Niobium Oxyhydroxide‐Polyoxometalate Composite as an Efficient Proton‐Conducting Solid Electrolyte

Abstract

It is still challenging to develop new and low-cost protonconductive solid electrolytes using a simple synthetic procedure. Herein, a new proton-conducting material was synthesized for the first time through a sol-gel method by merging niobium oxyhydroxide with polyoxometalate (POM). NbO 2 (OH)-PW 12 exhibited higher proton conductivity than that of niobium oxyhydroxide with varying humidity. Additionally, the molar ratio of Nb:{PW 12 } played a vital role in the proton conductivity and, when the molar ratio of Nb:{PW 12 } was 67 : 1, the material showed the maximum proton conductivity with a value of 7.25 mS cm À1 at 77 8C under 97 % RH, which was 10000 times higher than that of niobium oxyhydroxide. To the best of our knowledge, this is the first niobium-oxyhydroxide-based intrinsic proton conductor with such high proton conductivity below 100 8C. The kinetics study suggested that the proton conduction mechanism of NbO 2 (OH)-PW 12 might follow the Grotthuss mechanism.

Proton Conductivity in {Mo72Fe30}‐Type Keplerate

“…Nakamura, in 1979, reported Keggin heteropoly compounds H 3 PM 12 O 40 ⋅ 29H 2 O (M=Mo, W) as the first POM‐based proton conductors [28] . The high proton conductivity is attributed to the primary and secondary structures of POMs which are constituted of the proton coordinated peripheral oxygen atoms and hydrogen bonded water molecules with POM oxygen atoms respectively [29] . Since then, majorly five different types of POM‐based materials have been designed and studied for their proton conductivity: (i) POM‐based metal organic material; (ii) POM incorporated inside perfluorinated sulfonic acid polymer; (iii) POM immobilized on silica material via sol‐gel method; (iv) POM casted in inert polymer matrix and (v) POM directly attached to polymer through functionalization [30–36] .…”

“…[28] The high proton conductivity is attributed to the primary and secondary structures of POMs which are constituted of the proton coordinated peripheral oxygen atoms and hydrogen bonded water molecules with POM oxygen atoms respectively. [29] Since then, majorly five different types of POM-based materials have been designed and studied for their proton conductivity: (i) POM-based metal organic material; (ii) POM incorporated inside perfluorinated sulfonic acid polymer; (iii) POM immobilized on silica material via sol-gel method; (iv) POM casted in inert polymer matrix and (v) POM directly attached to polymer through functionalization. [30][31][32][33][34][35][36] POM-based proton conducting materials exhibit a wide range of temperature and humidity dependent proton conductivities (10 À 2 -10 À 8 S cm À 1 ), [20] the highest being reported by Yang et al for a polyoxotungstate host {P 8 W 48 } containing lewis acid guests.…”

Synthesis of highly water‐absorbing chromium oxyhydroxide as a dopant in a hybrid proton‐conducting membrane

“…40,41 Metal oxyhydroxide (MO x (OH)) tends to show high water absorption and moisture retention due to its abundant hydroxyl groups and free water molecules, making MO x (OH) a potential proton-conducting material. [42][43][44][45][46] In 2018 and 2020, our group continuously reported two cases about niobium oxyhydroxide materials: NbO 2 (OH)-H 3 PW 12 O 40 and NbO 2 (OH)-phytic acid, 47,48 showing high-efficiency proton conductivity. MO x (OH) can be synthesized by a simple solution-gel method, which is conducive to the large-scale preparation of proton conductor materials.…”

Role of Electric Field and Surface Protonics on Low-Temperature Catalytic Dry Reforming of Methane

“…So, the promotion for DRM activity was not due to increasing the temperature. Besides, many other reactions were also promoted by application of an electric field. − Surface protonics, with surface proton hopping via adsorbed water and hydroxyl groups, the so-called Grotthuss mechanism, − on the CeO 2 surfaces promotes catalytic performance. , The rate-determining step of conventional SRM (without the electric field) is known to be CH 4 dissociative adsorption step over Ni and precious metal-supported catalysts. , Proton collision to CH 4 in SRM with the electric field enables the formation of a transitional state and configures the three-atom (CH 3 –H–H) + transition state . Additionally, the energy level of produced (CH 3 + + H 2 ) was much lower than CH 4 physisorption and the transition state.…”