2024 Vol. 9, No. 4

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Short communication
Alcohol solvent effect on the self-assembly behaviors of lignin oligomers
Ya Ma, Zhicheng Jiang, Yafei Luo, Xingjie Guo, Xudong Liu, Yiping Luo, Bi Shi
2024, 9(4): 597-603. doi: 10.1016/j.gee.2023.05.001
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The interactions between lignin oligomers and solvents determine the behaviors of lignin oligomers self-assembling into uniform lignin nanoparticles (LNPs). Herein, several alcohol solvents, which readily interact with the lignin oligomers, were adopted to study their effects during solvent shifting process for LNPs’ production. The lignin oligomers with widely distributed molecular weight and abundant guaiacyl units were extracted from wood waste (mainly consists of pine wood), exerting outstanding self-assembly capability. Uniform and spherical LNPs were generated in H2O-n-propanol cosolvent, whereas irregular LNPs were obtained in H2O-methanol cosolvent. The unsatisfactory self-assembly performance of the lignin oligomers in H2O-methanol cosolvent could be attributed to two aspects. On one hand, for the initial dissolution state, the distinguishing Hansen solubility parameter and polarity between methanol solvent and lignin oligomers resulted in the poor dispersion of the lignin oligomers. On the other hand, strong hydrogen bonds between methanol solvent and lignin oligomers during solvent shifting process, hindered the interactions among the lignin oligomers for self-assembly.
Review articles
Ionic liquid derived electrocatalysts for electrochemical water splitting
Tianhao Li, Weihua Hu
2024, 9(4): 604-622. doi: 10.1016/j.gee.2023.06.004
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Hydrogen production from electrochemical water splitting is a promising strategy to generate green energy, which requires the development of efficient and stable electrocatalysts for the hydrogen evolution reaction and the oxygen evolution reaction (HER and OER). Ionic liquids (ILs) or poly (ionic liquids) (PILs), containing heteroatoms, metal-based anions, and various structures, have been frequently involved as precursors to prepare electrocatalysts for water splitting. Moreover, ILs/PILs possess high conductivity, wide electrochemical windows, and high thermal and chemical stability, which can be directly applied in the electrocatalysis process with high durability. In this review, we focus on the studies of ILs/PILs-derived electrocatalysts for HER and OER, where ILs/PILs are applied as heteroatom dopants and metal precursors to prepare catalysts or are directly utilized as the electrocatalysts. Due to those attractive properties, IL/PIL-derived electrocatalysts exhibit excellent performance for electrochemical water splitting. All these accomplishments and developments are systematically summarized and thoughtfully discussed. Then, the overall perspectives for the current challenges and future developments of ILs/PILs-derived electrocatalysts are provided.
Crystallinity-defect matching relationship of g-C3N4: Experimental and theoretical perspectives
Yuhan Li, Ziteng Ren, Zhengjiang He, Ping Ouyang, Youyu Duan, Wendong Zhang, Kangle Lv, Fan Dong
2024, 9(4): 623-658. doi: 10.1016/j.gee.2023.02.012
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Good crystallinity can reduce the charge recombination centers caused by defects, whilst structures with strong polycondensation have high charge mobility, leading to more charge transfer to the material surface for reaction. Much effort has been put into the preparation of a highly efficient g-C3N4 with defects to improve its application potential under the premise in high crystallinity. Hence, this review paper emphasizes the importance to balance the defect and crystallinity of g-C3N4. In addition, detailed discussion on the relationship between defects and activity of g-C3N4 was carried out based on its applications in environmental purification (e.g., VOCs oxidation, NO oxidation, H2O2 evolution, sterilization, pesticide oxidation) and energy conversion (H2 evolution, N2 fixation and CO2 reduction). Lastly, the challenge in developing more efficient defective g-C3N4 photocatalytic materials is summarized.
Recent advances and future prospects on Ni3S2-Based electrocatalysts for efficient alkaline water electrolysis
Shiwen Wang, Zhen Geng, Songhu Bi, Yuwei Wang, Zijian Gao, Liming Jin, Cunman Zhang
2024, 9(4): 659-683. doi: 10.1016/j.gee.2023.02.011
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Green hydrogen (H2) produced by renewable energy powered alkaline water electrolysis is a promising alternative to fossil fuels due to its high energy density with zero-carbon emissions. However, efficient and economic H2 production by alkaline water electrolysis is hindered by the sluggish hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Therefore, it is imperative to design and fabricate high-active and low-cost non-precious metal catalysts to improve the HER and OER performance, which affects the energy efficiency of alkaline water electrolysis. Ni3S2 with the heazlewoodite structure is a potential electrocatalyst with near-metal conductivity due to the Ni–Ni metal network. Here, the review comprehensively presents the recent progress of Ni3S2-based electrocatalysts for alkaline water electrocatalysis. Herein, the HER and OER mechanisms, performance evaluation criteria, preparation methods, and strategies for performance improvement of Ni3S2-based electrocatalysts are discussed. The challenges and perspectives are also analyzed.
Research papers
Pyridinic-N doping carbon layers coupled with tensile strain of FeNi alloy for activating water and urea oxidation
Guangfu Qian, Wei Chen, Jinli Chen, Li Yong Gan, Tianqi Yu, Miaojing Pan, Xiaoyan Zhuo, Shibin Yin
2024, 9(4): 684-694. doi: 10.1016/j.gee.2022.04.006
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Exploitation of oxygen evolution reaction (OER) and urea oxidation reaction (UOR) catalysts with high activity and stability at large current density is a major challenge for energy-saving H2 production in water electrolysis. Herein, we use the pyridinic-N doping carbon layers coupled with tensile strain of FeNi alloy activated by NiFe2O4 (FeNi/NiFe2O4@NC) for efficiently increasing the performance of water and urea oxidation. Due to the tensile strain effect on FeNi/NiFe2O4@NC, it provides a favorable modulation on the electronic properties of the active center, thus enabling amazing OER (η100 = 196 mV) and UOR (E10 = 1.32 V) intrinsic activity. Besides, the carbon-coated layers can be used as armor to prevent FeNi alloy from being corroded by the electrolyte for enhancing the OER/UOR stability at large current density, showing high industrial practicability. This work thus provides a simple way to prepare high-efficiency catalyst for activating water and urea oxidation.
Engineering hierarchical quaternary superstructure of an integrated MOF-derived electrode for boosting urea electrooxidation assisted water electrolysis
Jianjun Tian, Changsheng Cao, Yingchun He, Muhammad Imran Khan, Xin-Tao Wu, Qi-Long Zhu
2024, 9(4): 695-701. doi: 10.1016/j.gee.2022.05.001
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Controllable design of the catalytic electrodes with hierarchical superstructures is expected to improve their electrochemical performance. Herein, a self-supported integrated electrode (NiCo-ZLDH/NF) with a unique hierarchical quaternary superstructure was fabricated through a self-sacrificing template strategy from the metal–organic framework (Co-ZIF-67) nanoplate arrays, which features an intriguing well-defined hierarchy when taking the unit cells of the NiCo-based layered double hydroxide (NiCo-LDH) as the primary structure, the ultrathin LDH nanoneedles as the secondary structure, the mesoscale hollow plates of the LDH nanoneedle arrays as the tertiary structure, and the macroscale three-dimensional frames of the plate arrays as the quaternary structure. Notably, the distinctive structure of NiCo-ZLDH/NF can not only accelerate both mass and charge transfer, but also expose plentiful accessible active sites with high intrinsic activity, endowing it with an excellent electrochemical performance for urea oxidation reaction (UOR). Specially, it only required the low potentials of 1.335, 1.368 and 1.388 V to deliver the current densities of 10, 100 and 200 mA cm-2, respectively, much superior to those for typical NiCo-LDH. Employing NiCo-ZLDH/NF as the bifunctional electrode for both anodic UOR and cathodic HER, an energy-saving electrolysis system was further explored which can greatly reduce the needed voltage of 213 mV to deliver the current density of 100 mA cm-2, as compared to the conventional water electrolysis system composed of OER. This work manifests that it is prospective to explore the hierarchically nanostructured electrodes and the innovative electrolytic technologies for high-efficiency electrocatalysis.
An aqueous magnesium-ion hybrid supercapacitor operated at -50 ℃
Guoshen Yang, Gangrui Qu, Chi Fang, Jie Deng, Xianqi Xu, Yinghao Xie, Tian Sun, Yachao Zhu, Jiaxin Zheng, Hang Zhou
2024, 9(4): 702-712. doi: 10.1016/j.gee.2022.09.004
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The recent advances in aqueous magnesium-ion hybrid supercapacitor (MHSC) have attracted great attention as it brings together the benefits of high energy density, high power density, and synchronously addresses cost and safety issues. However, the freeze of aqueous electrolytes discourages aqueous MHSC from operating at low-temperature conditions. Here, a low-concentration aqueous solution of 4 mol L-1 Mg(ClO4)2 is devised for its low freezing point (-67 ℃) and ultra-high ionic conductivity (3.37 mS cm-1 at -50 ℃). Both physical characterizations and computational simulations revealed that the Mg(ClO4)2 can effectively disrupt the original hydrogen bond network among water molecules via transmuting the electrolyte structure, thus yielding a low freezing point. Thus, the Mg(ClO4)2 electrolytes endue aqueous MHSC with a wider temperature operation range (-50 ℃–25 ℃) and a higher energy density of 103.9 Wh kg-1 at 3.68 kW kg-1 over commonly used magnesium salts (i.e., MgSO4 and Mg(NO3)2) electrolytes. Furthermore, a quasi-solid-state MHSC based on polyacrylamide-based hydrogel electrolyte holds superior low-temperature performance, excellent flexibility, and high safety. This work pioneers a convenient, cheap, and eco-friendly tactic to procure low-temperature aqueous magnesium-ion energy storage device.
Pairing nitroxyl radical and phenazine with electron-withdrawing/-donating substituents in “water-in-ionic liquid” for high-voltage aqueous redox flow batteries
Zhifeng Huang, Rolf Hempelmann, Yiqiong Zhang, Li Tao, Ruiyong Chen
2024, 9(4): 713-722. doi: 10.1016/j.gee.2022.09.005
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Aqueous redox-active organic materials-base electrolytes are sustainable alternatives to vanadium-based electrolyte for redox flow batteries (RFBs) due to the advantages of high ionic conductivity, environmentally benign, safety and low cost. However, the underexplored redox properties of organic materials and the narrow thermodynamic electrolysis window of water (1.23 V) hinder their wide applications. Therefore, seeking suitable organic redox couples and aqueous electrolytes with a high output voltage is highly suggested for advancing the aqueous organic RFBs. In this work, the functionalized phenazine and nitroxyl radical with electron-donating and electron-withdrawing group exhibit redox potential of -0.88 V and 0.78 V vs. Ag, respectively, in “water-in-ionic liquid” supporting electrolytes. Raman spectra reveal that the activity of water is largely suppressed in “water-in-ionic liquid” due to the enhanced hydrogen bond interactions between ionic liquid and water, enabling an electrochemical stability window above 3 V. “Water-in-ionic liquid” supporting electrolytes help to shift redox potential of nitroxyl radical and enable the redox activity of functionalized phenazine. The assembled aqueous RFB allows a theoretical cell voltage of 1.66 V and shows a practical discharge voltage of 1.5 V in the “water-in-ionic liquid” electrolytes. Meanwhile, capacity retention of 99.91% per cycle is achieved over 500 charge/discharge cycles. A power density of 112 mW cm-2 is obtained at a current density of 30 mA cm-2. This work highlights the importance of rationally combining supporting electrolytes and organic molecules to achieve high-voltage aqueous RFBs.
F-doped orthorhombic Nb2O5 exposed with 97% (100) facet for fast reversible Li+-Intercalation
Xiaodi Liu, Yufeng Tang, Dan Zhang, Guangyin Liu, Xinwei Luo, Yi Shang, Xiu Li, Jianmin Ma
2024, 9(4): 723-731. doi: 10.1016/j.gee.2022.09.009
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Orthorhombic Nb2O5 (T-Nb2O5) is attractive for fast-charging Li-ion batteries, but it is still hard to realize rapid charge transfer kinetics for Li-ion storage. Herein, F-doped T-Nb2O5 microflowers (F-Nb2O5) are rationally synthesized through topotactic conversion. Specifically, F-Nb2O5 are assembled by single-crystal nanoflakes with nearly 97% exposed (100) facet, which maximizes the exposure of the feasible Li+ transport pathways along loosely packed 4g atomic layers to the electrolytes, thus effectively enhancing the Li+-intercalation performance. Besides, the band gap of F-Nb2O5 is reduced to 2.87 eV due to the doping of F atoms, leading to enhanced electrical conductivity. The synergetic effects between tailored exposed crystal facets, F-doping, and ultrathin building blocks, speed up the Li+/electron transfer kinetics and improve the pseudocapacitive properties of F-Nb2O5. Therefore, F-Nb2O5 exhibit superior rate capability (210.8 and 164.9 mAh g-1 at 1 and 10 C, respectively) and good long-term 10 C cycling performance (132.7 mAh g-1 after 1500 cycles).
Carbon-doped CuFe2O4 with C-O-M channels for enhanced Fenton-like degradation of tetracycline hydrochloride: From construction to mechanism
Hong Qin, Yangzhuo He, Piao Xu, Yuan Zhu, Han Wang, Ziwei Wang, Yin Zhao, Haijiao Xie, Quyang Tian, Changlin Wang, Ying Zeng, Yicheng Li
2024, 9(4): 732-747. doi: 10.1016/j.gee.2022.09.006
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Carbon-doped copper ferrite (C–CuFe2O4) was synthesized by a simple two-step hydrothermal method, which showed enhanced tetracycline hydrochloride (TCH) removal efficiency as compared to the pure CuFe2O4 in Fenton-like reaction. A removal efficiency of 94% was achieved with 0.2 g L-1 catalyst and 20 mmol L-1 H2O2 within 90 min. We demonstrated that 5% C–CuFe2O4 catalyst in the presence of H2O2 was significantly efficient for TCH degradation under the near-neutral pH (5–9) without buffer. Multiple techniques, including SEM, TEM, XRD, FTIR, Raman, XPS Mössbauer and so on, were conducted to investigate the structures, morphologies and electronic properties of as-prepared samples. The introduction of carbon can effectively accelerate electron transfer by cooperating with Cu and Fe to activate H2O2 to generate OH and O2-. Particularly, theoretical calculations display that the p, p, d orbital hybridization of C, O, Cu and Fe can form C–O–Cu and C–O–Fe bonds, and the electrons on carbon can transfer to metal Cu and Fe along the C–O–Fe and C–O–Cu channels, thus forming electron-rich reactive centers around Fe and Cu. This work provides lightful reference for the modification of spinel ferrites in Fenton-like application.
A general descriptor for guiding the electrolysis of CO2 in molten carbonate
Zhengshan Yang, Bowen Deng, Kaifa Du, Huayi Yin, Dihua Wang
2024, 9(4): 748-757. doi: 10.1016/j.gee.2022.09.011
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Molten carbonate is an excellent electrolyte for the electrochemical reduction of CO2 to carbonaceous materials. However, the electrolyte–electrode-reaction relationship has not been well understood. Herein, we propose a general descriptor, the CO2 activity, to reveal the electrolyte–electrode-reaction relationship by thermodynamic calculations and experimental studies. Experimental studies agree well with theoretical predictions that both cations (Li+, Ca2+, Sr2+ and Ba2+) and anions (BO2-, Ti5O148-, SiO32-) can modulate the CO2 activity to control both cathode and anode reactions in a typical molten carbonate electrolyzer in terms of tuning reaction products and overpotentials. In this regard, the reduction of CO32- can be interpreted as the direct reduction of CO2 generated from the dissociated CO32-, and the CO2 activity can be used as a general descriptor to predict the electrode reaction in molten carbonate. Overall, the CO2 activity descriptor unlocks the electrolyte–electrode-reaction relationship, thereby providing fundamental insights into guiding molten carbonate CO2 electrolysis.
Low carbon alcohol fuel electrolysis of hydrogen generation catalyzed by a novel and effective Pt–CoTe/C bifunctional catalyst system
Yang Zhou, Lice Yu, Jinfa Chang, Ligang Feng, Jiujun Zhang
2024, 9(4): 758-770. doi: 10.1016/j.gee.2022.08.007
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Low carbon alcohol fuels electrolysis under ambient conditions is promising for green hydrogen generation instead of the traditional alcohol fuels steam reforming technique, and highly efficient bifunctional catalysts for membrane electrode fabrication are required to drive the electrolysis reactions. Herein, the efficient catalytic promotion effect of a novel catalyst promoter, CoTe, on Pt is demonstrated for low carbon alcohol fuels of methanol and ethanol electrolysis for hydrogen generation. Experimental and density functional theory calculation results indicate that the optimized electronic structure of Pt–CoTe/C resulting from the synergetic effect between Pt and CoTe further regulates the adsorption energies of CO and H* that enhances the catalytic ability for methanol and ethanol electrolysis. Moreover, the good water activation ability of CoTe and the strong electronic effect of Pt and CoTe increased the tolerance ability to the poisoning species as demonstrated by the CO-stripping technique. The high catalytic kinetics and stability, as well as the promotion effect, were also carefully discussed. Specifically, 71.9% and 75.5% of the initial peak current density was maintained after 1000 CV cycles in acid electrolyte for methanol and ethanol oxidation; and a low overpotential of 30 and 35 mV was required to drive the hydrogen evolution reaction in methanol and ethanol solution at the current density of 10 mA cm-2. In the two-electrode system for alcohol fuels electrolysis, using the optimal Pt–CoTe/C catalyst as bi-functional catalysts, the cell potential of 0.66 V (0.67 V) was required to achieve 10 mA cm-2 for methanol (ethanol) electrolysis, much smaller than that of water electrolysis (1.76 V). The current study offers a novel platform for hydrogen generation via low carbon alcohol fuel electrolysis, and the result is helpful to the catalysis mechanism understanding of Pt assisted by the novel promoter.
Bilayer separator enabling dendrite-free zinc anode with ultralong lifespan >5000 h
Lu Wang, Feifei Wang, Zhe Ding, Yingxin Liu, Ziyi Zhang, Chunpeng Yang, Kian Ping Loh, Quan-Hong Yang
2024, 9(4): 771-776. doi: 10.1016/j.gee.2022.09.013
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Aqueous zinc (Zn) batteries with Zn metal anodes are promising clean energy storage devices with intrinsic safety and low cost. However, Zn dendrite growth severely restricts the use of Zn anodes. To effectively suppress Zn dendrite growth, we propose a bilayer separator consisting of commercial butter paper and glass fiber membrane. The dense cellulose-based butter paper (BP) with low zincophilicity and high mechanical properties prevents the pore-filling behavior of deposited Zn and related separator piercing, effectively suppressing the Zn dendrite growth. As a result, the bilayer separators endow the Zn||Zn symmetrical batteries with a superlong cycling life of Zn anodes (over 5000 h) at 0.5 mA cm-2 and the full batteries enhanced capacity retention, demonstrating the advancement of the bilayer separator to afford excellent cyclability of aqueous metal batteries.
Aqueous-phase reforming of hydroxyacetone solution to bio-based H2 over supported Pt catalysts
A.K.K. Vikla, K. Koichumanova, Songbo He, K. Seshan
2024, 9(4): 777-788. doi: 10.1016/j.gee.2022.09.002
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Aqueous-phase reforming (APR) is an attractive process to produce bio-based hydrogen from waste biomass streams, during which the catalyst stability is often challenged due to the harsh reaction conditions. In this work, three Pt-based catalysts supported on C, AlO(OH), and ZrO2 were investigated for the APR of hydroxyacetone solution in a fixed bed reactor at 225 ℃ and 35 bar. Among them, the Pt/C catalyst showed the highest turnover frequency for H2 production (TOF of 8.9 mol molPt-1 min-1) and the longest catalyst stability. Over the AlO(OH) and ZrO2 supported Pt catalysts, the side reactions consuming H2, formation of coke, and Pt sintering result in a low H2 production and the fast catalyst deactivation. The proposed reaction pathways suggest that a promising APR catalyst should reform all oxygenates in the aqueous phase, minimize the hydrogenation of the oxygenates, maximize the WGS reaction, and inhibit the condensation and coking reactions for maximizing the hydrogen yield and a stable catalytic performance.

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