The Iron Oxyhydroxide System

This subsection has been divided into two parts. The first will present results of two rather recent contributions from which considerable insight into the electrochemical behavior of the iron oxyhydroxide system has been obtained, whereas the second part will address studies of the passive film in borate buffer media. 

One of the earlier Mossbauer studies of the electrochemical properties or iron was that of Geronov et who investigated the spectral changes 

The actual samples were prepared by adding Vulcan XC-72, a high-area carbon of about 250 m g to a solution of FePc in pyridine under ultrasonic agitation. The carbon suspension was later transferred to a distillation apparatus and heated until all the excess solvent was removed. The dry dispersion, containing about 10% w/w FePc/XC-72, was then placed into a small crucible and heated in a furnace under a flowing inert gas atmosphere at 280°C so as to eliminate pyridine axially coordinated to the macrocycle. After two hours, the heating was interrupted and the sample allowed to cool without disconnecting the stream of inert gas. 

FIGURE 9. Cyclic voltammetry of 7% w/w iron phthalocyanine dispersed on Vulcan XC-72 carbon, after a heat treatment at 300°C in a flowing inert atmosphere. The measurement was conducted with the material in the form of a thin porous Teflon-bonded coating electrode in 1 M NaOH at 25 C. Sweep rate 5 mV s  

It may be noted that the quadrupole splitting of the heat-treated FePc/XC-72 electrode measured ex situ prior to the electrochemical experiments was larger than that found in situ. Smaller values for A have been reported for certain ferric hydroxide gels and for small particles of FeOOH (Table IV), and thus the effect observed for this specimen is most probably related to the incorporation of water into the oxide structure. Based on this information, the material observed in situ at this potential will be referred to hereafter as FeOOH (hydrated), without implying any specific stoichiometry. 

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