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Shi-zhang Qiao - One of the best experts on this subject based on the ideXlab platform.
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anomalous hydrogen evolution behavior in high ph environment induced by locally generated hydronium ions
Nature Communications, 2019Co-Authors: Xuesi Wang, Chaochen Xu, Mietek Jaroniec, Yao Zheng, Shi-zhang QiaoAbstract:Most fundamental studies of Electrocatalysis are based on the experimental and simulation results obtained for bulk model materials. Some of these mechanistic understandings are inapplicable for more active nanostructured electrocatalysts. Herein, considering the simplest and most typical electrocatalytic process, the hydrogen evolution reaction, an alternative reaction mechanism is proposed for nanomaterials based on the identification of a new intermediate, which differs from those commonly known for the bulk counterparts. In-situ Raman spectroscopy and electrochemical thermal/kinetic measurements were conducted on a series of nanomaterials under different conditions. In high-pH electrolytes with negligible hydronium (H3O+) concentration in bulk phase, massive H3O+ intermediates are found generating on the catalytic surface during water dissociation and hydrogen adsorption processes. These H3O+ intermediates create a unique acid-like local reaction environment on nanostructured catalytic surfaces and cut the energy barrier of the overall reaction. Such phenomena on nanostructured electrocatalysts explain their widely observed anomalously high activity under high-pH conditions. Most of the current understanding on Electrocatalysis is obtained on bulk catalysts but has not been fully verified on nanostructured materials. An alternative alkaline hydrogen evolution reaction mechanism is proposed here for nanostructured catalysts.
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Approaches for measuring the surface areas of metal oxide electrocatalysts for determining their intrinsic electrocatalytic activity
Chemical Society Reviews, 2019Co-Authors: Chao Wei, Shengnan Sun, Daniel Mandler, Xun Wang, Shi-zhang QiaoAbstract:Great attention has been recently drawn to metal oxide electrocatalysts for Electrocatalysis-based energy storage and conversion devices. To find the optimal electrocatalyst, a prerequisite is an activity metric that reasonably evaluates the intrinsic electrocatalytic activity of a particular catalyst. The intrinsic activity is commonly defined as the specific activity which is the current per unit catalyst surface area. Thus, the precise assessment of intrinsic activity highly depends on the reliable measurement of catalyst surface area, which calls for the knowledge of experimental approaches for determining the surface areas of metal oxide electrocatalysts. This tutorial review aims to summarize and analyze the approaches for measuring the surface areas of metal oxide electrocatalysts for evaluating and comparing their intrinsic electrocatalytic activities. We start by comparing the popular metrics for activity estimation and highlighting the importance of surface-area-normalized activity (i.e. specific activity) for intrinsic chemistry analysis. Second, we provide some general guidelines for experimentally measuring the electrochemically active surface area (ECSA). Third, we review the methods for the surface area measurement of metal oxide electrocatalysts. The detailed procedure for each method is explicitly described to provide a step-by-step manual that guides researchers to perform the measurement; the rationales and uncertainties for each method are discussed to help readers justify the reliable assessment of surface area. Next, we give our recommendations on selecting a rational experimental approach for the surface area measurement of a particular metal oxide electrocatalyst. Lastly, we discuss the future challenges of ECSA measurement and present an exemplary novel ECSA technique.
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the hydrogen evolution reaction in alkaline solution from theory single crystal models to practical electrocatalysts
Angewandte Chemie, 2018Co-Authors: Yao Zheng, Shi-zhang Qiao, Yan Jiao, Anthony VasileffAbstract:: The hydrogen evolution reaction (HER) is a fundamental process in Electrocatalysis and plays an important role in energy conversion for the development of hydrogen-based energy sources. However, the considerably slow rate of the HER in alkaline conditions has hindered advances in water splitting techniques for high-purity hydrogen production. Differing from well documented acidic HER, the mechanistic aspects of alkaline HER are yet to be settled. A critical appraisal of alkaline HER Electrocatalysis is presented, with a special emphasis on the connection between fundamental surface electrochemistry on single-crystal models and the derived molecular design principle for real-world electrocatalysts. By presenting some typical examples across theoretical calculations, surface characterization, and electrochemical experiments, we try to address some key ongoing debates to deliver a better understanding of alkaline HER at the atomic level.
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identifying the key role of pyridinic n co bonding in synergistic Electrocatalysis for reversible orr oer
Advanced Materials, 2018Co-Authors: Xuerui Wang, Weichao Wang, Shi-zhang Qiao, Jun Luo, Jieyu Liu, Ziwei Liu, Xiaopeng Han, Jing YangAbstract:For many regenerative electrochemical energy-conversion systems, hybrid electrocatalysts comprising transition metal (TM) oxides and heteroatom-doped (e.g., nitrogen-doped) carbonaceous materials are promising bifunctional oxygen reduction reaction/oxygen evolution reaction electrocatalysts, whose enhanced electrocatalytic activities are attributed to the synergistic effect originated from the TM-N-C active sites. However, it is still ambiguous which configuration of nitrogen dopants, either pyridinic or pyrrolic N, when bonded to the TM in oxides, predominately contributes to the synergistic effect. Herein, an innovative strategy based on laser irradiation is described to controllably tune the relative concentrations of pyridinic and pyrrolic nitrogen dopants in the hybrid catalyst, i.e., NiCo2 O4 NPs/N-doped mesoporous graphene. Comparative studies reveal the dominant role of pyridinic-NCo bonding, instead of pyrrolic-N bonding, in synergistically promoting reversible oxygen Electrocatalysis. Moreover, density functional theory calculations provide deep insights into the corresponding synergistic mechanism. The optimized hybrid, NiCo/NLG-270, manifests outstanding reversible oxygen electrocatalytic activities, leading to an overpotential different ΔE among the lowest value for highly efficient bifunctional catalysts. In a practical reversible Zn-air battery, NiCo/NLG-270 exhibits superior charge/discharge performance and long-term durability compared to the noble metal electrocatalysts.
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activity origin and catalyst design principles for electrocatalytic hydrogen evolution on heteroatom doped graphene
Nature Energy, 2016Co-Authors: Yan Jiao, Yao Zheng, K R Davey, Shi-zhang QiaoAbstract:The hydrogen evolution reaction (HER) is a fundamental process in Electrocatalysis and plays an important role in energy conversion through water splitting to produce hydrogen. Effective candidates for HER are often based on noble metals or transition metal dichalcogenides, while carbon-based metal-free electrocatalysts generally demonstrate poorer activity. Here we report evaluation of a series of heteroatom-doped graphene materials as efficient HER electrocatalysts by combining spectroscopic characterization, electrochemical measurements, and density functional theory calculations. Results of theoretical computations are shown to be in good agreement with experimental observations regarding the intrinsic electrocatalytic activity and the HER reaction mechanism. As a result, we establish a HER activity trend for graphene-based materials, and explore their reactivity origin to guide the design of more efficient electrocatalysts. We predict that by rationally modifying particular experimentally achievable physicochemical characteristics, a practically realizable graphene-based material will have the potential to exceed the performance of the metal-based benchmark for HER. Metal-free doped-graphene materials are emerging as electrocatalysts for energy conversions, but their activity remains low. Here, Jiao et al. explore the origins of catalytic activity for hydrogen evolution, suggesting pathways to metal-free catalysts with activity to rival metal-containing benchmarks.
Stephen A Campbell - One of the best experts on this subject based on the ideXlab platform.
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physical chemistry research toward proton exchange membrane fuel cell advancement
Journal of Physical Chemistry Letters, 2013Co-Authors: Karen E Swiderlyons, Stephen A CampbellAbstract:Hydrogen fuel cells, the most common type of which are proton exchange membrane fuel cells (PEMFCs), are on a rapid path to commercialization. We credit physical chemistry research in oxygen reduction Electrocatalysis and theory with significant breakthroughs, enabling more cost-effective fuel cells. However, most of the physical chemistry has been restricted to studies of platinum and related alloys. More work is needed to better understand electrocatalysts generally in terms of properties and characterization. While the advent of such highly active catalysts will enable smaller, less expensive, and more powerful stacks, they will require better understanding and a complete restructuring of the diffusion media in PEMFCs to facilitate faster transport of the reactants (O2) and products (H2O). Even Ohmic losses between materials become more important at high power. Such lessons from PEMFC research are relevant to other electrochemical conversion systems, including Li–air batteries and flow batteries.
Zongping Shao - One of the best experts on this subject based on the ideXlab platform.
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Ruddlesden–Popper perovskites in Electrocatalysis
Materials Horizons, 2020Co-Authors: Yangli Pan, Yijun Zhong, Ran Ran, Zongping ShaoAbstract:Electrocatalysis lies in the center of many clean energy conversion and storage technologies. Developing efficient electrocatalysts to promote the kinetics of the key chemical reactions involved in these processes represents an important research topic. Ruddlesden–Popper perovskites (An+1BnX3n+1), as a layered derivative of the perovskite family (ABX3), are an important class of solid-state materials, and are emerging as high-performing electrocatalysts due to their unique layered structure and rich chemical compositions. In this review, we provide a comprehensive understanding of the structure and properties of Ruddlesden–Popper perovskites in the context of their Electrocatalysis applications. We also summarize the recent developments of Ruddlesden–Popper perovskites for catalyzing a breadth of electrochemical reactions at both low and high temperatures. We highlight how Ruddlesden–Popper perovskites can be tailored through a range of design strategies to achieve improved Electrocatalysis. Finally, we provide perspectives on future research directions that further expand the electrocatalytic possibilities of Ruddlesden–Popper perovskites.
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scandium and phosphorus co doped perovskite oxides as high performance electrocatalysts for the oxygen reduction reaction in an alkaline solution
Journal of Materials Science & Technology, 2020Co-Authors: Meigui Xu, Wei Wang, Yujuan Shen, Wei Zhou, Jun Wang, Zhigang Chen, Zongping ShaoAbstract:Abstract The requirement for a sustainable and renewable energy has inspired substantial interests in designing and developing earth-abundant and high-effectiveness electrocatalysts/electrodes for fuel cells and metal-air batteries, in which oxygen reduction reaction (ORR) plays a crucial role. Perovskite oxides have acquired rapid attention as ORR electrocatalysts to replace noble-metal-based catalysts owing to their intrinsic electrocatalytic activity, compositional and structural flexibility. Herein, we report a new Sc and P co-doped perovskite oxide (La0.8Sr0.2Mn0.95Sc0.025P0.025O3-δ, LSMSP) as an active and robust electrocatalyst for the ORR in an alkaline solution. LSMSP electrocatalyst shows superior ORR activity and stability than those of pristine La0.8Sr0.2MnO3-δ (LSM), Sc-doped LSM and P-doped LSM due to the optimized average valence of Mn ions, the large surface area, the smaller particle size and the synergetic effect introduced by the co-doping. Moreover, compared to the benchmark Pt/C electrocatalyst, LSMSP electrocatalyst displays comparable ORR activity and superior durability. These above results suggest that the co-doping strategy of Sc and P into perovskites is a useful method to design high-performance electrocatalysts for the ORR, which can be used in other Electrocatalysis-based applications.
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Perovskite Materials in Electrocatalysis
Revolution of Perovskite, 2020Co-Authors: Yangli Pan, Zongping ShaoAbstract:Electrocatalysis-based technologies are central to enabling the vision of a sustainable energy future. One major challenge is to develop nonprecious, high-efficient electrocatalysts that can promote the electrocatalytic processes. Perovskite materials have recently been extensively studied as alternative electrocatalysts to noble metal-based materials owing to their low cost, tunable structure, and high catalytic activity. This chapter discusses perovskite materials in Electrocatalysis for several important reactions, including the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction. The electrocatalytic mechanisms are first introduced to offer a fundamental understanding of the Electrocatalysis occurring on the surface of perovskite catalysts. Following this is a detailed description of the rational design of perovskite materials toward efficient Electrocatalysis. Several activity descriptors for theoretically guiding the catalyst design are presented while many other practical parameters that can influence the catalyst behavior are also highlighted. In addition, concerns for the catalyst stability under realistic electrochemical conditions are expressed. In an effort to realize global energy sustainability, several key applications of perovskite materials in Electrocatalysis-related energy devices, for example, metal–air batteries and water electrolyzers, are presented, with an emphasis on how to enable the widespread penetration of these energy technologies.
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a universal strategy to design superior water splitting electrocatalysts based on fast in situ reconstruction of amorphous nanofilm precursors
Advanced Materials, 2018Co-Authors: Gao Che, Zongping Shao, Wei Zhou, Yanping Zhu, Yiju Zhong, Chiente CheAbstract:The development of efficient bifunctional electrodes with extraordinary mass activity and robust stability is an eternal yet challenging goal for the water-splitting process. Surface reconstruction during Electrocatalysis can form fresh-composition electrocatalysts with unusual amorphous phases in situ, which are more active but difficult to prepare by conventional methods. Here, a facile strategy based on fast reconstruction of amorphous nanofilm precursors is proposed for exploring precious-metal-free catalysts with good electronic conductivity, ultrahigh activity, and robust stability. As a proof of concept, an amorphous SrCoFePO (SCFP) nanofilm precursor with weak chemical bonds deposited onto a conductive nickel foam (NF) substrate (SCFP-NF) is synthesized by utilizing a high-energy argon plasma to break the strong chemical bonds in a crystalline SCFP target. The quickly reconstructed SCFP-NF bifunctional catalysts show ultrahigh mass activity of up to 1000 mA mg at an overpotential of 550 mV and extremely long operational stability of up to 650 h at 10 mA cm, significantly overperforming state-of-the-art precious-metal catalysts. Such a strategy is further demonstrated to be a universal method, which can be applied to accelerate the reconstruction of other material systems to obtain various efficient electrocatalysts.
Sanjeev Mukerjee - One of the best experts on this subject based on the ideXlab platform.
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role of structural and electronic properties of pt and pt alloys on Electrocatalysis of oxygen reduction an in situ xanes and exafs investigation
Journal of The Electrochemical Society, 1995Co-Authors: Sanjeev Mukerjee, Manuel P Soriaga, S Srinivasan, J McbreenAbstract:The Electrocatalysis of the oxygen reduction reaction (ORR) on five binary Pi alloys (PtCr/C, PtMn/C, PtFe/C, PtCo/C, and PtNi/C) supported on high surface area carbon in a proton exchange membrane fuel cell was investigated. All the alloy electrocatalysts exhibited a high degree of crystallinity with the primary phase of the type Pt3M (LI2 structure with fcc type lattice) and a secondary phase (only minor contribution from this phase) being of the type PtM (LIo structure with tetragonal lattice) as evidenced from x-ray powder diffraction (XRD) analysis. The electrode kinetic studies on the Pt alloys at 95~ and 5 atm pressure showed a two- to threefold increase in the exchange current densities and the current density at 900 mV as well as a decrease in the overvoltage at i0 mA em -2 relative to Pt/C eleetrocatalyst. The PtCr/C alloy exhibited the best performance. In situ EXAFS and XANES analysis at potentials in the double-layer region [0.54 V vs. reversible hydrogen electrode (RHE)] revealed (i) all the alloys possess higher Pt d-band vacancies per atom (with the exception of PtMn/C alloy) relative to Pt/C electrocatalyst and (it) contractions in the Pt-Pt bond distances which confirmed the results from ex situ XRD analysis. A potential excursion to 0.84 V vs. RHE showed that, in contrast to the Pt alloys, the Pt/C electrocatalyst exhibits a significant increase in the Pt d-band vacancies per atom. This increase, in Pt/C has been rationalized as being due to adsorption of OH species from the electrolyte following a Temkin isotherm behavior, which does not occur on the Pt alloys. Correlation of the electronic (Pt d-band vacancies) and geometric (Pt-Pt bond distance) with the electrochemical performance characteristics exhibits a volcano type behavior with the PtCr/C alloy being at the top of the curve. The enhanced Electrocatalysis by the alloys therefore can be rationalized on the basis of the interplay between the electronic and geometric factors on one hand and their effect on the chemisorption behavior of OH species from the electrolyte. The role of Pt/C and Pt alloys on the mechanism of the oxygen reduction reaction (ORR) has been investigated previously, 1-4 however the mechanism still remains elusive. One of the first investigations I of the ORR on Pt alloy electrocatalysts was in phosphoric acid; the effect of changes in the Pt-Pt interatomic distances, caused by alloying, was examined. The strength of the [M-HO2]aas bond, the intermediate formed in the rate-determining step of the molecular dioxygen reduction, was shown to depend on the Pt-Pt bond distance in the alloys. A plot of the electrocatalytic activity vs. adsorbate bond strength exhibited a volcano type behavior. 5 It was shown that the lattice contractions due to alloying resulted in a more favorable Pt-Pt distance (while maintaining the favorable Pt electronic properties) for dissociative adsorption of 02. This view was disputed by Glass et al. ~ in their investigation on bulk alloys of PtCr (the binary alloy at the top of the volcano plot) of different compositions. The latter investigation showed no activity enhancement for the ORR in phosphoric acid. This study therefore suggested the possibility of differences in electrochemical properties of bulk vs. supported alloy electrocatalysts (small particles of 35-85 A). A recent study on supported PtCo electrocatalysts ~ revealed the possibility that particle termination, primarily at the vicinal planes in the supported alloy electrocatalyst, is the reason for the enhanced ORR Electrocatalysis (i.e., vicinal planes are more active than ). Paffett et al., 3 attributed higher activities for the ORR on bulk PtCr alloys in phosphoric acid to surface roughening, and hence increased Pt surface area, caused by the dissolution of the more oxidizable alloying component Cr. In contrast to these findings on bulk alloys, the supported alloy electrocatalysts have been reported to retain their nonnoble alloying element in the electrode during long periods (6000-9000 h) of operation in phosphoric acid fuel cells (PAFCs) 6 and proton exchange membrane fuel ceils (PEMFCs). 7 Based on these previous investigations and in the context of the ORR mechanisms, the principle explanations for the
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Enhanced Electrocatalysis of oxygen reduction on platinum alloys in proton exchange membrane fuel cells
Journal of Electroanalytical Chemistry, 1993Co-Authors: Sanjeev Mukerjee, Supramaniam SrinivasanAbstract:Enhanced Electrocatalysis of the oxygen reduction reaction (ORR) on carbon-supported binary and ternary alloys of Pt in phosphoric acid fuel cells has been reported previously. This investigation focuses on the Electrocatalysis of the ORR on some binary alloys of Pt (Pt+Ni, Pt+Cr and Pt+Co) at interfaces with proton exchange membranes (Dow perfluorinated sulfonic acids). Comparison of the results of these studies with those on carbon-supported Pt electrocatalysts (electrodes containing same Pt loading of 0.3 mg/cm2) revealed enhanced activities, lower activation energies and different reaction orders for all the alloys. X-ray powder diffraction showed lattice contractions for the alloys, the predominant phase being Pt3M (LI2) f.c.c. crystalline. X-ray photoelectron spectroscopy studies on the constituent elements of the electrocatalyst showed no chemical energy shifts owing to alloying and/or the presence of oxides on the surface. Lifetime evaluations of proton exchange membrane fuel cells, using both electrochemical as well as scanning electron microscopy/energy-dispersive X-ray analysis techniques, revealed only small amounts of dissolution of the more oxidizable component during the testing periods, which ranged from 400 to 1200 h. Therefore, the enhanced Electrocatalysis exhibited by the binary Pt alloys appears to originate primarily as a result of changes in the lattice structure owing to alloying and the unique environment of the supported catalyst in the particle size range 35–75 A.
Karen E Swiderlyons - One of the best experts on this subject based on the ideXlab platform.
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physical chemistry research toward proton exchange membrane fuel cell advancement
Journal of Physical Chemistry Letters, 2013Co-Authors: Karen E Swiderlyons, Stephen A CampbellAbstract:Hydrogen fuel cells, the most common type of which are proton exchange membrane fuel cells (PEMFCs), are on a rapid path to commercialization. We credit physical chemistry research in oxygen reduction Electrocatalysis and theory with significant breakthroughs, enabling more cost-effective fuel cells. However, most of the physical chemistry has been restricted to studies of platinum and related alloys. More work is needed to better understand electrocatalysts generally in terms of properties and characterization. While the advent of such highly active catalysts will enable smaller, less expensive, and more powerful stacks, they will require better understanding and a complete restructuring of the diffusion media in PEMFCs to facilitate faster transport of the reactants (O2) and products (H2O). Even Ohmic losses between materials become more important at high power. Such lessons from PEMFC research are relevant to other electrochemical conversion systems, including Li–air batteries and flow batteries.