Multivalent Metal Research Articles

A flexible glucose biosensor modified by reduced-swelling and conductive zwitterionic hydrogel enzyme membrane.

This paper reports a flexible glucose biosensor which is modified by a reduced-swelling and conductive zwitterionic hydrogel enzyme membrane that contains two forms of chemical cross-links. One chemical cross-linking is induced by thermal initiators and forms the basal network of the hydrogel. Another cross-linking is achieved by the coordination interactions between the multivalent metal ion Al3+ and anionic group -COO- of zwitterionic poly-carboxy betaine (pCBMA), which significantly increase the cross-linking density of the zwitterionic hydrogel, improving the reduced-swelling property and reducing the pore size. The better reduced-swelling property and reduced diameters of pores within the zwitterionic hydrogel make less glucose oxidase (GOx) leakage, thus significantly improving the enzyme membrane's service life. By introducing the Al3+ and Cl-, the conductivity of the zwitterionic hydrogel is enhanced approximately 10.4-fold. According to the enhanced conductivity, the reduced-swelling property, and the high GOx loading capacity of the zwitterionic hydrogel, the sensitivity of the biosensor with GOx/pCBMA-Al3+ is significantly improved by 5 times and has a long service life. Finally, the proposed GOx/pCBMA-Al3+ biosensor was applied in non-invasive blood glucose detection on the human body, verifying the capability in practice.

Unexpected Self-Assembly of Nanographene Oxide Membranes upon Electron Beam Irradiation for Ultrafast Ion Sieving.

Nanographene oxide (nGO) flakes-graphene oxide with a lateral size of ≈100nm or less-hold great promise for superior flux and energy-efficient nanofiltration membranes for desalination and precise ionic sieving owing to their unique high-density water channels with less tortuousness. However, their potential usage is currently limited by several challenges, including the tricky self-assembly of nano-sized flakes on substrates with micron-sized pores, severe swelling in aqueous solutions, and mechanical instability. Herein, the successful fabrication of a robust membrane stacked with nGO flakes on a substrate with a pore size of 0.22µm by vacuum filtration is reported. This membrane achieved an unprecedented water permeance above 819.1 LMH bar-1, with a high rejection rate of 99.7% for multivalent metal ions. The nGO flakes prepared using an electron beam irradiation method, have uniquely pure hydroxyl groups and abundant aromatic regions. The calculations revealed the strong hydrogen bonds between two nGO flakes, which arise from hydroxyl groups, coupled with hydrophobic aromatic regions, greatly enhance the stability of stacked flakes in aqueous solutions and increase their effective lateral size. The research presents a simple yet effective approach toward the fabrication of advanced 2D nanographene membranes with superior performance for ion sieving applications.

Hierarchical nanoflowers of Bi/Fe-based selenide as a bifunctional electrocatalyst for alkaline water electrolysis

The current study presents a freestanding bifunctional electrocatalyst comprising hierarchically assembled Bi/Fe-based selenide with a nanoflower-like morphology on Ni foam for water electrolysis application. The impact of systematically adding Fe ions to Bi2Se3 on the phase and morphology is elaborately discussed. It is shown that tuning the Bi/Fe molar ratio governs the phase, electronic bandgap, and morphology, driven by the evolution of hetero-interfacial chemistry. The existence of multivalent metal ions, lattice defects, and an extended surface area remarkably improves the electrocatalytic activity. The optimized nanoflower-like composite electrode (1Bi1Fe-Se@NF) exhibits robust electrocatalytic efficacy with extremely low overpotentials of ∼53 mV and ∼230 mV at 10 mA cm−2 for hydrogen and oxygen evolution reactions, respectively. The symmetrical alkaline electrolyser, utilizing 1Bi1Fe-Se@NF electrodes (+,−), operates at a cell voltage of ∼1.52 V at 10 mA cm−2, lower than the device equipped with commercial Pt/C@NF (-) and RuO2@NF (+) (∼1.57 V). Even after 100 h of operation at 50 mA cm−2, the symmetrical cell maintains a stable voltage, highlighting the outstanding bifunctional catalytic activities of noble metal-free 1Bi1Fe-Se@NF for overall water electrolysis.

Bimetallic phosphidethe nanoparticles as photo-enhanced nanozymes for synergistic cancer immunotherapy

<p class="MsoNormal" style="margin-top: 12pt; text-align: justify;"><span lang="EN-US" style="font-family: 'times new roman', times, serif; font-size: 14pt;">Nanozyme with biomimetic enzyme activity has the advantages of good catalytic performance, high stability, and is not easily affected by temperature. However, the application of tumor microenvironment (TME) in the tumor is limited due to its low catalytic activity. Herein, a multifunctional nanozyme based on CuCoP with multivalent metal ions (Cu+/Cu2+ and Co2+/ Co3+) provides an innovative strategy for constructing acid-responsive cancer therapy. CuCoP has excellent photothermal properties (photothermal conversion efficiency of 66.9%) as well as glutathione (GSH) peroxidase activity and high photo-enhanced peroxidase-like (POD) enzyme activity in weak acid TME. CuCoP can consume the overexpressed GSH, thus alleviating the antioxidant capacity of the tumor, and reduces Cu2+/ Co3+ to Cu+/ Co 2+. Subsequently, the generated Cu+/Co2+ will react with endogenous H2O2 to generate cytotoxic hydroxyl radical (•OH), which have high catalytic efficiency in weakly acidic TME. Crucially, the synergistic effect of PTT and the cascade reaction of bimetallic atoms with GSH and H2O2 can effectively reduce antioxidant capacity, inhibit tumors and trigger effective immune cell death (ICD) process, which caused a strong immune response and inhibit tumor recurrence and metastasis. As a novel bimetallic sulfide nanoenzyme triggered by TME, CuCoP has great research value in cancer therapy.</span></p>

Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly-Efficient Rechargeable Batteries.

Alkali metals (Li, Na, and K) and multivalent metals (Zn, Mg, Ca, and Al) have become star anodes for developing high-energy-density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid-state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.

Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly‐Efficient Rechargeable Batteries

AbstractAlkali metals (e.g. Li, Na, and K) and multivalent metals (e.g. Zn, Mg, Ca, and Al) have become star anodes for developing high‐energy‐density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid‐state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.

Direct crystallization of deep eutectic solvent into solid-state electrolyte for magnesium metal batteries

Solid-state magnesium rechargeable battery is a promising post-Li battery technology due to the high abundance of Mg element, the competitive volumetric capacity and enhanced safety of Mg metal anodes. However, current solid electrolyte formulas failed to realize considerably reversible Mg anodes caused by the passive layer formed on their surface. Herein, a novel Mg2+-conducting solid-state electrolyte (MCE) is proposed by directly crystalizing deep eutectic solvents composing of Mg(TFSI)2 and urea at room temperature. Experimental and simulation results indicate the formation of anion-rich groups in urea-Mg2+ coordination structures, facilitating rapid Mg2+ migration in the MCE. When applied in the Mg//Mg symmetric cells, the new electrolyte derives a macroporous and fluoride-rich organic/inorganic hybrid interface layer on the Mg metal surface. The unique interfacial structure endows the interface layer with Mg2+ diffusion capability for reversible Mg metal stripping/plating. The practical feasibility of MCE is finally demonstrated by cycling in Mg//V2O5 full cells with competitive electrochemical performance. This work illustrates a new concept of crystalizing deep eutectic solvents into solid-state electrolytes at room temperature for multivalent metal batteries.

A Unified Charge Storage Mechanism to Rationalize the Electrochemical Behavior of Quinone-Based Organic Electrodes in Aqueous Rechargeable Batteries.

Due to their eco-sustainability and versatility, organic electrodes are promising candidates for large-scale energy storage in rechargeable aqueous batteries. This is notably the case of aqueous hybrid batteries that pair the low voltage of a zinc anode with the high voltage of a quinone-based (or analogue of quinone-based) organic cathode. However, the mechanisms governing their charge-discharge cycles remain poorly understood and are even a matter of debate and controversy. No consensus exists on the charge carrier in mild aqueous electrolytes, especially when working in an electrolyte containing a multivalent metal cation such as Zn2+. In this study, we comprehensively investigate the electrochemical reactivity of two model quinones, chloranil, and duroquinone, either diluted in solution or incorporated into carbon-based composite electrodes. We demonstrate that a common nine-member square scheme proton-coupled electron transfer mechanism allows us to fully describe and rationalize their electrochemical behavior in relation to the pH and chemical composition of the aqueous electrolyte. Additionally, we highlight the crucial role played by the pKas associated with the reduced states of quinones in determining the nature of the charge carrier that compensates for the negative charges reversibly injected in the active material. Finally, contrary to the widely reported findings for Zn/organic batteries, we unequivocally establish that the predominant solid-state charge carriers in Zn2+-based mild aqueous electrolytes are not multivalent Zn2+ cations but rather protons supplied by the weakly acidic hexaaqua metal ions (i.e., [Zn(H2O)6]2+]).

Effects of pH-varying thermal modification on sewage sludge: A focus on releasing nitrogen- and phosphorus-containing substances

Sewage sludge is promising for the recovery and utilisation of nutrient components, but its complex nature hinders the release of these components. The combination of pH and thermal modifications shows promise for the release of nutrient components from sludge. However, comprehensive studies on the full spectrum of pH levels and corresponding mechanisms of pH-varying thermal modification are lacking. In this study, the main nutrient components, physicochemical properties, molecular structure, and noncovalent interactions of sludge were comprehensively investigated through pH-varying thermal modification (within a pH range of 2.0 to 12.0 under the same thermal condition). The experimental results showed that the release of main organics, particularly nitrogen (N)-containing organics, was well-fitted, with a tick-like function (R2: 0.74–0.96). The thermal protons exhibited a notable accumulative mutagenic effect on the N-containing organics release, while the thermal hydroxyl ions had a more direct effect, as revealed by the changes in multivalent metals and molecular structures with the protonation–deprotonation of carboxyl groups. The driving force for the release of N-containing organics was identified as the fluctuation of electrostatic interactions at the solid–liquid interface of the sludge. However, the release of phosphorus (P)-containing substances exhibited a contrasting response to that of N-containing substances with varying pH, likely because the reaction sites of thermal protons and thermal hydroxyl ions for P-containing substances were different. Moreover, high concentrations of thermal protons and hydroxyl ions collapsed the Lifshitz–van der Waals interactions of sludge, resulting in a decrease in viscoelasticity and binding strength. These propositions were further confirmed through statistical analyses of the main indicators of the main nutrient components, physicochemical properties, and noncovalent interactions of sludge. These findings can provide a basis for optimising characteristic-specific methods to recovery nutrient components (N/P) from sludge.

Improved Mechanical Strength without Sacrificing Li-Ion Transport in Polymer Electrolytes.

Next-generation batteries demand solid polymer electrolytes (SPEs) with rapid ion transport and robust mechanical properties. However, many SPEs with liquid-like Li+ transport mechanisms suffer a fundamental trade-off between conductivity and strength. Dynamic polymer networks can improve bulk mechanics with minimal impact to segmental relaxation or ionic conductivity. This study demonstrates a system where a single polymer-bound ligand simultaneously dissociates Li+ and forms long-lived Ni2+ networks. The polymer comprises an ethylene oxide backbone and imidazole (Im) ligands, blended with Li+ and Ni2+ salts. Ni2+-Im dynamic cross-links result in the formation of a rubbery plateau resulting in, consequently, storage modulus improvement by a factor of 133× with the introduction of Ni2+ at rNi = 0.08, from 0.014 to 1.907 MPa. Even with Ni2+ loading, the high Li+ conductivity of 3.7 × 10-6 S/cm is retained at 90 °C. This work demonstrates that decoupling of ion transport and bulk mechanics can be readily achieved by the addition of multivalent metal cations to polymers with chelating ligands.

Multivalent-Ion versus Proton Insertion into Nanostructured Electrochromic WO3 from Mild Aqueous Electrolytes.

Mild aqueous electrolytes containing multivalent metal salts are currently scrutinized for the development of ecosustainable energy-related devices. However, the role of soluble multivalent metal ions in the electrochemical reactivity of transition metal oxides is a matter of debate, especially when they are performed in protic aqueous electrolytes. Here, we have compared, by means of (spectro)electrochemistry, the reversible electrochromic reduction of transparent nanostructured γ-WO3 thin films in mild aqueous electrolytes of various chemical composition and pH. This study reveals that reversible proton insertion is the only charge storage mechanism over a large pH range and that it is effective for aqueous electrolytes prepared from either organic (such as acetic acid) or inorganic (such as solvated multivalent cations) Bro̷nsted acids. By refuting charge storage mechanisms relying on the reversible insertion of multivalent metal ions, notably in aqueous electrolytes based on Al3+ ions or a mixture of Al3+ and Zn2+ ions, these fundamental results pave the way for the rational development of electrolytes and active materials for a range of aqueous-based devices, such as the emerging concept of an energy-saving smart window, which we also address in this study.

Drivers of rare earth elements (REEs) and radionuclides in changing subarctic (Nunavik, Canada) surface waters near a mining project

The emergence of mining projects for rare earth elements (REEs) in response to rising global demand and geopolitical factors introduces environmental concerns, such as the suspected release of anthropogenic REEs to aquatic systems and the coexistence of radionuclides (U, Th). Northern regions confront heightened challenges from limited research and accelerated climate change. Drivers of REEs in surface waters (including George and Koroc rivers, their tributaries, and thermokarst lakes) were studied (2017–2023) in subarctic Canada within a climate transition zone, near a prospective REE mine. Dissolved REEs (<0.45 μm) correlated positively with Al, Fe, Th, U, Cl– and DOC. A novel relationship with water temperature demonstrated an approximate 10-fold decrease in REE concentrations over the environmental gradient (2–20 ℃), suggesting complex implications for REE speciation under climate pressures. Optical analyses further predicted REEs were mobilized by humic-rich, terrestrial DOC, with correlations presenting a possible co-transport with Al, Fe and Th. Relationships for redox-sensitive Ce anomalies (Ce/Ce* = 0.18–1.2) with multi-valent trace metals (Al, Fe, Ti) and DOC were suggestive of a preferential adsorption of Ce by inorganic colloids in low-DOC systems. Findings emphasized the potential for changes in REE geochemistry with ongoing northern surface warming and vegetation shifts.

Robust Room Temperature Thermoelectric Performance of Mg3(Sb, Bi)2‐Based Alloys via Multivalent Mn Doping

Abstractn‐type Mg3(Sb, Bi)2 has excellent room temperature thermoelectric performance, which is, however, severely restricted by the negatively charged Mg vacancies that significantly deteriorate the carrier mobility. Herein, by manipulating the threshold solubility and defect formation energy of Mn, multivalent Mn is selectively introduced that synergistically promotes the carrier conduction according to different Mg chemical potentials; In Mg‐rich areas, interstitial Mn dominates which effectively reduces the migration and accumulation of Mg vacancies, while in Mg poor areas, interstitial Mn switches to substitutional sites that directly compensate for the negative charge. All the Mn centers possess Jahn–Teller inactive positions, leading to an ultra‐stable room temperature thermoelectric performance with a leading ZT up to 0.97. This work reveals the critical effect of multivalent and multifunctional transition metal incorporation in Mg3(Sb, Bi)2‐based alloys toward high room‐temperature thermoelectric performance.

High-Valence W6+ Ions Boost Cr2+ Activity in CrWO4 for Ideal Water Oxidation.

Electrocatalytic activity of multi-valence metal oxides for oxygen evolution reaction (OER) arises from various interactions among the constituent metal elements. Although the high-valence metal ions attract recent attentions due to the interactions with their neighboring 3d transition metal catalytic center, atomic-scale explanations for the catalytic efficiencies are still lacking. Here, by employing density functional theory predictions and experimental verifications, unprecedented electronic isolation of the catalytic 3d center (M2+) induced by the surrounding high-valence ions such as W6+ is discovered in multivalent oxides MWO4 (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn). Due to W6+'s extremely high oxidation state with the minimum electron occupations (d0), the surrounding W6+ blocks electron transfer toward the catalytic M2+ ions and completely isolates the ions electronically. Now, the isolated M2+ ions solely perform OER without any assistant electron flow from the adjacent metal ions, and thus the original strong binding energies of Cr with OER intermediates are effectively moderated. Through exploiting "electron isolators" such as W6+ surrounding the catalytic ion, exploring can be done beyond the conventional materials such as Ni- or Co-oxides into new candidate groups such as Cr and Mn on the left side of the periodic table for ideal OER.

Photochemically Inert Broad-Spectrum Sunscreen by Metal-Phenolic Network Coatings of Titanium Oxide Nanoparticles.

Titanium dioxide (TiO2) nanoparticles are extensively used as a sunscreen filter due to their long-active ultraviolet (UV)-blocking performance. However, their practical use is being challenged by high photochemical activities and limited absorption spectrum. Current solutions include the coating of TiO2 with synthetic polymers and formulating a sunscreen product with additional organic UV filters. Unfortunately, these approaches are no longer considered effective because of recent environmental and public health issues. Herein, TiO2-metal-phenolic network hybrid nanoparticles (TiO2-MPN NPs) are developed as the sole active ingredient for sunscreen products through photochemical suppression and absorption spectrum widening. The MPNs are generated by the complexation of tannic acid with multivalent metal ions, forming a robust coating shell. The TiO2-MPN hybridization extends the absorption region to the high-energy-visible (HEV) light range via a new ligand-to-metal charge transfer photoexcitation pathway, boosting both the sun protection factor and ultraviolet-A protection factor about 4-fold. The TiO2-MPN NPs suppressed the photoinduced reactive oxygen species by 99.9% for 6 h under simulated solar irradiation. Accordingly, they substantially alleviated UV- and HEV-induced cytotoxicity of fibroblasts. This work outlines a new tactic for the eco-friendly and biocompatible design of sunscreen agents by selectively inhibiting the photocatalytic activities of semiconductor nanoparticles while broadening their optical spectrum.

Defect-decorated Cu2MoS4 as a new efficient hydrogen evolution cocatalyst: Rich active sites, rapid charge transfer and optimized hydrogen adsorption

Herein, a new defect-decorated Cu2MoS4 cocatalyst was successfully synthesized using a sacrificial-template method. Detailed characterizations confirmed the presence of multivalent metal ions (Cu2+/Cu+, Mo6+/Mo4+) and abundant sulfur vacancies. To assess its cocatalytic performance, Cu2MoS4/Cd0.5Zn0.5S Schottky heterojunction was constructed and achieved a hydrogen production rate of 11.83 mmol∙g−1∙h−1, which is 6.33 and 2.03 times higher than pristine Cd0.5Zn0.5S and MoS2/Cd0.5Zn0.5S, respectively. The superior photocatalytic activity is attributed to multiple factors. Sulfur vacancies regulate the charge density of neighboring atoms and induce production of more coordination-unsaturated atoms as active sites to accelerate hydrogen generation. Meanwhile, the high conductivity of Cu2MoS4, Schottky heterojunction, and redox couples could synergistically boost charge transfer and separation efficiency. Theoretical calculations further illustrated the key role of sulfur vacancies in optimizing H2-evolution kinetics, which reduced the hydrogen adsorption free energy of in-plane S atoms. This work demonstrates that Cu2MoS4 has significant potential as an efficient cocatalyst material, enhancing the photocatalytic performance of metal sulfides.

Anionic species from multivalent metal salts are differentially retained during aqueous ionic gelation of sodium alginate and could fine-tune the hydrogel properties

The role of anionic counterions of divalent metal salts in alginate gelation and hydrogel properties has been thoroughly investigated. Three anions were selected from the Hofmeister series, namely sulphate, acetate and chloride, paired in all permutations and combinations with divalent metal cations like calcium, zinc and copper. Spectroscopic analysis revealed the presence of anions and their interaction with the respective metal cations in the hydrogel. The data showed that the gelation time and other hydrogel properties were largely controlled by cations. However, subtle yet significant variations in viscoelasticity, water uptake, drug release and cytocompatibility properties were anion dependent in each cationic group. Computational modelling based study showed that metal-anion-alginate configurations were energetically more stable than the metal-alginate models. The in vitro and in silico studies concluded that acetate anions preceded chlorides in the drug release, swelling and cytocompatibility fronts, followed by sulphate anions in each cationic group. Overall, the data confirmed that anions are an integral part of the metal-alginate complex. Furthermore, anions offer a novel option to further fine-tune the properties of alginate hydrogels for myriads of applications. In addition, full exploration of this novel avenue would enhance the usability of alginate polymers in the pharmaceutical, environmental, biomedical and food industries.

Conductive and capacitive network for enriching the exoelectrogens and enhancing the extracellular electron transfer in microbial fuel cells

Although lots of nanomaterials modified anodes have been reported to improve the bacterial attachment and extracellular electron transfer (EET) in microbial fuel cells (MFCs), the lack of a three dimensional (3D) conductive and capacitive network severely limited MFCs performance. In this work, 3D conductive networks derived from mucor mycelia were grown on carbon cloth (CC), and capacitive FeMn phosphides/oxides were further anchored on these 3D networks by electrochemical deposition (denoted as FeMn/CMM@CC) to simultaneously address the above challenges. As a result, the multivalent metal active sites were evenly distributed on 3D conductive network, which favored the enrichment of exoelectrogens, mass transport and EET. Consequently, the as-prepared FeMn/CMM@CC anode displayed accumulated charge of 131.4C/m2, higher than bare CC. Meanwhile, FeMn/CMM@CC anode substantially promoted flavin excretion and the amounts of nano conduits. The abundance of Geobacter was 63 % on bare CC, and greatly increased to 83 % on FeMn/CMM@CC. MFCs equipped by FeMn/CMM@CC anode presented the power density of 3.06 W/m2 and coulombic efficiency (29.9 %), evidently higher than bare CC (1.29 W/m2, 7.3 %), and the daily chemical oxygen demand (COD) removal amount also increased to 92.6 mg/L/d. This work developed a facile method to optimize the abiotic-biotic interface by introducing 3D conductive and capacitive network, which was proved to be a promising strategy to modify macro-porous electrodes.

Highly Selective and Reversible Detection of Simulated Breath Hydrogen Sulfide Using Fe-Doped CuO Hollow Spheres: Enhanced Surface Redox Reaction by Multi-Valent Catalysts.

The precise and reversible detection of hydrogen sulfide (H2S) at high humidity condition, a malodorous and harmful volatile sulfur compound, is essential for the self-assessment of oral diseases, halitosis, and asthma. However, the selective and reversible detection of trace concentrations of H2S (≈0.1ppm) in high humidity conditions (exhaled breath) is challenging because of irreversible H2S adsorption/desorption at the surface of chemiresistors. The study reports the synthesis of Fe-doped CuO hollow spheres as H2S gas-sensing materials via spray pyrolysis. 4 at.% of Fe-doped CuO hollow spheres exhibit high selectivity (response ratio ≥ 34.4) over interference gas (ethanol, 1ppm) and reversible sensing characteristics (100% recovery) to 0.1ppm of H2S under high humidity (relative humidity 80%) at 175 °C. The effect of multi-valent transition metal ion doping into CuO on sensor reversibility is confirmed through the enhancement of recovery kinetics by doping 4 at.% of Ti- or Nb ions into CuO sensors. Mechanistic detailsof these excellent H2S sensing characteristics are also investigated by analyzing the redox reactions and the catalytic activity change of the Fe-doped CuO sensing materials. The selective and reversible detection of H2S using the Fe-doped CuO sensor suggested in this work opens a new possibility for halitosis self-monitoring.

Zinc ion storage abilities of Mo3WOx nano-ceramic under extreme-cold environments

It is imperative to develop new electrode materials for aqueous multivalent metal ion batteries with electrochemistry abilities at extreme-low temperatures due to the possible extreme-cold operating conditions of batteries in the present or the future. Herein, as a proof-of-concept experiment, a new orthorhombic molybdenum-tungsten oxide (Mo3WOx) is synthesized by a wet-chemical method and tested as anode material for aqueous zinc ion batteries at extreme-cold temperatures (−40, −60 and −75 °C) for the first time. Two anti-freezing electrolytes are selected to examine the related half-cell performances, and 7.5 m ZnCl2 aqueous solution is more suitable for Mo3WOx half-cells than 2 m Zn(BF4)2 aqueous solution. At −40 °C, Mo3WOx exhibits reversible charge capacity of 104.1 mAh g−1 at 100 mA g−1 and the charge capacity can still maintain 82.3 mAh g−1 after 100 cycles; and under further test at 5000 mA g−1, Mo3WOx shows a high initial charge capacity of 42.5 mAh g−1 together with a capacity retention ratio of 81.6 % after 10,000 cycles. It is worth highlighting that the high capacities of Mo3WOx delivered at −40 °C are even comparable with the capacities of some “new-type” anode materials for aqueous zinc ion batteries exhibited at ambient temperature. At colder temperatures of −60 and −75 °C, the as-prepared compound still owns certain zinc ion storage abilities, especially high discharge/charge capacities of 48.9/48.7 mAh g−1 can be still achieved in the 100th cycle at −75 °C (100 mA g−1). Furthermore, a full-cell with operational capability at −40 °C is also built here, and it can exhibit discharge capacity of 66.1 mAh g−1 (coulombic efficiency of 99.7 %) in the 3rd cycle and discharge capacity of 48.2 mAh g−1 (coulombic efficiency of 99.7 %) in the 50th cycle.