Instead of theoretically, instabilities in the chemical network of the CO-electroxidation is analysed experimentally in the third chapter for a fundamental electrochemical cell of three-electrode. So, full parameter space is inspected and the temporal behaviour registered. Solely bistability is exhibited during CO-electroxidation, while oscillations are observed in presence of an extra surface process; the third chapter proposes a general principle regarding the mechanism in (electro)catalysis: three-degrees of freedom as a minimum requirement for harmonic oscillations (the fundamental oscillatory pattern). With that, in presence of hydrogen, the CO-electroxidation exhibit pretty harmonic oscillations; however, in a practical fuel cell, it exhibit chaotic pattern. Trends and usefulness of that chaotic behaviour is analysed in the first chapter, while second chapter analyses the activation energy under oscillations. Finally, the ending chapter presents an energetic balance for stationary and oscillatory states, laying foundation for the empirical and theoretical calculation of the thermodynamic efficiency for an electrochemical oscillator known as HNDR.