Fabrication Of Phosphate Glasses By Akali-Protton Substitution Process

Fuel cells(FC)are considerablely attend by countries around the world because of their high energy conversion efficiency and low environmental pollution.Intermediate-temperature fuel cells avoid the disadvantages of low-temperature fuel cells(low CO tolerance,high cost)and high-temperature fuel cells(high cost by high temperature,high thermal stability demand to components).At the same time,they keep advantages of high efficiency,safety and environmentally-friendly.So it has become a hot spot of fuel cell researches.It is the key for intermediate-temperature fuel cell to develop intermediate-temperature solid electrolyte.Phosphate glass,as a intermediate-temperature solid electrolyte,has advantages of low cost,simple process and high stability.But it also has a disadvantage of low carriers(H+)which cause low conductivity.In this research,two series of sodium phosphate glass,25NaOi/2-63PO5/2-5GeOi/2-5GdO3/2-2AO(PG-2A)(A=Mg,Ca,Sr,Ba)and XNaO1/2-(87-X)PO5/2-3GeO1/2-7GdO3/2-3MgO(XNa(87-X)P-PG)(X=25,30,35)were prepared by melting cooling method.Then,they were treated with alkali-proton substitution(APS)process.Substitution rate was confirmed.Thermomechanical propertities,the stabilites of carries,structure and conductivities were measured,respectively.The results showed that APS process on these glasses succeed.The substitution rate of PG-2A could get more than 80%,PG-2Mg got the highest substitution of 92.8%.XNa(87-X)P-PG glass samples all could get the substitution of more than 90%.After APS treatment,the thermal mechanical properties of these two series of glasses electrolytes decreased.The decrease of PG-2A samples was basically the same.The glass transition temperature Tg and the softening temperature At decreased by 144.7 and 162.4℃,respectively.At the same time,before and after APS treatment,with increase of radius of+2 valence alkaline metal atoms in PG-2A samples,both Tg and At decreased slightly.The reductions of Tg and At of XNa(87-X)P-PG samples after APS treatment increased with increase of Na+-H+substitution concentrations.With increase of Na+-H+substitution concentrations,the stability of carriers(H+)also decreased,from 680℃ for 25Na62P-PG to 490℃ for 35Na52P-PG.All samples before and after APS treatment could maintained structures itself.When the carriers after APS treatment began to lose,the structure of 35Na52P-PG sample had a tendency to become more ordered.In addition,the max conductivities of these samples could get 10-3 Scm-1,which increased by an order of magnitude compared with the reported phosphate glass electrolytes.The max conductivities and corresponding temperatures of samples were depended on the concentrations of Na+-H+substitution in samples.With increase of Na+-H+ substitution concentrations,the max conductivities of samples after APS treatment from 2.42 × 10-3Scm-1 for 25Na62P-PG increased to 6.2 × 10-3Scm-1 for 35Na52P-PG.The corresponding temperatures from 502℃ for 25Na62P-PG decreased to 396.2℃ for 35Na52P-PG,both of them were between 200-600℃.At the same time,we found that activate energy in XNa(87-X)P-PG samples after APS treatment decreased linearly with increase of H+concentration injected.