H2 Evolution Performance Research Articles

Photocatalytic dye degradation, H2 evolution, electrical and mechanical performances of mechano-synthesized multifunctional Bi2Te3 nanoparticles: Effect of milling time and thermal treatment

Bi2Te3 nanoparticles are synthesized by mechanical alloying the Bi and Te powders under the Ar and pressed powdered samples are sintered at 573 K. Rietveld refined XRD patterns, FESEM images and EDX spectra reveal the microstructure, morphology and phase purity of the samples. Bandgaps are obtained from the FTIR spectra and a blue shift with size reduction indicates the size confinement effect. The non Debye type ac conductivity and dielectric constant variations with milling time and sintering are measured. The improved photocatalytic degradation efficiency of the sintered sample (83.59 %) using Rhodamine B dye under visible light elucidates reduced porosity effect. The photocatalytic hydrogen evolution efficiencies of these nanoparticles are measured and a probable mechanism is depicted. The highest H2 generation efficiency (1462.5 μmol g−1h−1) is observed with the sintered sample. Microhardness measurement reveals normal indentation size effect. Empirical correlations among electrical conductivity, microhardness and photodegradation are established for the first time.

Surface cyano groups optimize the charge transfer of poly heptazine imide for enhanced photocatalytic H2 evolution

Surface functionalization has been considered as an effective strategy to manipulate charge separation of carbon nitride and therefore to largely improve the photocatalytic H2 evolution efficiency. Poly heptazine imide (PHI) is a new class of crystalline carbon nitride frameworks that exhibits remarkable photocatalytic performance for hydrogen evolution. To further improve the H2 evolution performance of PHI and explore the reaction mechanism, ammonium thiocyanate was used as a precursor for the synthesis of poly heptazine imide at elevated temperatures under molten salt conditions. The optimized PHI with an abundance of surface cyano groups shows a significantly enhanced photocatalytic performance for H2 evolution, which is 4.3 times that on pristine PCN. Most importantly, the surface cyano group adjusts the electron intensity of the polymeric framework, enhances the light absorbance, reduces the bandgap, and improves the charge separation efficiency. The synthetic technique also could be applied to other sulfur-containing precursors for the synthesis of PHI frameworks with excellent hydrogen evolution production performance.

Fabrication of CZS NRs/NiSx NPs hybrids with abundant S-vacancies for signally promoting photocatalytic hydrogen production

The cocatalysts play a key role in photocatalytic technology in remarkably improving the efficiency of H2 evolution. Herein, S vacancies-rich Cd0.6Zn0.4S nanorods (CZS NRs) were prepared via solvothermal method. Then, as-obtained CZS NRs were modified with Ni–Co PBA-derived NiSx nanoparticles (NPs) cocatalyst using grinding method. The optimized CZS/NiSx-N-1.5 hybrids (CZS/NiSx-N, where N represents nickel nitrate which was used as nickel source) exhibited outstanding stability and activity, the average rate of H2 was up to 192.82 mmolg−1h−1 in deionized water medium, which was 201.4% higher than that of CZS. Besides, NiSx-A and NiSx-C cocatalysts with different particle sizes were obtained using nickel acetate (A) and nickel chloride (C) as nickel source, respectively. The CZS/NiSx-C-1.5 and CZS/NiSx-A-1.5 exhibited the H2 evolution rate of 180.70 and 201.93 mmolg−1h−1 in deionized water medium, respectively. The as-prepared materials also exhibited the excellent H2 evolution performance in natural seawater medium. Besides, the photocatalytic mechanism of H2 evolution over CZS NRs/NiSs NPs was also discussed. This work develops a novel H2 evolution cocatalyst and unveils the relationship between the loading amount/particle size of cocatalyst on the H2 evolution rate.

Carbon Dots Anchoring Single-Atom Pt on C3N4 Boosting Photocatalytic Hydrogen Evolution.

Carbon nitride (C3N4) has gained considerable attention and has been regarded as an ideal candidate for photocatalytic hydrogen evolution. However, its photocatalytic efficiency is still unsatisfactory due to the rapid recombination rate of photo-generated carriers and restricted surface area with few active sites. Herein, we successfully synthesized a single-atom Pt cocatalyst-loaded photocatalyst by utilizing the anchoring effect of carbon dots (CDs) on C3N4. The introduction of CDs onto the porous C3N4 matrix can greatly enhance the specific surface area of C3N4 to provide more surface-active sites, increase light absorption capabilities, as well as improve the charge separation efficiency. Notably, the functional groups of CDs can efficiently anchor the single-atom Pt, thus improving the atomic utilization efficiency of Pt cocatalysts. A strong interaction is formed via the connection of Pt-N bonds, which enhances the efficiency of photogenerated electron separation. This unique structure remarkably improves its H2 evolution performance under visible light irradiation with a rate of 15.09 mmol h-1 g-1. This work provides a new approach to constructing efficient photocatalysts by using CDs for sustainable hydrogen generation, offering a practical approach to utilizing solar energy for clean fuel production.

Enhanced visible‐light‐driven photocatalytic application for water purification and hydrogen evolution by large‐sized nanofilm‐constructed hierarchical porous g‐C3N4/SiO2

AbstractThe large‐sized nanofilm‐constructed hierarchical porous SiO2 (LNCHPS) is successfully prepared by the dual templating approach and subsequently used as the support for g‐C3N4. A series of characterization techniques are conducted to evaluate the structure and property of the as‐prepared materials. The LNCHPS possesses two sets of explicated successive pass‐through macropores (0.5–1.0 µm) with large specific surface area. In addition, the macropore wall is constructed by uniform mesoporous nanofilms with the thickness ranging from 35 to 50 nm. Then, the photocatalytic property is investigated by degradations towards Rhodamine B (RhB) under simulated sunlight, in which experiments have been performed through controlling the g‐C3N4 loading contents, solution pH values, and photocatalyst dosages. The apparent rate constant of g‐C3N4/LNCHPS could reach 0.03 min−1 under optimum conditions, showing 6.0 times that of the bulk g‐C3N4. In addition, g‐C3N4/LNCHPS also exhibits significantly enhanced performance in H2 evolution (39.9 µmol h−1) compared to that of the bulk g‐C3N4. High light absorption and utilization, enhanced adsorption capability and quick electron hole separation can render this fine structure excellent photocatalytic performance. Our work enables a facile route for large‐scale preparation of g‐C3N4/LNCHPS for addressing the wastewater treatment and hydrogen energy production simultaneously.

1T/2H MoSe2 modified ZnIn2S4 with modulating internal electric field to boost efficient performance of photocatalytic H2 evolution and epoxide alcoholysis

Herein, the extended layer spacing 1T MoSe2 coupled with ZnIn2S4 nanosheets through in-situ growth, and ultimately obtained 1T /2H MoSe2/ZnIn2S4 photocatalysts with S-scheme heterojunction. This rational structure enables photogenerated carriers to rapidly transfer to MoSe2 via Mo-S bond. In order to further address the problem of wasted oxidative half-reaction, we rely on the dehydrogenation of benzyl alcohol as a carrier for hole depletion. Notably, optimized 1T/2H MoSe2/ZnIn2S4 has superior H2 evolution ability, reaching up to 11.271 mmol·g−1·h−1 and the apparent quantum efficiency at 420 nm is 10.3 %. Meanwhile, the conversion rate of benzyl alcohol to high value-added benzaldehyde is 60.60 %. In addition, the Zn acidic sites can achieve polarization of epoxides and precise cleavage C-O bond. Thus, it also has the ability to high selectivity and efficient photocatalytic epoxide alcoholysis. This work proposes a new insight for enhancing photocatalytic properties via regulating IEF to fabricate S-scheme heterostructure.

High-performance heterometallic photocatalysts afforded by polyoxometalate synthons for efficient H2 production

MoS2-based materials have emerged as photoelectric semiconductors characterized by a narrow band gap, high capacity for absorbing visible light, and reduced H2 adsorption energy comparable to Pt. These attributes render them appealing for application in photocatalytic hydrogen production. Despite these advantages, the widespread adoption of MoS2-based materials remains hindered by challenges associated with limited exposure to active sites and suboptimal catalytic hydrogen production efficiency. To address these issues, we have designed and synthesized a new class of highly dispersed bimetallic/trimetallic sulfide materials. This was achieved by developing polyoxometalate synthons containing Ni-Mo elements, which were subsequently reacted with thiourea and CdS. The resulting Ni3S2-MoS2 and Ni3S2-MoS2-CdS materials achieve photocatalytic hydrogen production rates of 2770 and 2873 μmol g–1h−1, respectively. Notably, the rate of 2873 μmol g–1h−1 for Ni3S2-MoS2-CdS surpassed triple (3.23 times) the performance of CdS and nearly sextuple (5.77 times) that of single MoS2. These materials outperformed the majority of MoS2-based photocatalysts. Overall, this study introduces a straightforward methodology for synthesizing bimetallic/trimetallic sulfides with enhanced photocatalytic H2 evolution performance. Our findings underscore the potential of transition metal sulfide semiconductors in the realm of photocatalysis and pave the way for the development of more sustainable energy production systems.

Bottom-Up Construction of Mesoporous Cerium-Doped Titania with Stably Dispersed Pt Nanocluster for Efficient Hydrogen Evolution.

Hydrogen generation is one of the crucial technologies to realize sustainable energy development, and the design of advanced catalysts with efficient interfacial sites and fast mass transfer is significant for hydrogen evolution. Herein, an in situ coassembly strategy was proposed to engineer a cerium-doped ordered mesoporous titanium oxide (mpCe/TiO2), of which the abundant oxygen vacancies (Ov) and highly exposed active pore walls contribute to good stability of ultrasmall Pt nanoclusters (NCs, ∼ 1.0 nm in diameter) anchored in the uniform mesopores (ca. 20 nm). Consequently, the tailored mpCe/TiO2 with 0.5 mol % Ce-doping-supported Pt NCs (Pt-mpCe/TiO2-0.5) exhibits superior H2 evolution performance toward the water-gas shift reaction with a 0.73 molH2·s-1·molPt-1 H2 evolution rate at 200 °C, which is almost 6-fold higher than the Pt-mpTiO2 (0.13 molH2·s-1·molPt-1 H2). Density functional theory calculations confirm that the structure of Ce-doped TiO2 with Ce coordinated to six O atoms by substituting Ti atoms is thermodynamically favorable without the deformation of Ti-O bonds. The Ov generated by the six O atom-coordinated Ce doping is highly active for H2O dissociation with an energy barrier of 2.18 eV, which is obviously lower than the 2.37 eV for the control TiO2. In comparison with TiO2, the resultant Ce/TiO2 support acts as a superior electron acceptor for Pt NCs and causes electron deficiency at the Pt/support interface with a 0.17 eV downshift of the Pt d-band center, showing extremely obvious electronic metal-support interaction (EMSI). As a result, abundant and hyperactive Ti3+-Ov(-Ce3+)-Ptδ+ interfacial sites are formed to significantly promote the generation of CO2 and H2 evolution. In addition, the stronger EMSI between Pt NCs and mpCe/TiO2-0.5 than that between Pt and mpTiO2 contributes to the superior self-enhanced catalytic performance during the cyclic test, where the CO conversion at 200 °C increases from 72% for the fresh catalyst to 99% for the used one. These findings reveal the subtle relationship between the mesoporous metal oxide-metal composite catalysts with unique chemical microenvironments and their catalytic performance, which is expected to inspire the design of efficient heterogeneous catalysts.

Oxygen vacancy-rich CoMoO4/Carbon nitride S-scheme heterojunction for boosted photocatalytic H2 production: Microstructure regulation and charge transfer mechanism

Developing highly efficient S-scheme photocatalysts is a subject of immense interest for harnessing solar energy towards sustainable hydrogen production. Herein, a novel S-scheme heterojunction of oxygen vacancy-rich CoMoO4/CN (CMO/CN) photocatalyst was rationally constructed through loading CoMoO4 nanorods on carbon nitride (CN) nanosheets via a direct one-pot calcination method. The CMO/CN S-scheme heterojunction exhibited enhanced surface area, fine CN dispersion, rich oxygen vacancies, and accelerated charge separation/transfer efficiency, which were conducive to improving photocatalytic H2 evolution performance. Of note, the optimal 3 %CMO/CN sample displayed the highest H2 production rate of 8.35 mmol g−1 h−1, which is 4.6 folds that of pristine CN. In situ irradiated X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) characterizations confirmed the S-scheme charge transfer path between CN and CMO, which greatly promoted spatial charge separation. Density functional theory (DFT) calculations together with contact angle tests revealed the reduced activation energies for H2O dissociation and enhanced hydrophilicity of the CMO/CN. The CMO/CN photocatalysts also presented high stability and fine reusability. This work may provide insights into the combination of defect engineering and heterojunction designing for high-efficiency solar-to-chemical energy conversion.

Oxygen Atom Coordinative Position Inducing Catalytic Sites Structure Reconstruction for Enhanced Photocatalytic H2 Evolution

AbstractOxygen‐inducing controllable surface reconstruction on the transition metal‐based (TMB) materials surface has a great impact on catalytic performance. However, regulating the oxygen coordinative position during the active sites reconstructive process is challenging and poorly understood. Here, the metastable isomeric catalytic site is reasonably designed and fabricated for enhancing photocatalytic hydrogen evolution. Due to the controlled coordinative position of the oxygen atom, a new ternary catalytic site Co‐P(‐‐O) is created, improving the photocatalytic performance of H2 evolution toward 20.7 mmol g−1 in 6 h and 0.56% apparent quantum efficiency. The reconstruction method not only changes the electronic state around the catalytic site but also tunes the adsorption energy of the hydrogen atom. Compared with Co‐Co, Co‐P, Co‐O, and O‐Co‐P catalytic sites, the remarkable Co‐P(‐‐O) sites would drive the H‐atom connecting with the Co‐P bridge style achieving the best performance and excellent stability. Such a reconstructed catalytic site is also proved efficient in electrocatalysis and photo‐electrocatalysis systems. In conclusion, this work provides a new insight that the controllable isomeric catalytic site reconstruction strategy can dramatically enhance the catalytic performance.

Ni3Se4/ZnIn2S4 S-scheme heterojunction for efficient photocatalytic H2 evolution

Photocatalytic water splitting is sustainable technology to obtain green H2. Herein, Ni3Se4/ZnIn2S4 heterojunction was obtained through a two-step hydrothermal method. 5 wt% Ni3Se4/ZnIn2S4 exhibits the most excellent H2 evolution performance and the H2 evolution rate can achieve 38778.0 μmol·g−1·h−1, which is 5.94 times higher than that of pure ZnIn2S4. Based on the ·OH free radical capture tests, the enhanced activity is attributed to S-scheme carriers migration mechanism and the abundant Se sites in Ni3Se4 can rapidly capture H+ to produce H2 efficiently. This work expands the application of transition metal selenides in the field of photocatalysis.

Synergizing copolymerization and thermal induction for carbon nitride: Reinforcing photocatalytic performance and mechanism insight

Structure optimization of photocatalyst graphitic carbon nitride (CN) is still a key endeavor. CN nanosheets were prepared via a facile one-pot copolymerization process, incorporating electron-withdrawing groups 5-cyanopyrimidine (CPM) and melamine under calcination. The synergistic effect of molecular doping and thermal induction effectively modulates the intrinsic electronic and band structure of CN. The post-optimized sample (CNMCPM0.03–700) exhibits a higher reduction potential, reduced nanosheet thickness, stronger crystallinity, and enhanced electron-holes separation efficiency, compared to pristine CN (CNM). Notably, significant morphological and textural alterations were observed in the modified CNMCPMX-T samples. Consequently, a remarkable enhancement in visible-light photocatalytic H2 evolution and CO2 reduction performance was achieved. Specifically, the CNMCPM0.03–700 retained an H2 evolution rate of 166.4 µmol·h−1, which was 14.8-fold higher than that of CNM (11.3 µmol·h−1), along with a 31.6-fold increase in CO evolution efficiency. Molecular and textural engineering demonstrate their universal applicability for different comonomers. This study showcases the feasibility of synergizing thermal induction and copolymerization strategies for synthesizing high-efficiency CN-based photocatalysts with unique topology and structural precision.

Carbon dots prepared from waste wood and residual adhesive and their use as catalysts for hydrogen production

Large quantities of waste wood with residual resin adhesives are not recycled efficiently. To address this issue, waste wood with residual resin adhesives was synthesized into carbon dots (CDs) via a facile hydrothermal self-assembly method to enhance the H2 evolution performance of graphite C3N4 (g-C3N4), a metal-free photocatalyst. Among all samples, the most significant enhanced sample was MCN-UF-3.5, which has an H2 evolution of 22.1 mmol·g-1·h-1, which is 3.91 times that of unmodified g-C3N4. The band gap and recombination of photogenerated charges were both improved by the doping of CDs. Meanwhile, the DFT calculation showed that adding CDs, especially with the -NH2 group, can significantly deform the structure and destroy the symmetry. This consequence implies an enhancement in the activity of the hydrogen evolution reaction, confirming the feasibility of the modification.

Construction of 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunction for dramatically boosted photocatalytic H2 evolution performance

One of the most crucial strategies for transforming solar energy into sustainable hydrogen energy is photocatalytic H2 evolution, and constructing an effective and durable photocatalyst remains a difficult task. Herein, a 1D/3D Co9S8/Mn0.3Cd0.7S Schottky heterojunctions were successfully fabricated by three-step hydrothermal procedure, in which 3D Mn0.3Cd0.7S solid solution particles were immobilized on the 1D tube-like Co9S8 surface, allowing for extremely effective charge separation and transfer. Through coupling Co9S8 with Mn0.3Cd0.7S, the photocatalytic H2 evolution activity and stability were significantly boosted. The 7 % Co9S8/Mn0.3Cd0.7S heterojunction possessed the highest photocatalytic activity with the H2 evolution rate of 1586.4 μmol⋅h−1, which was 3.73 times larger than that of pristine Mn0.3Cd0.7S, corresponding to 21.8 % apparent quantum efficiency (AQE) at 420 nm monochromatic light. The Schottky heterojunction mechanism between Co9S8 and Mn0.3Cd0.7S could plausibly explain the enhanced photocatalytic H2 evolution performance, according to density functional theory (DFT) calculations and ultraviolet photoelectron spectroscopy (UPS) measurements. This investigation would offer the useful insights to develop Co9S8 cocatalyst for application in photocatalytic H2 evolution.

Critical role of hydrogen bonding between microcrystalline cellulose and g-C3N4 enables highly efficient photocatalysis.

Developing a highly efficient photocatalyst for energy and environmental applications is urgently required. Herein, graphitic carbon nitride (CN) coupled with microcrystalline cellulose (MCC) (denoted as MCC-X/CN) shows excellent photocatalytic performance for tetracycline (TC) degradation and H2 evolution. And the optimized MCC-0.05/CN shows an improved TC degradation rate (Kapp = 0.019 min-1) and H2 evolution rate (642.71 μmol g-1 h-1), which are 1.9 and 22 times higher than those of pure CN, respectively. This improvement primarily results from hydrogen bonding (H-bonding) between CN and MCC, which enables excellent charge separation and migration, leading to the outstanding photoelectrochemical properties of MCC-0.05/CN.

Enhanced performance of a Na3.5Co4[Bi2Co2W19.75O70(H2O)6]/porous graphitic carbon nitride heterojunction based photocatalyst realized by the addition of copper sulfide nanoparticles.

Photocatalytic hydrogen (H2) evolution can effectively solve the global energy problem, in which the key factor is the synthesis of efficient photocatalytic materials. In this study, we successfully synthesized a novel photocatalyst, BiWCo/CuS/PGCN, by functionalizing porous graphitic carbon nitride (PGCN) with sandwich-type polyoxometalate Na3.5Co4[Bi2Co2W19.75O70(H2O)6]·39.5H2O (BiWCo) and introducing copper sulfide (CuS) nanoparticles as a cocatalyst. This approach was aimed at enhancing the built inner electric field between interfaces, resulting in a significant improvement in photocatalytic H2 evolution performance. This research adopts a step-by-step method to synthesize BiWCo/CuS/PGCN composites with p-n heterojunctions, which has high visible light absorption and a synergistic effect of multiple elements. PGCN with a high specific surface area contributes to the uniform distribution of active sites. In addition, the nano-CuS cocatalyst provides abundant active sites and more electron transfer pathways for photocatalysis. Therefore, the H2 production efficiency of BiWCo/CuS/PGCN is 6.3 times that of PGCN, 4.5 times that of BiWCo and 2.5 times that of BiWCo/PGCN under visible light. The H2 production rate of BiWCo/CuS/PGCN reaches 3477.58 μmol g-1 h-1. At the same time, the ternary photocatalyst shows high stability after 30 hours and 5 cycles. This work demonstrates that BiWCo/CuS/PGCN has good application prospects in H2 evolution, and provides a new strategy for the design of efficient ternary photocatalytic materials.

Applications of ZnSe quantum dots for solar energy harvesting

To reduce the large usage of fossil fuels, scholars have made great efforts to develop green energy such as wind energy, biomass energy, and solar energy. Solar energy has special benefits, thus solar energy harvesting technologies including solar cells, luminescent solar concentrators, photocatalysis have been studied widely. It is meaningful to study the working principle of those technologies. For the special properties of ZnSe, different kinds of nanostructure of it have been used for solar energy harvesting. Among them, since quantum qot structure has some specific characters, the application of it for solar energy harvesting are worthwhile to mention. This study aims to introduce solar cells, luminescent solar concentrators, photocatalysis technologies and the applications of ZnSe quantum dots for them. It found that ZnSe quantum dots enhanced the behavior of Si nanowire solar cells. Besides, the outstanding performance of luminescent solar concentrators based on InP/ZnSe quantum dots is partly own to ZnSe shell structure. Moreover, some quantum dots including ZnSe shell structure behave good photocatalytic H2 evolution performances. At the same time, the nanostructures of the quantum dots mentioned are shown.

Fabrication of visible-light-responsive ZnIn2S4 nanosheets wrapped onto MIL-125(Ti) hybrid structure with improved photocatalytic H2-evolution performance

Fabrication of visible-light-responsive ZnIn2S4 nanosheets wrapped onto MIL-125(Ti) hybrid structure with improved photocatalytic H2-evolution performance

Simultaneous hydrogen production from wastewater degradation by protonated porous g-C3N4/BiVO4 Z-scheme composite photocatalyst

Inspired by organic contaminants acting as sacrificial agents to accelerate the photocatalytic H2 evolution, protonated porous g-C3N4/BiVO4 Z-scheme photocatalysts was prepared through simple one-step hydrothermal method for the degradation of ofloxacin (OFL) wastewater with simultaneously hydrogen production. The optimal g-C3N4/BiVO4 (HCN/BV-5) sample could degrade the OFL wastewater with a hydrogen yield of 80.7 μmol·g−1∙h−1, demonstrating the potential in protonated porous g-C3N4/BiVO4 Z-scheme photocatalyst synchronous photocatalytic degradation antibiotic wastewater and hydrogen production. By carrying out the free radical quenching experiments and electron spin resonance experiments, it proved that the ·OH and h+ radicals played the most positive roles in the simultaneous OFL antibiotic wastewater degradation and hydrogen production process. Meanwhile, the HCN/BV-5 also exhibited a significantly H2 evolution performance in different real-world water bodies and universal applicability to the degradation of antibiotics wastewater. This work presents a new idea for alleviating current energy crisis and addressing environmental problems.

Decorating Thermodynamically Stable (101) Facets of TiO2 with MoO3 for Multifunctional Sustainable Hydrogen Energy and Ammonia Gas Sensing Applications.

The simultaneous realization of sustainable energy and gas sensors dealing with the emission of pollutants is indispensable as the former thrives on the minimization of the latter. However, there is a dearth of multifunctional nanocatalysts in the literature. This ascertains the importance of multifunctional semiconductors which can be utilized in H2 generation via overall water splitting and in the gas sensing of global pollutants such as NH3. MoO3-decorated TiO2 Z-scheme heterostructures exceptionally escalate the photochemical and photo/electrochemical H2 evolution performance and gas sensing response of TiO2 owing to the synergistic relationship between TiO2 and MoO3. Extensive structural, morphological, and optical characterizations, theoretical studies, and XPS results were exploited to develop a mechanistic framework of photochemical H2 evolution. The photochemical response of the optimum TiO2-MoO3 composition (20 wt % MoO3-TiO2) was found to be nearly 12- and 20-fold superior to the pristine TiO2 and MoO3 photocatalysts, respectively, with the remarkable H2 evolution rate of 9.18 mmol/g/h and AQY of 36.02%. In addition, 20 wt % MoO3-TiO2 also showed advanced photo/electrochemical efficiency with 0.61/0.7 V overpotential values toward HER due to the higher electrochemically active surface area and Tafel slope as low as 65 mV/dec. The gas sensing response of 20 wt % MoO3-TiO2 toward NH3 gas turned out to be 2.5-fold higher than that of the pristine TiO2 gas sensor.