Layered double metal hydroxides belonging to the pyroaurite group (pyroaurite-type compounds, abbreviated PTCs) consist of positively charged trioctahedral metal hydroxide layers, [M(a 1-x)(II)M(b x)(III)(OH)(2)](x+), with interlayers of charge-compensating anions and water molecules,(1,2) [A(x/n).yH(2)O](x-), with 0.15 < x < 0.70. Compounds with hydroxide layers of mono- and trivalent metal cations are also known,(3) and the possible existence of PTCs containing tetravalent cations (Si, Ti(IV), V(IV)) has been indicated.(4) Recently we described the synthesis of a (CoFeIII)-Fe-II-PTC with the composition [(Co0.678Fe0.309III)-Fe-II(OH)(2)][(CO3)(0.140).yH(2)O].(5) The blue variety of Co(OH)2 also has a layered structure which on anodic oxidation transforms topotactically to the layered CoOOH.(6) Hence it is likely that the Co(II)-dominated Co-II-Fe-III-PTC also can be oxidized electrochemically and still retain its layered structure. The oxyhydroxide formed by the electrochemical reaction will. be described here with emphasis on the oxidation state of the cations.-2]