Green Energy&Environment

Long-cycling and dendrite-free lithium metal anodes via salt chemistry

Sainan Liu, Wenchao Zhang

2021, 6(6): 791-793. doi: 10.1016/j.gee.2021.02.009

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Boron based hypergolic ionic liquids: A review

Zhenyu Zhang, Zirui Zhao, Binshen Wang, Jiaheng Zhang

2021, 6(6): 794-822. doi: 10.1016/j.gee.2020.12.002

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The advance of space technology is deeply affected by the breakthrough of high-performance fuels. Hypergolic ionic liquids (HILs) are one of the most potential fuels for bipropellant systems. However, high viscosity value and low specific impulse of traditional N-based HILs limit their application. Recently, boron-based HILs with low viscosity become the new candidates, and their derivatives are also found to promote the hypergolicity as additives in HILs. Here, the synthesis, physical chemical properties and thermal performance of boron-based HILs and HIL-additive system are reviewed.

Multidimensional (0D-3D) functional nanocarbon: Promising material to strengthen the photocatalytic activity of graphitic carbon nitride

Bin He, Mi Feng, Xinyan Chen, Jian Sun

2021, 6(6): 823-845. doi: 10.1016/j.gee.2020.07.011

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As a prospective visible-light-responsive photochemical material, graphitic carbon nitride (g-C₃N₄) has become a burgeoning research hot topics and aroused a wide interest as a metal-free semiconductor in the area of energy utilization and conversion, environmental protection due to its unique properties, such as facile synthesis, high physicochemical stability, excellent electronic band structure, and sustainability. However, the shortcomings of high recombination rate of charge carriers, relatively low electrical conductivity and visible light absorption impede its practical application. Various strategies, such as surface photosensitization, heteroatom deposition, semiconductor hybridization, etc., have been applied to overcome the barriers. Among all the strategies, functional nanocarbon materials with various dimensions (0D∼3D) attract much attention as modifiers of g-C₃N₄ due to their unique electronic properties, optical properties, and easy functionalization. More importantly, the properties of these functional nanocarbon materials can be tuned by various dimensions and thus there will be a way to overcome the defects of g-C₃N₄ by choosing different dimensional carbon materials. Distinguishing from some present reviews, this review starts with the fundamental physicochemical characteristics of g-C₃N₄ materials, followed by analyzing the advantages of functional nanocarbon materials modifying g-C₃N₄. Then, we present a systematic introduction to various dimensional carbon materials.The design philosophy of carbon/g-C₃N₄ composites and the advanced studies are exemplified in detail. Finally, a nichetargeting summary and outlook on the major challenges, opportunities for future research in high-powered carbon/g-C₃N₄ composites was proposed.

Building highly active hybrid double-atom sites in C₂N for enhanced electrocatalytic hydrogen peroxide synthesis

Yongyong Cao, JinYan Zhao, Xing Zhong, Guilin Zhuang, Shengwei Deng, Zhongzhe Wei, Zihao Yao, Jianguo Wang

2021, 6(6): 846-857. doi: 10.1016/j.gee.2020.12.006

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Two-electron (2e^-) oxygen reduction reaction (ORR) shows great promise for on-site electrochemical synthesis of hydrogen peroxide (H₂O₂). However, it is still a great challenge to design efficient electrocatalysts for H₂O₂ synthesis. To address this issue, the logical design of the active site by controlling the geometric and electronic structures is urgently desired. Therefore, using density functional theory (DFT) computations, two kinds of hybrid double-atom supported on C₂N nanosheet (RuCu@C₂N and PdCu@C₂N) are screened out and their H₂O₂ performances are predicted. PdCu@C₂N exhibits higher activity for H₂O₂ synthesis with a lower overpotential of 0.12 V than RuCu@C₂N (0.59 V), Ru₃Cu(110) facet (0.60 V), and PdCu(110) facet (0.54 V). In aqueous phase, the adsorbed O₂ is further stabilized with bulk H₂O and the thermodynamic rate-determining step of 2e^- ORR change. The activation barrier on PdCu@C₂N is 0.43 eV lower than the one on RuCu@C₂N with 0.68 eV. PdCu@C₂N is near the top of 2e^- ORR volcano plot, and exhibits high selectivity of H₂O₂. This work provides guidelines for designing highly effective hybrid double-atom electrocatalysts (HDACs) for H₂O₂ synthesis.

Continuous synthesis of few-layer MoS₂ with highly electrocatalytic hydrogen evolution

Meng Shao, Peican Wang, Yimeng Wang, Baoguo Wang, Yundong Wang, Jianhong Xu

2021, 6(6): 858-865. doi: 10.1016/j.gee.2020.04.008

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As one of the most promising alternative fuels, hydrogen is expected with high hopes. The electrolysis of water is regarded as the cleanest and most efficient method of hydrogen production. Molybdenum disulfide (MoS₂) is deemed as one of the most promising alternatives HER catalysts owing to its high catalytic activity and low cost. Its continuous production and efficient preparation become the key problems in future industrial production. In this work, we first developed a continuous micro-reaction approach with high heat and mass transfer rates to synthesize few-layer MoS₂ nanoplates with abundant active sites. The defective MoS₂ ultrathin nanoplates exhibit excellent HER performance with an overpotential of 260 mV at a current density of 10 mA cm^-2, small Tafel slope (53.6 mV dec^-1) and prominent durability, which are comparable to most reported MoS₂ based catalysts. Considering the existence of continuous devices, it's suitable for the synthesis of MoS₂ as high-performance electrocatalysts for the industrial water electrolysis. The novel preparation method may open up a new way to synthesize all two-dimension materials toward HER.

Boosting oxygen evolution reactivity by modulating electronic structure and honeycomb-like architecture in Ni₂P/N,P-codoped carbon hybrids

Menglei Yuan, Yu Sun, Yong Yang, Jingxian Zhang, Sobia Dipazir, Tongkun Zhao, Shuwei Li, Yongbing Xie, He Zhao, Zhanjun Liu, Guangjin Zhang

2021, 6(6): 866-874. doi: 10.1016/j.gee.2020.07.012

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Oxygen evolution reaction (OER) as the foremost stumbling block to generate cost-effective clean fuels has received extensive attention in recent years. But, it still maintains the challenge to manipulate the geometric and electronic structure during single reaction process under the same conditions. Herein, we report a simple self-template strategy to generate honeycomb-like Ni₂P/N,P-C hybrids with preferred electronic architecture. Experiments coupled with theoretical results revealed that the synthesized catalyst has two characteristics:firstly, the unique honeycomb-like morphology not only enables the fully utilization of catalytic active sites but also optimizes the mass/electron transportation pathway, which favor the diffusion of electrolyte to accessible active sites. Secondly, N,P-C substrate, on the one hand, largely contributes the electronic distribution near Fermi level (E_F) thus boosting its electrical conductivity. On the other hand, the support effect result in the upshift of d-band center and electropositivity of Ni sites, which attenuates the energy barrier for the adsorption of OH^- and the formation of *OOH. In consequence, the optimized Ni₂P/N,P-C catalysts feature high electrocatalytic activity towards OER (a low overpotential of 252 mV to achieve 10 mA cm^-2) and 10 h long-term stability, the outstanding performance is comparable to most of transition metal catalysts. This work gives a innovative tactics for contriving original OER electrocatalysts, inspirng deeper understanding of fabricating catalysts by combining theoretical simulation and experiment design.

Efficient hydrogen production through the chemical looping redox cycle of YSZ supported iron oxides

Li Ma, Yu Qiu, Min Li, Dongxu Cui, Shuai Zhang, Dewang Zeng, Rui Xiao

2021, 6(6): 875-883. doi: 10.1016/j.gee.2020.06.023

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The chemical looping process, where an oxygen carrier is reduced and oxidized in a cyclic manner, offers a promising option for hydrogen production through splitting water because of the much higher water splitting efficiency than solar electrocatalytic and photocatalytic process. A typical oxygen carrier has to comprise a significant amount of inert support, to maintain stability in multiple redox cycles, thereby resulting in a trade-off between the reaction reactivity and stability. Herein, we proposed the use of ion-conductive yttria-stabilized zirconia (YSZ) support Fe₂O₃ to prepare oxygen carriers materials. The obtained Fe₂O₃/YSZ composites showed high reactivity and stability. Particularly, Fe₂O₃/YSZ-20 (oxygen storage capacity, 24.13%) exhibited high hydrogen yield of ∼10.30 mmol g^-1 and hydrogen production rate of ∼0.66 mmol g^-1 min^-1 which was twice as high as that of Fe₂O₃/Al₂O₃. Further, the transient pulse test indicated that active oxygen diffusion was the rate-limiting step during the redox process. The electrochemical impedance spectroscopy (EIS) measurement revealed that the YSZ support addition facilitated oxygen diffusion of materials, which contributed to the improved hydrogen production performance. The support effect obtained in this work provides a potentially efficient route for the modification of oxygen carrier materials.

Zeolite-templated carbons as effective sorbents to remove methylsiloxanes and derivatives: A computational screening

Shiru Lin, Kaitlyn A. Jacoby, Jinxing Gu, Dariana R. Vega-Santander, Arturo J. Hernández-Maldonado, Zhongfang Chen

2021, 6(6): 884-892. doi: 10.1016/j.gee.2020.07.007

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Though widely used in our daily lives, volatile methylsiloxanes and derivatives are emerging contaminants and becoming a high-priority environment and public health concern. Developing effective sorbent materials can remove siloxanes in a cost-effective manner. Herein, by means of Grand Canonical Monte Carlo (GCMC) simulations, we evaluated the potentials of the recently proposed 68 stable zeolite-templated carbons (ZTCs) (PNAS 2018 , 115, E8116-E8124) for the removal of four linear methylsiloxanes and derivatives as well as two cyclic methylsiloxanes by the calculated average loading and average adsorption energy values. Four ZTCs, namely ISV, FAU1, FAU3, and H8326836, were identified with the top 50% adsorption performance toward all the six targeted contaminants, which outperform activated carbons. Further first principles computations revealed that steric hindrance, electrostatic interactions (further enhanced by charge transfer), and CH-π interactions account for the outstanding adsorption performance of these ZTCs. This work provides a quick procedure to computationally screen promising ZTCs for siloxane removal, and help guide future experimental and theoretical investigations.

Novel montmorillonite-sulfur composite for enhancement of selective adsorption toward cesium

Shangqing Chen, Jiayin Hu, Guoliang Mi, Yafei Guo, Tianlong Deng

2021, 6(6): 893-902. doi: 10.1016/j.gee.2020.07.016

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The selective elimination of radioactive cesium from complicated wastewater is imperative in view of environment and human health. Montmorillonite has been accepted as one of the most promising adsorbents for cesium purification. However, its poor selectivity still remains a major challenge. Herein, a novel montmorillonite-sulfur composite was developed via a facile one-step solvent-free method and used for Cs⁺ removal. Owing to the fact that soft Lewis base S^2- ligand interacted more strongly with softer Lewis acid Cs⁺ than other cations, the capacity and selectivity towards Cs⁺ was significantly enhanced. In this case, a large capacity of 160.9 mg g^-1 was achieved. The distribution coefficient value (∼4000 mL g^-1) was 3-times larger than that of pristine montmorillonite (∼1500 mL g^-1). Moreover, this composite could be easily recycled and reused within five times recycling experiments. Therefore, this low-cost and facilely prepared composite are expected to be used for the selective removal of Cs⁺ from complicated wastewater containing various competing ions.

Assisting effect of Al₂O₃ on MnO_x for NO catalytic oxidation

Denghui Wang, Hui Li, Qi Yao, Shien Hui, Yanqing Niu

2021, 6(6): 903-909. doi: 10.1016/j.gee.2020.07.005

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Various Mn-based catalysts for NO oxidation were prepared using MnO_x as active compound, while TiO₂ and Al₂O₃ were adopted as catalyst support. The performance of the catalysts was tested to study the effect of support on Mn-based catalyst activity. Performance of the catalysts followed as Mn_0.4/Al > Mn_0.2/Al > Mn_0.4/Ti > Mn_0.2/Ti > MnO_x > Al₂O₃ on the whole, indicating the synergism of MnO_x and Al₂O₃ for NO catalytic oxidation. Results were analyzed according to characterization data. Adsorbed oxygen on catalyst rather than lattice oxygen was detected as the active oxidizer for NO oxidation. As catalyst support, Al₂O₃ provided more sites to carry surface adsorbed oxygen than TiO₂, resulting in the presence of more active oxygen on MnO_x/Al₂O₃ than on MnO_x/TiO₂. Moreover, MnO_x/Al₂O₃ possessed high surface area and pore volume, which greatly benefited the adsorption of NO on catalyst and further favored the oxidation of NO by active oxygen. All these advantages helped Mn_0.4/Al exhibited the best catalytic efficiency.

Degradation of nitrobenzene-containing wastewater by sequential nanoscale zero valent iron-persulfate process

Jingjuan Qiao, Weizhou Jiao, Youzhi Liu

2021, 6(6): 910-919. doi: 10.1016/j.gee.2020.07.018

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As nitrobenzene (NB) is structurally stable and difficult to degrade due to the presence of an electron withdrawing group (nitro group). The sequential nanoscale zero valent iron-persulfate (NZVI-Na₂S₂O₈) process was proposed in this study for the degradation NB-containing wastewater. The results showed that the NB degradation efficiency and the total organic carbon removal efficiency in the sequential NZVI-Na₂S₂O₈ process were 100% and 49.25%, respectively, at a NB concentration of 200 mg L^-1, a NZVI concentration of 0.75 g L^-1, a Na₂S₂O₈ concentration of 26.8 mmol L^-1, an initial pH of 5, and a reaction time of 30 min, which were higher than those (88.53% and 35.24%, respectively) obtained in the NZVI/Na₂S₂O₈ process. Sulfate radicals (SO₄^·-) and hydroxyl radicals (·OH) generated in the reaction were identified directly by electron paramagnetic resonance spectroscopy and indirectly by radical capture experiments, and it was shown that both SO₄^·- and ·OH played a major role in the sequential NZVI-Na₂S₂O₈ process. The possible pathways involved in the reduction of NB to aniline (AN) and the further oxidative degradation of AN were determined by gas chromatography-mass spectrometry.

Ternary blend strategy in benzotriazole-based organic photovoltaics for indoor application

Yinglong Bai, Runnan Yu, Yiming Bai, Erjun Zhou, Tasawar Hayat, Ahmed Alsaedi, Zhan'ao Tan

2021, 6(6): 920-928. doi: 10.1016/j.gee.2020.07.017

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Organic photovoltaics (OPVs) suitable for application in indoor lighting environments can power a wide range of internet of things (IoT) related electronic devices. The ternary structure has huge advantages in improving the photovoltaic performance of OPVs, including broadening the light absorption, improving the charge transport, manipulating the energy loss (E_loss) and so on. Herein, we use wide-bandgap photo-active materials, including the benzotriazole-based polymer donor (J52-F), chlorinated polymer donor (PM7) and A₂-A₁-D-A₁-A₂-structured acceptor (BTA3), to construct ternary OPVs for indoor light applications. Benefitting from the introduction of PM7 as the third component in J52-F:BTA3-based blend, a gratifying PCE of 20.04% with a high V_OC of 1.00 V can be obtained under the test conditions with an illumination of 300 lx from an LED lighting source with a color temperature of 3000 K. The excellent device performance is inseparable from the matched spectrum, enhanced light absorption and the reduced E_loss, while the improved charge transport capability and suppression of carrier recombination also play an indelible role. Our work shows a potential material system to meet the requirement of devices applied under indoor light. Moreover, these findings demonstrate that designing multi-component OPVs is indeed a feasible way to further improve the performances of the photovoltaic energy conversion system for indoor applications.

Controllable synthesis of nitrogen-doped porous carbon from metal-polluted miscanthus waste boosting for supercapacitors

Zuo Chen, Man Zhang, Yuchen Wang, Zhiyu Yang, Di Hu, Yetao Tang, Kai Yan

2021, 6(6): 929-937. doi: 10.1016/j.gee.2020.07.015

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High-value reclamation of metal-polluted plants involved in phytoremediation is a big challenge. In this study, nitrogen-doped nanoporous carbon with large specific area of 2359.1 m² g^-1 is facilely fabricated from metal-polluted miscanthus waste for efficient energy storage. The synergistic effect of KOH, urea and ammonia solution greatly improve the nitrogen quantity and surface area of the synthesized carbon. Electrodes fabricated with this carbon exhibit the excellent capacitance performance of 340.2 F g^-1 at 0.5 A g^-1 and a low combined resistance of 0.116 Ω, which are competitive with most of previously reported carbon-based electrodes. In addition, the as-obtained carbon electrode shows a high specific capacitance retention of over 99.6% even after 5000 cycles. Furthermore, the symmetric supercapacitor fabricated using the synthesized carbon achieves a superior energy density of 25.3 Wh kg^-1 (at 400 W kg^-1) in 1 mol L^-1 Na₂SO₄ aqueous solution. This work provides an efficient route to upcycle metal-polluted plant waste for supercapacitor applications.

Photoreduction of CO₂ in the presence of CH₄ over g-C₃N₄ modified with TiO₂ nanoparticles at room temperature

Ming Chen, Jiachen Wu, Chongchong Lu, Xiao Luo, Yangqiang Huang, Bo Jin, Hongxia Gao, Xiaowen Zhang, Morris Argyle, Zhiwu Liang

2021, 6(6): 938-951. doi: 10.1016/j.gee.2020.07.001

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CO₂ reduction under simulated sunlight over photocatalysts has become an attractive researcher area recently. In this work, carbon nitride compounds modified by TiO₂ nanoparticles (TNPs) have been used for the photoreduction of CO₂ in the presence of CH₄ at room temperature. Briefly, a series of noble-metal-free TNP-graphitic-carbon nitride (g-C₃N₄, also abbreviated CN) photocatalysts with different TNPs loadings and calcination temperatures have been synthesized by a wet-chemical method. The characterization results of XRD, FTIR, SEM, TEM, BET, XPS, CO₂ Adsorption, UV-vis, and PL demonstrate that the BET surface area and CO₂ adsorption capacity have been improved after the calcination. Besides, the g-C₃N₄ has been successfully coupled with the TNPs and a heterojunction has formed at their interface. These characters contribute to increase the photocatalytic activity of TNPs-CN toward reducing CO₂ in the presence of CH₄, and its' performance is better than bare g-C₃N₄, Titania (P₂₅)-CN, MgO-CN, or Cu₂O-CN. Orthogonal experiments are then carried out to investigate the sensitivity factors and optimum conditions. The sensitivity results show that the reaction pressure makes little difference on the photocatalysis results, which verifies the photoinduced CO₂-CH₄ reaction has a tiny change in gas volume. In addition, under the optimum conditions, the turnover frequency (TOF) of CO after 4 h reaction can reach 9.98 μmol g-cat.^-1 h^-1, and traces of ethane and ethylene have been detected during the reactions. In addition, surface acetate and carbonaceous deposit are found on the (20)TNPs-CN/450 surface after continuous 24 h irradiation under the optimum conditions, which resulting in the inactivation of the catalyst. Finally, possible reaction mechanisms have been proposed based on the results.

Novel magnetic carbon supported molybdenum disulfide catalyst and its application in residue upgrading

Xiangyang Zhu, Dong Qiao, Liangrong Yang, Qinling Bi, Huifang Xing, Shan Ni, Menglei Yuan, Huizhou Liu, Luhai Wang, An Ma

2021, 6(6): 952-960. doi: 10.1016/j.gee.2020.06.025

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A novel hybrid material consisted of carbon covered Fe₃O₄ nanoparticles and MoS₂ nanoflower (FCM) was designed and prepared by micelle-assisted hydrothermal methods. Multiple techniques, including X-Ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize it. The results show that FCM has a flower-like morphology with a 330 nm Fe₃O₄ core as well as 70 nm highly crystalline MoS₂ shell. FCM is superparamagnetic with a saturation magnetization of 35 emu g^-1. Then hydrocracking of Canadian bitumen residue (CBR) was applied to estimate its catalytic activity. The results show that FCM exhibits superior catalytic hydrocracking activity compared to bulk MoS₂ and commercial oil-dispersed Mo(CO)₆ by the same Mo loading. Further measurement by elemental analysis, XPS and XRD reveals that the MoS₂ nanoflower with abundant catalytic active sites and covered carbon layer with anti-coke ability donate to the superior upgrading performance. Besides, the catalysts can be easily recovered by the external magnetic field. This work provides a novel kind magnetic nanocatalyst which is potential for slurry-phase hydrocracking applications.

Synthesis of HTLcs modified by K₃PO₄ for side chain alkylation of toluene with methanol

Chunyao Hao, Yueli Wen, Bin Wang, Faraz Ahmad, Yuhua Liu, Huijun Li, Wei Huang

2021, 6(6): 961-967. doi: 10.1016/j.gee.2020.06.007

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A series of calcined HTLcs catalysts were prepared and modified with potassium phosphate by impregnation method to clarify the influence of catalyst alkalinity on the side chain alkylation of toluene with methanol for synthesis of ethylbenzene and styrene. The catalysts were characterized by X-ray diffraction (XRD), N₂ physical adsorption-desorption, Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), NH₃ temperature-programmed desorption (NH₃-TPD) and CO₂ temperature-programmed desorption (CO₂-TPD). It was found that the selectivity of styrene was highest (39.25%) when the K₃PO₄ loading was 7.5 wt%. And the total yield of styrene and ethylbenzene could reach 65.08% with 10 wt% K₃PO₄ loading. This might due to the fact that the addition of K₃PO₄ could adjust the acid and basic sites of catalysts. In addition, appropriate strength and amount of basic sites were favorable to producing more styrene.

2021 Vol. 6, No. 6

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