Aligned nanotriangles of tantalum doped tungsten oxide for improved photoelectrochemical water splitting

Kalanur, Shankara S.,Seo, Hyungtak ELSEVIER SCIENCE 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.785 No.-

<P><B>Abstract</B></P> <P>Tuning the optical and electrical properties of WO<SUB>3</SUB> via doping is an efficient strategy to improve its photoelectrochemical (PEC) water splitting activity. In this article, a simple hydrothermal method is utilized to fabricate Ta-doped WO<SUB>3</SUB> nanotriangle thin films for the PEC water splitting applications. The doping of Ta converts the nanorod structure of undoped WO<SUB>3</SUB> into nanotriangle morphology. During the synthesis, the Ta is doped to orthorhombic WO<SUB>3</SUB>·0.33H<SUB>2</SUB>O and converted to hexagonal phase via annealing. The presence of Ta in the WO<SUB>3</SUB> lattice obstruct the reconstructive transformation of orthorhombic to monoclinic phase producing Ta-doped WO<SUB>3</SUB> with hexagonal phase. The optimum amount of Ta (1.88 at%) causes the reduction in the band gap and increase the oxygen vacancies and carrier density in WO<SUB>3</SUB> lattice. Compared to undoped WO<SUB>3</SUB>, Ta-doped WO<SUB>3</SUB> nanotriangles exhibit higher photocurrent and incident photon to current efficiency values. Finally, the possible band structure is proposed for the Ta-doped WO<SUB>3</SUB> based on the spectroscopic and electrochemical data. The results of the present work suggest that Ta doping alters the band edge positions of WO<SUB>3</SUB> and has the potential to improve the PEC water splitting activity of WO<SUB>3</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ta-doped WO<SUB>3</SUB> nanotriangles were synthesized using a facile hydrothermal method. </LI> <LI> •Doping Ta into WO<SUB>3</SUB> lattice obstructs the reconstructive transformation. </LI> <LI> •Ta-doped WO<SUB>3</SUB> exhibited hexagonal crystal phase instead of monoclinic. </LI> <LI> •Ta-doped WO<SUB>3</SUB> show improved photoelectrochemical activity compared to undoped WO<SUB>3</SUB>. </LI> <LI> •Band edge positions of WO<SUB>3</SUB> before and after Ta doping were determined. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fundamental investigation of Ti doped WO₃ photoanode and their influence on photoelectrochemical water splitting activity

Kalanur, Shankara S.,Yoo, Il-Han,Seo, Hyungtak Pergamon Press 2017 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>Herein, we utilize a facile hydrothermal method for the fabrication of Ti doped WO<SUB>3</SUB> thin films on fluorine-doped tin oxide (FTO) for the efficient photoelectrochemical water splitting activity. Doping of Ti into WO<SUB>3</SUB> is achieved during the condensation of a stable aqueous precursor solution of peroxopolytungstic acid (PTA) at 150°C. Characterization results show that, doping of Ti into WO<SUB>3</SUB> suppresses the crystal growth along (200) facet and shift the 2 θ values to higher degree with a corresponding decrease in d spacing. Elemental mapping along with EDS measurements show the uniform distribution and approximate at% of Ti doped in WO<SUB>3</SUB>. The WO<SUB>3</SUB> photoanode doped with 1.16 at% Ti displayed cathodic shift in onset potential with a maximum photocurrent density of 1.139mAcm<SUP>−2</SUP> (at 1.23 vs. RHE), which is found to be 3.5 times higher than undoped WO<SUB>3</SUB> (0.335mAcm<SUP>−2</SUP>) under simulated 1.5 AM sunlight. Spectroscopic and impedance measurements show that, the substitution of W with Ti, widens the band gap and shifts the conduction band edge (CBE) and flat band potential upwards to higher energies keeping the relative energy difference between valence band edge (VBE) and Fermi level constant. Such a change in band edge positions of WO<SUB>3</SUB> after Ti doping, shifts the conduction band minimum (CBM) towards the H<SUP>+</SUP>/H<SUB>2</SUB> redox potential. The study presented herein demonstrates a simple but systematic and efficient approach for the design and fabrication of band edge-tailored WO<SUB>3</SUB> photoanodes via Ti doping for the efficient photoelectrochemical water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ti doped WO<SUB>3</SUB> thins films are synthesized using facile hydrothermal method. </LI> <LI> The PEC properties of WO<SUB>3</SUB> are improved by Ti doping. </LI> <LI> Ti doping shifts both CBM, VBM and flat band potential of WO<SUB>3</SUB> upwards. </LI> <LI> Ti doping to WO<SUB>3</SUB> effects crystal facet, carrier density and oxygen vacancy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhancement of photoelectrochemical water splitting response of WO₃ by Means of Bi doping

Kalanur, Shankara S.,Yoo, Il-Han,Eom, Kiryung,Seo, Hyungtak Elsevier 2018 Journal of catalysis Vol.357 No.-

<P><B>Abstract</B></P> <P>Doping is a very effective strategy for tailoring the electronic band structure and improving the charge transport properties of WO<SUB>3</SUB>, which could in turn enhance its photoelectrochemical (PEC) activity. In this work, we report a facile hydrothermal route to synthesize Bi doped WO<SUB>3</SUB> thin films on fluoride-doped tin oxide (FTO) glass substrate and investigated the insights of its band alignment. Systematic doping of Bi into WO<SUB>3</SUB> was achieved during the condensation of peroxopolytungstic acid (PTA) in the course of hydrothermal synthesis. The effect of Bi doping on the morphology and crystal structure was investigated and the approximate amount of Bi incorporated into WO<SUB>3</SUB> was estimated using energy dispersive spectroscopy (EDS). Results of UV–Vis spectroscopy, Mott-Schottky analysis and valence-band (VB) X-ray photoelectron spectroscopy revealed that the insertion of Bi into the lattice of WO<SUB>3</SUB> changes the band gap, valence band maximum, and the conduction band minimum of WO<SUB>3</SUB>. PEC measurements displayed remarkable enhancement in photocurrent values from 0.401 mA cm<SUP>−2</SUP> for un-doped WO<SUB>3</SUB> to ∼1.511 mA cm<SUP>−2</SUP> (<I>ca</I>. 4-fold increase) for optimized Bi doped WO<SUB>3</SUB> samples at 1.23 V vs. RHE under simulated AM 1.5 G sunlight without the addition of catalysts. The results of electrochemical impedance spectroscopy confirmed that doping WO<SUB>3</SUB> with Bi lead to low charge transfer resistance across the electrode/electrolyte interface and an increase in charge-carrier density. This work suggests that Bi doping has the potential to significantly improve the PEC water splitting efficiency of WO<SUB>3</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Systematic doping of Bi into WO<SUB>3</SUB> was achieved by facile hydrothermal method. </LI> <LI> Insertion of Bi into WO<SUB>3</SUB> affects band gap, and band edge positions of WO<SUB>3</SUB>. </LI> <LI> Bi-doped WO<SUB>3</SUB> thin films exhibit enhanced PEC water splitting efficiencies. </LI> <LI> Bi insertion into WO<SUB>3</SUB> lattice improves carrier density of WO<SUB>3</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile growth of aligned WO3 nanorods on FTO substrate for enhanced photoanodic water oxidation activity

Kalanur, S.,Hwang, Y.,Chae, S.,Joo, O. Royal Society of Chemistry 2013 Journal of materials chemistry. A, Materials for e Vol.1 No.10

Pd on MoO₃ nanoplates as small-polaron-resonant eye-readable gasochromic and electrical hydrogen sensor

Kalanur, Shankara S.,Yoo, Il-Han,Seo, Hyungtak Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.247 No.-

<P><B>Abstract</B></P> <P>Hydrogen is a renewable, efficient, and clean energy carrier that can replace petroleum as the future of energy. Eventually, efficient hydrogen detection will become an important requirement for the successful and safe use of hydrogen as a fuel. Among the various hydrogen detection schemes available, gasochromic sensors have major advantages of being intrinsically safe, free of electric contacts in the sensing area, easy to use, and inexpensive. In view of these advantages, we developed an irreversible gasochromic and electrical sensor composed of MoO<SUB>3</SUB> nanoplates and Pd nanoparticles fabricated via green deposition. The amount, distribution, and particle size of the Pd nanoparticles can be controlled easily by modifying the deposition condition, which is necessary for efficient hydrogen sensing. The developed gasochromic sensor was found to change color from white to dark blue upon hydrogen exposure, owing to the polaron-resonance effect; this effect is induced by the coupling of atomic free d-electrons in reduced Mo ion states with H+ ions. Hydrogen concentrations as low as up to 0.1% could be easily detected by the developed sensor. The simple and green fabrication process and detection scheme make the developed sensor highly cost effective and widely applicable in various areas of the hydrogen industry.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrothermal synthesis of MoO<SUB>3</SUB> nanoplates. </LI> <LI> Green deposition of Pd on MoO<SUB>3</SUB> nanoplates. </LI> <LI> Polaron-Resonant Eye readable hydrogen gas sensor. </LI> <LI> Mechanism of sensing is presented. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced photoanode properties of CdS nanoparticle sensitized TiO₂ nanotube arrays by solvothermal synthesis

Kalanur, S.S.,Lee, S.H.,Hwang, Y.J.,Joo, O.S. Elsevier Sequoia 2013 Journal of photochemistry and photobiology Chemist Vol.259 No.-

We demonstrate the synthesis of CdS-sensitized TiO<SUB>2</SUB> (CdS/TiO<SUB>2</SUB>) nanotube arrays via the solvothermal method and describe their enhanced photoelectrochemical properties. Our new approach prevents the clogging of CdS quantum dots (QDs) at the TiO<SUB>2</SUB> nanotube mouth and promotes the uniform deposition of a polycrystalline CdS on the densely aligned TiO<SUB>2</SUB> nanotube arrays (TiO<SUB>2</SUB> NTAs). The deposition of CdS onto the TiO<SUB>2</SUB> NTA can be controlled by the deposition time and the concentration of the precursors. Photoelectrochemical measurements indicate that the electrode synthesized via the solvothermal method can achieve a stable photocurrent density of 5.7mA/cm<SUP>2</SUP> at 0-V versus Ag/AgCl under AM 1.5G illumination, which is approximately 10% higher than that prepared using the chemical bath deposition (CBD) method. Solvothermally prepared CdS/TiO<SUB>2</SUB> NTAs exhibit 125-fold enhancement in their photocurrent under visible light compared with bare TiO<SUB>2</SUB> NTAs, indicating facile photogenerated electron transfer from CdS to TiO<SUB>2</SUB>. Solvothermally prepared CdS/TiO<SUB>2</SUB> NTAs shows better photostability and longer lifetime of photoelectrons compared to those prepared by CBD method suggesting more favorable CdS-TiO<SUB>2</SUB> NTA interfacial contact. In general, we propose that this methodology can be useful in designing multijunction semiconductor configuration such as coating nanostructures.

2-D WO₃ decorated with Pd for rapid gasochromic and electrical hydrogen sensing

Kalanur, Shankara S.,Heo, Jaewoo,Yoo, Il-Han,Seo, Hyungtak Pergamon Press 2017 International journal of hydrogen energy Vol.42 No.26

<P><B>Abstract</B></P> <P>The ultrathin two-dimensional (2D) nanomaterials display unique properties owing to their ultrahigh specific surface area and strong quantum confinement of electrons in two dimensions. In this work, we fabricated a rapid gasochromic and electrical hydrogen sensing system containing 2D WO<SUB>3</SUB> and Pd nanoparticles. 2D WO<SUB>3</SUB> nano-plates (NP) are synthesized using sol–gel method and Pd nanoparticles are coated on WO<SUB>3</SUB> by green photochemical deposition method. The sensor is fabricated by dispersing the 2D WO<SUB>3</SUB>/Pd composite on filter paper. In presence of hydrogen gas, 2D WO<SUB>3</SUB>/Pd composite produces visible change in color from brown to dark blue. With the fabricated sensor, as low as 0.1% H<SUB>2</SUB> gas in air at room temperature can be easily detected using electrical sensing scheme whereas for higher concentration from 1 to 100%, eye readable gasochromic scheme can be utilized. The use of 2D WO<SUB>3</SUB> decreased the response time in great deal compared to WO<SUB>3</SUB> nanoparticles indicating the advantage of 2D structure in fabricating rapid response H<SUB>2</SUB> sensors. The proposed method is simple and can be easily employed to large scale fabrication system for commercial applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of 2-D WO<SUB>3</SUB> using sol–gel method. </LI> <LI> Photochemical deposition of Pd on 2-D WO<SUB>3</SUB>. </LI> <LI> Eye readable change in color from brown to dark blue. </LI> <LI> Rapid gasochromic and electrical hydrogen sensing. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile growth of compositionally tuned copper vanadate nanostructured thin films for efficient photoelectrochemical water splitting

Kalanur, Shankara S.,Seo, Hyungtak Elsevier 2019 Applied Catalysis B Vol.249 No.-

<P><B>Abstract</B></P> <P>Copper vanadates are considered as one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting owing to their narrow bandgap, stoichiometry-dependent optical and electrical properties, and high stability. However, for technological applications, it is imperative to develop stoichiometrically and structurally tuned copper vanadates for improved performance. In this study, we developed a facile and one-step hydrothermal method for the synthesis of Cu<SUB>2</SUB>V<SUB>2</SUB>O<SUB>7</SUB> nanoplates, Cu<SUB>5</SUB>V<SUB>2</SUB>O<SUB>10</SUB> nanorods, and Cu<SUB>11</SUB>V<SUB>6</SUB>O<SUB>26</SUB> micropillars on a fluorine-doped tin oxide substrate without using a seed layer. The presence of urea during the hydrothermal synthesis significantly affected the film formation and morphology of the copper vanadates. The crystallographic, chemical, and electrochemical properties of the synthesized copper vanadates were investigated. The optimized Cu<SUB>2</SUB>V<SUB>2</SUB>O<SUB>7</SUB>, Cu<SUB>5</SUB>V<SUB>2</SUB>O<SUB>10</SUB>, and Cu<SUB>11</SUB>V<SUB>6</SUB>O<SUB>26</SUB> electrodes exhibited the highest photocurrent densities of ˜0.41, 0.27, and 0.076 mA cm<SUP>−2</SUP> (at 1.23 V vs. reversible hydrogen electrode under 1-sun illumination) and incident photon to current efficiency values of ˜24%, 18%, and 7.5% (at 300 nm), respectively. The band edge positions of Cu<SUB>2</SUB>V<SUB>2</SUB>O<SUB>7</SUB>, Cu<SUB>5</SUB>V<SUB>2</SUB>O<SUB>10</SUB>, and Cu<SUB>11</SUB>V<SUB>6</SUB>O<SUB>26</SUB> were estimated on the basis of the spectroscopic and electrochemical results. The synthesis scheme and valuable insights provided in this work can be used for the development of chemically and morphologically optimized copper vanadates for efficient PEC water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New hydrothermal route is proposed for the synthesis of copper vanadate thin films. </LI> <LI> Cu<SUB>2</SUB>V<SUB>2</SUB>O<SUB>7</SUB> Nanoplates, Cu<SUB>5</SUB>V<SUB>2</SUB>O<SUB>10</SUB> nanorods, and Cu<SUB>11</SUB>V<SUB>6</SUB>O<SUB>26</SUB> micropillars were synthesized. </LI> <LI> Highest photocurrent of 0.27 mA cm<SUP>−2</SUP> at 1.23 V vs RHE was obtained for Cu<SUB>5</SUB>V<SUB>2</SUB>O<SUB>10.</SUB> </LI> <LI> Based on the results band edge positions of copper vanadates are constructed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of molybdenum doping on the structural, optical and electronic properties of WO₃ for improved solar water splitting

Kalanur, Shankara S.,Seo, Hyungtak Elsevier 2018 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.509 No.-

<P><B>Abstract</B></P> <P>Doping WO<SUB>3</SUB> with foreign atoms is a very efficient strategy to modify the structural, optical and electronic properties which could influence its photoelectrochemical (PEC) water splitting activity. In this study, we report a simple and efficient single-step strategy for the fabrication of molybdenum (Mo)-doped WO<SUB>3</SUB> thin films. The characterization results show that doping Mo into WO<SUB>3</SUB> leads to a significant change in the morphology without changing its crystal structure. Elemental mapping and EDS analysis revealed that Mo was homogeneously doped into the crystal lattice of WO<SUB>3</SUB> in the at.% range of 0–10.31. The incorporation of Mo into WO<SUB>3</SUB> reduced the band-gap of WO<SUB>3</SUB> and increased its light absorption ability. Notably, X-ray photoelectron spectroscopic valence band-edge analysis confirmed that substitution of Mo into WO<SUB>3</SUB> led to a downward shift in the conduction band minimum without any significant change in the valence band maximum with respect to Fermi level. The fabricated Mo-doped WO<SUB>3</SUB> electrodes exhibited a higher photocurrent compared to undoped WO<SUB>3</SUB> samples under simulated 1.5AM sunlight without the addition of a water oxidation catalyst. The procedure proposed herein provides a simple and systematic approach for the fabrication of band-gap-tailored WO<SUB>3</SUB> photoanodes by Mo doping for efficient PEC water splitting.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Recent Progress in Photoelectrochemical Water Splitting Activity of WO3 Photoanodes

Kalanur, Shankara S.,Duy, Le Thai,Seo, Hyungtak Springer-Verlag 2018 Topics in catalysis Vol.61 No.9