Methods for Characterizing Intercalation in Aqueous Zinc Ion Battery Cathodes: A Review.

Aqueous zinc ion batteries have gained research attention as a safer, economical and more environmentally friendly alternative to lithium-ion batteries. Similar to lithium batteries, intercalation processes play an important role in the charge storage behaviour of aqueous zinc ion batteries, with the pre-intercalation of guest species in the cathode being also employed as a strategy to improve battery performance. In view of this, proving hypothesized mechanisms of intercalation, as well as rigorously characterizing intercalation processes in aqueous zinc ion batteries is crucial to achieve advances in battery performance. This review aims to evaluate the range of techniques commonly used to characterize intercalation in aqueous zinc ion battery cathodes, providing a perspective on the approaches that can be utilized to rigorously understand such intercalation processes.

Challenges and Strategies in the Development of Zinc-Ion Batteries.

Although promising, the practical use of zinc-ion batteries (ZIBs) remains plagued with uncontrollable dendrite growth, parasitic side reactions, and the high intercalation energy of divalent Zn2+ ions. Hence, much work has been conducted to alleviate these issues to maximize the energy density and cyclic life of the cell. In this holistic review, the mechanisms and rationale for the stated challenges shall be summarized, followed by the corresponding strategies employed to mitigate them. Thereafter, a perspective on present research and the outlook of ZIBs would be put forth in hopes to enhance their electrochemical properties in a multipronged approach.

Pivotal role of reversible NiO6 geometric conversion in oxygen evolution.

Realizing an efficient electron transfer process in the oxygen evolution reaction by modifying the electronic states around the Fermi level is crucial in developing high-performing and robust electrocatalysts1-3. Typically, electron transfer proceeds solely through either a metal redox chemistry (an adsorbate evolution mechanism (AEM), with metal bands around the Fermi level) or an oxygen redox chemistry (a lattice oxygen oxidation mechanism (LOM), with oxygen bands around the Fermi level), without the concurrent occurrence of both metal and oxygen redox chemistries in the same electron transfer pathway1-15. Here we report an electron transfer mechanism that involves a switchable metal and oxygen redox chemistry in nickel-oxyhydroxide-based materials with light as the trigger. In contrast to the traditional AEM and LOM, the proposed light-triggered coupled oxygen evolution mechanism requires the unit cell to undergo reversible geometric conversion between octahedron (NiO6) and square planar (NiO4) to achieve electronic states (around the Fermi level) with alternative metal and oxygen characters throughout the oxygen evolution process. Utilizing this electron transfer pathway can bypass the potential limiting steps, that is, oxygen-oxygen bonding in AEM and deprotonation in LOM1-5,8. As a result, the electrocatalysts that operate through this route show superior activity compared with previously reported electrocatalysts. Thus, it is expected that the proposed light-triggered coupled oxygen evolution mechanism adds a layer of understanding to the oxygen evolution research scene.

Regulating Dendrite-Free Zn Deposition by a Self-Assembled OH-Terminated SiO2 Nanosphere Layer toward a Zn Metal Anode.

Zn dendrite growth during repeated plating and stripping of a Zn metal anode often causes short-circuiting by puncturing the separator. Herein, we propose a separator modification strategy to regulate the Zn-ion flux and achieve uniform Zn deposition through the OH-terminated SiO2 nanosphere coating. The interspaces between the uniform SiO2 nanospheres construct a network of Zn-ion transport channels, and the negatively charged hydroxyl groups on the surface of SiO2 nanospheres can electrostatically attract the Zn ions to direct the ion migration. The negative charges on SiO2 nanospheres are retained at a higher pH, which enables the SiO2 coating to consistently regulate the Zn-ion flux in the operating pH range of the Zn stripping/plating process. With a uniform Zn deposition guided by the SiO2 coating, the dendrite formation is suppressed and the side reactions are alleviated. As a result, the Zn||Zn symmetric cell achieves a cyclic life of 1000 h at both 3 and 5 mA cm-2. Meanwhile, the Zn||Cu asymmetric cell is able to maintain a Coulombic efficiency of 99.62% at 1 mA cm-2 for 2000 cycles, which outperforms many previously reported strategies.

Understanding of Oxygen Redox in the Oxygen Evolution Reaction.

The electron-transfer process during the oxygen evolution reaction (OER) often either proceeds solely via a metal redox chemistry (adsorbate evolution mechanism (AEM), with metal bands around the Fermi level) or an oxygen redox chemistry (lattice oxygen oxidation mechanism (LOM), with oxygen bands around the Fermi level). Unlike the AEM, the LOM involves oxygen redox chemistry instead of metal redox, which leads to the formation of a direct oxygen-oxygen (OO) bond. As a result, such a process is able to bypass the rate-determining step, that is, OO bonding, in AEM, which highlights the critical advantage of LOM as compared to the conventional AEM. Thus, it has been well reported that LOM-based catalysts are able to demonstrate higher OER activities as compared to AEM-based catalysts. Here, a comprehensive understanding of the oxygen redox in LOM and all documented and possible characterization techniques that can be used to identify the oxygen redox are reviewed. This review will interpret the origins of oxygen redox in the reported LOM-based electrocatalysts and the underlying science of LOM-induced surface reconstruction in transition metal oxides. Finally, perspectives on the future development of LOM electrocatalysts are also provided.

Magnetic hyperthermia induces effective and genuine immunogenic tumor cell death with respect to exogenous heating.

Immunogenic cell death (ICD) can improve the therapeutic effects of cancer immunotherapy by initiating adaptive immune responses. Unlike the exogenous hyperthermia modality in clinics, magnetic hyperthermia (MH) is characterized by an iron oxide nano-agent acting as a heating source and the effects induced by heating acting at the intracellular region. However, the immunological effects of endogenous heating generated during MH and exogenous heating, and the difference in damage-associated molecular pattern (DAMP) emissions correlating with the ICD are unclear; whether MH elicits genuine ICD remains unknown. Herein, we have identified 10 distinct DAMP correlates of ICD induced by intracellular MH, and found that only heat shock proteins 70/90 were expressed after water bath heating (exogenous hyperthermia) in human triple-negative breast cancer (TNBC) MDA-MB-231 cells, murine TNBC 4T1 cells, and surgically resected specimens of ductal breast cancer from patients. In vivo vaccination assays were performed in immunocompetent BALB/c mice. The results demonstrated that MH with endogenous heating could stimulate the genuine ICD on 4T1 cells and achieved optimal therapeutic effects on 4T1 tumors, whereas exogenous heating under the same conditions failed to elicit these effects. These findings with regard to the MH induced genuine ICD with high efficiency are critical for the development of safe and effective therapeutics to amplify the therapeutic responses of cancer immunotherapy.

Enhancement of CD8+ T-Cell-Mediated Tumor Immunotherapy via Magnetic Hyperthermia.

Magnetic hyperthermia (MHT) uses magnetic iron oxide nanoparticles (MIONs) to irradiate heat when subjected to an alternating magnetic field (AMF), which then trigger a series of biological effects to realize rapid tumor-killing effects. With the deepening in research, MHT has also shown significant potential in achieving antitumor immunity. On the other hand, immunotherapy in cancer treatment has gained increasing attention over recent years and excellent results have generally been reported. Using MHT to activate antitumor immunity and clarifying its synergistic mechanism, i. e., immunogenic cell death (ICD) and immunosuppressive tumor microenvironment (TME) reversal, can achieve a synergistically enhanced therapeutic effect on primary tumors and metastatic lesions, and this can prevent cancer recurrence and metastasis, which thus prolong survival. In this review, we discussed the role of MHT when utilized alone and combining MHT with other treatments (such as radiotherapy, photodynamic therapy, and immune checkpoint blockers) in the process of tumor immunotherapy, including antigen release, dendritic cells (DCs) maturation, and activation of CD8+ cytotoxic T lymphocytes. Finally, the challenges and future development of current MHT and immunotherapy are discussed.

Unraveling MoS2 and Transition Metal Dichalcogenides as Functional Zinc-Ion Battery Cathode: A Perspective.

The zinc-ion battery (ZIB) is considered as one of the most important alternative battery chemistries to date. However, one of the challenges in ZIB development is the limited selection of materials that can exhibit satisfactory Zn2+  storage. Transition metal dichalcogenides (TMDs) are widely investigated in energy-related applications due to their distinct physical and chemical properties. In particular, the wide interlayer spacings for these TMDs are particularly attractive as viable Zn2+  storage sites. Despite the suitability of TMDs in ZIB application, they are still not widely explored due to their limited report in this area. In this perspective review, the key challenge of TMDs, especially for MoS2 , in their utilization as ZIB cathode are discussed. The various reports on MoS2  and TMDs as ZIB cathodes are also summarized. In order to elicit reasonable Zn2+  storage ability in MoS2  and TMDs, four key modification strategies are proposed: 1) interlayer engineering, 2) defect engineering, 3) hybridization, and 4) phase engineering. These proposed modification strategies may be able to address the challenge of inadequate Zn2+  storage in MoS2  and TMDs. Finally, this review ends with a conclusion and outlook of MoS2  and TMDs in the future development of ZIB cathodes.

Electromagnetic Field-Programmed Magnetic Vortex Nanodelivery System for Efficacious Cancer Therapy.

Effective delivery of anticancer drugs into the nucleus for pharmacological action is impeded by a series of intratumoral transport barriers. Despite the significant potential of magnetic nanovehicles in electromagnetic field (EF)-activated drug delivery, modularizing a tandem magnetoresponsive activity in a one-nanoparticle system to meet different requirements at both tissue and cellular levels remain highly challenging. Herein, a strategy is described by employing sequential EF frequencies in inducing a succession of magnetoresponses in the magnetic nanovehicles that aims to realize cascaded tissue penetration and nuclear accumulation. This nanovehicle features ferrimagnetic vortex-domain iron oxide nanorings coated with a thermo-responsive polyethylenimine copolymer (PI/FVIOs). It is shown that the programmed cascading of low frequency (Lf)-EF-induced magnetophoresis and medium frequency (Mf)-EF-stimulated magneto-thermia can steer the Doxorubicin (DOX)-PI/FVIOs to the deep tissue and subsequently trigger intracellular burst release of DOX for successful nuclear entry. By programming the order of different EF frequencies, it is demonstrated that first-stage Lf-EF and subsequent Mf-EF operation enables DOX-PI/FVIOs to effectively deliver 86.2% drug into the nucleus in vivo. This nanodelivery system empowers potent antitumoral activity in various models of intractable tumors, including DOX-resistant MCF-7 breast cancer cells, triple-negative MDA-MB-231 breast cancer cells, and BxPC-3 pancreatic cancer cells with poor permeability.

Dendrite-Free Anodes Enabled by a Composite of a ZnAl Alloy with a Copper Mesh for High-Performing Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) have attracted considerable attention because of their low cost, high intrinsic safety, and high volumetric capacity. However, unexpected dendrite growth and side reactions that arise at the Zn anode can severely hinder the mass adoption of ZIBs in practical applications. Herein, we report a dendrite-free ZIB anode via the hybridization of a eutectic ZnAl alloy with a copper mesh (denoted as ZnAl@Cu-mesh). The eutectic structure of the ZnAl alloy is composed of alternating Zn blocks and Al nanoflakes. The Al nanoflakes sacrificially consume the oxygen in the electrolyte to form an Al2O3/Al shell-core structure, which in turn guides the Zn deposition process by restraining the lateral diffusion of zinc ions and hence reducing the extent of dendrite formation. This process can synergistically reduce the likelihood of Zn passivation, which allows the Zn region to remain electrochemically active for the Zn stripping/plating process. Meanwhile, a copper mesh is used as a scaffold to provide uniform electric field distribution. As a result, the symmetric ZnAl@Cu-mesh//ZnAl@Cu-mesh cell presents appreciably low polarization (30 mV at 0.5 mA cm-2) and excellent cycling stability (240 h at 0.5 mA cm-2), as compared to Zn//Zn. Based on the postmortem investigation, ZnAl@Cu-mesh is able to retain a dendrite-free morphology after cycling at 1 mA cm-2, while significant dendrite formation can be observed for Zn. More impressively, the ZnAl@Cu-mesh//V2O5 full cell is able to achieve a 95% capacity retention after 2000 cycles at 2 A g-1, whereas its counterpart assembled with Zn fails after only 750 cycles because of short-circuit. Thus, the composite alloying strategy proposed in this work may provide an appealing direction toward the future development of dendrite-free anodes for rechargeable secondary batteries.

Recent Development of Mn-based Oxides as Zinc-Ion Battery Cathode.

Manganese-based oxide is arguably one of the most well-studied cathode materials for zinc-ion battery (ZIB) due to its wide oxidation states, cost-effectiveness, and matured synthesis process. As a result, there are numerous reports that show significant strides in the progress of Mn-based oxides as ZIB cathode. However, ironically, due to the sheer number of Mn-based oxides that have been published in recent years, there remain certain contemplations with regards to the electrochemical performance of each type of Mn-based oxides and their performance comparison among various Mn polymorphs and oxidation states. Thus, to provide a clearer indication of the development of Mn-based oxides, the recent progress in Mn-based oxides as ZIB cathode was summarized systematically in this Review. More specifically, (1) the classification of Mn-based oxides based on the oxidation states (i. e., MnO2 , Mn3 O4 , Mn2 O3 , and MnO), (2) their respective polymorphs (i. e., α-MnO2 and δ-MnO2 ) as ZIB cathode, (3) the modification strategies commonly employed to enhance the performance, and (4) the effects of these modification strategies on the performance enhancement were reviewed. Lastly, perspectives and outlook of Mn-based oxides as ZIB cathode were discussed at the end of this Review.

Unravelling V6O13 Diffusion Pathways via CO2 Modification for High-Performance Zinc Ion Battery Cathode.

Vanadium-based oxide is widely investigated as a zinc ion battery (ZIB) cathode due to its ability to react reversibly with Zn2+. Despite its successful demonstration, modification with simple molecules has shown some promise in enhancing the performance of ZIBs. Thus, this presents an immense opportunity to explore simple molecules that can dramatically improve the electrochemical performance of electrodes. Thus, the effect of CO2 modification is studied in this work by decomposing oxalic acid within a hydrated V6O13 framework. Based on the collective results, the presence of CO2 drastically lowers the relative energy of Zn2+ diffusion through the pathways by forming weak electrostatic interactions between OCO2 and Zn2+. This leads to an enlarged diffusion contribution, which consequently results in enhanced stability and better rate performance. The as-synthesized CO2-V6O13 electrode delivers one of the highest specific capacities reported for vanadium-based oxides of ca. 471 mAh g-1. Furthermore, an excellent cyclic stability of 80% capacity retention after 4000 cycles at 2 A g-1 is recorded for CO2-V6O13, which suggests the importance of simple molecules in the material framework toward the enhancement of ZIB cathode performance.

Deciphering NH3 Adsorption Kinetics in Ternary Ni-Cu-Fe Oxyhydroxide toward Efficient Ammonia Oxidation Reaction.

Developing efficient catalysts for the ammonia oxidation reaction (AOR) is crucial for NH3 utilization as a large-scale energy carrier. This work reports a promising Ni-Cu-Fe-OOH material for ammonia oxidation, and density functional theory is used to investigate the AOR mechanism. It is revealed that the oxygen-atoms bonded with the metal-atom on the surface of electrode play an important role in AOR. By codoping Cu and Fe, the electron distribution around the oxygen-atom is affected, which helps to promote the occurrence of ammonia oxidation. The Ni-Cu-Fe-OOH material delivers one of the highest ammonia removal efficiency to date of ≈90% after 12 h. In addition, ≈55% of the initial ammonia is successfully degraded after 24 h in high ammonia concentration. Thus, this work reveals the mechanism of AOR that can provide new ideas to tailor more powerful and updated catalysts in the future.

Materializing efficient methanol oxidation via electron delocalization in nickel hydroxide nanoribbon.

Achieving a functional and durable non-platinum group metal-based methanol oxidation catalyst is critical for a cost-effective direct methanol fuel cell. While Ni(OH)2 has been widely studied as methanol oxidation catalyst, the initial process of oxidizing Ni(OH)2 to NiOOH requires a high potential of 1.35 V vs. RHE. Such potential would be impractical since the theoretical potential of the cathodic oxygen reduction reaction is at 1.23 V. Here we show that a four-coordinated nickel atom is able to form charge-transfer orbitals through delocalization of electrons near the Fermi energy level. As such, our previously reported periodically arranged four-six-coordinated nickel hydroxide nanoribbon structure (NR-Ni(OH)2) is able to show remarkable methanol oxidation activity with an onset potential of 0.55 V vs. RHE and suggests the operability in direct methanol fuel cell configuration. Thus, this strategy offers a gateway towards the development of high performance and durable non-platinum direct methanol fuel cell.

Binder-free V2O5/CNT paper electrode for high rate performance zinc ion battery.

Organic compounds, such as polyvinylidene fluoride (PVDF), have been widely used as a binder in battery electrode preparations. While such an approach does not have a significant impact on the performance of the batteries that utilize low valence ions, such as the Li ion battery (LIB), the diffusion of high valence ions (such as Zn2+) will be severely impaired. This will be especially pronounced if the polymeric binder contains highly electronegative atoms, such as fluorine. The high charge density ions, such as Zn2+, tend to adsorb onto these electronegative atoms, thus the mobility of these ions across the material is inevitably affected. As such, it becomes highly necessary to consider the binder-free electrode architecture when designing a high rate performing and cycling-stable zinc ion battery (ZIB) cathode. Herein, this work demonstrates an improved Zn ion battery by adopting a freestanding electrode. The obtained V2O5/CNT paper electrode delivers a specific capacity of 312 mA h g-1, while achieving a respectable 75% retention in capacity after increasing the current density by 10-fold. Furthermore, excellent cycling stability is recorded with 81% capacity retention after 2000 cycles at 1.0 A g-1. Thus, this work clearly demonstrated that the freestanding electrode is a promising approach for high valence ion batteries.

Enhancing Water Harvesting through the Cascading Effect.

Harvesting water from high humidity conditions is an attractive strategy toward strengthening water security due to its cost-effective and zero-energy mechanism. To facilitate this process, bio-inspired microstructures with heightened water accumulating ability are typically affixed onto atmospheric water harvesters. However, because of this surface morphology type harvester design, there is an inherent partition of regions with different water accumulating abilities: the active water harvesting region (AWHR) and passive water harvesting region (PWHR). Most of the water harvested by such water harvesters is usually attributed to the AWHR, while a large amount of uncollected water is present in the PWHR as numerous small water droplets that are prone to re-evaporation. This lack of PWHR utilization may be considered as the Achilles' heel toward optimal water harvesting. Hence, in this work, a cascading effect was proposed with a microstructure design to induce water harvesting from both AWHR and PWHR. The "clearing" of PWHR columns was demonstrated via a cascading effect, contributing to ca. 3 times more water harvested as compared to the unmodified water harvester. The successful demonstration of this cascading effect highlights the necessity of considering PWHR in the future water harvester designs so as to achieve efficient water harvesting.

Bi2S3 for Aqueous Zn Ion Battery with Enhanced Cycle Stability.

Aqueous Zn ion batteries (ZIBs) are promising in energy storage due to the low cost, high safety, and material abundance. The development of metal oxides as the cathode for ZIBs is limited by the strong electrostatic forces between O2- and Zn2+ which leads to poor cyclic stability. Herein, Bi2S3 is proposed as a promising cathode material for rechargeable aqueous ZIBs. Improved cyclic stability and fast diffusion of Zn2+ is observed. Also, the layered structure of Bi2S3 with the weak van der Waals interaction between layers offers paths for diffusion and occupancy of Zn2+. As a result, the Zn/Bi2S3 battery delivers high capacity of 161 mAh g-1 at 0.2 A g-1 and good cycling stability up to 100 cycles with ca. 100% retention. The battery also demonstrates good cyclic performance of ca. 80.3% over 2000 cycles at 1 A g-1. The storage mechanism in the Bi2S3 cathode is related to the reversible Zn ion intercalation/extraction reactions and the capacitive contribution. This work indicates that Bi2S3 shows great potential as the cathode of ZIBs with good performance and stability.

o-Benzenediol-Functionalized Carbon Nanosheets as Low Self-Discharge Aqueous Supercapacitors.

Widening the voltage window is often proposed as a way to increase the energy density of aqueous supercapacitors. However, attempting to operate beyond the aqueous supercapacitor stability region can undermine the supercapacitor reliability due to pronounced electrolyte decomposition, which can lead to a significant self-discharge process. To minimize this challenge, charge injection by grafting o-benzenediol onto the carbon electrode is proposed through a simple electrochemical cycling technique. Due to charge injection from o-benzenediol into the carbon electrode, the equilibrium potential of the individual electrode can be reduced. In addition, due to its small molecular size, charge distribution, which is commonly faced by bulk pseudocapacitive materials, is also avoided. The assembled supercapacitor based on the o-benzenediol-grafted carbon demonstrated a maximum energy density of 24 Wh kg-1 and a maximum power density of 69 kW kg-1 , with a retention of 89 % after 10 000 cycles at 10 A g-1 . A low self-discharge of about 4 h was recorded; this could be attributed to the low driving force arising from the lower equilibrium potential. Thus, the proposed technique may provide insight towards the tuning of the equilibrium potential to attain reliable, high-performing supercapacitors with a low self-discharge process.

Low Li+ Insertion Barrier Carbon for High Energy Efficient Lithium-Ion Capacitor.

Lithium-ion capacitor (LIC) is an attractive energy-storage device (ESD) that promises high energy density at moderate power density. However, the key challenge in its design is the low energy efficient negative electrode, which barred the realization of such research system in fulfilling the current ESD technological inadequacy due to its poor overall energy efficiency. Large voltage hysteresis is the main issue behind high energy density alloying/conversion-type materials, which reduces the electrode energy efficiency. Insertion-type material though averted in most research due to the low capacity remains to be highly favorable in commercial application due to its lower voltage hysteresis. To further reduce voltage hysteresis and increase capacity, amorphous carbon with wider interlayer spacing has been demonstrated in the simulation result to significantly reduce Li+ insertion barrier. Hence, by employing such amorphous carbon, together with disordered carbon positive electrode, a high energy efficient LIC with round-trip energy efficiency of 84.3% with a maximum energy density of 133 Wh kg-1 at low power density of 210 W kg-1 can be achieved.

High Lithium Insertion Voltage Single-Crystal H2 Ti12 O25 Nanorods as a High-Capacity and High-Rate Lithium-Ion Battery Anode Material.

H2 Ti12 O25 holds great promise as a high-voltage anode material for advanced lithium-ion battery applications. To enhance its electrochemical performance, control of the crystal orientation and morphology is an effective way to cope with slow Li+ -ion diffusion inside H2 Ti12 O25 with severe anisotropy. In this report, Na2 Ti6 O13 nanorods, prepared from Na2 CO3 and anatase TiO2 in molten NaCl medium, were used as a precursor in the synthesis of long single-crystal H2 Ti12 O25 nanorods with reactive facets. The as-prepared H2 Ti12 O25 nanorods with a diameter of 100-200 nm showed higher charge (extraction) specific capacity and better rate performance than previously reported systems. The reversible capacity of H2 Ti12 O25 was 219.8 mAh g-1 at 1C after 100 cycles, 172.1 mAh g-1 at 10C, and 144.4 mAh g-1 at 20C after 200 cycles; these values are higher than those of H2 Ti12 O25 prepared by the conventional soft-chemical method. Moreover, the as-prepared H2 Ti12 O25 nanorods exhibited superior cycle stability with more than 94 % retention of capacity with nearly 100 % coulombic efficiency after 100 cycles at 1C. On the basis of the above results, long single-crystal H2 Ti12 O25 nanorods synthesized in molten NaCl with outstanding electrochemical characteristics hold a significant amount of promise for hybrid electric vehicles and energy-storage systems.