TiO2 Nanotube Array Photoanode Research Articles

Binary junctions enhance electron storage and potential difference for photo-assisted electrocatalytic CO2 reduction to HCOOH

Photo-assisted electrocatalytic (PAEC) CO2 conversion is a crucial approach for achieving sustainable carbon neutrality. Here, we have developed a binary-junctions photoanode by integrating SrTiO3 and anatase-rutile TiO2 nanotube arrays (STO/A-R TNTAs), which exhibits exceptional activity and selectivity in converting CO2 to HCOOH. The synergetic effects of the SrTiO3/TiO2 heterogeneous junction and the anatase-rutile TiO2 heterophase junction effectively facilitate photoelectron separation and storage, leading to a potential difference between anode and cathode. The establishment of the electron storage strategy, triggered by hetero- junction/phase interfaces, serves as remarkably efficient electron trapping regions with dam-like characteristics. As a result, the STO/A-R TNTAs achieves a generation rate of 68.24 μmol cm−2 h−1 with 92.25% selectivity and 90.70% Faradic efficiency. This performance is approximately 8 times higher compared to the pristine TiO2 nanotube arrays photoanode. The implementation of the electron storage mechanism presents a promising approach to improve CO2 reduction activity and selectivity.

Construction of Photothermo-Electro Coupling Field Based on Surface Modification of Hydrogenated TiO2 Nanotube Array Photoanode and Its Improved Photoelectrochemical Water Splitting.

Solar water splitting has gained increasing attention in converting solar energy into green hydrogen energy. However, the construction of a photothermo-electro coupling field by harnessing light-induced heat and its enhancement on solar water splitting were seldom studied. Herein, we developed a full-spectrum responsive photoanode by depositing CdxZn1-xS onto the surface of hydrogenated TiO2 nanotube array (H-TNA), followed by modification with Ni2P. The resulting ternary photoanode exhibits a photocurrent density of 4.99 mA·cm-2 at 1.23 V vs. RHE with photoinduced heating, which is 11.9-fold higher than that of pristine TNA, with an optimal ABPE of 2.47%. The characterization results demonstrate that the ternary photoanode possesses superior full-spectrum absorption and efficient photogenerated carrier separation driven by the interface electric fields. Additionally, Ni2P reduces the hole injection barrier and increases surface active sites, accelerating the consumption of holes accumulating on the relatively unstable CdxZn1-xS to simultaneously improve the activity and stability of water splitting. Moreover, temperature-dependent measurements reveal that H-TNA and Ni2P significantly motivate the photothermal conversion to construct a photothermo-electro coupling field, optimizing photoelectric conversion and charge carrier-induced surface reactions. This work contributes to understanding the synergistic effect of the photothermo-electro coupling field on the photoelectrochemical water splitting.

Photoelectrocatalytic chemical oxygen demand analysis using a TiO2 nanotube array photoanode

The chemical oxygen demand (COD) is a widely used parameter to evaluate the quality of water for industrial applications. Currently, the standardized method for COD analysis employs expensive and harmful reagents that require a special treatment for disposal upon use. The photoelectrocatalytic COD detection, based on the photocatalytic activity of a reduced TiO2 nanotube array photoanode (Ti|NT-TiO2) under supply of a low bias potential, represents a fast, cheap and eco-friendly alternative to the standard COD method (CODSTD). Here, Ti|NT-TiO2 was synthesized by the anodization method followed by heat treatment and electrochemical reduction. Potassium hydrogen phthalate, glucose and acetic acid were used as model organic compounds. The photoelectrocatalytic detection of COD (CODPEC) is based on the photoelectrocatalytic oxidation of target compounds on the surface of the reduced Ti|NT-TiO2 under UV illumination. Photocurrent transients were recorded using chronocoulometry, and the net charge (Δq) was plotted as a function of the theoretical COD (CODTH). A linear relationship was found between these two parameters regardless of the model compound. That relationship was used to determine the CODPEC for acetylsalicylic acid and Terasil Blue dye solutions at concentrations within the range of 0–15 mg L−1. A good agreement between CODPEC and CODSTD was achieved. The limit of detection of the method was 3.6 mg L−1 COD, with the linear range established from 0 to 50 mg L−1.

Visible Light Driven CO2 Photoreduction Using TiO2 Nanotube Arrays Embedded with Low Bandgap Carbon Nitride Nanoparticles

The extraordinary thermal and photochemical stability, superior charge transport, and tunable band positions of graphitic carbon nitride (g-CN), which is constituted of elements that are plentiful on Earth, renders g-CN an important semiconductor photocatalyst for heterogeneous catalysis [1,2]. Despite these advantages, carbon nitride-based semiconductors do not function effectively as freestanding photocatalysts or photoelectrodes due to a rapid carrier recombination rate and a slightly wide bandgap that only enables them to capture blue and UV photons [3,4]. Anodically formed TiO2 nanotube arrays (TNTAs) are semiconducting wide bandgap scaffolds with excellent photocatalytic properties due to the intrinsic orthogonalization of charge generation/transport and charge transfer processes. Herein, we use a novel in situ electrophoretic anodization to embed low bandgap carbon nitride nanoparticles (CNNPs) in the walls of titania nanotubes. The likelihood of the CNNPs leaching off the TNTA photoanode during photoelectrochemical processes was eliminated by encapsulating CN inside a TiO2 matrix. CNNPs were formed by the thermal condensation polymerization of carbon nitride utilizing citric acid and urea as the precursors, and exhibited some unusual properties, including a lower bandgap of 2.1 eV, a highly redshifted fluorescence emission maximum at 2.35 eV, surface carboxylate groups, and the emergence of unique structural characteristics corresponding to amorphous yet graphitic carbon [5]. In contrast to bulk g-CN, which has a C:N ratio of 0.75, the CNNPs possessed an elevated C:N ratio as high as 1.87 at the surface. The additional carbon was found to be both amorphous and graphitic, although the structural characteristics of g-CN were mostly unaffected, as validated by diffractometric and spectroscopic data. Even in the absence of a sacrificial agent, the CNNP@TNT nanocomposite demonstrated enhanced performance in sunlight-driven CO2 photoreduction. When compared to the freestanding TNT photocatalyst, the CO yield of photoreduction for the CN@TNT hybrid was more than three times higher. UV-filtered illumination of the CNNP@TNT heterojunction photocatalyst generated appreciable quantities of methane and CO (3.41 and 8.78 μmolg–1h–1 respectively). In situ electrophoretic anodization is an innovative approach to incorporate semiconductor quantum dots into TiO2 nanotubes or other electrochemically grown nanostructures.REFERENCES1. Kessler, F. K. et al., Nature Reviews Materials (2017) 2 (6), 1.2. Chaulagain, N. et al., ACS Applied Materials & Interfaces (2022) 14 (21), pp.24309-24320.3. Kumar, P. et al., Advanced Optical Materials (2020) 8 (4), Art. No. 1901275.4. Fu, J. et al., Advanced Energy Materials (2018) 8 (3), Art. No. 1701503.5. Alam, K.M. et al., Chemical Engineering Journal (2023) 456, Art. No. 141067.

Synergistic mechanism of B doping and NiO loading on the excellent PEC performance and high stability of TiO2 nanotube photoanodes

The severe photogenerated charge recombination rate, poor visible light utilization and slow oxygen precipitation kinetics are the technical bottlenecks limiting the photo-electrolysis of TiO2 nanotube array (TNAs) photoanode for hydrogen production from water. To solve these problems, NiO nanoparticles were uniformly loaded into B-doped TNAs by the CV method. It is found that B-doping improves the energy band structure of TNAs, and doping-induced surface defects could become traps for photogenerated carriers to substantially improve the charge separation efficiency of the bulk phase. The P-N junctions formed between TiO2 anatase and NiO nanoparticles not only promoted the OER kinetics at the interface but also greatly improved the surface carrier separation efficiency of the catalyst, as well as ensured the stability and activity of the B-doping-induced surface defects. Moreover, the carrier concentration and visible light absorption properties of TNAs were enhanced and improved. Due to the synergistic effect of B doping and NiO loading, the bulk charge separation efficiency and surface charge separation efficiency of NiO/BT (B doping and NiO loading TNAs) were as high as 88.9 and 82.4%, respectively, at 1.23 V vs. RHE, and the photocurrent density reached 2.05 mA/cm2, which was 10 times higher than that of pure TNAs.

Nickel Phosphide Clusters Sensitized TiO2 Nanotube Arrays as Highly Efficient Photoanode for Photoelectrocatalytic Urea Oxidation

AbstractThe photoelectrocatalytic urea oxidation reaction (PEC‐UOR) holds a great promise for the wastewater remediation and energy production. However, the low efficiency of semiconductor/cocatalysts type photoanodes for UOR restricts their applications in photoelectrocatalytic system. Herein, a new semiconductor/cocatalyst, Ni2P clusters sensitized TiO2 nanotube arrays photoanode (Ni2P/TiO2‐NTAs) for PEC‐UOR with high efficiency are developed. The 1D TiO2‐NTAs structure accelerates urea molecules diffusion and promotes CO2 gas release at the electrode interface. Meanwhile, Ni2P is also beneficial to urea molecule absorption and CO2 desorption and enable to lower the energy barrier for amine (NH) dehydrogenation. Furthermore, the robust interfacial charge transfer pathway between Ni2P and TiO2 interface promotes the separation of photogenerated electrons and holes and the transfer of photogenerated electrons from Ni2P to TiO2. Therefore, this photoanode shows excellent PEC‐UOR performance with the potential of 1.43 V versus reversible hydrogen electrode (RHE) when the current density reaches 10 mA cm−2, which is much lower than that of 2.24 V versus RHE and 1.58 V versus RHE for TiO2‐NTAs and Ni(OH)2/TiO2‐NTAs, respectively.

Enhanced photoelectrocatalytic oxidation of hypophosphite and simultaneous recovery of metallic nickel via carbon aerogel cathode

Carbon aerogel (CA) cathode was adopted to an undivided-chamber photoelectrocatalytic system with TiO2 nanotube arrays (TNA) photoanode to enhance the oxidation of hypophosphite (H2PO2−) and simultaneous recovery of metallic nickel (Ni). Both the efficiencies of H2PO2− oxidation and Ni recovery were significantly enhanced after replacing Ti or carbon fiber paper cathode with CA cathode. With 1.0 mM H2PO2− and 1.0 mM Ni2+, the ratio of PO43− production increased from ∼41% or ∼54% to ∼100%, and the ratio of Ni recovery increased from ∼20% or ∼ 37% to ∼93% within 180 min at 3.0 V. H2PO2− was finally oxidized to PO43− by •OH radicals, which was speculated to be generated from UV/H2O2 and bound on TNA photoanode. Meanwhile, Ni2+ was eventually electro-reduced to metallic Ni by a two-electron reduction reaction. The efficiencies of H2PO2− oxidation and Ni recovery were favored at higher cell voltage, faintly acid conditions and larger H2PO2− concentration. The stability of this system exhibited that the ratio of PO43− production increased significantly in each cycle, which was attributed to the increase of H2O2 in-situ-generation via CA cathode caused by deposition of metallic Ni. Finally, the treatment of actual electroless nickel plating effluents was demonstrated.

3D radially-grown TiO2 nanotubes/Ti mesh photoanode for photocatalytic fuel cells towards simultaneous wastewater treatment and electricity generation

Photocatalytic fuel cell (PFC) represents a clean environment and energy technology to directly recover chemical energy contained in wastewater for electricity generation by using solar energy. It is advantageous for the PFC to adopt the TiO2 nanotube array photoanodes that usually grow on planar Ti substrates. But low specific surface area and light utilization limit the improvement in the PFC performance. This work is directed to the development of a 3D radially-grown TiO2 nanotubes/Ti mesh photoanode. The Ti mesh substrate provides a large specific surface area for growing TiO2 nanotubes and benefits light scattering, while TiO2 nanotubes with high length-diameter ratio enhances electron transfer. Because of these merits, the staggered PFC with the 3D radially-grown TiO2 nanotubes/Ti mesh photoanode yields a maximum power density (PMAX) of ∼0.074 mW/cm2, which is about 6.2 and 1.6 times as those with the TiO2 nanoparticles/Ti mesh and TiO2 nanotubes/Ti foil photoanodes, respectively. Increasing the mesh density of Ti mesh is synergic to improve the cell performance due to increased surface area and light utilization. The optimal PMAX of the ordinary PFC reaches as high as 0.15 mW/cm2 when using the Ti mesh of 300 per inch. Notably, using Ti mesh as a substrate makes it easy to integrate multiple Ti meshes to form a stacked 3D photoanode, which shows excellent performance when feeding various pollutants even with biogas slurry. Besides, good stability of the developed photoanode is also demonstrated. This work offers an innovative strategy for developing high-performance 3D structured photoanode for photoelectrochemical systems.

A multi-species transport model for one-dimensional TiO2 nanotube array photoanode of photocatalytic fuel cell

One-dimensional TiO2 nanotube array photoanode used in photocatalytic fuel cells exhibits excellent performance. However, a fundamental understanding of multi-species transport coupled with photoelectrochemical reactions in this type of photoanode remains unclear. In this work, a multi-species transport model with the consideration of the electron/hole transport in the nanotube wall, the organics/hydroxyl ion transport in the pore space and the photoelectrochemical reaction at the semiconductor/electrolyte interface is developed for one-dimensional TiO2 nanotube array photoanode. The simulated result is in good agreement with the experimental data. Effects of operation conditions and nanotube structures are also studied. It is found that increasing the organics/hydroxyl ion concentrations improves the photoanode performance because of enhanced mass transport. The increase of illumination intensity allows for more electron-hole pairs to be generated, leading to the improved photoanode performance. Decreasing the wavelength results in the lowered photoanode performance. Thinner nanotube wall thickness yields better performance, while there exists an optimum nanotube layer thickness leading to the optimum performance. The results obtained not only shed light on the characteristics of multi-species transport coupled with photoelectrochemical reactions but also benefits the design and operation of one-dimensional TiO2 nanotube array photoanode.

Enhanced visible light photoelectrocatalytic degradation of o-chloronitrobenzene through surface plasmonic Au nanoparticles and g-C3N4 co-modified TiO2 nanotube arrays photoanode

Chloronitrobenzenes are typical refractory aromatic halogenated nitroaromatic and high-toxic contaminants. The reduction process of chloronitrobenzenes cannot realize their mineralization, and the existence of chlorine group is detrimental to degradation through single chemical oxidation technology. Herein, the Au nanoparticles and graphitic carbon nitride co-modified TiO2 nanotube arrays (Au/g-C3N4/TNAs) photoanodes were fabricated to degrade o-chloronitrobenzene (o-CNB) target pollutant in photoelectrocatalytic (PEC) system. The Au/g-C3N4/TNAs fabricated with 0.20 mM HAuCl40.4 H2O (Au/g-C3N4/TNAs-0.20) had more superior optical and photoelectrochemical properties than other fabricated photoanodes. Au/g-C3N4/TNAs-0.20 photoanode increased dechlorination efficiency through reduction process, which was beneficial to o-CNB degradation and TOC removal. The coexistence of anions and humic acid inhibited the PEC degradation of o-CNB. The photogenerated electron, •O2−, hole and •OH participated in o-CNB degradation in PEC system. The degradation pathway of o-CNB was inferred through GC-MS spectra and DFT calculation. The acute toxicity and bioaccumulation factor of o-CNB were effectively reduced by PEC degradation.

PDA decorated spaced TiO2 nanotube array photoanode material for photocathodic protection of 304 stainless steels

Polydopamine (PDA) coating was prepared on TiO2 nanotubes array by dip-coating method to improve the photocathodic protection performance of TiO2. The morphology, crystal structure, valence state and elemental composition of the [email protected]2 were characterized. The electrochemical tests of open-circuit potential (OCP) and photocurrent density curves were used to characterize their photocathodic protection effects for 304 stainless steels (304SS). The result shows that the TiO2 combined with PDA can effectively prevent the corrosion of 304SS under visible light irradiation. Moreover, through stability test and immersion test, the sample has good stability and it also has protective effect for 304SS in the dark state.

Structural Characterization and Visible Light-Induced Photoelectrochemical Performance of Fe-Sensitized TiO2 Nanotube Arrays Prepared via Electrodeposition

Surface modification of TiO2 nanotube arrays via metal doping is one of the approaches to narrow the wide bandgap of TiO2 in order to increase its adsorption to the visible region. The present work focuses on the fabrication of a Fe-sensitized TiO2 nanotube arrays (Fe-TNT) photoanode. Ordered Fe-TNTs were successfully synthesized using a facile two-step electrochemical method by varying the deposition voltage (2-4 V). The morphology, structure, composition, and visible light response were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), UV-Vis diffusion reflection spectroscopy (DRS), and photoelectrochemical (PEC) test. The XRD investigation demonstrated that the sensitization of Fe did not destroy the nanotube array structure, and the Fe-TNTs had an anatase phase composed of cubic-like particles at higher deposition voltages. The UV–Vis absorption spectra of the Fe-TNTs showed a redshift of photoresponse towards visible light. Such a redshift was characterized by a decrease in bandgap energy and the photo efficiency was enhanced. The optimal photoelectrochemical performance was observed at 2.5 V deposition voltage for 10 minutes and surpassed that of pristine titania nanotube arrays. The present work demonstrates feasible modification of TiO2 with Fe as a potential photoanode in solar conversion devices. &nbsp

Room-temperature conversion of the photoelectrochemical oxidation of methane into electricity at nanostructured TiO2

The room-temperature operation of a methane-based photo-fuel cell is demonstrated for the first time. This is achieved using a TiO2nanotube arrays photoanode which shows effective oxidation of methane.

A photoelectrochemical biofuel cell based on a TiO2 nanotube array fluorine-doped tin oxide photoanode

Photoelectrochemical biofuel cells can convert light and chemical energy into electrical energy using a dye-sensitized titania (TiO2) fluorine-doped tin oxide photoanode and a platinum-coated fluorine-doped tin oxide cathode. TiO2 of the photoanode serves both as a support for dyes and as an electron-transporting medium, the structure of which can limit electron trapping and charge transporting and then affect the performance of the photoelectrochemical biofuel cells. TiO2 nanotube array films have been shown to enhance the efficiencies of both charge collection and electron injection, and hence a vertically aligned TiO2 nanotube array is investigated as a conductor for the tetrakis(4-carboxyphenyl)porphyrin dye to construct a new two-compartment photoelectrochemical biofuel cell. The photoelectrochemical biofuel cell containing the TiO2 nanotube array photoanode yields a short-circuit (Isc) current of 110 μA and an open-circuit (Voc) potential of 1010 mV. In contrast, the photovoltaic parameters, Isc and Voc of the photoelectrochemical biofuel cell with the mesoporous TiO2 nanocrystal fluorine-doped tin oxide photoanode, are 96.96 μA and 740 mV, respectively. Photovoltaic measurements show that the maximum incident photon-to-collected electron conversion efficiency was 58% at 430 nm through the spectral range (400–800 nm) for the photoelectrochemical biofuel cell with the TiO2 nanotube array fluorine-doped tin oxide photoanode. These results revealed that the TiO2 nanotube array had great potential for the photoelectrochemical biofuel cells.

Influence of ruthenium doping on UV- and visible-light photoelectrocatalytic color removal from dye solutions using a TiO2 nanotube array photoanode

The photocatalytic activity of TiO2 anodes was enhanced by synthesizing Ru-doped Ti|TiO2 nanotube arrays. Such photoanodes were fabricated via Ti anodization followed by Ru impregnation and annealing. The X-ray diffractograms revealed that anatase was the main TiO2 phase, while rutile was slightly present in all samples. Scanning electron microscopy evidenced a uniform morphology in all samples, with nanotube diameter ranging from 60 to 120 nm. The bias potential for the photoelectrochemical (PEC) treatment was selected from the electrochemical characterization of each electrode, made via linear sweep voltammetry. All the Ru-doped TiO2 nanotube array photoanodes showed a peak photocurrent (PP) and a saturation photocurrent (SP) upon their illumination with UV or visible light. In contrast, the undoped TiO2 nanotubes only showed the SP, which was higher than that reached with the Ru-doped photoanodes using UV light. An exception was the Ru(0.15 wt%)-doped TiO2, whose SP was comparable under visible light. Using that anode, the activity enhancement during the PEC treatment of a Terasil Blue dye solution at Ebias(PP) was much higher than that attained at Ebias(SP). The percentage of color removal at 120 min with the Ru(0.15 wt%)-doped TiO2 was 98% and 55% in PEC with UV and visible light, respectively, being much greater than 82% and 28% achieved in photocatalysis. The moderate visible-light photoactivity of the Ru-doped TiO2 nanotube arrays suggests their convenience to work under solar PEC conditions, aiming at using a large portion of the solar spectrum.

Black Phosphorus Quantum Dot-Sensitized TiO2 Nanotube Arrays with Enriched Oxygen Vacancies for Efficient Photoelectrochemical Water Splitting

Photon absorption, charge separation and transportation, and charge-induced reactions at the active sites are the main crucial factors involved in the photoelectrochemical (PEC) water splitting. Herein, a combination of black phosphorus quantum dot (BPQD) sensitization and defect engineering strategies is employed to optimize the PEC performance of one-dimensional TiO2 nanotube array (NTA) photoanodes. The as-prepared TiO2–x/BP electrode exhibits a strong photocurrent density under simulated solar light irradiation, which is almost ∼3 times higher than that of bare TiO2. Specifically, the photocurrent increment of TiO2–x/BP is even larger than the sum of TiO2–x and TiO2/BP, verifying the synergistic effect of oxygen vacancies and BPQD sensitization. The maximum photoconversion efficiency of TiO2–x/BP is as high as 0.35%, while the value of TiO2 NTAs is calculated to be 0.13%. The results reveal that oxygen vacancies and BPQDs in the TiO2–x/BP composite not only facilitate the charge separation and transportation but also enhance the activity and quantity of reactive sites for water oxidation. The present strategy might open new routes to develop high-performance photoelectrodes for water splitting.

One-dimensional TiO2 nanotube array photoanode for a microfluidic all-vanadium photoelectrochemical cell for solar energy storage

In this work, a highly efficient TiO2 nanotube array photoanode prepared by anodizing treatment of titanium foil is developed for an all-vanadium photoelectrochemical cell with a miniaturized design for solar energy storage.

Bi shell-BiOI core microspheres modified TiO2 nanotube arrays photoanode: Improved effect of Bi shell on photoelectrochemical hydrogen evolution in seawater

Photoelectrochemical (PEC) seawater splitting can relive the shortage of purified water feedstocks. However, the corrosion from seawater on the photoelectrode becomes an uncertain influence factor for PEC performance. Developing an efficient and stable photoelectrode is a challenge. Herein, we present a Bi–BiOI shell-core microspheres modified TiO2 nanotube arrays (TNA) photoanode prepared via solvothermal method, affording superior PEC hydrogen evolution activity in simulated seawater under AM1.5G light, which is 3.8 and 7.6 times than those of BiOI/TNA and TNA, respectively. Solar-to-hydrogen conversion efficiency of Bi–BiOI/TNA reaches to 2.21% with Faradaic efficiency up to 85.7%. Based on the optical and PEC measurements, it is verified that surface plasmon resonance effect of metallic Bi promotes transfer and separation of photogenerated charge and enhances visible-light absorption, thus benefiting higher PEC performance. Especially, Bi shell efficiently hinders the corrosion of BiOI by seawater. Our work provides a novel paradigm of photoanode for efficient and stable PEC seawater splitting.

Efficient degradation of refractory organics for carbonate-containing wastewater via generation carbonate radical based on a photoelectrocatalytic TNA-MCF system

Carbonate widely exist in wastewater and natural water. Here we proposed an efficient refractory organics degradation method for carbonate-containing wastewater via generating carbonate radical based on a photoelectrocatalytic TNA-MCF system. In the system, TiO2 nanotube arrays (TNA) and modified carbon felt (MCF) were used as photoanode and cathode, respectively. HCO3− was used as electrolyte. The results show that the system achieved 85.78% removal rate after 120 min in rhodamine B degradation, which is 30% higher than that using SO42− as electrolyte. The excellent performance is attributed to the strong oxidation of CO3− to organics, which originates from the reactions between HCO3− and hvb+ on TNA photoanode. It was also generated from the activation of HCO3− with H2O2 or O2− on MCF cathode. Moreover, the mechanism of CO3− formation and its efficient degradation of organics were investigated. These results demonstrate that this system has a potential application in refractory organics degradation.

How does cobalt phosphate modify the structure of TiO2 nanotube array photoanodes for solar water splitting?

TiO2 nanotube arrays (TNA) have been modified by cobalt phosphate (CoPi) through potentiostatic electrodeposition method. Different samples have been prepared by changing the loaded CoPi through the deposition time from 10 to 960 min. Formed catalytic materials have been characterized by different methods. Although charge transfer resistance of the CoPi/TNA photoanodes have been decreased from 5.5 to 4.0 kΩ by increasing the deposition time from 5 to 60 min, the maximum photoresponse was obtained for 10 min CoPi deposition leading to 24% more photocurrent compare to bare TNA which proposed optimum value for cobalt phosphate decoration. Based on field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) results, by depositing the electrocatalyst, nanotube walls have been spread and holes have been covered by CoPi. Correlation between observed change in surface morphology and Raman spectra of the samples along with electrocatalytic tests revealed how decoration time can influence structural properties and photoelectrochemical performance of the final CoPi/TNA photoanodes in solar water splitting system.