S. Bhattacharya et Kk. Kundu, ELECTROCATALYTIC ACTIVITIES OF SOME METALLIZED GRAPHITE-ELECTRODES FOR AQUEOUS FE(2+ 3+) REDOX COUPLES FROM POLARIZATION STUDIES/, Indian journal of chemistry. Sect. A: Inorganic, physical, theoretical & analytical, 33(8), 1994, pp. 754-757
Exchange current densities (i0) of the Fe2+/3+ redox couple in aq. H2S
O4 solution have been determined at three different temperatures on ba
re Pt, graphite C and on electrochemically deposited surfaces of some
noble metals (M = Pt, Pd, Rh, Ir, Ru and Au) over cheap C substrates,
so as to develop cheaper counter electrodes for a potential aqueous PE
C solar cell based on the said redox couple. The apparent electrocatal
ytic activities as based on the apparent area of the electrode substra
tes, have been found to follow the sequence (C) Ir > (C) Rh > (C) Ru >
(C) Pt > (C) Pd > (C) Au > C. As the roughness factor R(f)(= (i0)/(i0
)true) is likely to be independent of temperature, the virtual heats o
f activation DELTAH-0, double dagger obtained by means of the relation
DELTAH-0, double dagger = -R(deltaln i0/partial derivativeT-1 = - R (
partial derivative In (i0)tr/partial derivativeT-1), have been found t
o reflect the intrinsic catalytic activity of the electrode surfaces.
Analysis of the relative i0 and DELTAH-0, double dagger values lead to
the conclusion that surface geometry/microheterogeneity, electronic w
ork function and the coverage by water molecules (theta(w)) on the sur
faces play important role resulting in the observed order. The results
further suggest that although the cheapest C substrate is not that go
od an electrocatalyst, a thinly coated surface on cheap carbon substra
te might serve as the desired cheap but efficient counter electrode fo
r the reaction concerned.