Solar electroflotation uses saltwater to generate gas bubbles, but those same chloride ions can attack the electrodes. This study asks whether titanium can keep working under that challenge—and measures what happens at the surface. As climate change pushes conventional industrial processes toward greener or carbon-neutral processes, the goal is to reduce greenhouse gases and dependence on fossil fuels.

Electrochemical processes are increasingly considered in mineral processing because they are environment-friendly and can be electrically powered by renewable energy, mainly solar energy by photovoltaic panels. Electroflotation is one of the most widely used electrochemical processes in industry.

Electroflotation is based on electrolysis: the cathodic subprocess generates hydrogen bubbles, while the anodic subprocess evolves oxygen or chlorine bubbles depending on chloride concentration in the electrolyte. The mixture of gases generated during solar electroflotation is known as oxyhydrogen, or HHO, and these gases emerge simultaneously from the electrode surface as electrolytic bubbles.

The process has been applied to colloidal-particle separation, microalgae, oil, mineral recovery, microplastic, and wastewater. The increasing use of direct seawater in mineral processes has generated corrosion problems in several processes. Because several mineral processes use direct seawater, studying electrode behavior during solar electroflotation is important for enhancing current electrochemical devices.

Titanium is stable and generates a protective passive oxide film at high potential in contact with saline solutions such as seawater, geothermal water, or altitude brine. The use of seawater exacerbates electrode corrosion, especially at the anodic electrode, while operating at medium potentials helps reduce electrode mass demands.

The study investigates titanium corrosion during solar direct electroflotation in artificial seawater using a mixed-potential superposition model and SEM and EDS surface analysis after operation at 4 V/SHE for one hour. The experimental corrosion procedure examined the kinetics of partial electrochemical reactions on a titanium alloy electrode immersed in 0.5 M NaCl, focusing on HER, ORR, and the titanium oxidation reaction.

Polarization curves were measured in freshly prepared electrolyte using a titanium rotating disc electrode, with sodium chloride prepared in deionized water from 99.9 percent analytical-grade salt. The titanium alloy electrodes came from a cylindrical rod four millimeters in diameter and ten millimeters long, and all experiments were repeated in triplicate.

The electrochemical analysis used linear sweep voltammetry in a conventional three-electrode cell, with titanium as the working electrode, platinum wire as the counter electrode, and silver chloride as the reference electrode. The electroflotation system used two titanium-mesh electrodes with an area of two square centimeters, immersed in 0.5 M NaCl at twenty degrees Celsius for one hour.

The reactor volume was one hundred milliliters, and the electrodes were positioned at the bottom with a separation of one centimeter and no membrane. The experiments used a photovoltaic solar system with an output potential of four volts, and the sodium chloride solution was prepared from 99.9 percent analytical-grade salt in deionized water.

Each experiment lasted one hour at room temperature, with the cell open to the air atmosphere. Surface morphology was studied by scanning electron microscopy using a Zeiss EVO MA 10 microscope equipped with an energy-dispersive X-ray analyzer.

Figure three shows SEM views of the titanium-alloy cathode after one hour of solar electroflotation in zero point five molar sodium chloride at four volts versus SHE. Across magnifications, the surface appears rough and covered with pits, granular features, and localized deposits, consistent with the authors’ description of crevice corrosion and stress-corrosion cracking.

This matters because hydrogen-evolution and oxygen-reduction reactions, including hydrogen microbubble release, may contribute to these post-treatment surface modifications. The EDS mapping in Figure 4 indicates elemental analysis and modifications of the titanium alloy surface after solar electroflotation.

Iron, calcium, aluminum, silicon, and sulfur are identified as impurities that can come from air pollution in the local city. HER and ORR are simultaneous mechanisms as a result of hydrogen microbubble release from the cathode surface. The electrode mechanisms generated a gas volume equal to sixty milliliters of hydrogen per mole in one hour of electrolysis operation, calculated by Faraday law.

The content of iron in titanium improves HER performance at the catalytic site on the cathode during solar electroflotation at four volts per standard hydrogen electrode. Figure five shows the titanium-alloy anode surface after solar electroflotation at four volts versus the standard hydrogen electrode in zero point five molar sodium chloride.

The electron micrographs reveal a rough, cracked, and strongly malformed surface across several length scales, including porous-looking deposits and localized pits. The authors relate these features to simultaneous titanium oxidation, chlorine-related reactions, and oxygen evolution, with chloride attack contributing to pitting corrosion and cracking.

The EDS mapping in Figure 6 supports the possible presence of titanium oxide and titanium oxychloride solid products, with a lesser degree of complex products based on titanium and chloride. Surface malformations are associated with TOR, CER, and OER occurring simultaneously on the anode, generating an average weight loss of about one point zero five times ten to the minus seven millimeters per year in one hour at four volts per standard hydrogen electrode in 0.5 M NaCl.

Figure six presents EDS elemental maps of the titanium-alloy electrode after the anodic subprocess, at four volts per SHE in zero point five molar sodium chloride. The red, blue, and green maps identify titanium, oxygen, and chlorine across the surface, with visible localized features and uneven elemental distributions.

The authors use this pattern to propose titanium oxide and titanium-oxygen-chlorine solid products, while connecting the surface changes to chloride attack, pitting, cracks, and simultaneous electrode reactions. Figure 7 provides electrochemical-kinetic information for titanium used as both cathode and anode electrodes in 0.5 M NaCl during solar electroflotation.

The linear sweep voltammetry used a potential window from minus one thousand two hundred to one thousand six hundred millivolts per standard hydrogen electrode. The titanium alloy electrode showed a corrosion potential of minus seven point two seven millivolts per standard hydrogen electrode and a corrosion current density of zero point zero six nine amperes per square meter.

These low and unchanged corrosion-current and corrosion-potential values indicate a low corrosion rate, supported by the Tafel curve and the electrochemical kinetic parameters for TOR, HER, and ORR. Figure 7 characterizes the electrochemical and kinetic behavior of a titanium-alloy electrode in aerated zero point five molar sodium chloride at two millivolts per second.

Panels a through c show the linear polarization, Tafel, and slope–potential responses, while panel d separates the modeled partial currents associated with hydrogen, oxygen, and titanium-alloy processes. The close overlap between experimental and model curves supports the authors’ use of the superposition model to extract corrosion and reaction-control parameters.

Table one reports fitted electrochemical and corrosion parameters for a titanium mesh electrode in zero point five molar sodium chloride. The electrochemical section gives exchange current densities and Tafel slopes for titanium, oxygen, and hydrogen processes, including an oxygen current density of minus thirteen point sixty-eight amperes per square meter.

The corrosion parameters are a corrosion potential of minus seven point twenty-seven millivolts versus S-H-E and a corrosion current density of zero point zero six nine amperes per square meter, providing the quantitative inputs for the superposition model. Direct solar electroflotation is presented as a promising alternative for producing green hydrogen using solar energy as the primary source.

The technology can be technically and economically feasible for mineral and industrial processes in areas with high solar radiation, such as the Atacama Desert in northern Chile. The titanium anode electrode is corrosion-resistant at four volts per standard hydrogen electrode with a direct photovoltaic system and artificial seawater, resulting in minimal weight loss.

The nonlinear mixed-potential model contributes information about electrode corrosion performance in the electroflotation process. At 4 V/SHE in 0.5 M NaCl, titanium showed low corrosion and minimal anode weight loss, while surface analysis indicated oxide and chloride-containing products.

That supports solar saline electroflotation as a promising industrial route.