Synergy in the Hydrazine Assisted Electro-Oxidation of Formic Acid

In a recent paper, Schlogl have discussed thoroughly [1] the importance of chemistry on the energy scenario. It was pointed out that hydrogen could be an interesting source of energy, as long as storage problems could be fixed. Molecules such as formic acid and hydrazine are interesting hydrogen-carrier molecules, thus relevant in these energy-related systems. The mechanism by which the electro-oxidation of these molecules takes place was largely studied individually [2, 3]. However, few studies [4] have been done on the interaction present when these fuels are mixed. The present work aims at exploring the oscillatory instabilities present in the formic acid + hydrazine system to deepen the current understanding of surface reactions underlying these mixed fuels. The synergy in the electro-oxidation of mixtures of these two fuels is explored in this work. The electrochemical response obtained by the mixture is greater than the one obtained by the sum of the individual parts, as can be observed from the different oscillatory features in the separate and the complete system. The separate systems present limitations inherent to the characteristics of each fuel. For instance, formic acid has a self-poisoning process caused by the accumulation of oxygenated species that pulls the system away from the oscillatory condition in short times. On the other hand, hydrazine presents a deactivation of the electrode surface during time, as an effect of pH. When the two fuels are combined, long-last oscillations prevail, similarly to recently reported in our Group [5]. Additionally, the morphology of the time-series is different for the complete system comparing to the separate ones. Those evidences suggest that there is an intricate superficial interaction between the fuels, a synergy, to produce an unexpected oscillatory behavior.

Acknowledgements

EGM and HV acknowledge São Paulo Research Foundation (FAPESP) for financial support (grants #2009/07629-6, #2012/07313-1, #2012/24152-1, and # 12/21204-0). HV (#306151/2010-3) acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support.

References

1.         Schlogl, R., The role of chemistry in the energy challenge. ChemSusChem, 2010. 3(2): p. 209-22.

2.         Aldous, L. and R.G. Compton, The mechanism of hydrazine electro-oxidation revealed by platinum microelectrodes: role of residual oxides. Phys Chem Chem Phys, 2011. 13(12): p. 5279-87.

3.         Joo, J., et al., Importance of acid-base equilibrium in electrocatalytic oxidation of formic acid on platinum. J Am Chem Soc, 2013. 135(27): p. 9991-4.

4.         Aldous, L. and R.G. Compton, Towards Mixed Fuels: The Electrochemistry of Hydrazine in the Presence of Methanol and Formic Acid. ChemPhysChem, 2011. 12(7): p. 1280-1287.

5.         Perini, N.B., B. C.; Angelo, A. C. D.; Epstein, I. R.; Varela, H., Long-lasting oscillations in the electro-oxidation of formic acid on PtSn intermetallic surfaces. ChemPhysChem - in press., 2014.