Gojo M. Karšulin M.


In this paper an anodic oxidation of for-mic acid on rhodinized platinum elec-trodes, with and without pyridine addi-tion is investigated. During anodic oxi-dation of HCOOH, in the potential ran-ge from 600 to 1000 mv(SHE), periodic oscillations occurred (Fig. 1a).

As the speed of polarization is an essential for the oscillations occurrence; the speed at the rate of 0,3 mVs l was used. The oscillations disappear at higher speeds of polarization.

We can therefore propose the following formulation for the anodic behaviour of formic acid on Pt (Rh) anodes:


Rh° → Rh2+ + 2e-                                           (1)


(HCOOH)2 → 2 HCOOH                    (2)


Formic acid exists as dimer, and during the contact with Rh, a monomerization occurs.


2 HCOOH → 2 HCOO- + 2H+ ( 3 )


2 H+ goes to cathode and gives H2.


where Rh(OOCH)2 represents anodic layer: Further:


Rh(OOCH)2 → Rh° + H2 + 2 CO2       (5)







According to literature data it is po-ssible to synthesise a stable complex of Rh(OOCH)2L2, where as a ligand is either pyridine or NH3. By pyridine addition into formic acid a decom-position of Rh(OOCH)2 into CO and H2, is prevented, although it caused a periodic oscillations (Fig. 1b).

Our study gives an explanation for the mechanism of the HCOOH anodic be-haviour that is possible without the assumption of problematic radicals use, i.e. without very unstable Rh+. The interpretation of the mechanism of ano-dic process through Rh oxidation is also unlikely to occur, as the oxide formation occurs only at the very positive potential values.