Identify the impact of the covalent-bonded carbon matrix to FeN4 sites for acidic oxygen reduction

2021 ◽  
Author(s):  
Xueli Li ◽  
Zhonghua Xiang
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Carbon Matrix ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Synthetic Methods ◽  
Oxygen Intermediates ◽  
Orr Activity ◽  
The Impact

Abstract Atomically dispersed Fe and N co-doped carbon (Fe–N–C) catalysts exhibited superior acid oxygen reduction reaction (ORR) activities and recently been considered as the most promising alternatives to the benchmark Pt-based catalysts for proton exchange membrane fuel cells. The atomic configuration between Fe, N and C is one of the key factors to affect ORR activity. However, the traditional synthetic methods that rely on pyrolysis of the mixtures of Fe, N and C precursors often result in the plurality of local environment for the FeNx site. Unveiling the effect of covalent-bonded carbon matrix to FeNx sites towards ORR activity is important but still a great challenge due to inevitable connection of diverse N as well as random defects during the pyrolysis process. Here, we report a proof-of-concept study on the evaluation of covalent-bonded carbon environment connected to FeN4 sites on their catalytic activity via pyrolysis-free approach. Basing on the closed π conjugated phthalocyanine-based intrinsic covalent organic polymers (COPs) with well-designed structures, we directly synthesized a series of atomically dispersed Fe-N-C catalysts with various pure carbon environment without any N doping directly connected to the same FeN4 sites. Experiments coupled with density functional theory demonstrate that the catalytic activities appear a volcano plot with the increase of degree of delocalized π electrons from the carbon matrix. The delocalized π electrons changed anti-bonding d-state energy level of the single FeN4 moieties, hence tailored the adsorption between active centers and oxygen intermediates and altered the rate-determining step of oxygen reduction reaction.

scholarly journals Unveiling the high-activity origin of single-atom iron catalysts for oxygen reduction reaction

2018 ◽  
Vol 115 (26) ◽  
pp. 6626-6631 ◽  
Author(s):  
Liu Yang ◽  
Daojian Cheng ◽  
Haoxiang Xu ◽  
Xiaofei Zeng ◽  
Xin Wan ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Alkaline Media ◽  
Single Atom ◽  
Iron Catalysts ◽  
Grand Challenge ◽  
Orr Activity

It is still a grand challenge to develop a highly efficient nonprecious-metal electrocatalyst to replace the Pt-based catalysts for oxygen reduction reaction (ORR). Here, we propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG). The half-wave potential of SA-Fe/NG is only 30 mV less than 20% Pt/C in acidic medium, while it is 30 mV superior to 20% Pt/C in alkaline medium. Moreover, SA-Fe/NG shows extremely high stability with only 12 mV and 15 mV negative shifts after 5,000 cycles in acidic and alkaline media, respectively. Impressively, the SA-Fe/NG-based acidic proton exchange membrane fuel cell (PEMFC) exhibits a high power density of 823 mW cm−2. Combining experimental results and density-functional theory (DFT) calculations, we further reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N species, because such molecular incorporation is the key, leading to the active site increase in an order of magnitude which successfully clarifies the bottleneck puzzle of why a small amount of iron in the SA-Fe catalysts can exhibit extremely superior ORR activity.

Nano-geometric deformation and synergistic Co nanoparticles—Co-N4 composite sites for proton exchange membrane fuel cells

2021 ◽  
Author(s):  
Xiaoyang Cheng ◽  
Jian Yang ◽  
Wei Yan ◽  
Yu Han ◽  
Ximing Qu ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Proton Exchange Membrane ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Single Atom ◽  
Geometric Deformation ◽  
Orr Activity ◽  
Co Nanoparticles ◽  
Exchange Membrane

Co single-atom (CoSA) catalysts of the CoN4 moiety usually show an unsatisfactory oxygen reduction reaction (ORR) activity due to poor O2 activation.

scholarly journals Fe atoms anchored on defective nitrogen doped hollow carbon spheres as efficient electrocatalysts for oxygen reduction reaction

Nano Research ◽  
2020 ◽  
Author(s):  
Panpan Su ◽  
Wenjuan Huang ◽  
Jiangwei Zhang ◽  
Utsab Guharoy ◽  
Qinggang Du ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Reduction Reaction ◽  
Carbon Spheres ◽  
Coordination Structure ◽  
Nitrogen Doped ◽  
Orr Activity ◽  
Hollow Carbon ◽  
Hollow Carbon Spheres

AbstractDefective electrocatalysts, especially for intrinsic defective carbon, have aroused a wide concern owing to high spin and charge densities. However, the designated nitrogen species favorable for creating defects by the removal of nitrogen, and the influence of defects for the coordination structure of active site and oxygen reduction reaction (ORR) activity have not been elucidated. Herein, we designed and synthesized a pair of electrocatalysts, denoted as Fe-N/C and Fe-ND/C for coordination sites of atomic iron-nitrogen and iron-nitrogen/defect configuration embedded in hollow carbon spheres, respectively, through direct pyrolysis of their corresponding hollow carbon spheres adsorbed with Fe(acac)3. The nitrogen defects were fabricated via the evaporation of pyrrolic-N on nitrogen doped hollow carbon spheres. Results of comparative experiments between Fe-N/C and Fe-ND/C reveal that Fe-ND/C shows superior ORR activity with an onset potential of 30 mV higher than that of Fe-N/C. Fe-ND sites are more favorable for the enhancement of ORR activity. Density functional theory (DFT) calculation demonstrates that Fe-ND/C with proposed coordination structure of FeN4−x (0<x<4) anchored by OH as axial ligand during ORR, weakens the strong binding of OH* intermediate and promotes the desorption of OH* as rate-determining step for ORR in alkaline electrolyte. Thus, Fe-ND/C electrocatalysts present much better ORR activity compared with that of Fe-N/C with proposed coordination structure of FeN4.

scholarly journals The Activity Enhancement Effect of Ionic Liquids on Oxygen Reduction Reaction Catalysts: From Rotating Disk Electrode to Membrane Electrode Assembly

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 989
Author(s):  
Kan Huang ◽  
Oscar Morales-Collazo ◽  
Zhichao Chen ◽  
Tangqiumei Song ◽  
Liang Wang ◽  
...  
Keyword(s):  
Ionic Liquids ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Membrane Electrode Assembly ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Membrane Electrode ◽  
Enhancement Effect ◽  
Chemical Structures ◽  
The Impact

Ionic liquids (ILs) have been explored as a surface modification strategy to promote the oxygen reduction reaction (ORR) on Pt/C and their chemical structures were identified to have strong influence on the ORR activities. To better understand the roles of anion and cation of ILs on the catalytic reaction, two cations ([MTBD]+ and [bmim]+) were paired with three anions ([TFSI]−, [beti]−, and [C4F9SO3]−) to form various IL structures. By systematically varying the IL combinations and studying their effects on the electrochemical behaviors, such as electrochemical surface area and specific ORR activities, it was found that cation structure had a higher influence than anion, and the impact of the [MTBD]+ series was stronger than the [bmim]+ series. In addition to the investigation in the half-cell, studies were also extended to the membrane electrode assembly (MEA). Considerable performance enhancements were demonstrated in both the kinetic region and high current density region with the aid of IL. This work suggests that IL modification can provide a complementary approach to improve the performance of proton exchange membrane fuel cells.

scholarly journals Direct correlation of oxygen adsorption on platinum-electrolyte interfaces with the activity in the oxygen reduction reaction

2021 ◽  
Vol 7 (24) ◽  
pp. eabb1435
Author(s):  
Shiyi Wang ◽  
Enbo Zhu ◽  
Yu Huang ◽  
Hendrik Heinz
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Local Density ◽  
Oxygen Adsorption ◽  
Reduction Reaction ◽  
Functional Theory ◽  
Platinum Surfaces ◽  
Local Density Functional Theory ◽  
Orr Activity

The oxygen reduction reaction (ORR) on platinum catalysts is essential in fuel cells. Quantitative predictions of the relative ORR activity in experiments, in the range of 1 to 50 times, have remained challenging because of incomplete mechanistic understanding and lack of computational tools to account for the associated small differences in activation energies (<2.3 kilocalories per mole). Using highly accurate molecular dynamics (MD) simulation with the Interface force field (0.1 kilocalories per mole), we elucidated the mechanism of adsorption of molecular oxygen on regular and irregular platinum surfaces and nanostructures, followed by local density functional theory (DFT) calculations. The relative ORR activity is determined by oxygen access to platinum surfaces, which greatly depends on specific water adlayers, while electron transfer occurs at a similar slow rate. The MD methods facilitate quantitative predictions of relative ORR activities of any platinum nanostructures, are applicable to other catalysts, and enable effective MD/DFT approaches.

scholarly journals Identifying the impact of the covalent-bonded carbon matrix to FeN4 sites for acidic oxygen reduction

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Xueli Li ◽  
Zhonghua Xiang
Keyword(s):  
Density Functional ◽  
Carbon Matrix ◽  
Active Centers ◽  
Oxygen Intermediates ◽  
Functional Theory ◽  
Rate Determining Step ◽  
Local Environments ◽  
Orr Activity ◽  
The Impact ◽  
Random Defects

AbstractThe atomic configurations of FeNx moieties are the key to affect the activity of oxygen rection reaction (ORR). However, the traditional synthesis relying on high-temperature pyrolysis towards combining sources of Fe, N, and C often results in the plurality of local environments for the FeNx sites. Unveiling the effect of carbon matrix adjacent to FeNx sites towards ORR activity is important but still is a great challenge due to inevitable connection of diverse N as well as random defects. Here, we report a proof-of-concept study on the evaluation of covalent-bonded carbon environment connected to FeN4 sites on their catalytic activity via pyrolysis-free approach. Basing on the closed π conjugated phthalocyanine-based intrinsic covalent organic polymers (COPs) with well-designed structures, we directly synthesized a series of atomically dispersed Fe-N-C catalysts with various pure carbon environments connected to the same FeN4 sites. Experiments combined with density functional theory demonstrates that the catalytic activities of these COPs materials appear a volcano plot with the increasement of delocalized π electrons in their carbon matrix. The delocalized π electrons changed anti-bonding d-state energy level of the single FeN4 moieties, hence tailored the adsorption between active centers and oxygen intermediates and altered the rate-determining step.

scholarly journals Oxygen reduction reaction on Pt-skin Pt3V(111) fuel cell cathode: a density functional theory study

RSC Advances ◽  
2020 ◽  
Vol 10 (46) ◽  
pp. 27346-27356 ◽  
Author(s):  
Asnake Sahele Haile ◽  
Weldegebriel Yohannes ◽  
Yedilfana Setarge Mekonnen
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Proton Exchange Membrane ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
Fuel Cell Cathode ◽  
Exchange Membrane

Pt-non-precious transition metals (Pt-NPTMs) alloy electrocatalysts have gained considerable attention to develop cheaper and efficient electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs).

scholarly journals Pt-Based Intermetallic Nanocrystals in Cathode Catalysts for Proton Exchange Membrane Fuel Cells: From Precise Synthesis to Oxygen Reduction Reaction Strategy

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1050
Author(s):  
Peng Gao ◽  
Min Pu ◽  
Qingjun Chen ◽  
Hong Zhu
Keyword(s):  
Fuel Cells ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Proton Exchange Membrane ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Cathode Catalysts ◽  
Wide Range ◽  
Orr Activity ◽  
Exchange Membrane

Although oxygen reduction reaction (ORR) catalysts have been extensively investigated and developed, there is a lack of clarity on catalysts that can balance high performance and low cost. Pt-based intermetallic nanocrystals are of special interest in the commercialization of proton exchange membrane fuel cells (PEMFCs) due to their excellent ORR activity and stability. This review summarizes the wide range of applications of Pt-based intermetallic nanocrystals in cathode catalysts for PEMFCs and their unique advantages in the field of ORR. Firstly, we introduce the fundamental understanding of Pt-based intermetallic nanocrystals, and highlight the difficulties and countermeasures in their synthesis. Then, the progress of theoretical and experimental studies related to the ORR activity and stability of Pt-based intermetallic nanocrystals in recent years are reviewed, especially the integrated strategies for enhancing the stability of ORR. Finally, the challenges faced by Pt-based intermetallic nanocrystals are summarized and future research directions are proposed. In addition, numerous design ideas of Pt-based intermetallic nanocrystals as ORR catalysts are summarized, aiming to promote further development of commercialization of PEMFC catalysts while fully understanding Pt-based intermetallic nanocrystals.

scholarly journals The Transition Metal and Non-metal co-Doping Graphene for Oxygen Reduction Reaction Electrocatalysis: a Density Functional Theory Study

2021 ◽  
Vol 7 (2) ◽  
pp. 197-207
Author(s):  
Fengxiang Chen ◽  
Lei Yang
Keyword(s):  
Density Functional Theory ◽  
Transition Metal ◽  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Density Functional ◽  
Reduction Reaction ◽  
Proton Exchange ◽  
Central Metal ◽  
Orbital Theory ◽  
Functional Theory

Proton exchange membrane fuel cells (PEMFCs) are vital energy-conversion devices in a hydrogen-fueled economic. In this study, we performed density functional theory (DFT) calculations to study 4e− oxygen reduction reaction process on transition metal embedded in single and double vacancies (SV and DV) in a graphene. We calculated bonding energy and adsorption energy on CoX3 (X = B, C, N, Si, P and S) and CoX4 (X = B, C, N, Si, P and S) embedded in graphene. Our DFT results indicate that formation of CoX3 is unfeasible and the formation of CoX4 is feasible. In addition, the crucial role of ligand atoms near embedded metal atoms is revealed via the molecular orbital theory. Then the Gibbs free energy of CoX4 are calculated and the CoN4, CoS4, and CoP4 are predicted to be active for catalyzing ORR, and these also show ligand atoms’ coordination effect for catalytic activity of central metal. Furthermore, we observed that they have identical rate-determining step (RDS). This work can provide some references for transition atoms catalytic doped in carbon materials.

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