Frontiers in Energy最新文献

Bio-oil from biomass pyrolysis cannot directly substitute traditional fuel due to compositional deficiencies. Catalytic hydrodeoxygenation (HDO) is the critical and efficient step to upgrade crude bio-oil to high-quality bio-jet fuel by lowering the oxygen content and increasing the heating value. However, the hydrocracking reaction tends to reduce the liquid yield and increase the gas yield, causing carbon loss and producing hydrocarbons with a short carbon-chain. To obtain high-yield bio-jet fuel, the elucidation of the conversion process of biomass catalytic HDO is important in providing guidance for metal catalyst design and optimization of reaction conditions. Considering the complexity of crude bio-oil, this review aimed to investigate the catalytic HDO pathways with model compounds that present typical bio-oil components. First, it provided a comprehensive summary of the impact of physical and electronic structures of both noble and non-noble metals that include monometallic and bimetallic supported catalysts on regulating the conversion pathways and resulting product selectivity. The subsequent first principle calculations further corroborated reaction pathways of model compounds in atom-level on different catalyst surfaces with the experiments above and illustrated the favored C–O/C=O scission orders thermodynamically and kinetically. Then, it discussed hydrogenation effects of different H-donors (such as hydrogen and methane) and catalysts deactivation for economical and industrial consideration. Based on the descriptions above and recent researches, it also elaborated on catalytic HDO of biomass and bio-oil with multi-functional catalysts. Finally, it presented the challenges and future prospective of biomass catalytic HDO.

To increase the power generated by solid oxide fuel cells (SOFCs), multiple cells have to be connected into a stack. Nonuniformity of cell performance is a worldwide concern in the practical application of stack, which is known to be unavoidable and caused by manufacturing and operating conditions. However, the effect of such nonuniformity on SOFCs that are connected in parallel has not been discussed in detail so far. This paper provides detailed experimental data on the current distribution within a stack with nonuniform cells in parallel connection, based on the basics of electricity and electrochemistry. Particular phenomena found in such a parallel system are the “self-discharge effect” in standby mode and the “capacity-proportional-load sharing effect” under normal operating conditions. It is believed that the experimental method and results proposed in this paper can be applied to other types of fuel cell or even other energy systems.

Formic acid (FA) is a potential biomass resource of syngas with contents of carbon monoxide (CO, 60 wt.%) and hydrogen (H₂, 4.4 wt.%). Among the technologies for FA conversion, the photoreforming of FA has received widespread attention due to its use of green solar energy conversion technology and mild reaction conditions. Herein, a V–W bimetallic solid solution, V_xW_1−xN_1.5 with efficient co-catalytic properties was first and facilely synthesized. When CdS was used as a photocatalyst, the activity performance of the V_0.1W_0.9N_1.5 system was over 60% higher than that of the W₂N₃ system. The computational simulations and experiments showed the V_0.1W_0.9N_1.5 had great metallic features and large work functions, contributing a faster photo-generated carrier transfer and less recombination, finally facilitating a great performance in cocatalyst for syngas production in photoreforming FA. This work provides an approach to synthesizing novel transition metal nitrides for photocatalysis.

Due to its fascinating and tunable optoelectronic properties, semiconductor nanomaterials are the best choices for multidisciplinary applications. Particularly, the use of semiconductor photocatalysts is one of the promising ways to harness solar energy for useful applications in the field of energy and environment. In recent years, metal oxide-based tailored semiconductor photocatalysts have extensively been used for photocatalytic conversion of carbon dioxide (CO₂) into fuels and other useful products utilizing solar energy. This is very significant not only from renewable energy consumption but also from reducing global warming point of view. Such current research activities are promising for a better future of society. The present mini-review is focused on recent developments (2–3 years) in metal oxide semiconductor hybrid photocatalysts-based photo-electrochemical conversion of CO₂ into fuels and other useful products. First, general mechanism of photo-electrochemical conversion of CO₂ into fuels or other useful products has been discussed. Then, various metal oxide-based emerging hybrid photocatalysts including tailoring of their morphological, compositional, and optoelectronic properties have been discussed with emphasis on their role in enhancing photo-electrochemical efficienty. Afterwards, mechanism of their photo-electrochemical reactions and applications in CO₂ conversion into fuels/other useful products have been discussed. Finally, challenges and future prospects have been discussed followed by a summary.

As the next-generation oxy-fuel combustion technology for controlling CO₂ emissions, pressurized oxy-fuel combustion (POC) technology can further reduce system energy consumption and improve system efficiency compared with atmospheric oxy-fuel combustion. The oxy-fuel combustion causes high CO₂ concentration, which has a series of effects on the combustion reaction process, making the radiation and reaction characteristics different from air-fuel conditions. Under the pressurized oxy-fuel condition, the combustion reaction characteristics are affected by the coupling effect of pressure and atmosphere. The radiation and heat transfer characteristics of the combustion medium are also affected by pressure. In recent years, there have been many studies on POC. This review pays attention to the thermal-science fundamental research. It summarizes several typical POC systems in the world from the perspective of system thermodynamic construction. Moreover, it reviews, in detail, the current research results of POC in terms of heat transfer characteristics (radiant heat transfer and convective heat transfer), combustion characteristics, and pollutant emissions, among which the radiation heat transfer and thermal radiation model are the focus of this paper. Furthermore, it discusses the development and research direction of POC technology. It aims to provide references for scientific research and industrial application of POC technology.

The use of two-dimensional (2D) layered metal-organic frameworks (MOFs) as self-sacrificial templates has been proven to be a successful method to create high-efficiency Selenium (Se)-containing electrocatalysts for overall water splitting. Herein, two strategies are then utilized to introduce Se element into the Co–Fe MOF, one being the etching of as-prepared MOF by SeO₂ solution, and the other, the replacing of SCN⁻ with SeCN⁻ as the construction unit. The electrochemical activity of the pristine 2D MOF and their calcinated derivatives for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is evaluated and further discussed. It is found that the effect of introducing Se on improving electrochemical catalytic activity is significant for the HER process. Specifically, the calcinated derivative in the replacing method exhibits an overpotential of 235 mV for HER and 270 mV for OER at a current density of 10 mA/cm². For comparing the two methods of introducing Se element into MOF, similar electrocatalytic activity can be achieved on the their calcinated derivatives. The high electrochemical performance of 2D CoFe-MOF derivatives may be resulted from the unique 2D hierarchical porous structure and strong synergistic effect between different components in the material.

Great progress has been made in the electrochromic (EC) technology with potential applications in various fields. As one of the most promising EC materials, Prussian blue (PB) has attracted great attention due to its excellent EC performance, such as low cost, easy synthesis, rich color states, chemical stability, suitable redox potential, and fast color-switching kinetics. This review summarizes the recent progress in PB electrodes and devices, including several typical preparation techniques of PB electrodes, as well as the recent key strategies for enhancing EC performance of PB electrodes. Specifically, PB-based electrochromic devices (ECDs) have been widely used in various fields, such as smart windows, electrochromic energy storage devices (EESDs), wearable electronics, smart displays, military camouflage, and other fields. Several opportunities and obstacles are suggested for advancing the development of PB-based ECDs. This comprehensive review is expected to offer valuable insights for the design and fabrication of sophisticated PB-based ECDs, enabling their practical integration into real-world applications.

Spectral beam split is attracting more attention thanks to the efficient use of whole spectrum solar energy and the cogenerative supply for electricity and heat. Nanofluids can selectively absorb and deliver specific solar spectra, making various nanofluids ideal for potential use in hybrid photovoltaic/thermal (PV/T) systems for solar spectrum separation. Clarifying the effects of design parameters is extremely beneficial for optimal frequency divider design and system performance enhancement. The water-based SiO₂ nanofluid with excellent thermal and absorption properties was proposed as the spectral beam splitter in the present study, to improve the efficiency of a hybrid PV/T system. Moreover, a dual optical path method was applied to get its spectral transimissivity and analyze the impact of its concentration and optical path on its optical properties. Furthermore, a PV and photothermal model of the presented system was built to investigate the system performance. The result indicates that the transimissivity of the nanofluids to solar radiation gradually decreases with increasing SiO₂ nanofluid concentration and optical path. The higher nanofluid concentration leads to a lower electrical conversion efficiency, a higher thermal conversion efficiency, and an overall system efficiency. Considering the overall efficiency and economic cost, the optimal SiO₂ nanofluid concentration is 0.10 wt.% (wt.%, mass fraction). Increasing the optical path (from 0 to 30 mm) results in a 60.43% reduction in electrical conversion efficiency and a 50.84% increase in overall system efficiency. However, the overall system efficiency rises sharply as the optical path increases in the 0–10 mm range, and then slowly at the optical path of 10–30 mm. Additionally, the overall system efficiency increases first and then drops upon increasing the focusing ratio. The maximum efficiency is 51.93% at the focusing ratio of 3.