bluuebunny/crossref_metadata_2025_split huggingface dataset:
Challenges and Perspectives in Applying First-Principles Calculations for the Design of PGM-Free Catalyst for Oxygen Reduction Reaction
Authors: Matanovic Ivana , Artyushkova Kateryna , Atanassov Plamen 
Published: February 2020

Modeling and calculations play a crucial role in applied materials research by providing the link between the property of the material and its atomic-scale structure. First-principles calculations can provide a link between the synthesis conditions and catalyst structure or the activity of the catalyst and the atomic-scale structure of its active sites. Although extensive previous research has shed light on some aspects of ORR activity and durability of PGM-free catalysts consisting of a transition metal, nitrogen, and carbon (M-N-C), detailed fundamental understanding of the structure-activity relationship is one of the most critical challenges that we face currently. This lack of detailed understanding of the nature of the M-N-C electro-catalysts hinders any rational improvements in their efficiency and durability. One of the challenges that need to be addressed in this effort is linking the first principle calculations with precise structural analysis and electrochemical studies to identify realistic theoretical models/structures.
Density functional theory (DFT) calculations have become crucial in the accurate interpretation of the spectroscopic features of materials obtained by advanced spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy (MBS). Namely, structure-to-property relationships in catalytic materials are usually established through correlations of observed catalytic activity and structural data obtained by the surface sensitive spectroscopic methods. This is a challenging task that has recently become more feasible by coupling first principle calculations on model systems and spectroscopic measurements performed with real catalysts [1,2]. In this talk, we will discuss how DFT calculations of spectroscopies properties for well-defined defects of M-N-catalysts can facilitate the interpretation of XPS and MBS. These two methods are the primary surface analysis techniques for determining the chemical environment and coordination of nitrogen and transition metal (Fe) in these materials. Therefore, linking DFT modeling and ex situ and in situ spectroscopy might be a key to understanding the interplay between chemistry, morphology, and catalytic activity in M-N-C catalysts.
[1] K. Artyushkova, I. Matanovic, B. Halevi, P. Atanassov, Oxygen Binding to Active Sites of Fe-N-C ORR Electrocatalysts Observed by Ambient-Pressure XPS, J. Phys. Chem. C 2017, 121(5): 2836-2843.
[2] I. Matanovic, K. Artyushkova, M. B. Strand, M. J. Dzara, S. Pylypenko, P. Atanassov, Core Level Shifts of Hydrogenated Pyridinic and Pyrrolic Nitrogen in the Nitrogen-Containing Graphene-Based Electrocatalysts: In-Plane vs Edge Defects, J. Phys. Chem. C 2016, 120(51), 29225-29232.
Highly-Acidic Mixed-Metal-Oxides (WO3-ZrO2) As Active Supports for Dispersed Metal Centers: Enhancement of Electrocatalytic Reduction of Oxygen and Carbon Dioxide
Authors: Rutkowska Iwona Agnieszka , Zoladek Sylwia , Kulesza Pawel J 
Published: February 2020

Application of metal oxides as active matrices in electrocatalysis is particular importance. The hydrous behavior, which favors proton mobility and affects overall reactivity, reflects not only the oxide’s chemical properties but its texture and morphology as well. What is of importance to electrochemical science and technology, certain nonstoichiometric mixed-valence oxides could exhibit pseudo-metallic conductivity and possess appreciable catalytic activity.
Recently, mixed oxide systems stabilized through Zr-O-W bonds have been demonstrated to be very attractive acid catalysts exhibiting high catalytic activities and good stabilities in many demanding industrial reactions. For electrocatalytic applications, mixed-valent tungsten(VI,V) oxide and zirconium(IV) oxide have been sequentially deposited and integrated through voltammetric potential cycling to form sub-microstructured films on glassy carbon electrode. The mixed WO3/ZrO2 systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Pt or Cu electrocatalytic nanoparticles over such active WO3/ZrO2 supports, the electrocatalytic activities of the respective systems toward the reduction of oxygen or carbon dioxide have been enhanced even at decreased loadings in acid media. The enhancement effects should be attributed to features of the mixed metal oxide support such as porosity and high population of hydroxyl groups (due to presence of ZrO2), high Broensted acidity of sites formed on mixed WO3/ZrO2, fast electron transfers coupled to unimpeded proton displacements (e.g. in HxWO3), as well as strong metal-support interactions between nanosized metals (Pt or Cu) and the metal (W, Zr) oxo species. The fact that WO3/ZrO2 nanostructures are in immediate contact with the metallic catalytic sites leads to the specific interactions (via the surface hydroxyl groups) with the reaction intermediates (H2O2 or CO adsorbates). Further mechanistic studies involving rotating ring disk voltammetry and gas-diffusion electrode measurements are planned in addition to spectroscopic and XPS measurements. The mixed-metal systems will also be considered together with nanostructured carbon carriers such as reduced graphene oxide, carbon nanotubes or carbon black.
(Invited) Preparation and Active Sites of Pyrolyzed Fe/N/C Non-Precious Metal Catalysts for Oxygen Reduction Reaction
Authors: Zhou Zhi-You , Wang Yu-Cheng , Yang Xiao-Dong , Chen Chi , Sun Shi-Gang 
Published: February 2020

Pyrolyzed Fe/N/C catalyst is a promising non-precious-metal catalyst (NPMCs) for oxygen reduction reaction (ORR) in fuel cells, and substantial progresses have been made recently in this field. However, to meet the requirement of practical applications, it still needs to improve significantly the ORR activity and stability of Fe/N/C catalyst, and to reveal active site structure for rational design of NPMCs.
Herein, we report our recent progresses in preparation of high performance Fe/N/C catalyst and investigation of the active sites. The Fe/N/C catalyst was prepared by using precursor of poly-m-phenylenediamine (PmPDA), and exhibits an ORR performance of 12.8 A/g@0.80V in acid solution with H2O2 yield less than 1%.[1] When it was applied in proton exchange membrane cell (PEMFC), a peak power density could reach 0.81 W cm-2. We further improved the catalytic activity of PmPDA-Fe/N/C by co-doping of S element. The peak power density has exceed 1.0 W cm-
2. [2] The active sites of Fe/N/C catalyst are mostly located in micropores, so they are susceptible to water flooding. To this point, surface fluorination was applied to the Fe/N/C catalysts (such as the modification of Ar-CF3). The fluorinated Fe/N/C could perform stably over 120 h at 0.5 V with a current density of 0.56 A cm-2 in a H2-O2 PEMFC.[3] Alternatively, hydrophobic dimethyl silicon oil (DMS) was introduced into Fe/N/C catalyst layer, which leads to form triple-phase interface in micropores. As a result, Fe/N/C-based direct methanol fuel cell (DMFC) could yield a performance close to that of Pt-based DMFC.[4]

We developed a molecule/ion probe method to study the active sites. It has revealed that the ORR activity of PmPDA-Fe/N/C is not sensitive to CO and NOx, but can be suppressed significantly by halide ions (e.g., Cl−, F−, and Br−) and low valence state sulfur-containing species (e.g., SCN−, SO2 , and H2S).[1] This indicates that the active sites of the Fe/N/C catalyst contains Fe element in acid medium. We further designed a single-atomic-layer Fe/N/C model catalyst based on monolayer graphene (FeNMLG), and systematically investigated the effects of defect density, the number of graphene layers, and the doped nitrogen species on the ORR activity.[5] It has demonstrated also that such Fe/N/C model catalyst is also fit for in situ vibration spectroscopic studies.

Acknowledgement: This study was supported by grants from National Key Research and Development Program of China (2016YFB0101202), and NSFC (91645121 and 21621091).

References:

Wang, et al, J. Am. Chem. Soc. 2014, 136, 10882−10885.

C. Wang, et al, Angew Chem Int Ed. 2015, 54, 9907-9910.

C. Wang, et al, ChemElectroChem, 2017, in revision.

C. Wang, et al ACS Energy Lett. 2017, 2, 645-650.

D. Yang, et al ACS Catal, 2017, 7, 139−145.
Studies of the Oxygen Reduction Reaction of Pt Single Crystals Alloys in Alkaline Media
Authors: Jensen Kim Degn , Arnarson Logi , Rossmeisl Jan , Chorkendorff Ib , Escudero-Escribano María , Stephens Ifan 
Published: February 2020

Understanding the factors controlling trends in activity for electrocatalytic oxygen reduction is of fundamental interest; as this reaction is paramount for future energy conversion schemes.1 Recently, numerous reports have suggested significant divergences between catalytic performances of noble metal surfaces for this reaction in acidic and basic electrolyte.2

Prior work3 by us have elucidated the Sabatier volcano for the oxygen reduction reaction in 0.1 M HClO4 using the Cu/Pt(111) near-surface alloy system.
In the present work the surface binding of *OH reaction intermediates were weakened by ligand effects introduced by varying subsurface Cu coverage in Pt(111). Thus, we related the observed oxygen electroreduction activities to the shifts in OH adsorption potentials, derived from the base cyclic voltammograms, in both acidic3 and alkaline media. Remarkably, similar trend persists between *OH binding shifts and Cu/Pt(111) oxygen reduction activities relative to pure Pt(111); this being independent of the electrolyte going from acid to alkaline.
Notably, Cu/Pt(111) near-surface alloy surfaces in 0.1 M NaOH or KOH, while exhibiting similar trend in relative activity independent of electrolyte, exhibits a substantial ~2- and <4.5-fold improvement in activity compared to when in 0.1 M HClO4, respectively. This suggests a fundamental effect of changing the cation present in the electrolyte. Moreover, by optimizing the Cu subsurface content a substantial activity enhancement is observed, which in 0.1 M KOH results in exceptionally high specific activities on the order of 101±8 mA/cm2 at 0.9 V vs. the reversible hydrogen electrode.
Hence, our results confirm that *OH binding energies governs the activity in both acid and alkaline media i.e. a Sabatier volcano relationship persist in alkaline media. Furthermore, our results open up discussions of relevant aspects describing the cation interplay with the catalyst surface.

A. Kongkanand and M. F. Mathias, J. Phys. Chem. Lett., 7, 1127–1137 (2016).

J. Staszak-Jirkovský et al., ACS Catal., 5, 6600–6607 (2015).

I. E. L. Stephens et al., J. Am. Chem. Soc., 133, 5485–5491 (2011).
3D-Nanorod Fenton-like CuO/TiO2 Photocatalyst By Electrodeposition in AAO Template for Dye Degradation
Authors: Yang Li-Heng , Wang Yi-Jung , Chueh Yu-Lun , Chen Lih-Juann 
Published: February 2020

Recently, nanostructures such as nanorods and nanowires have drawn much interest because of their unique electronic and optical properties. Anodic aluminum oxide (AAO) method is a promising template-assisted technique which ensures high quality and repeatability for fabrication. Morphology of periodical nanoscale pores in AAO templates has been studied in relation with anodizing process for a few decades. The AAO templates are well prepared by a two-step anodization process method in 0.3 M oxalic acid solution at 10 °C and anodizing voltage 40 V. After first-step anodization, AAO layer was etched out in 5 wt.% phosphoric acid and 2.24 wt.% chromic acid at 60 °C for 1 HR. After barrier thinning, the AAO template was immersed into a 5 wt.% phosphoric acid solution at room temperature for 45 minutes. The pore length increases with electrochemical etching time, while the pore size and interpore distance depend on the applied potential. In our work, the AAO template is 45 nm in diameter and the interpore distance and pore length are 100 nm and 1 μm, respectively. In case that the Al2O3 barrier layer is too thick for the electrodeposition, barrier thinning proceeds by limited current is a necessary process to lower the working voltage and to create the nucleation site for the growth of Cu. The Cu/Cu2O composite nanorods are synthesized from aqueous solution prepared from 0.7 M of CuSO4 dissolved in DI water, with applied pulse potential -1.5 V at room temperature. The nanorods were annealed at 400 °C and resulted in the formation of CuO. After that, TiO2 thin film was deposited on the top followed by annealing at 550 °C to form anatase. Etching out the AAO template, we can obtain CuO nanorod arrays standing on TiO2 thin film nanostructure for application in water treatment. Besides, it can also be transferred on other flexible substrate or on the surface of the item promoting self-cleaning property.
CuO is a great Fenton-like photocatalyst which is active with H2O2 and produces free radicals reacting with the dye or pollutants. TiO2 is stable in water and possesses good photocatalytic property in anatase phase. CuO is a narrow bandgap p-type metal oxide semiconductor which provides electrons and holes and absorbs infrared light, while TiO2 is a n-type metal oxide semiconductor which absorbs UV light and has high transparency in sunlight. We combine two metal oxide to form heterojunction with AAO and electrodeposition method. When the infrared light is absorbed by CuO nanorods exciting electron and holes, the electrons shift to TiO2 and the holes stay in CuO. These electron-hole pairs can react with H2O2 producing free radicals and start dye degradation. Furthermore, CuO nanorods immobilized on TiO2 film nanostructure can also be applied as gas sensors or photodetectors and for water splitting.
Understanding the Activation and Stabilization of Electrocatalytic Single Atom Catalysts
Authors: Wan Gang , Chen Hangrong , Li Tao , Zhou Hua , Shi Jianlin 
Published: February 2020

The discovery of single atom catalysts (SACs) paths new frontier in heterogeneous catalysis. Recently, increasing interests have been focused on the construction of atomically-dispersed transition metal centers in nitrogen doped carbon through supports-assisted pyrolytic synthesis for various applications, such as electrocatalysis, CO oxidation, and organic synthesis. However, the evolution, activation and stabilization of SAC in synthesis and catalysis, which is critical for its applications, still remain unexplored yet. Here, we examined the critical importance of supports and anions for the single-atom transition-metal-sites(Co, Fe, and Ni) construction and modification, combing synchrotron X-ray absorption studies, and the electron microscopic characterizations, and electrochemical measurements.
The supports and anions are essential parts which are involved in the pyrolytic synthesis. However, both of them are often excluded from construction of catalytic sites in SACs. The formation of atomic metal sites is often accompanies with the evolution of metallic metal/metal carbide nanoparticles encased by graphite layers. Here, we demonstrate a versatile anions-regulated selective generation of metal sites in carbon and demonstrate the metal-sites dependence catalytic performances for oxygen reduction reaction (ORR) and hydrogen evolution reaction.
Besides achieving the controlled evolution of atomically-dispersed metal sites, we also demonstrate the roles of supports on the structural reconstruction and activation of SAC and the functional relationship between the electrocatalytic activity and electrochemical stability in SAC. Different from the previous models of integration of fragments on carbon, we initially reveal the supports-assisted structural reconstruction on the evolution of electrocatalytic SAC. More importantly, the enhanced catalytic activity and selectivity are found to result from more unoccupied 3d orbitals at low energy positions for single-atom-dispersed metal sites within non-planar coordination. This is mainly due to the facilitated interactions between metal sites and adsorbates. More importantly, such activity descriptors can further modified through controlling the atomic coordination geometry or structures. Interestingly, decreasing the atomic coordination numbers enhances the ORR activity, however, also damages the electrochemical stability of atomically dispersed metal sites under potentials, demonstrating the coordination-structure sensitivity of its electrochemical stability. Therefore, we present a functional relationship between the catalytic activity and electrochemical stability of SAC for electrocatalysis. Our studies offer molecular insights on the evolution of SAC, pathing new directions to SAC engineering with improved activity and stability for various reactions, such as ORR, water splitting, and CO2 reduction.

Figure 1
Carbon Black Supported Highly Stable and Active Electrocatalysts for ORR in Polymer Electrolyte Membrane Fuel Cells
Authors: Rauf Muhammad , Li Yong-Liang , Qu Jun-Le , Zhang Pei-xin , Mi Hong-wei 
Published: February 2020

Exploring low-cost and highly efficient non-precious metal electrocatalysts toward oxygen reduction reaction is crucial for the development of fuel cells. Pyrolyzed Fe/N/C electrocatalysts have received attention in recent years as a cathode catalyst for oxygen reduction reaction (ORR) in the polymer electrolyte fuel cell (PEFC). These kinds of non-precious metals electrocatalysts had shown high activity and stability in both acidic and alkaline media. [1, 2]. Herein, we organized our significant advances in performance of Fe/N/C catalysts and their applications in low temperature fuel cells:

We synthesized N-doped electrocatalysts using melamine as nitrogen precursor, ferric chloride as an iron precursor and oxidized carbon black kJ600 as support by solvothermal method. The final catalyst synthesized at 800°C (SNW-Fe/N/C@800°C) exhibited microporous structure with Brunauer−Emmett−Teller (BET) surface area up to 791 m2g-1 after second heat treatment. The catalyst exhibits high ORR activity (0.64 mA mg-1 at 1 V vs RHE, about half of Pt/C catalyst), stability and low percentage of hydrogen peroxide (% H2O2 < 1.5%) in O2-saturation 0.1 M NaOH solution. The alkaline anion exchange membrane fuel cell (AEMFC) test was performed by using SNW-Fe/N/C@800°C as cathode catalyst demonstrates a high power density of 266 mW cm-2.

We study the effect of active nitrogen species on ORR performance through comparison of Fe/N/C electrocatalysts in acidic and alkaline solution. These catalysts are synthesized from different rich-nitrogen polymers. We observed that pyridinic N is very important for oxygen reduction reaction through XPS analysis, especially in alkaline electrolyte. The sensitivity of these three catalysts to acidity/alkalinity highly depends on percentage of pyridinic N and found the reverse order of ORR activity between acidic and alkaline media

We designed a facile method for the synthesis of ORR catalysts with iron nanoparticles encapsulated in bamboo like structure of N-doped carbon nanotubes. Finally, pyrolyzed catalyst (Bg-CA-M)-Fe-C-800°C exhibited the efficient ORR performance with the onset potential 1.10 V, half-wave potential 0.93V, 4 electrons transfer number per oxygen molecule and high durability, as well as high ethanol tolerance in alkaline solution. (XPS measurements revealed that ORR activities of catalysts directly correlate with pyridinic and pyrrolic nitrogen active species. The direct ethanol fuel cell (DEFC) with (Bg-CA-M)-Fe-C as cathode catalyst displayed 64 mW cm-2 peak power density.

References
[1] Muhammad Rauf et al., Carbon 125, 605-613 (2017)
[2] Hoon T. Chung et al., Science 357, 479–484 (2017)
[3] Muhammad Rauf et al., Electrochemistry Communications, 73 (2016) 71-74
Observing Growth and Dissolution of Cuprous By Liquid Cell TEM
Authors: Lin Ya-Hsuan , Chen Fu-Chun , Chen Jui-Yuan , Wu Wen-Wei 
Published: February 2020

Metal oxides has attracted great attention due to the widely applications, which are commonly used in semiconductor industry due to their excellent physical and chemical properties. Also, it exhibits variety of structures. Among various metal oxides, cuprous (Cu2O, copper (I) oxide) is regarded as one of the most promising materials. It is cheap, earth-abundant, and nontoxic; therefore, it can be applied in catalysis, sensor, solar cell and p-type semiconductor. However, the redox reaction of cuprous is still uncertain, which strongly influent its size, morphology, and nanostructure.
In this work, the growth and dissolution of cuprous were observed via in situ liquid cell transmission electron microscopy (TEM). The study of cuprous nanoparticles formation, such as kinetics analysis, nucleation, growth, and reduction reaction in liquid phase can be achieved. In the cuprous growth, dendrite shape agglomeration dispersed everywhere inside the chip at the beginning. Few minutes later, the accumulation of copper ions resulted in a rapidly growth of cuprous nanostructures. The results indicated that the electron beam reduced the precursor which led the copper ions transfer into copper (I) oxide. Whereas in the cuprous dissolution, the cubic shape dissolved in specific {100} planes, and finally fully disappeared. The dissolution is resulted from the higher dose of electron exposure, the radiation-damage-caused vacancies accumulated and formed porous checkerboard-like nanostructure. The growth/dissolution results were systemically analyzed through the viewpoint of kinetics and dynamics. The direct observation of the dynamic process sheds light on the preparation of metal oxide by redox reaction method and extends the study of reaction kinetics.

Figure 1