Green Energy&Environment

Powerful qua-functional electrolyte additive for lithium metal batteries

Dawei Su

2022, 7(3): 361-364. doi: 10.1016/j.gee.2021.10.005

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Lithium metal batteries (LMBs) have attracted tremendous research attention because of the high theoretical capacity (3860 mAh g⁻¹) and the lowest electrochemical potential (−3.04 V vs. standard hydrogen electrode). However, the Lithium dendrites, forming from plating/stripping processes, cause the excessive consumption of electrolyte and active Li and the puncture on the separator. This limits the commercialization of LMBs. Recently, Ma's group proposed heptafluorobutyric anhydride (HFA) as qua-functional electrolyte additive and verified the protection mechanism from the structure and electrochemical properties. Such results creatively put forward qua-functional electrolyte additive for the improvement of LMBs and provides good experience for the exploration of multi-functional additive, inspiring researchers to explore new multi-functional electrolyte additives in future.

Etching oxide overlayers of NiFe phosphide to facilitate surface reconstruction for oxygen evolution reaction

Tehua Wang, Xian-Zhu Fu, Shuangyin Wang

2022, 7(3): 365-371. doi: 10.1016/j.gee.2021.03.005

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Transition-metal phosphides have been of concern as efficient electrocatalysts for oxygen evolution reaction (OER) due to its high conductivity and earth-abundance reserves. However, oxide overlayers formed on their surface by spontaneously atmospheric oxidation are usually neglected, thus confusing the establishment of structure-performance relationship. Herein, we successfully etched the oxide overlayers of NiFe phosphide (NiFeP) by a dielectric barrier discharge (DBD) plasma technique, aiming to reveal the influence of the oxide overlayers on its electrocatalytic performance for OER. It is found that etching the oxide overlayers can accelerate the surface reconstruction process of NiFeP and facilitate the formation of metal hydroxides, which are key intermediate phases for OER. Consequently, the etched NiFeP-DBD material shows remarkably enhanced OER activity with an overpotential of 265 mV at a current density of 10 mA cm⁻². The finding of this work probably brings a significant impact to understand the structure-performance relationship of metal phosphide in electrooxidation reaction.

The fabrication of atomically thin-MoS₂ based photoanodes for photoelectrochemical energy conversion and environment remediation: A review

Zexu Chi, Jingyun Zhao, Yi Zhang, Han Yu, Hongbing Yu

2022, 7(3): 372-393. doi: 10.1016/j.gee.2021.05.002

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Photoelectrochemical (PEC) technology has been proved a promising approach to solve the problems of energy shortages and environmental pollution damages. It can convert unlimited solar energy resources into energy forms needed by mankind. The development of highly efficient photoanodes is a key step in realizing the large-scale practical application of PEC systems. However, the development of PEC photoanodes has been severely hindered by the issues of easy recombination of photo-generated charge carriers, low photon-to-electron conversion efficiency, poor photo-corrosion resistance, and low catalytic activity. Therefore, constructing high-performance and stable photoanodes is an urgent research field to promote the progress of PEC technology. The atomically thin molybdenum disulfide (AT-MoS₂) with unique physical and chemical properties has been widely applied in the fabrication of PEC photoanodes. The AT-MoS₂ based photoanodes have exhibited excellent PEC performance, which providing promising candidates for ideal PEC application. Here, we summarize the fundamental natures of MoS₂ and present the research efforts in the preparation of AT-MoS₂ based photoanodes. Strategies for the fabrication of high-efficient AT-MoS₂ based photoanodes are emphasized to provide guidelines to advance emerging PEC photoanodes. Besides, perspectives for the development of more efficient AT-MoS₂ based photoanodes are proposed.

CO₂ capture and conversion to value-added products promoted by MXene-based materials

Yu Chen, Chong Liu, Shien Guo, Tiancheng Mu, Lei Wei, Yanhong Lu

2022, 7(3): 394-410. doi: 10.1016/j.gee.2020.11.008

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Carbon dioxide (CO₂) capture and conversion is the key route for the mitigation of the greenhouse effect and utilization of carbon sources to obtain value-added products or fuels. Much attention is paid to the development of novel materials with high CO₂ adsorption capacity and conversion rate. MXene is the graphene-like two-dimensional metal carbide/nitride/carbonitride owning favorable structure, morphology, high surface-bulk ratio, and physicochemical properties. Here, we review the CO₂ capture, sensing, and conversion by MXene and MXene-based materials. Furthermore, the underlying mechanism involved the capture, sensing, and conversion of CO₂ is summarized. This review would open a new horizon for CO₂ valorization with high efficiency and promising widespread applications.

Converting poly(ethylene terephthalate) waste into N-doped porous carbon as CO₂ adsorbent and solar steam generator

Changyuan Song, Boyi Zhang, Liang Hao, Jiakang Min, Ning Liu, Ran Niu, Jiang Gong, Tao Tang

2022, 7(3): 411-422. doi: 10.1016/j.gee.2020.10.002

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Sustainable conversion of waste plastics into valuable carbon materials for diverse applications provides a promising strategy to dispose the municipal and industrial waste plastics. However, it remains a challenge to precisely control the crosslinking reaction for transforming waste polyesters into N-doped porous carbon (NPC) with well-defined microstructures. Herein, we put forwards a strategy of stepwise crosslinking using melamine and ZnCl₂/NaCl eutectic salts to convert poly (ethylene terephthalate) (PET) into NPC at 550 °C. We prove that firstly melamine reacts with PET degradation products to form a crosslinking structure, and subsequently ZnCl₂/NaCl promote the dehydration and decarboxylation of the crosslinking structure to generate a more thermally stable crosslinking structure. The coordination of two tandem crosslinking reactions is critical to control the microstructure of NPC. Without activations, NPC shows large specific surface area of 1173 m² g⁻¹, abundant N dopants, and rich oxygen-containing groups. These combined features endure NPC with excellent performance in CO₂ capture and solar steam generation, e.g., high CO₂ adsorption capacity of 6.47 mmol g⁻¹ and evaporation rate of 1.62 kg m⁻² h⁻¹. More importantly, NPC is compared to or prevails over previous carbon-based CO₂ adsorbents or photothermal materials. This work will advance the research on “green” reutilization of low-cost polyester wastes to prepare sustainable carbon for solar energy conversion, environmental protection, etc.

MOFs derived FeNi₃ nanoparticles decorated hollow N-doped carbon rod for high-performance oxygen evolution reaction

Gaopeng Liu, Bin Wang, Lin Wang, Wenxian Wei, Yu Quan, Chongtai Wang, Wenshuai Zhu, Huaming Li, Jiexiang Xia

2022, 7(3): 423-431. doi: 10.1016/j.gee.2020.10.007

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The sluggish electrochemical oxygen evolution reaction (OER) is a crucial process for clean energy conversion technology. The preparation of non-precious electrocatalysts with high performance for OER is still a main challenge. Herein, we report a FeNi₃ nanoparticles incorporated on N-doped hollow carbon rod with extraordinary performance toward OER by in situ annealing the Ni-doped Fe based metal-organic frameworks (MOFs) precursors. Meanwhile, the pristine N atoms of MOFs doped into carbon frameworks can enhance the electrical conductivity, boost electron mass transport and electron transfer, and construct more active sites. Furthermore, constructing the Fe-Ni alloy structure can facilitate the formation of O-O bond, optimize the free energy for intermediate adsorption and improve OER performance. The as-prepared Fe-Ni bimetal decorated hollow N-doped nanocarbon hybrid structure possesses superior OER performance, which is surpass commercial IrO₂ at a overpotential of only 340 mV to achieve the current density of 10 mA cm⁻², as well as a small Tafel slope of 86.67 mV dec⁻¹ in alkaline electrolyte. The Fe-Ni alloy/hollow N-doped nanocarbon hybrid structure shining the bright future for obtaining earth-abundant and superior efficient anode OER electrocatalyst.

Synergistic effect of Ni^II and Co/Fe^III in doped mixed-valence phosphonate for enhancing electrocatalytic oxygen evolution

Juan-Juan Hou, Jian-Tao Yuan, Wei Zhang, Ying-Xia Wang, Xian-Ming Zhang

2022, 7(3): 432-439. doi: 10.1016/j.gee.2020.10.003

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Metal organophosphonates have been explored in energy-related fields due to their high chemical and thermal stability as a type of uniformly precursor, but only few of pristine metal organophosphonate are directly used for oxygen evolution reaction (OER) catalysts. Here, a mixed-valence iron phosphonate ( Fe-ppat ) has been constructed and applied to OER catalysis considered the potential active sites in pillars Fe^II(H₂O)₄(COO)₂ and inorganic layers Fe^III(μ₂-OH)PO₃. Specifically, isostructural trimetallic framework FeCoNi-ppat possesses a minimum overpotential (291 mV), small Tafel slope (91.65 mV dec⁻¹), and high stability up to 83 h. The enhanced catalytic performance could be mainly ascribed to the synergistic effect of Ni^II equivalent occupancy in pillars and Co/Fe^III in layers.

A facial synthesis of nitrogen-doped reduced graphene oxide quantum dot and its application in aqueous organics degradation

He Zhao, Juehua Wang, Zhuangjun Fan, Yongbing Xie, Di Zhang, Shanshan Sun, Yi Zhang, Hongbin Cao

2022, 7(3): 440-448. doi: 10.1016/j.gee.2020.10.008

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N-doped reduced graphene oxide quantum dots (N-rGQDs) have attracted more and more attention in efficient catalytic degradation of aqueous organic pollutants. However, the synthesis of N-rGQDs is generally a complex and high energy required process for the reduction and N-doping steps. In this study, a facile and green fabrication approach of N-rGQDs is established, based on a metal-free Fenton reaction without additional energy-input. The N structures of N-rGQDs play a significant role in the promotion of their catalytic performance. The N-rGQDs with relatively high percentage of aromatic nitrogen (N_Ar-rGQDs) perform excellent catalytic activities, with which the degradation efficiency of pollutant is enhanced by 25 times. Density functional theory (DFT) calculation also indicates aromatic nitrogen structures with electron-rich sites are prone to transfer electron, presenting a key role in the catalytic reaction. This metal-free Fenton process provides a green and cost-effective strategy for one-step fabrication of N-rGQDs with controllable features and potential environmental catalytic applications.

Mechanistic aspects of facet-dependent CH₄/C₂₊ selectivity over a χ-Fe₅C₂ Fischer-Tropsch catalyst

Thanh Hai Pham, Junbo Cao, Nan Song, Yueqiang Cao, Bingxu Chen, Gang Qian, Xinggui Zhou, De Chen, Xuezhi Duan

2022, 7(3): 449-456. doi: 10.1016/j.gee.2020.10.015

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Structure-performance relationship is a complex issue in iron-catalyzed Fischer-Tropsch synthesis, and it is not easy to elucidate it by experimental investigations. First-principle calculation is a powerful method for explaining experimental results and guiding catalyst design. In this study, we investigated the reaction mechanisms of CH₄ formation and C-C coupling on four χ-Fe₅C₂ surfaces and established the kinetic equations to compare the rates of CH₄ formation and C₁+C₁ coupling reactions and determine the CH₄/C₂₊ selectivity. The results show that the geometry of the χ-Fe₅C₂ surfaces has little effect on the formation rate of CH₄; however, the C₁+C₁ coupling reactions are significantly affected by the surface geometry. The C₁+C₁ coupling reaction rates on the terraced-like (510) and (021) surfaces are much higher than those on the stepped-like (001) and (100) surfaces. Based on these results, we established a Brønsted-Evans-Polanyi (BEP) relationship between the effective barrier difference for CH₄ formation and C₁+C₁ coupling (ΔE_eff) and the adsorption energy of C+4H (ΔE_C+4H) on χ-Fe₅C₂ surfaces. ΔE_C+4H can be used as a descriptor for CH₄/C₂₊ selectivity on different surfaces of χ-Fe₅C₂.

Preparation of bimetal Co-Ni supported on Mg-Al oxide for chemocatalytic upgrading of tailored fermentation products to energy intensive fuels

Jiajun Liu, Kui Wu, Zhengke Li, Wensong Li, Yuqing Ning, Weiyan Wang, Yunquan Yang

2022, 7(3): 457-466. doi: 10.1016/j.gee.2020.10.011

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The great challenge in the aldol condensation of tailored fermentation products (acetone-butanol-ethanol, ABE) into energy intensive fuels is to develop a suitable catalyst with high activity and low-cost. In this study, Co, Ni, and Co-Ni supported on Mg-Al oxide catalysts were prepared and their pore diameters were enlarged via adding active carbon as a hard template into Mg-Al hydrotalcite. During the aldol condensation reaction, the catalyst activity was enhanced after enlarging the pore diameter and Co-Ni bimetal supported catalyst presented the highest activity, which was resulted from that the electron transfer between Co and Ni in Co-Ni alloy enhanced the dehydrogenation activity and large pore lowered the mass transfer resistance. After optimizing the reaction conditions, acetone conversion and the total selectivity of C₅-C₁₁ desired products in the aldol condensation of ABE reached up to 76% and 90%, respectively. The stability study showed that the activity was decreased with the increase of reaction number because of the oxidation of metallic Co and Ni, but this could be solved via a simple hydrogen reduction method.

NiCoP/NiOOH nanoflowers loaded on ultrahigh porosity Co foam for hydrogen evolution reaction under large current density

Yuantao Pei, Liang Huang, Lei Han, Haijun Zhang, Longhao Dong, Quanli Jia, Shaowei Zhang

2022, 7(3): 467-476. doi: 10.1016/j.gee.2020.10.019

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Developing user-friendly electrodes for efficiently producing hydrogen from water to substitute non-renewable fossil fuels is one of the challenges in the hydrogen energy field. For the first time, we have prepared self-supporting ultrahigh porosity cobalt foam loaded with NiCoP/NiOOH nanoflowers (NiCoP/CF) via freeze-drying and phosphorization. The as-prepared hierarchical NiCoP/CF electrodes showed superior catalytic activity for hydrogen evolution reaction (HER) in alkaline media. The one resulted from phosphorization at 350 °C (NiCoP/CF-350) only required overpotential of −47, and −126 mV to deliver geometrical current density of −10 mA cm⁻² and −100 mA cm⁻², respectively, demonstrating improved catalytic activity than the electrodes prepared using a commercial nickel foam as a support. Moreover, it could retain its superior stability at a current density higher than −500 mA cm⁻² for 16 h. Such an outstanding performance can be attributed to the ultrahigh porosity of Co foam support, optimal adsorption energies of HER intermediates (H∗), facile water dissociation on the NiCoP/NiOOH hetero-interfaces, and the assistance of NiOOH facilitating the electrons transfer from the Co foam inside to the NiCoP outside. The work would provide a new strategy for future design of advanced HER electrocatalysts.

Cyclic oligourea synthesized from CO₂: Purification, characterization and properties

Ruhui Shi, Haiyang Cheng, Hongxiang Li, Peixuan Wu, Chao Zhang, Masahiko Arai, Fengyu Zhao

2022, 7(3): 477-484. doi: 10.1016/j.gee.2020.10.016

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Carbon dioxide (CO₂) as a sustainable resource instead of toxic reagents has attracted considerable attention in synthesis of chemicals and polymeric materials. Herein, a kind of cyclic oligourea was synthesized via polycondensation of CO₂ with 4,7,10-trioxa-1,13-tridecanediamine (TTD) followed by effective separation and purification processes. We developed an efficient separation strategy in which the linear oligourea molecules were selectively transformed to macromolecular polyurea molecules by a reaction of the -NH₂ end group with 4,4′-diphenylmethane diisocyanate (MDI), followed by separation from cyclic oligourea using selected solvents. The structure and physicochemical properties were confirmed by MALDI-TOF mass spectra, NMR, Cryo-EM, thermal analysis and solubility measurement. The well-defined cyclic oligourea was produced with a high purity (99.4%) and the average-number molecular weight (M_n) of 1040 Da. It is semi-crystalline in structure with a melting point of 106 °C and glass transition point of −10 °C. The cyclic oligourea presented characteristically difference to its linear analogue. This work provides a new member to cyclic polymer family.

In-situ growth of TiO₂ film on carbonized eggshell membrane as 3D electrode for high-performance lithium storage

Xiao Yu, Xinyi Zhang, Yongjian Lai, Donghai Wang, Yong Liu

2022, 7(3): 485-491. doi: 10.1016/j.gee.2020.10.018

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3D electrodes have shown extraordinary promise for electrochemical energy storage devices in wearable electronics. However, it is still a significant challenge to rationally design 3D electrode that has the characteristics of lightweight, flexibility, low cost, high performance and miniaturization. In this work, we present a novel design of 3D electrode by directly growing the nanocrystalline TiO₂ film on carbonized eggshell membrane. The unique architecture can supply not only a continuous electron transport pathway through an interconnected carbon fibrous network but also an efficient electrolyte flux via an interpenetrating porous network. Besides, nanocrystalline TiO₂ film on carbonized eggshell membrane offers a short ion diffusion path in the solid-phase, leading to a rapid kinetic of electrochemical reaction. When tested as an anode for Li-ion battery, TiO₂ film in 3D electrode demonstrated excellent electrochemical performance with a large reversible capacity, excellent rate capacity and long life cycling property.

A mechanically durable, excellent recyclable 3D hierarchical Ni₃S₂@Ni foam photothermal membrane

Zhongping Yao, Kailun Yu, Mengyao Pan, Hongbo Xu, Tianqi Zhao, Zhaohua Jiang

2022, 7(3): 492-499. doi: 10.1016/j.gee.2020.10.010

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Solar-driven water evaporation is considered to be a viable and very efficient technology for fresh water production. Unfortunately, the photothermal membrane has a low absorptivity, low photothermal conversion and poor recyclability, which are difficult to meet the demands of self-floating solar driven evaporators in practical applications. Herein, a hierarchical nanostructure Ni₃S₂ has been prepared by in-situ growing method on Ni foam (NF), which shows excellent absorptivity, outstanding recyclable and high mechanically durable properties. The photothermal membrane was composed of hierarchical nanostructure Ni₃S₂@NF, which exhibited excellent solar absorption (93.13%) in the wavelength range of 250 -2500 nm and sustained anti-corrosion capacity for one month. In addition, the hierarchical nanostructure Ni₃S₂ @NF has good hydrophilicity and strong binding force, indicating this photothermal membrane exhibits good stability and outstanding photothermal conversion efficiency. An evaporation system based on 3D Ni₃S₂@NF membrane exhibited excellent water evaporation ability，the highest water evaporation rate (1.53 kg m⁻² h⁻¹) and the photothermal conversion efficiency （84.7%） under 1 sun illumination. In the desalination experiment, the water evaporation rate and photothermal conversion efficiency almost keep constant over 5 cycles tests and do not decrease compared with the experiment in pure water. This result demonstrated that the Ni₃S₂@NF membrane has shown good corrosion resistance and outstanding recyclability. Due to the simple preparation method, low cost, outstanding recyclability and high mechanical durability in the sea water, this Ni₃S₂@NF membrane have great potential for long-term solar distillation applications.

C₂H₂ semi-hydrogenation on the Pd_xM_y cluster/graphdiyne catalysts: Effects of cluster composition and size on the activity and selectivity

Ying Wang, Yamin Qi, Maohong Fan, Baojun Wang, Lixia Ling, Riguang Zhang

2022, 7(3): 500-511. doi: 10.1016/j.gee.2020.10.020

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C₂H₂ semi-hydrogenation has been widely applied in industry to eliminate trace C₂H₂ from C₂H₄ feed. C₂H₂ semi-hydrogenation to C₂H₄ on a series of the newly designed catalysts, graphdiyne (GDY) as a new carbon allotrope supported different sizes of Pd_xM_y clusters (Pd_xM_y/GDY, M = Cu, Ag, Au, Ni; x+y = 1-3), were studied using DFT calculations. The results found that C₂H₂ semi-hydrogenation to C₂H₄ on Pd_xM_y/GDY catalysts exhibits that both the activity and selectivity greatly depend on the composition and size of Pd_xM_y/GDY catalysts. Surprisingly, our results for the first time discovered the Pd₁/GDY catalyst with GDY supported the single atom Pd that presents the best selectivity and activity toward C₂H₄ formation compared to the previously reported catalysts so far in C₂H₂ semi-hydrogenation. This study would provide a theoretical clue for designing and screening out the potential catalysts with GDY supported small sizes of Pd_xM_y and other metal clusters in C₂H₂ hydrogenation.

Ultra-small UiO-66-NH₂ nanoparticles immobilized on g-C₃N₄ nanosheets for enhanced catalytic activity

Zhuizhui Su, Bingxing Zhang, Xiuyan Cheng, Fanyu Zhang, Qiang Wan, Lifei Liu, Xiuniang Tan, Dongxing Tan, Lirong Zheng, Jianling Zhang

2022, 7(3): 512-518. doi: 10.1016/j.gee.2020.10.023

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UiO-66-NH₂, an important metal-organic framework, is usually synthesized by solvothermal method and the particle size is generally larger than 200 nm, which limits its catalytic applications in chemical reactions. It is very meaningful to produce UiO-66-NH₂ nanoparticles with ultra-small size, but remains challenging. Herein, we synthesized UiO-66-NH₂ nanoparticles in size of 8-15 nm that are immobilized on g-C₃N₄ nanosheets. Compared with the UiO-66-NH₂ synthesized by the traditional solvothermal method (> 200 nm), the ultra-small UiO-66-NH₂ nanoparticles immobilized on g-C₃N₄ have more unsaturated coordination positions and increased Lewis acidity. Owing to these combined advantages, the ultra-small UiO-66-NH₂ nanoparticles exhibit greatly improved catalytic activity for Meerwein-Ponndorf-Verley reaction than larger UiO-66-NH₂ particles.

Synthesis of dihydrocapsaicin and dihydrocapsiate exclusively from lignocellulosic platform chemicals

Yan-Bing Li, Hui-Ying Guo, Chen-Qiang Deng, Jin Deng

2022, 7(3): 519-524. doi: 10.1016/j.gee.2020.11.001

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Biorefinery is pivotal to the sustainability of modern chemical industry. However, since biomass is oxygen-enriched, new and green chemical strategies are required for expanding the biomass derived chemical space. In this work, synthesis of natural products dihydrocapsaicin and dihydrocapsiate was achieved exclusively from lignocellulosic platform chemicals. Natural products dihydrocapsaicin and dihydrocapsiate were synthesized exclusively from lignocellulosic platform chemicals, using furfural (from hemicellulose) and methyl isopropyl ketone (from cellulose) through aldol condensation-hydrolysis-hydrodeoxygenation to synthesize 8-methylnonanoic acid and then combined with vanillin derivates (from lignin). This synthesis demonstrates the feasibility of constructing natural products entirely from renewable biomass platform through green processes. The utilization of inherent functional groups of biomass demonstrates their potential to open up chemical space.

Two-dimensional metallic tantalum ditelluride with an intrinsic basal-plane activity for oxygen reduction: A microkinetic modeling study

Yu Wang, Kun Zhou

2022, 7(3): 525-532. doi: 10.1016/j.gee.2020.11.003

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Two-dimensional (2D) materials have exhibited great potential for replacing costly Pt for oxygen reduction reaction (ORR) because of their distinctive structural features and high pre-site activity. However, their performance is generally hindered by the limited density of active sites (e.g., at the layer edges). Although they feature a high exposure of surface sites, these sites are typically inert for ORR. Herein, through density functional theory calculations, we propose a promising ORR catalyst candidate, a 2D TaTe₂ nanosheet, which has an intrinsic high basal-plane activity. Both of the thermodynamic and kinetic processes are explored, which demonstrates that the basal-plane Te sites of the TaTe₂ nanosheet have great potential for facilitating ORR. Specifically, we construct a microkinetic model of ORR proceeding on TaTe₂, which unveils its dynamic intermediate coverage under different electrode potentials and identifies the dominating associative pathway. The theoretical half-wave potential of TaTe₂ is predicted to be 0.87 V, which exceeds those of the well-established Pt (111) and Fe-N-C single-atom catalysts computed at the same level. This study not only presents the first 2D, non-Pt ORR catalyst candidate with an intrinsic basal-plane activity but also offers a rational methodology for unveiling the mechanism/activity of ORR and other electrochemical reactions.

Mechanistic study of vacuum UV catalytic oxidation for toluene degradation over CeO₂ nanorods

Muyan Wu, Yingguang Zhang, Haibao Huang, Dennis Y.C. Leung

2022, 7(3): 533-544. doi: 10.1016/j.gee.2020.11.002

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The present study specifically investigates vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation over CeO₂ nanorods. Synergetic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) were manifested in the results of toluene removal and COx generation, while the combination of UV-PCO and OZCO (UV-OZCO) did not lead to improvement of mineralization. All the processes contribute to ozone decomposition, but no obvious synergetic effects of the different processes can be observed. Intermediate analysis results indicated that more toluene was oxidized into by-products, such as benzyl alcohol and benzaldehyde, by UV-OZCO rather than forming COx. Both hydroxyl radical (·OH) and superoxide radical (·O₂⁻) were found in all the processes of the VUV-PCO-OZCO system (combination of VUV photolysis, UV-PCO, OZCO and UV-OZCO processes). In the UV-OZCO process, the formation of hydroxyl radical was promoted, while that of superoxide radical was impeded, resulting in lower mineralization level of toluene. The mechanistic study of toluene degradation over CeO₂ nanorods in the VUV-PCO-OZCO system revealed that with the formation of ·O₂⁻ and ·OH, toluene is first oxidized to intermediates, followed by further ring-opening reaction and, finally, degradation into CO₂ and H₂O. CeO₂ nanorods function as both ozonation catalyst and photocatalyst, and the redox pair of Ce³⁺ and Ce⁴⁺ are interconvertible and can keep a balance.

Efficient photoelectrochemical conversion of CO₂ to syngas by photocathode engineering

Sheng Chu, Pengfei Ou, Roksana Tonny Rashid, Yuyang Pan, Daolun Liang, Huiyan Zhang, Jun Song, Zetian Mi

2022, 7(3): 545-553. doi: 10.1016/j.gee.2020.11.015

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The synthesis of renewable chemical fuels from CO₂ and H₂O via photoelectrochemical (PEC) route reprensents a promising room-temperature approach for transforming greenhouse gas into value-added chemicals (e.g., syngas), but to date it has been hampered by the lack of efficient photocathode for CO₂ reduction. Herein, we report efficient PEC CO₂ reduction into syngas by photocathode engineering. The photocathode is consisting of a planar p-n Si junction for strong light harvesting, GaN nanowires for efficient electron extraction and transfer, and Au/TiO₂ for rapid electrocatalytic syngas production. The photocathode yields a record-high solar energy conversion efficiency of 2.3%. Furthermore, desirable syngas compositions with CO/H₂ ratios such as 1:2 and 1:1 can be produced by simply varying the size of Au nanoparticle. Theoretical calculations reveal that the active sites for CO and H₂ generation are the facet and undercoordinated sites of Au particles, respectively.

Pomegranate-like porous NiCo₂Se₄ spheres with N-doped carbon as advanced anode materials for Li/Na-ion batteries

Xin Liu, Liwen Yang, Guobao Xu, Juexian Cao

2022, 7(3): 554-565. doi: 10.1016/j.gee.2020.08.012

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Design and preparation of dual-role anode materials with extraordinary performance for rechargeable Li/Na-ion batteries (LIBs/NIBs) remains highly challenging. Herein, three-dimensional (3D) pomegranate-like porous bimetallic NiCo₂Se₄ spheres with N-doped carbon (termed as NC@NiCo₂Se₄) are synthesized by solvothermal method and annealing. Microstructure investigations reveal that the NC@NiCo₂Se₄ spheres include nano-sized NiCo₂Se₄ particles as inner core and NiCo₂Se₄ with the modification of thin-walled N-doped carbon layer as inner/outer shell. The bimetallic NC@NiCo₂Se₄ spheres possess synergistic interaction of Ni/Co atoms to enhance intrinsic conductivity and electrochemical activity, unique pomegranate-like structure with an inner void space and robust shell to mitigation volume expansion, and intimate contact of N-doped carbon layer to improve interface effect and accelerate conversion kinetics. As anode materials, the NC@NiCo₂Se₄ exhibits superior lithium/sodium storage performances (1401.6 and 794.8 mA h g⁻¹ at current density of 0.5 and 5 A g⁻¹ after 500 cycles for LIBs as well as 433.9 mA h g⁻¹ at 3 A g⁻¹ after 1000 cycles and a high capability of 306.6 mA h g⁻¹ at 20 A g⁻¹ for NIBs). This work represents an impressive strategy for future research of bimetallic selenides as anode materials for advanced high-performance LIBs/NIBs.

Sunlight-controlled CO₂ separation resulting from a biomass-based CO₂ absorber

Shiming Zhang, Qianhao Pan, Yapei Wang

2022, 7(3): 566-574. doi: 10.1016/j.gee.2021.09.001

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Renewable solid sorbents for CO₂ capture and storage have shown great potentials for the sake of gaseous separation, tail gas treatment, environmental regulation and climate governance. However, current existed preparation and reusability of solid sorbents are generally subject to high energy consumption and complicated procedure. Herein, a light-controlled CO₂ separation system with high working temperature resulting from natural sawdust combined with polyethyleneimine is fabricated, which involves low energy input and few operating sequences. This system shows a direct and ratiometric response to sunlight illumination by which CO₂ can be reversibly adsorbed and released. This light-controlled CO₂ separation process is prospective to become an attractive alternative to traditional alkaline CO₂ collection method in terms of its convenience and low cost. As a practical demonstration, CO₂ mixed with N₂ is successfully separated through this light-controlled carbon capture and storage (CCS) system, which offers great promise for CO₂ capture and enrichment with applicability across a wide range of scales.

2022 Vol. 7, No. 3

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