In this work, we presented a novel, facile, and template-free strategy for fabricating graphene-like N-doped carbon as oxygen reduction catalyst in sustainable microbial fuel cells (MFCs) by using an ion-inducing and spontaneous gas-flow tailoring effect from a unique nitrogen-rich polymer gel precursor which has not been reported in materials science. Remarkably, by introduction of trace platinum- and cobalt- precursor in polymer gel, highly dispersed sub-10 nm PtCo nanoalloys can be in situ grown and anchored on graphene-like carbon. The as-prepared catalysts were investigated by a series of physical characterizations, electrochemical measurements, and microbial fuel cell tests. Interestingly, even with a low Pt content (5.13 wt %), the most active Co/N codoped carbon supported PtCo nanoalloys (Co–N–C/Pt) exhibited dramatically improved catalytic activity toward oxygen reduction reaction coupled with superior output power density (1008 ± 43 mW m–2) in MFCs, which was 29.40% higher than the state of the art Pt/C (20 wt %). Notability, the distinct catalytic activity of Co–N–C/Pt was attributed to the highly efficient synergistic catalytic effect of Co–Nx–C and PtCo nanoalloys. Therefore, Co–N–C/Pt should be a promising oxygen reduction catalyst for application in MFCs. Further, the novel strategy for graphene-like carbon also can be widely used in many other energy conversion and storage devices.Keywords: graphene-like carbon; microbial fuel cells; N/Co-dual doping; PtCo nanoalloys; synergistic catalyst;

Porous C/Ag nanohybrids were one type of emerging and promising alternative oxygen reduction catalysts for Pt, which was crucial to energy conversion and storage devices. Herein, a template-free, sustainable and in-situ method was employed for preparing N-doped hollow carbon tube @ hierarchically porous carbon supporting homogeneous Ag nanoparticles (HCT@HPC@AgNPs) by one-pot carbonization with the assist of “chelating effect”. It was very interesting that the “chelating effect” can inhibit the self-aggregation of AgNPs during its growing process, since Ag+ can be well immobilized on precursor. Moreover, during the carbonization process, an amazing N-doped hollow carbon tube @ porous carbon was also achieved by the synergistic effect of thermal degradation, spontaneous bubble-template and self-doping. The resultant HCT@HPC@AgNPs was investigated by physical characterizations and electrochemical tests. The results indicated that HCT@HPC@AgNPs delivered distinct electrocatalytic activity towards oxygen reduction reaction (ORR), long-term durability and anti-toxic capacity in alkaline electrolyte, which was comparable or even better than Pt/C. Thus, HCT@HPC@AgNPs was a promising ORR catalyst for application in the field of energy and catalysis.

The exploration of highly active and cost-effective catalysts for the oxygen reduction reaction is vitally important to facilitate the improvement of metal–air batteries and fuel cells. Herein, super-active catalysts made from an interesting metal–polymer network (MPN) that consist of Fe–Nx–C, B–N and Fe3O4/Fe3C alloys were prepared via facile one-pot carbonization. The achieved catalysts possessed an amazing porous structure that was derived from the MPN with the assistance of a “bubble-template”. Remarkably, the content of highly active Fe–Nx–C can be regulated by introducing graphene, and the ORR activity of the catalyst was enhanced dramatically with an increase in the Fe3O4/Fe3C alloy content. The most active BNFe–C–G2 catalyst exhibited superior ORR activity/stability, and was then employed as an air cathode electrocatalyst in a microbial fuel cell. The results showed that the output voltage and power density of BNFe–C–G2 were significantly improved to 575 ± 11 mV and 1046.2 ± 35 mW m−2, respectively. These values are 4.5% and 44.44% higher than those of commercial Pt/C. Thus, due to the synergistic electrocatalysis of the Fe–Nx–C, B–N and Fe3O4/Fe3C alloys, the super-active and low-cost BNFe–C–G2 material should be a promising ORR catalyst for application in biofuel cells, and in many other energy conversion and storage devices.

A highly active and cost-effective Pt-free catalyst for oxygen reduction reaction (ORR) is significantly important for air-cathode microbial fuel cells (MFCs). In this study, a novel low-cost iron–nitrogen–carbon nanorod network-anchored graphene (Fe–N–C/G) nanohybrid was prepared for use as an efficient ORR catalyst. The morphology, chemical composition, and ORR catalytic activity of the as-prepared Fe–N–C/G were investigated by a series physical measurements and electrochemical tests. Finally, it the nanohybrid was employed as an ORR electrocatalyst in the practical air-cathode MFCs. Remarkably, Fe–N–C/G exhibited a comparable catalytic performance and stability in a neutral medium along with even better power generation performance (1601 ± 59 mW m−2) in MFCs as compared to the-state-of-the-art Pt/C catalyst (1468 ± 58 mW m−2). The superior ORR activity of Fe–N–C/G should be attributed to its N/Fe co-doping, the introduction of graphene, as well as the unique micro-nano structure, which can dramatically favor the oxygen reduction kinetics. Therefore, the cost-effective Fe–N–C/G can be one of the most promising ORR catalysts for application in a neutral medium and practical air-cathode MFCs.

•1 Low-cost N/B co-doped carbon was prepared from renewable biomass.•2 NB-HCT exhibited comparable ORR activity and better stability than Pt/C.•3 Superior ORR activity of NB-HCT was ascribed to synergistic catalysis effect.Low-cost and highly active catalysts for oxygen reduction reaction (ORR) were of great importance to the development of fuel cell. Herein, we presented a novel N/B co-doped carbon as cost-effective and stable ORR catalyst from renewable biomass. The as-prepared carbon showed an interesting hollow tube morphology that derived from its precursor. The N/B co-doped sample (NB-HCT) possessed bigger electrochemical active area (296.4 m2 g−1), and also contained much more ORR active-N/B species than those of single N or B doped carbon. Notability, the on-set potential and half-wave potential of NB-HCT were 0.929 V (vs. RHE) and 0.810 V (vs. RHE), respectively, which were much more positive than others and even comparable to Pt/C, revealing it had distinct ORR activity. Remarkably, the superior ORR activity of NB-HCT could be mainly ascribed to the synergistic effect of ORR active-N and B-C, which might result in the possible formation of high-active B-C-N nanostructure. Therefore, NB-HCT should be one of promising ORR catalysts to alternative precious Pt/C and promote the development of fuel cell.Download high-res image (208KB)Download full-size image

•A novel method is used to study the extracellular electron transfer (EET) mechanism.•The mediated EET process can be studied alone by “resolution-contrast” method.•The dominant bacteria and the evolution of microbial community have been analyzed.•The main potential redox active compounds have been discussed.Due to the synergy existing in mixed bacteria, electricity-generation performances of the mixed bacteria microbial fuel cell (m-MFC) are better than that of the pure bacteria microbial fuel cell (p-MFC). It is necessary to explore the electron transfer mechanisms of the m-MFC to further improve electricity generation. In this study, a facile “resolution-contrast” method was employed in the two-chamber m-MFC to investigate the electron transfer mechanism using mixed bacteria as the anodic inoculums. The anode was wrapped with a mixed cellulose esters membrane to eliminate the effects of direct extracellular electron transport, while the mediator electron transport was investigated by electrochemical methods. The results showed that both transfer methods existed simultaneously in the m-MFC. The main exoelectrogens were Escherichia coli, Pseudomonas aeruginosa, and Brevundimonas diminuta, and the main redox mediators included 1-hydroxyanthracene-9,10-dione, phenazine-1-carboxylic acid and 2,4-diacetyl phloroglucinol.

A “Spontaneous bubble-template” method is fascinating in that bubbles are formed in situ during material processing and employed as a template for fabricating unique structures, which has not been reported in material science. It is sustainable, green and efficient in that no extra additives or post-treatment are used. Herein, novel metal–polymeric framework derived hierarchically porous carbon/Fe3O4 nanohybrids are prepared using a “spontaneous bubble-template” method by one-step carbonization. During the carbonization process, N and Co are self-doped on porous carbon in which in situ grown nano Fe3O4 is embedded (Fe3O4@N/Co–C). The as-prepared Fe3O4@N/Co–C displays a three-dimensional interpenetrating morphology (electrochemical active area: 729.89 m2 g−1) with well-distributed Fe3O4 nanoparticles (20–50 nm) which are coated with a carbon layer (3–5 nm). Fe3O4@N/Co–C exhibits remarkable oxygen reduction activity in biofuel cells with a distinct output voltage (576 mV) and power density (918 mW m−2), which are 3.6% and 17.8% higher than those of Pt (0.5 mg cm−2), respectively. Besides biofuel cells, Fe3O4@N/Co–C may also have the potential for application in chemical fuel cells, since it demonstrates better oxygen reduction activity in electrochemical measurements. Thus, with the virtues of its low-cost, facile synthesis and large-scale preparation, Fe3O4@N/Co–C is a promising electrocatalyst for the oxygen reduction reaction and application in biofuel cells.

•Stainless steel fiber felt (SSFF) is used as a novel cathode for hydrogen production.•SSFF cathode significantly enhance the hydrogen production performance in MEC.•SSFF is a low-cost and high efficient cathode to replace Pt catalytic cathode.Microbial electrolysis cell (MEC) is a promising technology for sustainable production of hydrogen from biodegradable carbon sources. Employing a low-cost and high efficient cathode to replace platinum catalyzed cathode (Pt/C) for hydrogen generation is a challenge for commercialization of MEC. Here we show that a 3D macroporous stainless steel fiber felt (SSFF) with high electrochemical active surface area has an excellent catalytic activity for hydrogen generation, which is comparable to Pt/C cathode and superior to stainless steel mesh (SSM) cathode in the single-chamber MEC. The SSFF cathode (mean filter rating 100 μm) produces hydrogen at a rate of 3.66 ± 0.43 m3 H2 m−3d−1 (current density of 17.29 ± 1.68 A m−2), with a hydrogen recovery of 76.37 ± 15.04% and overall energy efficiency of 79.61 ± 13.07% at an applied voltage of 0.9 V. The performance of SSFF cathode improves over time due to a decrease in overpotential which caused by corrosion. These results demonstrate that SSFF can be a promising alternative for Pt catalytic cathode in MEC for hydrogen production.

So far, the effect of the carbon matrix on ORR catalytic efficiency over carbon/cobalt oxide nanohybrids in biofuel cells has not been investigated, which is vital to guiding the scientific research on ORR catalysts. Moreover, although cobalt oxide crystals have been reported with electrocatalytic activity, studies on square-like nano cobalt oxide are very few, and it has not been reported as an oxygen reduction reaction (ORR) catalyst, let alone used in biofuel cells. Thus, herein, square-like nano cobalt oxide anchored on nitrogen-doped graphene (NG/Co-NS), carbon nanotube (CNT/Co-NS) and carbon black (CB/Co-NS) were prepared by a one-pot hydrothermal method for the application as an ORR catalyst in microbial fuel cells (MFC). The results indicated that NG/Co-NS exhibited outstanding ORR activity with a more positive on-set potential (−0.05 V vs. Ag/AgCl) and higher limiting diffusion current (5.8 mA cm−2 at −0.8 V) than CB/Co-NS and CNT/Co-NS, attributed to the synergistic catalytic effect of NG and Co-NS. Besides, in MFC tests, the maximum power density of NG/Co-NS was improved significantly to 713.6 mW m−2, which was 24.9% higher than Pt/C (571.3 mW m−2, 0.2 mg Pt cm−2). In addition, the internal resistance of MFCs with NG/Co-NS was lower than CB/Co-NS and CNT/Co-NS, which favored the electricity generation performance. Thus, NG/Co-NS was promising material for an alternative oxygen reduction reaction electrocatalyst of Pt/C in MFCs.

Novel three-dimensional (3D) macroporous cathodes for microbial fuel cells (MFCs) are constructed by using stainless steel felt (SSF) as the diffusion backing and the current collector, instead of two-dimensional (2D) materials such as a carbon cloth (CC) or stainless steel mesh (SSM), thereby resulting in an enlarged surface area for the oxygen reduction reaction (ORR). Different amounts of carbon black (CB) are applied in the base layers to optimize the performance of those SSF cathodes. The MFCs using the SSF cathodes with CB loading of 1.56 mg cm−2 (SSF-1.56) achieve a maximum power density of 1315 ± 6 mW m−2, which is 60% and 42% higher than those using the CC and SSM cathodes, respectively. The results show that the cathode of SSF-1.56 exhibits an excellent catalytic activity for ORR as well as a reduced total internal resistance, thanks to the improved three-phase interface (TPI) that not only facilitates the electron transfer, the proton transfer and the oxygen diffusion, but also offers a large surface for the ORR at the cathode. Our research also demonstrates that the SSF cathodes with an optimal CB loading will benefit the advancement of MFCs in practical application.

Biocathodes have shown great promise for developing low-cost cathodes for hydrogen production in microbial electrolysis cells (MEC). To promote the performance of hydrogen production with a biocathode, we constructed a graphene modified biocathode and assessed the performance of the modified biocathode by setting different cathode potentials. The results indicated that it was feasible to promote the current density, electron recovery efficiency (ERE) and hydrogen production rate by a modified biocathode using graphene. At −1.1 V (vs. Ag/AgCl), the hydrogen production rate of the graphene modified biocathode even achieved 2.49 ± 0.23 m3 per m3 per day with 89.12 ± 6.03% of ERE at a current density of 14.07 ± 0.06 A m−2, which were about 2.83 times, 1.38 times and 2.06 times that of the unmodified biocathode, respectively. The hydrogen production performance of the graphene modified biocathode was close to that of the platinum catalyzed cathode and superior to that of the stainless steel mesh cathode at −1.1 V.

•The effect of Cu2+ concentration on biohydrogen production was examined.•The concentration of Cu2+ had effect on the distribution of soluble metabolite.•6.4 mg/L Cu2+ is the optimum concentration for the CSTR at HRT 4 h.In this paper, the effect of hydraulic retention time (HRT, 16 h–4 h) on fermentative hydrogen production by mixed cultures was firstly investigated in a sucrose-fed anaerobic continuous stirred tank reactor (CSTR) at 35 °C and initial pH 8.79. After stable operations at HRT of 16–6 h, the bioreactor became unstable when the HRT was lowered to 4 h. The maximum hydrogen yield reached 3.28 mol H2/mol-Sucrose at HRT 4 h. Supplementation of Cu2+ at HRT 4 h improved the operation stability through enhancement of substrate degradation efficiency. The effect of Cu2+ concentration ranging from 1.28 to 102.4 mg/L on fermentative hydrogen production was studied. The results showed that Cu2+ was able to enhance the hydrogen production yield with increasing Cu2+ concentration from 1.28 to 6.4 mg/L. The maximum hydrogen yield of 3.31 mol H2/mol-Sucrose and the maximum hydrogen production rate of 14.44 L H2/Day/L-Reactor were obtained at 6.4 mg/L Cu2+ and HRT 4 h Cu2+ at much higher concentration could inhibit the hydrogen production, but it could increase substrate degradation efficiency (12.8 and 25.6 mg/L Cu2+). The concentration of Cu2+ had effect on the distribution of soluble metabolite.

•Effect of different anodic pH microenvironments on MFC performance was discussed.•The main influence factors to electricity generation were analyzed.•Optimum conditions for the maximum output voltage of MFC were available.•The major metabolites produced by the mixed culture were observed.The two-chamber microbial fuel cell (MFC) was operated in batch mode, using acclimated hydrogen-producing mixed bacteria as the anodic inoculum, artificial sucrose wastewater as the substrate (sucrose concentration 10.0 g/L). The performance of the MFC was analyzed at different anodic pH microenvironments, such as the initial pH of the anolyte of 8.57, 7.3, 7.0 and 6.0, respectively, while anodic pH-controlled of 7.3 and 7.0. It showed that the best performance was obtained when the MFC was carried out at anodic pH-controlled of 7.3. Taking the interaction of factors into consideration, we adopted response surface methodology (RSM) to investigate the effects of sucrose concentration, operating temperature and ferrous sulfate concentration on the performance of MFC. The optimum condition for maximum output voltage of the two-chamber MFC (external resistance 1000 Ω) was thus obtained.

•The optimal concentrations of nitrogen sources were in the range of 0.4–0.8 g/L.•Ammonium sulphate was much better than sodium glutamate as nitrogen source.•Orthogonal array design optimized the hydrogen-producing condition.In this study, hydrogen production by Rhodobacter sphaeroides RV from acetate was investigated. Ammonium sulphate and sodium glutamate were used to study the effects of nitrogen sources on photosynthetic hydrogen production. The results showed the optimal concentrations for ammonium sulphate and sodium glutamate were in the range of 0.4–0.8 g/L. Orthogonal array design was applied to optimize the hydrogen-producing conditions of the concentrations of yeast, FeSO4 and NiCl2. The theoretical optimal condition for hydrogen production was as follow: yeast 0.1 g/L, FeSO4 100 mg/L and NiCl2 20 mg/L.

•Halogen and tungsten lamps were better than it for fluorescent lamp as light source.•The best light intensity of hydrogen production was 3600 lux for tungsten lamp.•The optimum inoculum quantity was acquired at initial OD660 of 0.931.•The maximum hydrogen yield reached to 653.2 mmol H2/mol acetate at initial pH 7.0.The study of photosynthetic hydrogen production by using Rhodobacter sphaeroides RV from acetate was described. We investigated the effects of light source (fluorescent, halogen and tungsten lamps), light intensity (1200–6000 lux), inoculum quantity (OD660 0.212–OD660 1.082) and initial pH (4.0–10.0) on biohydrogen production. The results indicated that the hydrogen production for halogen and tungsten lamps was better than it for fluorescent lamp as light source. The best light intensity of hydrogen production was 3600 lux for tungsten lamp as light source. Inoculum quantity experiments indicated that the higher hydrogen production volume and hydrogen conversion rate were obtained at initial OD660 of 0.931. The effect of initial pH on hydrogen production indicated that the maximum hydrogen yield reached to 653.2 mmol H2/mol acetate at initial pH 7.0.

Rhodobacter sphaeroides RV was employed to produce hydrogen for the photo-fermentation of sole (acetate, propionate, butyrate, lactate, malate, succinate, ethanol, glucose, citrate and sodium carbonate) and compound carbon sources (malate and succinate, lactate and succinate). The concentrations of sole carbon sources on hydrogen production were investigated in batch assays at 0.8 g/L sodium glutamate and the maximum hydrogen yield was 424 mmol H2/mol-substrate obtained at 0.8 g/L sodium propionate. The maximum hydrogen yield reached 794 mmol H2/mol-substrate for 2.02 g lactate and 2.0 g succinate as the compound carbon source. The results showed hydrogen production for the compound carbon source was better than the sole carbon source.Highlights► The effect of sole carbon source on photo-hydrogen production was examined. ► The effect of compound carbon source on photo-hydrogen production was investigated. ► Hydrogen production for compound carbon source was better than sole carbon source.

Treatment of highly concentrated organic wastewater is characterized as cost-consuming. The conventional technology uses the anaerobic-anoxic-oxic process (A2/O), which does not produce hydrogen. There is potential for energy saving using hydrogen utilization associated with wastewater treatment because hydrogen can be produced from organic wastewater using anaerobic fermentation. A 50 m3 pilot bio-reactor for hydrogen production was constructed in Shandong Province, China in 2006 but to date the hydrogen produced has not been utilized. In this work, a technical-economic model based on hydrogen utilization is presented and analyzed to estimate the potential improvement to a citric wastewater plant. The model assesses the size, capital cost, annual cost, system efficiency and electricity cost under different configurations. In a stand-alone situation, the power production from hydrogen is not sufficient for the required load, thus a photovoltaic array (PV) is employed as the power supply. The simulated results show that the combination of solar and bio-hydrogen has a much higher cost compared with the A2/O process. When the grid is connected, the system cost achieved is 0.238 US$ t−1 wastewater, which is lower than 0.257 US$ t−1 by the A2/O process. The results reveal that a simulated improvement by using bio-hydrogen and a FC system is effective and feasible for the citric wastewater plant, even when compared to the current cost of the A2/O process. In addition, lead acid and vanadium flow batteries were compared for energy storage service. The results show that a vanadium battery has lower cost and higher efficiency due to its long lifespan and energy efficiency. Additionally, the cost distribution of components shows that the PV dominates the cost in the stand-alone situation, while the bio-reactor is the main cost component in the parallel grid.

Leaves are one of the main by-products of forestry. In this study, batch experiments were carried out to convert poplar leaves pretreated by different methods into hydrogen using anaerobic mixed bacteria at 35 °C. The effects of acid (HCl), alkaline (NaOH) and enzymatic (Viscozyme L, a mixture of arabanase, cellulase, β-glucanase, hemicellulase and xylanase) pretreatments on the saccharification of poplar leaves were studied. Furthermore, the effects of acid and enzymatic pretreatment on hydrogen production, together with their corresponding degradation efficiencies for the total reducing sugar (TRS) and metabolites were compared. A maximum cumulative hydrogen yield of 44.92 mL/g-dry poplar leaves was achieved from substrate pretreated with 2% Vicozyme L, which was approximately 3-fold greater than that in raw substrate and 1.34-fold greater than that from substrate pretreated with 4% HCl. The results show that enzymatic pretreatment is an effective method for enhancing the hydrogen yield from poplar leaves.

Continuous biohydrogen production with calcium supplementation at low hydraulic retention time (HRT) in a continuous stirred tank reactor (CSTR) was studied to maximize the hydrogen productivity of anaerobic mixed cultures. After stable operations at HRT of 8–4 h, the bioreactor became unstable when the HRT was lowered to 2 h. Supplementation of 100 mg/L calcium at HRT 2 h improved the operation stability through enhancement of cell retention with almost two-fold increase in cell density than that without calcium addition. Hydrogen production rate and hydrogen yield reached 24.5 L/d/L and 3.74 mol H2/mol sucrose, respectively, both of which were the highest values our group have ever achieved. The results showed that calcium supplementation can be an effective way to improve the performance of CSTR at low HRT.

The micellar formation and entrapment of bacteria cell in reverse micelles were investigated by ultraviolet spectrum (UV), fluorescence spectrum, and scanning electron microscope (SEM). The hydrogen production in reverse micelles was confirmed. The Gompertz equation was employed to evaluate the hydrogen-producing behavior in reverse micellar systems. Different systems including dioctyl sulfosuccinate sodium salt (AOT)–isooctane, sodium dodecyl sulfate (SDS)–benzene and SDS–carbon tetrachloride (CCl4) reverse micelles were analysized. The results revealed that the maximum rate of hydrogen production (Rm) was also suitable to formulate the relationship between hydrogen-producing rate and hydrogen productivity in reverse micelles.

Beer lees are the main by-product of the brewing industry. Biohydrogen production from beer lees using anaerobic mixed bacteria was investigated in this study, and the effects of acidic pretreatment, initial pH value and ferrous iron concentration on hydrogen production were studied at 35 °C in batch experiments. The hydrogen yield was significantly enhanced by optimizing environmental factors such as hydrochloric acid (HCl) pretreatment of substrate, initial pH value and ferrous iron concentration. The optimal environmental factors of substrate pretreated with 2% HCl, pH = 7.0 and 113.67 mg/l Fe2+ were observed. A maximum cumulative hydrogen yield of 53.03 ml/g-dry beer lees was achieved, which was approximately 17-fold greater than that in raw beer lees. In addition, the degradation efficiency of the total reducing sugar, and the contents of hemicellulose, cellulose, lignin and metabolites are presented, which showed a strong dependence on the environmental factors.

Biohydrogen production using anaerobic mixed bacteria in dioctyl sulfosuccinate sodium salt (AOT)/isooctane/water reverse micelles has been investigated. It was found that hydrogen production was enhanced by optimizing some relevant parameters, such as surfactant concentration, water content (w0), initial pH, temperature, and substrate concentration. The maximum hydrogen productivity was obtained as 3.51 mol H2/mol glucose, which was 2.28-fold in aqueous solutions. Analysis of volatile fatty acid suggested that variation of AOT concentration resulted in a dominated metabolic alteration of microorganisms, whereas the dominated acetic acid products were always found at a wide range of water content (w0), which was much different with the dominated butyric acid products in aqueous phase. Peak value of hydrogen productivity occurred at initial pH 7.5 in aqueous solutions in contrast that hydrogen production kept stable at pH range from 7.0 to 8.5 in reverse micellar systems. Temperatures of 30–35 °C were optimum for hydrogen production both in aqueous phase and reverse micellar systems. Organic substrates such as glucose, sucrose and starch, were found with similar behaviors that increasing substrate concentration (>11.1 g/l) had no apparent enhancement for hydrogen production in reverse micellar systems.

By adding a small amount of l-cysteine (0.1–1.0 mM) to nutrient solution, the dark fermentative hydrogen production using anaerobic mixed culture at two mesophilic temperatures, 35 °C and 30 °C, were largely enhanced. Compared to those of the blank tests, the hydrogen productivities and substrate degradation efficiencies of the tests with l-cysteine were all increased. Moreover, the maximum hydrogen production rates were increased to 1.5–2.9 times. In particular, the hydrogen yields peaked at 3.10 mol H2/mol sucrose with addition of 0.6 mM l-cysteine at 35 °C and at 3.28 mol H2/mol sucrose with addition of 0.1 mM l-cysteine at 30 °C, which were 15.2% and 70% higher than those of the corresponding blank ones, respectively. The results show that l-cysteine can be used as a low-cost and highly efficient bioactive agent to increase dark fermentative hydrogen production.

It was the first time to study the enhancement effect of nanometer-sized gold particles on fermentative hydrogen production from artificial wastewater. A biohydrogen production system coupling the polysaccharide degradation by two cultures and hydrogen production using gold nanoparticles as a catalyst was investigated. Data were obtained from tests operating with cultures enriched from natural environment, which included preheat-treated mixed culture and non-heat-treated mixed culture. The percentages and yields of hydrogen produced in the tests using gold nanoparticles were all higher than the corresponding blank test. The tests with 5-nm-gold particles behaved better than others, especially for the preheat-treated one. The maximum cumulative yield of hydrogen obtained at the test with 5-nm-gold particles was 4.48 mol per mol sucrose, which represents the conversion efficiency of sucrose to hydrogen reached 56%. The results indicated that gold nanoparticles could remarkably improve the bioactivity of hydrogen-producing microbes and the enhancement effect strongly depended on the size of gold particles. This work suggests a promising method to enhance the catalytic activity of hydrogenases in the microbes and will be of great importance in biohydrogen production.

In this study, continuous biological hydrogen production using wastewater from citric acid factory as raw materials was investigated. And enrichment cultures from facultative hydrogen-producing anaerobe together with citric acid wastewater were utilized. For finding out the industrialized feasibility of continuous H2H2 bio-production, the ability of H2H2-production via facultative anaerobe, optimum hydraulic retention time (HRT) and optimum volume loading rate (VLR) were also studied. The experimental results showed that facultative anaerobic bacteria could yield hydrogen as high as 0.84molH2/molhexose consumed at the VLR of 38.4kgCOD/m3d. Butyric acid was the dominant product among volatile fatty acids (VFAs). An improved upward-flow anaerobic sludge blanket (UASB) reactor with a working volume 50m3 was used. Continuous hydrogen yield was 0.72m3H2/m3reactord under the following conditions: temperature at 35–38∘C, initial pH at 6.8–7.2, HRT=12h. The study also indicates that the reactor used has a better operational stability and the facultative anaerobe has an excellent adaptive capacity for organic loading rate. Furthermore, the chemical oxygen demand (COD) removal efficiency exceeded 60% and the total sugar degradation efficiency (TSDE) was close to or over 90%, even up to 96.6% at HRT of 12 h during the experiment.

Anaerobic mixed culture acclimated with sucrose was used as inoculum in batch experiments to investigate the effects of various parameters on biological hydrogen production from sucrose. In particular, the effect of the culture temperature has been investigated in detail. The optimum of the iron concentration in the external environment on hydrogen production was also studied at different temperatures. Experimental results show that the hydrogen production ability of the anaerobic bacteria was deeply affected by both culture temperature and iron concentration. Increasing the culture temperature favored the production of hydrogen when it was in the range of 25–40 °C, and high sucrose conversion efficiencies (ca. 98%) were consistently obtained with the mixed bacteria at the same time. While the temperature went on increasing to 45 °C, the hydrogen production was almost inhibited. The optimum concentrations of iron for hydrogen production decreased obviously along with increasing the reactor's temperature. For 25, 35, and 40 °C, the maximum production yield of hydrogen were 356.0, 371.7, and 351.1 ml obtained at the iron concentration of 800, 200, and 25 mg FeSO4l-1l-1, respectively.

Both batch experiments (initial pH value was 7.0 and 8.0, respectively) were conducted to convert soluble starch to hydrogen at 35∘C. Anaerobic mixed bacteria acclimated with soluble starch was used as inoculum. At initial pH=8.0pH=8.0, the H2H2 yield significantly increased from 106.4 to 274.0 ml/g starch with increasing iron concentration from 0 to 200 mg FeSO4/lFeSO4/l. When iron concentration continued to increase from 200 to 4000 mg FeSO4/lFeSO4/l, iron inhibition did not happen. On the contrary, hydrogen production was efficiently accelerated. Here, lag-phase time and end time all had about 22 h shortened. However, corresponding cumulative H2H2 volumes were adjacent to the maximum value (225 ml) required at [FeSO4]=150mg/l. As for pH 7.0 systems, though flocculation still appeared, superfluous iron (over 800 mg FeSO4/lFeSO4/l) slightly inhibited hydrogen production. The difference in two strains of iron experiments resulted from the variance in initial solubility of iron under various initial pH values. The experiment results show that superfluous soluble iron shows slightly inhibitive influence on H2H2 production, and that the optimum soluble iron concentration is 150 mg FeSO4/lFeSO4/l from soluble starch (10.0 g/l). Furthermore, the effect of the starch concentration (5.0–40.0 g/l) on hydrogen production also was investigated under 150 mg FeSO4/lFeSO4/l. The result shows that high starch concentration has no remarkable effect on H2H2 production. The maximum cumulative hydrogen was 260.5 ml at starch concentration of 20 g/l.

The effect of the iron concentration on hydrogen yield was investigated in batch tests by heat-shocked mixed cultures growing on a sucrose mineral medium at 35 °C. The hydrogen production yield increased obviously with increasing iron concentration from 0 to 1600 mg FeSO4l-1, and then slightly decreased when the iron concentration increased from 1600 to 5000 mg FeSO4l-1. The maximum amount of hydrogen production (2.73 mol/mol sucrose) was obtained at the iron concentration of 1600 mg FeSO4l-1. The hydrogen production yield and the butyric acid/acetic acid ratio followed a similar trend, suggesting that the formation of butyrate seems to favor hydrogen production.

•NiCo2O4 nanoplatelets were in-situ growing on carbon cloth as ORR catalyst in biofuel cells.•Binder-free cathode with the lower internal resistance.•Binder-free cathode was low-cost.•NiCo2O4-CFC shows better power generation performance than Pt/C.Air-cathode microbial fuel cells (MFCs) was one of most promising sustainable new energy device as well as an advanced sewage treatment technology, and thoroughly studies have been devoted to lower its cost and enhance its power generation. Herein, a binder-free and low-cost catalyst air-cathode was fabricated by in-situ electro-deposition of NiCo2O4 nanoplatelets on carbon cloth, followed by feasible calcinations. The catalytic activity of catalyst air-cathode was optimized by varying the deposition time. And the optimal air-cathode was installed in real MFCs and exhibited distinct maximum out-put power density (645 ± 6 mW m−2), which was 12.96% higher than commercial Pt/C (571 ± 11 mW m−2). Noted that its remarkable electricity generation performance in MFCs should absolutely attributed to the well catalytic activity for oxygen reduction reaction, and more likely ascribed to its low internal resistance since binder-free catalyst air-cathode can facilitate the electron/charge transfer process. Therefore, it was an efficient strategy to improve the electricity generation performance of MFCs by using this binder-free catalyst air-cathode, which was also potential for application in many other electrochemical devices.

•CTAC is used to produce thin-film composite membranes for forward osmosis.•CTAC micelles have ionic interaction with MPD in solution of MPD/CTAC system.•Molecular structures of polyamide are controlled by concentrations of CTAC.•Regular arrangement of molecules improves salt selectivity greatly.In this article, cetyltrimethylammonium chloride (CTAC) was used to produce novel thin-film composite (TFC) forward osmosis (FO) membranes through interfacial polymerization with 1,3,5-benzenetricarbonyl trichloride (TMC) and m-phenylenediamine (MPD). The effects of the CTAC concentrations on the structure of the polyamide skin layer were investigated by ATR–FTIR, XPS, WAXD, NMR and SEM analyses. FO performance of TFC membranes was detected using 2 M each of four different salt solutions (NaCl, Na2SO4, MgCl2 and MgSO4) as draw solutions. The results indicate that the skin layer is significantly affected by the CTAC micelles. CTAC micelles in aqueous solution have ionic interactions with MPD molecules and affect interfacial polymerization process of MPD and TMC. With an increase of the CTAC concentration, the linear molecular structure of the skin layer gradually increases and the more microcrystalline structure appears. The pure water flux of the TFC FO membranes has been negatively affected in FO process by the special polyamide structures as a result of CTAC; however, the rates of rejection and reverse selectivity of salts are significantly improved with the increase of the CTAC concentrations (maximum 99.9% of MgCl2), and they are all greater than 90% (MgSO4 > MgCl2 > Na2SO4 > NaCl).

A “Spontaneous bubble-template” method is fascinating in that bubbles are formed in situ during material processing and employed as a template for fabricating unique structures, which has not been reported in material science. It is sustainable, green and efficient in that no extra additives or post-treatment are used. Herein, novel metal–polymeric framework derived hierarchically porous carbon/Fe3O4 nanohybrids are prepared using a “spontaneous bubble-template” method by one-step carbonization. During the carbonization process, N and Co are self-doped on porous carbon in which in situ grown nano Fe3O4 is embedded (Fe3O4@N/Co–C). The as-prepared Fe3O4@N/Co–C displays a three-dimensional interpenetrating morphology (electrochemical active area: 729.89 m2 g−1) with well-distributed Fe3O4 nanoparticles (20–50 nm) which are coated with a carbon layer (3–5 nm). Fe3O4@N/Co–C exhibits remarkable oxygen reduction activity in biofuel cells with a distinct output voltage (576 mV) and power density (918 mW m−2), which are 3.6% and 17.8% higher than those of Pt (0.5 mg cm−2), respectively. Besides biofuel cells, Fe3O4@N/Co–C may also have the potential for application in chemical fuel cells, since it demonstrates better oxygen reduction activity in electrochemical measurements. Thus, with the virtues of its low-cost, facile synthesis and large-scale preparation, Fe3O4@N/Co–C is a promising electrocatalyst for the oxygen reduction reaction and application in biofuel cells.