Nanowire Catalysts Research Articles

Confined nanoreactor for synthesis of MnCe composite oxide nanowires with enhanced catalytic activity towards aromatic VOCs oxidation

A novel Mn–Ce composite oxide nanowires (MnCe-NWs) catalyst with a high specific surface area has been successfully fabricated via restricting the growth of nanocrystal within a confined nanoreactor offered by the Santa Barbara Amorphous-15 (SBA-15) template. The characterizations of X‐ray diffraction (XRD), N 2 adsorption-desorption, and Energy Dispersive X-Ray mapping (EDX-mapping) showed the Mn–Ce oxide nanowires generated in a confined nanoreactor had a homogeneous cubic fluorite structure with good metal distribution and high porosity. The X‐ray photoelectron spectroscopy (XPS), Raman, H 2 temperature-programmed reaction (H 2 -TPR), and O 2 temperature‐programmed desorption (O 2 -TPD) determined that the Mn–Ce oxide nanowire increased the lattice defects, active oxygen species, and reducibility compared to the one (MnCe-DC) generated by direct calcination in open space. Owing to these excellent properties, the Mn–Ce oxide nanowire exhibited much better catalytic performance in both toluene and benzene oxidation. The conversion efficiency of toluene and benzene can reach 90% at 199 °C and 211 °C over MnCe-NWs (100 ppm, space velocity = 60,000 mL g −1 h −1 ) while the corresponding temperature increased by 30 and 52 °C respectively over MnCe-DC. The influence of space velocity and concentration of toluene/benzene on the catalytic oxidation of toluene/benzene has also been investigated. The catalytic oxidation mechanisms of toluene/benzene and main intermediates are deduced based on the meditator of the reactions. Moreover, the durability test and the water effect test demonstrated that it has remarkable stability and high toleration of high moisture.

Nitrite Electroreduction to Ammonia Promoted by Molecular Carbon Dioxide with Near-unity Faradaic Efficiency.

Electrochemical reduction of nitrite (NO2 - ) offers an energy-efficient route for ammonia (NH3 ) synthesis and reduction of the level of nitrite, which is one of the major pollutants in water. However, the near 100 % Faradaic efficiency (FE) has yet to be achieved due to the complicated reduction route with several intermediates. Here, we report that carbon dioxide (CO2 ) can enhance the nitrite electroreduction to ammonia on copper nanowire (Cu NW) catalysts. In a broad potential range (-0.7∼-1.3 V vs. RHE), the FE of nitrite to ammonia is close to 100 % with a 3.5-fold increase in activity compared to that obtained without CO2. In situ Raman spectroscopy and density functional theory (DFT) calculations indicate that CO2 acts as a catalyst to facilitate the *NO to *N step, which is the rate determining step for ammonia synthesis. The promotion effect of CO2 can be expanded to electroreduction of other nitro-compounds, such as nitrate to ammonia and nitrobenzene to aniline.

Nitrite Electroreduction to Ammonia Promoted by Molecular Carbon Dioxide with Near‐unity Faradaic Efficiency

AbstractElectrochemical reduction of nitrite (NO2−) offers an energy‐efficient route for ammonia (NH3) synthesis and reduction of the level of nitrite, which is one of the major pollutants in water. However, the near 100 % Faradaic efficiency (FE) has yet to be achieved due to the complicated reduction route with several intermediates. Here, we report that carbon dioxide (CO2) can enhance the nitrite electroreduction to ammonia on copper nanowire (Cu NW) catalysts. In a broad potential range (−0.7∼−1.3 V vs. RHE), the FE of nitrite to ammonia is close to 100 % with a 3.5‐fold increase in activity compared to that obtained without CO2. In situ Raman spectroscopy and density functional theory (DFT) calculations indicate that CO2 acts as a catalyst to facilitate the *NO to *N step, which is the rate determining step for ammonia synthesis. The promotion effect of CO2 can be expanded to electroreduction of other nitro‐compounds, such as nitrate to ammonia and nitrobenzene to aniline.

Efficient electrocatalytic desulfuration and synchronous hydrogen evolution from H2S via anti-sulfuretted NiSe nanowire array catalyst

Decreasing energy consumption of water splitting strategy by replacing oxygen evolution reaction (OER) with more facile sulfide oxidation reaction (SOR) to H2 evolution and value-added sulfur products is a promising technology. Nevertheless, the unsatisfactory catalyst long-term stability and passivation issues substantially limit the overall productivity. Herein, we report an anti-sulfuretted NiSe nanowire array catalyst on nickel foam (NiSe/NF), this catalyst exhibits a significantly reduced anode potential of 0.49 V vs. RHE at 100 mA cm−2 compared to the oxygen evolution reaction (1.78 V vs. RHE) and remains admirable stability for more than 500 h without passivation. Particularly, the skillful combination of UV–vis, in situ Raman, and attenuated total reflection Fourier transform infrared spectra, we reveal that S2-/HS- has been selectively converted to Sn2- and by-product S2O32- rather than sulfur, which avoids long-perplexing passivation issue of solid sulfur. For the first time, we demonstrate the feasibility of the system (SOR + HER) in a commercial membrane electrode assembly stack, which affords 19.0 mL min−1 H2 at a low cell voltage of 1.0 V with consuming the electricity of 2.63 kWh Nm−3 H2. This work provides a new avenue for low-cost H2 production by H2S electrooxidation desulfurization.

Efficient CO2 fixation with acetophenone on Ag-CeO2 electrocatalyst by a double activation strategy

AbstractThe electrocarboxylation reaction is an attractive means to convert CO2 into valuable chemicals under ambient conditions, while it still suffers from low efficiency due to the high stability of CO2. In this work, we report a double activation strategy for simultaneously activating CO2 and acetophenone by silver-doped CeO2 (Ag-CeO2) nanowires, featuring as an effective electrocatalyst for electrocarboxylation of acetophenone with CO2. Compared to the Ag foil, Ag nanoparticles and CeO2 nanowires, the Ag-CeO2 nanowire catalyst allowed to reduce the onset potential difference between CO2 and acetophenone activation, thus enabling efficient electrocarboxylation to form 2-phenyllactic acid. The Faradaic efficiency for producing 2-phenyllactic acid reached 91% at −1.8 V versus Ag/AgI. This double activation strategy of activating both CO2 and organic substrate molecules can benefit the catalyst design to improve activities and selectivities in upgrading CO2 fixation for higher-value electrocarboxylation.

Layered Pd oxide on PdSn nanowires for boosting direct H2O2 synthesis

Hydrogen peroxide (H2O2) has the wide range of applications in industry and living life. However, the development of the efficient heterogeneous catalyst in the direct H2O2 synthesis (DHS) from H2 and O2 remains a formidable challenge because of the low H2O2 producibility. Herein, we develop a two-step approach to prepare PdSn nanowire catalysts, which comprises Pd oxide layered on PdSn nanowires (PdL/PdSn-NW). The PdL/PdSn-NW displays superior reactivity in the DHS at zero Celcius, presenting the H2O2 producibility of 528 mol kgcat−1·h−1 and H2O2 selectivity of >95%. A layer of Pd oxide on the PdSn nanowire generates bi-coordinated Pd, leading to the different adsorption behaviors of O2, H2 and H2O2 on the PdL/PdSn-NW. Furthermore, the weak adsorption of H2O2 on the PdL/PdSn-NW contributes to the low activation energy and high H2O2 producibility. This surface engineering approach, depositing metal layer on metal nanowires, provides a new insight in the rational designing of efficient catalyst for DHS.

Operando X-Ray Absorption Spectroscopic Study of Pt-Based Nanowire Catalysts Under Oxygen Reduction Reaction

Polymer electrolyte fuel cells (PEFCs) are attracting attention as an environmentally friendly electrochemical device that uses hydrogen as a fuel. The application of PEFC has been limited by the consumption of platinum due to the sluggish kinetics of the cathode reaction and limiting platinum reserves. It has been noted that the interaction between the cathode catalyst and the oxygen intermediate species results in an overpotential in the ORR process. Therefore, it is very important to evaluate the interaction between the oxygen species and the catalyst based on the electronic structure. Pt nanowires are known to be highly active as ORR catalysts because they tend to expose more active planes for ORR, such as (111) planes1. Pt oxides formed on Pt nanowires with such 1D anisotropy are different from conventional nanoparticle catalysts in terms of structure and electronic structure2. However, this has not been fully clarified yet under oxygen reduction conditions. In this study, we analyzed the oxidation state of Pt nanowire catalysts in the ORR by operando analysis and analyzed the electronic and local structures.Synthesis of Pt nanowire catalyst : Oleylamine (5 mL) was used as a solvent and Pt(acac)2, Ni(acac)2, W(CO)6 and CTAC (hexadecyltrimethylammonium chloride) were added and sonicated for 1 hour. The product was dissolved and allowed to react in an oil bath at 160°C for 2 hours. The product particles were collected by centrifugation, and the washing and centrifugation were repeated three times with a mixture of cyclohexane: ethanol = 1:9. The nanowires were then loaded on Vulcan XC-72. ORR activity evaluation and XAS measurement: The rotating disk electrode (RDE) method was used for electrochemical measurements. A tripolar cell was used for the measurements. catalyst ink containing Pt nanowires was prepared and applied to a glassy carbon electrode for the RDE to prepare the electrode. A catalyst-coated electrode was used as the working electrode, a platinum mesh as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. The electrolyte was 0.1 M HClO4. The cell temperature was controlled at 25 oC. XAS measurements were performed using a home-made measuring cell and the same electrochemical measurement conditions as for the RDE.The morphology and structure of the prepared Pt nanowires were observed by electron microscopy. As shown in Figure 1, the nanowires were uniformly distributed on the carbon and no significant aggregation was observed. The average diameter of the nanowires was 2.0 nm.To analyze the local structure of the Pt nanowire catalyst, the Pt-Pt bond length was estimated from EXAFS. Figure 2 shows the fitting results of the Pt-Pt bond lengths of Pt nanowire and Pt nanoparticle (TEC10V30E, TKK) catalysts in the range 0.5-1.1 V vs. RHE. With increasing potential, the Pt-Pt bond lengths of both catalysts gradually increased, but the Pt nanowire catalyst maintained a short Pt-Pt bond, and this nanowire characteristic structure may be the reason for its higher ORR activity than the nanoparticle. Acknowledgements: This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Operando X-Ray Absorption Spectroscopic Study on Electrochemical Oxygen Reduction Mechanism of Novel Platinum-Based Nanostructured Catalysts

Polymer electrolyte fuel cells (PEFCs) have been developed for electric device applications such as fuel cell vehicles (FCV). PEFC cathode catalyst requires an excess Pt due to the degradation of oxygen reduction reaction (ORR) activity. Many research efforts aim to design Pt-based nanomaterials with controllable composition and structure to increase their activity while reducing the amount of Pt, like core-shell structure. The core-shell structure is obtained by Adzic’s method (Cu-UPD)1, where the underpotential deposition (UPD) of Cu mediator on Pt and the displacement of Cu mediator by Pt are conducted. This method requires the highly precise potential control for the UPD of Cu by means of potentiostats. In contrast, our previous research demonstrated the spontaneous two-step method (Galvanic cell) to synthesize spherical Pd@Pt core-shell catalyst without a special control of electrochemical equipment and reducing/stabilizing agents2. In this study, this Galvanic cell method was applied for Pd@Pt core-shell nanowire catalysts. Compared with the conventional Cu-UPD method, this method can synthesize the catalysts on a larger scale and form more uniform monolayer Pt shells, resulting in a higher ORR activity.Ultrathin Pd nanowires were prepared using surfactants as templates3. Briefly, palladium nitrate, ODA, and DTAB were dissolved in toluene under strong magnetic stirring. The mixture was placed in an inert atmosphere and sonicated for 20 min. NaBH4 was added to the above solution as a reducing agent. One hour later, the organic phase was recovered using distilled water and chloroform as extractants. After centrifugation, Pd nanowires can be obtained. After mixing the catalyst with carbon, the Pd/C powder is dispersed in the N2-saturated 0.01M CuSO4 and 0.5 M H2SO4 solution, with continual stirring. Then, a Cu wire is immersed in the above mixture2. Near 5 hours later, Cu wire is extracted, and successively N2-saturated 10 mM K2PtCl4 solution is added to the suspension to obtain Pd-nanowire@Pt/C. Electrochemical tests were performed in 0.1 M HClO4, and the catalyst ORR activity was evaluated at 0.9 V. XAS measurements of Pt L-edge were also performed under the same conditions.In contrast to the previously reported method (Cu-UPD)4, our proposed method does not require electrochemical equipment, or reducers/stabilizers, and uniform Pt shells in Pd-nanowire@Pt/C can be obtained. As shown in Figure 1, Core-shell catalysts have a lower white line intensity than Pt/C, meaning that they are more difficult to oxidize. The ligand effect causes surface Pt compression, and after calculating, the first-shell Pt-Pt bond length in the Pd-NW@Pt Gal. catalyst is shorter than that of the nanoparticle, which means a stable structure and less oxygen species generation. So, the catalysts synthesized using the Galvanic Cells method can provide higher ORR activity (specific activities: 0.8 mA/cm2 and mass activities: 1.3 A/mgPt) compared to the Cu-UPD method. Acknowledgement This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References; [1] Zhang, J.; Mo, Y.; Vukmirovic M. B.; Klie R; Sasaki K.; Adzic R R.; J. Phys. Chem. B 2004 108 (30), 10955-10964.[2] Wang, X.; Orikasa, Y.; Inaba, M.; Uchimoto, Y.; et al. ACS Catal., 2020, 10, 430– 434.[3] Teng, X.; Han, W.; Ku, W.; Hucker, M.; et al. Angew. Chem., Int. Ed. 2008, 47, 2055– 2058.[4] Koenigsmann, C., Adzic, R. R.; et al. J. Am. Chem. Soc., 2011 , 133, 9783– 9795. Figure 1

Ex situ flame vapor-doped oxophilic metals on WP/WOx nanowires for enhanced alkaline hydrogen evolution activity

Developing effective non-noble hydrogen evolution reaction (HER) electrocatalysts in alkaline electrolyte is desirable for efficient water splitting, but it is challenging. In this work, various oxophilic metals (Co, Cu, Mn, and Cr) were incorporated into WP/WOx films as water dissociation promotors to enhance the HER activity. Flame vapor deposition (FVD) was used for ex situ facile doping of metals on WP/WOx. The prepared metal-doped WP/WOx catalysts exhibited improved HER activities in alkaline solution, resulted from promoted water dissociation step by oxophilic doping metals on WP/WOx. Specifically, Co-doped WP/WOx (Co:WP/WO) film showed the highest intrinsic activity of HER among metal dopants owing to an optimum oxophilicity of Co. Nanostructure engineering was employed to further enhance the HER performance of the Co:WP/WO catalysts. A nanowires (NWs) array of WP/WO was fabricated by thermal evaporation, providing numerous active sites and faster pathways for mass transport and charge transfer. With the synergistic effect of Co dopants and the NWs structure, the Co:WP/WO NWs catalyst exhibited a superior HER performance in alkaline media with an overpotential of 104 mV at a current density of 10 mA cm−2 and stability of over 50 h in 1.0 M KOH solution. Lastly, combining our Co:WP/WO NW – Ir/NF (HER – OER catalysts) with tandem perovskite solar cell demonstrates unassisted solar hydrogen generation by photovoltaic electrochemical (PV-EC) system, generating a solar to hydrogen (STH) efficiency of 10.2 %. Our study provides a rational strategy for developing efficient non-noble HER electrocatalysts that are highly active in alkaline media.

Chemically dezincified copper nanowires catalysts with competitive selectivity for ethylene production by carbon dioxide reduction reaction

Chemically dezincified copper nanowires catalysts with competitive selectivity for ethylene production by carbon dioxide reduction reaction

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires Via Surface Segregation: Application in Electrochemical Methanol Oxidation

The reaction kinetics and efficiency in any catalytic process is controlled by the adsorption and desorption of reactant and intermediates on the surface of catalyst. As a consequence, the surface properties, composition and geometry of the catalyst dictates the mechanism of reactions. The surface electronic structure is modulated by variations in surface and subsurface atomic configurations, e.g., ordering and surface segregation, which in turn can vividly affects catalytic properties.1,2 A great deal of efforts are being devoted to develop efficient heterogenous catalyst by critically controlling the surface structure and chemistry. Here, I would like to present results on two different strategies for controlling the surface composition in ultrathin bimetallic AuPd nanowires. Au nanowire template-based method was used to grow AuPd wires by gradually increasing the amount of Pd.3 Percentage of composition of Au and Pd in AuPd nanowires gave either alloy nanowires with Au-rich compositions or core-shell structure at higher Pd compositions with Au-rich core and Pd-rich shell. Surface morphology of alloyed nanowires were induced through segregation of Pd to the surface by annealing under controlled CO atmosphere. High resolution microscopic imaging was possible due to the fact of substantial difference in the atomic number between Au and Pd. Electrocatalytic methanol oxidation reaction (MOR) in alkaline medium is important for energy conversion and was selected to study the catalytic activity of AuPd nanowires. A nearly monotonic increase of MOR potential was observed with increase in Pd content. Interestingly, a typical volcano type behavior of the specific activity was observed with different composition and with 40 and 50% Pd samples showed the optimum values in terms of current, potential and If/Ib values. Owing to a higher Pd content of CO-annealed nanowires, a lowering of potential was observed though the specific activity was maintained. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts with smaller amounts of the expensive active metal. The compositional effects on the electronic structure of the AuPd nanowires (catalyst surface) as well as binding energy of intermediates involved in the MOR was investigated using DFT calculations. d-band center analysis was employed to check interaction of CO* which a major intermediate of MOR with the catalyst surface. The theoretical investigation align well with the experimental results where it was found that the MOR potential increases with increasing amount of Pd and for the Au rich case the reaction does not reach up to CO2 but yields HCHO as a product at lower potentials. From our experimental finding it was evident that it is possible to lower the MOR potential to attain comparable or better activity through enrichment with the precious metal on the surface while essentially dropping the real quantity used.

Enhancing the Low-Temperature CO Oxidation over CuO-Based α-MnO2 Nanowire Catalysts.

A series of CuO-based catalysts supported on the α-MnO2 nanowire were facilely synthesized and employed as the CO oxidation catalysts. The achieved catalysts were systematically characterized by XRD, SEM, EDS-mapping, XPS and H2-TPR. The catalytic performances toward CO oxidation had been carefully evaluated over these CuO-based catalysts. The effects of different loading methods, calcination temperatures and CuO loading on the low temperature catalytic activity of the catalyst were investigated and compared with the traditional commercial MnO2 catalyst with a block structure. It was found that the slenderness ratio of a CuO/α-MnO2 nanowire catalyst decreases with the increase in CuO loading capacity. The results showed that when CuO loading was 3 wt%, calcination temperature was 200 °C and the catalyst that was supported by the deposition precipitation method had the highest catalytic activity. Besides, the α-MnO2 nanowire-supported catalysts with excellent redox properties displayed much better catalytic performances than the commercial MnO2-supported catalyst. In conclusion, the CuO-based catalysts that are supported by α-MnO2 nanowires are considered as a series of promising CO oxidation catalysts.

Strained Pt(221) Facet in a PtCo@Pt-Rich Catalyst Boosts Oxygen Reduction and Hydrogen Evolution Activity

Over the last years, the development of highly active and durable Pt-based electrocatalysts has been identified as the main target for a large-scale industrial application of fuel cells. In this work, we make a significant step ahead in this direction by preparing a high-performance electrocatalyst and suggesting new structure-activity design concepts which could shape the future of oxygen reduction reaction (ORR) catalyst design. For this, we present a new one-dimensional nanowire catalyst consisting of a L10 ordered intermetallic PtCo alloy core and compressively strained high-index facets in the Pt-rich shell. We find the nanoscale PtCo catalyst to provide an excellent turnover for the ORR and hydrogen evolution reaction (HER), which we explain from high-resolution transmission electron microscopy and density functional theory calculations to be due to the high ratio of Pt(221) facets. These facets include highly active ORR and HER sites surprisingly on the terraces which are activated by a combination of sub-surface Co-induced high Miller index-related strain and oxygen coverage on the step sites. The low dimensionality of the catalyst provides a cost-efficient use of Pt. In addition, the high catalytic activity and durability are found during both half-cell and proton exchange membrane fuel cell (PEMFC) operations for both ORR and HER. We believe the revealed design concepts for generating active sites on the Pt-based catalyst can open up a new pathway toward the development of high-performance cathode catalysts for PEMFCs and other catalytic systems.

Efficient conversion of low-concentration nitrate sources into ammonia on a Ru-dispersed Cu nanowire electrocatalyst.

Electrochemically converting nitrate ions, a widely distributed nitrogen source in industrial wastewater and polluted groundwater, into ammonia represents a sustainable route for both wastewater treatment and ammonia generation. However, it is currently hindered by low catalytic activities, especially under low nitrate concentrations. Here we report a high-performance Ru-dispersed Cu nanowire catalyst that delivers an industrial-relevant nitrate reduction current of 1 A cm-2 while maintaining a high NH3 Faradaic efficiency of 93%. More importantly, this high nitrate-reduction catalytic activity enables over a 99% nitrate conversion into ammonia, from an industrial wastewater level of 2,000 ppm to a drinkable water level <50 ppm, while still maintaining an over 90% Faradaic efficiency. Coupling the nitrate reduction effluent stream with an air stripping process, we successfully obtained high purity solid NH4Cl and liquid NH3 solution products, which suggests a practical approach to convert wastewater nitrate into valuable ammonia products. Density functional theory calculations reveal that the highly dispersed Ru atoms provide active nitrate reduction sites and the surrounding Cu sites can suppress the main side reaction, the hydrogen evolution reaction.

Study on PtNWs/c Catalyst for Proton Exchange Membrane Fuel Cell

With the development of PEMFC, the process of commercial fuel cell is also accelerating. As one of the key points of fuel cell, catalyst is facing the problem of how to improve its performance and life. In order to improve the durability of fuel cell catalyst, this paper will study the preparation of Pt nanowire catalyst, so as to improve the electrochemical performance and durability of the catalyst. PtNWs were prepared by soft template method. By TEM, we can clearly see that PtNWs with uniform length were obtained by soft template method. Because of the special structure, the ORR performance of the catalyst was better. The test results showed that the hydrogen peroxide desorption from PtNWs was easier, and the half wave potential of LSV curve shifted forward, which indicated that the NWs catalyst performed better ORR performance. The linear structure of PtNWs is not easy to dissolve and lose compared with Pt particles, and the linear structure is more conducive to the transfer of materials and electrons at the reaction interface, so it can show better performance and life.

N-doped carbon nanotubes supported Pt nanowire catalysts for proton exchange membrane fuel cells

The large-scale practical application of proton exchange membrane fuel cells (PEMFCs) is difficult to achieve if their performance and durability cannot be improved. We successfully synthesized N-doped carbon nanotube (NCNT) supported Pt nanowire catalysts (PtNW/NCNTs) using the soft template method with NCNTs as support. The results of transmission electron microscopy show that the Pt nanowires are uniformly loaded on the support (NCNTs). X-ray photoelectron spectroscopy reveals that the N atom doped on the surface is in the form of graphite N and pyridine N. The electrocatalytic activity of PtNW/NCNTs is studied via the half-cell electrochemistry test. The PtNW/NCNTs show better oxygen reduction reaction activity than commercial Pt/C catalysts. The results of the single-cell polarization experiment reveal that the performance of PEMFCs with PtNW/NCNTs is improved, and the maximum power density is 966 mW cm−2. After 500 h dynamic cycle durability test, the average voltage loss of the single cell is 3.6% for the PtNW/NCNTs catalyst and 7.2% for the Pt/C catalyst. The Pt/C catalyst demonstrates severe Pt nanoparticle growth and aggregation with a broad size distribution, the PtNW along with minimal changes observed. PtNW/NCNTs are a promising replacement to traditional Pt/C catalysts as electrocatalyst in PEMFC applications.

High throughput screening driven discovery of Mn5Co10Fe30Ni55Ox as electrocatalyst for water oxidation and electrospinning synthesis

The electrochemical reduction of water or CO2 holds great potential for storage of intermittently produced renewable energy and requires highly active electrocatalyst to speed up water oxidation at anode. Metal oxides containing multiple components are promising electrocatalyst for the oxygen evolution reaction (OER); but their development demands exhaustive experiments, resulting in long term cycles and high cost in research. In this paper, a high-throughput experimental scheme is employed for searching effective OER oxide electrocatalysts. Combining inkjet printing technology and scanning electrochemical microscopy, a material library of Mn-Co-Fe-Ni oxide is rapidly prepared and its OER activity is screened. The composition of Mn5Co10Fe30Ni55Ox has been found to exhibit the highest catalytic activity. Nanowire catalyst of the corresponding composition has been prepared by electrospinning method, which achieves a low overpotential of 280 mV at current density of 10 mA·cm−2 and a Tafel slope of 60.4 mV·dec−1.

Hydrogen Production and Degradation of Ciprofloxacin by Ag@TiO2-MoS2 Photocatalysts

The photocatalytic activity of silver-based catalysts containing different amounts of molybdenum disulfide (MoS2; 5, 10 and 20 wt.%) was evaluated by the degradation of the antibiotic ciprofloxacin and the production of hydrogen via water splitting. All the silver (Ag)-based catalysts degraded more than 70% of the antibiotic in 60 min. The catalyst that exhibited the best result was 5%Ag@TiO2-P25-5%MoS2, with ca. 91% of degradation. The control experiments and stability tests showed that photocatalysis was the degradation pathway and the selected silver-based catalysts were stable after seven cycles, with less than 2% loss of efficiency per cycle and less than 7% after seven cycles. The catalyst with the highest hydrogen production was 5%Ag@TiO2 NWs-20%MoS2, 1792 μmol/hg, at a wavelength of 400 nm. This amount was ca. 32 times greater than that obtained by the pristine titanium oxide nanowires catalyst. The enhancement was attributed to the high surface area of the catalysts, along with the synergism created by the silver nanoparticles and MoS2. All the catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area analysis and energy dispersive X-ray spectroscopy (EDS).

Investigating the product distribution behaviour of CO2 methanation through thermodynamic optimized experimental approach using micro/nano structured titania catalyst

Catalytic CO2 hydrogenation yields a wide range of products, making products selectivity a major challenge. This study provides a comprehensive investigation on CO2 hydrogenation to CH4 by involving thermodynamic optimized experimental approach. First, thermodynamic analysis was carried out using equilibrium rate constants and Gibbs free and insights on the behaviour and product distribution of CO2 methanation were investigated. A low temperature (150–450 °C), elevated pressure and H2/CO2 feed ratio above 4 are essential for CH4 production. More importantly, as temperature rises, the product formation shifts from CH4 to CO, C2H6 and finally solid carbon. Upon thermodynamic optimization, an experimental approach was conducted using micro/nano structured conductive catalysts. CO2 methanation over Ni-dispersed conductive TiO2 microparticles (MPs)/nanowires (NWs) catalysts involves various complex reactions such as the adsorption, desorption and activation of molecules. An ideal Ni loading of 15 wt%, with GHSV of 6,300 mL g-1h−1 is beneficial for the CH4 production. Furthermore, TiO2 NWs provided a 1.32-fold enhancement in activity and CH4 production comparing to MPs, elucidating the enhancement effect of a one-dimensional (1D) nanowire structure over zero-dimensional (0D) spherical microparticle structure. YCH4, SCH4 and XCO2 over 15% Ni/TiO2 NWs achieved 88.9%, 99.1% and 89.8%, respectively. Despite a good agreement between the thermodynamic and experimental results, there was a slight difference in trend because the theoretical values can be obtained by just considering the feasibility of reactions in terms of ΔG and ln (K). Besides, catalytic experimental runs involves complex reactions through adsorption and desorption, leading to CH4 formation via different pathways. Due to the conductive characteristics and 1D structure of TiO2, the products distribution was close to thermodynamics value and exhibited higher stability that would be beneficial for further investigation in catalytic reactions.

Electro-Reforming Polyethylene Terephthalate Plastic to Co-Produce Valued Chemicals and Green Hydrogen.

Upcycling plastic waste pollution for sustainable resources and energy is an ideal solution to plastic waste-related environmental issues. Polyethylene terephthalate (PET), one of the most prominent single-use daily plastics with up to millions of tons produced annually, has recently been explored with respect to chemical recycling to ameliorate its environmental impact. In this work, we report an electrochemical upcycling approach to electrocatalytic oxidation of PET hydrolysate using Cu-based nanowire catalysts. We demonstrate that the electrocatalyst can catalyze the ethylene glycol (EG) molecule derived from PET waste toward formate with high selectivity and exhibit a lower onset potential for EG oxidation than for water oxidation. Experimental and density functional theory calculation results reveal that the oxidation pathway of EG on CuO can selectively break the C-C bond to generate formic acid. This work sheds light on employing earth-abundant metal catalysts to convert PET plastic waste to produce valued chemicals and green hydrogen.