bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Water Management and Carbon Dioxide Contamination Effects in Anion-Exchange Membrane Fuel Cells
Authors: Gerhardt Michael R. , Pant Lalit M. , Weber Adam Z.
Published: February 2020

Anion-exchange membrane fuel cells (AEMFCs) offer a potential advantage over their traditional proton-exchange membrane counterparts in that many non-precious metal catalysts are chemically compatible with the alkaline environment in an AEMFC [1]. Recently, high-power operation of AEMFCs has been demonstrated, including achieving 1 W/cm2 using silver metal cathode catalysts [2], [3]. The performance of AEMFCs, however, can be highly sensitive to small changes in relative humidity, as water is a reactant in the alkaline oxygen reduction reaction. Additionally, performance degradation due to carbon dioxide contamination remains a major issue. The absorption of carbon dioxide and subsequent conversion to carbonate anions reduces membrane conductivity and worsens fuel cell performance.

In this work, we use our previously developed two-dimensional model [4] to illustrate and explore the effects of membrane and ionomer properties, relative humidity changes, and absorption of carbon dioxide on AEMFC performance. A 2+1D modeling approach is used, where an external stepping model is used to move along the gas channels. At each step, the 2D cross-section model [4] is used to simulate cell performance. Mass and energy balances are performed at each step to obtain the channel conditions, such as concentration, relative humidity, and temperature, for the subsequent step. The 2+1D model accounts for the performance changes due to concentration and relative humidity changes along the channel, especially at integral cell conditions. Finally, we show how performance limitations from carbon dioxide absorption, flooding, and dry-out could be alleviated through changes in operating parameters or ionomer properties.

Acknowledgements

The work was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231. We thank Bryan Pivovar and the members of the Fuel Cells group of the National Renewable Energy Laboratory for helpful discussion and model validation data.

[1] J. R. Varcoe et al., “Anion-exchange membranes in electrochemical energy systems,” Energy Environ. Sci., vol. 7, pp. 3135–3191, 2014.

[2] D. R. Dekel, “A mini-review on cell performance in anion exchange membrane fuel cells,” J. Power Sources, p. submitted, 2017, 2017.

[3] L. Wang and J. R. Varcoe, “The first anion-exchange membrane fuel cell to exceed 1 W cm-2 at 70 °C with a non-Pt cathode,” Chem. Commun., pp. 1–3, 2017.

[4] H.-S. Shiau, I. V. Zenyuk, and A. Z. Weber, “Elucidating Performance Limitations in Alkaline-Exchange- Membrane Fuel Cells,” J. Electrochem. Soc., vol. 164, no. 11, pp. E3583–E3591, 2017.
Monolayer Graphene Based Membrane to Replace Nafion in PEM Fuel Cells
Authors: Sahoo Madhumita , Perez-page Maria , Kalangi Vasu , Nair Rahul Raveendran , Holmes Stuart
Published: February 2020

Low temperature, proton exchange membrane fuel cells (PEMFC) are one of the promising and much investigated electrochemical energy conversion devices as a solution to the enormous world energy consumption demand. Hydrogen and methanol fuelled cells are of particular interest because of their high efficiency and low emission. However commercialization of these cells is hindered by their high cost, which mostly comes from the noble platinum catalyst and conventional Nafion membrane electrolyte. Research to reduce the amount of Pt by dispersing onto, high surface area support materials or to replace with non-precious catalysts have been studied widely to achieve minimal (~ µgPt/cm2 loading) expenditure in this area. However, an alternative to expensive Nafion is still a challenge.

In our previous work [1], we have shown that the incorporation of monolayer graphene (grown on copper foil by chemical vapour deposited (CVD) method) on the membrane electrode assembly (MEA) reduces the problematic methanol crossover in a direct methanol fuel cell by 26 % without affecting the proton conductivity [2]. 45 % improvement in the fuel cell performance for the single layer graphene (SLG) fused cell was achieved in comparison to the cell without SLG [1].

Herein we report two approaches as an alternative to completely replace the solid Nafion membrane in PEMFC. In the first method, SLG incorporated direct membrane deposited [3] MEA is used in the cell. The thickness of the modified electrolyte layer was controlled and optimized by varying the quantity of used Nafion ionomer and scanning electron microscope (SEM) image analysis. Cheaper polybenzimidazole (PBI) membrane is used as the mechanical backing support for the SLG and used to assemble the MEA in conventional method for the second route. Polarization curve, linear sweep voltammetry, impedance spectroscopy and durability testing is implemented to test the practical fuel cell performance for the systems. Obtained results are analysed, compared and discussed with respect to thickness, fuel crossover and membrane resistance for the modified electrolyte cells over conventional solid membrane cell.

References

[1] Stuart M. Holmes, Orabhuraj Balakrishnan, Vasu. S. Kalangi, Xiang Zhang, Marcelo Lozada-Hidalgo, Pulickel M Ajayan, Rahul R. Nair., 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Advanced Energy Materials 7 (2017) 1601216.

[2] S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu, A. K. Geim, Proton transport through one-atom-thick crystals. Nature 516 (2014) 227-230.

[3] M. Klingele, M. Breitwieser, R. Zengerle, S. Thiele, Direct deposition of proton exchange membranes enabling high performance hydrogen fuel cells. Journal of Materials Chemistry A 3 (2015) 11239-11245.
Estimation of Cation Contamination Level in Polymer Electrolyte Membrane Fuel Cells By Electrochemical Impedance Spectroscopy
Authors: Shibata Masao , Kitano Naoki , Shinohara Akihiro , Asaoka Takahiko , Takeuchi Norimitsu , Morita Touru , Kumei Hideyuki
Published: February 2020

One of the fundamental hurdles for further commercialization of fuel cell vehicles (FCV) using polymer electrolyte membrane fuel cells (PEMFC) is their upper limitation of operating temperature. Operating temperature of current PEMFC is much lower than that of internal-combustion engines and it makes FCV require huge radiators for high power operation. Raising operating temperature is beneficial for downsizing and cost reduction for FCV system because it downsizes not only cooling system but also PEMFC stack.

One of the root causes of this limitation is the decrease in proton conductivity of the membrane during long term operation. In order to avoid the decrease in proton conductivity, reducing the contamination of metal cations in the membrane is an effective way. Metal cations, which contaminate into the membrane during operation, reduce the proton conductivity of the membrane due to decrease in the proton path in the membrane. Proton conductivity loss by contamination of metal cations is critical for the high temperature performance.

In order to reduce cation contamination into the membrane, it is necessary to understand its mechanism. An in-situ measurement for the amount of metal cations should be helpful to understand the phenomena. For this reason, we propose an in-situ quantitative measurement for cation contamination ratio in PEMFC.

Electrochemical impedance spectroscopy (EIS) was adapted to the measurement because cation transport inside the membrane was expected to be detectable with EIS. Experimental results showed that EIS spectrum under a certain condition reflects metal cation contamination ratio strongly, which was proposed to be an indicator of cation contamination ratio. The mechanism of EIS spectrum change is explained theoretically by a numerical simulation using a simple model of cation and water transport. Detail of the measurement will be shown in the conference.

Therefore this EIS measurement is proposed for the analysis of metal cation contamination mechanisms in PEMFC. Further study will elucidate the impact of catalyst layer, membrane and metal cation species against the EIS spectrum.
3M Ionomer Adsorption on Polymer Electrolyte Membrane Fuel Cell Electrodes
Authors: Cantillo Nelly M. , Peng Jing , Sneed Brian , Goenaga Gabriel A. , More Karren L. , Zawodzinski Thomas A.
Published: February 2020

Previous ionomer adsorption (Figure 1) explorations in our group have shown significantly lower adsorption (lower Keq) of ionomer when platinum (Pt) nanoparticles are present on the carbon support.1 Such differences can suggest a higher affinity of the polymer chain to carbon, which could suggest that acidic groups on the carbon surface might participate in hydrogen bonding on dipole-dipole interactions with the hydrophilic unit in the polymer.1,2 This disagrees with many recent suggestions that the interactions with ionomer are driven by specifc adsorption of sulfonic acid or sulfonate on the Pt. Understanding such interactions can be key to further improve the Pt/Carbon/ionomer electrodes structure and, consequently, proton exchange membrane fuel cell (PEMFC) performance.

In this study, the adsorption of ionomer on a series of Pt:C (0:100, 30:70, 50:50 and 70:30) ratios using Vulcan XC-72 Carbon and Ketjenblack (KJB) supports were evaluated to further understand this interaction. The adsorption properties of water-dissolved 3M 825 equivalent-weight (EW) ionomer on both the carbon supports and the series of carbon-supported platinum (Pt/C) catalysts were studied with 400 MHz 19F Nuclear Magnetic Resonance Spectroscopy (NMR) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

A detailed structure characterization of the pristine supports and catalyst materials was achieved through Brunauer-Emmet-Teller (BET) nitrogen adsorption-desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The adsorbed ionomer structure was also explored through NMR and Fourier-Transform Infrared (FTIR).

These results will be reported along with context from other studies of ionomer-supported catalyst interactions in the actual catalyst layer.

Acknowledgements

NMC gratefully acknowledges the support from a Fulbright Fellowship as well as the Office of Naval Research. Research was supported at ORNL by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy.

References

N. M. Cantillo, L. Li, J. Peng, G. A. Goenaga, and Thomas A. Zawodzinski ECS Trans., 80, 259–268 (2017) http://ecst.ecsdl.org/content/80/8/259.full.pdf.

S. Ma, Q. Chen, F. H. Jøgensen, P. C. Stein, and E. M. Skou, Solid State Ionics, 178, 1568–1575 (2007).

Figure 1
Unveilling the Degradation Pathway of Highly Defective Hollow PtNi/C in Operando Conditions
Authors: Dubau Laetitia , Asset Tristan , Nelayah Jaysen , Chattot Raphaël , Bordet Pierre , Drnec Jakub , Maillard Frederic
Published: February 2020

Due to strain and ligand effects, the simultaneous presence of concave and convex surfaces and their highly-defective nanostructure (atomic vacancies, grain boundaries), highly defective hollow PtNi/C electrocatalysts have proven to enhance remarkably the oxygen reduction reaction (ORR) kinetics [1,2]. However, a technologically-relevant proton-exchange membrane fuel cell (PEMFC) cathode catalyst should be able to maintain its initial catalytic activity on the long-term. This is hardly feasible on nanocatalysts based on platinum alloyed with transition metals (PtM alloys, M being a transition metal) or M-rich core@Pt-rich shell nanoparticles due to the dissolution of the transition metal in the harsh operating conditions of a PEMFC cathode but the question remains open for nanocatalysts in which catalytic activity is not solely due to alloying effects. Herein, the stability of highly defective hollow PtNi/C nanoparticles was evaluated in X-Rays operando conditions under simulated PEMFC operating conditions (5,000 potential cycles between 0.6 and 1.0 V or 1.1 V vs. RHE at T = 80°C). The combined physical, chemical and electrochemical results show that the degradation pathway of highly defective hollow PtNi/C nanoparticles closely depends on the upper potential limit of the cycling protocol (Figure 1). Beyond 1V, the restructuring kinetics is accelerated compared to the 0.6 – 1.0 V protocol and the losses in ORR activity are related to both the weakening of strain and ligand effects associated with the dissolution of Ni atoms and to the decrease of the concentration of structural defects.

[1] L. Dubau, T. Asset, C. Bonnaud, R. Chattot, V. van Peene, F. Maillard, ACS Catal., 5 (2015) 5333-5341.

[2] L. Dubau, J. Nelayah, S. Moldovan, O. Ersen, P. Bordet, J. Drnec, T. Asset, R. Chattot, F. Maillard, ACS catal., 6 (2016) 4673-4684.

Figure 1
Employment of Fiber-Shaped Cobalt Modified with Gold Nanoparticles As Anode in Direct Borohydride and Hydrazine Fuel Cells
Authors: Balciunaite Aldona , Zabielaite Ausrine , Tamasauskaite-Tamasiunaite Loreta , Norkus Eugenijus
Published: February 2020

In this study fiber-shaped cobalt was electroplated on the copper surface and modified with various amounts of gold nanoparticles (denoted as AuCofiber/Cu) with the aim to use it as the anode in direct borohydride and hydrazine fuel cells (DBFC and DHFC). Single fuel cell tests were performed by employing the prepared AuCofiber/Cu catalysts with the Au loadings in the range of 11-84 µgAu cm-2 as the anode and a Pt sheet as the cathode. The anolyte was composed of an alkaline mixture of 1 M NaBH4 + 4 M NaOH or 1 M N2H4 + 4 M NaOH and the acidic catholyte contained 5 M H2O2 + 1.5 M HCl. The performance parameters of the fuel cell was evaluated by recording the cell polarization and obtaining the corresponding power density curves at 25 ºC. А Nаfion®N117 membrаne wаs used to sepаrаte the аnodic аnd cаthodic compаrtments of the single fuel cells.

It was found that the direct N2H4-H2O2 and NaBH4-H2O2 fuel cells exhibited аn open circuit voltаge of cа. 1.7 and 1.9 V, respectively. Peаk power densities up to 162 and 188 mW cm-2 аt a temperature of 25oC were obtained from N2H4-H2O2 and NaBH4-H2O2 fuel cells, respectively. It is worth to note that the highest specific peаk power density values of ca. 12 kW g–1
Аu and 15 kW g–1
Аu were obtаined, when employing the АuCofiber/Cu catalyst with the Аu loаding of 11 µgАu cm–2 аs the аnode cаtаlyst.

Acknowledgment

This research was funded by a M-ERA.NET grant (No. M-ERA.NET-1/2016) from the Research Council of Lithuania.
Low Cost PCB Fuel Cells Based for Small Electronic Applications
Authors: Parra Puerto Andres , Hakola Liisa , Kucernak Anthony R. J.
Published: February 2020

An important aspect to enhance the introduction of the fuel cells systems in the market, is decreasing the cost of manufacturing, obtaining a flexible way to extend their use in different applications. The possibility to use the well-defined PCB manufacturing technic to develop fuel cells stacks can help to obtain a low-cost and tuneable method for their production [1]. Using this manufacturing method is easy to control the size and adjust the power requirements for different electronic devices as electrochromic devices, smartphone chargers, electric vehicles, etc. As well, due to their flat configuration is very easy to stack many of them in small spaces. In this work we design and develop a mini and micro stack DMFC open cathode PCB cell using low cost materials on the bipolar plates and electrodes. In general, for the bipolar plates different metal and ink coatings were used to improve the durability and the electrical contact. But them requires few steps to obtain the final stage, in our case we moved to a graphitic flexible material with very high corrosion resistance and conductivity giving the possibility to avoid the coating steps. In the case of the electrodes, a non-precious metal and very high poison resistance catalyst developed in our lab was used as cathode [2]. In the anode part, an inkjet printed electrodes where used. This method gives the possibility to decrease the loading of catalyst obtaining a really good performance in the Fuel Cell. For the micro-DMFC we developed two setups, one similar to the mini stack cell and the other one, in a complete passive configuration. The design of the fully passive cells gives the possibility to inject the methanol solution in the anode reservoirs. This micro stack cell was developed to power up an autonomous electrical biosensor synergistically assembled inside a passive DMFC for screening cancer biomarkers included in the European 2020 project called Symbiotic.

[1] O. A. Obeisun et al., “Development of open-cathode polymer electrolyte fuel cells using printed circuit board flow-field plates: Flow geometry characterisation,” Int. J. Hydrogen Energy, vol. 39, no. 32, pp. 18326–18336, 2014.

[2] D. Malko, T. Lopes, E. Symianakis, and A. R. Kucernak, “The intriguing poison tolerance of non-precious metal oxygen reduction reaction (ORR) catalysts,” J. Mater. Chem. A, vol. 4, no. 1, pp. 142–152, 2016.

Figure 1
The Enhancement of Hydrogen Oxidation Activity and the Optimization of Alloy Composition in PdRu Nanoparticle Catalysts
Authors: Kwon Kyungjung , Jin Seon-ah , Cho Jinwon , Ham Hyung Chul , Pak Chanho
Published: February 2020

Fuel cells are believed as promising power sources with many advantages including their high efficiency and environment-friendliness. Proton exchange membrane fuel cells (PEMFCs), of which usage can be expected as power sources as automobiles and so on, have yet several problems to resolve for the commercialization. Among them, the high price due to the scarcity of Pt, which is used as anode and cathode catalysts, is one of the most serious issues. Pd is a natural choice to replace Pt because the hydrogen oxidation reaction (HOR) activity of Pd is the next to that of Pt, and Pd is at least fifty times more abundant on earth than Pt. Pd is a more attractive substitute for Pt because of its higher intrinsic CO tolerance than Pt, especially as HOR catalysts for PEMFC where the tolerance of CO, a major impurity of hydrogen fuel, is crucial. Although Pd has comparable HOR activity to Pt, the exclusive use of Pd as anode catalysts of PEMFC has not been satisfactory for the replacement of Pt. We confirmed in our previous report (K. Kwon et al., Catal Today, 232 (2014) 175) that the insufficient HOR activity of Pd could be supplemented by coupling with other elements or compounds such as Ru and tungsten oxide. To investigate the effect of alloying with Ru thoroughly, the calculation of hydrogen binding energy was performed on the basis of spin polarized density functional theory. Pure Pd(001) and Ru(001), Pd monolayer on Ru, and Pd bilayer on Ru are considered as model systems in the calculation. Strain and ligand effects are only applicable to bimetallic models (Pd monolayer on Ru and Pd bilayer on Ru). The negative sign of strain and ligand effects stands for a decrease in binding energy for PdRu alloy.

Meanwhile, instead of making an effort to turn the model alloy systems into nanoparticles of Pd mono/bilayer on Ru, which would not be realistic in a few nm dimension, the actual confirmation of HOR enhancement at the level of half cell and PEMFC single cell was obtained by fabricating homogeneous PdRu alloy nanoparticles on carbon support. PdRu nanoparticles of different Pd:Ru atomic ratios of 1:0, 9:1, 1:9, and 0:1 were characterized with TEM and XRD, and compared with a commercial state-of-the-art Pt-based anode catalyst (PtRu1.5/C) in electrochemical experiments. The PdRu9 catalyst shows the highest HOR activity among the PdRu samples, which is comparable to the PtRu catalyst, even though the respective Pd and Ru have lower activity than PtRu. The highest HOR activity of the Ru-richest PdRu nanoparticles could be in line with the highest HOR activity of the Ru-richest PdRu model system (Pd monolayer on Ru).
Zirconia Doped Ceria Cathodic Interlayer By Atomic Layer Deposition for Low Temperature Solid Oxide Fuel Cell
Authors: Yang Byung Chan , Go Dohyun , Oh Seongkook , Shin Jeong Woo , An Jihwan
Published: February 2020

Solid oxide fuel cell (SOFC) has the advantages of high energy conversion efficiency, fuel flexibility, and environment friendliness. However, conventional SOFC also has limitations in applying to various fields due to the high operating temperature of 800-1000℃. Therefore, low temperature SOFC (LT-SOFC) (≤ 500 ℃), which can be operated at relatively low temperature, are being widely researched these days. Operation losses of LT-SOFCs, however, have to be minimized to maintain the performance even at low temperature; especially, at low temperature, the activation loss at cathode is the dominant loss due to sluggish oxygen reduction reaction (ORR). The adoption of cathode interlayer such as doped ceria has been researched as an effective method to dramatically lower the cathodic activation loss in LT-SOFCs.

In this study, we used zirconia-ceria composite cathodic interlayer fabricated by atomic layer deposition (ALD) to improve the performance of SOFC at low temperature. Ceria-based materials with high oxygen ion conductivity and high oxygen surface exchange coefficient at relatively low temperatures have been widely used as cathodic interlayers for LT-SOFCs, but the relatively low chemical stability has been the practical issue. Zirconia doped ceria (ZDC), on the contrary, is known to have better catalytic properties than pure ceria with even improved chemical stability. We show that the performance of LT-SOFC can be significantly enhanced by using ZDC as cathodic interlayer. The ZDC interlayer was deposited on the cathode side surface of yttria stabilized zirconia (YSZ) electrolyte using ALD. ALD is beneficial in depositing ultra-thin film with the capability to precisely control the composition and the thickness of films. Each interlayer of 20 nm-in-thickness was deposited with different ratios of zirconia and ceria; the molar ratio of zirconia was varied at 0, 30, 50, 80, and 100 mol%, respectively. The composition of the interlayer was analyzed by X-ray Photoelectron Spectroscopy (XPS) and the electrochemical performance was measured at 450℃ by using current-voltage characterization and electrochemical impedance spectroscopy (EIS). The maximum power density of the cell with the ZDC interlayer improved by 50% compared to that of the reference cell without the interlayer, which is even higher those of the cells with zirconia-only or ceria-only interlayers. In addition, the activation resistance of the cell with ZDC was decreased by ~50% in comparison with the cell without interlayers as shown in EIS measurements.
On the Effect of Clamping Pressure and Method on the Current Mapping of Proton Exchange Membrane Water Electrolysis
Authors: Al Shakhshir Saher , Zhou Fan , Kær Søren Knudsen
Published: February 2020

The degradation of the electrochemical reaction of the proton exchange membrane water electrolysis (PEMWE) can be characterized using in-situ current mapping measurements (CMM). CMM is significantly affected by the amount of clamping pressure and method. In this work the current is mapped downstream at the cathode side of 50 cm2 active area single PEMWE cell at different clamping pressure and different clamping methods. Two clamping methods are used; bolting the cell with 8 bolts around the active area and clamping the cell from the whole area of the end plate using highly pressurized clamping set-up. CMM is carried out using S++ setup, where the segmented plate is placed between the current distributor and flow field plate downstream at the cathode side of the PEMWE cell. The segmented plate consists of 100 segments over the 50 cm2, thus each segment area is 0.5 cm2.

Initial results show that, the clamping pressure effect on the CMM is not symmetrical in both clamping method and it directly affects the CMM homogeneity. Also it is concluded that higher PEMWE cell performance not necessary means more homogeneous CMM over the cell area.

Figure 1
Rutile-Anatase Core-Shell TiO2 Nanostructured Array for Photoelectrochemical Water Oxidation and CO2 Photoconversion
Authors: Yang Jih-Sheng , Chang Hao-Chun , Wu Jih-Jen
Published: February 2020

In this work, TiO2-based nanostructured arrays with the core-shell structure composed of the anatase NPs (ANP) on the surface of rutile nanostructures arrays are used to be photocatalysts for photoelectrochemical water splitting and CO2 photoconversion. A superior PEC performance in alkaline electrolyte can be achieved in the hierarchical ANPs/rutile TiO2 nanodendrite (RND) array photoanode due to the formation of type-II heterojunction of anatase/rutile TiO2. However, the anodic-shift onset potential and decreased saturation photocurrent density are shown in the J-V curve of the ANP/RND array photoanode obtained in neutral electrolyte. An ultra-thin In2S3 layer is further deposited on the surface of the ANP/RND array photoanode to construct additional type-II heterojuntion for the enhancement of the charge separation of the ANP/RND array array photoanode in neutral electrolyte. By the surface modification of the photoanode with the transparent In2S3 layer, a photocurrent density of 1.6 mA cm−
2 at 1.23 V vs. RHE is attained using the In2S3/ANP/RND array photoanode in neutral electrolyte under illumination of AM 1.5G (100 mWcm−2). On the other hand, the rutile TiO2 NR array (RNR) shows an ability to convert CO2 and H2O into CH4, CO, and H2 under Hg-lamp irradiation. Compared to the RNR array, ANP/RNR array shows superior photocatalytic activity for CO2 photoconversion. Both the overall conversion efficiency and the selectivity of CH4 production are improved as the formation of core-shell structure. The details will be discussed in this presentation.
Stable Silicon-Based Sandwich Photoelectrode for Efficient Solar Hydrogen Evolution
Authors: Cheng Chaoqun , Du Kang , Zhang Zengxing , Li Gang , Wang Kaiying
Published: February 2020

Photoelectrochemical water splitting, consisting of photoanode and photocathode used for water reduction and oxidation, is a potential route to store the solar energy into chemical fuels. In terms of the required earth abundance, cheapness and proper band gap edges (1.12 eV), silicon is an attractive photoelectrode material. Unfortunately, silicon suffered from the instability and low efficiency due to the severe photocorrosion and passivation in the reaction electrolyte, even though limited performance has been achieved for water splitting development. [1-3].

In this work, in order to enhance the stability and photoelectrochemical efficiency, we fabricated silicon-based sandwich photoelectrodes with mediated protection layer of sputtered Molybdenum thin film, which is covered with hand-sprayed MoS2 as the catalyst, as shown in the fig. 1(a). The samples are marked with a, b, c and d separately after different thermal annealing time of 0h, 1h, 2h, 3h in the static Nitrogen atmosphere. After proper annealing, the formed nanoporous surficial structure could be observed in the SEM images (fig. 1(b)) with pore diameters ranging from 10 to 50 nm. These porous networks offer much more active sites for water splitting. The effect of annealing temperature on optical response is shown in fig. 2(a). The UV-Vis spectra show that the annealed surficial MoS2 exhibits extended optical responses to the longer wavelength region, indicating the potential enhanced visible light absorption. What’s more, in the photoluminescence (PL) spectra (Fig. 2(b)), the weaker PL intensity are observed after covering MoS2 on the top surface of Mo and essential annealing process, suggesting the suppressed recommendation of the photoexcited electrons and holes in the interface and therefore improved solar energy conversion.

In conclusion, the silicon-based sandwich photoelectrode with enhanced visible light absorption and conversion is fabricated through facile processes. This novel low-cost silicon-based photoelectrode possess potential enhanced efficiency and stability applied in the photoelectrochemical water splitting system.

Acknowledgments: The authors gratefully acknowledge the financial support from Norwegian Research Council FRINATEK programme (231416/F20), and China Scholarship Council (CSC, Grant No.201506930002). The Research Council of Norway is acknowledged for the support to the NorFab, project number 245963/F50.

References

[1] M. J. Kenney, M. Gong, Y. Li, J. Z. Wu, J. Feng, M. Lanza, H. Dai, Science, 343 (6160), 836-840 (2013).

[2] S. Hu, M. R. Shaner, J. A. Beardslee, M. Lichterman, B. S. Brunschwig, N. S. Lewis, Science, 344 (6187), 1005-1009 (2014).

[3] J. Feng, M. Gong, M. J. Kenney, J., Z. Wu, B. Zhang, Y. Li, H. Dai, Nano Res., 8 (5), 1577–1583 (2015).

Figure 1
(Invited) Electrochemical Ammonia Synthesis Using Intermediate Temperature Proton Conducting Membranes
Authors: Kreller Cortney R. , Ramaiyan Kannan Pasupathikovil , Maurya Sandip , Parker Nia , Mukundan Rangachary , Kim Yu Seung , Garzon Fernando H
Published: February 2020

Due to the intermittency of many renewable energy sources, their potential to significantly participate in the overall energy mix is strongly dependent on our ability to identify and develop efficient and cheap energy storage technologies1. Liquid fuels are an appealing option with energy densities typically 10-100x higher than batteries. Ammonia, in particular, has many attributes that make it the ideal energy storage compound including high energy density and an existing infrastructure for transportation. The highly developed, large-scale production of ammonia via Haber-Bosch process is not suitable for energy storage applications due to the high-temperatures and pressures used. Theory2 and experiment3 suggest that a more suitable approach is the production of ammonia from nitrogen and water via electrosynthesis whereby small-scale reactors could enable distributed ammonia production closer to the consumer and be more compatible with energy inputs from intermittent renewable energy resources - improvements that could dramatically reduce the energy and carbon intensity of ammonia production and distribution.

Prior research pursuing the electrosynthesis of ammonia has focused primarily on the use of proton conducting electrolytes at high temperatures, >600˚C or low temperatures, <100˚C due to materials limitations in the intermediate temperature range. The intermediate temperature range is particularly advantageous as lower temperatures favor the thermodynamics of the forward reaction to form NH3, while higher temperatures aid in the breaking of the incredibly stable di-nitrogen bond (946 kJ/mol). In order to access this intermediate temperature range of operation, we have developed a composite SnP2O7/Nafion based electrolyte material that exhibits conductivity on the order of 20 mScm-1 at 200˚C. We have demonstrated a maximum ammonia production rate of ~1x10-8molcm-2s-1 at 200˚C using N2 and H2 as reactant gases and Pt-based electrodes. This talk will discuss the factors influencing production rates and current efficiencies of these intermediate temperature devices.

References

J. B. Goodenough, H. D. Abruna and M. V. Buchanan, 2007.

T. H. Rod, A. Logadottir and J. K. Nørskov, The Journal of Chemical Physics 112 (12), 5343 (2000).

G. Marnellos and M. Stoukides, Science 282 (1998).

Acknowledgements

This project is supported by ARPA-E under Award No. DE-AR0000687.
Modeling Hypochlorous Acid Generation on Carbon Fabric Surface
Authors: Ben Sahil Ahmed , Beyenal Haluk
Published: February 2020

Hypochlorous acid (HOCl) can be electrochemically generated on carbon fabric surfaces made from carbon fibers for wound healing purposes and removing biofilms. HOCl is an oxidizer and deproteinizer with antimicrobial activity that gives carbon fabric surfaces biocidal properties. HOCl is of particular interest in wound disinfection as it offers lower toxicity, and lower irritability to mammalian cells than other biocidal agents such as hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl). In principle, carbon fiber surfaces can be typically applied on the infected wound or biofilms grown in test surfaces. In this work, a COMSOL Multiphysics ® finite element model of HOCl generation on carbon fabric surface is developed. In addition, we developed a new all-in-one microelectrode to measure local HOCl concentrations. The new microelectrode offers accurate measurements on polarized carbon surfaces due to its robustness against potential perturbations caused by the electric field generated on polarized carbon fiber surface. The novel microelectrode is used to 1) measure depth profiles and 2) probe local variations near the electrode surface using cyclic voltammetry. The model kinetic parameters are fit to experimental local HOCl concentrations on the surface of the working electrode of the carbon fabric in phosphate buffer saline (PBS). The predicted parameters are integrated to the model to predict HOCl and Cl- concentrations as function of time. In addition, the time needed to reduce the buffer capacity is determined. This information is of interest as it provides the experimenter with tools to determine the application time necessary to reach an effective HOCl concentration required to eradicate biofilm or the point in time when replenishing of Cl- is needed.
Doping Engineering in Type-II Homojucntion to Enhance the Photoelectrochemical Performance of Thin-Film BiVO4 Photoanode
Authors: Baek Ji Hyun , Lee Jae Myeong , Jung Hyun Suk
Published: February 2020

Photoelectrochemical (PEC) water splitting with metal oxides photoelectrodes is a promising renewable technology because of their good performance for light harvesting and stability as well as good properties such as naturally earth-abundant, harmless and economical. BiVO4 has been regarded as a major metal oxide material in the PEC photoanode due to the suitable band gap for efficient light absorption and advantage of solar-to-hydrogen conversion efficiency. However, the PEC performance of this single absorber material is limited due to its charge recombination in bulk, interface and surface derived by poor carrier diffusion property, electrical conductivity and water oxidation kinetics. Until now, many attempts of junction of two materials such as BiVO4/WO3, BiVO4/ZnO or BiVO4/Bi2WO6 to form a type-II heterojunction has been introduced to be a feasible mean to improve the charge separation and transport efficiencies.

In this study, we have modified the BiVO4 single absorber with Zn and Mo doping and introduced the type-II homojunction BiVO4 photoanode for efficient PEC water splitting via a facile solution method. Interestingly, the Zn and Mo doping treatment let BiVO4 thin-film change the Fermi level and form the staggered band alignment. It is helpful to enhance the charge separation in bulk and charge transfer in surface of BiVO4 due to the interference of surface trapping of photogenerated charge carriers with type-II homojunction followed by the enhancement of PEC water splitting performances.
(Invited) Hollow Doped Carbon Nanopolyhedra with Exclusive Fe–Nx Active Sites As Advanced Cathode Catalyst Achieving Ultra High Polymer Electrolyte Membrane Fuel Cells Performance
Authors: LIao Shijun
Published: February 2020

Developing high-efficiency and low-cost cathodic oxygen reduction reaction catalyst for large-scale application of proton exchange membrane fuel cell is highly significant but still full of challenges. Herein, well defined Fe–N co-doped hollow carbon nanopolyhedra catalyst, with exclusive Fe–Nx active sites derived from the addition of C3N4 in the precursor, have been prepared by a facile and effective strategy, where hollow ZIF-8 is first synthesized by a chemical etching process, followed by impregnating with ferric acetylacetonate and g-C3N4, and pyrolyzing in Ar atmosphere. The catalyst inherits the good polyhedra morphology from its precursor, and the resulting optimal catalyst exhibits superior ORR performance in both acidic and alkaline mediums, with a half-wave potential of 0.78 V comparable to that of commercial Pt/C catalysts in acidic medium, and a half-wave potential of 0.85 V, ca. 30 mV more positive than that of commercial Pt/C catalyst in alkaline medium, making it one of the best doped carbon catalysts in an acidic and alkaline medium up to now; It is important that our hollow nanopolyhedra catalyst exhibits superior stability both in acidic and alkaline mediums, superior to commercial Pt/C. Furthermore, in the H2-O2 single PEM cell test, the MEA with our optimal hollow nanopolyhedra catalysts as cathodeachieved a current density of 700 mA cm−2 @ 0.6 V and 400 mA cm−2 @ 0.7 V, which is one the best PEMFC’s performance reported for doped carbon cathode. Combining 57Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy results, we ascribe the outstanding performance of our catalyst to the homogeneous distributions of high-density of Fe–Nx active sites (D1: FeN4/C and D3: N–FeIIN2+2…Nprot/C) and pyridinic-N, caused by the addition of C3N4.
Electrochemical Preparation of Nanostructured Silicon from Rice Husks As a Sustainable Source for High Performance Anode in Secondary Lithium Ion Battery
Authors: Wu Ding Chou , Wu Shu-Chi , Ai Yuanfei , Chueh Yu-Lun
Published: February 2020

Silicon is one of the most promising anode material candidates for lithium ion batteries because of its high specific capacity (3579 mAh/g), which is ten times higher than existing graphite anodes. One of the most important issues toward commercialization is the high cost of nanostructured silicon related to the complex fabrication amd expansive raw materials. In this work, we demonstrate the recycling of pure silicon nanoporous particles from rice husks (RHs) directly, which is an abundant agricultural byproduct (108 tons/year) in worldwide. Besides, the massive amount of RHs has unique nanoporous structure on the RHs to preform the function as protection and ventilation. In the first step of our experiment, the metal ions in the RHs by HCl leaching were removed and then incinerate the leached RHs to produce silica with nanostructure. Next step, we convert the silica to silicon by electrochemical reduction method, which is a potential process for large scale reduction in a relative low tempareture compared with conventional carbothermal reduction. Owing to the nanoporous nature, these recovered silicon nano-particles show high performance as lithium ion battery anodes, with high reversible capacity and long cycle life. Recycling RHs as the source of silicon, this work presents a process to produce Si based Li-ion battery with cost effective, energy-efficient, green, and potential of large scale synthesis in industry.

Key words: rice husk, electrochemical reduction, Li-ion battery
Oxidation-Reduction Potential Control for One Step Synthesis of Cu-Pt Core-Shell Nanoparticles
Authors: Nakamoto Tatsuichiro , Tsuchida Shuzo , Seki Ryohei , Ueyama Yasuhiro , Yokoyama Shun , Takahashi Hideyuki , Tohji Kazuyuki
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are promising power source because of their high power generation efficiency and low environmental pollution. However, PEFCs contain precious platinum catalyst in cathode and this leads to be expensive. Thus, PEFCs have to reduce the catalyst cost to be used more widely. In order to decrease the amount of platinum in the cathode, core-shell structured nanoparticles have been tried to synthesize. Core-shell structured nanoparticles mean, for example, Pt nanoparticles whose core is displaced by copper.

However, most of the synthesis methods of Cu-Pt core-shell nanoparticles require high energy and multiple processes. To cut the cost of PEFCs fundamentally, low cost synthesis method of core-shell nanoparticles needs to be developed. Therefore, in this study, one step synthesis method of Cu-Pt core-shell nanoparticles was researched under a mild condition such as aqueous solution of room temperature and atmospheric pressure.

Although the mild condition can cut the process cost, there are several problems. Therefore, possibility to synthesize Cu-Pt core-shell nanoparticles on the mild condition have to be evaluated before trying one step synthesis. Carbon supported Cu nanoparticles were synthesized as the first step. In the second step, the surface of the Cu nanoparticles was displaced by platinum, then Cu-Pt core-shell nanoparticles were synthesized on the mild condition in two steps.

To synthesize Cu-Pt core-shell nanoparticles in one step, oxidation-reduction potential (ORP) of metal complexes was calculated and controlled. Generally, ORP of Pt is higher than that of Cu and this leads to form Pt core Cu shell structure when Pt and Cu are reduced together. To achieve Cu core Pt shell structure, ORP calculation technique was developed and the synthesis condition which can invert the ORPs of Pt and Cu was found. Therefore, one step synthesis of Cu-Pt core-shell nanoparticles was performed on this condition and several properties of low cost PEFC cathode catalyst were measured. Detailed results will be shown in our session.
Molecular Dynamics Simulation of Modified Nafion 117 Based Anion Exchange Membrane Fuel Cell: Transport and Nanophase-Segregated Structure Properties
Authors: Caliendo Charles , Jang Seung Soon , Lee Jihoon
Published: February 2020

In this research, we investigate the effect of structural variation of Nafion 117 on the nanophase-segregation and transport properties using molecular modeling approach. In this study we replace the sulfate group of nafion117 with three different phosphate groups, and characterize its effect on nanophase-segregated structure and transport of water/protons at 80oC with various water contents. The three groups that will be tested are: simply changing the sulfur to phosphorus in the Nafion117 tail group, changing the entire tail group to a polyvinyl phosphate, and changing the tail group to a difluoromethandiphosphonic acid. This will be done by simulating the new molecular structures using molecular dynamic simulations at 80oC under isobaric conditions using LAMMPS. Dreiding force field will be partially modified to handle perfluorocarbon compounds, water, and hydronium. The equations of motion will be integrated using Verlet algorithm with a 1-fs time step, and the PPPM method to evaluate the electrostatic interactions. After an equilibration cycle, each system will then be simulated for an extra 2 ns to sample structures for statistical treatment. By simulating the proton conductivity of these molecules we seek to understand the relationship among underlying polar groups, nanophase-segregated structure, and transport which would serve in designing new polymer electrolyte membranes.
Comprehensive Analysis of a Tubular, Reversible Solid Oxide Fuel Cell By Using a 3-D Computational Fluid Dynamics Model
Authors: Yoo Jae Young , Kang Juhyun , Bae Joongmyeon
Published: February 2020

Hydrogen technology has recently gained wide attention in the field of renewable energy. This technology needs to either consume hydrogen to generate electricity or produce the gas to store energy. A reversible solid oxide fuel cell (SOFC) can perform the two tasks by simply changing its operating conditions. Experiments can determine the performance of the SOFC but has economic limitations in changing its design parameters. A computational fluid dynamics (CFD) model, on the other hand, can test various design options at a relatively low cost. This study performed a CFD analysis of a tubular, reversible cell in its SOFC and SOEC modes in COMSOL Multiphysics 5.3. The model performed calculations by considering fluid dynamics, mass diffusion, heat transfer, and electrochemistry. The calculation results were then compared with experimental data to verify the model at various values of the cell voltage. The results showed that the hydrogen, steam, oxygen, and nitrogen distributions had certain, distinguishable effects from the model parameters. The results agreed with those from the literature both qualitatively and quantitatively. The IV data of the model matched with the experimental IV curves to an acceptable degree, further supporting the credibility of the model. Other authors who seek to model a tubular SOFC in the future can refer to this study as a reference. The results are also important in designing and building a stack of tubular, reversible SOFCs because the design parameters of the current cell can be adjusted to result in a more suitable cell for the stack build-up.
All-Carbon Supercapacitor, Fullerene-Grafted 3D Graphene As Electrical Energy Storage Material
Authors: Cerón Maira R. , Vedharathinam Vedasri , Campbell Patrick G. , Pham Tuan Anh , Wood Brandon C. , Biener Juergen , Echegoyen Luis , Biener Monika M.
Published: February 2020

Supercapacitors have the potential to replace Li ion batteries as the next-generation electrical energy storage technology in demanding applications due to their high power density and excellent cycling stability. Graphene-based supercapacitor electrodes are very attractive because they feature high surface area, high electrical conductivity, and chemical inertness; however their capacitance is limited by their low density of states at the Fermi level (ca. 1 e- per 100 C atoms). To overcome the current charge storage limitations of graphene-based supercapacitors, researchers at Lawrence Livermore National Laboratory have developed an all-carbon composite graphene/fullerene supercapacitor combining the high charge storage capacitance of fullerenes (up to 6 e- per C60) with the high electrical conductivity of 3D mesoporous graphene macro-assemblies (GMAs) (Figure 1).

Fig. 1:

Fullerene-grafted 3D graphene bulk material.

Funding was provided by Lawrence Livermore National Laboratory Directed Research and Development (LDRD) Grant 17-ERD-017. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344. IM Release Number LLNL-ABS-741683.

Figure 1
(Invited) Flexible Li-Ion Batteries Made of Binder and Collector Free Electrodes Based on Pristine Carbon Nanotubes
Authors: Harutyunyan Avetik R , Kuznetsov Oleg Anatoli , Chen Gugang , Pigos Elena
Published: February 2020

Despite many newly proposed concepts and a variety of materials applied, Li-ion batteries remain as the most reliable energy storage system for a broad range of applications. As a result, intense research is underway worldwide for further enhancement of their key parameters such as energy/power densities, charge/discharge rates and safety. These attempts include discovering new cathode/anode materials, electrolytes, additives, binders and optimization of metal collectors. Here we present Li-ion battery based on freestanding anode and cathode electrodes consisting only of active material and single wall carbon nanotubes, eliminating the need of additives, binders and collectors. Since, those components constitute about a 30 % in a battery weight, then it is expect an increase of energy density. Our freestanding electrodes have been obtained, for the first time, by a one-step in situ mixing of the active material powder with pristine carbon nanotubes, providing homogenous mixing, preventing nanotubes bundling, and thereby reducing percolation point of electrical conductivity of obtained electrodes. Controlling this parameter is also important for enhancement of power density. Moreover, our method allows continuous production of freestanding, flexible sheets of electrodes that open new perspectives for powering flexible electronics and sensors/actuators for wearable devices. The results of battery performance, evaluations, and impedance studies depending on C-rates, nanotube concentrations, density of electrodes and their conductivities will be presented for two different configurations: coin and pouch cells for half and full cells, respectively.