Publisher：Solar RRL  

Perovskite solar cells (PSCs) have undergone an unprecedentedly rapid development in both power conversion efficiency (PCE) and operational durability. However, a number of unknown challenges remain before PSC products are ready to launch. Herein, it is demonstrated that the vacuum deposition of gold (Au) onto the organic hole-transport layer (HTL) results in Au penetration into the perovskite layer. This Au penetration proves to be a limiting factor in PCE due to detrimental carrier recombination caused by the penetrated Au component inside the perovskite light absorber. To mitigate this issue, a thin molybdenum oxide (MoOx) interlayer between the organic HTL and the Au electrode is introduced, effectively reducing the Au penetration and suppressing the carrier recombination. Consequently, this MoOx introduction increases PCEs from ≈16.9% to ≈19.6% by ≈2.7%. Furthermore, using the MoOx interlayer improves the long-term durability of PSCs. These findings are crucial in elucidating a basic mechanism that limits PCE and in advancing the fabrication of PSC products with even higher performance.

DOI： 10.1002/solr.202400029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society of Japan  

<p>A dense NiO-Fe₂O₃ (NiFe) pellet has been developed as a potential anode-support for thin-film solid oxide fuel cells (SOFCs). However, preparation of dense NiFe is very challenging. Hole-formed NiFe pellets or porous NiFe pellets are frequently formed, which cannot be used as a support (substrate) for thin-film SOFCs. Therefore, this hole-formed NiFe support is simply wasted. In this report, we attempt to re-qualify this NiFe support to be a valuable substrate, which can be used for fabricating thin-film SOFCs. By deposition of smaller NiFe particles to cover the hole-formed NiFe support, the surface of this NiFe pellet is modified. Large holes on the surface disappear. The newly formed NiFe support can be used for fabricating a single cell with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ as thin-film electrolyte operated at intermediate temperature. Maximum power density generated from this cell is 0.45, 0.86 and 1.28 W cm⁻² at 873, 923 and 973 K, respectively.</p>

DOI： 10.5796/electrochemistry.23-00164

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Language：English   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

NH3 is an important chemical fertilizer and expecting as H2 carrier. Several methods have been investigated for eco-friendly NH3 production under mild conditions instead of Haber-Bosch process using 400 °C, 20 MPa. Here, cyanobacterial Anabaena variabilis was utilized as a nitrogenase-producing biocatalyst that converts N2/H2O to NH3 under ambient conditions. Biocatalytic reactions revealed that MV•+ can penetrate cell membrane and transfer electrons generated in inorganic photocatalyst. We first reported photobiocatalytic NH3 production of cyanobacteria and TiO2. Comparing with natural system, NH3 formation rate of the hybrid system increased 81.3 times with an initial rate of 2031.7 nmol·h−1 and turnover number of 216.8.

DOI： 10.1016/j.apcatb.2023.123431

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Publisher：Solar RRL  

All-inorganic CsPbI2Br mixed halide perovskites show promise as wide-bandgap photoabsorbers in photovoltaics. However, the rapid crystal growth observed in solution-processed CsPbI2Br often leads to morphologies plagued by pinholes and defects, which limit device performance. This study introduces 2-Amino-5-nitrothiazole (ANT), an innovative precursor additive, to enhance film quality. ANT's selective interactions with the perovskite precursor moderate the crystal growth, resulting in a dense, flawless CsPbI2Br film characterized by superior crystallinity and coverage. Furthermore, the -NH2 group in ANT coordinates with Pb octahedra, effectively mitigating charge defects through NH=I/Br bonds. Simultaneously, S=C-N sites interact with uncoordinated Pb2+ ions, reducing defect states and nonradiative recombination. This innovation achieves an impressive device efficiency of 17.13% with a fill factor (FF) of 83.41%, surpassing the control's efficiency of 15.21% (FF of 80.45%). Notably, the champion device maintains an efficiency of 29.47% under indoor light-emitting diode lighting at 1000 lux. Additionally, the optimized perovskite solar cell demonstrates remarkable stability, retaining ≈90% of its efficiency for over 720 h at 85 °C in air, even without encapsulation.

DOI： 10.1002/solr.202300912

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Publisher：International Journal of Energy Research  

The processing of halide perovskites in the air significantly influences their morphology and surface coverage, often leading to the presence of numerous trap densities that adversely affect device performance. In this study, we explored the development of perovskite films using a solvent extraction method, where the temperature of the anisole antisolvent was varied. Our findings demonstrate that the hot-antisolvent strategy effectively controls nucleation, resulting in the formation of highly dense, pinhole-free, and crack-free perovskite films with reduced surface roughness. Films fabricated using this hot-antisolvent approach exhibited enhanced photoluminescence, indicating lower trap density and increased recombination resistance. They also showed slower charge carrier recombination rates and efficient charge extraction, suggesting the suppression of nonradiative recombination. Furthermore, the superior quality of perovskite films obtained through the hot-antisolvent strategy significantly enhanced the power conversion efficiency (PCE) of hot-pressed semitransparent perovskite solar cells. The PCE remarkably increased from 0.13% to an impressive 12.65% while maintaining an average visible transmittance of 26.55% and exceptional air stability for 2000 hours with no significant degradation in initial PCE. This study achieves a record-breaking light utilization efficiency of 3.36% in the realm of research on hot-press processes.

DOI： 10.1155/2024/9417829

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

In this study, a hybrid photocatalyst with titanium oxide using reduced graphene nanoribbons (rGNR) was fabricated.

DOI： 10.1039/d3tc03622g

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Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society  

Effects of channel size in NiO-YSZ porous substrate were studied on power density in solid oxide fuel cell mode and electrolysis current in steam electrolysis mode. It was found that the cell deposited on anode substrate with larger pore diameter shows a superior performance. The LSGM cell prepared on Ni-YSZ tube with average channel diameter of ca. 2.5 μm shows the maximum power density of 0.36 W cm⁻² in SOFC mode and 0.42 A cm⁻² at 1.6 V in SOEC mode at 873 K. Spike potential noise which may be caused by insufficient gas diffusion in NiO-YSZ porous substrate was observed under constant current electrolysis condition in case of NiO-YSZ tube with narrow channel and the spike noise is suppressed by increasing channel size. NiO-YSZ tube with large channel size is also effective for increasing long term stability in electrolysis mode.

DOI： 10.1149/1945-7111/ad2815

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Other Link： https://iopscience.iop.org/article/10.1149/1945-7111/ad2815/pdf

Language：English   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Photocatalytic hydrogen peroxide (H2O2) by oxygen and phosphorus co-doped graphitic carbon nitride (C3N4) with cobalt phosphate (CoP) cocatalyst is investigated. The photocatalyst powder of CoP-C3N4 1:n, n = 0–4, n is the weight ratio of cyanuric acid added) was synthesized by melamine cyanurate template method. Characterization of the catalyst was performed by X-ray diffraction analysis, and scanning electron microscopy, X-ray photoemission spectra, and fluorescence decay spectra. Oxygen doping was performed by the melamine and cyanuric acid template method, followed by phosphorus doping of the C3N4 backbone by the introduction of CoP. Co-doping of O and P atom facilitated charge transfer on the C3N4 backbone, while CoP facilitated charge separation at the C3N4 interface. The CoP-C3N4 (1:4) photocatalyst increased H2O2 production rate by 293 % compared to that of the cyanuric acid-free photocatalyst and also achieved the photocatalytic oxygen evolution from water. These results indicate that O,P co-doped CoP-C3N4 can perform sacrificial agent-free hydrogen peroxide under visible light irradiation.

DOI： 10.1016/j.cattod.2023.114400

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Language：English   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Mullite-phase bismuth gallate (Bi2Ga4O9) was successfully synthesized with partial substitution of bismuth with alkaline-earth cation, Mg2+, Ca2+, Sr2+, and Ba2+. The effect of this substitution on the electrical conductivity was investigated. In this study, substitution with Ca2+ of Bi site was further studied for increasing the ionic conductivity as well as the phase stability in reducing atmospheres. Substitution with Ca2+ was found to be the most effective and with 12.5 mol% of Ca2+ as the optimized doping amount. Conductivity and stability in reducing atmospheres was increased down to pO2 ≤ 10−19 atm while keeping the conductivity of σ = 2.6 × 10−2 S·cm−1 at 973 K largely independent of oxygen partial pressure. Oxygen permeation analysis estimates 76% of theoretical oxygen permeation rate at 973 K suggesting main charge carrier is oxide ion. Partial electronic conductivity was measured with the ion blocking method. Oxide ion conductivity is dominated over wide pO2 range excepting for hole conduction at high pO2. Density functional theory (DFT) analysis on oxide ion diffusion route suggests oxygen hoping through lattice vacancy is main pathway for oxide ion conductivity in this doped Bi2Ga4O9. Despite the low oxide ion conductivity in Mullite-phase oxide, it was found that Ca doped Bi2Ga4O9 shows good oxide ion conductivity over wide pO2 range.

DOI： 10.1016/j.ssi.2023.116343

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Publisher：Applied Surface Science  

All-inorganic α-CsPbI2Br perovskite has garnered considerable interest due to its optical bandgap (∼1.92 eV) suitable for tandem architectures and superior thermal stability. However, CsPbI2Br based perovskite solar cells (PSCs) exhibit severe energy loss due to presence of various surface defects like uncoordinated Pb2+ ions, halide ion vacancies and pinholes, which causes serious non-radiative recombination and limit the further improvement in power conversion efficiency (PCE). Surface passivation strategy is an effective approach to produce high quality α-CsPbI2Br film. Herein, we introduce fluorinated ionic liquid, 3-(Trifluoromethyl) benzylamine (CFBA), as surface passivating agent. The chemical analysis shows that the trifluoro (-CF3) and amine groups of CFBA strongly interacted with perovskite surface via forming Pb-F and H-I bonding, respectively. The high electronegative fluoride atoms of -CF3 group allow for electrostatic interaction with uncoordinated Pb2+ ions, which built a robust shield that protected against surrounding moisture as well. In addition, CFBA modification passivates the dangling bonds, enhanced crystallinity, reduced pinholes, improved the surface coverage and compactness, increased hydrophobicity, and decreased non-radiative recombination, leading to high PCE. With optimum concentration of 3 μL-CFBA, CsPbI2Br PSC revealed an impressive PCE of 17.07% with FF of 83.21% as compared to pristine device (PCE of 15.24% with FF of 79.81%). Moreover, champion device showed an excellent thermal stability by retaining ∼ 86.23% of its initial PCE, whereas pristine device maintained ∼ 48.26% of its original PCE after 1440 h aging at 85 ℃ in a dry box without any encapsulation. In addition, optimized PSC showed a decent indoor PCE of 23.24% as compared to pristine device (18.35%) under dim lighting conditions (LED, 3200 K) at 1000 lx. These results suggested that surface passivation strategy with CFBA is a promising approach for developing efficient all-inorganic CsPbI2Br outdoor/indoor PSCs with better thermal stability.

DOI： 10.1016/j.apsusc.2023.157901

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Language：English   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Optimizing hydrogen production in ascorbic acid solutions: enhancing BODIPY dye-sensitized processes through alkyl-chain-enhanced second coordination sphere effects.

DOI： 10.1039/d3ta03682k

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

For increasing the performance of PCFC (Protonic Ceramic Fuel Cells), it is important to prepare high-quality thin films of electrolyte materials. In this study, the preparation condition of the thin film of BaZr0.8Yb0.2O2.9 (BZYb) by pulsed laser deposition (PLD) method was optimized and the electrical conductivities of the obtained films were measured. The thin film was prepared by PLD using two kinds of BZYb targets, which were prepared by solids state reaction and Pechini method. Both thin-film samples have the single phase of the cubic perovskite-type structure, however, morphology as well as the orientation of the BZYb film was significantly different. The thin film using the target material by Pechini method is a high crystalline orientation and partially oriented [211] direction. The electrical conductivities of the obtained thin films at reduction atmosphere are dominated by proton conductivity, which is almost the same as that of the bulk sample despite [211] orientation.

DOI： 10.1016/j.ssi.2023.116240

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Repository Public URL： https://hdl.handle.net/2324/7172331

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

In the CO2 electrocatalytic reduction reaction (CO2RR) technology, high CO2 conversion rate is highly required for efficient CO2 utilization from the CO2 resource. In this study, we propose the strategy of combining UiO-66 metal organic framework (MOF) structure with Bi electrocatalyst for highly active CO2RR with selective formic acid production. The synthesized Bi/UiO-66 catalyst shows superior CO2 reduction property, 4.6 times higher current density at −0.7 V vs. reversible hydrogen electrode (RHE) than bare Bi without UiO-66 despite of low electrochemical surface area. Also, NH2 functionalized UiO-66 shows almost no effect on CO2RR as compared to without NH2 probably due to disassembled linkers during CO2RR. Various characterizations such as Fourier transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) indicate carbonate species captured form of CO2 at Zr-MOF site should contribute the high CO2 conversion rate. Our findings demonstrate the feasibility of Zr-MOF as a Supporting material to achieve efficient CO2 reduction.

DOI： 10.1016/j.apcatb.2023.122400

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Photobiocatalytic system has been developing as a promising approach for H2 production. Herein, the rational characteristics of biocatalysts and the role of individual components affecting the efficiency of the system were investigated. Photocatalytic studies showed that tris (2-amino-2-hydroxymethyl-1,3-propanediol) was an ideal electron donor for viologen reduction by TiO2. Biocatalytic reaction revealed that cell permeability, the redox potential of electron mediators and the cell envelope were crucial to the activity of whole-cell biocatalysts. In photobiocatalytic system, recombinant Escherichia coli with a turnover frequency of 39.43 +/- 3.77 s-1 based on [FeFe]-hydrogenase activity was a more rational biocatalyst than Anabaena variabilis. A comprehensive study found that the presence of TiO2, light and biocatalysts strongly enhanced H2 production, whereas Tris and MV2+ had less influence. A maximum rate was found at 16.73 +/- 1.03 mu mol/min with a solar-to-H2 conversion of 1.58 +/- 0.10 %. Understanding the role of each component will guide the development of high-efficient photobiocatalysis.

DOI： 10.1016/j.apcata.2022.119019

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Squaraine dyes are organic dyes having strong and narrow absorption properties in the near-infrared region that are widely used in photovoltaic and biomedical applications. In this work, squaraine dye (SA1) was synthesized as a dye sensitizer for a dye-sensitized photocatalytic system, which was composed of SA1 and Pt-loaded TiO2 powder photocatalyst (SA1/Pt-TiO2). The SA1/Pt-TiO2 system exhibited a good hydrogen production performance within 150 h and an apparent quantum yield of 1.4% under 800 nm monochromatic light irradiation. However, during the photocatalytic reaction, the photocatalytic activity of SA1/Pt-TiO2 decreased due to photodecomposition. Ultraviolet–visible absorption spectroscopy, 1H nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry measurements were performed to investigate the mechanism of the decomposition of the squaraine moiety of SA1, the decomposition process, and the structure of the decomposed material. The results show that even without the Pt-loaded TiO2 powder photocatalyst, SA1 undergoes photodissociation, which cleaves the bond between the indoline moiety and the square acid. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s00339-022-06281-7

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Other Link： https://link.springer.com/article/10.1007/s00339-022-06281-7/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Intentionally introducing tensile strain into TiO₂ by using a spark plasma sintering process could stabilize reduced Ti species and improve the solid acid activity for acetalization.

DOI： 10.1039/d2cy00736c

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Language：Japanese   Publisher：The Japan Petroleum Institute  

<p>The particle size effect of platinum nanoparticles on the conversion of methane (CH₄) into hydrogen cyanide (HCN) using nitric oxide (NO) as an oxidant over the Pt supported (γ + θ)-alumina was investigated. The Pt catalysts with various average particle size in the range of 1.6 to 4.1 nm were obtained by controlling the loading amount and calcination temperature. Amount of the Pt surface sites was determined by CO titration using a pulse method and the catalytic activity was evaluated under same contact time. In case of the catalysts having small particle size (1.6-3.2 nm) of Pt, NO conversion was lower than the large one. The catalysts having large particle size (4.1-4.2 nm) exhibited high selectivity of HCN reaching 53.5 % at 1.3 % C-based yield at 400 °C over 10 wt% Pt/Al₂O₃. One of the reasons for higher activity with the larger Pt particles is suppression of the sequential reaction of HCN to carbon dioxide and ammonia which likely proceeded at the interface between metal and support. Pt L₃-edge X-ray adsorption fine structure (XAFS) spectra showed that the small particle catalysts were covered with Pt–CN species after the reaction test. In contrast, Pt–CO was observed as main adsorbed species on the large particle catalysts, suggesting that HCN desorption process was facile for the larger Pt particle case.</p>

DOI： 10.1627/jpi.65.184

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

NiO-Y2O3 stabilized ZrO2 (YSZ) tubular type cell using La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte film was prepared by dip-coating method. Effects of Ce infiltration or Ce, Ni sequential-infiltration into NiO-YSZ substrate were studied and it was found that Ce infiltration after Ni is highly effective for increasing the cell performance and the stability in fuel cell and electrolysis mode at 873 K in spite of decrease in performance by simple Ni infiltration. Cyclic operation of the fuel cell and electrolysis of LSGM tubular cell using Ce or Ce[sbnd]Ni sequential-infiltrated NiO-YSZ substrate was measured at 873 K using 17% steam-25%H2 in Ar as fuel. After 100 cycles at ±0.1 A cm−2, OCV was almost the same with the initial value. The terminal potential in SOFC operation became slightly lower with increasing cycle number in case of simple Ce infiltration. The main reason for degradation during cyclic performance seems to be assigned to the increased fuel electrode overpotential. However, degradation rate is much decreased by Ce[sbnd]Ni sequential-infiltration.

DOI： 10.1016/j.ssi.2022.115914

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Porous boron nitride was synthesized using boric acid with urea and/or hexamethylenetetramine (HMTA) via pyrolysis method. X-ray diffraction and Fourier transform infrared measurements indicated that the synthesized boron nitride has a turbostratic structure with both amino and hydroxyl group on the surface. The synthesis using a mixture of two nitrogen-containing precursors was found to not only significantly increase the porosity, but also improve the surface functionality. X-ray photoelectron spectroscopy and B K-edge and O K-edge X-ray absorption fine structure measurements revealed that the proportion of amino and hydroxyl groups on the surface increased with increasing concentration of HMTA during synthesis. Solid-state 11B nuclear magnetic resonance spectroscopy indicated that all samples contained trigonal B-N, trigonal B-O and tetrahedral B-O sites, and that samples prepared with high concentrations of HMTA had less tetrahedral B-O sites, suppressing the formation of BOx species as byproducts. Solid base catalytic activity was evaluated through Knoevenagel condensation, and the catalytic performance was significantly improved by synthesizing boron nitride catalyst using a mixture of the two nitrogen-containing precursors. The enhancement of the activity was influenced by the development of the pore structure as well as the emergence of functional groups on the surface.

DOI： 10.1016/j.apcata.2022.118635

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Fast oxide-ion conductivity in Bi_3.9Sr_0.1NbO_{8−<italic>δ</italic>}Cl is reported for the first time, and this oxide is stable under a reducing atmosphere.

DOI： 10.1039/d1ta07335d

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DOI： 10.1016/j.cej.2021.131063

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

SrTiO3 is a well-known highly active photocatalyst with high energy conversion efficiency. In this study, we investigated the formation of oxygen vacancy by using the chemo-mechanical effect that was introduced by the dispersion of metal particles into grain and photocatalytic activity to water splitting. Au dispersion on SrTiO3 followed by sintering treatment was studied for introduction of chemo-mechanical strain because of a different thermal expansion coefficient; the introduced chemo-mechanical strain generated oxygen vacancy in SrTiO3. Thus, induced chemo-mechanical strain shows change in electronic band structure resulting in increasing lowest unoccupied molecular orbital (LUMO) level with increasing Au content. Since photoluminescence was significantly decreased by sintering after Au dispersion, the introduced strain effects may work for increasing a charge separation efficiency and adsorption site in water splitting. Therefore, the photocatalytic activity was much increased by sintering treatment after Au dispersion on SrTiO3.

DOI： 10.1016/j.apcatb.2020.119292

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DOI： 10.1016/j.apcata.2020.117843

Language：English   Publishing type：Research paper (scientific journal)  

Selective conversion of CO2 to fuels and chemicals has been considered one of the key challenges in the electrochemical CO2 reduction reaction (CO2RR). Here, we demonstrate the reaction pathways for CO and C2H4 formation on Cu can be regulated by supplying different CO2 partial pressures. Although it is believed high concentration of surface bound CO is required for C2H4 formation, we show excessive supply of CO2 interferes with C-C coupling and suppress C2H4 reaction pathways. This indicates C2H4 reaction pathways are limited by the surface recombination of surface bound CO and hydrogen, and the kinetics is affected by adsorbate-adsorbate interactions and/or by physical blocking of active sites on Cu with excess CO2. Through systematic study, we demonstrate a dilute CO2 stream selectively activates C2H4 formation with significant reduction of the overpotentials (similar to 400 mV) to achieve similar to 50% C2H4 Faradaic efficiency and enhancement in the C2H4 current density (similar to 50 mA cm(-2)).

DOI： 10.1016/j.apcatb.2020.119049

Language：English   Publishing type：Research paper (scientific journal)  

Electrochemical CO production from CO2 electrolysis has been considered the most economically viable approach among various candidate products. AuCu bimetallic alloys are currently receiving attention for their potential to tailor catalytic activity. Here, we synthesized a dilute AuCu alloy nanostructure with an AuCu atomic composition ratio of 3% by using a simple electrochemical treatment method on a 200 nm-thick Au thin film. The dilute AuCu alloy catalyst shows an exceptional CO2 reduction activity in terms of selectivity and overpotential for CO production. In addition, the stability property is more significantly enhanced as compared to pure Au nanostructures. In addition, we describe an in situ tailoring method of catalytic activity for Au nanostructures by repeating an electrochemical treatment process that is performed for forming the Au nanostructure. This approach will be a promising and facile strategy not only for reactive Au catalysts but also to increase the stability activity simultaneously by utilizing Cu impurities existing in an aqueous electrolyte for CO2 reduction.

DOI： 10.1063/5.0009340

Language：Others  

Language：English   Publishing type：Research paper (scientific journal)  

Direct decomposition of NO on Ba3Y4O9 doped with Cu and Sc was studied and it was found that co-doping of Sc and Cu into Ba3Y4O9 was effective for increasing both lattice stability and NO decomposition activity. In particular, Ba3Y3Sc0.6Cu0.4O9 (10 % Cu and 15 % Sc doping) catalyst showed N-2 and O-2 yield of 90 % and 99 %, respectively, in NO decomposition reaction at 700 degrees C. Comparing with the pristine and single-metal doped system, the optimized catalyst showed superior long-term stability and increased activity under O-2, and water vapor co-existence conditions because of the increased stability of crystal structure, improved lattice oxygen mobility and weakened oxygen adsorption on the surface. TPD and in-situ FT-IR results suggested that the co-doping effect was assigned to the easier removal of surface NO2- or NO3- species which blocks the active site to NO decomposition.

DOI： 10.1016/j.apcata.2020.117743

Language：English   Publishing type：Research paper (scientific journal)  

Dye-sensitized photocatalytic hydrogen production using a boron-dipyrromethene (BODIPY) organic material having a pyridyl group at the anchor site was investigated. Phenyl, carbazole, and phenothiazine derivatives were introduced into BODIPY dyes, and their photocatalytic activities were examined. Identification was performed by nuclear magnetic resonance (NMR), infrared (IR), mass (MS) spectra, and absorption spectra, and catalyst evaluation was performed by using visible-light irradiation and photocatalytic hydrogen production and photocurrent. These dyes have strong absorption at 600-700 nm, suggesting that they are promising as photosensitizers. When the photocatalytic activity was examined, stable catalytic performance was demonstrated, and the activity of the Pt-TiO(2)photocatalyst carrying a dye having a carbazole group was 249 mu mol/g(cat)center dot h. Photocurrent measurements suggest that dye-sensitized photocatalytic activity is occurring. This result suggests that BODIPY organic materials with pyridyl groups as anchor sites are useful as novel dye-sensitized photocatalysts.

DOI： 10.3390/catal10050535

Language：English   Publishing type：Research paper (scientific journal)  

We report for the first time to our knowledge the identification of heteroatom-doped and undoped C3N4 with the energy-resolved distribution of electron traps (ERDT) near the conduction band bottom position (CBB) using reversed double-beam photoacoustic spectroscopy. The ERDT/CBB pattern is used to classify the type of elemental doping in C3N4, related to photocatalytic efficiency.

DOI： 10.1039/c9cc09988c

Language：English   Publishing type：Research paper (scientific journal)  

Electrocatalytic CO2 reduction is a promising way to provide renewable energy from gaseous CO2. The development of nanostructures improves energy efficiency and selectivity for value-added chemicals, but complex nanostructures limit the CO2 conversion rates due to poor mass transport during vigorous electrolysis. Herein, we propose a three-dimensional (3D) hierarchically porous Au comprising interconnected macroporous channels (200-300 nm) and nanopores (similar to 10 nm) fabricated via proximity-field nanopatterning. The interconnected macropores and nanopores enable efficient mass transport and large active areas, respectively. The roles of each pore network are investigated using reliable 3D nanostructures possessing controlled pore distribution and size. The hierarchical nanostructured electrodes show a high CO selectivity of 85.8% at a low overpotential of 0.264 V and efficient mass activity that is maximum 3.96 times higher than that of dealloyed nanoporous Au. Hence, the systematic model study shows the proposed hierarchical nanostructures have important value in increasing the efficiency of expensive Au.

DOI： 10.1073/pnas.1918837117

Language：English   Publishing type：Research paper (scientific journal)  

Development of efficient and selective electro-catalysts is a key challenge to achieve an industry-relevant electrochemical CO2 reduction reaction (CO2RR) to produce commodity chemicals. Here, we report that Au-25 clusters with Authiolate staple motifs can initiate electrocatalytic reduction of CO2 to CO with nearly zero energy loss and achieve a high CO2RR current density of 540 mA cm(-2) in a gas-phase reactor. Electrochemical kinetic investigations revealed that the high CO2RR activity of the Au-25 originates from the strong CO2 binding affinity, leading to high CO2 electrolysis performance in both concentrated and dilute CO2 streams. Finally, we demonstrated an 18.0% solar-to-CO conversion efficiency using a Au-25 electrolyzer powered by a Ga0.5In0.5P/GaAs photovoltaic cell. The electrolyzer also showed 15.9% efficiency and a 5.2% solar-driven single-path CO2 conversion rate in a 10% CO2 gas stream, the CO2 concentration in a typical flue gas.

DOI： 10.1021/acsenergylett.9b02511

Language：English   Publishing type：Research paper (scientific journal)  

In this study, ZnTi-mixed metal oxides (ZTM), such as ZnTiO3, were synthesized from ZnTi layered double hydroxides by varying the molar ratio of Zn/Ti, calcination temperatures, and synthesis methods (hydrothermal or reflux). The surface electronic characteristics of ZTM were investigated by the energy-resolved distribution of electron traps (ERDTs) using reversed double-beam photoacoustic spectroscopy. The ZTM samples obtained by conducting hydrothermal synthesis at 500 degrees C showed similar ERDT patterns independent of the molar ratio of Zn/Ti, although ZnTiO3 phase was not observed in the X-ray diffraction pattern, when the Zn/Ti ratio was high. When the ERDT patterns demonstrated a high electron accumulation level near the conduction band bottom in hydrothermal products at 500 degrees C, a higher photocatalytic phenol degradation efficiency was observed due to the formation of ZnTiO3 phase. This suggested that the product with the high Zn/Ti molar ratio (Zn/Ti = 6) constituted amorphous ZnTiO3.The enhanced photocatalytic performance of ZTM could be attributed to the heterojunction of electrons among ZnO, TiO2, and ZnTiO3, which enabled electron transfer in the composites, prevented charge recombination, and promoted a wider visible light adsorption by ZnTiO3 phase irrespective of its crystallinity.

DOI： 10.1021/acsami.9b18785

Language：English  

Electrochemical CO2 conversion offers a promising route for value-added products such as formate, carbon monoxide, and hydrocarbons. As a result of the highly required overpotential for CO2 reduction, researchers have extensively studied the development of catalyst materials in a typical H-type cell, utilizing a dissolved CO2 reactant in the liquid phase. However, the low CO2 solubility in an aqueous solution has critically limited productivity, thereby hindering its practical application. In efforts to realize commercially available CO2 conversion, gas-phase reactor systems have recently attracted considerable attention. Although the achieved performance to date reflects a high feasibility, further development is still required in order for a well-established technology. Accordingly, this review aims to promote the further study of gas-phase systems for CO2 reduction, by generally examining some previous approaches from liquid-phase to gas-phase systems. Finally, we outline major challenges, with significant lessons for practical CO2 conversion systems.

DOI： 10.3390/catal9030224

Language：English   Publishing type：Research paper (scientific journal)  

Increasing the surface area to improve chemical activity is an unending task from conventional catalysis to recently emerging electrochemical energy conversion and storage. Here, a simple, vacuum-deposition-based method to form nanoporous structures of metals is reported. By utilizing thermal evaporation at a high pressure, fractal-like nanoporous structures of Sn with porosity exceeding 98% are synthesized. The obtained nanostructure consists of nanoparticle aggregates, and the morphology can be controlled by adjusting the working pressure. The formation of the nanoporous structure is explained by homogeneous nucleation and diffusion-limited aggregation, where nanoparticles produced by the repeated collisions of evaporated atoms adhere to the substrate without diffusion, forming porous aggregates. Due to the easy oxidation of Sn, the constituent nanoparticles are covered with amorphous SnOx and crystalline SnO phases. When the nanoporous Sn/SnOx aggregates are applied to a lithium-ion battery anode through direct deposition on a Cu foil current collector without binders or conducting additives, the nanoporous Sn/SnOx anode shows greatly enhanced cyclability and exceptional rate performance compared to those of a dense Sn thin film anode. The approach investigated in this work is expected to provide a new platform to other fields that require highly porous structures.

DOI： 10.1002/ppsc.201800331

Language：English   Publishing type：Research paper (scientific journal)  

Cobalt oxide (CoOx), an earth-abundant and low-cost oxygen evolving catalyst (OEC), has notable advantages as a top protection layer of photoanodes for solar-driven water oxidation because of its desirable durability. However, cobalt oxides exist as various phases, such as Co(II)O, Co2(III)O3, Co3(II,III)O4, and the (photo)electrochemical properties of CoOx are significantly governed by its phase. Atomic layer deposition (ALD) is a suitable method to form a multifunctional layer for photoelectrochemical (PEC) water splitting because it allows direct growth of a conformal high-quality film on various substrates as well as facile control over its chemical phases by adjusting the deposition conditions. Here, a well-controlled CoOx/SiOx/n-Si heterojunction prepared by ALD is demonstrated for solar-driven water splitting. The phase of the ALD CoOx films can be easily controlled from CoO to Co3O4 by varying the deposition temperature. In addition, this systematic study reveals that its energetic as well as electrochemical properties are changed significantly with the phase. Whereas CoO grown at 150 degrees C produces high photovoltage by building desirable hole-selective heterojunctions with n-Si, Co3O4 formed at 300 degrees C has a better catalytic property for water oxidation. To address this competitive correlation, we developed a double-layered (DL) ALD CoO, film that has advantages of both CoO and Co3O4. The DL ALD CoOx/SiOx/Si heterojunction photoanode produces a photocurrent density of 3.5 mA/cm(2) without a buried junction and maintains a saturating current density of 32.5 mA/cm(2) without noticeable degradation during 12 h in 1 M KOH under a simulated 1 sun illumination.

DOI： 10.1021/acscatal.8b03520

Language：English   Publishing type：Research paper (scientific journal)  

Mass transfer, kinetics, and mechanism of electrochemical CO2 reduction have been explored on a model mesostructure of highly-ordered copper inverse opal (Cu-IO), which was fabricated by Cu electrodeposition in a hexagonally-closed packed polystyrene template. As the number of Cu-IO layers increases, the formation of C-2 products such as C2H4 and C2H5OH was significantly enhanced at reduced overpotentials (similar to 200 mV) compared to a planar Cu electrode. At the thickest layer, we observe for the first time the formation of acetylene (C2H2), which can be generated through a kinetically slow reaction pathway and be a key descriptor in the unveiling of the C-C coupling reaction mechanism. Based on our experimental observation, a plausible reaction pathway in Cu mesostructures is rationalized.

DOI： 10.1016/j.apcatb.2018.03.071

Language：English   Publishing type：Research paper (scientific journal)  

Electrochemical conversion of CO2 has been considered as a promising method for producing value-added chemicals. Here, we report a systematic study on the formation of Au nanostructures via electroreduction of anodic Au(OH)(3) for selective CO production by an electrochemical CO2 reduction reaction (CO2RR). First, we demonstrate the influence of electrochemical process parameters on the formation of Au nanostructures and Au(OH)(3). The Au nanostructure morphologies can be tuned into either pore-like or pillar-like structures by controlling the anodic potential and/or reduction current density. This distinctive morphology is associated with the electric-field-assisted transport of Au3+ at/near the Au(OH)(3)/Au interface. Additionally, we report the catalytic activity of the morphology-controlled Au nanostructures in the CO2RR. Both Au nanostructures exhibit significantly higher CO selectivity at a low overpotential than the untreated Au film due to the high density of grain boundaries which can assist with faster stabilization of the CO2- intermediate. In particular, the pore-like structures have a higher CO selectivity than the pillar-like ones at 280 mV overpotential although the pillar-like Au nanostructures have a higher CO selectivity and CO producing current density at high overpotentials. This potential-dependent CO2RR performance of the two different Au nanostructures is discussed.

DOI： 10.1039/c8ta01010b

Language：English   Publishing type：Research paper (scientific journal)  

Electrochemical CO2 reduction is one of the promising ways to convert CO, to value-added products such as CO. Many studies have dealt with suppressing the hydrogen evolution reaction (HER) and increasing the CO, reduction reaction (CO2RR) through modification of the metal surface with additives such as anchoring agent, anion, etc. However, there are only a few studies about modifying the Au surface with additives. We present here a theoretical prediction that the addition of the CN and Cl species on an Au electrode would enhance the electrochemical CO2RR due to van der Waals interactions with these large anionic species. On the basis of this suggestion, we then prepared functionalized Au electrodes by electroplating in an aqueous solution containing CN- or Cl- and experimentally verified that the CO2RR of functionalized Au indeed shows exceptional CO2RR activity in comparison to pristine Au.

DOI： 10.1021/acscatal.7b03449

Language：English   Publishing type：Research paper (scientific journal)  

We report the effect of metal-oxide interfaces on CO oxidation catalytic activity with inverse TiO2-nano-structured Au catalysts. The inverse nanocatalysts were prepared by depositing TiO2 via the liquid-phase immersion method on electrochemically synthesized Au nanostructure supports. The catalytic performance for CO oxidation was investigated using various amounts of Ti (i.e. 0.1-1.0 wt%) on two different morphologies of Au nanostructures (i.e. nanoporous and nanorod). In comparing the different Au morphologies, we found an overall higher TOF and lower activation energy for the TiO2/nanoporous Au than those for the TiO2/nanorod Au. In addition, the CO oxidation activity increased as the Ti content increased up to 0.5 wt% probably due to active TiO2-Au interface sites enhancing CO oxidation via the supply of adsorption sites or charge transfer from TiO2 to Au. However, a higher titania content (i.e. 1.0 wt% TiO2) resulted in decreased activity caused by high surface coverage of TiO2 decreasing the number of TiO2 Au interface sites. These results implied that the perimeter area of the metal-oxide interface played a significant role in determining the catalytic performance for CO oxidation.

DOI： 10.1039/c7nr08168e

Language：English   Publishing type：Research paper (scientific journal)  

Generating syngas (H-2 and CO mixture) from electrochemically reduced CO2 in an aqueous solution is one of the sustainable strategies utilizing atmospheric CO2 in value-added products. However, a conventional single-component metal catalyst, such as Ag, Au, or Zn, exhibits potential-dependent CO2 reduction selectivity, which could result in temporal variation of syngas composition and limit its use in large-scale electrochemical syngas production. Herein, we demonstrate the use of Ag nanowire (NW)/porous carbon sheet composite catalysts in the generation of syngas with tunable H-2/CO ratios having a large potential window to resist power fluctuation. These Ag NW/carbon sheet composite catalysts have a potential window increased by 10 times for generating syngas with the proper H-2/CO ratio (1.7-2.15) for the Fischer-Tropsch process and an increased syngas production rate of about 19 times compared to that of a Ag foil. Additionally, we tuned the H-2/CO ratio from similar to 2 to similar to 10 by adjusting only the quantity of the Ag NWs under the given electrode potential. We believe that our Ag NW/carbon sheet composite provides new possibilities for designing electrode structures with a large potential window and controlled CO2 reduction products in aqueous solutions.

DOI： 10.1021/acsomega.7b00846

Language：English   Publishing type：Research paper (scientific journal)  

Molybdenum disulfide (MoS2) is an earth-abundant and low-cost hydrogen evolving electrocatalyst that can substitute noble metal catalysts. Atomic layer deposition (ALD) is a reliable and scalable process where MoS2 nanomaterials grow directly on Si with a precise film thickness and composition. Here, we demonstrate high-performance Si photocathodes with MoS2 cocatalysts using ALD for the photoelectrochemical (PEC) water reduction reaction. While the morphology and thickness of MoS2 is controlled by ALD reaction cycles, post-sulfurization at high temperatures is conducted to form stoichiometric MoS2 and dramatically enhances the crystallinity of MoS2 to maximize the catalytically active edge sites of basal planes. A systematic study was performed to investigate the role of ALD and post-sulfurization parameters on PEC performances of MoS2 on Si photocathodes. By optimizing the crystallinity, edge site density, stoichiometry, and morphology of MoS2 for maximum electrochemical HER performance and minimum optical and electrical losses, our Si photocathodes with ALD-MoS2 cocatalysts showed reduction of an overpotential of about 630 mV compared to bare Si. The photocathodes also showed a saturating photocurrent density of 31 mA cm(-2) without noticeable degradation during a 24 hour stability test in 0.5 M H2SO4 under a simulated 1 sun illumination.

DOI： 10.1039/c6ta10707a

Language：English   Publishing type：Research paper (scientific journal)  

An Si photoelectrode with a nanoporous Au thin film for highly selective and efficient photoelectrochemical (PEC) CO2 reduction reaction (CO2RR) is presented. The nanoporous Au thin film is formed by electrochemical reduction of an anodized Au thin film. The electrochemical treatments of the Au thin film critically improve CO2 reduction catalytic activity of Au catalysts and exhibit CO Faradaic efficiency of 96% at 480 mV of overpotential. To apply the electrochemical pretreatment of Au films for PEC CO2RR, a new Si photoelectrode design with mesh-type co-catalysts independently wired at the front and the back of the photoelectrode is demonstrated. Due to the superior CO2RR activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO2 to CO with 91% Faradaic efficiency at positive potential than the CO2/CO equilibrium potential.

DOI： 10.1002/aenm.201601103

Language：English   Publishing type：Research paper (scientific journal)  

Photoelectrochemical (PEC) water splitting has emerged as a potential pathway to produce sustainable and renewable chemical fuels. Here, we present a highly active Cu2O/TiO2 photocathode for H-2 production by enhancing the interfacial band-edge energetics of the TiO2 layer, which is realized by controlling the fixed charge density of the TiO2 protection layer. The band-edge engineered Cu2O/TiO2 (where TiO2 was grown at 80 A degrees C via atomic layer deposition) enhances the photocurrent density up to -2.04 mA/cm(2) at 0 V vs. RHE under 1 sun illumination, corresponding to about a 1,200% enhancement compared to the photocurrent density of the photocathode protected with TiO2 grown at 150 A degrees C. Moreover, band-edge engineering of the TiO2 protection layer prevents electron accumulation at the TiO2 layer and enhances both the Faraday efficiency and the stability for hydrogen production during the PEC water reduction reaction. This facile control over the TiO2/electrolyte interface will also provide new insight for designing highly efficient and stable protection layers for various other photoelectrodes such as Si, InP, and GaAs.

DOI： 10.1007/s13391-017-6316-1

Language：English   Publishing type：Research paper (scientific journal)  

Photoelectrochemical (PEC) carbon dioxide (CO2) reduction on a 3C-SiC photoanode is demonstrated in aqueous solution with Pt and Ag counter electrodes. It is demonstrated that 3C-SiC has sufficient potential for CO2 reduction by confirming the band-edge structure. Then, the CO2 reduction is realized by connecting the 3C-SiC photoanode with the counter electrode. As the products of the PEC reaction with an applied bias of 1V (vs counter electrode) to the 3C-SiC photoanode, hydrogen (H-2) and carbon monoxide (CO) were analyzed by highly sensitive micro-gas chromatography, by which the time dependence of the gas products can be analyzed. Under light illumination of the 3C-SiC photoanode, CO2 reduction occurred while producing 2.5 and 9 nmol of CO gas with the Pt and Ag counter electrodes, respectively, after the reaction for 3000 s. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.04DR05

Language：English   Publishing type：Research paper (scientific journal)  

The effect of Pt co-catalyst fabricated with various annealing temperatures on photoelectrochemical (PEC) properties of 3C-SiC photo-anode was investigated. 3C-SiC with Pt co-catalyst shows the greater PEC reaction compared with bare 3C-SiC. A further enhancement is found by annealing process due to the Pt particle structure and enhanced contact of 3C-SiC and Pt. The formation of Pt particles improves the PEC reaction of samples annealed at 500 and 700 degrees C. Here, 3C-SiC with the Pt annealed at 500 degrees C shows the largest photocurrent, 3.47mA/cm(2) at an applied bias of 1V (vs Ag/AgCl) and the lowest onset potential, 0.74V with the optimum particle size. It is also considered to have appropriate contact by the proper Pt2Si formation, revealed by X-ray photoelectron microscopy. Although photocurrent is improved after anneal at 700 degrees C, the onset potential becomes almost same as bare 3C-SiC. Furthermore, the photo-activity after anneal at 900 degrees C is even degraded compared to the bare 3C-SiC because of the evolution of immoderate carbon compounds suppressing Pt co-catalyst effect. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.05FZ04

Language：English   Publishing type：Research paper (scientific journal)  

We propose the n-type 3C-SiC with Pt nanoparticles (Pt NPs) as photo-anode for photoelectrochemical hydrogen (H-2) generation. We found that band-edge structure of 3C-SiC is suitable for H-2 generation, and the property can be optimized by dopant (nitrogen) concentration in 3C-SiC. We also confirmed that Pt NPs enhance photoelectrochemical properties showing 0.2%-0.8% higher Incident Photon-to-Current Efficiency than bare 3C-SiC in visible wavelength despite diminished light absorption. Solar-conversion efficiency increases approximately 6.3 times, and H-2 production is improved by 6.5 times with 33% of Faradaic efficiency. Lastly, 3C-SiC surface corrosion is effectively inhibited. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4832333

Language：English   Publishing type：Research paper (scientific journal)  

In this study, we proposed a square-patterned narrow-band infrared (IR) emitter for a filterless IR gas sensor. As a new method of infrared gas sensing compared with previous research, it is proposed that a narrow-band IR emitter fabricated by micro-electro-mechanical-systems (MEMS) technology be applied to analyze dimethyl ether [(CH3)(2)O] gas. The proposed IR emitter consists of a TiN/SiO2/TiN trilayer, where the top TiN layer is square-patterned. The IR emitter radiates emissions at wavelengths of 7.68 and 7.88 mu m in accordance with the type of sample. The wavelength can be adjusted by changing the period of the surface pattern. The proposed IR emitter shows a narrow peak width (Delta lambda/lambda) of 0.16-0.23. The apparatus for gas detection consists of the proposed IR emitter, a gas cell and a bolometric IR sensor based on amorphous SiGe:H. The change in electrical resistance of the gas detector during inflow of (CH3)(2)O gas, which has a fingerprint wavelength in the range of 7.6-10 mu m, was much smaller than that during inflow of CO2 gas, because (CH3)(2)O absorbed its corresponding wavelength in the range of 7.6-10 mu m. Because of the concentrated radiation of the IR emitter at the wavelength of 7.88 mu m, (CH3)(2)O absorbs relatively large amounts of infrared energy. The electrical resistance of the gas detector changed linearly as the concentration of (CH3)(2)O gas increased in the range of 0 to 500 ppm. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.06FL18

Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul   Country：Korea, Republic of  

Event date： 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.6

Language：Japanese  

Venue：オンライン   Country：Japan  

Event date： 2021.6

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：TBD   Country：Korea, Republic of  

Language：English  

Venue：Kirishima Spa and Resort Hotel   Country：Japan  

Language：Japanese  

Venue：九州大学筑紫キャンパス   Country：Japan