To address the poor adhesion and high interface resistance of TiO₂ electrodes, a novel approach combining laser cladding and dealloying is proposed to fabricate porous Ti-based coatings with metallurgical bonding on pure titanium substrates. In this paper, we investigate the polarization characteristics of Cu-Ti alloys with different compositions, the effect of laser cladding on dealloying, and the photocatalytic performance of laser-clad, dealloyed, and porous Ti-based electrode materials.

Laser cladding technology was used to deposit Cu-Ti alloy powders with different compositions onto Ti substrates, forming a metallurgically bonded Cu-Ti alloy coating. Electrochemical dealloying was then performed to selectively remove the Cu component, resulting in a porous Ti-based electrode material. The coatings were characterized via scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and ultraviolet (UV)-visible spectrophotometry. The elemental composition, phase structure, polarization curves, UV-visible absorption spectra, transient photocurrent, and electrochemical impedance spectroscopy (EIS) results were analyzed.

Laser cladding produces Cu-Ti alloys with varying compositions, each generating different phases that directly influence the electrochemical dealloying process. Specifically, the Cu₂₈Ti₇₂ alloy mainly consists of CuTi₂, Ti, and CuTi phases; the Cu₃₃Ti₆₇ alloy contains CuTi₂, Ti, and CuTi phases; and the Cu₄₂Ti₅₈ alloy exhibits similar phases. As the Cu atomic fraction increases to 47%, the Cu₄₇Ti₅₃ alloy consists only of Ti and CuTi phases. A further increase in the Cu content leads to more complex phase compositions. For instance, the Cu₅₂Ti₄₈ alloy contains Ti, CuTi, Cu₄Ti₃, and Cu₂Ti phases, while Cu₅₈Ti₄₂ includes Ti, CuTi, Cu₄Ti₃, Cu₂Ti, and Cu₄Ti phases. The phase composition of the Cu₆₃Ti₃₇ alloy is simplified to Ti, Cu₂Ti, and Cu₄Ti phases, and the Cu₆₈Ti₃₂ alloy consists mainly of Cu₃Ti, Cu₄Ti₃, and Cu₄Ti phases. As the Cu atomic fraction reaches 73% or higher value, the alloy phases stabilize. The Cu₇₃Ti₂₇ alloy is composed of Cu, Cu₂Ti, and Cu₄Ti phases, whereas the Cu₇₇Ti₂₃, Cu₈₃Ti₁₇, and Cu₈₇Ti₁₃ alloys predominantly consist of Cu and Cu₄Ti phases. The polarization curves for the Cu-Ti alloys exhibit distinct regions, including active-dissolution, passivation, and over-passivation regions, with different dealloying characteristics. Dealloying occurs rapidly in the active-dissolution and over-passivation regions, whereas the process slows down significantly or even halts in the passivation region. When the Cu atomic fraction exceeds 87%, the alloys only exhibit active dissolution; when the Cu atomic fraction falls below 87%, the alloys exhibit passivation behavior. In the >28%?<73% Cu atomic fraction range, the active-dissolution region disappears, and dealloying only proceeds under over-passivation. When the Cu atomic fraction decreases below 28%, the over-passivation region disappears, and dealloying ceases, indicating a dealloying limit of 28% (Cu atomic fraction). The porous Ti-based electrode material exhibits significant absorption peaks at 200 nm and 300 nm, with increasing absorbance as the wavelength increases. This indicates a strong response to UV light and enhanced visible-light absorption. Transient photocurrent measurements reveal a rapid and clear response to light. Electrochemical impedance spectroscopy (EIS) data fitted using Z-view software reveal a relatively low impedance for the porous Ti-based electrode, with solution resistance and charge transfer resistance of 8.66 Ω and 12.13 Ω, respectively, providing favorable conditions for photocatalytic reactions.

In this study, the dealloying corrosion behavior of Cu-Ti alloy precursors with different compositions prepared via laser cladding is investigated, revealing the impact of laser cladding on the separation limits and critical potential of Cu-Ti alloys. The photocatalytic performance of the porous Ti-based electrodes prepared via a combined laser-cladding?dealloying process is also analyzed. Based on the results, the following conclusions can be drawn. The Cu-Ti alloys prepared via laser cladding exhibit significant phase compositional differences, which result in distinct characteristics in their polarization curves, which in turn can generally be divided into three regions: the active-dissolution, passivation, and over-passivation regions. The electrochemical dealloying process proceeds rapidly in both the active-dissolution and over-passivation regions; however, it is extremely slow or even halts in the passivation region. For a Cu atomic fraction of ≥87%, the Cu-Ti alloy exhibits only an active-dissolution region; when the Cu atomic fraction is <87%, the polarization curves exhibit passivation behavior. For a Cu atomic fraction of >28%?<73%, the active-dissolution region disappears, and sustained dealloying requires the over-passivation process. For a Cu atomic fraction of ≤28%, passivation prevents continued dealloying, indicating that the separation limit of Cu-Ti alloys prepared via laser cladding is 28% (Cu atomic fraction). Based on the characteristic potentials of the polarization curves for Cu-Ti alloys with different compositions, dealloying composition?potential diagrams for Cu-Ti alloys can be successfully constructed. These diagrams can guide the selection of dealloying processes for Cu-Ti systems and provide a reference for the dealloying corrosion behavior study of other alloy systems containing passivating elements. The porous Ti-based electrode materials prepared via the combined laser-cladding?dealloying process effectively limit light escape and exhibit a wide light-absorption range. Additionally, these electrodes respond rapidly to light, and the metallurgical bonding between the porous layer and substrate reduces the interface resistance. These factors significantly enhance their photocatalytic performance, providing new insights for the preparation of photocatalytic and other types of electrode materials.