Sharif Digital Repository

Cupric oxide (CuO) nanostructures are grown on fluorine doped tin oxide (FTO) coated glass substrate using aqueous solution approach. The concentration of precursor's solution has significant impact on morphology of CuO nanostructure. By varying concentration of precursor, the growth of two different morphologies (oriented nanosheets and nanoleaves) is achieved. X-ray diffraction pattern and X-ray photoelectron spectroscopy reveals formation of pure CuO crystalline phase. Mott-Schottky characteristic confirms the p-type semiconducting nature. Ultrathin structures of nanoleaves lead to higher light trapping and light absorption in visible-NIR region. The nanoleaves film has lower bandgap in... 

This study aims to investigate the hydrogen production process using an integrated system based on solar energy. This system includes an evacuated tube collector to absorb solar energy as input energy of the system. A parametric analysis was conducted to determine the most important design parameters and evaluate these parameters' impact on the system's objective functions. For identifying the optimum system conditions, multi-objective optimization was performed using particle swarm optimization (PSO) algorithm. The results obtained from the parametric analysis show that an increment in the collector mass flow rate and the turbine inlet temperature, as well as a decrement in the collector... 

Xwt% Pt/Al 2 O 3 (X = 1, 3, 5, 8, 10) and 5 wt% Pt-1wt% M/AlO 3 (M = Pd, Rh, Re, Ru, Ir, Cr) catalysts were prepared, characterized and tested for aqueous phase reforming of pure and crude glycerol. Results show drastic dependence of catalytic performance of catalysts on both the active metal loading and the type of applied promoters. 5 wt% was the best Pt loading and Pt[sbnd]Rh/Al₂O₃ shows the best catalytic activity which has the highest hydrogen production rate (mmol/g cat h −1 ) and selectivity (89%) in continuous aqueous phase reforming of 10 wt% pure glycerol solution  

Quantum dots (QDs) with unique properties have been widely employed for energy, environmental, and health care applications. Green natural resources, because of their renewability, sustainability, abundance, low cost, and environmental-friendliness, can be utilized for the synthesis of diverse nanoarchitectures. This critical review highlights the recent advancements in the greener and sustainable synthesis of carbon, graphene and metal-based QDs, as well as their significant environmental applications such as photocatalytic hydrogen production, degradation of hazardous contaminants/pollutants and reduction of CO2, with emphasis on the important challenges and future perspectives. © The... 

A highly efficient, cost-effective, and durable electrocatalysts based on CoNi metal–organic framework (MOF) nanosheets on highly porous conductive graphene (PCG) is introduced for the hydrogen evolution reaction (HER). The electrocatalyst was fabricated by template-assisted chemical vapor deposition of graphene followed by solvothermal growth of CoNi-MOF nanosheets. Highly porous 3D structure of PCG with open channels of 200–500 nm sizes provided high active surface area and facilitates gas evolution. In a highly alkaline solution, the electrocatalyst exhibits superior figures of merits, e.g. overpotential of 265 mV at −10 mA cm−2 and Tafel slope of 44.5 mV dec-1, to existing hydrogen... 

Photovoltaic-electrolyzer systems are one of the most promising alternatives for obtaining hydrogen from a renewable energy source. Determining size and the operational conditions are always a key issue while coupling directly renewable electricity sources to PEM electrolyzer. In this research, the multi objective optimization approach based on an imperialist competitive algorithm (ICA), which is employed to optimize the size and the operating conditions of a directly coupled photovoltaic (PV)-PEM electrolyzer. This allows the optimization of the system by considering two different objectives, including, minimization of energy transfer loss and maximization of hydrogen generation. Multi... 

Today, regarding the limitation and environmental side effects of fossil fuel resources, solar hydrogen production is one of the main interests in the energy research area. The development of visible light sensitized semiconductors based on non-toxic components, low cost and available bio-species is an ongoing approach for H2 generation based on water splitting reactions. Here, two different morphologies of TiO2 photoanodes, nanoparticulated and nanotubular, have been modified with simply extracted bacteriorhodopsin (bR) without any linker. Achieving a significant enhancement in photoconversion efficiency of TiO2 photoanodes, η% was increased from 2.9 to 16.5 by bR addition to the TiO2... 

A series of M-doped Pt[sbnd]MgO (M = Pd, Ir, Re, Ru, Rh and Cr) sheet-shaped nano-catalysts were synthesized by the controlled co-precipitation method. The effects of M-doping on both the physicochemical and the chemisorption characteristics of Pt[sbnd]MgO catalysts were examined. The performance of the catalysts for the aqueous phase reforming (APR) of glycerol was also investigated. The APR activity of Pt[sbnd]M[sbnd]MgO catalysts depended on the type of the M dopant used. The APR activity varied in the following order: Rh > Pd > Cr > Ir > undoped ≈ Ru > Re, with the Rh-promoted catalyst having an activity of about one order of magnitude higher than the Re-promoted catalyst at 250 °C. It... 

This study aims to construct a quantitative framework to assess biological production of hydrogen from agricultural residues in a country or region. The presented model is able to determine proper crops for biohydrogen production, its possible applications and use as well as environmental aspects. A multiplicative decomposition method was designed to forecast future production and Monte Carlo simulation was employed in the model to evaluate the risk of estimations. From 2013 to 2050, the hydrogen production capacity could increase from 53.59 to 164.41 kilotonnes (kt) in Iran. The highest contribution to biohydrogen production (52.1% in 2013 and 73.3% in 2050) belongs to cereal crops... 

The paper presents a comparison of steam methane reforming (SMR), sorption enhanced steam methane reforming (SE-SMR), auto-thermal reforming (ATR), and sorption enhanced auto-thermal reforming (SE-ATR) in a fixed bed reformer for hydrogen production. A one-dimensional, unsteady-state heterogeneous reactor model for each process which includes mass and thermal dispersion in the direction of flow and axial pressure distribution, has been simulated using gPROMS® 4.0.1 model builder, while CEA and Aspen Plus® have been employed to analyze the equilibrium performance and simulate the process flowsheets of individual process respectively. The performance of the individual hydrogen production... 

The objective of this study was to construct a novel model to be applied in a general manner to simulate microbial electrochemical cells (MXCs); for both microbial fuel cell (MFC) and microbial electrolysis cell (MEC). The liquid bulk was modeled based on the organic matters degradation to acetate via the anaerobic digestion process. Biofilm simulation was established based upon one-dimensional distribution and the dynamical electron transfer was completed by means of the conduction-based mechanism. We, for the first time, introduced biofilm local potential modeling for MEC simulation with general and simplified linear boundary conditions. The MFC-related part of the model was evaluated... 

Microbial electrolysis cells (MECs) are bioelectrochemical reactors in which chemical energy stored in organic compounds are converted to hydrogen through biocatalytic oxidation by microorganisms. The performance of MECs is highly affected by microbial communities that are impartible parts of this technology. A better understanding of microbial interactions and competitions mechanisms, has aided the comprehension of ideas and guidelines for cost effective commercial scales design. In this study, a comprehensive review of current knowledge in the microbial characterization, enrichment, and evaluation of effective parameters of microbial community in microbial electrolysis cells for typical... 

Solar energy will make a valuable contribution for power generation in the future. However the intermittency of solar energy has become an important issue in the utilization of PV system, especially small scale distributed solar energy conversion systems. The issue can be addressed through the management of production and storage of the energy in the form of hydrogen. The hydrogen can be produced by solar photovoltaic (PV) powered electrolysis of water. The amount of transferred energy to an electrolyzer from a PV module is a function of the distance between maximum power points (MPP) of PV module and the electrolyzer operating points. The distance can be minimized by optimizing the number... 

The present study deals with the feasibility of a microfluidic microbial electrolysis cell (MEC) as an efficient biohydrogen generator for medical usage for the first time. The evaluation of nickel in microfluidic MEC as an alternative for conventional electrodes indicates successful performance in the improvement of bioenergy production. The maximum biohydrogen production rate and produced power density of 2.2 μW cm−2 and 1.4 μl H2 μl substrate−1 day−1 were obtained, respectively. It is considered a promising technology for medical usage due to the following factors: significant biohydrogen generation, low consumption of expensive materials, simple construction, and utilization of human... 

Nowadays, fossil fuel limitations and environmental concerns push researchers to find clean and renewable energy resources. Solar hydrogen production via water splitting reactions in electrochemical and/or photo-electrochemical systems has been accepted as a promising route and efficient electrocatalysts are involved in both. Here, cobalt nanoflakes with an oxide/hydroxide surface and a conductive metallic core are grown on commercially available steel mesh modified with carbon based nanocomposites as a support layer. The portion of reduced graphene oxide sheets was changed from 0 to 100 wt% and the correlation of this concentration with the surface morphology and electro-catalytic activity... 

The effect of organosolv pretreatment on the structure of rice straw was analyzed under different treatment severities and solvent concentrations. At higher severities, on account of a greater fragmentation of less crystalline parts, including amorphous cellulose, hemicellulose, and lignin, the severer the pretreatment was, the higher the crystallinity index became; however, changes in the index was less tangible with a severity factor lower than 3.3. At the low to mild pretreatment temperatures (120 °C and 150 °C), higher ethanol concentrations led to the lower crystallinity index. Despite an increasing trend of crystallinity index at harsh conditions, SEM images indicated the formation of... 

In the present study, an attempt was made to investigate the potential of some of the major world’s crops, including wheat, corn, rice, barley, sugarcane, sugar beet, potatoes, and oats, to produce biohydrogen. The collectable amount of agricultural residues that could especially be used to produce hydrogen was estimated in Africa, Asia, Central America, Europe, Northern America, Oceania, and South America, and the potential amount of ammonia as the main nitrogen fertilizer was estimated. Double exponential smoothing method was employed to forecast the future crop production and area harvested. It was calculated that about 10.56 (in 2013) and 15.5 (in 2030) Mt of biohydrogen and 59.84 (in... 

In the present study, an attempt was made to investigate the potential of some of the major world’s crops, including wheat, corn, rice, barley, sugarcane, sugar beet, potatoes, and oats, to produce biohydrogen. The collectable amount of agricultural residues that could especially be used to produce hydrogen was estimated in Africa, Asia, Central America, Europe, Northern America, Oceania, and South America, and the potential amount of ammonia as the main nitrogen fertilizer was estimated. Double exponential smoothing method was employed to forecast the future crop production and area harvested. It was calculated that about 10.56 (in 2013) and 15.5 (in 2030) Mt of biohydrogen and 59.84 (in... 

Aqueous-phase reforming (APR) of oxygenated hydrocarbons for hydrogen production presents several advantages as feed molecules might be easily found in a wide range of biomass; there is no need for its vaporization and the process allows thorough exploitation of the environmental benefits of using hydrogen as an energy carrier. In this contribution, catalysts with active phase Ni supported on Al2O3-MgO were synthesized at different loadings (1, 3, 5, 7, and 10 wt%) through the co-precipitation technique and tested for the Glycerol APR reaction. Effects of the Ni loading on physicochemical characteristics of Ni/Al2O3-MgO catalysts were examined. Moreover, catalytic performance was... 

Due to the importance of hydrogen as an effective antioxidant for its applications in therapy, this research reports the fabrication of a coupled microfluidic microbial electrochemical cell (MXC), including microfluidic microbial fuel cells (MFCs) and a microfluidic microbial electrolysis cell (MEC) series in order to perform it as a self-powered biohydrogen generator. Being able to be a platform of implantable medical devices, utilization a non-phatogenic strain of Escherichia coli as the biocatalyst in order to exploit the embodied energy from human blood and excrement and finally the use of cheap and facile materials (<$2 per device) are the exceptional features of the system. The...