Atomically dispersed single iron sites for promoting Pt and Pt3Co fuel cell catalysts: performance and durability improvements

Significantly reducing platinum group metal (PGM) loading while improving catalytic performance and durability is critical to accelerating proton-exchange membrane fuel cells (PEMFCs) for transportation. Here we report an effective strategy to boost PGM catalysts through integrating PGM-free atomically-dispersed single metal active sites in the carbon support toward the cathode oxygen reduction reaction (ORR). We achieved uniform and fine Pt nanoparticle (NP) (∼2 nm) dispersion on an already highly ORR-active FeN4 site-rich carbon (FeN4–C). Furthermore, we developed an effective approach to preparing a well-dispersed and highly ordered L12 Pt3Co intermetallic nanoparticle catalyst on the FeN4–C support. DFT calculations predicted a synergistic interaction between Pt clusters and surrounding FeN4 sites through weakening O2 adsorption by 0.15 eV on Pt sites and reducing activation energy to break O–O bonds, thereby enhancing the intrinsic activity of Pt. Experimentally, we verified the synergistic effect between Pt or Pt3Co NPs and FeN4 sites, leading to significantly enhanced ORR activity and stability. Especially in a membrane electrode assembly (MEA) with a low cathode Pt loading (0.1 mgPt cm−2), the Pt/FeN4–C catalyst achieved a mass activity of 0.451 A mgPt−1 and retained 80% of the initial values after 30 000 voltage cycles (0.60 to 0.95 V), exceeding DOE 2020 targets. Furthermore, the Pt3Co/FeN4 catalyst achieved significantly enhanced performance and durability concerning initial mass activity (0.72 A mgPt−1), power density (824 mW cm−2 at 0.67 V), and stability (23 mV loss at 1.0 A cm−2). The approach to exploring the synergy between PGM and PGM-free Fe–N–C catalysts provides a new direction to design advanced catalysts for hydrogen fuel cells and various electrocatalysis processes

Atomic Structure Evolution of Pt–Co Binary Catalysts: Single Metal Sites versus Intermetallic Nanocrystals

Due to their exceptional catalytic properties for the oxygen reduction reaction (ORR) and other crucial electrochemical reactions, PtCo intermetallic nanoparticle (NP) and single atomic (SA) Pt metal site catalysts have received considerable attention. However, their formation mechanisms at the atomic level during high-temperature annealing processes remain elusive. Here, the thermally driven structure evolution of Pt–Co binary catalyst systems is investigated using advanced in situ electron microscopy, including PtCo intermetallic alloys and single Pt/Co metal sites. The pre-doping of CoN4 sites in carbon supports and the initial Pt NP sizes play essential roles in forming either Pt3Co intermetallics or single Pt/Co metal sites. Importantly, the initial Pt NP loadings against the carbon support are critical to whether alloying to L12-ordered Pt3Co NPs or atomizing to SA Pt sites at high temperatures. High Pt NP loadings (e.g., 20%) tend to lead to the formation of highly ordered Pt3Co intermetallic NPs with excellent activity and enhanced stability toward the ORR. In contrast, at a relatively low Pt loading (<6 wt%), the formation of single Pt sites in the form of PtC3N is thermodynamically favorable, in which a synergy between the PtC3N and the CoN4 sites could enhance the catalytic activity for the ORR, but showing insufficient stability

Three-Dimensional Assembly of PtNi Alloy Nanosticks with Enhanced Electrocatalytic Activity and Ultrahigh Stability for the Oxygen Reduction Reaction

A three-dimensional (3D) assembly of PtNi alloy nanosticks (NSA) is synthesized through an effective organic solvothermal approach to enhance the specific activity and long-term durability for the oxygen reduction reaction (ORR). The 3D PtNi NSA is composed of interconnected nanosticks with an average diameter of approximately 5 nm, which are confirmed to be of high crystallinity with ordered atomic arrangement of ORR-favorable PtNi (111). After an electrochemical dealloying process, the surface of the nanosticks becomes rough with a large quantity of step-like nanostructures, which are verified to effectively improve the ORR activity. The electrochemical results of half-cell tests demonstrate that the 3D PtNi alloy NSA exhibits a 4.5 times higher mass activity than the Pt/C (20 wt%, JM) catalyst (0.58 A/mg) and a 5.1 times higher specific activity (742 mu A/cm(2)). Most importantly, after the accelerated deterioration test, the 3D PtNi alloy NSA catalyst shows almost no activity decrease, both in half- and single-cell tests. The 3D PtNi alloy NSA prepared here is indeed a promising electrocatalyst for practical electrocatalytic applications

Improvement of PEMFC water management by employing water transport plate as bipolar plate

In this study, a porous hydrophilic water transport plate (WTP) has been employed as a bipolar plate to improve water management in proton exchange membrane fuel cells (PEMFCs). The electric conductivity, gas blocking property, water permeability and wettability of the WTP were characterized. The performance, electrochemical impedance spectroscopy (EIS) and water balance of fuel cells with WTPs and solid plates were evaluated. Benefiting from the humidification and drainage functions of the WTP, the performance of fuel cells with WTPs significantly improved compared with fuel cells with traditional solid plates. As indicated from the experiments, a WTP that was placed on the cathode side is favorable for cell performance and system complexity. Additionally, hydrogen stoichiometry hardly affects the water transport, whereas a decrease in air stoichiometry can switch the main function of the WTP from humidification to water drainage. The results show that the use of WTP technology is promising for water management improvement in PEMFCs. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

A Carbon Emission Calculation Model for Roadside Parking

With the sustained and rapid development of China’s national economy, the number of motor vehicles owned by families in cities is rapidly growing. Consequently, problems of traffic congestion and air pollution have also appeared in these cities. Roadside parking traffic has also become an important part of the transportation system in cities. However, there is no specific measurement model for carbon emissions caused by roadside parking in the proposed traffic carbon emission model. Therefore, we aim to establish a carbon emission measurement model for roadside parking. In this paper, we first study the characteristics of the deceleration and maneuvering of parking vehicles and the blocking impact on running vehicles in a typical roadside parking scenario. We then establish and fit models of the direct and indirect carbon emissions during roadside parking. Based on the carbon emission model, we propose a calculation method for roadside parking carbon emissions, including accounting and estimation methods. These models can be used to calculate the carbon emissions from roadside parking in a traffic carbon emissions system. We also hope that these models will help future research on the optimization of roadside parking facilities for energy saving and emission reduction

High-Performance Low-Platinum Electrode for Proton Exchange Membrane Fuel Cells: Pulse Electrodeposition of Pt on Pd/C Nanofiber Mat

A novel electrode (E-P electrode) with a nanofiber structure and Pd/C@dendritic Pt catalysts is prepared by using electrospinning and pulse electrodeposition (PED) techniques. The maximum power density of the E-P electrode is 1.43-fold larger than that of the conventional electrode at the same cathode Pt loadings of 0.1 mg cm(-1). Owing to the in situ deposition of dendritic Pt on the surface of Pd in the Pd/C nanofiber mat, almost all Pt catalysts are accessible for oxygen. The electronic tuning between Pd and Pt enhances the oxygen reduction reaction activity of Pt catalysts. The large Pt surface area of the E-P electrode mitigates the oxygen-transport resistance in comparison with that of the conventional electrode. After the accelerated degradation test for 10000 cyclic voltammetry cycles, the maximum power density of the E-P electrode only decreases by 12%. The long-term stability of the E-P electrode is ascribed to the Pd/C@dendritic Pt catalysts and nanofiber structure

Varying Amplitude Vibration Phase Suppression Algorithm in ISAL Imaging

Platform vibration introduces sinusoidal modulation in inverse synthetic aperture lidar (ISAL) imaging, which causes paired echoes in ISAL imaging. In this paper, a varying amplitude vibration phase suppression algorithm is proposed. Working without prior knowledge, the proposed algorithm can suppress paired echoes under the condition of varying vibration amplitude and will not introduce new phase errors. Furthermore, the method is suitable for the imaging scene without isolated points. Both the simulated and real experiment results of ISAL turntable data demonstrate the effectiveness of the proposed algorithm

Investigation of water transport in fuel cells using water transport plates and solid plates

Water management of proton exchange membrane fuel cells (PEMFCs) is of vital importance to achieve better performance and durability. In this study, porous hydrophilic water transport plates (WTPs) with different pore structures were prepared and employed to improve water management in PEMFCs. Polarization curves, electrochemical impedance spectroscopy (EIS) and water balance were tested to investigate the effect of pore structure on cell performance and water transport process. The results show that pore structure has little effect on drainage function due to excess liquid water flux of WTPs, while the membrane hydration is improved with increased surface evaporation rate of WTPs, resulting in better cell performance. The favorable cell performance shows that WTP is a promising technique to improve water management in PEMFCs

enhancedelectrocatalyticperformanceofultrathinptnialloynanowiresforoxygenreductionreaction

In this paper, ultrathin Pt nanowires （Pt NWs） and PtNi alloy nanowires （PtNi NWs） supported on carbon were synthesized as electrocatalysts for oxygen reduction reaction （ORR）. Pt and PtNi NWs catalysts composed of interconnected nanoparticles were prepared by using a soft template method with CTAB as the surface active agent. The physical characterization and electrocatalytic perfor- mance of Pt NWs and PtNi NWs catalysts for ORR were investigated and the results were compared with the commercial Pt/C catalyst. The atomic ratio of Pt and Ni in PtNi alloy was approximately 3 to 1. The results show that after alloying with Ni, the binding energy of Pt shifts to higher values, indicating the change of its electronic structure, and that Pt3Ni NWs catalyst has a significantly higher electrocatalytic activity and good stability for ORR as compared to Pt NWs and even Pt/C catalyst. The enhanced electrocatalytic activity of Pt3Ni NWs catalyst is mainly resulted from the downshifted-band center of Pt caused by the interaction between Pt and Ni in the alloy, which facilitates the desorption of oxygen containing species （Oads or OHads） and the release of active sites