Zidong Wei

Bio: Zidong Wei is an academic researcher from Chongqing University. The author has contributed to research in topics: Catalysis & Electrocatalyst. The author has an hindex of 55, co-authored 272 publications receiving 13087 citations.

Recent advancements in Pt and Pt-free catalysts for oxygen reduction reaction

Abstract: Developing highly efficient catalysts for the oxygen reduction reaction (ORR) is key to the fabrication of commercially viable fuel cell devices and metal–air batteries for future energy applications. Herein, we review the most recent advances in the development of Pt-based and Pt-free materials in the field of fuel cell ORR catalysis. This review covers catalyst material selection, design, synthesis, and characterization, as well as the theoretical understanding of the catalysis process and mechanisms. The integration of these catalysts into fuel cell operations and the resulting performance/durability are also discussed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.

Understanding the High Activity of Fe-N-C Electrocatalysts in Oxygen Reduction: Fe/Fe3C Nanoparticles Boost the Activity of Fe-N(x).

Abstract: Understanding the origin of high activity of Fe–N–C electrocatalysts in oxygen reduction reaction (ORR) is critical but still challenging for developing efficient sustainable nonprecious metal catalysts in fuel cells and metal–air batteries. Herein, we developed a new highly active Fe–N–C ORR catalyst containing Fe–Nx coordination sites and Fe/Fe3C nanocrystals (Fe@C-FeNC), and revealed the origin of its activity by intensively investigating the composition and the structure of the catalyst and their correlations with the electrochemical performance. The detailed analyses unambiguously confirmed the coexistence of Fe/Fe3C nanocrystals and Fe–Nx in the best catalyst. A series of designed experiments disclosed that (1) N-doped carbon substrate, Fe/Fe3C nanocrystals or Fe–Nx themselves did not deliver the high activity; (2) the catalysts with both Fe/Fe3C nanocrystals and Fe–Nx exhibited the high activity; (3) the higher content of Fe–Nx gave the higher activity; (4) the removal of Fe/Fe3C nanocrystals sever...

Space-confinement-induced synthesis of pyridinic- and pyrrolic-nitrogen-doped graphene for the catalysis of oxygen reduction

Abstract: The development of high-performance and low-cost catalytic materials for the oxygen reduction reaction (ORR) has been a major challenge for the large-scale application of fuel cells. Currently, platinum and platinum-based alloys are the most efficient ORR catalysts in fuel-cell cathodes; however, they cannot meet the demand for the widespread commercialization of fuel cells because of the scarcity of platinum. Thus, the ongoing search for platinum-free catalysts for the ORR has attracted much attention. Graphene, single-layer sheets of sp-hybridized carbon atoms, has attracted tremendous attention and research interest. The abundance of free-flowing p electrons in carbon materials composed of sp-hybridized carbon atoms makes these materials potential catalysts for reactions that require electrons, such as the ORR. However, these p electrons are too inert to be used directly in the ORR. In N-doped electron-rich carbon nanostructures, carbon p electrons have been shown to be activated through conjugation with lone-pair electrons from N dopants; thus, O2 molecules are reduced on the positively charged C atoms that neighbor N atoms. Recently, Hu and co-workers found that as long as the electroneutrality of the sp-hybridized carbon atoms is broken and charged sites that favor O2 adsorption are created, these materials will be transformed into active metal-free ORR electrocatalysts regardless of whether the dopants are electron-rich (e.g., N) or electrondeficient (e.g., B). Nitrogen-doped carbon (NC) materials are considered to be promising catalysts because of their acceptable ORR activity, low cost, good durability, and environmental friendliness. However, their ORR activity is less competitive, especially in acidic media. Relative to commercial Pt/C, the difference in the half-wave potential for ORR is within 25 mV in alkaline electrolytes but is greater than 200 mV in acidic electrolytes. The activity of NC materials can be enhanced through efficient N doping with sufficient active species that favor ORR and through an increase in electrical conductivity. The annealing of graphitized carbon materials, such as carbon nanotubes and microporous carbon black, in NH3 leads to insufficient substitution of nitrogen because of the well-ordered structure of the host materials. Alternatively, the direct pyrolysis of nitrogen-containing hydrocarbons or polymers produces NC materials with good incorporation of nitrogen. However, suitable pyrolysis temperatures are difficult to pinpoint; without optimization, temperatures that are excessively low or excessively high lead to low electronic conductivity or a remarkable loss of active N species, respectively. Recently, mesoporous-alumina-assisted and silica-template-assisted nitrogen incorporation, which can preserve a high content of N in synthesized NC materials, have been reported. However the activities of the resulting NC materials in the ORR were still significantly lower than that of Pt/C, even when the N content was as high as 10.7 atm%. Among three types of N atoms, that is, pyridinic, pyrrolic, and quaternary N, only the pyridinic and pyrrolic forms, which have planar structures, have been proven to be active in the ORR. In contrast, quaternary N atoms, which possess a 3D structure, are not active in the ORR. The low electrical conductivity of NC materials with quaternary N atoms results from the interruption of their p–p conjugation by the 3D structure and is thought to be predominantly responsible for the poor catalysis. Therefore, the synthesis of NC materials with more planar pyridinic and pyrrolic N atoms and fewer quaternary N atoms is important for the preparation of ORR-active catalysts. Herein, we present a novel strategy for the selective synthesis of pyridinicand pyrrolic-nitrogen-doped graphene (NG) by the use of layered montmorillonite (MMT) as a quasi-closed flat nanoreactor, which is open only along the perimeter to enable the entrance of aniline (AN) monomer molecules. The flat MMT nanoreactor, which is less than 1 nm thick, extensively constrains the formation of quaternary N because of its 3D structure but facilitates the formation of pyridinic and pyrrolic N. Nitrogen is well-known to be incorporated into quaternary N in tetrahedral sp hybridization but incorporated into pyridinic and pyrrolic N in planar sp hybridization. The confinement effect of MMT ensures that N is incorporated into the structure and that the graphitization is successful without significant loss of N species. Furthermore, planar pyridinic and pyrrolic N can be [*] Dr. W. Ding, Prof. Z.-D. Wei, Dr. S.-G. Chen, Dr. X.-Q. Qi, Dr. T. Yang, Dr. S. F. Alvi, Dr. L. Li The State Key Laboratory of Power Transmission Equipment and System Security and New Technology, College of Chemistry and Chemical Engineering, Chongqing University Shapingba 174, Chongqing (China) E-mail: zdwei@cqu.edu.cn

Nitrogen and Phosphorus Dual-Doped Graphene/Carbon Nanosheets as Bifunctional Electrocatalysts for Oxygen Reduction and Evolution

Abstract: It is highly desirable but challenging to develop bifunctional catalysts for efficiently catalyzing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy storage and conversion systems. Here a simple yet cost-effective strategy is developed to fabricate nitrogen and phosphorus dual-doped graphene/carbon nanosheets (N,P-GCNS) with N,P-doped carbon sandwiching few-layers-thick graphene. The as-prepared N,P-GCNS shows outstanding catalytic activity toward both ORR and OER with a potential gap of 0.71 V between the OER potential at a current density of 10 mA cm–2 and the ORR potential at a current density of −3 mA cm–2, illustrating that it is the best metal-free bifunctional electrocatalysts reported to date. The superb bifunctional catalytic performance is attributed to the synergistic effects between the doped N and P atoms, the full exposure of the active sites on the surface of the N,P-GCNS nanosheets, the high conductivity of the incorporated graphene, and the large surf...

Nanostructured Polyaniline-Decorated Pt/C@PANI Core-Shell Catalyst with Enhanced Durability and Activity

Abstract: We have designed and synthesized a polyaniline (PANI)-decorated Pt/C@PANI core-shell catalyst that shows enhanced catalyst activity and durability compared with nondecorated Pt/C. The experimental results demonstrate that the activity for the oxygen reduction reaction strongly depends on the thickness of the PANI shell and that the greatest enhancement in catalytic properties occurs at a thickness of 5 nm, followed by 2.5, 0, and 14 nm. Pt/C@PANI also demonstrates significantly improved stability compared with that of the unmodified Pt/C catalyst. The high activity and stability of the Pt/C@PANI catalyst is ascribed to its novel PANI-decorated core-shell structure, which induces both electron delocalization between the Pt d orbitals and the PANI π-conjugated ligand and electron transfer from Pt to PANI. The stable PANI shell also protects the carbon support from direct exposure to the corrosive environment.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

2D metal carbides and nitrides (MXenes) for energy storage

Abstract: The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.

Noble metal-free hydrogen evolution catalysts for water splitting

Abstract: Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

25th Anniversary Article: MXenes: A New Family of Two‐Dimensional Materials

Abstract: Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2AlC, Ti3AlC2, and Ta4AlC3. MXenes ­combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. This article reviews progress—both ­experimental and theoretical—on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.