International Journal of Photoenergy

Review Article

Fabrication, Modification, and Emerging Applications of TiO₂ Nanotube Arrays by Electrochemical Synthesis: A Review

Brief summary of various synthesis generations of TNAs.


Generation	Electrolyte type	Potential	Anodized time	Morphology	Main Factor	Reference

First generation: inorganic aqueous electrolytes (HF-based electrolyte)	0.5 wt% HF	10–23 V	≥20 min	Short nanotubes Length: 200–500 nm Diameter: 10–100 nm Wall thickness: 13–27 nm	Potential, electrolyte	[13]
	0.3–0.5 wt% HF + 1 M H₃PO₄	1–25 V	2 h	Length: 20–1000 nm Diameter: 15–120 nm Wall thickness: 20 nm	Potential, electrolyte	[32]
Second generation: buffered electrolytes (F⁻-based electrolytes)	1 M Na₂SO₄ + 0.1–1.0 wt% NaF	20 V	10 min–6 h	Roughwall with rings Length: 0.5–2.4 μm Diameter: 100 nm Wall thickness: nm	Potential, pH, time	[28]
	1 M (NH₄)₂SO₄ + 0.5 wt% NH₄F	20 V	15–30 min	Length: 0.5–1.0 μm Diameter: 90–110 nm	Potential, pH, time	[33]
Third generation: organic electrolyte containing F⁻ ions	0.5 wt% NH₄F + 0–5 wt% H₂O in glycerol	20 V	13 h	Smooth tube Length: 7.0 μm Diameter: ≈40 nm Wall thickness: nm	Potential, water content, time	[17]
Third generation: organic electrolyte containing F⁻ ions	0.1–0.7 wt% NH₄F + 2–3.5 wt% H₂O in ethylene glycol	60 V	216 h	Ultra-long tube Length: 1000 μm Diameter: nm	Potential, water content, time	[22]
Fourth generation: fluoride-free electrolytes	0.01–3 M HClO₄	1 min	15–60 V	Disordered tubes Length: 30 μm Diameter: 20–40 nm Wall thickness: 10 nm	Electrolyte, time	[30]