Key Takeaways & Executive Findings
- •• • Optimal porous layer thickness of 260.8 μm (8 h dealloying) yields a photocurrent density of 4.54 μA/cm2 and charge transfer resistance of 47.28 Ω·cm2, outperforming all other thicknesses. This demonstrates that precise thickness control is essential for maximizing charge separation efficiency, directly impacting solar fuel production rates. • • The npT-8h sample achieves a methyl orange degradation rate constant of 0.00529 min−1 and 61% degradation within 180 min, significantly surpassing other samples. This degradation rate is critical for industrial wastewater treatment, where faster kinetics reduce reactor volume and operational costs. • • Double-layer capacitance peaks at 5.53 mF/cm2 for the 8 h sample, indicating maximum electrochemically active surface area. This correlates with abundant reactive sites, directly enhancing photocatalytic activity and suggesting a route to optimize catalyst loading in practical systems. • • Dealloying time beyond 8 h reduces performance due to structural degradation, with thickness decreasing after 8 h. This identifies a narrow processing window (8 h) for optimal thickness, highlighting the need for precise time control in scalable manufacturing to avoid performance losses.
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Abstract
Bulk TiO2 photoanodes suffer from low specific surface area and rapid recombination of photogenerated electron-hole pairs, limiting practical photocatalytic efficiency. This study systematically investigates the quantitative relationship between nanoporous layer thickness and photoelectrochemical performance of Ti/TiO2 photoanodes fabricated via a two-step laser cladding-electrochemical dealloying route. Cu67Ti33 precursor coatings were deposited on pure Ti substrates by laser cladding, followed by selective dealloying in 20 wt.% HNO3 for durations of 1 to 40 h. This process yielded a controllable porous layer thickness ranging from 0 to 260.8 μm. The sample dealloyed for 8 h (npT-8h) exhibited optimal performance: a photocurrent density of 4.54 μA/cm2, charge transfer resistance of 47.28 Ω·cm2, double-layer capacitance of 5.53 mF/cm2, and a methyl orange degradation rate constant of 0.00529 min−1, achieving 61% degradation within 180 min. The enhanced performance is attributed to a synergistic balance between charge separation/transport efficiency and surface reactive site density at the optimal thickness, with auxiliary light-trapping effects from the three-dimensional hierarchical porous network. This work establishes porous layer thickness as an independent, critical parameter for optimizing nanoporous Ti/TiO2 photoanodes, providing a theoretical and experimental framework for high-performance photoelectrode design.
1. Introduction
Semiconductor photocatalysis offers a sustainable route to address energy shortages and environmental pollution, with TiO2 favored for its chemical stability, non-toxicity, and low cost. However, bulk TiO2 suffers from low specific surface area and rapid recombination of photogenerated electron-hole pairs, severely limiting practical efficiency. Conventional nanostructuring methods often yield poor substrate adhesion or lack precise control over structural parameters, particularly the thickness of the active porous layer—a critical dimension governing light absorption and charge transport distances.
This study introduces a composite fabrication strategy combining laser cladding with electrochemical dealloying to systematically investigate the quantitative structure-property relationship between nanoporous Ti/TiO2 layer thickness and photoelectrochemical performance. By dealloying Cu67Ti33 precursor coatings in 20 wt.% HNO3 for 1–40 h, porous layer thickness was tuned from 0 to 260.8 μm. The 8 h dealloying yielded a 260.8 μm layer with optimal performance: 4.54 μA/cm2 photocurrent, 47.28 Ω·cm2 charge transfer resistance, and 61% methyl orange degradation in 180 min. This protocol addresses the bottleneck of independent thickness control, providing a theoretical basis for rational design of high-performance photoanodes.
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XIANG Yihou, FANG Yongyong, LUO Chengyang, ZHENG Yafeng, WU Guolong, YAO Jianhua (2026). Effect of Porous Layer Thickness on Photocatalytic Performance of Ti/TiO2 Photoanodes Fabricated by Laser Cladding-electrochemical Dealloying. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.12.010
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Frequently Asked Questions
What is the failure mechanism when the porous layer thickness exceeds the optimal 260.8 μm?
Excessive dealloying beyond 8 h leads to structural degradation and a decrease in thickness, as the porous network collapses or coarsens. This reduces surface area and increases charge recombination, causing performance decline. The study shows that thickness peaks at 8 h and then decreases, indicating a narrow processing window.
How does the laser cladding-electrochemical dealloying route compare cost-wise to conventional TiO2 photoanode fabrication?
Laser cladding ensures robust metallurgical bonding, minimizing interfacial resistance, while dealloying in 20 wt.% HNO3 is a scalable wet process. Although laser cladding requires capital investment, it eliminates adhesion layers and enables precise thickness control, potentially reducing overall manufacturing costs by simplifying steps and improving durability.
What are the scalability bottlenecks for producing 260.8 μm porous layers uniformly over large areas?
Uniform dealloying across large substrates requires precise control of electrolyte flow, temperature, and time. The 8 h window is critical; deviations lead to thickness variations. Scaling up may need optimized reactor design and real-time monitoring to maintain the 260.8 μm target, as longer times cause degradation.
Does the 61% methyl orange degradation in 180 min translate to realistic pollutant concentrations, and what are the kinetics?
The degradation rate constant of 0.00529 min−1 indicates first-order kinetics. For industrial wastewater, this rate may require longer residence times or catalyst optimization. However, the 61% removal in 3 h demonstrates feasibility, and the rate constant is significantly higher than other samples, suggesting potential for scale-up with enhanced light delivery.
What is the long-term stability of the npT-8h photoanode under continuous operation?
The study does not report long-term stability tests, but the robust metallurgical bond from laser cladding likely enhances durability. The TiO2 layer is chemically stable, but photocorrosion or fouling could occur. Future work should assess performance over multiple cycles to ensure industrial viability.
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