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>

Modification of the structural properties of NiTiO₃ materials by transition metal dopants: The dopant size effect

Jiang, Kaiming,Pham, Thanh-Truc,Kang, Sung Gu,Men, Yong,Shin, Eun Woo Elsevier 2018 Journal of alloys and compounds Vol.739 No.-

<P><B>Abstract</B></P> <P>In this study, we investigated the changes of the structural and optical properties of NiTiO<SUB>3</SUB> materials modified by transition metal doping. Cobalt (Co) or tungsten (W)-doped NiTiO<SUB>3</SUB> materials were successfully prepared by a modified Pechini method via solvothermal treatment. Raman, FTIR, and XRD spectroscopic analyses showed that the Co<SUP>2+</SUP> ions were selectively doped into Ni<SUP>2+</SUP> sites in the NiTiO<SUB>3</SUB> lattice while maintaining an ilmenite structure, resulting in a solid solution of triple transition metal oxides. The size similarity between Co and Ni induced the formation of a solid solution, Co<SUB>x</SUB>Ni<SUB>1-x</SUB>TiO<SUB>3</SUB>, in the ilmenite structure. In contrast, W doping into the NiTiO<SUB>3</SUB> ilmenite structure resulted in an irregularity of the materials due to the characteristics of the heavy transition metal dopant. Along with increasing the W content, the crystallite size in the ilmenite structure decreased from 90.2 to 74.5 nm and new Raman bands at 831 and 892 cm<SUP>−1</SUP> for WO<SUB>x</SUB> appeared at high W contents. However, the PL emission intensities gradually decreased with increasing doping content, implying that the recombination process was inhibited in the NiTiO<SUB>3</SUB> materials by the dopants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co (W)-doped NiTiO<SUB>3</SUB> materials were successfully prepared by a modified Pechini method. </LI> <LI> Selective Co<SUP>2+</SUP> ion doping into Ni<SUP>2+</SUP> sites in the NiTiO<SUB>3</SUB> lattice formed a solid solution. </LI> <LI> W doping into the NiTiO<SUB>3</SUB> lattice resulted in an irregularity in the lattice structure. </LI> <LI> The PL emission intensities gradually decreased with increasing dopant concentration. </LI> <LI> The recombination process in the NiTiO<SUB>3</SUB> materials was inhibited by the metal dopants. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electical and optical properties of amorphous tungsten-doped In2 O3 thin films prepared using solution coating method

정지혜,이도경 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.0

Thermochromic Hybrid Nanoparticles Comprising a Tungsten-Doped Vanadium Dioxide Core and a Poly(N-isopropylacrylamide) Shell Structure

Sang Won Jung(정상원),Sang Hwi Park(박상휘),Jung Whan Yoo(유중환),Juhyun Park(박주현) 한국고분자학회 2021 폴리머 Vol.45 No.2

열변색 스마트 창호 소재로서 텅스텐이 도핑된 바나듐이산화물(WxVO₂) 나노입자와 폴리이소프로필아크릴아미드(PNIPAm)의 하이브리드 나노입자가 실리카 쉘 형성 및 PNIPAm의 표면라디칼 중합반응에 의해 합성되었다. 하이브리드 나노입자의 수분산액은 섭씨 28도의 금속-절연체 전이온도를 보유한 WxVO₂ 코어와 섭씨 32도의 하한임계 용액온도를 보유한 PNIPAm 쉘의 특성으로 인해 가시광선에서 근적외선까지의 넓은 스펙트럼 범위에서 효과적인 열변색 특성을 보였다. 하이브리드 나노입자에서 PNIPAm의 함량을 고정시키고 WxVO₂의 함량을 변화시키며 특성을 측정한 결과 섭씨 20도에서 40도의 온도 변화에서 25% 이상의 태양광 변조 변화를 구현하였으며 WxVO₂의 함량증가에 따라 입자의 증가된 뭉침현상에 의해 투과도는 85%에서 15%까지 급격하게 감소하였다. 본 연구결과는 WxVO₂효율적인 열변색 소재를 제조하기 위한 주요 기술이 될 수 있음을 보여준다. Hybrid nanoparticles based on tungsten-doped vanadium dioxide (WxVO₂) nanoparticles and poly(N-isopropylacrylamide) (PNIPAm) for thermochromic smart window applications were synthesized via silica layer formation using (3-mercaptopropyl)trimethoxysilane (MPTMS) followed by the surface-mediated free radical polymerization of PNIPAm, resulting in the aqueous dispersion of the hybrid nanoparticles. The metal-insulator transition of the WxVO₂ core at around 28 °C and the lower critical solution temperature of PNIPAm at around 32 °C enable the aqueous dispersion of the hybrid nanoparticles to present an efficient thermochromicity depending on the temperature over a broad spectral range from visible to near-infrared light. The difference in the solar modulation was over 25%, while the luminous transmittance (Tlum) significantly decreased from 85% to 15% with increasing WxVO₂ composition in the hybrids. Our results suggest that the hybridization of WxVO₂ and PNIPAm is a potential methodology for preparing efficient thermochromic materials.

Trace surface fluorination and tungsten-intercalation cooperated dual modification induced photo-activity enhancement of titanium dioxide

Yifan Xu,Zhongyuan Liu,Kunlun Wang,Chunyao Niu,Pengfei Yuan,Jin You Zheng,Young Soo Kang,Xiao Li Zhang 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.108 No.-

General modification that utilizes insoluble tungstic acid or highly toxic hydrofluoric acid to improvecharge separation and transfer in TiO2 results in considerable issues such as uneven doping, significantimpacts on particle size and morphology, as well as environmental hazards. In the present work, an environmentalbenign one-pot dual-modification approach was demonstrated that uses soluble sodium tungstateand only trace-level sodium fluoride as replacements. The photoactivity efficiency for decolorationof methylene blue (MB) solution was improved by 33.6% and 119.5% under ultraviolet and visible light,respectively. Meanwhile, the photocurrent density reached an enhancement by 181.2% by this dualmodification. The dual-modification had negligible influence on the crystal structure and the surface areaof the TiO2 nanoparticles. Density functional calculation suggested the remarkable improvements of thephotocatalysis of TiO2 can be ascribed to the rapid charge separation and transfer owing to the downshiftof conduction band from the tungsten doping and localized spatial charge separation from the surfacefluorination enabled by the dual-modification approach.

Coupling of W-Doped SnO2 and TiO2 for Efficient Visible-Light Photocatalysis

Sher Bahadur Rawal,Devi Prashad Ojha,최영식,이완인 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.3

Five mol % tungsten-doped tin oxide (W0.05Sn0.95O2, TTO5) was prepared by co-precipitation of SnCl4·5H2O and WCl4, followed by calcination at 1000 oC. The as-prepared TTO5 was in the pure cassiterite phase with a particle size of ~50 nm and optical bandgap of 2.51 eV. Herein it was applied for the formation of TTO5/TiO2 heterojunctions by covering the TTO5 surface with TiO2 by sol-gel method. Under visible-light irradiation (λ ≥ 420 nm), TTO5/TiO2 showed a significantly high photocatalytic activity in removing gaseous 2-propanol (IP) and evolving CO2. It is deduced that its high visible-light activity is caused by inter-semiconductor holetransfer between the valence band (VB) of TTO5 and TiO2, since the TTO5 nanoparticle (NP) exhibits the absorption edge at ~450 nm and its VB level is located more positive side than that of TiO2. The evidence for the hole-transport mechanism between TTO5 and TiO2 was also investigated by monitoring the holescavenging reaction with 1,4-terephthalic acid (TA).

Coupling of W-Doped SnO₂ and TiO₂ for Efficient Visible-Light Photocatalysis

Rawal, Sher Bahadur,Ojha, Devi Prashad,Choi, Young Sik,Lee, Wan In Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.3

Five mol % tungsten-doped tin oxide ($W_{0.05}Sn_{0.95}O_2$, TTO5) was prepared by co-precipitation of $SnCl_4{\cdot}5H_2O$ and $WCl_4$, followed by calcination at $1000^{\circ}C$. The as-prepared TTO5 was in the pure cassiterite phase with a particle size of ~50 nm and optical bandgap of 2.51 eV. Herein it was applied for the formation of TTO5/$TiO_2$ heterojunctions by covering the TTO5 surface with $TiO_2$ by sol-gel method. Under visible-light irradiation (${\lambda}{\geq}420$ nm), TTO5/$TiO_2$ showed a significantly high photocatalytic activity in removing gaseous 2-propanol (IP) and evolving $CO_2$. It is deduced that its high visible-light activity is caused by inter-semiconductor holetransfer between the valence band (VB) of TTO5 and $TiO_2$, since the TTO5 nanoparticle (NP) exhibits the absorption edge at ~450 nm and its VB level is located more positive side than that of $TiO_2$. The evidence for the hole-transport mechanism between TTO5 and $TiO_2$ was also investigated by monitoring the holescavenging reaction with 1,4-terephthalic acid (TA).

Room-temperature tensile strength and thermal shock behavior of spark plasma sintered W-K-TiC alloys

Ke Shi,Bo Huang,Bo He,Ye Xiao,Xiaoliang Yang,Youyun Lian,Xiang Liu,Jun Tang 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.1

W-K-TiC alloys with different titanium carbide concentrations (0.05, 0.1, 0.25, 0.5, 1, 2) wt.% werefabricated through Mechanical Alloying and Spark Plasma Sintering. The effects of the addition of nanoscaledTiC particles on the relative density, Vickers micro-hardness, microstructure, crystal information,thermal shock resistance, and tensile strength were investigated. It is revealed that the doped TiC nanoparticleslocated at the grain boundaries. The relative density and Vickers micro-hardness of W-K-TiCalloys was enhanced with TiC addition and the highest Vickers micro-hardness is 731.55. As the TiCaddition increased from 0.05 to 2 wt%, the room-temperature tensile strength raised from 141 to353 MPa. The grain size of the W-K-TiC alloys decreased sharply from 2.56 mm to 330 nm with theenhanced TiC doping. The resistance to thermal shock damage of W-K-TiC alloys was improved slightlywith the increased TiC addition

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>

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>