bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-Life Lithium-Sulfur Batteries with a Bifunctional Cathode Substrate Configured with Boron Carbide Nanowires
Authors: Luo Liu , Manthiram Arumugam
Published: February 2020

Developing high-energy-density lithium-sulfur (Li-S) batteries relies on the design of electrode substrates that can host a high sulfur loading and still attain high polysulfide-retention capability. Recently, the application of transition-metal oxides, sulfides, carbides, and nitrides as sulfur cathode substrates has witnessed greatly improved polysulfide-retention capability by introducing Lewis acid–base interaction, forming strong chemical bonding, or exerting a catalytic effect on the diffusing polysulfides. Among them, transition-metal carbides such as TiC, Ti2C, Mo2C, and WC have been applied to sulfur cathode configurations and proved to be effective in improving the electrochemical functionality of Li-S batteries. However, most of them suffer from a critical drawback of low sulfur content (< 56 wt.%) and low sulfur loading (< 2 mg cm-2). Besides, most carbides have much higher density than sulfur, which also limits the sulfur content achievable. It is thus essential to explore lightweight, yet efficient, materials with a binder/current collector-free fabrication strategy to improve polysulfide-retention ability and realize acceptable electrochemical performance with Li-S batteries. Boron carbide (B4C), due to its low density (~ 2.5 g cm-3), good conductivity (1.25 ~ 3.33 S cm-1), and superior catalytic effect, is a promising candidate for battery applications. Herein, for the first time, the lightweight B4C substrate is successfully applied in the Li-S system by a facile catalyst-assisted fabrication process and in-situ grown on carbon-nanofibers (CNF) to form a free-standing bifunctional cathode substrate (B4C@CNF). The B4C nanowires acting as chemical-anchoring centers provide strong polysulfide adsorptivity, as validated by experimental adsorption test and first-principle calculations. Meanwhile, the catalytic effect of B4C also accelerates the redox kinetics of polysulfide conversion, contributing to improved active-material utilization and enhanced rate capability. As a result, a remarkable capacity retention of 80% after 500 cycles, a low capacity-fading rate of 0.04% per cycle, and good cyclability at varying cycling rates (C/20 – 4C) are accomplished with the cells employing B4C@CNF as a cathode substrate for sulfur. Moreover, the B4C@CNF substrate enables the cathode to achieve both high sulfur content (70 wt.%) and sulfur loading (10.3 mg cm-2) in coin cells, delivering a superb areal capacity of 9 mA h cm-2. Additionally, the B4C@CNF substrate is further applied to pouch cells with a high sulfur mass (40 – 200 mg per cathode), delivering high discharge capacities (40 – 160 mA h) with good cyclability (50 – 100 cycles). This work presents a strategy to construct high-loading cathodes for practically viable, high-performance Li-S batteries.

Figure 1
Atomic Layer 2D MoS2 Coated Li-Metal for Advanced Li-Metal Rechargeable Batteries
Authors: Choi Wonbong
Published: February 2020

Rapidly increasing markets for electric vehicles (EVs), energy storage for backup support systems and high-power portable electronics demand batteries with higher energy density, higher power density, and longer cycle life. The success of Li-S cells depends in large part to the utilization of metallic lithium as anode material. Metallic lithium, however, is prone to grow parasitic dendrites and is highly reactive to several electrolytes; it is also susceptible to polysulfides when used in Li-S cells. Here, we show that a ~10 nm thick 2D MoS2 can act as a protective layer for Li-metal anodes, greatly improving the performances of Li-S batteries [2, 3]. In particular, we observe stable Li electrodeposition and the suppression of dendrite nucleation sites. The deposition and dissolution process of a symmetric MoS2 coated Li-metal cell operates at a current density of 10 mA cm-2 with low voltage hysteresis, and a three-fold improvement in cycle-life than using bare Li-metal. In a Li-S full cell configuration, using the MoS2 coated Li as anode and a 3D carbon nanotube-sulfur cathode, we obtain a specific energy density of ~600 Wh kg-1 and a Coulombic efficiency of ~98% for over 1200 cycles at 0.5 C. Our approach can lead to the realization of high energy density and safe Li-metal based rechargeable batteries.

Figure. Long-term cycling performance of Li–S battery with the MoS2-coated Li anode measured at 0.5 C for 1,200 cycles [3]

References:

High performance rechargeable Li-S batteries using binder-free large sulfur-loaded three- dimensional carbon nanotubes, M Patel, E Cha, C Kang, B Gwalani, W Choi, Carbon http://dx.doi.org/10.1016/j (2017)

Recent development of 2D materials and their applications, Wonbong Choi, Nitin Choudhary, Juhong Park, Deji Akinwande, Younghee Lee, Materials Today, 116-130, 20, (2017).

2D MoS2 as an efficient protective layer for lithium metal anodes in high performance Li-S batteries, Cha, E., Patel, M.D., Park, J., Hwang, J., Prasad, V., Cho, K., and Choi, W., Nature Nanotechnology, 13, pages337–344 (2018).

Figure 1
Opportunity for High Performance Lithium-Metal Batteries Enabled By in Situ Formation of Highly Stable Solid Electrolyte Interphase Layer
Authors: Park Seong-Jin , Lee Seon-Hwa , Sun Yang-Kook
Published: February 2020

Lithium(Li)-metal has been considered most promising candidates as anode to increase the energy density of Li-ion batteries because of its ultrahigh specific capacity (3,860 mAh g-1) and lowest redox potential (-3.040 V vs SHE).1 However, unstable dendritic electrodeposition, low Coulombic efficiency and infinite volume changes severely hinder its practical uses.2 To stabilize the Li metal anode , the electrolyte used in this study, consisting of ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC), ensures a stable robust solid electrolyte interphase (SEI) layer on the anode surface. In a LMBs using a commercialized Ni-rich Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) and 1M LiPF6 in EMC : FEC = 3 : 1 electrolyte exhibit a high initial capacity of 1.8 mAh cm-2 with superior cycling stability and high Coulombic efficiency above 99.8 % for 500 cycles while delivering a unprecedented energy density. The present work also highlights a significant improvement in scaled-up pouch-type Li/NCM622 cells. Moreover, the postmortem characterization of the cycled cathodes, separators and Li-metal anodes collected from the pouch-type Li/NCM622 cells helped identifying the improvement or degradation mechanisms behind the observed electrochemical cycling.3

References

A. Varzi, R. Raccichini, S. Passerini, B. Scrosati, J. Mater. Chem. A
2016, 4, 17251-17259.

W.-J. Kwak, S.-J. Park, H.-G. Jung, Y.-K. Sun, Adv. Energy, Mater.
2018, 8, 1702258.

S.-J. Park, J.-Y. Hwang, C. S. Yoon, H.-G. Jung, Y.-K. Sun, ACS Appl. Mater. Interfaces 2018, 10, 17985-17993.
In-Situ Growth of Conductive Copper Metal Organic Framework on Silicon Nanoparticles for High Performance Lithium Ion Batteries
Authors: Nazir Aqsa , Park Chan-Jin
Published: February 2020

The race in developing rechargeable lithium ion batteries (LIBs) with higher capacity and longer cycle life is getting severer. Currently, LIBs are the ideal choice as power source ranging from portable electronic devices to electric vehicles (EVs) and implantable medical devices. However, conventional LIBs are not enough to satisfy the consumer’s demands due to the inherent capacity restriction of conventional electrode materials such as graphite. Si, which can form alloys with Li at low electrode potential, has ability to substitute the carbon based anodes due to its high theoretical specific capacity (4200 mAh g−1, almost 10 times higher than the commercial carbon anode), natural abundance (27.7%, Si is the second most abundant element in earth) and environmental friendliness. However, the cyclability and capacity of bare Si based electrodes are still insufficient. In actual, poor Li diffusivity, intrinsic low electrical conductivity, and large volume variation (>400%) during alloying have restricted the practical application of Si based electrodes. Thus far, to address all these issues, scientists have focused on making Si nanostructures (nanowires, nanorods, nanotubes, and nanoparticles) and using carbon s. Nevertheless, for Si anode, to prevent the capacity fading and maintain longer cycle life to the level comparable to that of graphite, a breakthrough is needed.

In the present work, we introduce in-situ growth of novel two dimensional conducting copper metal organic framework (MOF) on Si nanoparticles for high power density and longer cycle life. The Cu MOF exhibited two dimensional network structure around the Si nanoparticles. Although carbon offers low capacity, its presence around the Si nanoparticles in MOF form can function as a mechanical support against volume expansion and may provide an effective electron conducting route. In this way, MOF coated Si electrode could show structural stability. Furthermore, the porous carbon framework of MOF with evenly distributed Cu metal cores was also advantageous for improving conductivity and Li storage of Si anode. A full cell composed of MOF coated Si anode and LiCoO2 cathode with better cycle life and rate capability is also demonstrated.
The Reaction between Metal Disulfides Interlayer and Polysulfides in Lithium-Sulfur Batteries
Authors: Paolella Andrea , Zaghib Karim
Published: February 2020

Many scientists think that in Li-S batteries polysulfides have catalytic[1-2] reactions when are in contact with heterogeneous separators. In our work[3], we investigated the reactivity of layered metal disulfides MS2 (M=W,Mo) as interlayer in a Li–S battery and observed a reduction chemical reaction involving the removal of metal ions by polysulfides after a chemical (and not catalytic) reaction. Interestingly we observed the formation of metallic tungsten nanoparticles (confirmed by ex situ Transmission Electron Microscopy characterization) in the sulfur cathode is the result of tungsten ion oxidation reaction and their subsequent recrystallization during discharge. In situ Raman spectroscopy technique shows i) the efficacy of WS2 separator to filter and suppress polysulfides at lithium metal side (and then shuttle reaction) and ii) the polysulfides species involved in heterogeneous chemical reaction between interlay WS2 and polysulfides.

References

Thangavel, N. K., Gopalakrishnan, D., Mohana, L. & Arava, R. Understanding Heterogeneous Electrocatalysis of Lithium Polysulfide Redox on Pt and WS 2 Surfaces. J. Phys. Chem. C 121, 12718–12725 (2017).

Lei, T. et al. Multi-Functional Layered WS 2 Nanosheets for Enhancing the Performance of Lithium – Sulfur Batteries. Adv. Energy Mater. 1601843 (2016). doi:10.1002/aenm.201601843

Paolella, A. et al. The Role of Metal Disulfide Interlayer in Li − S Batteries. J. Phys. Chem. C 122, 1014–1023 (2018).
On the Potentialities of Lithiated Iron Hydroxisulfides for Lithium Ion Battery
Authors: Mir Caroline , Giaume Domitille , Chakir Mohamed , Barboux Philippe
Published: February 2020

LiFeOHCh family of materials is a family of materials developed for supraconductivity application, linked with iron mixed valence properties 1. In this paper, we present their great opportunity as active material for lithium ion batteries. The electrochemical characterizations show a sustainable reversible capacity of 250 mAh/g at C/10 (up-taking 1Li at an average potential of 1.65V) and interesting performances in quick charge with 230 mAh/g at 1C and 130 mAh/g at 5C, putting this material as a good challenger of Li4Ti5O12
2. The lithiation mechanism of this material through cycling has been investigated and shows very original results: insertion of lithium and reduction of the hydroxyl into gaz hydrogen H2.

Zhou, X. et al. Superconductivity and magnetism in iron sulfides intercalated by metal hydroxides. Chem. Sci.
8, 3781–3788 (2017).

Sun, X. Advances in spinel Li4Ti5O12 anode materials for lithium-ion batteries. New J. Chem.
39, 38–63 (2014).

Figure 1
(Invited) Controlling Nanotube-Nanotube Interactions in Carbon Nanotube Networks: Implications for Energy Transport and Harvesting
Authors: Ferguson Andrew John , Blackburn Jeffrey L.
Published: February 2020

While the unique chemical and physical structure of semiconducting single-walled carbon nanotubes (s-SWCNTs) were identified decades ago, marking these nanoscale materials as promising candidates for constituents in a variety of optical and electronic applications, the ability to generate high-purity samples has hampered efforts to validate these expectations. The intervening years have played witness to a number of elegant enrichment strategies aimed at extracting tailored semiconducting SWCNT species from the raw soot, from the use of subtly tunable surfactant interactions to the exploitation of specific DNA sequences. In contrast, we employ an enrichment approach based on conjugated polymers, typically derived from the fluorene moiety, since they show great promise with regards to their high selectivity and viability for scalable manufacturing approaches.

As alluded to above, these fluorene-based (co-)polymers confer solubility on the s-SWCNT species, allowing for the preparation of highly enriched s-SWCNT dispersions that can be deposited using a variety of solution-processing approaches. Unfortunately, the strong van de Waals forces between the π-electron systems of the polymer and SWCNT that enable the selective extraction of semiconducting SWCNTs with high purity also make removal of the polymer difficult. Since these polymers typically have a wide bandgap they can act as an insulating coating on the surface of the individual SWCNTs within functional networks, inhibiting the transport of energy in the form of excitons and/or charge carriers.

Here we demonstrate approaches that allow us to replace the strongly-bound polymers with derivatives that can be removed using simple solution-based chemical strategies, resulting in networks with modified energy transport properties. We show that removal of the polymer results in a significant enhancement of the charge carrier mobility and electrical conductivity in doped s-SWCNT networks. Finally, we extend the approach to samples strongly enriched in a single chiral s-SWCNT species, which allows us to employ transient spectroscopic techniques to probe exciton transport within the s-SWCNT network with high spectral fidelity. We show that the efficiency of exciton transport is subtly dependent on the complex interplay between polymer removal and carbon nanotube bundling. Our studies highlight a methodology by which high-performance s-SWCNT thin films can be prepared and discuss the implications of our findings on the potential to realize their promise for electronic and optoelectronic applications.
FET Based Heavy Metal Ion Selective Sensors for Lead Ion Detection in Whole Blood
Authors: Wang Shin-Li , Hsieh Ching-Yen , Wang Yu-Lin
Published: February 2020

With significant industrial development, heavy metal pollution is worsening and causing serious environmental and health issues. Until now, if people want to check for heavy metal contamination in their environment, they have to send the sample to laboratory, and wait for several days to get back the results. In this study, we developed a lead ion selective sensor which can rapidly detect lead ion in whole blood, in the convenience of home/office. Previously, our group developed a high sensitivity FET biosensor to detect proteins in physiological fluids. Following this methodology we had developed ion selective membrane (ISM) FET sensor for heavy metal ion detection in tap water. The present research combines novel extended gate FET structure and lead ISM, and demonstrates the detection of lead ion in whole blood. The ion selective sensor consists of ISM, narrowly separated metal electrodes and field effect transistor (FET) for signal transduction. In this structure, there are two gold electrodes on the epoxy substrate, one is sensing electrode and another one is reference electrode. The sensing electrode is connected to the FET, and we apply short pulse gating voltage to the reference electrode. The high field modulation of FET enables good signal to noise ratio. The ion selectivity membrane (ISM) consists of lead ionophore IV, tetraphenylborate, 2-Nitrophenyl octyl ether (2NOE) and Poly vinyl chloride (PVC). The ISM is selectively immobilized on the reference and sensing electrodes. In order to avoid the interference of cells in whole blood during the electrical measurement, we will invert the chip to faces downwards, to gravitationally separate the cells, allowing only blood plasma to contact the ISM. Our ISM-FET sensor has a short response time of 15 minutes, and the operation method is quite easy and convenient which is suitable for home-care, as opposed to laboratory standard equipment like ICP-MS. This ion selective sensor has a comparable detection limit with ICP-MS (detection limit of Pb2+: 10-10 M).

Figure 1
(Keynote) Nature Communications: Overview and Research Highlights
Authors: Brant Jacilynn
Published: February 2020

Nature Communications is an open access, multidisciplinary journal that is dedicated to publishing high-quality research from all areas of the natural sciences, including solid-state electronics and photonics. This presentation will include an overview of publishing in Nature Communications as well as other Nature journals. Recent publications on self-powered devices, triboelectric nanogenerators, energy harvesting, wearable devices, etc. will be highlighted.
(Invited) Single Nanoarray Sensor for Multi-Analyte Detection
Authors: Gao Pu-Xian
Published: February 2020

Chemical sensors usually adopted a single resistance-metric mode, which has a drawback of significant cross-sensitivities in mixed analytes scenario, thus showing a poor selectivity towards target analytes. By integration of multiple sensors in a so-called sensor array platform, multi-analyte detection and enhanced selectivity can be achieved. However such a strategy requires significant device integration work involving sophisticated electrical interconnects with increasing circuit complexity. In the past few years, we has been focused on establishing a multi-mode sensing platform based on a single nanostructure array (nanoarray) device. Such a single device platform can be operated at variable temperatures with different modes such as photocurrent, resistance, and impedance. These nanoarray sensors have been fabricated with good scalability using a variety of synthetic methods ranging from vapor to solution phase depositions. The array composition could be rationally designed from pristine homogeneous to dissimilar heterogeneous across metals, ceramics, and polymers. Depending on the comprised material composition, decoration of a nanolayer of perovskite, metal oxide, or noble metal may enable formation of electronic and catalytic sensitizers, as well as hetero-contacts that can drastically boost sensor performance under various gaseous analyte atmospheres. Toward mixed multi-analyte conditions, such a new type of multi-mode nanoarray sensors allows selective and sensitive detection of multiple chemical species in a single-device configuration. By relating the multiple sensing modes using a single nanoarray sensor, efficient and selective detection of multiple gas analytes has been accomplished. A database was established based on multiple sets of data, namely the sensitivities for different analytes obtained from the outputs of different sensing modes. The signals of multiple gas analytes could be differentiated through the principal component analysis process. The linear and non-linear decision boundaries could be readily derived for pattern recognition, and the multi-analyte quantification and detection.
Enhancing the Hydrogen Evolution Reaction with Alloy-TiO2 Composites
Authors: Wang Cheng , Zhang Yujia , Podlaha Elizabeth J.
Published: February 2020

Titania particles embedded into metals that are known hydrogen evolution reaction (HER) electrocatalysts have been shown to further accelerate HER in a number of different systems. In the case of electrodeposited Ni-W-TiO2, the improved HER was attributed to surface roughening,1 in a report of Ni-P-TiO2 nonstoichiometric oxides were responsible for facilitating H reduction/adsorption,2 sol-gel prepared Ni-TiO2 and Ni-Co-TiO2 with and without carbon nanotubes also showed enhanced HER thought to be due to a hypo–hyper d-electronic configuration effect,3 and reports of an electrodeposited Ni-Mo-TiO2 composite attributed HER enhancement with titania to changes in Ni-Mo composition, porosity and surface roughening.4 In order to better understand this phenomenon, two different alloy systems, Ni-W and Co-Mo, were electrodeposited in an electrolyte containing titania to fabricate the alloy composites. The HER behavior was characterized with and without TiO2 in an alkaline electrolyte. Alloys and composites with low amounts of TiO2 ~ 1-5 wt % were galvanostatically deposited onto copper rotating cylinder electrodes. The HER behavior was also characterized with the working electrode rotated to ensure the elimination of mass transport effects. The compositional target of the alloys were those with comparable amounts of W (in Ni-W) and Mo (in Co-Mo) to achieve favorable HER even without TiO2 addition. The presence of the titania particles in the electrodeposition electrolyte influenced both the HER occurring during electrodeposition from a citrate-boric acid electrolyte and the metal partial current densities. HER in a sodium hydroxide electrolyte was indeed enhanced with the TiO2 composites. The composites exhibited a favorable decrease in the HER overpotential, HER Tafel slope and in some cases an increase in the exchange current density when the electroactive area and alloy metal ratio was the same. The results confirm a dominant Volmer-Heyrovsky type of HER mechanism. There is a similarity between both the reduction reactions occurring during the electrodeposition fabrication process and the HER alone in the alkaline electrolyte; in both cases it is hypothesized that TiO2 reduces adsorbed species that facilitates the electrochemical reactions during deposition of the composites and also helps to promote the HER in an alkaline electrolyte.

References

Y. Zou, Z. Xiao, X. Fei, X. Ren, Materials Protection
37 24–26 (2004).

B. Łosiewicz, A. Budniok, A. Lasia, and E. Łągiewka, Polish Journal of Chemistry
78, 1457-1476 (2004).

P. Paunović, O. Popovski, A. Dimitrov, D. Slavkov, E. Lefterova, S. H. Jordanov, Electrochimica Acta
52 1810-1817 (2006).

A. R. Shetty, A. C. Hegde, Materials Science for Energy Technologies
1, 97-105 (2018).
(Invited) Fundamental Insights into Catalyst Stability in Low-Temperature Electrolysis
Authors: Mayrhofer Karl , Cherevko Serhiy , Kasian Olga , Geiger Simon , Ledendecker Marc
Published: February 2020

Stability of catalyst materials during operation is essential for long-term operation of large-scale chemical reactors. This is particularly true for costly electrochemical reactors and their harsh reaction conditions in terms of potential and pH, as for instance also occurring during low temperature electrolysis. Fundamental studies can provide quick and deep insights into material performance, optimized operation conditions, or degradation mechanism and extent, which altogether can contribute to the development of improved materials and membrane-electrode assemblies. In this presentation I will show recent results with a special focus on catalyst dissolution during oxygen and hydrogen evolution in electrolysis. I will discuss denominators for the assessment of stability of novel materials, degradation mechanism, measurement artifacts and pitfalls, as well as the relevance of the results for reactor operation.
Synthesis of Co-Fe Alloy 1D Nanocone Array Electrodes with Aluminum Oxide Template for Water Spliting Reaction.
Authors: Skibinska Katarzyna , Kutyla Dawid , Kolczyk Karolina , Kowalik Remigiusz , Zabinski Piotr
Published: February 2020

Nanostructured materials have an enormous application potential because of their novel physical and chemical properties which appear upon reduction of the length scales toward a few nanometer. Among the nano-structured materials, nano-cone arrays have received particular attention in the last years. Due to their specific structure and properties, nano-cones are attractive for very different applications. Producing and designing proper nano-crystalline structures could further improve the catalytic properties and replace expensive precious metals (platinum). Hence, the fabrication of Co alloy nano-cones opens the window to promising applications in the field of electrocatalysis

Porous anodic aluminum oxide (AAO) is a popular template for synthesis of ordered arrays of nanostructured materials. By the controlling of anodization conditions or applying an appropriate post-anodization treatment the internal pore structure can be changed. Conical pores can be obtained basing on alternating repetition of the anodization and pore widening process during fabrication of AAO. To obtain free standing metallic nanocones the Al2O3 template was chemically etched in dilute phosphoric acid solution.

In this case the process of cobalt electrodeposition was carried out in a two-electrode cell. The working electrode was AAO sample, the anode was a platinum plate. Influence of temperature and H3PO4 and H2SO4 solutions in the first step of anodization was examined. An attempt was made to synthesize Co based alloy nanocones.

Acknowledgement

This work was financially supported by Polish National Science Center (NCN) under grant UMO-2016/23/G/ST5/04058. The authors would like to acknowledge the COST MP1407 Action for networking.
Mechanistic Investigation with Kinetic Parameters on Water Oxidationcatalyzed By Manganese Oxide Nanoparticle Film
Authors: Seo Hongmin , Jin Kyoungsuk , Park Sunghak , Cho Kang Hee , Lee Kang-Gyu , Nguyen Đăng Thành , Lee Jong-Sook , Nam Ki Tae
Published: February 2020

Water electrolysis has been regarded an attractive approach to produce sustainable energy without undesirable byproducts. The anodic half reaction, oxygen evolving reaction (OER), is a major bottleneck for overall water electrolysis process because of its complex four electron transfer steps and high activation energy for O-O bond formation. Thus, transition-metal-based film-type electrocatalysts have been extensively reported with moderate efficiency due to their low price and abundance. Interestingly, transition metal based OER catalyst film generally exhibited optimal catalytic performance at considerable thickness (~ hundreds nanometers). The overall catalytic performance for the film-type catalysts are determined by various electrochemical processes, such as surface catalysis and electron transport. Therefore, to establish rational design rule for efficient OER electrocatalyst, it is necessary to extract well-defined kinetic parameters describing each electrochemical processes. In this regard, electrochemical impedance spectroscopy (EIS) is effective analysis to decouple and parametrize complicated electrochemical behavior in the catalyst film during OER.

Here, we conducted EIS analysis for sub 10 nm-sized partially oxidized MnO nanoparticles (Mn-oxide NPs) operating with superb activity under neutral condition. Furthermore, we proposed a transmission line model with Havriliak-Negami capacitors to obtain reliable kinetic parameters for OER on the Mn-oxide NPs film. From this analysis, we explained the rationale for the optimum thickness. Also, we revealed that protons are involved in transport on the surface of p-MnO NPs, which directly proved the ongoing hypothesis of the oxo-hopping mechanism during catalysis. Furthermore, from correlation between the reaction rate constant (22.1 s-1 at 1.35 V vs. NHE) and TOF values, only small ratio of Mn sites served as factual active sites for OER. We believe that this mechanistic investigation using EIS analysis with our circuit model could be an effective platform to investigate comprehensive electrochemical processes in general film-type electrocatalysts.

Figure 1
Graphene-Dot Wrapped PtMo Nanosponge As a Highly Efficient Electrocatalyst for Hydrogen Evolution Reactions in Both Acidic and Alkaline Media
Authors: Nguyen Van-Toan , Nguyen Ngoc-Anh , Ali Yousuf , Choi Ho-Suk
Published: February 2020

A three-dimensional PtMo nanosponge wrapped with ultra-thin layers of graphene dots (denoted as 3D PtxMo1-x@graphene) has been developed for catalysis of the hydrogen evolution reaction (HER). The graphene-dot wrapping carries out by exfoliating carbon dots during the co-reduction of Pt and Mo precursors at a low temperature in an aqueous solution. The outstanding HER performance and superb durability, in both acidic and alkaline electrolytes, are attributed to the synergistic effects of inner metallic alloy networks and outer graphene dots in the 3D PtxMo1-x@graphene. The 3D PtxMo1-x@graphene reveals a low Tafel slope together with a low overpotential to produce a current density of -10 mA cm-2 in acidic media. Especially, the 3D PtxMo1-x@graphene catalyst overcomes a large amount of repeated potential cycling exceeding 5000 cycles in acidic solution and long-term durability of over 50,000 seconds in an alkaline solution. This work addresses a new feasible approach of synthesis of graphene-dot-wrapped Pt-based nanostructures with highly efficient catalytic activity and superior stability for HER without using surfactants or stabilizers.
Preparation of Sb-Doped SnO2 Nanoparticle with High Surface Area for Use As a Stable Anode Catalyst Support for PEM Electrolyzers.
Authors: Zhou Xiangyang , Li Bing , Yang Daijun , Lv Hong , Zhang Cunman
Published: February 2020

Proton exchange membrane (PEM) water electrolysis has been considered as one of the most promising technologies for large H2 production. While the cost and stability of PEM are the main obstacles for the commercial application. Here we report a cost-effective catalyst, which consists of IrO2 nanoparticles supported on Sb-doped SnO2 (ATO). ATO support is synthesized by using templating process and hydrothermal method to improve its thermal stability. It has a mesoporous structure, small particle size, and high surface area. After loading IrO2 via Adams fusion method, the IrO2/ATO catalyst shows high electrochemical stability, according to repetitive potential cycling. This catalyst also shows a good electrochemical performance in single cell.

Firstly, we prepared a series of ATO samples and named them as the Brunauer Emmett Teller model (BET) surface area. The surface area and pore size distribution of the obtained ATO samples were calculated by BET and nonlocal density functional theory (NLDFT). As shown in Fig.1a, the pore size become smaller with the increases of BET surface area, and the high surface area may be contributed to high synthesize temperature and long synthesize time. Secondly, we use the as-prepared ATO samples as catalysts support for IrO2, the catalysts named as BET surface area-IrO2 (e.g. 107-IrO2) and the IrO2 loading is 40 wt%. Fig.1b shows the cyclic voltammetry (CV) performance of different catalysts, it is quite clear that when supported by ATO, the voltammograms of these supported catalysts are dissimilar in shape from that of unsupported IrO2. The electrochemically active surface area (ECSA) of 170-IrO2 is obvious higher than the other ATO supported catalyst and a little higher than pure IrO2. This indicate that the 170 sample has the appropriate surface area as well as pore size distribution and it is best used as for IrO2 catalyst support. Finally, the accelerated degradation testing (ADT) was performed to investigated the durability of the 170-IrO2 catalyst in rotating disk electrode (RDE) test. As shown in Fig.1c the CV curves almost overlap before and after 9000 cycles’ ADT. Fig.1d shows the Linear sweep voltammetry (LSV) results of the catalyst samples before and after ADT. It is quite obvious that the 170-IrO2 catalyst is maintained stable with only a little loss in the catalytic activity.

We have successfully made a series of ATO through templating process followed by hydrothermal method with different BET surface area and used as catalyst support for IrO2. The 170-IrO2 catalyst demonstrates high electrochemical performance and good stability. Herein, the as-synthesized ATO is considered to be a promising oxygen evolution catalyst support for solid polymer electrolyte water electrolyzer applications.

Figure 1
A NOVEL CELL Design of Alkaline-Based ZINC -Iodide FLOW Battery for Enhancing Energy and POWER Performance
Authors: Pham Hiep , Landers Robert G. , Park Jonghyun
Published: February 2020

An alkaline-based Zinc-Iodide Flow Battery (ZIFB) is considered one of the promising electrochemical energy storage devices with a prospective application in the transport systems due to their high specific energy. To improve the battery performances of this zinc-iodide system, numerous researches have been conducted by considering new materials, electrode structures, various system design and operating conditions. However, there is a very useful prospect to adopt alternative cell geometries that can produce higher power per cell unit volume and/or reduce the overall system cost to commercialize the product. In this work, a novel cell structure is designed for ZIFB, which includes embedded serpentine flow channels in a non-porous and non-brittle case. This new design eliminates end plates and gaskets to improve safety, extend life, and promote ease of assembly with fewer components than traditional ZIFB cells. In particular, a key challenge of conventional graphite flow field plates in which solution penetration can occur due to an easily broken and porous structure is solved by using rigid impermeable polyvinyl chloride (PVC) sheets with flow channels embedded in the sheets. Various tests, such as cycling and polarization measurements of a wide range of current and flow rates, and Electrochemical Impedance Spectroscopy (EIS) for internal resistance analysis, are performed to compare new and traditional designs. The results show that the new design keeps cycling performance stable, with better stability and energy efficiency, than conventional ZIFB cells do. High power performance is also observed for the same external cell size. In addition, an abrupt potential drop caused by high contact resistance between the current collector and a porous electrode is solved by introducing a layer of the patterned graphite sheet to improve contact and electronic conductivity and, also, to function as a flow channel.
Two-Phase Flow Characterization in PEM Fuel Cells Using Machine Learning
Authors: Santamaria Anthony D. , Mortazavi Mehdi , Chauhan Vedang , Benner Jingru
Published: February 2020

Two-phase flow pressure drop in PEM fuel cells remains a critical area of research as next generation high power density systems are developed. The dynamic behavior of water in PEM fuel cell flow channels is complex due to a wide range of flow-field designs and electrode materials. Many experimental and numerical studies have been carried out to understand the underlying physics. As researchers are working to gather more data, this work proposes to use machine learning, specifically artificial neural networks (ANNs), to analyze two-phase data sets. The data of interest is the distribution of liquid water in a flow-field and the two-phase pressure drop down it. A transparent single channel flow-field was constructed and a digital syringe was used to inject water through the gas-diffusion layer simulating PEM fuel cell operation. A CCD camera was placed above the flow-field and images of the liquid distribution were gathered. Simultaneously, the two-phase pressure drop was measured using pressure transducers at the inlet and outlet of the channel. The images were post processed to differentiate liquid water from background and the processed images and pressure data were used to train an ANN in MATLAB. The resulting model utilizes an image of the flow-field water distribution as input and predicts the pressure drop as an output. The model may be used to test the effect of actual or artificial water distributions to understand fundamentally how a flow-field geometry and material handles flooding as well as to generate phase diagrams. Early results show these methods may be used to guide novel flow-field design and characterization as well as be implemented in advanced PEM fuel cell control algorithms to prevent flooding.

Figure 1
MOF-Derived Alloy Nanoparticles for Highly Durable Fuel Cell Electrocatalysts
Authors: Yoo Ji Mun , Chung Dong Young , Ahn Chi-Yeong , Sung Yung-Eun
Published: February 2020

Tailoring material properties of electrode is of great importance because both high activity and durability are required for oxygen reduction electrocatalysts in a fuel cell. However, effective strategy for rational material design should be developed to guarantee stable long-term operation of active electrocatalysts, which unfortunately has been overlooked often.

Here, we report an effective strategy of utilizing metal-organic framework (MOF) as precursor for multimetallic alloy nanocrystals. Due to its coordinated metal and N-containing organic molecules, MOF is a highly desirable material to make nanocrystals hybridized with N-doped carbon via simple heat treatment. With delicate selection of composition and controlled heat treatment condition, highly durable and active alloy nanoparticles were successfully derived and showed excellent electrochemical stability in oxygen reduction reaction. This strategy was also extended to other electrocatalysis too, where alloy nanocrystals coated in the N-doped carbon layers shows excellent durability for long term operation. Through this study, we highlight the rational design for highly durable and active electrocatalysts.
(Invited) Bioinspired Water Oxidation Electrocatalysts Based on Manganese Oxide
Authors: Nam Ki Tae
Published: February 2020

Water splitting is regarded as a promising step towards environmentally sustainable energy schemes. The oxygen evolution reaction (OER) requires extremely high overpotential due to its slow reaction kinetics. The water oxidizing cluster in photosystem II, in the form of cubical Mn4CaO5 cluster, efficiently catalyzes water oxidation. Inspired by Mn4CaO5 cluster, we previously identified a new crystal structure, Mn3(PO4)2-3H2O, and demonstrated its superior catalytic performance at neutral pH. We revealed that structural flexibility can stabilize Jahn-Teller distorted Mn(III), and thus facilitate Mn redox during catalysis. Additionally, we verified influence of Mn valency and asymmetric geometry on water oxidation catalysis using Li2MnP2O7and its derivatives.

Next, we translate the underlying principles in Mn4CaO5 cluster into synthetic heterogeneous catalysts. Sub-10 nm-sized monodispersed partially oxidized manganese oxide nanoparticles were shown to exhibit not only superior catalytic performance for oxygen evolution, but also unique electrokinetics, as compared to their bulk counterparts. In the present work, the water-oxidizing mechanism of partially oxidized MnO nanoparticles was investigated using integrated in situ spectroscopic and electrokinetic analyses. We successfully demonstrated that, in contrast to previously reported manganese (Mn)-based catalysts, Mn(III) species are stably generated on the surface of MnO nanoparticles via a proton-coupled electron transfer pathway. Furthermore, we confirmed as to MnO nanoparticles that the one-electron oxidation step from Mn(II) to Mn(III) is no longer the rate-determining step for water oxidation and that Mn(IV)═O species are generated as reaction intermediates during catalysis.
Conformal and Continuous Deposition of Bifunctional Cobalt Phosphide Layers on p-Silicon Photocathodes for Improved Solar Hydrogen Evolution
Authors: Liu Lifeng , Thalluri Sitaramanjaneva Mouli
Published: February 2020

p-Silicon (Si) has been extensively investigated in recent years as a promising photocathode for solar-driven hydrogen evolution. However, it remains challenging to fabricate Si photocathodes having both high photoelectrocatalytic activity and long-term operational stability through a simple and affordable approach. Herein, we report conformal and continuous deposition of a di-cobalt phosphide (Co2P) layer on lithography-patterned highly-ordered Si nanowire (SiNW) arrays via a cost-effective drop-casting method followed by a low-temperature phosphorization treatment [1]. The as-deposited Co2P layer consists of crystalline nanoparticles and has an intimate contact with SiNWs, forming a well-defined SiNW@Co2P core/shell nanostructure. The conformal and continuous Co2P layer endows dual functions: on the one hand, it serves as a highly-efficient catalyst capable of substantially improving the photoelectrocatalytic activity towards the hydrogen evolution reaction (HER); on the other hand, it can effectively passivate SiNWs to protect them from photo-oxidation, thus prolonging the lifetime of the electrode. As a consequence, when used for solar-driven hydrogen evolution, the SiNW@Co2P photocathode with an optimized Co2P layer thickness exhibits a high photocurrent density of -21.9 mA cm-2 at 0 V versus reversible hydrogen electrode (RHE) and excellent operational stability of up to 20 hours, outperforming many nanostructured silicon photocathodes reported in the literature. Furthermore, we fabricate inverted pyramid textured Si (SiIP) photocathodes coated with a conformal and continuous layer of Co2P [2], which show a photocurrent density as high as -35 mA cm-2 and can constantly split water up to 150 hours without obvious degradation. The combination of passivation and catalytic functions in a single continuous layer represents a promising strategy for designing high-performance semiconductor photoelectrodes for use in solar-driven water splitting, which may simplify the fabrication procedures and potentially reduce the production cost.

Acknowledgement

This work was funded by ERDF funds through the Portuguese Operational Programme for Competitiveness and Internationalization COMPETE 2020, and national funds through FCT – The Portuguese Foundation for Science and Technology, under the project “PTDC/CTM-ENE/2349/2014” (Grant Agreement No. 016660). The work is also partially funded by the Portugal-China Bilateral Collaborative Programme (FCT/21102/28/12/2016/S).

References:

[1] S. M. Thalluri, J. Borme, K. Yu, J. Y. Xu, I. Amorim, J. Gaspar, L. Qiao, P. Ferreira, P. Alpuim, L. Liu, Nano Res. 11 (2018) 4823.

[2] S. M. Thalluri, B. Wei, R. Thomas, L. Qiao, Z. C. Wang, L. Liu, Small submitted.
Probing Adsorption on Platinum Group Metals to Understand Fuel Production Via Electrocatalytic Reduction
Authors: Richards Danielle , Akinola James , Liu Jin-Xun , Goldsmith Bryan , Singh Nirala
Published: February 2020

Renewable electricity generated from solar or wind is inherently intermittent, so finding routes to electrochemically store this energy in chemical bonds as fuels or chemicals is an important scientific challenge. For electrocatalytic reduction reactions such as bio-oil hydrogenation1,2 or nitrate conversion to ammonia,3 the rates and efficiency of converting electricity to energy stored in chemical bonds is related to the surface chemistry steps. A particular challenge in understanding and controlling these surface chemistry steps at a molecular level for electrocatalysis is that the complexity of the liquid phase makes it hard to characterize the catalyst surface and adsorbed species. A further challenge is that it is unclear when insight from first-principles calculations such as density functional theory will apply to electrocatalysis, because modeling solvation and the double layer accurately remains a matter of intense effort.

In this talk we will discuss a few techniques to detect surface coverages and intermediates for aqueous electrocatalytic reduction reactions (i.e., phenol hydrogenation and nitrate reduction), and how these techniques have given insight into observed reaction rates. We will discuss how site counting of adsorbed hydrogen on platinum group metals using cyclic voltammetry can be used to determine reactant species coverages as a function of concentration (Figure 1). We will also compare these results to electrochemical impedance spectroscopy measurements of the change in the double layer with adsorption (i.e., decreases in capacitance due to adsorbed organic molecules). Also, we report results of in situ spectroscopy under reaction conditions, including near edge (XANES) and extended X-ray absorption fine structure (EXAFS) to determine catalyst oxidation state, structure, and adsorbate distances. Time permitting, we will discuss vibrational spectroscopy techniques to understand adsorbed species structure, such as surface enhanced Raman spectroscopy applied in the aqueous phase under electrochemical conditions,4 and our efforts to extend the work in this area to understand the effect of applied potential and catalyst surface for bio-oil hydrogenation. We compare our experimental results to first-principles calculations to show where trends allow us to better understand changes in reactivity with catalyst, and how a combined experimental and computational effort can give insight into the electrocatalyst/electrolyte interface in terms of reactant adsorption.

References

(1) Singh, N.; Song, Y.; Gutiérrez, O. Y.; Camaioni, D. M.; Campbell, C. T.; Lercher, J. A. ACS Catal.
2016, 6 (11).

(2) Song, Y.; Gutiérrez, O. Y.; Herranz, J.; Lercher, J. A. Appl. Catal. B Environ.
2016, 182, 236.

(3) Duca, M.; Koper, M. T. M. Energy Environ. Sci.
2012, 5, 9726.

(4) Weaver, M. J. J. Raman Spectrosc.
2002, 33 (5), 309.

Figure 1
(Invited) Understanding Metal-Based Catalysts for Electrochemical Ammonia Synthesis
Authors: Feng Xiaofeng
Published: February 2020

Electrochemical reduction of N2 to NH3 under ambient conditions may provide an alternative to the Haber−Bosch process for sustainable NH3 synthesis when powered by solar- or wind-generated electricity. However, the development of this process has been hindered by the lack of efficient electrocatalysts for the N2 reduction reaction (N2RR), due to the barrier for N2 activation and the competing hydrogen evolution reaction (HER). Here we present our recent studies of electrochemical ammonia synthesis on Pd and Fe/Fe-oxide catalysts. First, we found that Pd nanoparticles can catalyze the electrohydrogenation of N2 to NH3 in 0.1 M phosphate buffer solution (PBS) with a high yield rate and a Faradaic efficiency of 8.2% for NH3 production at 0.1 V vs the reversible hydrogen electrode (RHE). In operando X-ray absorption spectroscopy (XAS) study revealed the formation of α-phase Pd hydride during the reaction. The unique N2RR activity of Pd at low overpotentials outperforms that of Au and Pt nanoparticle catalysts, which is attributed to a new electrohydrogenation mechanism that involves an electrochemical formation of PdHx and a chemical hydride transfer from PdHx to *N2 to form *N2H, thus to lower the energy barrier for the rate-limiting step of N2RR. Second, we developed an Fe/Fe3O4 catalyst for N2RR, which was prepared by oxidizing an Fe foil at 300 oC in O2 atmosphere followed by in situ electrochemical reduction until a stable state was reached. The derived Fe/Fe3O4 catalyst shows greatly enhanced activity and selectivity for N2RR under ambient conditions than the original Fe foil, achieving a Faradaic efficiency of 8.29% for NH3 production at −0.3 V vs RHE in 0.1 M PBS electrolyte, which is around 120 times higher than that of the Fe foil. The high selectivity is enabled by an enhancement of the intrinsic (surface-area-normalized) N2RR activity as well as an effective suppression of the undesired HER. Comparative studies indicate that the N2RR activity may depend on the Fe/Fe-oxide ratio. Furthermore, the N2RR selectivity of the Fe/Fe3O4 catalyst is superior to that of Fe, Fe3O4, and Fe2O3 nanoparticle catalysts, which may provide new insights into the understanding and development of efficient electrocatalysts for ambient NH3 synthesis.