Preparation Of Niobium Oxyhydroxide Based Composites And Their Proton Conductivity

With the development of the field of proton exchange membrane fuel cells(PEMFCs),it is still a challenge to develop new and low cost proton conductor electrolyte materials with a simple synthetic method.Due to the ion conductivity is greatly affected by the number of carriers and charge,therefore,we believe that the material with rich charge and proton carrier could be used as the effective proton conductor.For example,polyoxometalates is a kind of transition metal oxide clusters.As the proton conductor material,it could provide a large number of protons,also the water molecular in the structure can be used as the proton carrier.Moreover,the cluster surface is rich in oxygen atoms,which can also be used as proton hopping sites,thus providing a pathway for proton transport.In recent years,a new type of amorphous nanomaterials based on transition metal oxyhydroxide(MOx(OH))has attracted much attention because of its unique properties.The structure is rich in hydroxyl groups,can effectively build a hydrogen bond network,which is conductive to proton hopping.In addition,the introduction of sulfonic acid,phosphoric acid,carboxyl group and some other oxygen functional groups to a certain extent could improve the proton conductivity.This paper mainly studies the following two aspects:1.We use simple sol-gel method,hydrolysis synthesized a metal oxyhydroxide compound based on niobium as a new type of proton conductor material with the niobium chloride(NbCl5)as raw material.We introduce an abundant proton carrier-polyoxometalate(phosphotungstic acid)to form a rich hydroxyl and 3D hydrogen bonding network of the proton conductor material(NbHyOx(OH)-PW12).The results showed that the composite NbHyOx(OH)-PW12 reveals higher proton conductivity than NbOx(OH)-Cl.According to the data,the material showed the highest proton conductivity with the value of 6.52 mS cm-1 at 90 °C,97 % RH,which 4 orders of magnitude higher than that of niobium oxyhydroxide.Finally,we analyzed the effect of different doping ratio on the performance and we found that the material could exhibit relatively high proton conductivity when the molar ratio of Nb:{PW12} is up to 67:1.2.We introduce the phytic acid(PA)in the niobium compound skeleton,and synthesized a rich hydroxyl and phosphate functional groups of niobium oxyhydroxide composite NbHyOx(OH)-PA by sol-gel method in situ.Then the performance as proton conductor was studied.The experimental results indicated that when the molar ratio of Nb:PA was 17:1,the material can be reach to the highest proton conductivity(9.8 mS cm-1)at 75 °C and 97 % RH.