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

It is still challenging to develop new and low‐cost proton‐conductive 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). NbO2(OH)‐PW12 exhibited higher proton conductivity than that of niobium oxyhydroxide with varying humidity. Additionally, the molar ratio of Nb:{PW12} played a vital role in the proton conductivity and, when the molar ratio of Nb:{PW12} was 67 : 1, the material showed the maximum proton conductivity with a value of 7.25 mS cm−1 at 77 °C 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 °C. The kinetics study suggested that the proton conduction mechanism of NbO2(OH)‐PW12 might follow the Grotthuss mechanism. Amorphous solid electrolyte: A niobium oxyhydroxide–polyoxometalate composite is synthesized by using a sol‐gel method. The NbO2(OH)‐PW12 material shows proton conductivity with a value of 7.25 mS cm−1 at 77 °C under 97 % relative humidity, which is the first niobium‐oxohydroxide‐based intrinsic proton conductor that operates below 100 °C.