Electrocatalysts with high activity and stability for polymer electrolyte membrane fuel cells

In addressing the activity and durability challenges facing electrocatalysts in polymer electrolyte membrane fuel cells (PEMFCs), atomic layer deposition (ALD) is emerging as a powerful technique for deposition of noble metals and transition metal oxides due to its exclusive advantages over other methods. The primary advantages of ALD are derived from the sequential, self-saturating, gas-surface reactions, and angstrom level control that take place during the deposition process. Therefore, ALD possesses the advantage in precisely control the particle size and uniform distribution on the substrate. By forming chemical bonds between the initial layer of ALD precursor and support atoms during the first cycle of deposition, the strong interaction between the deposited material and support could be enabled, which is benefit for achieving the highly stable NPs. In this thesis, an area-selective ALD of tantalum oxide (TaOx) on Pt/C catalyst to fabricate TaOx-anchored Pt NPs with triple-junction structure of Pt–TaOx–C was investigated in the first part of research work. By introducing a protective agent (oleylamine) to the Pt surface, TaOx NPs were selectively nucleated and grown around Pt NPs, thus forming the TaOx anchored-Pt NPs on the carbon surface. The electrochemical durability tests indicated that the 35ALD–TaOx–Pt/C catalyst exhibited superior durability compared to Pt/C. The enhanced stability of the 35ALD–TaOx–Pt/C catalyst is attributed to the anchoring effect of TaOx via the strong triple-junction of TaOx–Pt–C, which plays a significant role in stabilizing the Pt catalyst by preventing Pt NPs from migration/coalescence and detachment from the carbon support. Afterwards, to both improve the Pt/C catalyst activity and durability, a nitrogen-doped Ta2O5 was developed by ALD approach. It was found that the as-prepared Pt/N-ALDTa2O5/C catalyst showed enhanced catalytic activity and significantly improved electrochemical durability toward oxygen reduction reaction (ORR). X-ray absorption spectroscopy provided direct evidence of change of the electronic structure of Pt NPs on N-ALDTa2O5/C support compared to other supports, indicating the strong metal-support interactions formed between Pt NPs and the modified N-ALDTa2O5/C support. It was revealed that by tuning the metal support interface, the highly active and stable Pt catalyst could be enabled. To achieve the extremely low Pt loading while maintaining the high catalytic activity and long-life stability, ALD technique was applied to deposit Pt NPs into the PEMFCs anode layer. By controlling the ALD cycle number, the Pt NPs with different size and loading amount were directly deposited on the carbon coating layers to form the anode catalyst layers. The PEMFCs composed with ALD catalyst showed much better performance and durability than that prepared by the commercial catalyst with a conventional method. The electron microscopy reveals that the application of ALD for Pt deposition directly on the electrode carbon layers could effectively reduce the Pt loading while enhance the Pt dispersion, utilization, and Pt-support interaction, which achieve the high PEMFCs performance and excellent durability under the ultra-low Pt loading. Furthermore, downsizing Pt NPs size to subnano-clusters or even single atoms is highly desirable to maximize Pt atom utilization efficiency. Here we report on a practical synthesis method to produce isolated Pt single atoms and subnano-clusters using ALD technique. The Pt single atoms/subnano-clusters catalysts supported on metal-organic framework-derived nanocarbon support are investigated for the ORR, where they exhibit significantly enhanced catalytic activity and superior stability in comparison with the Pt NPs catalysts. The X-ray absorption indicates that the partially unsaturated coordination environment of Pt single atoms/subnano-clusters on nanocarbon support is responsible for the excellent performance. The last experimental investigation of this thesis is development of an alternative non-noble-metal electrocatalyst of nitrogen and sulfur-co-doped nanocarbon (N,S-co-doped nanocarbon) for ORR. The N,S-co-doped nanocarbon is synthesized using metal organic frameworks as a solid precursor, followed by carbonizing and pore size design, then further co-doping sulfur to generate more active sites. The resulting N,S-co-doped nanocarbon demonstrates a high catalytic activity toward ORR, remarkable long-term stability and strong methanol tolerance in alkaline media. First-principles calculations reveal that N,S-co-doped nanocarbons possess enhanced ORR activity compared to N-doped carbon. More importantly, this work for the first time report that the N,S-coupled dopants can create active sites with higher activity than the isolated N and S dopants. The approach and analysis adopted in this work offer a strategic consideration for designing the high performance nanocarbon electrocatalyst

Recent Progress on MOF-Derived Nanomaterials as Advanced Electrocatalysts in Fuel Cells

Developing a low cost, highly active and durable cathode material is a high-priority research direction toward the commercialization of low-temperature fuel cells. However, the high cost and low stability of useable materials remain a considerable challenge for the widespread adoption of fuel cell energy conversion devices. The electrochemical performance of fuel cells is still largely hindered by the high loading of noble metal catalyst (Pt/Pt alloy) at the cathode, which is necessary to facilitate the inherently sluggish oxygen reduction reaction (ORR). Under these circumstances, the exploration of alternatives to replace expensive Pt-alloy for constructing highly efficient non-noble metal catalysts has been studied intensively and received great interest. Metal–organic frameworks (MOFs) a novel type of porous crystalline materials, have revealed potential application in the field of clean energy and demonstrated a number of advantages owing to their accessible high surface area, permanent porosity, and abundant metal/organic species. Recently, newly emerging MOFs materials have been used as templates and/or precursors to fabricate porous carbon and related functional nanomaterials, which exhibit excellent catalytic activities toward ORR or oxygen evolution reaction (OER). In this review, recent advances in the use of MOF-derived functional nanomaterials as efficient electrocatalysts in fuel cells are summarized. Particularly, we focus on the rational design and synthesis of highly active and stable porous carbon-based electrocatalysts with various nanostructures by using the advantages of MOFs precursors. Finally, further understanding and development, future trends, and prospects of advanced MOF-derived nanomaterials for more promising applications of clean energy are presented

A Pitman Style Fiber Bragg Grating Displacement Sensor Based on Wedge Cavity Structure

In this paper, a new design of fiber Bragg grating (FBG) displacement sensor is presented based on wedge cavity structure. A new type of pitman FBG displacement sensor with a simple structure, small size and anti-electromagnetic interference is invented. Calibration of the FBG displacement sensor is carried out. The calibrating data shows that the sensitivity is 5.58 pm/mm, adjusted R square is up to 0.99 and the static error is 5.168%. Moreover, the FBG displacement sensor is applied in the hysteresis test of steel frame-reinforced concrete infill wall. The monitoring results from the FBG displacement sensor in this test match well with the resistance strain displacement meter, to prove the FBG displacement sensor with a good accuracy. It is also showed that this new FBG displacement sensor produces smaller influence on the structure, and it is suitable for long-term displacement monitoring of engineering structures

Current status and development trend of intelligent transportation technology in China's open-pit mines

As one of the most important factors in the production process of open-pit mine, the intelligence of transportation is an important research content of the whole intelligence technology of mine. This paper introduces the composition and classification of the transportation system in open-pit mine. It is clarified that the intelligent transportation system in open-pit mine takes the efficient transportation of coal and rock in open-pit mine as the application scenario and the intelligent transportation equipment as the core carrier. The digital technologies such as the Internet of things, cloud computing, big data, artificial intelligence, and mobile Internet are integrated with the operating principles and technological requirements of the open-pit mine transportation system. The autonomous collaborative and efficient operation system of equipment, environment and materials in the transportation system is established. And the real-time, accurate and efficient transportation integrated management system that plays a role in a wide range is further established. The components of the intelligent transportation system in open-pit mine mainly include infrastructure, transportation tools and computing technology. It is pointed out that the difference between the traditional transportation system and the intelligent transportation system in open-pit mine lies in that the intelligent transportation system takes improving the safety and efficiency of field production operation as the goal. The service object is changed from the original production management personnel to the production operating personnel. The research and application status of intelligent transportation system in open-pit mine in China are summarized from five aspects, including intelligent infrastructure, intelligent equipment, intelligent management and control, intelligent maintenance and intelligent design. The key technologies of the truck transportation system and the belt conveyor transportation system in the open-pit mine to realize the intelligence are analyzed in this paper. The key technologies of intelligent truck transportation include environment perception technology for complex road conditions in mines, line control transformation technology for unmanned driving truck, multi-objective intelligent scheduling technology, and intelligent collaboration technology for manned-unmanned mixed equipment group. The key technologies of intelligent belt conveyor transportation include autonomous traverse technology of belt conveyor in working face, transportation technology of self-moving large-angle belt conveyor, operation control technology of belt conveyor, on-line status detection technology of belt conveyor, intelligent inspection technology of belt conveyor, unmanned maintenance technology of belt conveyor, intelligent management and control platform of belt conveyor transportation system. It is pointed out that the development trend of intelligent transportation in open-pit mine is continuous, unmanned, low-carbon, efficient coordination and intrinsic safety

Reliable metal alloy contact for Mg3+δBi1.5Sb0.5 thermoelectric devices

Proper contacts between thermoelectric (TE) materials and electrodes are critical for TE power generation or refrigeration. The Bi-rich n-type Zintl material Mg3+δBi2-xSbx exhibits very good TE performance near room temperature, which makes Mg3+δBi2-xSbx-based compounds highly promising candidates to replace the Bi2Te3-ySey alloys, but ideal contacts that can match their TE performance have not yet been well studied. Here we investigate different metal (Ni and Fe) and metal alloy (NiFe, NiCr, NiCrFe, and stainless steel) contacts on n-type Mg3+δBi1.5Sb0.5. It is first shown that the low Schottky barrier and narrow depletion region resulting from the band degeneracy and high carrier concentration of a heavily doped TE material are beneficial for the formation of a low-resistivity ohmic contact with a metal or a metal alloy. Most fully optimized TE materials can take advantage of this. Second, it is found that the NiFe/Mg3+δBi1.5Sb0.5 contact exhibits excellent thermal stability and the lowest ohmic contact resistivity among those studied after aging for over 2100 h, which is attributed to the formation of metallic NiMgBi between the NiFe and Mg3+δBi1.5Sb0.5 layers. As a buffer phase, NiMgBi can effectively prevent elemental diffusion without negatively affecting the electron transport. Benefiting from such low contact resistance, a Mg3+δBi1.5Sb0.5/Bi0.4Sb1.6Te3 unicouple exhibits competitive conversion efficiency, 6% with a 150 K temperature difference and a hot-side temperature of 448 K

Experimental studies on the characteristics of chisel picks in coal cutting for bucket wheel excavators

Abstract Chisel pick is a basic and important rock cutting tool, and the performance of chisel pick directly affects rock mining. In this paper, a rock cutting device was developed for chisel picks cutting experiments. The influence of the depth of cutting, width of chisel pick, rake angle, back clearance angle and tip fillet radius on the cutting performance such as cutting force, normal force, and specific energy has been comprehensively studied. In addition to the general conclusions, the experimental results show that the back clearance angle has an influence range on the cutting, and the ratio of the normal force to the cutting force decreases with the increase of the rake angle; the tip fillet radius greatly improve the mean cutting force and specific energy. The experimental results will provide data support for the design of chisel picks on rock excavation machinery and a more reasonable chisel pick cutting rock mechanics model

Single‐atom surface anchoring strategy via atomic layer deposition to achieve dual catalysts with remarkable electrochemical performance

Abstract Pt‐Ir catalysts have been widely applied in unitized regenerative fuel cells due to their great activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the application of noble metals is seriously hindered by their high cost and low abundance. To reduce the noble metals loading and catalyst cost, the atomic layer deposition is applied to selectively surface anchoring of Ir single atoms (SA) on Pt nanoparticles (NP). With the formation of SA‐NP composite structure, the IrSA‐PtNP catalyst exhibits significantly improved performance, achieving 2.0‐ and 90‐times mass activity by comparison with the benchmark Pt/C catalyst for the ORR and OER, respectively. Density functional theory calculations indicate that the SA‐NP cooperation synergy endows the IrSA‐PtNP catalyst to surpass the bifunctional catalytic activity limit of Pt‐Ir NPs. This work provides a novel strategy for the construction of high‐performing dual catalyst through designing the single atom anchoring on NPs

Combined prediction model of truck multi-section travel time in open-pit mine based on velocity field

Due to the complexity of road in open-pit mine, the existing truck travel time prediction methods are difficult in the actual deployment. This leads to the truck optimal scheduling system only realizing scheduling instead of optimization. A combined prediction model of truck multi-section travel time in open pit mine based on velocity field is proposed. The open-pit mine road is divided into multiple road sections. the random forest algorithm is used to construct the unit prediction model to predict the travel time of the truck in each section. Then the predicted values of the unit prediction models are accumulated to obtain the travel time predicted value of the truck on in the composite road section. In order to improve the prediction precision, the average velocity of the truck is taken as an influence factor of the travel time. The velocity field is constructed according to the collected velocity information of the truck. The average value of the truck velocity at all points on a road section is calculated, which is approximate to the average velocity of the truck on the road section, and the average velocity is input into the unit prediction model. Based on the data of truck schedule information in truck dispatching system of Yimin Open-pit Mine, the combined prediction model is trained, and the prediction precision and real-time performance of the model are tested. The results show that the combined prediction model of truck travel time in multiple sections of open-pit mine based on velocity field has high prediction precision for truck travel time in composite road sections. The average absolute error percentage is 4.81%, which is more than 2% lower than the single prediction model based on random forest algorithm. The operation time of the combined prediction model is less than 1 s, which can realize the real-time prediction of truck travel time