Exsolution of Ru Nanoparticles on BaCe0.9Y0.1O3-δ Modifying Geometry and Electronic Structure of Ru for Ammonia Synthesis Reaction Under Mild Conditions

Green ammonia is an efficient, carbon-free energy carrier and storage medium. The ammonia synthesis using green hydrogen requires an active catalyst that operates under mild conditions. The catalytic activity can be promoted by controlling the geometry and electronic structure of the active species. An exsolution process is implemented to improve catalytic activity by modulating the geometry and electronic structure of Ru. Ru nanoparticles exsolved on a BaCe_0.9Y_0.1O_3-δ support exhibit uniform size distribution, 5.03 ± 0.91 nm, and exhibited one of the highest activities, 387.31 mmol_NH3 g_Ru⁻¹ h⁻¹ (0.1 MPa and 450 °C). The role of the exsolution and BaCe_0.9Y_0.1O_3-δ support is studied by comparing the catalyst with control samples and in-depth characterizations. The optimal nanoparticle size is maintained during the reaction, as the Ru nanoparticles prepared by exsolution are well-anchored to the support with in-plane epitaxy. The electronic structure of Ru is modified by unexpected in situ Ba promoter accumulation around the base of the Ru nanoparticles.     

Constructing Ru@C3N4/Cu Tandem Electrocatalyst with Dual-Active Sites for Enhanced Nitrate Electroreduction to Ammonia

Electroreduction of nitrate to ammonia reaction (NO₃⁻RR) is considered as a promising carbon-free energy technique, which can eliminate nitrate from waste-water also produce value-added ammonia. However, it remains a challenge for achieving satisfied ammonia selectivity and Faraday efficiency (FE) due to the complex multiple-electron reduction process. Herein, a novel Tandem electrocatalyst that Ru dispersed on the porous graphitized C₃N₄ (g-C₃N₄) encapsulated with self-supported Cu nanowires (denoted as Ru@C₃N₄/Cu) for NO₃⁻RR is presented. As expected, a high ammonia yield of 0.249 mmol h⁻¹ cm⁻² at −0.9 V and high FE_NH3 of 91.3% at −0.8 V versus RHE can be obtained, while achieving excellent nitrate conversion (96.1%) and ammonia selectivity (91.4%) in neutral solution. In addition, density functional theory (DFT) calculations further demonstrate that the superior NO₃⁻RR performance is mainly resulted from the synergistic effect between the Ru and Cu dual-active sites, which can significantly enhance the adsorption of NO₃⁻ and facilitate hydrogenation, as well as suppress the hydrogen evolution reaction, thus lead to highly improved NO₃⁻RR performances. This novel design strategy would pave a feasible avenue for the development of advanced NO₃⁻RR electrocatalysts.     

Enhanced C?O Functionality on Carbon Papers Ensures Lowering Nucleation Delay of ALD for Ru towards Unprecedented Alkaline HER Activity

The success in lowering the nucleation delay for Atomic Layer Deposition (ALD) of Ru on carbon surfaces is mitigated by constructive pretreatments resulting enhancement of C O functionality. Treatment of the carbon papers (CP) allowed Ru species deposition for minimum number of ALD cycles (25 cycles) with good conformality. The development of electrocatalysts from single atoms to nanoparticles (NPs) on conductive supports with low metal loadings, thus improving performance, is essential in electrocatalysis. For alkaline hydrogen evolution reaction, ALD decorated CPs with Ru exhibit low onset potentials of ≈4.7 mV versus reversable hydrogen electrode (RHE) (at 10 mA cm⁻²) and a high turnover frequency of 1.92 H₂ s⁻¹ at 30 mV versus RHE. The Ru decorated CPs show comparable to higher catalytic activity than of Platinum (Pt) decorated CP also developed by ALD. The current representation of unfamiliar catalytic activities of Ru active centers developed by ALD, pave a bright and sustainable path for energy conversion reactions.     

Synthesis of TiO2 nanotubes coupled with CdS nanoparticles and production of hydrogen by photocatalytic water decomposition

The CdS/TiO₂NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO₂NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV-Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO₂NTs and the absorption spectrum of TiO₂NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO₂NTs composite was examined under visible light irradiation (λ > 400 nm) and the quantity of H₂ evolution was ca. 1708 μL/g for 6 h.     

Activating nano-bulk interplays for sustainable ammonia electrosynthesis

Small changes in a catalyst’s composition, modification, and/or integration into a reactor can have significant yet often poorly understood effects on (electro)catalysis. Here we demonstrate the careful tailoring of Ru/La_0.25Ce_0.75O_2−x catalysts through the post-synthesized hydrothermal treatment together with control over the Ru loadings to create hydroxyl groups and electronic restructuring for ammonia electrosynthesis. When integrated into a protonic ceramic electrolyzer, the in situ formed Ce³⁺−OH/Ru sites facilitate both the NN decoupling and NH formation at 400 °C and 1 bar of N₂, boosting the ammonia production rate (2.92 mol h⁻¹ m⁻²) up to 100-fold higher than the current state-of-the-art electrolyzers. Moreover, such catalysts and electrolyzer design concepts can be readily tuned to more complex applications such as coproducing ammonia and other chemicals with hydrocarbons as direct hydrogen sources. The creation of coordinated saturated support –OH/metal sites in the advanced electrolyzer offers an attractive approach for future clean-energy and green-chemical industries.     

Novel UV–Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self‐ordered TiO₂ nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO₂ NTs and Se in combination with the surface trap states at TiO₂ help regulate the electron transport and facilitate the separation of photogenerated electron–hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W^?1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p‐type Se into TiO₂ NTs broadens the detection range to UV–visible (280–700 nm) with a large detectivity of over 10¹² Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈10⁷ A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 10⁴) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy‐efficient optoelectronic devices for practical applications.     

Dense-Packed RuO2 Nanorods with In Situ Generated Metal Vacancies Loaded on SnO2 Nanocubes for Proton Exchange Membrane Water Electrolyzer with Ultra-Low Noble Metal Loading

Proton exchange membrane water electrolyzer (PEMWE) is a green hydrogen production technology that can be coupled with intermittent power sources such as wind and photoelectric power. To achieve cost-effective operations, low noble metal loading on the anode catalyst layer is desired. In this study, a catalyst with RuO₂ nanorods coated outside SnO₂ nanocubes is designed, which forms continuous networks and provides high conductivity. This allows for the reduction of Ru contents in catalysts. Furthermore, the structure evolutions on the RuO₂ surface are carefully investigated. The etched RuO₂ surfaces are seen as the consequence of Co leaching, and theoretical calculations demonstrate that it is more effective in driving oxygen evolution. For electrochemical tests, the catalysts with 23 wt% Ru exhibit an overpotential of 178 mV at 10 mA cm⁻², which is much higher than most state-of-art oxygen evolution catalysts. In a practical PEMWE, the noble metal Ru loading on the anode side is only 0.3 mg cm⁻². The cell achieves 1.61 V at 1 A cm⁻² and proper stability at 500 mA cm⁻², demonstrating the effectiveness of the designed catalyst.     

Superior Energy Storage Properties and Optical Transparency in K0.5Na0.5NbO3-Based Dielectric Ceramics via Multiple Synergistic Strategies

Eco-friendly transparent dielectric ceramics with superior energy storage properties are highly desirable in various transparent energy-storage electronic devices, ranging from advanced transparent pulse capacitors to electro-optical multifunctional devices. However, the collaborative improvement of energy storage properties and optical transparency in KNN-based ceramics still remains challenging. To address this issue, multiple synergistic strategies are proposed, such as refining the grain size, introducing polar nanoregions, and inducing a high-symmetry phase structure. Accordingly, outstanding energy storage density (W_total ≈7.5 J cm⁻³, W_rec ≈5.3 J cm⁻³) and optical transmittance (≈76% at 1600 nm, ≈62% at 780 nm) are simultaneously realized in the 0.94(K_0.5Na_0.5)NbO₃-0.06Sr_0.7La_0.2ZrO₃ ceramic, together with satisfactory charge-discharge performances (discharge energy density: ≈2.7 J cm⁻³, power density: ≈243 MW cm⁻³, discharge rate: ≈76 ns), surpassing previously reported KNN-based transparent ceramics. Piezoresponse force microscopy and transmission electron microscopy revealed that this excellent performance can be attributed to the nanoscale domain and submicron-scale grain size. The significant improvement in the optical transparency and energy storage properties of the materials resulted in the widening of the application prospects of the materials.     

Biophotofuel cell anode containing self-organized titanium dioxide nanotube array

We made a biophotofuel cell consisting of a titanium dioxide nanotube array photosensitive anode for biomass decomposition, and a low-hydrogen overpotential metal, Pt, as the cathode for hydrogen production. The titanium dioxide nanotubes (TiO₂ NTs) were prepared via electrochemical oxidation of pure Ti in NaF solutions. Scanning electron microscopy was used to analyze the morphology of the nanotubes. The average diameter, wall thickness and length of the as-prepared TiO₂ NTs were 88 ± 16 nm, 10 ± 2 nm and 491 ± 56 nm, respectively. Such dimensions are affected by the NaF concentration and the applied voltage during processing. Higher NaF concentrations result in the formation of longer and thicker nanotubes. The higher the voltage is, the thicker the nanotubes. The photosensitive anode made from the highly ordered TiO₂ NTs has good photo-catalytic property, as can be seen from the test results of ethanol, apple vinegar, sugar and tissue paper decomposition under ultraviolet (UV) radiation. It is concluded that the biophotofuel cell with the TiO₂ nanotube photoanode and a Pt cathode can generate electricity, hydrogen and clean water depending on the pH value and the oxygen presence in the solutions.     

Constructing Co@TiO2 Nanoarray Heterostructure with Schottky Contact for Selective Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical nitrate (NO₃⁻) reduction reaction (NO₃⁻RR) is a potential sustainable route for large-scale ambient ammonia (NH₃) synthesis and regulating the nitrogen cycle. However, as this reaction involves multi-electron transfer steps, it urgently needs efficient electrocatalysts on promoting NH₃ selectivity. Herein, a rational design of Co nanoparticles anchored on TiO₂ nanobelt array on titanium plate (Co@TiO₂/TP) is presented as a high-efficiency electrocatalyst for NO₃⁻RR. Density theory calculations demonstrate that the constructed Schottky heterostructures coupling metallic Co with semiconductor TiO₂ develop a built-in electric field, which can accelerate the rate determining step and facilitate NO₃⁻ adsorption, ensuring the selective conversion to NH₃. Expectantly, the Co@TiO₂/TP electrocatalyst attains an excellent Faradaic efficiency of 96.7% and a high NH₃ yield of 800.0 µmol h⁻¹ cm⁻² under neutral solution. More importantly, Co@TiO₂/TP heterostructure catalyst also presents a remarkable stability in 50-h electrolysis test.     

Efficient Nitrate Synthesis via Ambient Nitrogen Oxidation with Ru-Doped TiO2/RuO2 Electrocatalysts

A facile pathway of the electrocatalytic nitrogen oxidation reaction (NOR) to nitrate is proposed, and Ru-doped TiO₂/RuO₂ (abbreviated as Ru/TiO₂) as a proof-of-concept catalyst is employed accordingly. Density functional theory (DFT) calculations suggest that Ru^δ+ can function as the main active center for the NOR process. Remarkably doping Ru into the TiO₂ lattice can induce an upshift of the d-band center of the Ru site, resulting in enhanced activity for accelerating electrochemical conversion of inert N₂ to active NO*. Overdoping of Ru ions will lead to the formation of additional RuO₂ on the TiO₂ surface, which provides oxygen evolution reaction (OER) active sites for promoting the redox transformation of the NO* intermediate to nitrate. However, too much RuO₂ in the catalyst is detrimental to both the selectivity of the NOR and the Faradaic efficiency due to the dominant OER process. Experimentally, a considerable nitrate yield rate of 161.9 µmol h⁻¹ g_cat⁻¹ (besides, a total nitrate yield of 47.9 µg during 50 h) and a highest nitrate Faradaic efficiency of 26.1% are achieved by the Ru/TiO₂ catalyst (with the hybrid composition of Ru_xTi_yO₂ and extra RuO₂ by 2.79 wt% Ru addition amount) in 0.1 m Na₂SO₄ electrolyte.     

Self-Supported Pd Nanorod Arrays for High-Efficient Nitrate Electroreduction to Ammonia

Electrochemical nitrate (NO₃⁻) reduction to ammonia (NH₃) offers a promising pathway to recover NO₃⁻ pollutants from industrial wastewater that can balance the nitrogen cycle and sustainable green NH₃ production. However, the efficiency of electrocatalytic NO₃⁻ reduction to NH₃ synthesis remains low for most of electrocatalysts due to complex reaction processes and severe hydrogen precipitation reaction. Herein, high performance of nitrate reduction reaction (NO₃⁻RR) is demonstrated on self-supported Pd nanorod arrays in porous nickel framework foam (Pd/NF). It provides a lot of active sites for H* adsorption and NO₃⁻ activation leading to a remarkable NH₃ yield rate of 1.52 mmol cm⁻² h⁻¹ and a Faradaic efficiency of 78% at −1.4 V versus RHE. Notably, it maintains a high NH₃ yield rate over 50 cycles in 25 h showing good stability. Remarkably, large-area Pd/NF electrode (25 cm²) shows a NH₃ yield of 174.25 mg h⁻¹, be promising candidate for large-area device for industrial application. In situ FTIR spectroscopy and density functional theory calculations analysis confirm that the enrichment effect of Pd nanorods encourages the adsorption of H species for ammonia synthesis following a hydrogenation mechanism. This work brings a useful strategy for designing NO₃⁻RR catalysts of nanorod arrays with customizable compositions.     

Influence of the size-controlled TiO<Subscript>2</Subscript> nanotubes fabricated by low-temperature chemical synthesis on the dye-sensitized solar cell properties

Titanium dioxide nanotubes (TiO₂ NTs) with various sizes have been prepared by low-temperature chemical synthesis using commercial anatase TiO₂ particles with different crystallite size in NaOH solution and used as a photoelectrode in a dye-sensitized solar cell (DSSC). The relationship between the physicochemical properties of electrode materials and photovoltaic performance was investigated. The electrodes made from modified TiO₂ NTs showed a strong dependency on their specific surface area and resultant amount of dye adsorption; the surface area decreased with increase in the diameter of the NT from 9.8 to 23.6 nm. The conversion efficiency of the cell made from TiO₂ NT, 12.9 nm in diameter, was enhanced by 12% compared to that of the smallest NT. These results suggested that the photovoltaic performance improved by the suppression of photogenerated charge recombination in spite of a 25.3% reduction in the specific surface area. In addition, larger TiO₂ NTs could be utilized as a scattering layer on the top of the TiO₂ nanoparticulate working electrode. It was observed that this controlled TiO₂ photoelectrode architecture exhibited enhanced conversion efficiency without TiCl₄ treatment.     

Piezoelectricity regulated ohmic contact in M/BaTiO3 (M = Ru,Pd, Pt) for charge collision and hydrogen free radical production in ammonia electrosynthesis

Electrochemical nitrate reduction reaction (NO₃RR) is a promising alternative technique for NH₃ generation toward the energy-consuming Haber-Bosch process. Nevertheless, it remains hindered by the competitive hydrogen evolution reaction (HER). Herein, the piezoelectric effect of electron-rich BaTiO₃ with oxygen vacancies is introduced to promote NO₃RR performance. Combining with metal particles (Ru, Pd and Pt), the catalyst achieves a maximal Faradaic efficiency of 95.3% and NH₃ yield rate of 6.87 mg h⁻¹ mg_cat.⁻¹. Upon piezoelectricity, the interface between metal nanoparticles and BaTiO₃ is effectively modulated from Schottky contact to ohmic contact, which leads to unobstructed electron transfer. Abundant hydrogen radicals (·H) can be then produced from the collision between plentiful electrons and polar water molecules adsorbed on the polar surface. Such ·H can significantly facilitate the hydrogenation of reaction intermediates in NO₃RR. Meanwhile, this process suppresses the Volmer-Heyrovsky step, therefore inhibiting the HER within a wide range of external potential. This work suggests a new strategy for promoting the performance of multi-electron-involved catalytic reactions.     

Synthesis of micro-sized hierarchical TiO2 particles of nano-scale effectiveness and their photocatalytic activities at various surface hydroxyl concentrations

The 3-dimensional hierarchical TiO₂ particles of micro-sized diameter were synthesized through modified sol–gel process with polyethylene glycol (PEG) as a structure-controlling agent. The anatase crystal structure was obtained after calcination at 450 °C. The size and specific surface area of particles were 1.0–1.8 μm and 96.85 m² g⁻¹, respectively. The specific surface area of the TiO₂ particles corresponded to that of the spherical nanoparticles with average size of 15.9 nm. Although the size of synthesized TiO₂ was micro-scale, they had the specific surface area similar to that of nano-scale particles due to the effect of PEG on the formation of particles. Subsequently, the surface modification with various concentration of ammonia solution was carried out for the preparation of hydroxyl-rich TiO₂ particles at surfaces. As the concentration of ammonia solution was increased, the amount of chemically adsorbed hydroxyl groups on the TiO₂ surface was increased. As an application of prepared TiO₂ for water treatment, their catalytic performances for the degradation of methylene blue (MB) were examined by using UV–Vis spectrophotometer with the assistance of UV lamp. After hydroxylation treatment, the micro-sized TiO₂ particles showed the higher performance of MB degradation than that of nano-sized P25 particles because of their large specific surface area and hydroxyl-rich surface.     

Heterointerface and Tensile Strain Effects Synergistically Enhances Overall Water-Splitting in Ru/RuO2 Aerogels

Designing robust electrocatalysts for water-splitting is essential for sustainable hydrogen generation, yet difficult to accomplish. In this study, a fast and facile two-step technique to synthesize Ru/RuO₂ aerogels for catalyzing overall water-splitting under alkaline conditions is reported. Benefiting from the synergistic combination of high porosity, heterointerface, and tensile strain effects, the Ru/RuO₂ aerogel exhibits low overpotential for oxygen evolution reaction (189 mV) and hydrogen evolution reaction (34 mV) at 10 mA cm⁻², surpassing RuO₂ (338 mV) and Pt/C (53 mV), respectively. Notably, when the Ru/RuO₂ aerogels are applied at the anode and cathode, the resultant water-splitting cell reflected a low potential of 1.47 V at 10 mA cm⁻², exceeding the commercial Pt/C||RuO₂ standard (1.63 V). X-ray adsorption spectroscopy and theoretical studies demonstrate that the heterointerface of Ru/RuO₂ optimizes charge redistribution, which reduces the energy barriers for hydrogen and oxygen intermediates, thereby enhancing oxygen and hydrogen evolution reaction kinetics.     

Utilizing Metal-Thiocatecholate Functionalized UiO-66 Framework for Photocatalytic Hydrogen Evolution Reaction

Exploiting clean energy is essential for sustainable development and sunlight-driven photocatalytic water splitting represents one of the most promising approaches toward this goal. Metal-organic frameworks (MOFs) are competent photocatalysts owing to their tailorable functionality, well-defined structure, and high porosity. Yet, the introduction of the unambiguous metal-centered active site into MOFs is still challenging since framework motifs capable of anchoring metal ions firmly are lacking. Herein, the assembly using 1,4-dicarboxylbenzene-2,3-dithiol (H₂ dcbdt ) and Zr-Oxo clusters to give a thiol-functionalized UiO-66 type framework,  UiO-66-dcbdt, is reported. The thiocatechols on the struts are allowed to capture transition metal (TM) ions to generate  UiO-66-dcbdt-M  ( M   = Fe, Ni, Cu) with unambiguous metal-thiocatecholate moieties for photocatalytic hydrogen evolution reaction (HER).  UiO-66-dcbdt-Cu  is found the best catalyst exhibiting an HER rate of 4.18 mmol g⁻¹ h⁻¹ upon irradiation with photosensitizing Ru-polypyridyl complex. To skip the use of the external sensitizer,  UiO-66-dcbdt-Cu  is heterojunctioned with titanium dioxide (TiO₂) and achieves an HER rate of 12.63 mmol g⁻¹ h⁻¹ (32.3 times that of primitive TiO₂). This work represents the first example of MOF assembly employing H₂ dcbdt  as the mere linker followed by chelation with TM ions and undoubtedly fuels the rational design of MOF photocatalysts bearing well-defined active sites.     

Kinetic-Modulated Crystal Phase of Ru for Hydrogen Oxidation

Crystal-phase-engineering provides a powerful strategy for regulating the catalytic performance yet remains great challenge. Herein, the kinetic-modulated crystal-phase-control of Ru nanosheet assemblies (Ru NAs) is demonstrated by simply altering the concentration of citric acid (CA). Detailed experimental results reveal that high concentration of CA retards the growth kinetics and thus leads to the formation of metastable face-centered cubic (fcc) Ru NAs, while low concentration of CA results in the fast growth kinetics and the preferential formation of Ru NAs with stable hexagonal close packed (hcp) phase. Moreover, Ru NAs with different phases are used as catalyst for hydrogen oxidation reaction (HOR) to evaluate the effects of crystal phase on catalytic performance. Impressively, Ru NAs with fcc phase display a mass activity of 2.75 A mg_Ru⁻¹ at 50 mV, which is much higher than those of Ru NAs with fcc/hcp (1.02 A mg_Ru⁻¹) and hcp (0.74 A mg_Ru⁻¹) phases. Theoretical calculations show that fcc Ru NAs display weaker adsorption toward ^*H and lower energy barrier toward the rate-determining step (RDS) during HOR. This work provides a facile strategy for regulating the crystal phase of Ru nanocrystals, which may attract rapid interests of researchers in materials, chemistry, and catalysis.     

Synthesis of Hierarchical 4H/fcc Ru Nanotubes for Highly Efficient Hydrogen Evolution in Alkaline Media

Hierarchical metal nanostructures containing 1D nanobuilding blocks have stimulated great interest due to their abundant active sites for catalysis. Herein, hierarchical 4H/face‐centered cubic (fcc) Ru nanotubes (NTs) are synthesized by a hard template‐mediated method, in which 4H/fcc Au nanowires (NWs) serve as sacrificial templates which are then etched by copper ions (Cu²⁺) in dimethylformamide. The obtained hierarchical 4H/fcc Ru NTs contain ultrathin Ru shells (5–9 atomic layers) and tiny Ru nanorods with length of 4.2 ± 1.1 nm and diameter of 2.2 ± 0.5 nm vertically decorated on the surface of Ru shells. As an electrocatalyst for the hydrogen evolution reaction in alkaline media, the hierarchical 4H/fcc Ru NTs exhibit excellent electrocatalytic performance, which is better than 4H/fcc Au‐Ru NWs, commercial Pt/C, Ru/C, and most of the reported electrocatalysts.