eScience

The direct use of enzymatic biofuel cells as functional bioelectronics

Xiao Xinxin

2022, 2(1): 1-9. doi: 10.1016/j.esci.2021.12.005

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Enzymatic biofuel cells (EBFCs) are a subgroup of fuel cells that use enzymes as catalysts. EBFCs that utilize physiological substrates such as glucose or lactate are of great interest as implantable or wearable power sources to activate medical devices. This contribution introduces the working principles of EBFCs and summarizes recent progress in EBFC-enabled biosensors, pulse generators, and therapy. Biosensors with self-powered characteristic enjoy high selectivity, leading to potential “instrument-free” or “expensive-instrument-free” measurement. Autonomous pulse generation is based on the hybrid of EBFC and supercapacitor, which is promising for the application in medical related electrostimulation. By providing the direct electrical stimulation, or controllably releasing drug, EBFCs can also be used for self-powered therapeutic system. The further combination of self-powered sensing and treating enables EBFC as a possible platform of diagnostics and therapeutics. Future efforts can be focused on resolving the limited power density and lifetime of EBFC.

Advanced characterizations and measurements for sodium-ion batteries with NASICON-type cathode materials

Liu Yukun, Li Jie, Shen Qiuyu, Zhang Jian, He Pingge, Qu Xuanhui, Liu Yongchang

2022, 2(1): 10-31. doi: 10.1016/j.esci.2021.12.008

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NASICON (Na superionic conductor)-type cathode materials for sodium-ion batteries (SIBs) have attracted extensive attention due to their mechanically robust three-dimensional (3D) framework, which has sufficient open channels for fast Na⁺ transportation. However, they usually suffer from inferior electronic conductivity and low capacity, which severely limit their practical applications. To solve these issues, we need to deeply understand the structural evolution, redox mechanisms, and electrode/electrolyte interface reactions during cycling. Recently, rapid developments in synchrotron X-ray techniques, neutron-based resources, magnetic resonance, as well as optical and electron microscopy have brought numerous opportunities to gain deep insights into the Na-storage behaviors of NASICON cathodes. In this review, we summarize the detection principles of advanced characterization techniques used with typical NASICON-structured cathode materials for SIBs. The special focus is on both operando and ex situ techniques, which help to investigate the relationships among phase, composition, and valence variations within electrochemical responses. Fresh electrochemical measurements and theoretical computations are also included to reveal the kinetics and energy-storage mechanisms of electrodes upon charge/discharge. Finally, we describe potential new developments in NASICON-cathodes with optimized SIB systems, foreseeing a bright future for them, achievable through the rational application of advanced diagnostic methods.

Emerging design principles, materials, and applications for moisture-enabled electric generation

Sun Zhaoyang, Wen Xian, Wang Liming, Ji Dongxiao, Qin Xiaohong, Yu Jianyong, Ramakrishna Seeram

2022, 2(1): 32-46. doi: 10.1016/j.esci.2021.12.009

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Smart generators that collect energy from the ambient environment are a new approach for meeting growing global energy needs. Moisture is one of the most abundant resources in the ambient environment, and using it to generate electricity has aroused great interest in recent years. In this review, we first summarize the emerging design principles of moisture power generation, including ion diffusion, streaming potential, and charged surface potential. Then, based on these fundamental principles, we systematically summarize the materials thus far known to be suitable for moisture power generation. Finally, we highlight the application of moisture energy generators in various fields, such as thermoelectricity, solar thermal evaporation, capacitors, strain sensors, and information storage, and discuss current challenges and future prospects for the development of moisture energy generators.

Controlling Li deposition below the interface

Cao Wenzhuo, Li Quan, Yu Xiqian, Li Hong

2022, 2(1): 47-78. doi: 10.1016/j.esci.2022.02.002

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The desire for high-energy-density batteries calls for the revival of the Li metal anode. However, its application is hindered by enormous challenges associated with Li deposition/desolvation behaviors, such as side reactions, volume change, and dendrite formation. To overcome these challenges, Li deposition must be controlled to remain below the separator. Further, to enable longer cycle life, Li deposition should be constrained below the solid electrolyte interphase (SEI). To achieve these goals, it is critical to have a deep theoretical understanding and corresponding strategies. This paper examines Li plating/stripping in terms of behaviors, mechanisms, and influencing factors, and it proposes general strategies to control Li deposition. Comprehensive design strategies for the electrode, electrolyte, and their interface are essential. Three dimensional (3D) anodes are recommended to store most of the Li deposited below the surface of the anode. Artificial interface engineering can reduce the risk of Li deposition outside of the 3D anode, while electrolyte engineering favors Li transport, regulates Li deposition, and suppresses dendrites, serving as the final barrier to uncontrolled Li deposition. This paper reviews systemic theories and solutions to control Li deposition below the interface, paving the way for a promising route to build safer lithium metal batteries.

Li-rich channels as the material gene for facile lithium diffusion in halide solid electrolytes

Yang Guohao, Liang Xianhui, Zheng Shisheng, Chen Haibiao, Zhang Wentao, Li Shunning, Pan Feng

2022, 2(1): 79-86. doi: 10.1016/j.esci.2022.01.001

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Halide solid electrolytes have attracted intense research interest recently for application in all-solid-state lithium-ion batteries. Herein, we present a systematic first-principles study of the Li₃MX₆ (M: multivalent cation; X: halogen anion) halide family that unveils the link between Li-rich channels and ionic conductivity, highlighting the former as a material gene in these compounds. By screening a total of 180 halides for those with high thermodynamic stability, wide electrochemical window, low chemical reactivity, and decent Li-ion conductivity, we identify seven unexplored candidates for solid electrolytes. From these halides and another four prototype compounds, we discover that the facile Li diffusion is rooted in the availability of diffusion pathways which can avoid direct connection with M cations—that is, where the local environment is Li-rich. These findings shed light on strategies for regulating cation and anion frameworks to establish Li-rich channels in the design of high-performance inorganic solid electrolytes.

Methanol electro-oxidation to formate on iron-substituted lanthanum cobaltite perovskite oxides

Meng Fanxu, Dai Chencheng, Liu Zheng, Luo Songzhu, Ge Jingjie, Duan Yan, Chen Gao, Wei Chao, Chen Riccardo Ruixi, Wang Jiarui, Mandler Daniel, Xu Zhichuan J.

2022, 2(1): 87-94. doi: 10.1016/j.esci.2022.02.001

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Electrochemically producing formate by oxidizing methanol is a promising way to add value to methanol. Noble metal-based electrocatalysts, which have been extensively studied for the methanol oxidation reaction, can catalyze the complete oxidation of methanol to carbon dioxide, but not the mild oxidation to formate. As a result, exploring efficient and earth-abundant electrocatalysts for formate production from methanol is of interest. Herein, we present the electro-oxidation of methanol to formate, catalyzed by iron-substituted lanthanum cobaltite (LaCo₁_−xFe_xO₃). The Fe/Co ratio in the oxides greatly influences the activity and selectivity. This effect is attributed to the higher affinity of Fe and Co to the two reactants: CH₃OH and OH⁻, respectively. Because a balance between these affinities is favored, LaCo_0.5Fe_0.5O₃ shows the highest formate production rate, at 24.5 mmol h⁻¹ g_oxide⁻¹, and a relatively high Faradaic efficiency of 44.4% in a series of (LaCo₁_−xFe_xO₃) samples (x = 0.00, 0.25, 0.50, 0.75, 1.00) at 1.6 V versus a reversible hydrogen electrode.

Advanced cathode for dual-ion batteries: Waste-to-wealth reuse of spent graphite from lithium-ion batteries

Yang Jia-Lin, Zhao Xin-Xin, Li Wen-Hao, Liang Hao-Jie, Gu Zhen-Yi, Liu Yan, Du Miao, Wu Xing-Long

2022, 2(1): 95-101. doi: 10.1016/j.esci.2021.11.001

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The amount of spent lithium-ion batteries (LIBs) is constantly increasing as their popularity grows. It is important to develop a recycling method that cannot only convert large amounts of waste anode graphite into high value-added products but is also simple and environmentally friendly. In this work, spent graphite from an anode was transformed into a cathode for dual-ion batteries (DIBs) through a two-step treatment. This method enables the crystal structure and morphology of spent graphite to recover from the adverse effects of long cycling and be restored to a regular layered structure with appropriate layer spacing for anion intercalation. In addition, pyrolysis of the solid electrolyte interphase into an amorphous carbon layer prevents the electrode from degrading and improves its cycling performance. The recycled negative graphite has a high reversible capacity of 87 mAh g⁻¹ at 200 mA g⁻¹, and its rate performance when used as a cathode in DIBs is comparable to that of commercial graphite. This simple recycling idea turns spent anode graphite into a cathode material with attractive potential and superior electrochemical performance, genuinely achieving sustainable energy use. It also provides a new method for recovering exhausted batteries.

Platinum single-atom catalyst with self-adjustable valence state for large-current-density acidic water oxidation

Su Hui, Soldatov Mikhail A., Roldugin Victor, Liu Qinghua

2022, 2(1): 102-109. doi: 10.1016/j.esci.2021.12.007

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The design of active acidic oxygen evolution reaction (OER) catalysts is of paramount importance to achieve efficient large-current-density industrial hydrogen fuel production via water electrolysis. Herein, we develop a Pt-based catalyst with high electrochemical activity for the OER in acidic conditions under a large current. We achieve this by modulating the electronic structure of Pt into a high-valence, electron-accessible Pt₁^(2.4+δ)+ (δ = 0–0.7) state during the reaction. This electron-accessible Pt₁^(2.4+δ)+ single-site catalyst can effectively maintain a large OER current density of 120 mA cm⁻² for more than 12 h in 0.5 M H₂SO₄ at a low overpotential of 405 mV, and it shows a high mass activity of ∼3350 A g_metal⁻¹ at 10 mA cm⁻² current density and 232 mV overpotential. Using in situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe in an experiment that a key (∗O)–Pt₁–C₂N₂ intermediate is produced by the potential-driven structural optimization of square pyramidal Pt₁–C₂N₂ moieties; this highly favors the dissociation of H₂O over Pt₁^(2.4+δ)+ sites and prevents over-oxidation and dissolution of the active sites.

Effect of electrolyte anions on the cycle life of a polymer electrode in aqueous batteries

Zhang Ye, Zhao Lihong, Liang Yanliang, Wang Xiaojun, Yao Yan

2022, 2(1): 110-115. doi: 10.1016/j.esci.2022.01.002

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Redox polymers are a class of high-capacity, low-cost electrode materials for electrochemical energy storage, but the mechanisms governing their cycling stability are not well understood. Here we investigate the effect of anions on the longevity of a p-dopable polymer through comparing two aqueous zinc-based electrolytes. Galvanostatic cycling studies reveal the polymer has better capacity retention in the presence of triflate anions than that with sulfate anions. Based on electrode microstructural analysis and evolution profiles of the cell stacking pressure, the origin of capacity decay is ascribed to mechanical fractures induced by volume change of the polymer active materials during repeated cycling. The volume change of the polymer with the triflate anion is 61% less than that with the sulfate anion, resulting in fewer cracks in the electrodes. The difference is related to the different anion solvation structures—the triflate anion has fewer solvated water molecules compared with the sulfate anion, leading to smaller volume expansion. This work highlights that anions with low solvation degree are preferable for long-term cycling.

Crack-free single-crystalline Co-free Ni-rich LiNi_0.95Mn_0.05O₂ layered cathode

Ni Lianshan, Guo Ruiting, Fang Susu, Chen Jun, Gao Jinqiang, Mei Yu, Zhang Shu, Deng Wentao, Zou Guoqiang, Hou Hongshuai, Ji Xiaobo

2022, 2(1): 116-124. doi: 10.1016/j.esci.2022.02.006

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The rapid growth in global electric vehicles (EVs) sales has promoted the development of Co-free, Ni-rich layered cathodes for state-of-the-art high energy-density, inexpensive lithium-ion batteries (LIBs). However, progress in their commercial use has been seriously hampered by exasperating performance deterioration and safety concerns. Herein, a robust single-crystalline, Co-free, Ni-rich LiNi_0.95Mn_0.05O₂ (SC-NM95) cathode is successfully designed using a molten salt-assisted method, and it exhibits better structural stability and cycling durability than those of polycrystalline LiNi_0.95Mn_0.05O₂ (PC-NM95). Notably, the SC-NM95 cathode achieves a high discharge capacity of 218.2 mAh g⁻¹, together with a high energy density of 837.3 Wh kg⁻¹ at 0.1 C, mainly due to abundant Ni²⁺/Ni³⁺ redox. It also presents an outstanding capacity retention (84.4%) after 200 cycles at 1 C, because its integrated single-crystalline structure effectively inhibits particle microcracking and surface phase transformation. In contrast, the PC-NM95 cathode suffers from rapid capacity fading owing to the nucleation and propagation of intergranular microcracking during cycling, facilitating aggravated parasitic reactions and rock-salt phase accumulation. This work provides a fundamental strategy for designing high-performance single-crystalline, Co-free, Ni-rich cathode materials and also represents an important breakthrough in developing high-safe, low-cost, and high-energy LIBs.

2022 Vol. 2, No. 1