A wafer-scale antireflective protection layer of solution-processed TiO2 nanorods for high performance silicon-based water splitting photocathodes

Andoshe, D.,Choi, S.,Shim, Y. S.,Lee, S.,Kim, Y.,Moon, C.,Kim, D.,Lee, S.,Kim, T.,Park, H. Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.24

<P>Sustainable and efficient conversion of solar energy to transportable green energy and storable fuels, hydrogen, represents a solution to the energy crisis and reduces the consumption of fossil fuels, which are mainly responsible for the rise in global temperature. Solar water splitting using semiconductors, such as silicon, is promising to satisfy the global energy demand by producing hydrogen molecules. However, the solar to hydrogen conversion efficiency of a silicon photoelectrode is suppressed by overpotential, high reflectance and/or instability in liquid electrolytes. Herein, we report the synthesis of multifunctional solution-processed TiO2 nanorods on a 4-inch p-silicon wafer with controllable heights and diameters for highly efficient water splitting photocathodes. The solution-processed passivation layer of TiO2 nanorods reduces the overpotential of the silicon photocathode due to its catalytic properties. The TiO2 NRs also dramatically improves the light absorption of silicon due to the antireflective ability of the nanorods. The reflectance of silicon is decreased from 37.5% to 1.4% and enhances the saturated photocurrent density. The Pt-decorated (1-2.5 nm diameter) TiO2 nanorods/p-Si photocathodes show a short circuit current density of up to 40 mA cm(-2), an open circuit voltage similar to 440 mV and incident photon to current conversion efficiency of >90% using 0.5 M H2SO4 electrolyte with simulated 1 sun irradiation. The heterostructure photocathodes are stable for more than 52 h without noticeable degradation and an ideal regenerative cell efficiency of 2.5% is achieved.</P>

Two-dimensional transition metal dichalcogenide nanomaterials for solar water splitting

Andoshe, D. M.,Jeon, J. M.,Kim, S. Y.,Jang, H. W. SPRINGER SCIENCE AND BUSINESS MEDIA 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.3

One-pot synthesis of sulfur and nitrogen codoped titanium dioxide nanorod arrays for superior photoelectrochemical water oxidation

Andoshe, Dinsefa M.,Yim, Kanghoon,Sohn, Woonbae,Kim, Changyeon,Kim, Taemin Ludvic,Kwon, Ki Chang,Hong, Kootak,Choi, Seokhoon,Moon, Cheon Woo,Hong, Seung-Pyo,Han, Seungwu,Jang, Ho Won Elsevier 2018 Applied Catalysis B Vol.234 No.-

<P><B>Abstract</B></P> <P>Despite its abundant, nontoxicity and photochemical stability, titanium dioxide shows low solar water oxidation performance due to low photogenerated carrier transport and wide optical band gap, which results in substantially low photogenerated carrier density that impair the solar to hydrogen conversion efficiency. Herein, highly enhanced water oxidation performance of high-aspect-ratio TiO<SUB>2</SUB> nanorods doped with dual heteroatoms, sulfur and nitrogen, for photoelectrochemical solar water oxidation is demonstrated. The codoped TiO<SUB>2</SUB> NRs have shown enhanced optical absorption coefficient due to the induced impurities energy states near to the top of the valance band and result in a red shift in the optical absorption edges. Consequently, a 2.82 mAcm<SUP>−2</SUP> photocurrent density at 1.23 V vs. RHE is obtained from the sulfur and nitrogen codoped TiO<SUB>2</SUB> nanorods, and pristine TiO<SUB>2</SUB> nanorods photoanode shows 0.7 mAcm<SUP>−2</SUP>. The applied bias photon-to-current conversion efficiency and external quantum efficiency of the codoped TiO<SUB>2</SUB> nanorods are 1.49% and 97.0% at λ = 360 nm and 0.69% and 19.1% at λ = 370 nm for pristine TiO<SUB>2</SUB> nanorods, respectively. Our study offers experimental and theoretical evidence for codoping of sulfur and nitrogen improve the optical and electrical properties of TiO<SUB>2</SUB> for efficient photoelectrochemical solar water oxidation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Our S, N codoped TiO<SUB>2</SUB> NRs photoanodes synthesized by one-pot synthesis method exhibit the excellent photoelectrochemical performance. </LI> <LI> The influence of dual heteroatom doping with sulfur and nitrogen on optical and electrical properties was elucidated by experiments and theoretical calculation. </LI> <LI> The dual heteroatom doping with sulfur and nitrogen decreases the dopant formation energy and improves the optical absorption coefficient of TiO<SUB>2</SUB> NRs. </LI> <LI> In UV wavelength region, our samples show the incident photon up to a current efficiency of 97%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A photoanode prepared using titanium dioxide nanorods Arrays codoped with sulfur and nitrogen shows the highest water oxidation performance relative to cocatalyst-free TiO<SUB>2</SUB> photoanodes reported to date for photoelectrochemical water splitting. The outperformance of the TiO<SUB>2</SUB> (S, N) NRs mainly resulted from the induced energy states between the conduction and valence band of TiO<SUB>2</SUB>, which enhances the optical absorption and charge transport of the TiO<SUB>2</SUB> NRs.</P> <P>[DISPLAY OMISSION]</P>

Toward High-Performance Hematite Nanotube Photoanodes: Charge-Transfer Engineering at Heterointerfaces

Kim, Do Hong,Andoshe, Dinsefa M.,Shim, Young-Seok,Moon, Cheon-Woo,Sohn, Woonbae,Choi, Seokhoon,Kim, Taemin Ludvic,Lee, Migyoung,Park, Hoonkee,Hong, Kootak,Kwon, Ki Chang,Suh, Jun Min,Kim, Jin-Sang,Lee American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.36

<P>Vertically ordered hematite nanotubes are considered to be promising photoactive materials for high-performance water-splitting photoanodes. However, the synthesis of hematite nanotubes directly on conducting substrates such as fluorine-doped tin oxide (FTO)/glass is difficult to be achieved because of the poor adhesion between hematite nanotubes and FTO/glass. Here, we report the synthesis of hematite nanotubes directly on FTO/glass substrate and high-performance photoelectrochemical properties of the nanotubes with NiFe cocatalysts. The hematite nanotubes are synthesized by a simple electrochemical anodization method. The adhesion of the hematite nanotubes to the FTO/glass substrate is drastically improved by dipping them in nonpolar cyclohexane prior to postannealing. Bare hematite nanotubes show a photocurrent density of 1.3 mA/cm(2) at 1.23 V vs a reversible hydrogen electrode, while hematite nanotubes with electrodeposited NiFe cocatalysts exhibit 2.1 mA/cm(2) at 1.23 V which is the highest photocurrent density reported for hematite nanotubes-based photoanodes for solar water splitting. Our work provides an efficient platform to obtain high-performance water-splitting photoanodes utilizing earth-abundant hematite and noble-metal-free cocatalysts.</P>

Tungsten disulfide thin film/p-type Si heterojunction photocathode for efficient photochemical hydrogen production

Kwon, Ki Chang,Choi, Seokhoon,Hong, Kootak,Andoshe, Dinsefa Mensur,Suh, Jun Min,Kim, Changyeon,Choi, Kyoung Soon,Oh, Jeong Hyeon,Kim, Soo Young,Jang, Ho Won Cambridge University Press (Materials Research Soc 2017 MRS Communications Vol.7 No.2

<▼1><B>Abstract</B><P/></▼1><▼2><P>We demonstrate the tungsten disulfide (WS2) thin film catalysts prepared by the sulfurization of vacuum deposited WO3 thin films for efficient hydrogen production with over 90% Faradaic efficiency. The 23-nm-thick WS2 thin film catalyst heterojunction with <I>p</I>-type silicon photocathode could exhibit a photocurrent density of 8.3 mA/cm<SUP>2</SUP> at 0 V versus a reversible hydrogen electrode (RHE), a low onset potential of 0.2 V versus RHE when photocurrent density reaches −1 mA/cm<SUP>2</SUP> and long-term stability over 10 h. The enhanced catalytic activities of WS2/<I>p</I>-Si photocathodes compared with the bare <I>p</I>-Si photocathode originate from a number of edge sites in the synthesized polycrystalline thin films, which could act as hydrogen evolution catalyst.</P></▼2>

Drastically enhanced hydrogen evolution activity by 2D to 3D structural transition in anion-engineered molybdenum disulfide thin films for efficient Si-based water splitting photocathodes

Chang Kwon, Ki,Choi, Seokhoon,Lee, Joohee,Hong, Kootak,Sohn, Woonbae,Andoshe, Dinsefa Mensur,Choi, Kyoung Soon,Kim, Younghye,Han, Seungwu,Kim, Soo Young,Jang, Ho Won The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.30

<▼1><P>Efficient photoelectrochemical hydrogen production is demonstrated by sulphur-doped molybdenum phosphide/p-Si heterojunctions.</P></▼1><▼2><P>We synthesized transferrable and transparent anion-engineered molybdenum disulfide thin-film catalysts through a simple thermolysis method by using [(NH4)2MoS4] solution and powder precursors with different sulphur/phosphorus weight ratios. The synthesized sulphur-doped molybdenum phosphide (S:MoP) thin film changed from a two-dimensional van der Waals structure to a three-dimensional hexagonal structure by introduction of phosphorus atoms in the MoS2 thin film. The S:MoP thin film catalyst, which is composed of cheap and earth abundant elements, could provide the lowest onset potential and the highest photocurrent density for planar p-type Si photocathodes. The density functional theory calculations indicate that the surface of S:MoP thin films absorb hydrogen better than that of MoS2 thin films. The structurally engineered thin film catalyst facilitates the easy transfer of photogenerated electrons from the p-Si light absorber to the electrolyte. Anion-engineering of the MoS2 thin film catalyst would be an efficient way to enhance the catalytic activity for photoelectrochemical water splitting.</P></▼2>