We report the fabrication, structure, and heteropolyanion structure effect of polyoxometalate (POM)/ionic liquid (IL) supramolecular gels. These supramolecular gels exhibit ordered structures, as a result of their excellent reversible self-assembly, and they show various physicochemical properties, determined by the heteropolyanion structure effect of POM anions. Specifically, the formation of POM/IL supramolecular gels results in a highly ordered layer-shape structure, which has been calculated using X-ray powder diffraction patterns and proven by transmission electron microscopy images for the first time. When these POM/IL supramolecular gels are heated, they become viscous liquid sols, with melting isotropic drops and even flowerlike structures on microscopic scales, while it undergoes a reversible gel–sol phase transformation from gel to sol. The heteropolyanion structure effect in these two IL gels, [TBTP]5PW10V2O40 and [TBTP]8P2W16V2O62, on their physicochemical properties is demonstrated. The POM structures have a strong structure effect on the physicochemical properties. As the size of heteropolyanions increases, there is a significant improvement in the conductivity, thermal performance, and oxidizability, with a lower phase inversion temperature, which means that the Dawson-type compound, [TBTP]8P2W16V2O62, has a higher conductivity, lower melting point, stronger oxidizability, and better thermal performance than the Keggin-type compound, [TBTP]5PW10V2O40, under the same conditions.

Two new polyoxometalate-based ionic liquids, [TBTP]4PW11VO40 and [TBTP]4PMo11VO40, composed of ternary Keggin polyoxometalates and tetraalkylphosphonium cation have been synthesized and characterized. Their layered structures, thermal stability, conductive performance and electrochemical properties are investigated. The two compounds possess layered structures, and both can exhibit a reversible phase transformation process below 100 °C. Their ionic conductivities are dependent on temperature and follow the Arrhenius behavior. Cyclic voltammetry is carried out to study their electrochemical properties in organic solution. The potential values of redox waves indicate that the oxidability of [TBTP]4PMo11VO40 is greater than that of [TBTP]4PW11VO40.

The substitution effect in a series of POM-type reversible gel-liquid phase transformation ionic liquid compounds, [MIMPS]8P2W16V2O62, [MIMPS]6H2P2W16V2O62 and [MIMPS]4H4P2W16V2O62, has been investigated. Interestingly, there is an obvious substitution effect on the physicochemical properties of these compounds. When protons are substituted in place of ammonium, both the conductivity and the thermo-stability of the compounds can be increased a lot, and more protons can enhance this tendency.

A series of temperature-dependent gel-type ionic liquid compounds have been synthesized from 1-(3-sulfonic group) propyl-3-methyl imidazolium (abbreviated as MIMPS) and three vanadium-substituted heteropoly acids H5SiW11VO40, H5SiMo11VO40 and H7SiW9V3O40. The designed and synthesized gel-type polyoxometalate ionic liquids (POM-ILs) have demonstrated a tendency to exhibit a layered structure. Moreover, they can undergo a phase transformation from a viscous gel-state to a liquid-state below 100 °C, and ionic conductivity up to 10−3 S cm−1 was observed at 120 °C. Cyclic voltammetry was carried out to study their electrochemical properties in organic solutions, and it was found that the oxidizability of the three POM-ILs decreases in the order: [MIMPS]7SiW9V3O40 > [MIMPS]5SiMo11VO40 > [MIMPS]5SiW11VO40. This result indicates that the redox behavior can be tuned by changing the chemical composition of the heteropolyanions.

Two new high-proton conductors, indium-substituted ternary heteropoly acids with Keggin structures, H4[In(H2O)PW11O39]·11H2O and H5[In(H2O)SiW11O39]·8H2O, have been synthesized and characterized using elemental analysis, IR, UV, XRD and TG-DTA. Their proton conductivities were measured using electrochemical impedance spectroscopy (EIS), and the results indicate that H4[In(H2O)PW11O39]·11H2O and H5[In(H2O)SiW11O39]·8H2O are solid high-proton conductors with a conductivity of 2.60 × 10−4 S cm−1 and 5.25 × 10−4 S cm−1, respectively, at 18 °C and 80% relative humidity (RH). Their activation energies are 33.40 kJ mol−1 and 28.52 kJ mol−1, which suggests that the mechanism of proton conduction is the vehicle mechanism. In the range of the measured temperatures, the conductivity of both heteropoly acids increases with higher temperatures.

•A Dawson structure heteropoly acid, H8P2W16V2O62·20H2O, has been synthesized.•Its conductivity is 1.89×10−2 S cm−1 at 18 °C, 80% relative humidity.•Its conductive mechanism is Vehicle mechanism.A Dawson structure vanadium-substituted heteropoly acid, H8P2W16V2O62·20H2O, has been synthesized and characterized by elemental analysis, IR, UV and XRD. Its proton conductivity was measured by the electrochemical impedance spectrum (EIS), and the result indicates that H8P2W16V2O62·20H2O is a kind of solid high-proton conductor with conductivity of 1.89×10−2 S cm−1 at 18 °C, and 80% relative humidity (RH). Its activation energy is 31.91 kJ mol−1, suggesting that Vehicle mechanism of proton conduction. In the range of measured temperature, the conductivity of the heteropoly acid increases with higher temperature.

•A novel SPEEK/PW11V/rGO hybrid film was prepared.•It shows a good proton conductivity of 2.22 × 10− 2 S cm− 1 at ambient condition.•It is a new solid high proton conductor.•Conduction mechanism has been investigated.A SPEEK/PW11V/rGO hybrid film was prepared by a simple method through sulfonated polyether ether ketone (SPEEK), tungstovanadophosphoric acid (H4PW11VO40, abbreviated as PW11V) and reduced graphene oxide (rGO) in this work. The results indicate that the Keggin framework of PW11VO404 − anion still remain in the hybrid film and confirm the homogeneous dispersion of PW11V on the surface of graphene sheet, which results in a better stability of PW11V. The electrochemical impedance spectroscopy shows that this film exhibits high proton conductivity of 2.22 × 10− 2 S cm− 1 at 17 °C and 6.43 × 10− 2 S cm− 1 at 65 °C (65% relative humidity). Its activation energy value for proton conduction is 18.9 kJ mol− 1, suggesting that the conduction mechanism for this film is a mix of Vehicle mechanism and Grotthuss mechanism. It is an alternative film material which may be applied in the field of fuel cells.

A series of reversible phase transformation ammonium- and phosphonium-based polyoxometalate ionic liquid (POM-IL) gels were synthesized and studied with a focus on the correlation between their physicochemical properties and their chemical structure. The products were successfully characterized by IR, UV, XRD and TG-DTA, and their ionic conductivities were measured. The Keggin-type heteropolyanion clusters decorated with long alkyl chains demonstrated a tendency to exhibit a gel state at room temperature, while all the gels transformed into liquids after heating and then recovered after cooling. With a decrease in the alkyl chain length, a significant improvement in the thermal stability and conductivity of the ammonium-based POM-IL gels can be achieved. Moreover, compared with the corresponding ammonium compound, phosphonium-based POM-IL gel was found to be more stable at high temperature and exhibited better conductivity.

Correction for ‘The invertible electrochemical properties and thermal response of a series of gel-type ionic liquids based on polyoxometalates’ by Xuefei Wu et al., Phys. Chem. Chem. Phys., 2014, 16, 24598–24603.

A series of vanadium-substitutive polyoxometalate-based ionic liquids, [PyPS]6PW9V3O40, [PyPS]4PW11VO40, [PyPS]4PMo11VO40 and [PyPS]7P2W17VO62, bearing sulfo-group grafted ammonium (PyPS), are transformed to reversible thermal-response gel-type compounds. Interestingly, these gel-type compounds exhibit an obvious increase in their conductivity during the reversible phase transformation, which means that they are a novel series of reversible thermal-response gelation electrolytes. The relationship between the component elements of the polyoxometalate-based ionic liquids and their electrochemical performances has been studied. The Dawson-type compound ([PyPS]7P2W17VO62) has a higher conductivity than the Keggin-type one ([PyPS]4PW11VO40) with the same number of vanadium atoms in the structure. What’s more, the W-containing compounds ([PyPS]6PW9V3O40 and [PyPS]4PW11VO40) have higher conductivities than the Mo-containing one ([PyPS]4PMo11VO40).

•POM-based hybrid materials, P2W17In/PVP and P2W17In/PVP/SiO2, are prepared.•Their conductivities are 1.70 × 10− 3 and 1.82 × 10− 3 S·cm− 1 at 18 °C with 70% humidity.•Their activation energies of conduction are 8.80 and 15.53 kJ·mol− 1.•The conduction mechanism of P2W17In/PVP is Grotthuss mechanism.•The conduction mechanism of P2W17In/PVP/SiO2 is Grotthuss-dominant mixing mechanism.Hybrid polyoxometalate-based inorganic–organic proton conductors formed through Dawson structure heptadecatungstodiphosphoindic heteropoly acid (P2W17In), polyvinylpyrrolidone (PVP) and silica gel (SiO2), P2W17In/PVP and P2W17In/PVP/SiO2, have been investigated. These hybrid materials are characterized by IR, XRD and electrochemical impedance spectrum (EIS). The results reveal that, at room temperature (18 °C), and 70% relative humidity (RH), the conductivities of hybrid materials are 1.70 × 10− 3 S·cm− 1 and 1.82 × 10− 3 S·cm− 1, respectively. Their activation energy values are 8.80 kJ·mol− 1 and 15.53 kJ·mol− 1. Their mechanisms of proton conduction are also proposed.

•[TEAPS]8P2W16V2O62, is made of sulfo-group grafted ammonium (TEAPS) and POM anions.•With layered structure, it forms nano-size parts through supermolecular interactions.•It happens invertible electrochemical reactions in nonaqueous solvent.A novel kind of self-assembly polyoxometalate-type hybrid material, [TEAPS]8P2W16V2O62, bearing of sulfo-group grafted ammonium (TEAPS) and vanadium-substituted heteropoly anions has been prepared. This compound has a layered-shape structure in total and it can process self-assembly to nano-size particle and chrysanthemum-like assemblies through supermolecular interactions. Moreover, from cyclic voltammetry studies, this kind of polyoxometalate-based hybrid compounds exhibit unique electrochemical properties that the vanadium in the complexes can process reduction in anhydrous environment, which is unlikely in water solution as a simple hydrated ion because of the water protonation about the substrate.

•The single crystal of H5SiW11VO40·15H2O was firstly determined.•It has excellent conductivity, which is 7.93 × 10−3 S cm−1 at 15 °C and 50% RH.•The mechanism of proton conduction of H5SiW11VO40·15H2O is Vehicle mechanism.Tungstovanadosilicic heteropoly acid H5SiW11VO40·15H2O has been successfully synthesized and characterized. The single crystal of this solid proton conductor was firstly obtained and the crystal structure was determined from single crystal X-ray diffraction. The complex crystallizes in the monoclinic system, space group C2/c, with a = 12.716(3) Å, b = 19.881(5) Å, c = 19.099(5) Å, α = 90°, β = 90.796°, γ = 90°, V = 4828(2) Å, Z = 4. Its proton conductivity was measured using electrochemical impedance spectroscopy (EIS) in the temperature range 15–55 °C, and the activation energy of the conductivity was determined. The results show that it has appreciable proton conductivity (7.93 × 10−3 S cm−1) at 15 °C and 50% relative humidity, with an activation energy of 21.59 kJ mol−1 for proton conduction. The conductive mechanism is Vehicle mechanism.

•This is a new Keggin-type quaternary heteropoly acid.•Its conductivity is 8.92×10−3 S cm−1 at 22 °C and 80% relative humidity.•Its conductive mechanism is Vehicle mechanism.A new vanadium and molybdenum-substituted Keggin-type quaternary heteropoly acid H5PW9MoV2O40·10H2O has been synthesized by the stepwise acidification and the stepwise addition of element solutions. The product is characterized by the IR, UV, XRD, TG–DTA and electrochemical impedance spectroscopy (EIS). EIS measurement shows the conductivity value of H5PW9MoV2O40·10H2O is 8.92×10−3 S cm−1 at 22 °C and 80% relative humidity, which increases with higher temperature. Its mechanism of proton conduction is Vehicle mechanism for its conductive activation energy of 23.45 kJ mol−1.

Reversible phase transformation-type electrolyte, consisting of 1-(3-sulfonic group)propyl-3-methyl imidazolium cation (MIMPS) and tungstovanadophosphoric anion with Keggin structure, [MIMPS]4PW11VO40, is synthesized and characterized using elemental analysis, IR, UV, XRD, and TG-DTA. This product is in quasi-solid-state, a novel type of ionic liquid, with a layered type of structure. This compound can process the phase transition from a crystal phase to an isotropic phase below 100 °C. Moreover, the DTA and conductivity–temperature plot shows an observable increase in conductivity above 84.2 °C, which is caused by the phase transformation from crystal phase to isotropic phase. This novel electrolyte material exhibits high conductivity (8.60 × 10−2 S cm−1 at 83 °C and 80% relative humidity). In the range of the measured temperature, its conductivity increases with higher temperature, indicating that the conductive activation energy for this conduction step is 42.06 kJ mol−1.

A series of vanadium-substituted Dawson-structure POM-type ionic liquids, [TEAPS]7P2W17VO62 and [TEAPS]9P2W15V3O62, bearing sulfo-group grafted ammonium (TEAPS) cations and Dawson-type polyoxoanions have been formed which are reversible-thermal-response type gels. These gel-type compounds exhibit a phase transition from a quasi-solid gel phase to an isotropic sol phase. What's more, this series of hybrid compounds can undergo reversible electrochemical reactions in dimethyl formamide (DMF) owing to the reduction of the vanadium in POM anions as a simple anion, which is unlikely to happen in water solution because of water protonation.

Ammonium- and phosphonium-based polyoxometalate ionic liquids (POM-ILs) have been synthesized and characterized. The results of small-angle XRD indicate that phosphonium-based POM-IL possesses a layered type structure. They are temperature control-type POM-ILs and can exhibit a phase transformation below 100 °C. Phosphonium-based POM-IL exhibits higher thermal stability and conductivity than its ammonium analogue.

•This polyoxometalate-based ionic liquid shows a phase transition at 81 °C.•It has better thermal stability owing to the tetraalkylphosphonium cations.•Its conductivity is 2×10−4 S cm−1 at 104 °C and 30% relative humidity.A reversible phase transformation polyoxometalate-based ionic liquid has been synthesized from tetraalkylphosphonium cation and tungstovanadophosphoric anion with monovanadium-substituted Keggin structure. Results of XRD and SEM indicate the product has amorphous structure due to the influence of the cations. It is quasi-solid-state at room temperature and the TG–DTA curves show a phase transformation around 81 °C. Its conductivity is 2×10−4 S cm−1 at 104 °C and 30% relative humidity and the conductivity enhances with increasing temperatures.

•We synthesized a heteropoly acid and characterized its structure.•We determined its proton conductivity by impedance spectroscopy.•We investigated its proton conduction mechanism.A proton conductor solid electrolyte tri-vanadium-substituted tungstosilicic acid H7SiW9V3O40·9H2O with Keggin structure was prepared by the stepwise acidification and the stepwise addition of element solutions. The product is characterized by Infrared (IR) spectroscopy, UV spectrum and X-ray powder diffraction (XRD). Its proton conductivity has been measured by the electrochemical impedance spectroscopy (EIS) in the temperature region 18–58 °C and 50% relative humidity. The conductivity increases from 2.05×10−3 S cm−1 at 18 °C to 8.11×10−3 S cm−1 at 58 °C, with an activation energy of 26.69 kJ mol−1 for proton conduction. The conductive mechanism is Vehicle mechanism.

The material (TOAMe)5[SiW11VO40] was synthesized from a heteropoly acid and a simple quaternary ammonium ionic liquid as a new organic-inorganic hybrid material. It has a phase transition and ion conductivity of ∼2.03×10–3 Ω–1 cm–1 at 26 °C.

Two new solid hybrid molecular materials [PyPS]H6P2W17VO62 and [PyPS]H8P2W15V3O62 have been synthesized from 1-(3-sulfonic group) propyl-pyridine ionic liquid cation and tungstovanadophosphoric anion with the Dawson structure. They were characterized by element analysis, impedance spectroscopy (IS), IR- and UV-spectroscopy. The formation of the hybrid molecular compounds with the Dawson structure was showed. Ion conductivity of [PyPS]H6P2W17VO62 and [PyPS]H8P2W15V3O62 are 3.99 × 10−3 and 7.37 × 10−3 S cm−1 at 18°C and 55% relative humidity respectively. The activation energies of proton conductivity are 28.2 and 26.7 kJ mol−1 respectively.

•We prepared three composite materials containing heteropoly acid and matrices.•Their conductivities are up to 10−2 S cm−1 at 26 °C and 75% relative humidity.•The activation energies of proton conduction are lower than that of pristine HPAs.•Their mechanisms of proton conduction are proposed.The composite materials were prepared by 90 wt.% tungstovanadophosphoric heteropoly acids with Dawson structure (H7P2W17VO62·nH2O and H9P2W15V3O62·nH2O, abbreviated as P2W17V and P2W15V3), 5 wt.% silica gel (SiO2) and 5 wt.% organic polymers (polyvinylpyrrolidone, PVP or polyethylene glycol, PEG). The products were characterized by the infrared (IR), X-ray powder diffraction (XRD) and electrochemical impedance spectroscopy (EIS). EIS measurements show that the conductivity values PVP/P2W17V/SiO2, PVP/P2W15V3/SiO2 and PEG/P2W15V3/SiO2 are 1.89 × 10−2, 2.32 × 10−2 and 2.67 × 10−2 S cm−1 at 26 °C and 75% relative humidity, which increase with higher temperature. They exhibit low activation energies of 16.12, 16.85 and 14.02 kJ mol−1 for proton conduction, respectively. The mechanisms of proton conduction of the composite materials are also proposed.

Tungstovanadophosphoric heteropoly acid H6PW9V3O40·(13.81 ± 0.13)H2O (abbreviated as PW9V3) has been synthesized by the stepwise acidification and the stepwise addition of element solutions. The crystal structure was determined from single crystal X-ray diffraction. The complex crystallizes in the space group R3̅m, with a = 16.4374 (9) Å, b = 16.4374 (9) Å, c = 25.3866 (14) Å, α = 90°, β = 90°, γ = 120°, V = 5940.20 Å, and Z = 6. The product possesses Keggin structure, and its conductivity was 1.730 × 10–2 S·cm–1 at 26 °C and 75% relative humidity by electrochemical impedance spectroscopy (EIS) measurement. Two conducting systems were prepared with a mixture of as-synthesized PW9V3 and organic polymers [polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG)] at the weight ratio 80:20. The hybrid materials exhibit high proton conductivities with 7.110 × 10–3 and 1.050 × 10–2 S·cm–1 (PW9V3/PEG) at 26 °C and 75% relative humidity, respectively. Their activation energies of proton conduction are 15.23 and 13.67 kJ·mol–1, which are lower than that of pristine heteropoly acid (25.68 kJ·mol–1). Their mechanisms of proton conduction are also proposed.

A general strategy in terms of degradating and ion-exchange synthesis was used to design pentadecatungstotrivanadodiphosphoric heteropoly acid H9P2W15V3O62·28H2O with Dawson structure and excellent conductivity. The product was characterized by ICP-MS, IR, UV, XRD, 31P NMR, TG-DTA and electrochemical impedance spectroscopy (EIS). The results indicate that H9P2W15V3O62·28H2O possesses the Dawson structure. EIS measurements show a high conductivity (3.64 × 10−2 S cm−1 at 26 °C and 75% relative humidity), with an activation energy of 31.34 kJ mol−1 for proton conduction. Its mechanism for proton conduction is the Vehicle mechanism.

A new solid high-proton conductor, substituted heteropoly acid with Dawson structure H7[In(H2O)P2W17O61]·23H2O, has been synthesized by the degradation/ion exchange/freezing method. The pH of the synthesis reaction was given. The product was characterized by chemical analysis, IR, UV, XRD and TG-DTA. The determination of conductivity shows that H7[In(H2O)P2W17O61]·23H2O is an excellent solid high-proton conductor with conductivity of 1.34 × 10−3 S cm−1 at 18 °C, and 70% relative humidity (RH). Its activation energy is 37.72 kJ mol−1, which suggests that its mechanism of proton conduction is the Vehicle mechanism.

Tungstovanadophosphoric heteropoly acid H4PW11VO40·8H2O with Keggin structure has been synthesized by the stepwise acidification and the stepwise addition of element solutions. The optimal proportion of component compounds and pH value in the synthesis reaction were given. The crystal structure was determined from single crystal X-ray diffraction. The complex crystallises in the space group I-4, with a = 18.7648(9) Å, b = 18.7648(9) Å, c = 14.5762(9) Å, α = 90°, β = 90°, γ = 90°, V = 5132.5(6) Å, Z = 2. The product possesses Keggin structure and its conductivity was 1.50 × 10−2 S cm−1 at 26 °C and 75% relative humidity by electrochemical impedance spectroscopy (EIS) measurement, with an activation energy of 25.66 kJ mol−1 for proton conduction. The mechanism of proton conduction for this compound is vehicle mechanism.Highlights► The single crystal of a solid proton conductor was firstly obtained. ► The conductivity of H4PW11VO40·8H2O is 1.50 × 10−2 S cm−1 at 26 °C and 75% RH. ► The mechanism of proton conduction of H4PW11VO40·8H2O is vehicle mechanism.

A new solid high-proton conductor, heptadecatungstovanadodiphosphoric heteropoly acid H7P2W17VO62·28H2O with Dawson structure was synthesized by the stepwise acidification and the stepwise addition of element solutions. The optimal proportion of component compounds in the synthesis reaction was given. The product was characterized by chemical analysis, potentiometric titration, IR, UV, XRD, 31P NMR, TG-DTA and electrochemical impedance spectroscopy (EIS). The results indicate that H7P2W17VO62·28H2O possesses the Dawson structure. EIS measurements show a high conductivity (3.10 × 10−2 S cm−1 at 26 °C and 75% relative humidity), with an activation energy of 32.23 kJ mol−1 for proton conduction. The mechanism of proton conduction for this heteropoly acid is Vehicle mechanism.

A new solid high-proton conductor, H7[Ga(H2O)P2W17O61]·18H2O, a substituted heteropoly acid with Dawson structure, has been synthesized by the degradation/ion-exchange/freezing method. The product was characterized by potentiometric titration, chemical analysis, IR, UV, XRD and TG-DTA. Complex impedance measurements show a high conductivity (5.44×10−3 S/cm at 50°C), with an activation energy for proton conduction of 36.04 kJ/mol. The mechanism of proton conduction is the Vehicle mechanism.

The ruthenium-substituted polyoxometallic acid H6[Ru(H2O)FeW11O39]·18H2O was synthesized by stepwise acidification and stepwise addition of solutions of the component elements, and an ion-exchange-cooling method. The product was characterized using inductively coupled plasma spectrometry (ICP), Infrared Spectroscopy (IR), Ultraviolet Spectroscopy (UV), and X-ray diffraction (XRD). The results show that this complex has the Keggin structure. The determination of the thermal stability and proton conductivity of this polyoxometallic acid was carried out by a thermogravimetric-differential thermal analysis (TG-DTA) and electrochemical impedance spectroscopy (EIS).

A simple synthesis of single crystal like mesoporous SBA-16 silica with decaoctahedron shape and rhomb-dodecahedron shape has been accomplished by finely tuning of overall composition of the synthesis mixture (F127–TEOS–H2O–HCl), under static condition at 26–34 °C in 3–72 h.

A new vanadium and molybdenum-substituted quaternary silicon-containing heteropoly acid H6SiW9MoV2O40·15H2O has been synthesized in this paper by the stepwise acidification and the stepwise addition of elemental solutions. The structural feature and hydration of this product were characterized by IR, UV, XRD and TG-DTA, and its proton conductivity was measured by electrochemical impedance spectroscopy (EIS). The result of EIS shows that H6SiW9MoV2O40·15H2O is a solid high-proton conductor with a conductivity of 6.01 × 10−3 S cm−1 at 22 °C and 80% relative humidity, which increases at higher temperatures. Its conductive activation energy is 27.5 kJ mol−1, which suggests that the mechanism of proton conduction is dominated by the vehicle mechanism.

A series of vanadium-substituted Dawson-structure POM-type ionic liquids, [TEAPS]7P2W17VO62 and [TEAPS]9P2W15V3O62, bearing sulfo-group grafted ammonium (TEAPS) cations and Dawson-type polyoxoanions have been formed which are reversible-thermal-response type gels. These gel-type compounds exhibit a phase transition from a quasi-solid gel phase to an isotropic sol phase. What's more, this series of hybrid compounds can undergo reversible electrochemical reactions in dimethyl formamide (DMF) owing to the reduction of the vanadium in POM anions as a simple anion, which is unlikely to happen in water solution because of water protonation.

Correction for ‘The invertible electrochemical properties and thermal response of a series of gel-type ionic liquids based on polyoxometalates’ by Xuefei Wu et al., Phys. Chem. Chem. Phys., 2014, 16, 24598–24603.

Reversible phase transformation-type electrolyte, consisting of 1-(3-sulfonic group)propyl-3-methyl imidazolium cation (MIMPS) and tungstovanadophosphoric anion with Keggin structure, [MIMPS]4PW11VO40, is synthesized and characterized using elemental analysis, IR, UV, XRD, and TG-DTA. This product is in quasi-solid-state, a novel type of ionic liquid, with a layered type of structure. This compound can process the phase transition from a crystal phase to an isotropic phase below 100 °C. Moreover, the DTA and conductivity–temperature plot shows an observable increase in conductivity above 84.2 °C, which is caused by the phase transformation from crystal phase to isotropic phase. This novel electrolyte material exhibits high conductivity (8.60 × 10−2 S cm−1 at 83 °C and 80% relative humidity). In the range of the measured temperature, its conductivity increases with higher temperature, indicating that the conductive activation energy for this conduction step is 42.06 kJ mol−1.

A new solid high-proton conductor, substituted heteropoly acid with Dawson structure H7[In(H2O)P2W17O61]·23H2O, has been synthesized by the degradation/ion exchange/freezing method. The pH of the synthesis reaction was given. The product was characterized by chemical analysis, IR, UV, XRD and TG-DTA. The determination of conductivity shows that H7[In(H2O)P2W17O61]·23H2O is an excellent solid high-proton conductor with conductivity of 1.34 × 10−3 S cm−1 at 18 °C, and 70% relative humidity (RH). Its activation energy is 37.72 kJ mol−1, which suggests that its mechanism of proton conduction is the Vehicle mechanism.

A general strategy in terms of degradating and ion-exchange synthesis was used to design pentadecatungstotrivanadodiphosphoric heteropoly acid H9P2W15V3O62·28H2O with Dawson structure and excellent conductivity. The product was characterized by ICP-MS, IR, UV, XRD, 31P NMR, TG-DTA and electrochemical impedance spectroscopy (EIS). The results indicate that H9P2W15V3O62·28H2O possesses the Dawson structure. EIS measurements show a high conductivity (3.64 × 10−2 S cm−1 at 26 °C and 75% relative humidity), with an activation energy of 31.34 kJ mol−1 for proton conduction. Its mechanism for proton conduction is the Vehicle mechanism.

Ammonium- and phosphonium-based polyoxometalate ionic liquids (POM-ILs) have been synthesized and characterized. The results of small-angle XRD indicate that phosphonium-based POM-IL possesses a layered type structure. They are temperature control-type POM-ILs and can exhibit a phase transformation below 100 °C. Phosphonium-based POM-IL exhibits higher thermal stability and conductivity than its ammonium analogue.

The substitution effect in a series of POM-type reversible gel-liquid phase transformation ionic liquid compounds, [MIMPS]8P2W16V2O62, [MIMPS]6H2P2W16V2O62 and [MIMPS]4H4P2W16V2O62, has been investigated. Interestingly, there is an obvious substitution effect on the physicochemical properties of these compounds. When protons are substituted in place of ammonium, both the conductivity and the thermo-stability of the compounds can be increased a lot, and more protons can enhance this tendency.

Two new high-proton conductors, indium-substituted ternary heteropoly acids with Keggin structures, H4[In(H2O)PW11O39]·11H2O and H5[In(H2O)SiW11O39]·8H2O, have been synthesized and characterized using elemental analysis, IR, UV, XRD and TG-DTA. Their proton conductivities were measured using electrochemical impedance spectroscopy (EIS), and the results indicate that H4[In(H2O)PW11O39]·11H2O and H5[In(H2O)SiW11O39]·8H2O are solid high-proton conductors with a conductivity of 2.60 × 10−4 S cm−1 and 5.25 × 10−4 S cm−1, respectively, at 18 °C and 80% relative humidity (RH). Their activation energies are 33.40 kJ mol−1 and 28.52 kJ mol−1, which suggests that the mechanism of proton conduction is the vehicle mechanism. In the range of the measured temperatures, the conductivity of both heteropoly acids increases with higher temperatures.

A series of temperature-dependent gel-type ionic liquid compounds have been synthesized from 1-(3-sulfonic group) propyl-3-methyl imidazolium (abbreviated as MIMPS) and three vanadium-substituted heteropoly acids H5SiW11VO40, H5SiMo11VO40 and H7SiW9V3O40. The designed and synthesized gel-type polyoxometalate ionic liquids (POM-ILs) have demonstrated a tendency to exhibit a layered structure. Moreover, they can undergo a phase transformation from a viscous gel-state to a liquid-state below 100 °C, and ionic conductivity up to 10−3 S cm−1 was observed at 120 °C. Cyclic voltammetry was carried out to study their electrochemical properties in organic solutions, and it was found that the oxidizability of the three POM-ILs decreases in the order: [MIMPS]7SiW9V3O40 > [MIMPS]5SiMo11VO40 > [MIMPS]5SiW11VO40. This result indicates that the redox behavior can be tuned by changing the chemical composition of the heteropolyanions.