The overlooked reaction of H2O2 decomposition over carbonaceous cathodes

Abstract

Electrochemical 2-electron oxygen reduction over carbon cathode is an important method to produce H2O2 in situ. Besides the H2O2 generation rate, the H2O2 decomposition rate is also crucial to the cumulative concentration of H2O2. It is generally believed that H2O2 decomposition will produce H2O and O2 by electro-reduction or carbon catalysis. Herein, a new H2O2 decomposition pathway is proved: carbonaceous materials may react with H2O2 spontaneously to release CO2 and CO at room temperature and atmospheric pressure. At low H2O2 concentrations, the reaction produced CO mainly and then CO2. But at high H2O2 concentrations, CO2 was a preponderant product over CO. The reaction was exothermal which causes the rise of solution temperature, promoting H2O2 decomposition to produce O2. The continuous decomposition of H2O2 raised the pH value, while the generated CO2 dissolved in the solution to reduce the pH value. These two effects together determined pH tendency. With the increase of pH value, H2O2 decomposition triggered by alkaline conditions produced H2O and O2. The applied negative voltage accelerated H2O2 decomposition via reacting with charcoal. Furthermore, this reaction showed universality to carbonaceous materials. The above results are of great value for understanding the decomposition mechanism of H2O2 and setting a reasonable target for cumulative H2O2 concentration via electrochemical oxygen reduction.