Roles of H2 evolution overpotential, materials porosity and cathode potential on mineral electro-precipitation in microfluidic reactor -New criterion to predict and assess interdependency

Overview & Synopsis

The influence of cathode materials including carbonaceous electrode on the cathodic mineral scaling behavior in a context of wastewater treatment is investigated for the first time and particularly in thin film microfluidic reactors. The kinetics of CaCO3 and Mg(OH)2 electro-precipitations were evaluated with different cathode materials (with distinct porosities, electroactive surface area (Selec) and hydrogen (H2) evolution overpotential (HEP)) and by varying the applied current densities and interelectrode distances (delec). Three electrode materials were tested, carbon paper (porosity = 89%; Selec = 175 cm 2), graphite (porosity = 15%; Selec = 85 cm 2), stainless steel (porosity = 0%; Selec = 80 cm 2). An optimal condition to minimize the mineral deposition could be found in microfluidic configuration (100 µm delec) and by using graphite material being able to increase cathodic potential (EC) so to decrease OHproduction. At higher delec, stainless steel led to less electro-precipitation compared with graphite. These results newly highlight that the electro-precipitation rate strongly depends on EC values, which vary with current density and delec, as well as with the materials properties (porosity, Selec, HEP). A new criterion, namely EC/HEP, has been introduced to assess the interdependency of those parameters. Interestingly, a maximal electro-precipitation was noticed at EC/HEP  1.3 for porous and non-porous materials. This further announces the possibility to predict the range of required EC according to the electro-precipitation objective, which is crucial in real applications of electrolysis for wastewater treatment.