Ion-Exchange Properties of Alkali-Metal Redox-Intercalated Vanadyl Phosphate

Ion exchange of alkali metals in MxVOPO4·yH2O (M=H, Na, K, Rb, Cs) is reported. The role of valence, size, and affinity of the cations in the exchange process is discussed. The interlayer distance in the H1–xKxVOPO4·yH2O system is discussed in terms of finite layer rigidity theory. Different behavior is observed for KxNa1–xVOPO4·yH2O dependening on the starting compound used. When potassium in KVOPO4·H2O is exchanged for Na+, one phase compound is formed. In contrast, KxNa1–xVOPO4·yH2O formed from NaVOPO4·H2O and K+ is a multiphase system. Ion exchange does not proceed when exchanging ions differ distinctly from each other in size, e.g., sodium and cesium.