon source potential, proximity of the grid, costs of grid transmission and investment costs of the technology itself. By combining these types of data, it is possible to identify the investment costs of the power-to-gas plants. The method focuses on two paths: biogas upgrade and CO₂ methanation. The method is applied to a specific case by investigating the power-to-gas potential in Denmark. The potential and spatial deployment is found by examining the investment costs of plants with an annual gas production of 60 GWh. The findings of the analysis indicate that the biogas upgrade path is the cheapest one of the two, at the present cost level, but due to the relatively small number of biogas plants in Denmark, the chosen plant size is limited to around 55 plants. CO₂ methanation is a more costly path, but it has a larger potential of around 800 plants. As the analysis is based on the current sources for biogas and CO₂, it is important to emphasise that the potential for CO₂ methanation plants can be expected to diminish in the future as more renewable energy is introduced, lowering the need for thermal energy producers, while biogas production could see an increase. Nevertheless, the analysis of a specific case shows that the method gives a good indication of the extent of the power-to-gas resources by using a novel approach to the matter. The method can be applied in other countries as well, giving it a wide appeal.     

Glucose electro-fermentation as main driver for efficient H2-producing bacteria selection in mixed cultures

Electro-fermentation has been recently proposed as a new operational mode of bioprocess control using polarized electrodes. This paper aims to evaluate how polarized electrodes are affecting microbial metabolic fermentative pathways, with a special focus on how the bacterial populations are affected during hydrogen production by dark fermentation. Four different potentials were applied on the working electrode in batch electro-fermentation tests operated with mixed culture and using glucose as a substrate. Two different metabolic behaviours for H₂ production were observed in electro-fermentation. The first one led to a higher H₂ production compared to conventional fermentation with a strong selection of Clostridium sp. The second behaviour led to lower H₂ production along with ethanol, and strongly correlated with the selection of Escherichia and Enterobacter genera. However, the effect of the applied potential on population selection was mostly non-linear and no simple relationship was found between these two parameters. Overall, electro-fermentation process has shown its potential as a new type of control for mixed-culture bioprocesses with significant effects of polarized electrodes on glucose fermentation.     

Synergistic effect of {101} crystal facet and bulk/surface oxygen vacancy ratio on the photocatalytic hydrogen production of TiO2

Anatase titanium dioxide (TiO₂) nanocrystals with different percentages (up to 95%) of exposed {101} facet and different concentration ratios of bulk single-electron-trapped oxygen vacancies (SETOVs) to surface oxygen vacancies (SOVs) were prepared by alcohol-thermal method with nanotube titanic acid as the precursor in combination with solid-state reduction by NaBH₄. The as-prepared TiO₂ nanocrystals were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and ultraviolet–visible light spectrometry. The effects of the percentage of crystal facets and the concentration ratio of bulk SETOVs/SOVs on the photocatalytic hydrogen production rate of TiO₂ nanocrystals were investigated with positron annihilation lifetime spectroscopy as well as photocurrent test. Findings indicate that the percentage of the exposed {101} facets of the as-prepared TiO₂ nanocrystals and their concentration ratios of bulk SETOVs/SOVs can be well tuned by properly adjusting the amount of NaBH₄ and the reduction reaction time as well. Increasing percentage of the {101} facet of anatase TiO₂ nanocrystals contributes to improving their photocatalytic hydrogen production activity, because the {101} facets of the anatase TiO₂ nanocrystals possess enriched electrons and can act as the reduction sites to enhance the reduction reaction of H⁺ affording H₂ in the sacrifice system of splitting water. Both the bulk SETOVs and SOVs contribute to the improvement of the light absorption while SOVs can facilitate the separation of photogenerated charges, thereby adding to the photocatalytic activity. However, the bulk SETOVs and excessive SOVs are also the combination centers of photogenerated charges, which means it is essential to maintain a suitable concentration ratio of the bulk SETOVs/SOVs so as to enhance the light absorption and achieve the best separation efficiency of photogenerated charges and achieve the best photocatalytic activity for hydrogen production. Particularly, when anatase TiO₂ nanocrystal with a high percentage (95%) of exposed {101} facet is reduced by NaBH₄ at a mass ratio of 2: 1 for 20 min, the resultant reduced H-TiO₂ nanocrystal (denoted as H-TiO₂-R20(2:1)) provides the highest photocatalytic hydrogen productive rate. Furthermore, the combination of 0.5% Pt/H-TiO₂-R20(2:1) with 0.5% Pt/WO₃ can split water to simultaneously produce H₂ and O₂, showing promising potential for splitting water affording hydrogen and oxygen.