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Photocatalytic carbon dioxide (CO2) reduction to obtain hydrocarbon solar fuels is one of the promising strategies to solve energy crisis and complement carbon cycle. However, the low ...activity and poor product selectivity greatly limit its practical application. Tuning product selectivity is of great significance to improve the yield of target product and deepen the understanding of CO2 reduction reaction mechanism. In this review, we firstly summarize the widely accepted pathways of photocatalytic CO2 reduction reactions. Secondly, important factors affecting product selectivity are analyzed, mainly including light-excitation attributes, band structure of photocatalysts, separation of photogenerated charge carriers, adsorption/activation of reactants, surface active sites of catalytic reaction, and adsorption/desorption of intermediates. Finally, the challenges and perspectives in developing photocatalysts with high CO2 reduction efficiency and product selectivity are presented.
The ever‐increasing demand of lithium‐ion batteries (LIBs) caused by the rapid development of various electronics and electric vehicles will be hindered by the limited lithium resource. Thus ...sodium‐ion batteries (SIBs) have been considered as a promising potential alternative for LIBs owing to the abundant sodium resource and similar electrochemical performances. In recent years, significant achievements regarding anode materials which restricted the development of SIBs in the past decades have been attained. Significantly, the sodium storage feasibility of carbon materials with abundant resource, low cost, nontoxicity and high safety has been confirmed, and extensive investigation have demonstrated that the carbonaceous materials can become promising electrode candidates for SIBs. In this review, the recent progress of the sodium storage performances of carbonaceous materials, including graphite, amorphous carbon, heteroatom‐doped carbon, and biomass derived carbon, are presented and the related sodium storage mechanism is also summarized. Additionally, the critical issues, challenges and perspectives are provided to further understand the carbonaceous anode materials.
Carbon materials have been considered as promising anode candidate for sodium‐ion batteries (SIBs) due to their unique merits. Tremendous efforts have been made to exploit appropriate carbon materials and unveil the corresponding sodium storage mechanism. Here, recent progress, challenges, and prospects of carbon anode materials for SIBs are presented.
Photocatalytic reaction rate (R) is determined by the multiplication of light absorption capability (α) and quantum efficiency (QE); however, these two parameters generally have trade-off relations. ...Thus, increasing α without decreasing QE remains a challenging issue for developing efficient photocatalysts with high R. Herein, using Fe(III) ions grafted Fe(III) doped TiO2 as a model system, we present a novel method for developing visible-light photocatalysts with efficient R, utilizing the concept of energy level matching between surface-grafted Fe(III) ions as co-catalysts and bulk-doped Fe(III) ions as visible-light absorbers. Photogenerated electrons in the doped Fe(III) states under visible-light efficiently transfer to the surface grafted Fe(III) ions co-catalysts, as the doped Fe(III) ions in bulk produced energy levels below the conduction band of TiO2, which match well with the potential of Fe(3+)/Fe(2+) redox couple in the surface grafted Fe(III) ions. Electrons in the surface grafted Fe(III) ions efficiently cause multielectron reduction of adsorbed oxygen molecules to achieve high QE value. Consequently, the present Fe(III)-FexTi1-xO2 nanocomposites exhibited the highest visible-light R among the previously reported photocatalysts for decomposition of gaseous organic compounds. The high R can proceed even under commercial white-light emission diode irradiation and is very stable for long-term use, making it practically useful. Further, this efficient method could be applied in other wide-band gap semiconductors, including ZnO or SrTiO3, and may be potentially applicable for other photocatalysis systems, such as water splitting, CO2 reduction, NOx removal, and dye decomposition. Thus, this method represents a strategic approach to develop new visible-light active photocatalysts for practical uses.
Graphitic carbon nitride nanosheets (CNNs) become the most promising member in the carbon nitride family benefitted from their two-dimensional structural features. Recently, great endeavors have been ...made in the synthesis and modification of CNNs to improve their photocatalytic properties, and many exciting progresses have been gained. In order to elucidate the fundamentals of CNNs based catalysts and provide the insights into rational design of photocatalysis system, we describe recent progress made in CNNs preparation strategies and their applications in this review. Firstly, the physicochemical properties of CNNs are briefly introduced. Secondly, the synthesis approaches of CNNs are reviewed, including top-down stripping strategies (thermal, gas, liquid, and composite stripping) and bottom-up precursor molecules design strategies (solvothermal, template, and supramolecular self-assembly method). Subsequently, the modification strategies based on CNNs in recent years are discussed, including crystal structure design, doping, surface functionalization, constructing 2D heterojunction, and anchoring single-atom. Then the multifunctional applications of g-C3N4 nanosheet based materials in photocatalysis including H2 evolution, O2 evolution, overall water splitting, H2O2 production, CO2 reduction, N2 fixation, pollutant removal, organic synthesis, and sensing are highlighted. Finally, the opportunities and challenges for the development of high-performance CNNs photocatalytic systems are also prospected.
This review is dedicated to recent advances of g-C3N4 nanosheets based materials, including preparation methods, modification strategies for improving their photocatalytic properties, and their photochemical applications. Moreover, the opportunities and challenges of photocatalytic applications based on g-C3N4 nanosheets are prospected. Display omitted
Over the past decade, many efforts have been made in passive image forensics. Although it is able to detect tampered images at high accuracies based on some carefully designed mechanisms, ...localization of the tampered regions in a fake image still presents many challenges, especially when the type of tampering operation is unknown. Some researchers have realized that it is necessary to integrate different forensic approaches in order to obtain better localization performance. However, several important issues have not been comprehensively studied, for example, how to select and improve/readjust proper forensic approaches, and how to fuse the detection results of different forensic approaches to obtain good localization results. In this paper, we propose a framework to improve the performance of forgery localization via integrating tampering possibility maps. In the proposed framework, we first select and improve two existing forensic approaches, i.e., statistical feature-based detector and copy-move forgery detector, and then adjust their results to obtain tampering possibility maps. After investigating the properties of possibility maps and comparing various fusion schemes, we finally propose a simple yet very effective strategy to integrate the tampering possibility maps to obtain the final localization results. The extensive experiments show that the two improved approaches used in our framework significantly outperform the state-of-the-art techniques, and the proposed fusion results achieve the best F 1 -score in the IEEE IFS-TC Image Forensics Challenge.
Electrolysis of water is regarded as an attractive and feasible way for producing hydrogen. So far, various non‐noble metal nanomaterials have been reported as excellent electrocatalysts for hydrogen ...evolution reaction. Especially, due to the low cost, earth‐abundance and tunable properties, transition metal selenides with different compositions, sizes and structures have been explored broadly as efficient catalysts with the relatively high activities, high stabilities and high efficiencies in full pH range of electrolyte for electrochemical hydrogen evolution reaction. Thus, in this Minireview, after introducing several commonly used electrochemical terms about hydrogen evolution reaction, we mainly focus on various kinds of the transition metal selenides that have been documented as electrocatalysts for hydrogen evolution reaction. Particularly, the merits and demerits of transition metal selenides for hydrogen evolution reaction are systematically discussed. Moreover, we also analyze the encountered challenges and present an outlook for the rapid development of transition metal selenides. We hope this Minireview can bring some fundamental understanding for the readers interested in the transition metal selenides and hydrogen evolution reaction.
Abundant and efficient: Thanks to low cost, earth‐abundance, and tuneable properties, transition metal selenides (TMSs) have been explored as efficient catalysts for electrochemical hydrogen evolution reaction. The advances of the synthesis methods, physical and chemical properties of TMSs for electrocatalysis in hydrogen production has been summarized in this Minireview. Moreover, the application and perspective for TMSs in electrocatalytic hydrogen evolution reaction, including single‐metal selenides and multi‐metal selenides, have been discussed systematically.
Designing and synthesizing efficient molecular catalysts may unlock the great challenge of controlling the CO2 reduction reaction (CO2RR) with molecular precision. Nickel phthalocyanine (NiPc) ...appears as a promising candidate for this task due to its adjustable Ni active‐site. However, the pristine NiPc suffers from poor activity and stability for CO2RR owing to the poor CO2 adsorption and activation at the bare Ni site. Here, a ligand‐tuned strategy is developed to enhance the catalytic performance and unveil the ligand effect of NiPc on CO2RR. Theoretical calculations and experimental results indicate that NiPc with electron‐donating substituents (hydroxyl or amino) can induce electronic localization at the Ni site which greatly enhances the CO2 adsorption and activation. Employing the optimal catalyst—an amino‐substituted NiPc—to convert CO2 into CO in a flow cell can achieve an ultrahigh activity and selectivity of 99.8% at current densities up to −400 mA cm−2. This work offers a novel strategy to regulate the electronic structure of active sites by ligand design and discloses the ligand‐directed catalysis of the tailored NiPc for highly efficient CO2RR.
A ligand‐tuned strategy is developed to boost the electrocatalytic reduction of CO2 and unlock the ligand‐directed molecular catalysis strategy. Nickel phthalocyanine decorated with electron‐donating substituents such as hydroxyl or amino can evoke electronic localization on the Ni site, enhancing the CO2 adsorption and activation. This promotes the catalytic reaction, which is positively associated with the electron‐donating abilities of substituents.
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•1. Single-atom Co modified g-C3N4 prepared by one-step thermal-polymerization of cobalt phthalocyanine (CoPc) and urea.•2. Strong interaction between Co 3d electrons and C 2p ...electrons of CO2 activate C = O bonds in CO2 molecule.•3. Optimal 1%Co-CN sample exhibits higher CO yield of 94.9 umol/g/h than pure g-C3N4 0.25 umol/g/h.
Using solar energy to realize photoreduction of CO2 into valuable chemicals is a potential way to solve energy crisis and carbon cycle. Due to the extremely stable molecular configuration of CO2, activating CO2 molecule is the key and difficult step in the whole CO2 conversation process. In this work, we used density functional theory (DFT) to calculate the reaction pathways of CO2 to CO on pure g-C3N4 and single-atom cobalt (Co) modified g-C3N4. Theoretical calculation predicts that single-atom Co sites modified g-C3N4 (Co-CN) possess stronger CO2 adsorption ability and lower barrier of CO2 hydrogenation activation than pure g-C3N4. The strong interaction between Co 3d electrons and C 2p electrons of CO2 is the crucial factor to activate C = O bonds of CO2 molecule. Better CO2 adsorption and activation abilities also are proved in Co-CN by CO2 adsorption, temperature programmed desorption (TPD), and sensor tests. As a result, the optimal 1%Co-CN exhibits higher CO yield of 94.9 umol/g/h than pure g-C3N4 (0.25 umol/g/h). This work provides a new insight of the role of single-atom sites in CO2 reduction reactions.
The photoreduction of CO2 to hydrocarbon products has attracted much attention because it provides an avenue to directly synthesize value‐added carbon‐based fuels and feedstocks using solar energy. ...Among various photocatalysts, graphitic carbon nitride (g‐C3N4) has emerged as an attractive metal‐free visible‐light photocatalyst due to its advantages of earth‐abundance, nontoxicity, and stability. Unfortunately, its photocatalytic efficiency is seriously limited by charge carriers′ ready recombination and their low reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to be an efficient way to improve the charge transfer and reaction efficiency. Here, boron (B) is doped into the large cavity between adjacent tri‐s‐triazine units via coordination with two‐coordinated N atoms. Theoretical calculations prove that the new electron excitation from N (2px, 2py) to B (2px, 2py) with the same orbital direction in B‐doped g‐C3N4 is much easier than N (2px, 2py) to C 2pz in pure g‐C3N4, and improves the charge transfer and localization, and thus the reaction dynamics. Moreover, B atoms doping changes the adsorption of CO (intermediate), and can act as active sites for CH4 production. As a result, the optimal sample of 1%B/g‐C3N4 exhibits better selectivity for CH4 with ≈32 times higher yield than that of pure g‐C3N4.
Graphitic carbon nitride (g‐C3N4) exhibits unsatisfactory photocatalytic CO2 reduction activity due to its low charge transfer and reaction dynamics. Modifying the local electronic structure of g‐C3N4 is predicted to improve the charge transfer and reaction efficiency. In this work, B atoms are doped into g‐C3N4 for improving charge transfer and localization, and boosting the photocatalytic activity.
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