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Through the use of ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, carbon dioxide (CO2) electrolysis reactions (CO2 + 2e−→ CO + O2−) and carbon monoxide (CO) electro-oxidation reactions (CO + O2−→ CO2 + 2e−) over cerium oxide electrodes have been investigated in the presence of 0.5 Torr CO–CO2 gas mixtures at ∼600 °C. Carbonate species (CO32−) are identified on the ceria surface as reaction intermediates. When CO2 electrolysis is promoted on ceria electrodes at +2.0 V applied bias, we observe a higher concentration of CO32− over a 400 μm-wide active region on the ceria surface, accompanied by Ce3+/Ce4+ redox changes. This increase in the CO32− steady-state concentration suggests that the process of pre-coordination of CO2 to the ceria surface to form a CO32− intermediate (CO2(g) + O2−(surface)→ CO32−(surface)) precedes a rate-limiting electron transfer process involving CO32− reduction to give CO and oxide ions (CO32−(surface) + 2Ce3+→ CO(g) + 2O2−(surface) + 2Ce4+). When the applied bias is switched to −1.5 V to promote CO electro-oxidation on ceria, the surface CO32− concentration slightly decreases from the equilibrium value, suggesting that the electron transfer process is also a rate-limiting process in the reverse direction. [ABSTRACT FROM AUTHOR]

Room–temperature hydrogen sensors usually suffer from dramatic response drop in humid air. Aiming to solve such issue of H 2 sensing Schottky diodes, a platinum/graphene oxide/titanium dioxide (Pt/GO/TiO 2) Schottky diode is designed. The GO interlayer between the 50–nm–thick Pt nanolayer and TiO 2 substrate significantly improves resistance to humidity interference. Remarkably, the diode with a GO loading of 0.969 mg cm−2 exhibits a response retention rate (R RH95% /R dry) of nearly 100%. To reveal the mechanism for the improved anti–humidity performance, the H 2 O adsorption behavior of Pt/GO/TiO 2 diode was investigated by quartz crystal microbalance and near ambient pressure X–ray photoelectron spectroscopy. H 2 O molecules are absent on the Pt surface of Pt/GO/TiO 2 in water vapor. This is a result of the H 2 O adsorption effect of the GO interlayer, which stems from the superior H 2 O adsorption ability of the GO interlayer and causes the diffusion of H 2 O molecules adsorbed on the Pt surface into the GO interlayer through nanochannels in the Pt nanolayer. Additionally, the GO interlayer serves as a blocking layer for the diffusion of hydroxyl species generated on the TiO 2 surface to the Pt nanolayer. Such hydroxyl blocking effect prevents the consumption of adsorbed H atoms at the Pt/GO interface. • Compared to Pt/TiO 2 diode, the designed Pt/GO/TiO 2 diode exhibits higher H 2 response in dry air and has high resistance to humidity interference. • QCM and NAP-XPS were used to clarify the mechanism for the significantly improved anti-humidity H 2 sensing performance of Pt/GO/TiO 2. • The GO interlayer has the H 2 O adsorption and hydroxyl blocking effects, thus offering the Pt/GO/TiO 2 high resistance to humidity interference. [ABSTRACT FROM AUTHOR]

We report a new method to probe the solid-liquid interface through the use of a thin liquid layer on a solid surface. An ambient pressure XPS (AP-XPS) endstation that is capable of detecting high kinetic energy photoelectrons (7 keV) at a pressure up to 110 Torr has been constructed and commissioned. Additionally, we have deployed a 'dip &pull' method to create a stable nanometers-thick aqueous electrolyte on platinum working electrode surface. Combining the newly constructed AP-XPS system, 'dip &pull' approach, with a 'tender' X-ray synchrotron source (2 keV-7 keV), we are able to access the interface between liquid and solid dense phases with photoelectrons and directly probe important phenomena occurring at the narrow solid-liquid interface region in an electrochemical system. Using this approach, we have performed electrochemical oxidation of the Pt electrode at an oxygen evolution reaction (OER) potential. Under this potential, we observe the formation of both Pt2+ and Pt4+ interfacial species on the Pt working electrode in situ. We believe this thin-film approach and the use of 'tender' AP-XPS highlighted in this study is an innovative new approach to probe this key solid-liquid interface region of electrochemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Develop a bimetallic Pd-Rh catalyst for both hydrogenation and dehydrogenation reaction. • The catalyst structure that Rh clusters isolated by the surrounding Pd atoms was proved by various ex- and in-situ characterizations. • The mechanism of NEC hydrogenation was proposed and verified by DFT calculations. Hydrogen is a promising candidate to replace the exhausting fossil fuels. However, it is still a big challenge for hydrogen storage. Liquid organic hydrogen carrier (LOHC), which possesses high safety and purity, easy transport and reversibility, is highly attractive for hydrogen storage. Herein we report a new reusable bimetallic Pd-Rh nanoparticles (NPs) catalyst with synergy effect, boosting both the hydrogenation of N-ethylcarbazole (NEC) and dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC), which allows multiple cycles of reversible high-weight% hydrogen storage and uptake in short reaction time. Various ex- and in-situ characterizations evidenced that the superior activity was attributed to the bimetallic Pd-Rh NPs cluster structure on the surface of γ-Al 2 O 3 support. The mechanism of NEC hydrogenation over the Pd-Rh catalyst was proposed and verified by density functional theory (DFT) calculations. Such a strategy can be extended to other LOHCs and sheds light onto the development of LOHCs as energy vectors. [ABSTRACT FROM AUTHOR]

Electricity consumption of metro stations increases sharply with expansion of a metro network and this has been a growing cause for concern. Based on relevant historical data from existing metro stations, this paper proposes a support vector regression (SVR) model to estimate daily electricity consumption of a newly constructed metro station. The model considers some major factors influencing the electricity consumption of metro station in terms of both the interior design scheme of a station (e.g., layout of the station and allocation of facilities) and external factors (e.g., passenger volume, air temperature and relative humidity). A genetic algorithm with five-fold cross-validation is used to optimize the hyper-parameters of the SVR model in order to improve its accuracy in estimating the electricity consumption of a metro station (ECMS). With the optimized hyper-parameters, results from case studies on the Beijing Subway showed that the estimating accuracy of the proposed SVR model could reach up to 95% and the correlation coefficient was 0.89. It was demonstrated that the proposed model could outperform the traditional methods which use a back-propagation neural network or multivariate linear regression. The method presented in this paper can be an adequate tool for estimating the ECMS and should further assist in the delivery of new, energy-efficient metro stations. [ABSTRACT FROM AUTHOR]

Autonomous vehicle technology is poised to revolutionize shared vehicle systems, offering the potential for increased efficiency and convenience. To better devise management strategies for shared autonomous vehicles, this paper addresses a real-time dispatch problem with hybrid requests, where on-demand (immediate) and pre-booked (reserved) trip requests coexist. The coexistence of these two types of request behaviors introduces considerable complexity to real-time dispatch due to the uncertainty in trip demand. We design an approximate dynamic programming (ADP) approach for making vehicle–trip assignments and vehicle relocation decisions. We first formulate the real-time vehicle dispatch problem as a dynamic program and decompose it into time-staged subproblems. To effectively handle the high-dimensional state space, we replace the value functions with tractable approximations and propose a piecewise-linear functional approximation method that captures the spatiotemporal value of vehicles. To calibrate the parameters in the approximations, we propose DualT and DualNext algorithms to provide precise dual information, thereby enhancing the accuracy of our approach. Furthermore, we propose a lookahead strategy that incorporates pre-booked request information into the ADP approach for improving real-time decision-making. We validate the effectiveness of the ADP approach through numerical experiments conducted using taxi data from Brooklyn, New York. The ADP approach outperforms benchmark policies in solution quality while maintaining computational efficiency, and the incorporation of the lookahead strategy significantly enhances the performance of the ADP approach, yielding substantial improvements. Numerical results demonstrate that integrating pre-booked requests into vehicle dispatch management can greatly enhance the system efficiency. • We address a real-time SAV dispatch problem with hybrid on-demand and pre-booked trip requests. • An ADP modeling and algorithmic approach is proposed. • A lookahead strategy is integrated to improve the performance of the ADP approach. • The results demonstrate the potential for pre-booking behaviors to enhance the system efficiency. [ABSTRACT FROM AUTHOR]

Energy-efficient metro operation has received increasing attention because of the energy cost and environmental concerns. This paper developed an integrated optimization model on train control and timetable to minimize the net energy consumption. The extents of train motoring and braking as well as timetable configurations such as train headway and interstation runtime are optimized to minimize the net energy consumption with consideration of utilizing regenerative energy. An improved model on train control is proposed to reduce traction energy by allowing coasting on downhill slopes as much as possible. Variations of train mass due to the change of onboard passengers are taken into account. The brute force algorithm is applied to attain energy-efficient speed profiles and an NS-GSA algorithm is designed to attain the optimal extents of motoring/braking and timetable configurations. Case studies on Beijing Metro Line 5 illustrate that the improved train control approach can save traction energy consumption by 20% in the sections with steep downhill slopes, in comparison with the commonly adopted train control sequence in timetable optimization. Moreover, the integrated model is able to significantly prolong the overlapping time between motoring and braking trains, and the net energy consumption is accordingly reduced by 4.97%. [ABSTRACT FROM AUTHOR]

This paper proposes a bi-level model to solve the timetable design problem for an urban rail line. The upper level model aims at determining the headways between trains to minimize total passenger cost, which includes not only the usual perceived travel time cost, but also penalties during travel. With the headways given by the upper level model, passengers’ arrival times at their origin stops are determined by the lower level model, in which the cost-minimizing behavior of each passenger is taken into account. To make the model more realistic, explicit capacity constraints of individual trains are considered. With these constraints, passengers cannot board a full train, but wait in queues for the next coming train. A two-stage genetic algorithm incorporating the method of successive averages is introduced to solve the bi-level model. Two hypothetical examples and a real world case are employed to evaluate the effectiveness of the proposed bi-level model and algorithm. Results show that the bi-level model performs well in reducing total passenger cost, especially in reducing waiting time cost and penalties. And the section loading-rates of trains in the optimized timetable are more balanced than the even-headway timetable. The sensitivity analyses show that passenger’s desired arrival time interval at destination and crowding penalty factor have a high influence on the optimal solution. And with the dispersing of passengers' desired arrival time intervals or the increase of crowding penalty factor, the section loading-rates of trains become more balanced. [ABSTRACT FROM AUTHOR]

5 nm Co-Rh bimetallic nanoparticles with narrow size distributions and three different atomic compositions (2, 10, and 16 % Rh) were synthesized using a colloidal method. The bimetallic nanoparticles were loaded into mesoporous silica support MCF-17 and utilized in the catalytic hydrogenation of CO (Fischer-Tropsch synthesis). As compared to the pure 5 nm Co/MCF-17 catalyst, the bimetallic Co-Rh catalysts showed a similar activity while enhancing the selectivity towards alcohols, as evidenced by an increased ratio of alcohol to hydrocarbon products. Furthermore, larger alcohols such as propanol were formed with the addition of Rh, which is not observed with the pure Co/MCF-17 catalyst. In situ synchrotron based Ambient Pressure X-ray Photoelectron Spectroscopy studies on the Co-Rh samples revealed that Rh is segregated to the surface of the nanoparticles under reaction conditions, which plays an important role in altering the selectivity towards alcohol production. An optimum surface Rh concentration exists at ~9 at.%, where a fivefold enhancement in the alcohol-to-hydrocarbon ratio was achieved. Graphical Abstract: [ABSTRACT FROM AUTHOR]

• An effective opportunistic model arranges multi-level maintenance for multi-component systems. • A reliability model evaluates complex degradation processes concerning imperfect maintenance. • Embedded dynamic strategy coordinates the maintenance schedules on the system and components. • An adapted renewal theory accommodates the maintenance optimization for variable horizons. • Real case studies are carried out to prove the efficiency and generality of proposed models. A suitable maintenance schedule is crucial for large-scale, complex multi-component systems undertaking a long-term operation to reduce failure risks and improve availability and profitability. Opportunistic maintenance is a popular solution when cost consideration is paramount. However, the extensively adopted single-level preventive maintenance action and single-stage degradation process limit the development and application of opportunistic maintenance. Multi-level preventive maintenance including both perfect and imperfect maintenance actions on multi-stage degradation is considered within an opportunistic model to address this challenge. A reliability evaluation model is first formulated to describe a multi-stage degradation process involving the effect of imperfect maintenance. An opportunistic model is then proposed to arrange reliability proportion thresholds for components in systems. The cost rate is considered as the objective function to accommodate the opportunistic model to variable scheduling horizons. A flexible dynamic strategy is developed within the opportunistic model to coordinate the schedules on the system and components by updating component schedules once a system maintenance action is executed. An improved hybrid genetic algorithm combining differential evolution is adopted to optimize the complex problem. The case studies on a locomotive system provide a better understanding of the proposed models and demonstration of its effectiveness, generality, and robustness. [ABSTRACT FROM AUTHOR]

In this work, the particulate matter less than 10 μm (PM 10) emissions from a medium-sized passenger vehicle's front brake wear were studied using a finite element analysis (FEA) and experimental approaches. The world harmonised light-duty vehicle test procedure-brake (WLTP-B) cycle was chosen to simulate real-world driving. An electrical low-pressure impactor (ELPI+) was used to count the brake wear particles on a brake dynamometer sealed in a chamber. In addition, a machine learning method, namely, extreme gradient boosting (XGBoost), was employed to capture the feature importance rankings of braking conditions contributing to brake wear PM 10 emissions. The simulated PM 10 emissions were quite consistent with the measured ones, with an overall relative error of 9%, indicating that the proposed simulation approach is promising to predict brake wear PM 10 during the WLTP-B cycle. The simulated and experimental PM 10 emission factors during the WLTP-B cycle were 6.4 mg km−1 veh−1 and 7.0 mg km−1 veh−1, respectively. Among the 10 trips of the WLTP-B cycle, the measured PM 10 of trip #10 was the largest contributor, accounting for 49% of total PM 10 emissions. On the other hand, the XGBoost results revealed that the top five most important factors governing brake wear PM 10 emissions were dissipation energy, initial braking speed, final rotor temperature, braking power, and deceleration rate. From the perspective of friendly driving behaviour and regulation, limiting severe braking and high-speed braking has the potential to reduce PM 10 emissions from brake wear. [ABSTRACT FROM AUTHOR]

Abstract: We report Ambient pressure X-ray Photoelectron Spectroscopy Endstation with an integrated chemical analytical system that consists of a residual gas analyzer in the 2nd differential pumping stage and a new low-reactive sample holder heating assembly. This system has a linear response to the reaction chamber gas pressure. The sample heating assembly also has a low dark reaction rate up to 400 °C for H2 and CO oxidation. We expect this chemical analytical system will expand our capabilities in conducting in-operando catalysis research. [Copyright &y& Elsevier]

• A collaborative transportation plan of passengers and freight on urban rail lines. • Both the dedicated freight trains and existing passenger trains to transport goods. • A MILP model to jointly optimize train stopping plans and schedules. • An iterative scheduling approach to solve the problem. • A case study based on the UP Express in Toronto and Beijing New Airport Line. This paper develops an operational strategy in which urban rail transit is used for freight transport. An environment-friendly urban freight transportation alternative is analyzed by employing optimization techniques to support the collaborative transportation of passengers and freight. Practical cases are investigated to test the technical feasibility of this transportation scheme. The paper formulates the train service design problem on a single urban rail line with passenger and freight. Passenger trains have a prescribed timetable which is allowed to be slightly modified to facilitate the freight service. Freight can be transported by inserting dedicated freight trains or utilizing the extra space inside the passenger train carriages. Station platforms are able to load and unload both goods and passengers. An optimization model for combined train service design is proposed to maximize profit resulting from the balance of revenues and costs brought by the freight service. The efficient schedules of trains and freight allocation plans are to be determined. This problem is formulated as a mixed-integer linear programming model. An iterative scheduling approach which includes a pre-processing method and two heuristic iterative algorithms is designed to solve the model. Two numerical examples are introduced to demonstrate the efficiency of the proposed model and the iterative scheduling approach. [ABSTRACT FROM AUTHOR]

CO 2 electrochemical reduction in solid oxide electrolysis cells is an effective way to combine CO 2 conversion and renewable electricity storage. A Au layer is often used as a current collector, whereas Au nanoparticles are rarely used as a cathode because it is difficult to keep nanosized Au at high temperatures. Here we dispersed a Au layer into Au nanoparticles (down to 2 nm) at 800 °C by applying high voltages. A 75-fold decrease in the polarization resistance was observed, accompanied by a 38-fold improvement in the cell current density. Combining electronic microscopy, in situ near-ambient pressure X-ray photoelectron spectroscopy, and theoretical calculations, we found that the interface between the Au layer and the electrolyte (yttria-stabilized zirconia (YSZ)) was reconstructed into nano-Au/Zr-suboxide interfaces, which are active sites that show a much lower reaction activation energy than that of the Au/YSZ interface. The formation of Zr-suboxides promotes Au dispersion and Au nanoparticle stabilization due to the strong interaction between Au and Zr-suboxides.

Development of spinel oxides as low-cost and high-efficiency catalysts is highly desirable; however, rational synthesis of efficient and stable spinel systems with precisely controlled structure and components remains challenging. We demonstrate the design of complex nanostructured cobalt-based bimetallic spinel catalysts for low-temperature CO oxidation by a simple template-free method. The self-assembled multi-shelled mesoporous spinel nanostructures provide high surface area (203.5 m 2 /g) and favorable unique surface chemistry for producing abundant active sites and lead to the creation of robust microsphere configured by 16-nm spinel nanosheets, which achieve satisfactory water-resisting property and catalytic activity. Theoretical models show that O vacancies at exposed {110} facets in cubic spinel phase guarantee the strong adsorption of reactive oxygen species on the surface of catalysts and play a key role in the prevention of deactivation under moisture-rich conditions. The design concept with architecture and composition control can be extended to other mixed transition metal oxide compositions., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Recent advances of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) have enabled the chemical composition and the electrical potential profile at a liquid/electrode interface under electrochemical reaction conditions to be directly probed. In this work, we apply this operando technique to study the surface chemical composition evolution on a Co metal electrode in 0.1 M KOH aqueous solution under various electrical biases. It is found that an ∼12.2 nm-thick layer of Co(OH) 2 forms at a potential of about -0.4 V Ag/AgCl , and upon increasing the anodic potential to about +0.4 V Ag/AgCl , this layer is partially oxidized into cobalt oxyhydroxide (CoOOH). A CoOOH/Co(OH) 2 mixture layer is formed on the top of the electrode surface. Finally, the oxidized surface layer can be reduced to Co 0 at a cathodic potential of -1.35 V Ag/Cl . These observations indicate that the ultrathin layer containing cobalt oxyhydroxide is the active phase for oxygen evolution reaction (OER) on a Co electrode in an alkaline electrolyte, consistent with previous studies.

The controllable and efficient electrochemical preparation of highly crystalline graphene quantum dots (GQDs) in an aqueous system is still challenging. Here, we developed a weak electrolyte-based (typically an ammonia solution) electrochemical method to enhance the oxidation and cutting process and therefore achieve a high yield of GQDs. The yield of GQDs (3-8 nm) is 28%, approximately 28 times higher than the yield of GQDs prepared by other strong electrolytes. The whole preparation process can be accomplished within 2 h because of the effective free radical oxidation process and the suppressed intercalation-induced exfoliation in weakly ionized aqueous electrolytes. The GQDs also showed excellent crystallinity which is obviously better than the crystallinity of GQDs obtained via bottom-up approaches. Moreover, amino-functionalization of GQDs can be realized by manipulating the electrolyte concentration. We further demonstrate that the proposed method can also be expanded to other weak electrolytes (such as HF and H 2 S) and different anode precursor materials (such as graphene/graphite papers, carbon fibers, and carbon nanotubes).

We report, for the first time, that an encapsulated silver nanoparticle can be directly converted to a silver nanoshell through a nanoscale localized oxidation and reduction process in the gas phase. Silver can be etched when exposed to a mixture of NH3/O2 gases through a mechanism analogous to the formation of aqueous Tollens' reagent, in which a soluble silver-ammonia complex was formed. Starting with Ag@resorcinol-formaldehyde (RF) resin core-shell nanoparticles, we demonstrate that RF-core@Ag-shell nanoparticles can be prepared successfully when the etching rate and RF thickness were well controlled. Due to the strong surface plasmon resonance (SPR) coupling effect among neighboring silver nanoparticles, the RF@Ag nanoparticle showed great SPR and SERS performance. This process provides a general route to the conversion of Ag-core to Ag-shell nanostructures and might be extended to other systems.

Through the use of ambient pressure X-ray photoelectron spectroscopy and specially designed ceria-based solid oxide electrochemical cells, carbon dioxide (CO2) electrolysis reactions (CO2 + 2e(-)→ CO + O(2-)) and carbon monoxide (CO) electro-oxidation reactions (CO + O(2-)→ CO2 + 2e(-)) over cerium oxide electrodes have been investigated in the presence of 0.5 Torr CO-CO2 gas mixtures at ∼600 °C. Carbonate species (CO3(2-)) are identified on the ceria surface as reaction intermediates. When CO2 electrolysis is promoted on ceria electrodes at +2.0 V applied bias, we observe a higher concentration of CO3(2-) over a 400 μm-wide active region on the ceria surface, accompanied by Ce(3+)/Ce(4+) redox changes. This increase in the CO3(2-) steady-state concentration suggests that the process of pre-coordination of CO2 to the ceria surface to form a CO3(2-) intermediate (CO2(g) + O(2-)(surface)→ CO3(2-)(surface)) precedes a rate-limiting electron transfer process involving CO3(2-) reduction to give CO and oxide ions (CO3(2-)(surface) + 2Ce(3+)→ CO(g) + 2O(2-)(surface) + 2Ce(4+)). When the applied bias is switched to -1.5 V to promote CO electro-oxidation on ceria, the surface CO3(2-) concentration slightly decreases from the equilibrium value, suggesting that the electron transfer process is also a rate-limiting process in the reverse direction.

Work function is a fundamental property of a material's surface. It is playing an ever more important role in engineering new energy materials and efficient energy devices, especially in the field of photovoltaic devices, catalysis, semiconductor heterojunctions, nanotechnology, and electrochemistry. Using ambient pressure X-ray photoelectron spectroscopy (APXPS), we have measured the binding energies of core level photoelectrons of Ar gas in the vicinity of several reference materials with known work functions (Au(111), Pt(111), graphite) and PbS nanoparticles. We demonstrate an unambiguously negative correlation between the work functions of reference samples and the binding energies of Ar 2p core level photoelectrons detected from the Ar gas near the sample surface region. Using this experimentally determined linear relationship between the surface work function and Ar gas core level photoelectron binding energy, we can measure the surface work function of different materials under different gas environments. To demonstrate the potential applications of this ambient pressure XPS technique in nanotechnology and solar energy research, we investigate the work functions of PbS nanoparticles with various capping ligands: methoxide, mercaptopropionic acid, and ethanedithiol. Significant Fermi level position changes are observed for PbS nanoparticles when the nanoparticle size and capping ligands are varied. The corresponding changes in the valence band maximum illustrate that an efficient quantum dot solar cell design has to take into account the electrochemical effect of the capping ligand as well.