bluuebunny/crossref_metadata_2025 huggingface dataset:
Etch Damage Reduction of Ultra Low-k Dielectric By Using Pulsed Plasmas
Authors: Jang Jun Ki , Tak Hyun Woo , Yang Kyung Chae , Shin Ye Ji , Kwon Sang Duk , Yeom Geun Young
Published: February 2020

To reduce interconnect resistance and capacitance delay, the dielectric material with increased porosity is used in recent interconnection for lower dielectric constant. However, it is difficult to use highly porous low-k materials at the narrowest pitch because it is easily damaged during plasma etching processes. During plasma etching processes, plasma ions, reactive radicals, and VUV photon from the plasma tend to break Si-CH3 bonds in the low-k materials and change the material hydrophilic. This makes the damaged dielectric material to be bonded with moisture and makes dielectric constant to be increased and, eventually, it degrades RC time delay. In this study, as one of the plasma induced damage reduction methods in the etching of porous low-k dielectric, RF pulsed plasma methods have been investigated by using a dual frequency CCP system. RF pulsed plasmas generated lower energy ions compared to continuous wave plasmas and showed reduced damaged layer compared to the conventional continuous wave plasma etching. Porous SiCOH dielectric with a patterned TiN hard mask etched using RF pulsed plasmas and showed more anisotropic etching profile with less sidewall damage, which was estimated by the thickness loss of sidewall low-k material after dipping into a diluted HF solution. The results demonstrated that the RF pulsed plasma etching process of ultra low-k dielectric can improve RC delay related with plasma damage for next interconnect technology.
Morphological Evolution of Photoelectrodeposited Semiconductor Nanopatterns in Response to Dynamic Optical Inputs
Authors: Hamann Kathryn R , Carim Azhar I , Meier Madeline Claire , Lewis Nathan S
Published: February 2020

Chalcogen and chalcogenide semiconductor materials photoelectrochemically deposited from aqueous precursors, yield highly periodic nanostructured films over macroscopic square centimeter areas without the use of lithographic processing nor templating agents (ligands, surfactants, etc.). The in-plane feature morphology is controlled by the illumination utilized during growth: extremely anisotropic lamellar-type features can be generated simply by using linearly polarized light and the periodicity of the features can be modulated by adjusting the illumination wavelength. Use of temporally static illumination results simply in increased feature heights as the light-directed pattern is extended in the out-of-plane dimension. Significant morphological complexity can be effected by utilizing temporally-varying illumination inputs. An abrupt, dynamic change in the input wavelength effects evolution of the interfacial morphology and the establishment of a new morphological period. The mechanism may involve branching or fusion of neighboring nanoscale features depending on wavelength inputs used. This evolution was simulated using a two-step iterative model which used a finite-difference time domain method to examine light absorption and weight probabilistic simulations of mass addition. These simulations matched the experimentally observed morphologies despite minimal input of empirical parameters. Modeling of light absorption in simulated structures was used to evaluate the fundamental light-material interactions that govern the morphology determination. This work demonstrates that photoelectrochemical deposition can provide rapid, template-free fabrication of complex 3D nanoarchitectures.
Study of Se and Ge Solutions at Different Phs to Form Gese Via E-ALD
Authors: Howell Pauline , Stickney John Lewellen
Published: February 2020

GeSe is a two-dimensional chalcogenide with ovonic threshold switching properties. Its properties strongly depend on the stoichiometry and the quality of the film.1 Electrochemical atomic layer deposition (E-ALD) is an electrochemical method that utilizes surface limited reactions to deposit materials layer by layer.2 Using E-ALD will allow growth of higher quality GeSe films. Before attempting deposition, cyclic voltammetry studies of the individual solutions were done to determine the best deposition potentials. Ge solutions made at different pHs show maximum deposition in more basic solutions, such as pH 9. Studies of Se solutions at pH 1.6, 3, 5, 7, and 9 were done to find complimentary deposition potentials to the basic Ge solution. By investigating the behavior of Se and Ge using cyclic voltammetry, better understanding of the chemistry was garnered for the development of an E-ALD cycle. Further research will evaluate the deposition patterns of Ge on Se and vice versa. Finally attempts at depositing a stoichiometric GeSe deposit will be made using E-ALD.

References:

Hu, Y.; Zhang, S.; Sun, S.; Xie, M.; Cai, B.; Zeng, H. Applied Physics Letters
2015, 107(12), 122107.

Stickney, J. Encyclopedia of Applied Electrochemistry
2014, 1947–1953.
Boosting the Hydrogen Evolution Performance of Transition Metal Phosphide Catalysts on 3D Electrode Supports
Authors: Sanchez Joel , Hellstern Thomas , King Laurie , Jaramillo Thomas F.
Published: February 2020

To date, platinum-based catalysts have been employed for the hydrogen evolution reaction (HER) in PEM-electrolyzers.1 However, due to high costs and price volatility associated with Pt, there exists a need to investigate non-platinum-group metals (PGM) based catalysts. Tremendous efforts have been surmounted to develop non-noble metal catalysts that have the desirable properties of Pt during reaction without the associated costs, scarcity, and volatility.2 For non-PGM catalysts in various electrode configurations, an increase in performance is often accomplished by increasing the loading of the catalyst; while this strategy increases the density of active sites, it may lead to low mass activities, low utilization efficiencies, and potential suboptimal catalyst performance at excessive loadings.3,4 This motivates research into engineering catalyst support interactions to achieve highly active non-PGM catalysts at low-loadings.

To this end, utilizing various oxidation methods, the surface O/C ratio, and thus the hydrophilicity, is varied and is directly correlated to the cobalt phosphide dispersion onto the surface of the carbon electrode. The improved hydrophilicity (high O/C ratio) synergistically improves catalyst dispersion and yields electrodes with extraordinary performance as measured by low overpotentials (-51 mV at -10 mA cm-2), unprecedented mass activities (>800 A/g at -100 mV overpotential), high turnover frequencies (6.96 H2 s-1 at -100 mV overpotential), and promising stability (>8 hours at -10 mA cm-2) for a precious metal free catalyst at low loadings (~40-200 µg). Compared to reported HER catalysts, whether planar or 3D, in terms of mass activities and on a turnover frequency basis, our catalysts showed the highest values for non-PGM systems. Additionally, we show that the electrode fabrication process presented here is applicable to other phosphide catalysts (Ni and Fe phosphides) and can be used as a general methodology to reduce catalyst loading, improve overpotentials, mass activities, and TOFs.

References:

(1) Vesborg, P. C. K.; Seger, B.; Chorkendorff, I. Recent Development in Hydrogen Evolution Reaction Catalysts and Their Practical Implementation. J. Phys. Chem. Lett.
2015, 6 (6), 951–957.

(2) Zou, X.; Zhang, Y. Noble Metal-Free Hydrogen Evolution Catalysts for Water Splitting. Chem. Soc. Rev.
2015, 44 (15), 5148–5180.

(3) Cheng, Y.; Liao, F.; Shen, W.; Liu, L.; Jiang, B.; Li, Y.; Shao, M. Carbon Cloth Supported Cobalt Phosphide as Multifunctional Catalysts for Efficient Overall Water Splitting and Zinc–air Batteries. Nanoscale
2017, 9 (47), 18977–18982.

(4) Ursua, A.; Gandia, L. M.; Sanchis, P. Hydrogen Production From Water Electrolysis: Current Status and Future Trends. Proc. IEEE
2012, 100 (2), 410–426.
Carbon Nanofiber-Supported Fe3O4 nanoestructures As Efficient Electrocatalyst for the Oxygen Reduction Reaction
Authors: Fernández-Cori Rey , Baena Moncada Angélica María
Published: February 2020

Fe3O4 nanostructures were supported on carbon nanofiber synthesized at two different temperatures (600 and 700 °C) and tested as cathode catalyts for oxygen reduction reaction (ORR) in alkaline medium. Briefly, an iron oxide precursor, Fe(NO3)3.9H2O, is impregnated in carbon nanofiber (CNF 600 and CNF 700), followed by heat-treatment at 400 ° C for 4 h under Ar. The structure and morphology of the catalyst was evaluated by x-ray diffraction, raman spectroscopy scanning electron microscopy and nitrogen sorption isotherms. The electrocatalytic activity towards ORR was investigated by cyclic and linear voltammetries in 0.1 mol.L-1 KOH. Analysis of polarization curves showed the electrocatalytic activity of the materials towards oxygen reduction expressed by on-set potentials which Fe3O4/CNF 600 (+0.68 V vs RHE) presents more positive potential than Fe3O4/CNF 700 (+0.65 V vs RHE) and mass activity at +0.55 V vs RHE with values of 25.4 A.g-1 (Fe3O4/CNF 600) and 14.4 A.g-1 (Fe3O4/CNF 700). Nevertheless, the variation of number of exchage electrons (n) and peroxide ion percentage (%H2O-) with applied voltage indicate a direct oxygen reduction starts (4 electrons pathway) at more positive potential in Fe3O4/CNF 700 (+0.21 V vs RHE) than Fe3O4/CNF 600 (+0.12 V vs RHE). These results were obtained by indirect calculation using the Koutecky-Levich equation and confirmed by direct determination of ion peroxide intermediate formation with rotating-ring disk electrode measurements.

Figure 1
(Invited) In Situ Stimulated Raman Spectroscopy of Amorphous Cobalt Oxide Catalyst during Oxygen Evolution Electrocatalysis
Authors: Eom Chuhyon , Suntivich Jin
Published: February 2020

Understanding the functionality of a catalyst requires understanding its in-reaction structure. Vibrational techniques can reveal detailed structural information; however, a number of challenges including background absorption in infrared and small cross sections in Raman have made the measurement difficult. In this contribution, we demonstrate stimulated Raman spectroscopy (SRS) as an in-situ probe to tackle the challenge of small cross sections in Raman. As a nonlinear spectroscopic technique, SRS has several advantages including efficiency, which will be discussed. Leveraging the improved efficiency, we apply SRS to measure the vibrational structure of an amorphous cobalt oxide catalyst during the oxygen evolution reaction (OER). Additional experiments using isotope labeling are used to identify the nature of the vibration structure. These results present the potential of SRS as a useful tool to investigate the much sought-after catalyst structure in-situ. The spectroscopic techniques, methods of analysis, and the experimental results will be presented.
Electrocatalysis of Ketjenblack-Supported Ru-Ir Cathode for the Electrohydrogenation of Toluene to Methylcyclohexane in the Organic Hydride System
Authors: Inami Yuta , Nagamatsu Shinichi , Asakura Kiyotaka , Iguchi Shoji , Yamanaka Ichiro
Published: February 2020

Hydrogenation of toluene (TL) and dehydrogenation of methylcyclohexane (MCH) has been paid great attention for a highly efficient H2 storage technology [1,2]. At energy supply area, TL is hydrogenated to MCH by the catalytic hydrogenation using H2 produced by the water-electrolysis. We can easily transport and store MCH using the current infrastructures, because MCH is a component of petroleum and liquid state at ambient conditions. At energy demanding area, the catalytic dehydrogenation of MCH to TL and H2 (47.4 kg-H2/m3-MCH) is conducted. H2 can be used as an energy source, and TL is reused as the H2 carrier, repeatedly. To improve the H2 storage system to more efficient one, a direct electrohydrogenation of TL with water using a solid polymer electrolyte (SPE) electrolysis cell and 50 wt% Pt/Ketjenblack (KB) cathode has been proposed (Fig. 1) [3]. In those system, water is oxidized at the anode, and TL is electrochemically reduced to MCH at the cathode; however, the high loading of Pt is disadvantage from the viewpoints of system cost. For the efficient hydrogenation of TL, it is essential to reduce Pt or other precious metal loadings with keeping suppression of the competitive H2 evolution.

In this study, we found that Ru-Ir alloy supported on KB (Ru-Ir/KB) electrocatalyst showed superior electrocatalytic activity for the electrohydrogenation of TL to MCH under galvanostatic electrolysis conditions at 0.20 A cm-2. 5 wt% Ru-5 wt% Ir/KB loaded on a gas-diffusion layer (GDL) cathode (0.2 mgRu-Ir cm-2) showed a higher faradic efficiency of MCH formation than the 50 wt% Pt/KB loaded on the GDL cathode (1.0 mgPt cm-2), though the working potential of -0.183 V (SHE) at the former was slightly negative than that of -0.071 V (SHE) at the later. This indicated the significant reduction of amount of precious metals used for the electrohydrogenation of TL. Characterization studies for the Ru-Ir/KB electrocatalyst were conducted by using X-ray diffraction (XRD), transmission electron microscopy with energy dispersive spectroscopy (TEM-EDS) and X-ray absorption fine structure spectroscopy (XAFS), and a formation of hcp-structured Ru-Ir alloy was revealed. Based on the electrochemical and kinetic studies, synergy mechanisms of Ru and Ir for the electrohydrogenation of TL were proposed. To be concrete, a fast hydrogenation of TL to MCH on the Ru site, a fast electrocatalytic reduction of H+ to H-species on the Ir site, and a fast spillover of H-species from Ir to Ru, these three steps cooperate.

References

[1] J. Gretz, J. P. Baselt, O. Ullmann, H. Wendt, Int. J. Hydrogen Energy, 15, 419 (1990)

[2] Y. Okada, E. Sasaki, E. Watanabe, S. Hyodo, H. Nishijima, Int. J. Hydrogen Energy, 31, 1347 (2006)

[3] S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis, 7, 127 (2016)

Figure 1
Study and Modeling of PEM Fuel Cell Using Electrochemical Impedance Spectroscopy
Authors: Konduru Vinaykumar , Arisetty Srikanth , Kumaraguru Swami
Published: February 2020

Electrochemical Impedance Spectroscopy (EIS) is a powerful diagnostic tool for fuel cells. A wide variety of information can be obtained from EIS measurements. In the current study, we have systematically performed EIS measurements by varying the operating conditions using H2-O2 and H2-Air. A comparative EIS study with different catalysts is also performed. A computational model describing the observed phenomena is also presented.
Preparation of Platinum Nanostructures Directly Grown on Microporous Layer By an Electrodeposition Technique for a Commercial-Scale PEMFC
Authors: Chiang Cheng-Hsuan , Wang Mei-Ya , Yeh Tsung-Kuang
Published: February 2020

Proton exchange membrane fuel cells (PEMFC) have a lot of attention due to their low operating temperature and quick startup. Pt-based catalysts, usually used in the PEMFC electrodes, are the main contributor to the high cost. An electrodeposition technique that could significantly improve the deposition of platinum (Pt) nanostructures onto on carbon cloths was adopted in this study. The electrolyte used for electrodeposition was a mixed solution of 0.1 M sulfuric acid and Pt precursor chemical of 0.5 mM hexachloroplatinic acid (H2PtCl6·6H2O) to fabricate a 3D structural catalyst layer as an electrode used in proton exchange membrane fuel cell (PEMFC). Without using any catalyst supports, the catalyst nanostructure would enhance the catalytic activity area. In this study, the dimensions of the working electrode were 1, 9, and 25 cm2. The sizes of the Pt nanostructures are 100-300 nm in diameter. This new technique could further enhance the catalyst activities and lead to a significantly improved Pt uniformly distribution on the carbon clothes.
Electrolyzer Components and Coatings: Methods for Ex-Situ Accelerated Stress Testing
Authors: Callahan Will , Guerrero Trent , Klein Ellis , Vidal Judith C , Bender Guido , Young James L.
Published: February 2020

Lowering electrolyzer capital costs and increasing material durability are key efforts toward furthering the commercial penetration of PEM electrolysis technology. This work focuses on bipolar plate and porous transport media materials, typically consisting of a titanium alloy coated with a protective thin-film of Pt, Au, or Ir. The titanium alloy serves as a corrosion-resistant base material and the coating material is selected with the purpose of delaying titanium oxidation that leads to increasing contact resistance and performance decline during operation. Potential alternative, lower-cost materials and coatings exist and/or could be developed. To avoid time, equipment, and labor intensive in-situ durability testing, accelerated high-throughput screening methods are desirable and explored in this work..

The explored ex-situ testing methodologies involve the preparation of coated material samples which are used as oxygen evolution electrodes. The materials are submersed in liquid electrolyte and degradation stressors such as temperature, pH, and potential are directly controlled. By varying each stressor independently, the influence that each has on the rate of degradation can be quantified. Such an approach may ultimately be useful in translating ex-situ results toward predicting in-situ performance. Periodic measurement of contact resistance and coating thickness during durability testing are also used toward this end. We further developed the use of time-lapse microscopy monitoring and analysis for our ex-situ testing setup. This technique allows identification and comparison of distinct corrosion modes and enables visual observations to be related to electrochemical durability data, which can improve its interpretation.

We will first present results that have guided our methodology development, in which electrode surface preparation and mounting variants were evaluated using a model system of sputtered Pt coatings on Ti coupons. With improved electrode preparation, we then evaluate some common Pt deposition techniques that include evaporation, sputtering, and electrodeposition. We also make a direct comparison between sputtered Pt and Ir coatings while using time-lapse microscopy to identify the corrosion modes of each. Coatings of Pt show a progression of yellowing, blistering, and peeling while Ir corrodes via darkening and dissolution. By processing the time-lapse microscopy to determine the change in apparent active area with time, we show that performance decline trends closely with the loss of active area. Some discrepancy at the beginning and end of the durability test have yet to be explained and additional analyses of the time-lapse data are ongoing. We will also present results of work in progress that includes investigation of Pt and Ir coating thickness, adhesion layers, and post-deposition annealing.
Activity and Durability of Organic Ligands Modified Platinum Catalyst for Oxygen Reduction Reaction
Authors: Ikehata Yuta
Published: February 2020

Last decade witnessed significant advances of PEMFC technology, which has led to the commercialization of several fuel cell electric vehicles (FCEVs) such as Toyota Mirai and others. However, various technical hurdles remained to be solved for future development toward large scale of deployment. One major issue involves the high cost of the cathode catalyst, which has been identified as the most expensive among stack materials for high production volume. Current PEMFCs use platinum-based catalysts to accelerate oxygen reduction reaction (ORR) on the cathode. ORR has a sluggish kinetics, as it involves multiple sequential steps of proton coupled electron transfer processes and a “scaling” issue makes it difficult to optimize every elemental reaction step simultaneously. While many research efforts have focused on ORR catalyst material design, for example, alloy, core-shell, shape control and so on., engineering catalyst-electrolyte interface properties may offer another way to overcoming the problem. It has been reported that the modification of Pt catalyst surface with organic ligands could enhance catalyst activity. The improvement was mostly derived from either the change of surface electronic structure of the catalyst, or the mitigation of ionomer poisoning by strong anion adsorption. In this study, we systematically examined a series of organic ligands with different structures. Combining material characterization with electrochemical analysis allowed us to evaluate not only the catalyst activity, but also the ligand stability. The modified Pt/C catalyst was further examined in MEA for the validation of the possible effect of ligand modification to catalyst layer properties and performance.
Effect of NH3 Etching on Fe-N-C Catalyst for Oxygen Reduction Reaction in Direct Methanol Fuel Cell
Authors: Luo Zhijun , Hou Chenjun , Zhang Xuelin , Zhang Yufeng , Liu Xiaowei
Published: February 2020

Globally, because of the consumption of fossil fuel, the proton exchange membrane fuel cells (PEMFC) have received great attention. Direct methanol fuel cells(DMFC) have been applied into many fields, such as computers, global positioning systems(GPS) and portable devices. Platinum catalysts are considered as one of the most efficient catalysts for the oxygen reduction reaction(ORR),which is one of the most essential process for the DMFC. However, due to the high cost, the development of the DMFC calls for the non-precious metal catalyst, such as the Fe-N-C catalyst.

We report a process to synthesize a Fe-N-C catalyst. Firstly, 80 ml 1.5M HCl, 2 ml aniline, 3 ml cyanamide, and 3 g ferric chloride were fixed and stirred for 20 min, with 5 g (NH4)2S2O8 dissolved into 80 ml 1.5M HCl dropped slowly. The mixture after being stirred for 4 h was mixed with the BP2000 carbon black dissolved into 80 ml 1.5M HCl for 40 min. Secondly,the mixture was heated at 80 degrees and stirred at 300rpm until dried. After being boiled in 2M H2SO4 for 5 h at 90 ℃ and milled at 400rpm for 3h, the sample was filtered and dried. Finally, half of the precursor was calcined for 2.5 h in N2, and 0.5 h in NH3 at 900℃, and the others were calcined in N2 for 3 h. After being heated for 5 h in 0.5 M H2SO4 at 90℃, and calcined for 3 h in N2 at 900℃ to gain the catalyst. The catalysts were named Fe-N-C00 and Fe-N-C30 separately.

For RDE and RRDE tests on the Fe-N-C catalyst, the ink was prepared by mixing 15mg catalyst dissolved into 525µl ethanol and 145µl Nafion, which was stirred for 40min to achieve a good dispersion. 7µl ink was coated on the surface of RDE, making the loading of the catalyst 800µg cm-2. The staircase voltammetry(SCV) tests were conducted at the speed of 1600rpm in O2-saturated 0.5M H2SO4 solution. The half-wave of the potential of Fe-N-C00 catalysts were about 20mV lower than Fe-N-C30(0.685V vs 0.705V). According to the Koutecky-Levich equation, we calculated the electron transfer number was 3.97, and the productivity of H2O2 was 1.3%, which proved a four-electrons transfer process.

The Fe-N-C catalyst used as the cathodic catalyst,which was sprayed onto a carbon paper gas diffusion(GDL,SGL 29BC), was applied into a single DMFC. A Nafion® 117 membrane from Dupont worked as the electrolyte. The membrane was pre-treated following a standard procedure before use. A commercial Pt-Ru (30% Pt-Ru/C)catalyst was used as anodic catalyst.The anode gas diffusion electrode (GDE), the cathode GDE and the membrane were put together in sequence and hot-pressed by 135℃and 5MPa for 5 min to form a MEA separately. The loading of the catalysts including Fe-N-C and Nafion was 4mg cm-2,and the ratio of the Fe-N-C catalyst was 55%. The polarization curve of the DMFC with the different MEA was tested to reflect the effect of Fe-N-C00 and Fe-N-C30 catalyst on DMFC.

Figure 1
Efficient Electroreduction of CO2 in an Ultra-Slim Pressurized Electrolyzer
Authors: Edwards Jonathan P. , Xu Yi , Gabardo Christine M. , Dinh Cao-Thang , Li Jun , Qi ZhenBang , Sargent Edward H. , Sinton David
Published: February 2020

Society’s consumption of fossil fuels has caused a surge in atmospheric carbon dioxide (CO2) concentrations which, if left unchecked, will have tremendous implications for all life on our planet. Consequently, new approaches are being investigated to utilize CO2 instead of releasing it into the atmosphere. One of these approaches is the electrochemical CO2 reduction reaction (CO2RR) which can store intermittent renewable energy in the form of valuable chemicals and fuels.

To encourage the implementation of industrial CO2RR systems, such systems must demonstrate economic benefits in conjunction with environmental benefits. To make such systems economical, electricity inputs, the single largest operating cost in these systems, must be minimized. A great deal of recent work has been devoted to optimizing the cathode catalyst and electrolyte to attain high selectivity towards specific products at low overpotentials. However, few studies optimize the full cell design, which includes the cathode, anode, ion exchange membranes, and electrolytes to demonstrate an efficient CO2RR process. These additional full cell elements require some consideration when designing industrial systems as improved cathode energetics may be overshadowed by increased losses in other areas of the system resulting from the cathode optimization.

Here we present an ultra-slim pressurized electrolyzer whose membrane-free operation with minimized electrode spacing yields negligible cell resistances. To showcase this cell design, we employ a silver catalyst for carbon monoxide (CO) generation at the cathode coupled with a nickel anode for oxygen evolution on the anode. In conjunction with the low cell resistances, we demonstrate further improvements in the uncorrected full cell energetic efficiency. First, we show that operation at elevated pressures, up to 51 bar, offers benefits to the reaction rates and helps to maintain high CO selectivities, resulting in energetic efficiency improvements. We then couple these high pressures with high alkalinity to demonstrate even greater improvements in energetic efficiencies due to improved kinetics. The system presented demonstrates substantial improvements in full cell energetic efficiency, enabling efficiencies > 65% to be attained while operating at industrially relevant current densities above 100 mA/cm2.
(Invited) Photocatalytic Water-Splitting Composites Working Under UV to Near-Infrared Lights
Authors: Zhang Junying
Published: February 2020

To make full use of solar energy, the photocatalytic activity in the visible to near-infrared region should be greatly improved. Photocatalysts that could split water under UV to near-infrared lights were prepared by composing wide band-gap semiconductors with narrow band-gap semiconductor, plasmonic nano-sized Au, and black phosphorus. The lifetimes of the charge-carriers generated by the photosensitizers were substantially prolonged via achieving effective charge transfer on the interface. A serial of materials were obtained that could efficiently release hydrogen from water under solar light irradiation.

References

Cai, J.Y. Zhang, M. Fujitsuka, T. Majima, Appl. Catal. B: Environ. 2017, 202,191

S. Zhu, X.Y. Cai, M. Fujitsuka, J.Y. Zhang, T. Majima, Angew. Chem. Int. Ed. 2017, 129,2064

Y.Cai, J.Y.Zhang, M.Fujitsuka, T. Majima, J. Mater. Chem A 2017, 5,10442

Y. Cai, M. S. Zhu, O. A. Elbanna, M. Fujitsuka, S. Kim, L. Mao, J. Y. Zhang, T. Majima, ACS Catal, 2018, 8,122

Mao, X.Y. Cai, H. Gao, X. G. Diao, J.Y. Zhang, Nano Energy, 2017, 39, 172

Y. Cai, L. Mao, S.Q. Yang, K. L. Han, J.Y. Zhang, ACS Energy Lett. 2018, 3, 932

Mao, X.Y. Caia, S. Q. Yang, Keli Han, J. Y. Zhang, ppl. Catal. B: Environ. 2019, 242, 441
(Invited) Rational Design of Plasmonic Photocatalysts
Authors: Wu Nianqiang
Published: February 2020

This talk will discuss the rational design of plasmonic metal-semiconductor photocatalysts for solar water splitting. There are three plasmonic energy transfer mechanism from a metal to a semiconductor: light scattering/trapping, hot carrier injection and plasmon-enhanced resonance energy transfer (PIRET). This talk shows how to design metal-semiconductor photocatalysts using the three mechanisms.
(Invited) Exotic Electronic Excitation of a Single-Layer Graphene By Surface Localized Plasmons Under Electrochemical Potential Control
Authors: Zhang Jinjiang , Zhou Ruifeng , Minamimoto Hiro , Murakoshi Kei
Published: February 2020

Localized surface plasmons (LSPs) of novel metal nanoparticles has distinct electromagnetic interactions with matter compared with the case using far-filed light. The high field gradient near metal nanostructures opens up the possibility for additional transitions beyond those allowed by normal selection rules, enhancing light-matter interactions. Moreover, plasmon-induced ‘hot carriers’ can accelerate chemical reactions. The energy distribution, lifetime, and transfer of ‘hot carriers’ are key factors affecting electrochemical processes. We find that the LSPs of the Au nanodimer structures prepared on defect-free graphene provide highly-confined electromagnetic field to generate holes and electrons with the electrochemical potentials beyond the limit of those under normal light illumination.
(Invited) Nanohybrids for Manipulating Solar Energy
Authors: Yurtsever Aycan , Ma Dongling
Published: February 2020

With unique physical and chemical properties, and high potential for many important applications, nanomaterials have attracted extensive attention in the past two decades. For instance, due to their unique, size- and shape-tunable surface plasmon resonance, plasmonic nanostructures have recently been explored for increasing the efficiency of solar cells and photocatalysis. Essentially they enhance and/or broaden solar photon harvesting via improved light scattering, strong near field effect and/or hot electron injection. Combination of different nanomaterials into a single architecture leads to greatly enhanced properties, or even better, promising, multifunctional nanomaterials. In this talk, I will present our recent work on the synthesis of hybrid nanomaterials (the assemblies of different types of nanoscale materials) as well as their applications in smart windows, solar cells, solar fuel, photocatalysis, etc. [1-8]. Rational design of hybrid nanomaterials, which is the key to maximize the benefits from respective nano-components, is highlighted.

References: 1. Am. Chem. Soc., 2013, 135, 9616; 2. Adv. Energy Mater. 2018, 1703658; 3. Adv. Funct. Mater. 2018, 1706235; 4. ACS Catalysis, 2017, 7, 6225; 5. Adv. Funct. Mater, 2015, 25, 2950; 6. Adv. Funct. Mater. 2015, 25, 6650; 7. Adv. Funct. Mater., 2012, 22, 3914; 8. Adv. Mater., 2012, 24, 6289.
First-Principles Simulations of Stability, Optical and Electronic Properties of Competing Phases in Chalcopyrite-Based Photoelectrodes
Authors: Varley Joel Basile , Sharan Abhishek , Ogitsu Tadashi , Janotti Anderson , DeAngelis Alexander D , Gaillard Nicolas
Published: February 2020

Photoelectrochemical (PEC) hydrogen production is one promising approach to economically generating renewable fuels, yet the widescale deployment of leading photoelectrodes (e.g. GaInP-based devices) has been hampered by issues with durability, efficiency and cost. Chalcopyrite-based tandem photoelectrodes are attractive alternatives in that they offer a great flexibility in the choice of component materials necessary that drive the reactions for different device designs, offering ways to reduce the cost and to improve the performance. The synthesis of low-band gap chalcopyrites like CuInSe2 and alloys with CuGaSe2 (CIGSe) are known to exhibit a variety of Cu-poor phases (ordered-vacancy compounds or OVCs) that can greatly influence the resulting properties of fabricated devices, while the existence and properties of these phases in wider-band gap chalcopyrite compounds and alloys remains largely unexplored. Using hybrid functional calculations, we discuss the stability, optical and electrical properties of OVCs in a number of other chalcopyrite chemistries beyond CIGSe. We discuss the influence of such phases on the resulting absorption and band offsets that would result upon their formation, which have implications in device design. We additionally discuss experimental fingerprints that could be used to identify the existence of such phases in synthesized material.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the HydroGEN Consortium within the Department of Energy Office of Energy Efficiency & Renewable Energy (EERE) and Fuel Cell Technologies Office.
Integrated Membrane-Electrode-Assembly Photoelectrochemical Cell Under Various Feed Conditions for Solar Water Splitting
Authors: Kistler Tobias , Larson David M , Agbo Peter , Walczak Karl , Sharp Ian D , Weber Adam Z. , Danilovic Nemanja
Published: February 2020

Photoelectrochemical (PEC) water splitting cells have the potential to significantly reduce the costs associated with electrochemical hydrogen production through the direct utilization of solar energy. Many of these cells utilize liquid electrolytes that are detrimental to the durability of the photovoltaic (PV) or photoactive materials at the heart of the device. The membrane-electrode-assembly (MEA) style, PEC cell presented herein is a deviation from that paradigm as a solid electrolyte is used, which allows the use of a water vapor feed. The result of this is a correspondent reduction in the amount of liquid and electrolyte contact with the PV, thereby opening the possibility of longer PEC device lifetimes. In this study, we demonstrate the operation of a liquid and vapor-fed PEC device utilizing a commercial III-V photovoltaic that achieves a solar-to-hydrogen (STH) efficiency of 7.5% (12% as a PV-electrolyzer). While device longevity using liquid water was limited to less than 24 hours, replacement of reactant with water vapor permitted 100 hours of continuous operation under steady-state conditions and diurnal cycling. Key findings include the observations that the exposure of bulk water or water vapor to the PV must be minimized, and that operating in mass-transport limited regime gave preferable performance.
Electroreduction of CO2 to High-Value Products Using Selenide Based Electrocatalysts
Authors: Saxena Apurv , Masud Jahangir , Nath Manashi
Published: February 2020

Electrochemical conversion of carbon dioxide (CO2) to useful chemicals presents both the potential for advantageous processes to the industry and for environmental benefits. Anthropogenic gas emissions has increased to a new level (413 ppm) in past few years. Concerns are high about impacts on climate due to high CO2 gas levels. Intergovernmental Panel on Climate Change (IPCC) report has indicated a strong risk of crisis as early as 2040 which includes worsening food shortages and wildfires, and a mass die-off of coral reefs.3 Fossil fuels has been predicted to last only for 100 years. Also the common renewable resources like wind energy or solar energy depends on the whim of weather. CO2 has been believed to cause the rise in temperature of earth’s atmosphere by 1°C. If we can use CO2 to produce energy then it can prove an everlasting energy source. Copper based catalysts are mostly active for the electrochemical reduction of CO2. Cu nanocrystals when used for CO2 electrochemical reduction give some C2 products which contain a C-C bond. Cu nanowires also reduced CO2 to CO with a faradaic efficiency of ∼50% at a moderate overpotential of 490 mV. Electrochemical reduction of CO2 if incorporated in the modern day energy resources can serve two purpose: make environment clean and provide energy too.

In this work we have shown for the first time, electrocatalytic activity of Cu2Se for CO2 electroreduction to value-added chemicals. The Cu­2Se catalyst was synthesized hydrothermally and was dropcasted on Carbon Fiber paper substrate (CFP) using very low quantity of nafion as binder. The Cu2Se modified CFP served as the working electrode for CO2 electroreduction and the electrochemical measurement was measured in KHCO3 electrolyte under flowing CO2 using a two-compartment electrochemical cell. The electrocatalyst was characterized by XRD, XPS, SEM, TEM, and EDS for morphology, and elemental chemical compositions. It was observed that the reduction products could be controlled by tuning the reduction potential, and a highly selective formate production was obtained at a higher potential with a high total current density approximately 30 mA cm-2. C2 products such as ethanol and acetic acid were obtained as reduction products. The details of catalyst synthesis, characterization and activity will be presented in the meeting.
SnOx Nanosheets Anchored on Mwcnts Modified with Different Functional Groups for Selective Electrochemical Reduction of CO2 to C1 Products
Authors: Zhang Qi , Qiao Jinli
Published: February 2020

Electrochemcial reduction of CO2 (CO2RR) into the industrial feedstocks and low carbon fuels could be a promising strategy to alleviate the excessive emission of CO2. In CO2RR, C1 products are more feasible due to their low electron transfer and relative fast kinetics. By applying a facile and green hydrothermal assembling method, we here report the synthesis of a hierarchical SnOx (x=1, 2) nanosheets anchored on the surface of the commercial MWCNTs, which were functionalized by -NH2, -COOH, -OH or without any functional group, in order to investigate the influence of functional groups on the properties of SnOx@MWCNTs catalysts for enhanced electrochemical CO2 reduction reaction (CO2RR). A noteworthy improvement in catalytic performance was obtained for all the catalysts modified with -NH2, -COOH, -OH compared with that without any functional group. X-ray diffraction shows that the SnO (101) surface is the active phase for CO2RR. Density functional theory (DFT) calculations indicates that the presence of -COOH significantly improves the adsorption energy of SnOx on MWCNTs, yet, -NH2 was favorable for the adsorption of CO2, facilitating CO2RR. SnOx@MWCNT-COOH achieved remarkably high faradaic efficiency (FE) for formate of 77% at -1.25 V vs. SHE and a low overpotential of only 246 mV, while SnOx@MWCNT-NH2 exhibited high activity and selectivity for C1 products (formate and CO). Furthermore, SnOx@MWCNT-COOH as well as SnOx@MWCNT-NH2 both effectively inhibited hydrogen evolution reaction (no more than 0.5% for FEH2) and proved to be stable without any obvious degradation over 20 h of continuous electrolysis at -1.25 V vs. SHE.

Keywords: CO2 electroreduction, functional groups, formate, DFT calculations
(Invited) A Systematic Study of Ammonia Synthesis By Electrochemical Reduction of N2 over Cu
Authors: Balaji Nishithan , Prajapati Aditya , Singh Meenesh R
Published: February 2020

The Haber-Bosch process for NH3 synthesis is extremely energy intensive requiring a temperature of around 500 oC and a pressure reaching up to 300 atm. Therefore, the development of an alternative, sustainable, efficient, and a selective approach for reducing N2 to NH3 is of great importance. The current work explores the electrochemical route for reducing N2 to NH3 close to ambient conditions using an alkaline electrolyte. A major challenge for following this route is the development of an efficient electrocatalyst and effective electrochemical cell to yield a higher Faradaic efficiency for NH3 synthesis as the N2 reduction reaction (N2RR) competes with the hydrogen evolution reaction (HER) in the aqueous medium. Here we report the use of a carbon-supported Cu as the electrocatalyst for N2RR. The catalyst is synthesized by electrodepositing Cu from a copper (II) nitrate solution on a porous carbon paper and characterized by SEM, XRD, and XPS. We designed and fabricated a compact electrochemical cell to perform the electrochemical studies. The electrochemical cell accommodates a gas diffusion electrode (GDE) that acts as an interface between the continuously recycled aqueous electrolyte on one side and the constantly fed N2 gas on the other. The product distribution is determined by the in-situ GC analysis to monitor the HER and NH3 formation is measured by UV-Vis absorbance spectra of Nessler’s Reagent sparged with product gases. The effects of different operating parameters such as pH, temperature, catalyst loading, and gas and liquid flow rates are studied to determine the optimum operating conditions and kinetics of N2RR.
(Keynote) Emergent Effects of Global Surfaces on Local Microstructure Designs for Functionality in Heterogeneous Functional Materials
Authors: Reifsnider Kenneth L , Cao Ye
Published: February 2020

Heterogeneous functional materials are of special importance to the design of functional devices such as fuel cells, batteries, and capacitors, but they are also critical to applications like energy storage and the confinement of nuclear waste materials. Morphology design is critical to all of these (and other) applications, and much literature records the science and engineering of that subject. But the rules we generate and recite that control particle / void space and shape, surface to volume / phase shape selections, constituent distributions and other aspects of those microstructure designs do not predict the emergent properties and functionalities of such materials when a global surface influences or controls the basic transport or diffusion of active species into and out of those microstructures when they act as functional materials. Examples of such emergent properties and functionalities will be identified and discussed in the present paper, with the intent of identifying general concepts and principles that help us to design successful microstructures in those situations. Subjects of the discussion will include threshold volume fractions, short vs. long term response, surface to volume ratios, interface / interphase effects, and critical path concepts. Examples will be provided from several application fields, and some directions will be suggested.
(Invited) Electrochemical Reduction of Carbon Dioxide: Controlling Selectivity to Formic Acid and Methanol
Authors: Yeo Boon Siang
Published: February 2020

Currently, more than 80% of the world’s energy needs are met by burning fossil fuels. Supplies of these fuels are intrinsically limited and will eventually run out. Combustion of fossil fuels also generates carbon dioxide, whose rapidly increasing atmospheric concentration is suspected to be an accelerant of global warming. One solution for mitigating atmospheric concentrations of CO2 is to electrochemically reduce these molecules into chemical fuels. If the energy used for these processes is generated from renewable sources such as solar and wind, we can envisage a chemical production cycle that is closed-loop with net zero carbon emission. In this talk, we share our works related to the development of catalysts for the selective electroreduction of CO2. We shall discuss our work on how copper catalysts, by a simple sulfur doping procedure, can be made almost exclusively selective for the reduction of CO2 to formic acid. We shall also discuss a new class of catalysts based on zinc, for the selective formation of methanol. Through a series of control experiments and density functional theory calculations, we pinpoint strained undercoordinated Zn sites as the catalytically-active sites for methanol formation, in a reaction pathway mediated by adsorbed carbon monoxide and formaldehyde.
(Invited) A Rapid Method for Detecting CO2 Reduction Products and Local pH
Authors: Co Anne C. , Zhang Fen
Published: February 2020

We present a systematical study of using RRDE as a fast and reliable detection method for quantifying CO2RR products generated from both heterogeneous (e.g. Pt, Au, Sn) and homogeneous (e.g. [NiII(cyclam)]2+) catalysts. Local pH change during Au and Sn catalyzed CO2RR are also carefully investigated. The fast detection towards single product systems (e.g. H2, CO) and mixture product systems (e.g. H2 and HCOO-, H2 and CO) are discussed in detail. Our results show that, compared with traditional detection methods (e.g. GCMS, NMR), RRDE shows a superior detection sensitivity (e.g. LOD
ring ~10-18 moles of H2, defined in this work) as well as a significant short detection time (<1 min). Meanwhile, the product distribution as a function of applied electrolysis potential could be easily extracted from the detected ring voltammograms, which provides important information for the evaluation of catalysts’ performance.
Atomic Layer Deposition to Design Internal Surface of Porous Electrode for Accelerating Charge and Mass Transfer in Fuel Cells
Authors: Chen Yun , Gerdes Kirk , Song Xueyan
Published: February 2020

The inadequate catalytic activity and conductivity from the porous electrode hinder the power density of the ceramic fuel cells operated at high temperatures. For the first generation Solid Oxide Fuel Cells (SOFCs) with yttria stabilized zirconia (YSZ) electrolyte, the present work employs atomic layer deposition (ALD) and implanted nanoscale eletrocatalysts on the internal surface of the composite cathode consisting lanthanum strontium manganite and YSZ. Upon electrochemical operation, the ALD layer with optimized nanostructure develops into a nano-porous uniform and conformal heterostructured electrochemical active percolating network, provides additional charge and mass transfer pathways, and subsequently extends the electrochemical active area from the original localized triple phase boundaries (TPBs) to the entire internal surface of porous cathode. For the as-fabricated commercial SOFCs, such ALD coating of LSM/YSZ cathode resulted in a large reduction of cell polarization resistance by up to over 50 % and an enormous increase of cell peak power density by over 300 %, which is significantly outperforming that of the state-of-the-art SOFCs with mixed ionic and electronic conducting cathode.
(Invited) Role of Imaging in Modeling of Cathode Catalyst Layers in Proton Exchange Membrane Fuel Cells
Authors: Fuller Thomas F.
Published: February 2020

The predominate model of electrodes used for proton exchange membrane fuel cells (PEMFCs) is based on the macrohomogeneous porous electrode formulation. As valuable as this formulation is it cannot explain important phenomena that are present. A key example is the effect of low loadings of catalyst on the cathode. Experimentally, a reduction in the mass-transfer limiting current is observed, but the model predicts no effect. Additionally, the dynamics of liquid water in the catalyst layer are believed to be important, but predicting water transport even under steady-state conditions is challenging.

The development of tomographic and 3D imaging techniques, such as focused ion beam scanning electron microscopy, FIB/SEM, offers new opportunities in modeling of electrode. The challenges are twofold. First, obtaining an accurate reconstruction of the electrode structure is still difficult. Our efforts to measure these structures using FIB/SEM is described for samples subjected to accelerated stress testing designed to probe carbon loss are described.[i] The second challenge is simulation using these structures. Two routes for modeling are explored. The primary is direct simulation using the detailed, measured geometry. This direction is computationally expensive, but more and more it becoming viable. The alternate route also uses the actual geometry, relying on mathematically exact and statistically significant definitions of geometric tortuosity and geometric constrictivity, but seeks efficient means to find effective transport properties.

[i] Star, A. G. & Fuller, T. F. FIB-SEM Tomography Connects Microstructure to Corrosion-Induced Performance Loss in PEMFC Cathodes. J Electrochem Soc
164, F901-F907 (2017)