The electrochemical discharge phenomenon is a high current density electrochemical process with intrinsic physicochemical properties suitable for the synthesis of nanosized materials. At this mesoscopic range of physics, matter takes on drastically new properties and activities different from its bulk counterpart, which explains the dynamic research activity in building nano-structures. This thesis focuses on the macroscopic and microscopic descriptions of the electrochemical discharges and on the application of the phenomenon for the synthesis of nanoparticles. 
It starts by establishing the leading variables to control the process from the perspective of entropy production. The nonequilibrium thermodynamics analysis is successfully adapted to the process to extract a global expression for its entropy balance. Based on the excess entropy production in the system, the conjugated thermal and electrochemical fluxes and forces are the hierarchically top constraints affecting the process and its stability. This approach is supported by experimental evidences on the dynamic analysis of the electrochemical system which is performed through a designed wavelet-based signal processing algorithm. The gas film, covering and insulating the electrode during the process from the rest of the solution, has a life-time and building-time which are respectively an increasing and decreasing positive definite functions of the applied terminal voltage and the bulk temperature.
With the successful synthesis of nickel and platinum nanoparticles, characterized morphologically, chemically and electrochemically, the second part of this thesis presents a comprehensive methodological procedure to apply the process in nanoparticles manufacturing. Two synthesis mechanisms of nano-materials by the electrochemical discharges and supported by the experiment are treated in detail. The first one involves the continuous competition of direct reduction of metal ions by the hydrated electron, e^–_{aq}, the hydrogen radical, H·, and secondary generated species, versus the back reaction of oxidation by the hydroxide radical OH·. The second mechanism is based on electrode sputtering physics by which the positively charged ions are accelerated in the gas film gap and strike the outermost atoms at the electrode surface to be diffused afterwards in the bulk solution. Zero-valent atoms will then undergo time-dependent nucleation and crystal growth processes to form colloidal suspension of nano-sized particles in the bulk solution. The performances of the synthesized nickel oxide nano-materials by electrochemical discharges as supercapacitors for energy storage applications are investigated and discussed. It is shown that the pseudocapacitance behavior and consequently the energy and power densities are size-dependent.