• Energy Research

Abstract Enhancement of biogas combustion characteristics will increase the possibility of the direct utilization of such an eco-friendly fuel in practical combustors. We report a full study of biogas combustion under partially premixed mode to investigate the stability of biogas free-jet flames using a concentric flow slot burner was used to evaluate the biogas combustion characteristics. Five mixtures of biogas ranging from 0%CO2 up to 40%CO2 were investigated to study the effect of CO2 proportion on the stability of biogas flames. A new well-defined stability procedure was followed by studying the four major observed phenomena in biogas flames: Stable Flame, Partially-lifted Flame, Fully-lifted Flame, and Extinction. Each phenomenon was clearly defined in addition to describing the operating conditions in terms of Reynolds Number (Re) and Equivalence ratio (ϕ). The effect of the premixing ratio (LD) on the combustion stability of biogas flames was also studied for five premixing ratios LD3, LD5, LD7, LD10, and LD16 to optimize the flame stability. The temperature of stable biogas flames was also measured at different CO2 percentages. The results showed that LD10 is the optimum premixing ratio to generate a stable biogas flame at all tested CO2 proportions. Partially premixed combustion in slot burner manages to sustain a stable biogas flame up to 30%CO2. However, increasing the CO2 to 40% eventually led to a weak and unstable flame regardless of the premixing ratio.

Abstract We report on the facile synthesis of anatase multi-doped TiO2 mesocrystals with highly energetic {001} facets and their outstanding photocatalytic activity. The structural and compositional properties were investigated via different techniques such as XRD, XPS, Raman photoluminescence, and electron paramagnetic resonance, which confirmed the fabrication of C, Co, and Ti3+-doped anatase single crystal-like mesocrystals. The Mott-Schottky analysis showed a drastic increase in the carrier density upon cobalt doping, resulting in a 6-fold increase in the photoelectrochemical performance compared to the undoped sample. Besides, the photocatalytic efficiency of the as-fabricated mesocrystals in the photochemical production of hydrogen was estimated under AM1.5 conditions without using any hole scavengers. The Co-doped C/Ti3+ TiO2 mesocrystals showed an unprecedented hydrogen production rate when compared to the other similar titanium-based mesocrystals. Finally, the unprecedented enhancement of Co-doped C/Ti3+ TiO2 mesocrystals in water splitting makes them promising candidates for various photocatalytic applications.

AbstractNanoparticles (NPs) supplementation to biodigesters improves the digestibility of biowaste and the generation of biogas. This study investigates the impact of innovative nanoadditives on the microbiome of biodigesters. Fresh cow manure was anaerobically incubated in a water bath under mesophilic conditions for 30 days. Three different NPs (zinc ferrite, zinc ferrite with 10% carbon nanotubes and zinc ferrite with 10% C76 fullerene) were separately supplemented to the biodigesters at the beginning of the incubation period. Methane and hydrogen production were monitored daily. Manure samples were collected from the digesters at different time points and the microbial communities inside the biodigesters were investigated via real‐time PCR and 16 S rRNA gene amplicon‐sequencing. The results indicate that zinc ferrite NPs enhanced biogas production the most. The microbial community was significantly affected by NPs addition in terms of archaeal and bacterial 16 S rRNAgene copy numbers. The three ZF formulations NPs augmented the abundance of members within the hydrogenotrophic methanogenic phyla Methanobacteriaceae. While Methanomassiliicoccacaea were enriched in ZF/C76 supplemented biodigester due to a significant increase in hydrogen partial pressure, probably caused by the enrichment of Spirochaetaceae (genus Treponema). Overall, NPs supplementation significantly enriched acetate‐producing members within Hungateiclostridiaceae in ZF/CNTs, Dysgonomonadaceae in ZF and Spirochaetaceae ZF/C76 biodigesters.

Abstract We report on the optimized growth of catalyst-free GaN nanowires (NWs)/p-Si by the vapor–solid (V-S) method using chemical vapor deposition (CVD). The effect of NH3 gas flow rate on the morphology and photovoltaic behavior of the material has been investigated. The length and the diameter of the NWs decrease as the NH3 flow rate increases. Raman and X-ray diffraction (XRD) analyses reveal lower internal stress in the prepared NWs. The photoluminescence (PL) spectra indicate strong near band-edge (NBE) peaks extending from 365 to 368 nm and their intensity varied significantly with the NH3 flow rate. The assembled n-GaN NWs/p-Si solar cell devices reveal a maximum conversion efficiency of ∼7.87% under AM 1.5G illumination. This study shows that the morphology, optical, and performance of the fabricated n-GaN NWs on p-Si are strongly affected by the gas flow rate.

Abstract We report, for the first time, on the effect of the cathode material in controlling the morphology and properties of TiO2 nanotube arrays fabricated by electrochemical anodization of Ti foil in both aqueous and ethylene glycol (EG) electrolytes. Some of the alternative less-expensive cathode materials result in TiO2 nanotube architectures and photoelectrochemical properties similar to or in some cases superior to those obtained using a Pt cathode.

Abstract Biogas combustion is a very essential topic for the development of many industrial combustion systems and engines. This fuel can replace current fossil fuels used in burners, engines, and many other applications. Understanding the combustion characteristics of this fuel and its stability in highly turbulent flames of practical interest is the aim of this work. The percentage of CO2 in Biogas varies between 25% and 45%, which affects the combustion stability and flame structure. The present work shows that the generation of Biogas is improved by adding Ni-Co-Ferrite or Ni-ferrite nano-additives. In this work, we selected 25 flames of mixtures of natural gas and CO2, where the ratio of CO2 varies from 0% to 40%. The flames are generated in a concentric flow slot burner that produces planar two-dimensional flames. The stability characteristics and the flame structure were investigated. The flame structure is presented in the form of temperature profiles in some selected flames using fine wire thermocouple measurements. The stability characteristics are illustrated for two limits of lifted flames and blow out. The production rate of Biogas can be increased by almost 30% using nano-additives of Ni-Co-Ferrite or Ni-ferrite. The data show that the stability of the flames is affected significantly for the 40% CO2 mixture. Therefore, it is recommended to keep CO2 percentage up to 30% for stable turbulent Biogas flames. On the other hand, partially premixed flames are highly stable for a certain level of mixture inhomogeneity at a mixing length ratio of L/D = 16. At this level, the mixture fraction fluctuations are expected to be within the flammability limits range based on previous investigations in round jet configuration.

Abstract Third generation photovoltaic technologies based on perovskites have demonstrated an exceptional progress in solar energy conversion since their first use in 2009. Herein, we investigated the effect of using light trapping nanostructures on the absorption, carrier collection, and overall efficiency of perovskite (CH 3 NH 3 PbI 3 ) solar cells using three dimensional (3D) finite element method (FEM) technique. A combined optical-electrical model was constructed to full characterize the proposed devices. Upon the use of nanotubular architecture, the optimized active area absorption enhanced by 6% and the total generation rate increased by 7% compared to the planar architecture. Under one sunlight illumination (AM1.5G), with normal incident angle, the solar cells containing nanostructured light trapping architecture showed a drastic enhancement in the short circuit current ( J sc ), the quantum efficiency (EQE), and the overall efficiency compared to the planar film-based solar cell. The obtained enhancements would open a new route for integrating light trapping nanostructures in CH 3 NH 3 PbI 3 perovskite-based solar cells for better efficiency.

Abstract Solar-driven water splitting promises a step towards large-scale solar energy storage. However, the bottleneck is always the poor performance of the used photoanodes, particularly in their capability to harvest the visible light. Herein, we report the design of visible-light active anatase titanium dioxide nanocrystals (sub 10 nm in size and with a surface area of ∼99 m 2 /g) using the sol-gel method followed by hydrothermal treatment with H 2 O 2 at relatively low temperature (180 °C). The fabricated nanocrystals demonstrate a band gap of 2.85 eV, with an increased amount of surface defects that overcome the negative effects of bulk defects as revealed by the positron annihilation measurements. These prepared nanocrystals have notable enhancement in solar light harvesting and water splitting efficiency compared to the commercial Degussa P25 counterpart. The photoactivity, structural and electrochemical behavior of the synthesized nanocrystals were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), photocurrent measurements, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), positron annihilation, and Doppler broadening analysis.

AbstractPoint defects play important and crucial roles in the design of high performance photocatalysts. We report on the electrochemical fabrication of black Ti−Mo‐Ni−O nanotubes as a promising electrode material for solar‐assisted water splitting. The ternary Ti−Mo‐Ni−O catalyst was annealed in hydrogen atmosphere to induce point defects in the material to enhance its conductivity, charge carriers density, and performance. The effect of annealing duration on the performance of ternary Ti−Mo‐Ni−O nanotube films was investigated. The hydrogen‐annealed nanotubes showed enhanced optical characteristics in the visible spectrum, which can be related to the formation of defect states upon hydrogen annealing. The 10 h‐annealed sample showed an exceptionally enhanced photocurrent density of ∼10 mA/cm2 with a remarkable open‐circuit voltage of ∼−1.0 VAg/AgCl under AM 1.5G illumination. This improved photocurrent is in agreement with the obtained 75 % incident‐photon‐to‐current‐conversion‐efficiency (IPCE), confirming the improved photoactivity of the hydrogen‐treated mixed oxide nanotubes.