Two frequently neglected topics in the field of polymer electrolytes a
re discussed, namely the structure of crystalline polymer:salt complex
es and the redox electrochemistry at the metal electrode/polymer elect
rolyte interface. The crystal structure of the PEO(3):LiCF3SO3 complex
has been obtained from powder X-ray data. The PEO chains adopt a heli
cal conformation with Li+ ions located in each turn of the helix and c
oordinated by three ether oxygens plus one oxygen from each of two CF3
SO3- anions completing a trigonal bipyramidal coordination around the
Lif ion. Each CF3SO3- anion bridges two adjacent Li+ ions along the ch
ain, the -CF3 groups project into the interchain space. The polymer el
ectrolyte may be regarded as an infinitely extended columnar coordinat
ion complex with no ionic crosslinking between the helical columns. Cy
clic voltammetry and ac impedance measurements have been carried out o
n the Eu-3+/2+ couple in PEO at 80 degrees C. The voltammetric results
are consistent with an EC mechanism, involving reduction of Eu3+ to E
u2+ followed by a chemical step in which Eu2+ is consumed. Both electr
on transfer and Eu3+ diffusion appear to be slow. Ac impedance suggest
s that D-Eu3+ is approximately 4 X 10(-16) cm(2) s(-1).