The work presented in this thesis focuses on two different structures, the Ruddlesden Popper and perovskite, which have shown promise as catalysts in fuel cell devices. The Ruddlesden Popper materials have interesting structural properties allowing the possible incorporation of anions within the interstitial sites. The possible incorporation of water and fluorine into these interstitial sites was investigated for the systems La\(_2\)N\(_i\)\(_O\)\(_4\)\(_+\)\(_δ\), Nd\(_2\)NiO\(_4\)\(+\)\(_δ\), La\(_2\)CuO\(_4\)\(_+\)\(_δ\) and Sr\(_3\)Fe\(_2\)O\(_7\)\(_-\)\(_y\). In the case of water incorporation, the most interesting results were observed in La\(_2\)NiO\(_4\)\(_+\)\(_δ\). For this system, large amounts of water were shown to be incorporated using an indirect method which involved fluorination of the materials followed by ion exchange. This is the first time such a method has been demonstrated. The work on the perovskite materials (SrCoO\(_3\), SrMnO\(_3\), SrFeO\(_3\) and CaMnO\(_3\)) focused on doping with various oxyanions (phosphate, silicate and sulphate). It was discovered that small amounts of oxyanion doping could be achieved, which caused a large increase in the conductivity. This increase was correlated either to a phase change on doping or in the case of the CaMnO\(_3\) material due to the resultant electron doping. Electrochemical tests were performed to determine if the materials would be of use as cathode materials in fuel cells.