bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Development and Application of Core-Shell Cathode Catalysts in PEM Fuel Cell
Authors: Yang Lijun , Banham Dustin , Markiewicz Matthew , Knights Shanna , Ye Siyu
Published: February 2020

Platinum group metals (PGM) catalysts are presently the most promising catalysts for the oxygen reduction reaction (ORR). However, the total PGM content in the PEM fuel cell should be reduced. To meet longer term passenger vehicle automotive targets, catalyst with at least 4 times higher mass activity over the currently available commercial Pt/C is required. One promising approach to meet this goal is the development of Pt monolayer core-shell catalysts through electro under-potential deposition of Cu onto a core (Pd, PdAu, etc.), followed by galvanic replacement of the Cu by Pt salt [1]. It is widely accepted that Pt monolayer catalysts exhibit at least 4-8 times higher mass activity vs. Pt/C, while also demonstrating excellent durability during accelerated stress testing on rotating disk electrodes (RDE) [2]. However, the scale-up synthesis of the platinum monolayer core-shell catalysts and the retention of favorable catalytic performance in the membrane electrode assemblies (MEA) are still quite challenging [3].

In this work, we will present the results of Pd@Pt/C core-shell catalysts successfully scaled up (in-house) from a conventional synthetic approach (micro gram level) to a large 3-electrodes reactor (gram level). It is demonstrated that this scale up is successful, with the gram level batch showing comparable activity to the small scale batch, based on RDE testing. In addition, preliminary in-situ MEA tests of commercial core-shell catalysts will be presented, demonstrating the performance and durability of these monolayer core-shell catalysts under fuel cell operating conditions.

[1] R. R. Adzic. Electrocatalysis, 2012, 3 (3-4):163-169.

[2] J. Hu, L. Wu, K. A. Kuttiyiel, K. R. Goodman, C. Zhang, Y. Zhu, M. B. Vukmirovic, M. G. White, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 2016, 138: 9294-9300.

[3] L. L. Zhang, S. Zhu, Q. Zhang, D. Su, J. Yue, Z. Du, M. Shao. ACS Catal. 2016, 6: 3428 −3432.
(Keynote) Correlating Fundamental Properties of Materials to Fuel Cell Catalysts
Authors: Lopes Pietro Papa , Strmcnik Dusan , Markovic Nenad M , Stamenkovic Vojislav
Published: February 2020

Fuel cells technology rely on electrochemical processes that need to provide satisfactory energy density in order to be used in applications for transportation; however, a major challenge lies in the insufficient activity and durability of materials that are currently employed as cathode catalysts for electrochemical reduction of oxygen. These limitations inevitably lead to a lower operating efficiency of the devices, which highlights the need for development of more active and durable oxygen reduction reaction (ORR) catalysts. Consequently, the majority of research efforts are placed on the catalyst design and synthesis aiming to improve their efficiency. It has been found that properties such as surface structure, surface and subsurface composition are determining electronic properties and have distinguished roles in defining the functional properties of electrocatalysts 1. The material-by-design-approach, would be used here as an example to emphasize the transfer of the knowledge obtained from the well-defined systems towards tailor-made real-world catalysts 2. Considering current state-of-the-art in fuel cells, most of the research is centered on platinum, which is the best monometallic catalyst for the ORR. Special emphasis will be placed on utilization of multimetallic systems that could provide additional benefits by bringing together highly diverse constituents to alter and tune both catalytic activity and durability 3.

[1] Stamenkovic et al. Science 315 (2007) 493.

[2] Stamenkovic et al. Nature Materials 6 (2007) 241.

[3] Wang et al. Nano Letters 11 (2011)919.
(Invited) Solar Fuel Production for a Sustainable Energy: Water Splitting to Hydrogen and CO2 to Fuel
Authors: Chu Deryn , Li Jiangtian
Published: February 2020

Chemical fuel generation by solar driven water splitting to hydrogen and CO2 reduction to hydrocarbons is attractive to supply the sustainable energy. The design and fabrication of photoelectrode materials that are able to harvest sunlight and then produce excitons for chemical reactions is an important scientific undertaking. In this presentation, we will present our recent experimental and theoretical efforts to engineer both photoanode and photo/cathode materials from the perspectives of light absorption improvement by forming heterojunctions, electronic band structure manipulation by controlling the surface states and energetic level alignment, as well as surface catalysts optimization with the aim to improve their capability in the sunlight harvesting range, charge carrier transport efficiency, and the product selectivity. The resultant nanostructures could be employed as photocathode and photoanode separately in a photoelectrochemical tandem cell for unbiased solar fuel generation.

Keywords: Solar fuels, Water Splitting, CO2 Reduction, Photoelectrochemical Tandem Cell.
Pd/Fe3O4 Nanocatalysts for Highly Effective and Simultaneous Removal of Humic Acids and Cr(VI) By Electro-Fenton with H2O2 in-Situ Electro-Generated on the Catalyst Surface
Authors: Huang Binbin , Guo Qian , Lei Chao
Published: February 2020

The widespread presence of humic acids (HAs) and chromium (Cr) in aquatic systems and drinking water sources is a serious threat to the environment and human being, which attracts great concerns from the protection of public health.1,2 However, no attempts on the potential interaction and simultaneous removal of these two types of contaminants have been made. Here, an electro-Fenton process was reported for the effective and simultaneous removal of HAs and Cr(VI), where H2O2 was in-situ produced from the electro-generated H2 and O2 by the presence of Pd/Fe3O4 nanocatalysts and Fe(II) was provided from the support. The effects of solution pH, applied current, Pd loading, and initial concentrations of HAs and Pd/Fe3O4 on the removal efficiency of HAs and Cr(VI) were carefully investigated. Under the optimized electrolysis conditions (pH 3.0, 40 mA, 5.0 wt % Pd, 100 mg•L-1 HAs and 5.0 g•L-1 Pd/Fe3O4), HAs were effectively mineralized, as revealed by a total organic carbon removal efficiency of 90%, and Cr(VI) was completely reduced accompanying with 90% total Cr removal. The HAs degradation driven by the contribution of anodic oxidation was found to be important but not dominant, whereas electro-Fenton process played a fundamental role for the mineralization of HAs. The reduction of Cr(VI) was primarily attributed to the contributions from Pd/Fe3O4 and atomic hydrogen on the Pd catalyst surface as well as the cathodic reduction. In a similar manner, a good recycle of Fe3+ to Fe2+ was accelerated. Moreover, most chromium was removed by the deposit of chromite from the solution, which is the most common and stable mineral of chromium in the environment. Importantly, the energy consumption of this electro-Fenton process for HAs degradation was almost 2 orders of magnitude lower than those of reported electrochemical oxidation. The Pd/Fe3O4 nanocatalysts showed excellent removal performances for HAs and Cr(VI) after eight times repeated treatment. This work reports a cost-effective methodology for simultaneous removal of HAs and Cr(VI) and provides a new insight for efficient elimination of complex contaminants.

Figure 1
Electrochemical Reduction of Aqueous CO2 to Synthesis Gas Using β Palladium Hydride
Authors: Sheng Wenchao , Kattel Shyam , Yao Siyu , Chen Jingguang G
Published: February 2020

Electrochemical reduction of CO2 (CO2RR) to value-added liquid fuels or chemical feedstocks using off-peak electricity or intermittent renewable energy sources is a green approach for energy storage and carbon recycling. However, the difficult activation of CO2 to form the CO2
∙−
intermediate and the competitive hydrogen evolution (HER) in aqueous electrolytes make the Faradaic efficiency and selectivity for the CO2RR remain very low. From another perspective, CO2 reduction to CO, with co-production of H2 from water, is very appealing as the mixture of CO and H2 with controlled ratio can be used as syngas for methanol synthesis and Fischer-Tropsch reactions. In this approach, catalyst search is therefore no longer limited to metals with low HER activity such as Au and Ag. Materials with fair HER activity can be potentially considered for the CO2RR. Interestingly, Pd, a good HER catalyst, has been found to continuously produce CO in the CO2RR, which is however counterintuitive to that Pd is prone to CO poisoning.[1] In this work, we have re-examined Pd for the CO2RR using in situ XAS and in situ XRD, and have found that Pd transforms into β-PdH under the CO2RR condition. DFT calculations suggest that CO adsorption energy on the PdH surface is greatly reduced compared to that on the Pd surface, which is most likely the cause for high selectivity of CO2RR to CO when using Pd as the electrocatalyst.[2]

[1] Y. Hori, Modern Aspects of Electrochemistry, Springer, New York, 2008, vol. 42, ch. 3, pp. 89–189.

[2] Wenchao Sheng, Shyam Kattel, Siyu Yao, Binhang Yan, Zhixiu Liang, Christopher J. Hawxhurst, Qiyuan Wu and Jingguang G. Chen, Energy & Environmental Science, 10, 1180-1185 (2017)
(Keynote) Tuning the Properties of Biological Catalysts for Biofuel Cells Applications: From Site-Directed Mutagenesis to the Design of Macroscopic Redox Matrices
Authors: Léger Christophe , Fourmond Vincent , Dementin Sébastien
Published: February 2020

Microorganisms make large metalloenzymes which catalyse the production and recycling of biological "solar fuels" such as O2, H2 and CO2. Using these enzymes in biotechnological applications requires that they be selected according to their particular properties or that these properties be tuned. It may be important for example that a particular enzyme resists inhibition by oxygen or work with high efficiency in one particular direction of the reaction (e.g. H2 oxidation versus H2 production). Here we shall summarise our efforts to understand the molecular determinants of catalytic bias and oxygen sensitivity in hydrogenases and CO-dehydrogenases (enzymes that catalyse the H+/H2 and CO2/CO conversion), and explain why and how these properties are affected when the enzymes are incorporated in a redox hydrogel that allows mediated electron transfer to the electrode.

References:

http://bip.cnrs-mrs.fr/bip06/~leger/

http://orcid.org/0000-0002-8871-6059

Figure 1
Transmembrane Electric Conductivity Modulation in PCBM Doped Free-Standing Lipid Bilayers By Visible Light Irradiation
Authors: Kanomata Kensaku , Haseyama Takumi , Deguchi Takashi , Tadaki Daisuke , Ma Teng , Hirano-Iwata Ayumi , Hirose Fumihiko
Published: February 2020

A cell membrane has a thickness of several nanometer and function as an insulating film having a resistance of more than 100 GΩ in a biological body. The cell membrane has a structure in which phospholipid molecules are aligned as a bilayer. Researches have been conducted to artificially construct cell membranes in vivo and to apply them as highly sensitive biosensors and drug screening devices by embedding biological membrane proteins in cell membranes. On the other hand, photovoltaic properties of lipid bilayer membranes have been reported by introducing fullerene (C60) in the lipid bilayer membrane. Although this technique suggests the function of the cell membrane as a photosensor, the mechanism has not been discussed yet. If we modulated the trans-electrical-conduction with external energies of electric filed or light irradiation, we could expect to control of carrier and/or ion incorporation at the cell membrane, that would be used a biosensing and bio-ion-incorporation devices. In this work, we investigated that modulation of transmembrane electric conductivity in Phenyl-C61-Butyric-Acid-Methyl Ester (PC60BM) doped free-standing lipid bilayers by the visible light irradiation.
(Invited) Proton Transport in Metal-Organic Frameworks
Authors: Paesani Francesco
Published: February 2020

Metal­-organic frameworks (MOFs) have recently attracted much interest as potential proton conducting materials. Unlike other porous materials (e.g., zeolites), MOFs are highly tunable, which allows not only the size and the shape but also the physicochemical properties of the frameworks to be tuned for specific applications. In this contribution, I will describe our recent theoretical/computational efforts aimed at developing a microscopic picture of the mechanisms associated with water­-mediated proton transport in MOFs as a function of temperature, water loading, and pore size/shape. Particular focus will be on establishing a molecular-level correlation between proton mobility and both structural and chemical properties of the frameworks as well as on characterizing the dynamical behavior of water inside the pores.
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
High-Performance PGM-Free and Fe-Free Catalysts for Oxygen Reduction in Acidic Media
Authors: Wang Xiaoxia , Cullen David A. , Pan Yung-Tin , Spendelow Jacob S , More Karren L. , Wu Gang
Published: February 2020

Significant progress has been made in platinum group metal (PGM)-free oxygen reduction reaction (ORR) catalysts derived from Fe. However, Fenton chemistry due to the presence of Fe and peroxide in electrodes causes serious degradation of ionomer and membrane, limiting the use of these Fe-based catalysts in proton exchange membrane fuel cells (PEMFCs). Therefore, PGM-free catalysts that are also free of Fe are urgently needed to enable durable and inexpensive PEMFCs. Here, we report a new type of highly dispersed nitrogen-coordinated single-atom Co site catalyst. This catalyst is derived from Co-doped metal-organic frameworks through a one-step controlled thermal activation. A combination of aberration-corrected electron microscopy couple with electron energy loss spectra and X-ray absorption spectroscopy clearly verify the co-location of Co and N at the atomic level in the form of CoN4. Such a catalyst with properly controlled Co doping content and thermal activation achieved comparable activity to state of the art Fe-based catalysts, showing a respectful half-wave potential of 0.80 V vs. RHE in acids, only 60 mV lower than Pt catalysts (60 mgPt/cm2) in challenging acidic media. Exceptional stability was observed in both potential cycling and constant potential (e.g., 0.7 V) tests. The high ORR performance is attributed to the presence of well-dispersed single CoN4 active sites embedded in the porous carbon matrix without formation of inactive Co aggregates. Fuel cell tests further confirmed that the intrinsic high ORR activity and stability translate to a high-performance cathode in PEMFCs. This atomic single Co site catalyst is a promising step toward replacement of Fe in PGM-free catalysts for advanced fuel cell technologies.
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
Atomic Layer Deposition Nanoelectrode Array As a Platform for Ion Transport Studies
Authors: Zenyuk Iryna V. , Sabarirajan Dinesh C
Published: February 2020

Ionic conductivity in electrochemical application is a function of the number of charge carriers and their mobility. In the electrodes containing ionomer both numbers are high, whereas in deionized water, the ion concentration is ~7 orders of magnitude lower than that in a polymer electrolyte, such as Nafion. In ionomer-free electrodes for fuel cell applications, such as Pt-black or extended-surface Pt electrodes, water assists in ion conduction and expected ionic conductivity should be close to that of deionized (DI) water. However, ionic conductivity of ionomer-free electrodes was measured to be 2-3 orders of magnitude higher than DI water (1, 2). These findings suggest that local confinement and electric double layers (EDLs) affect ion concentration or/and ion mobility, especially in porous high surface area electrodes. Over the years several experimental and modeling studies propose two ion transport mechanisms: 1) Ions transport through surface adsorption and subsequent neutral species surface diffusion and 2) water-mediated ion conduction due to EDLs (3). To understand these mechanisms, model electrodes with controlled geometry and active area have to be designed.

In this study, Atomic Layer Deposition (ALD) was used to fabricate model thin-film electrodes to study ion-transport mechanisms under varied levels of relative humidity. The ALD gas-phase fabrication process provides a uniform and conformal Pt layer with precise thickness on a high aspect-ratio substrates. Here, we fabricate Pt electrodes with a novel thermal ALD process. The activity of the deposited electrodes is characterized with RDE tests and within actual fuel cell hardware. Ionic conductivity studies are conducted in a membrane electrode assembly (MEA) fuel cell set-up under various relative humidities and operating potentials to elucidate the range of proton transport mechanisms. Furthermore, various interlayers were added to the MEA to switch on and off the ion transport processes to separate Had surface diffusion from charged proton surface migration mechanisms.

Figure 1. SEM images of the Pt nanoelectrode array a) after 500 cycles showing a thickness of 8 µm b) honeycomb structured in-plane view after 500 cycles c) cross sectional side view of 5 µm after 300 cycles d) In-plane view of the nanoelectrode array after 300 cycles e) In-plane view of the nanoelectrode array fabricated using 100 nm pore sized AAO and 200 cycles.

References

K. C. Hess, W. K. Epting and S. Litster, Analytical Chemistry, 83, 9492 (2011).

P. K. Sinha, W. Gu, A. Kongkanand and E. Thompson, Journal of Electrochemical Society, 158, B831 (2011).

I. V. Zenyuk and S. Litster, Electrochimica Acta, 146, 194 (2014).

Figure 1
A Cathodic Electro-Fenton Catalyst Derived from Ionic-Liquid: Peroxide Generation and Di-Valent Iron Regeneration
Authors: Ko Young-Jin , Kim Hee-Gon , Choi Jae-Woo , Lee Wook-Seong , Hong Seok Won
Published: February 2020

The highly nitrogen-doped porous carbon materials for peroxide generation and di-valent iron regeneration were synthesized by the pyrolysis of ionic-liquid, which are precursor of carbon and nitrogen, using a silica nanoparticle template. In acidic solution, both of two/four electron oxygen reduction reaction (ORR) activities of ionic-liquid derived nitrogen-doped carbon catalyst increased significantly with pyridinic/graphitic N ratio in their structure. From the cyclic voltammogram, we confirmed that di-valent/tri-valent iron redox property enhanced with increasing surface carbonyl functional group, formed during removal of silica template. The degradation experiments of azo-dye and trace pharmaceutical compounds showed that the Fenton reaction (hydroxyl radical formation) drastically increased when double working electrodes (electrode 1: peroxide generation, electrode 2: di-valent iron regeneration) were used at the same time, and as a result, the removal efficiency was drastically increased. Based on the physical/electrochemical analysis, the ionic-liquid is a candidate precursor of highly nitrogen-doped carbon as energy effective electro-Fenton catalyst.

Acknowledgements

This work was supported by the Korea Ministry of Environment as a “Global Top Project” (Project No. 2016002190003).
Effect of Pretreatment on Carbon Materials
Authors: Singh Ashutosh Kumar , Yasri Nael , Karan Kunal , Roberts Edward P.L.
Published: February 2020

Carbon materials find application in numerous fields because of its large specific surface area, good electronic conductivity, inexpensive and inertness under corrosive conditions. These materials on appropriate pre-treatment have shown to give better performance which is attributed to different functional groups on surface. Surface functionalization, apart from showing improved performance also impact structure and charge carrier concentration of carbon materials and as we move towards large scale production there is a need to understand effect of these pretreatments to envision long term effects on device performance to minimize losses. We attempted to study, structural changes because of functionalization of carbon paper. Carbon paper electrodes are used widely for various electrochemical applications such as flow batteries, catalyst support in fuel cells, waste water treatment, Bioelectrochemistry. We employed Raman spectroscopy technique to study defects on carbon paper before and after functionalization and effect of these functionalization on charge carrier concentration. Carbon papers, pretreated employing different methods to study its effect on fibre structure in terms of defects and charge carrier distribution. This study could assist us to gain an important understanding on impact of conventional pretreatment methods being currently followed which is not ideal. This conventional pretreatment was also compared with nitrogen functionalization treatment which showed superior catalytic activity and a promising pretreatment method for large scale application.
Anodic TiO2 Nanotube Layers: Excellent Platform for Secondary Materials
Authors: Zazpe Raul , Sopha Hanna , Krbal Milos , Prikryl Jan , Macak Jan M.
Published: February 2020

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 10 years, which are motivated for their possible range of applications including photo-catalysis, solar cells, hydrogen generation and biomedical uses [1]. The synthesis of 1D TiO2 nanotube structure is carried out by a conventional electrochemical anodization of Ti sheet. The main drawback of TiO2 is its applicability in the UV light (wavelengths < 390 nm). In order to enhance the efficiency, TiO2 has been doped by N [2] or C [3] to shift its absorption into the visible light.

Except of doping, one of the major issues to extend the functional range of nanotubes is to coat homogenously tube interiors by a secondary material. It has been shown that additional ultrathin surface coating of TiO2 by secondary materials such as Al2O3 [4], ZnO [5] or MgO [6] annihilates electron traps at the TiO2 surface and thus increases the concentration of the photogenerated charge carriers. The presentation will focus in detail on the coating of the nanotube arrays by various secondary materials using ALD. The deposited materials influence strongly photo-electrochemical properties of nanotube layers. Experimental details and some very recent photocatalytic [7, 8], sensing [9] and solar cell [10] results will be presented and discussed.

References:

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Opin. Solid State Mater.
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C. Burda et al., Nano Lett. 3 (2003) 1049.

S. Sakthivel et al., Angew. Chem., Int. Ed. 42 (2003) 4908.

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Adv. Mater. Inferf., in press

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M. Krbal et al., Nanoscale 9 (2017) 7755
A Portable System for Plant Volatile Detection
Authors: Fang Yi , Ramasamy Ramaraja P.
Published: February 2020

Volatile organic compounds (VOCs) have been proven to be important biomarkers for predicting pathogen/pest-induced diseases in plants1. Methyl salicylate (MeSA) has been identified as one such important biomarker for biotic stress in plants2-4. Advanced detection of MeSA could help in early identification of plant diseases and has a profound significance for precision agriculture industry to maintain effective use for disease precautions. Previous research has demonstrated the development of biosensor consisting salicylate hydroxylase (SH) / tyrosinase (TYR) for salicylate detection. However, the method requires high temperature hydrolysis and pH neutralization steps before detection, rendering it more complex for device miniaturization5. In this project, we aim to eliminate these additional steps by developing a tri-enzyme detection platform consisting of esterase (ES), SH and TYR for direct MeSA detection without additional hydrolysis or pH neutralization steps. Two different immobilization strategies were used and compared using a lab-on-chip model and the sensitivity and specificity were determined to be 3.1 ± 0.2 µA·cm-2·µM-1 and 0.8 ± 0.2 µM respectively. An open source computer hardware and software Arduino was used for fabricating the computer-controlled automatic collection device for VOC collection. The prototype of a portable device for MeSA detection device was designed and fabricated, and the measurement was carried with the enzymatic biosensor strip.

Reference

(1) Laothawornkitkul, J., et al., Discrimination of plant volatile signatures by an electronic nose: a potential technology for plant pest and disease monitoring. Environmental Science & Technology, 2008. 42(22): p. 8433-8439.

(2) Buttery, R., et al., Characterization of some volatile constituents of bell peppers. Journal of Agricultural and Food Chemistry, 1969. 17(6): p. 1322-1327.

(3) Seskar, M., V. Shulaev, and I. Raskin, Endogenous methyl salicylate in pathogen-inoculated tobacco plants. Plant Physiology, 1998. 116(1): p. 387-392.

(4) Zhu, J. and K.-C. Park, Methyl salicylate, a soybean aphid-induced plant volatile attractive to the predator Coccinella septempunctata. Journal of chemical ecology, 2005. 31(8): p. 1733-1746.

(5) Fang, Y., et al., Detection of methyl salicylate using bi-enzyme electrochemical sensor consisting salicylate hydroxylase and tyrosinase. Biosensors and Bioelectronics, 2016. 85: p. 603-610.