Electrochemical systems
Electrochemical systems allow either the conversion of electricity into valuable chemicals, in an electrolytic cell; or the other way around, in a galvanic one. In the particular case of electrolyzers, the focus is on optimizing yield of hydrogen per unit of energy.
The key element of any electrochemical reaction is to segregate the flow of electrons ( e^- ), and the flow of ions ( A^\pm ), producing a much more ordered reaction. This necessarily involves the presence of electrodes, which conduct electrons, and an electrolyte conducting ions. As a result, the overall reaction is split into oxidation, at the anode; and reduction, at the cathode. Consequently, electrons flow from the anode to the cathode as direct current, while the flow of ions trough the electrolyte depends on their charge. While the flow of electrons is always set, the flow of ions determines the exact reactions taking place at the electrodes. This is why the cells are named, most of the times, after the electrolyte.
Electrochemical reactions occur at the electrode-electrolyte interface, and so are inherently heterogeneous. Adsorption and charge transfer reactions are in coordination with surface diffusion and (bulk) mass transport, configuring a complex reaction mechanism. It is the coordinated action of all these mechanisms that determines the net rate of reaction and, in particular, the polarization curve of an electrochemical system.
In the context of Solid Oxide Fuel Cell (SOFC), we assessed the coordinated role of adsorption, diffusion, and charge transfer reactions in the concurrent electrochemical reaction of H_2 and CO [1], in which equilibrium theory of single electroactive species fail. Even when active sites where preferably occupied by CO rather than H_2, the electrochemical performance of cell was kept relatively consistent up CO concentrations of up to 75\% , in agreement with previous experimental data. The findings of the study helped explain those by suggesting a non-negligible contribution of CO to electrochemical performance.
In the case of a water electrolyzer, electrons, ions, and water need to be brought to the active sites efficiently; and conversely, hydrogen needs to be removed as well. This involves a complex mass-transfer problem that needs to be optimized. For low-temperature electrolyzers, this involves the simultaneous presence of both liquid water and hydrogen bubbles.
Typical electrode designs for PEM electrolyzers involve porous structures, which maximize the number of reacting sites. However, this design complicates the removal of gas bubbles, which may be trapped in the porous structure. Gas build-up hinders the arrival of fresh reactants to the active sites, and may eventually block some of them.
Recent works suggest that the replacement of porous electrodes with (micro) patterned ones may be beneficial. However, what is the most optimal geometry, and their interplay with the other design decisions, such as catalyst loading, remain unclear.
My research spins around the optimization of the electrode geometry to improve mass transfer phenomena.
In particular, my research is focused on finding ways to leverage the bubbles departing from the electrode surface as an effective stirring mechanism. In their rise, bubbles produce a wake that accelerates the arrival of fresh reactants.