bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Ball-Milling on the Oxygen Reduction Reaction Activity of Iron and Nitrogen Co-Doped Carbide-Derived Carbon Catalysts in Acid Media
Authors: Ratso Sander , Sougrati Moulay-Tahar , Käärik Maike , Kook Mati , Merisalu Maido , Rähn Mihkel , Kisand Vambola , Kikas Arvo , Paiste Päärn , Sammelselg Väino , Leis Jaan , Jaouen Frederic , Tammeveski Kaido
Published: December 2020

Storing renewable energy to complete the energy cycle is a crucial challenge in the movement from a fossil fuel-based economy to a circular one. In the hydrogen cycle, stored hydrogen is converted back to usable energy in a fuel cell. The biggest issue in proton exchange membrane fuel cells (PEMFC) is the replacement of noble metal catalysts with a non-precious metal catalysts (NPMC). Iron and nitrogen doped nanocarbon materials are among the most promising alternatives.

In our previous works on iron and nitrogen doped carbide-derived carbons (CDC) we discovered that ball-milling of CDCs has a crucial effect on their porosity and the final activity of the catalyst.1,2 In this work,3 we study the effect of ball-milling conditions and compositions of catalyst precursors comprising a silicon carbide-derived carbon (SiCDC) on the properties of the final catalysts, most importantly their activity toward the oxygen reduction reaction (ORR). Ball-milling rates from 100 to 800 rpm were investigated with 400 rpm proving to be the optimum value. The effect of 1,10-phenanthroline-to-iron ratio in the precursor mixture was also studied, with a 12-1 molar ratio leading to the highest activity. Finally, ZnCl2 addition to the precursor mixture was explored as a pore former during pyrolysis. A ZnCl2-to-CDC mass ratio of 1 resulted in the highest ORR activity. 57Fe Mössbauer spectroscopy confirmed that most of the iron was atomically dispersed as Fe-Nx moieties (Figure 1, left). The most active catalyst showed a kinetic current density of 4.6 mA cm-2 at 0.8 V in rotating disk electrode tests and a current density of 18.6 mA cm-2 at 0.8 V in a single-cell proton exchange membrane fuel cell (Figure 1, right).

References

Ratso, N.R. Sahraie, M.T Sougrati, M. Käärik, M. Kook, R. Saar, P. Paiste, Q. Jia, J. Leis, S. Mukerjee, F. Jaouen, and K. Tammeveski, J. Mater. Chem. A, 6, 14663–14674 (2018).

Ratso, M. Käärik, M. Kook, P. Paiste, J. Aruväli, S. Vlassov, V. Kisand, J. Leis, A. M. Kannan, and K. Tammeveski, Int. J. Hydrogen Energy, 44, 12636–12648 (2019).

Ratso, M. T. Sougrati, M. Käärik, M. Merisalu, M. Rähn, V. Kisand, A. Kikas, P. Paiste, J. Leis, V. Sammelselg, F. Jaouen, and K. Tammeveski, ACS Appl. Energy Mater., 2, 7952–7962 (2019).

Figure 1
Alternative Me-N-C Based Carbon Foams As Fe-Free and Non-PGM Electrocatalysts
Authors: Suzuki Shoyo , Mufundirwa Albert , Sasaki Kazunari , Hayashi Akari , Lyth Stephen Matthew
Published: December 2020

There is a demand for reducing the environmental load of automobiles to solve the current environmental problems. Fuel cell electric vehicles (FCEVs) which use hydrogen as fuel emit no carbon dioxide, and have already been commercialized. platinum-based materials are widely used as oxygen reduction reaction (ORR) catalysts. However, their high cost and limited durability impedes large-scale implementation. Until now, non-platinum group metal (non-PGM) Fe and N doped carbon (Fe-N-C) catalysts have achieved promising ORR activity [1]. However, these Fe-N-C catalysts still suffer from poor durability, due to the formation of reactive peroxide radicals as a side reaction during the ORR. Meanwhile, the use of Co species avoids the production of such radicals, potentially preserving the electrocatalyst [2]. Therefore, in this study we investigate the dependence of ORR activity on a variety of different metal ions by synthesizing alternative Me-N-C carbon foam electrocatalysts (Me = Co, Ni, Sn).

Pt-free electrocatalysts were synthesized from nitrogen-doped carbon foams (N-C) and various metal salt and small molecule precursors. Porous nitrogen-doped carbon foams with large surface area were made in-house. These were adsorbed with metal acetate and then heated in inert atmosphere, followed by acid washing to remove metallic phases. Finally, heat treatment under ammonia was performed. The effect of heat treatment temperature and metal loading on the microstructure and porosity was evaluated. The resulting catalysts were evaluated for catalytic activity using rotating-ring disk electrode voltammetry (RRDE) in acid.

For Co-N-C electrocatalysts it was found that heat treatment of the nitrogen-doped carbon foam support has a significant effect on catalyst performance, largely due to changes in surface area and porosity. The metal loading also has a strong effect on the performance, with an optimum Co loading of 0.1 wt% resulting in an onset potential of 0.8 VRHE and a half-wave potential of around 0.65 VRHE. Different metal ions were also systematically investigated, and it was found that Sn is highly promising as an alternative to Fe in non-PGM electrocatalysts.

References

[1] Albert Mufundirwa et al., Journal of Power Sources, 2018, 375, 244-254.

[2] Qingqing Cheng et al., Nano Energy, 2018, 52, 485-493.
Stability Design Principles of Mn-Based Oxides for Acidic Electrolytes
Authors: Peng Jiayu , Giordano Livia , Davenport Timothy , Shao-Horn Yang
Published: December 2020

Manganese-based oxides are promising, earth-abundant candidate materials in many electrochemical energy applications in aqueous environments, including supercapacitors,1 electrocatalysis2 and solar fuels.3 The use of these oxides in acidic systems, such as proton-exchange membrane fuel cells and electrolyzers,4,5 is, however, severely limited by the bulk instability of Mn oxide phases according to their Pourbaix diagrams.2 Designing active and stable Mn-based oxide catalysts in acidic electrolytes therefore requires fundamental understanding towards their aqueous stability and dissolution mechanism in acid.

In this study, we systematically examined the aqueous stability of Mn-based oxides with a diverse range of chemistry, structures and oxidation states in acidic electrolytes. Decreasing the metal-oxygen covalency, e.g. by having Mn ions with lower nominal oxidation states, was found to weaken the manganese-oxygen bonds, reduce the energy penalty for the formation of Mn vacancies and subsequent ion solvation, rendering poorer stability in acidic solutions. Moreover, we identified the critical role of oxide acid-base chemistry6 in dictating the stability of Mn-based oxides, where lifting up the Fermi levels on the absolute energy scale by decreasing covalency can lead to greater thermodynamic driving force for the surface protonation of these metal oxides, which further weakens the surface metal-oxygen bonds and contributes to the instability of Mn-based oxides in acidic electrolytes. This work highlights the importance of understanding the physical origin of the aqueous stability trends for metal oxides with electronic and/or energetic descriptors, and provides guiding principles for designing oxide catalysts with enhanced stability in acidic systems.

References:

1. J. T. Mefford, W. G. Hardin, S. Dai, K. P. Johnston, K. J. Stevenson, Nat. Mater. 2014, 13, 726.

2. K. A. Stoerzinger, M. Risch, B. Han, Y. Shao-Horn, ACS Catal. 2015, 5, 6021.

3. A. Shinde, S. K. Suram, Q. Yan, L. Zhou, A. K. Singh, J. Yu, K. A. Persson, J. B. Neaton, J. M. Gregoire, ACS Energy Lett. 2017, 2, 2307.

4. R. Frydendal, E. A. Paoli, I. Chorkendorff, J. Rossmeisl, I. E. L. Stephens, Adv. Energy Mater. 2015, 5, 1500991.

5. L. Zhou, A. Shinde, J. H. Montoya, A. Singh, S. Gul, J. Yano, Y. Ye, E. J. Crumlin, M. H. Richter, J. K. Cooper, H. S. Stein, J. A. Haber, K. A. Persson, J. M. Gregoire, ACS Catal. 2018, 8, 10938.

6. J. Portier, P. Poizot, G. Campet, M. A. Subramanian, J. M. Tarascon, Solid State Sci. 2003, 5, 695.
High Performance Nitrogen-Doped Intermetallic Pt-Ni Catalyst for the Oxygen Reduction Reaction
Authors: Zhao Xueru , Xi Cong , Zhang Rui , Song Neal , Wang Chenyu , Spendelow Jacob S , Frenkel Anatoly , Yang Jing , Xin Huolin L , Sasaki Kotaro
Published: December 2020

PtM (M = transition metals) nanomaterials have been recognized as promising catalysts for the oxygen reduction reaction (ORR) in fuel cells, with a much higher performance than pure Pt. However, the insufficient durability issue of PtM is often raised due to the fast dissolution of M in acidic media, impeding their commercialization. In this paper, we present a new Ketjenblack (KB)-supported, nitrogen (N)-doped intermetallic PtNiN (Int-PtNiN/KB) catalyst that exhibits remarkably enhanced ORR activity and stability in an acidic electrolyte, superior to those of disordered PtNi/KB, disordered PtNiN/KB, and commercial Pt/C. The rotating disk electrode (RDE) measurements demonstrated that the mass activity (MA) and specific activity (SA) of the Int-PtNiN/KB is 1.83 A mgPt
-1 and 2.92 mA cm-2 at 0.9 V, which are approximately 10-fold and 8-fold as high as the commercial Pt/C, respectively. In MEA testing, the Int-PtNiN/KB meets DOE targets for MA, loss in MA after accelerated durability test (ADT), and performance at 0.8 V. The in situ X-ray absorption spectroscopy (XAS) revealed that the enhanced stability of ORR is ascribed to the formation of ordered structure, while the Pt shells can stabilize the cores against corrosion in acidic media. The density functional theory (DFT) calculations indicated that the optimal strains induced by N doping and formation of intermetallic phase result in weakening the binding of intermediates on the strained Pt surface, thus enhancing the intrinsic ORR activity. This work provides an effective strategy to improve the intrinsic activity and stability of binary or even ternary Pt-based electrocatalysts for the ORR.
(Invited) Promising Methods for Overcoming Trade-Offs Among Catalytic Activity, Durability, and Power Density By Controlling Pt/Ionomer Interfaces
Authors: Kodama Kensaku , Yamada Haruhiko , Yoshino Shuhei , Kudo Kenji , Suzuki Takahisa , Shinohara Akihiro , Jinnouchi Ryosuke , Morimoto Yu
Published: December 2020

For improving the efficiency and reducing Pt use in polymer electrolyte fuel cells, it is essential to improve the catalytic activity per Pt mass for oxygen reduction reaction (ORR) in the cathode. In addition, recent studies have demonstrated that a high surface area of the catalyst per Pt mass is necessary for reducing the oxygen transport resistance in the catalyst layer. Alloying inner cores of nanoparticles by introducing base metals and reducing particle sizes are established methods to increase the mass activity and the surface area, respectively. Both the methods are, however, disadvantageous for the catalyst durability. Thus, the activity, durability, and power density are generally in trade-off relations.

A promising method for solving this problem is to change the properties of the surrounding rather than the catalyst itself. Ionomers adsorbed on Pt catalyst have been confirmed to inhibit ORR and oxygen permeation to the interface [1, 2]. In other words, both the reaction and permeation can be promoted without deteriorating the catalyst durability by mitigating the ionomer adsorption. We have indeed shown that the ionomer adsorption can be suppressed by modifying the molecular structure of ionomer [3]. The ionomer adsorption can be suppressed also by inserting a sub-nanometer thin porous carbon layer between the Pt surface and ionomer. The inserted carbon layer has been also shown to suppress the catalyst degradation during potential cycles [4].

In this talk, we first summarize our analytical works on Pt/ionomer interfaces, focusing on the mechanisms of the adsorption of anionic moieties in ionomers and its effect on ORR. Then, we discuss the effectiveness of various approaches for mitigating ionomer adsorption, as well as their limitations. The future direction of cathode catalyst developments is also discussed.

[1] Subbaraman et al., ChemPhysChem 11, 2825 (2010).

[2] Jinnouchi et al., Electrochim. Acta, 188, 767 (2016)

[3] Kodama et al., ACS Catal. 8 694 (2018).

[4] Yamada et al., J. Electrochem. Soc., in press.
Lifetime Study of High Performance LiNi0.5Mn0.3Co0.2O2/Graphite Pouch Cells Under Fast Charging Conditions Via in Situ Synchrotron X-Ray Diffraction
Authors: Charalambous Harry , Wiaderek Kamila Magdalena , Ren Yang
Published: December 2020

High performance LiNi0.5Mn0.3Co0.2O2/graphite pouch cell batteries have been studied via high energy X-ray diffraction whole cell mapping over 1200 cycles of extended, fast charge cycling. Position dependent lithium balance quantification in the anode and cathode has been developed via a diffraction-based method and used to visualize and quantify heterogeneity and capacity fade mechanisms. Early, middle, and late stage cycle life are studied in terms of lithium heterogeneity, lithium inventory, and lithium plating as a function of areal position and compared to corresponding electrochemistry.
Operando Measurements of Electrolyte Lithium Ion Concentration during Fast-Charging
Authors: Meyer Lydia , Porter Jason Morgan , Brow Ryan , Santhanagopalan Shriram
Published: December 2020

The ability to charge a Li-ion battery at high charging rates is critical for widespread electric vehicle adoption, but fast-charging rates can cause battery degradation and performance issues. A primary challenge for fast charging is finding electrolytes with sufficient lithium ion transport to operating under high current densities. However, there are few options for measuring ion transport in operating batteries. A novel diagnostic using Fourier transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR) is reported for operando measurements of lithium ion concentration in a liquid electrolyte during battery operation. This diagnostic uses solvation shifting of solvent molecule vibrational modes to quantify lithium concentration. The diagnostic was calibrated using EC/EMC/LiPF6 electrolytes with known lithium concentrations from 0.03 mol/liter to 1.83 mol/liter. The concentration of PF6
- was also determined with a similar procedure. The resulting diagnostic can measure lithium concentrations from 0.001 to over 2 mol/liter with a minimum detection limit of 0.0011 moles/liter. The diagnostic is demonstrated using a lithium-ion half cell with a graphite anode and EC/EMC/LiPF6 electrolyte assembled in an argon-filled glove box. Measurements on the current collector side of the anode showed that as charging rates increased (i.e. during lithiation), lithium ion concentrations in the adjacent electrolyte decreased. The reverse trend was observed upon delithiation. These results demonstrate the utility of this diagnostic in quantifying ion depletion in electrolytes under fast charge conditions.
Modeling Cyclic Voltammetry of Reduced Graphene Oxide/ Aramid Nanofiber Structural Supercapacitors
Authors: Aderyani Sarah , Ardebili Haleh
Published: December 2020

Cyclic voltammetry is an important technique to characterize the electrochemical performance of electrical energy storage devices under various conditions. The cyclic voltammetry characterization also can be obtained through physical modeling and simulations to improve the understanding of experimental measurements and to guide the optimization of the electrode and electrolyte. In this study, the physics based generalized Poisson-Nernst-Planck model is used to simulate cyclic voltammetry measurements of reduced graphene oxide (rGO)/ aramid nanofiber (ANF) structural supercapacitors through a multiphysics computational modeling. The cyclic voltammetry is simulated for a supercapacitor with a binary electrolyte and two identical electrodes with “layered” and “house of cards” nanostructures. The capacitance and resistance values are determined for different compositions of aramid nanofiber. The modeling results show a very good agreement with experimental measurements. The results demonstrate an ideal supercapacitor's behavior which are compared to various electrode kinetics such as Butler-Volmer equation and Tafel equation with very low local current density. Modeling cyclic voltammetry can provide useful information about kinetics and thermodynamics of structural supercapacitors which enables better design and control over the performance and life cycle of the supercapacitors. Comparison of predicted and measured voltammograms enables determination of unknown system parameters and material properties such as diffusion coefficient, resistance and capacitance of the structural supercapacitors.

Figure 1
Ultrasonic Spray Chemistry: In-Situ Synthesis of Thin-Film Conjugated Microporous Polymers and Their Energy Storage Applications
Authors: Shin HyeonOh , Roh Deok-Ho , Kim Hyun-Tak , Kwon Tae_Hyuk
Published: December 2020

Conjugated microporous polymers (CMP) are potential energy storage materials owing to their rigid and cross-linked microporous structures. However, the fabrication of nano- and microstructured CMP films for practical applications is currently limited by processing challenges. We report ultrasonic spray chemistry (USC) as an effective method for synthesizing CMP films. The combined effect of ultrasonic cavitation and nebulization in USC provides enough energy to initiate chemical reactions. Thus, USC simultaneously achieves oxidative C–C coupling polymerization and fabrication of thin films. The reaction yield, porosity, and capacitance of the prepared CMP films were strongly dependent on the applied ultrasonic frequency (120 and 180 kHz). Furthermore, USC was used to prepare highly conductive, 3D porous electrodes by a layer-by-layer sequential deposition of CMP and single-walled carbon nanotubes. These supercapacitors demonstrated high specific capacitances (755.7 F/g and 61.3 mF/cm2 at 10 mV/s) with high cycling stability of 95% retention after 20,000 cycles.
Catalytic Performance Study of Ptni-Nanowires for the Oxygen Reduction Reaction (ORR) with Temperature-Controlled Experiments in Alkaline Medium
Authors: Soto Joesene J. , Trinidad Pedro , Larios Eduardo , Rojas-Pérez Arnulfo , Cabrera Carlos R
Published: December 2020

Fuel cells (FC) are emerging technologies that will eventually sustain energy demands replacing fossil fuels. However, the Oxygen reduction reaction (ORR) behaves sluggishly in acidic medium, where actual commercialization of FC concentrates. An alternative is to use alkaline environment were the ORR have demonstrated great activity using less expensive metals, replacing the more frequent catalyst, Pt/C. In this study we focused our interests in PtNi-nanowires (NWs), based on the promotive results that Ni offers to Pt on it's d valency. Moreover, the addition of Ni will lower the cost of the catalyst. Preliminary results demonstrated current densities of ~ 5 mA/cm2 with an E1/2 = 0.85 V for the PtNi-NWs at 1,600 rpm and 0.100 (mgPt/cm2) in alkaline medium at (25.00 ± 0.01) °C. Additionally, the number of electrons was calculated using the Koutecký-Levich analysis with and without temperature-controlled instrumentation resulting in n= 3.79 ± 0.05 and n=3.99 ± 0.05, respectively. Furthermore, durability experiments demonstrated that the PtNi-NWs maintained optimal catalytic activity for ORR along 10,000 cycles. The initial reported E1/2 was of 0.817 V and after 10,000 cycles E1/2 = 0.812 V, this represents a remarkable 5mV change in the E1/2. Operando X-ray spectroscopy (XAS) electrochemical were completed to evaluate changes in electronic structure for Ni and Pt. Results showed that the white line of Pt L3 edge in the PtNi-NWs changed while the electrochemical potential was lowered to negatives values. Showing changes in the electronic structure of Pt. The results presented here suggest that PtNi-NWs is a sustainable catalyst for the ORR in alkaline medium and that it can be consider for future Alkaline Fuel Cells (AFCs) experiments.
Paraffin Removal in the Synthesis of Novel Janus Carbon Nano-Onions
Authors: Del Valle-Perez Angelica , Rivera-Rivera Lineris , Gonzalez-Sanchez Osvaldo E , Cunci Lisandro
Published: December 2020

Carbon materials have been awakening scientific interest for research because it allows chemical functionalization for multiple applications in the sciences, especially in energy applications. Carbon Nano-onions (CNO) are spherical structures composed of multilayers of fullerenes, these layers are connected in a way that shows the shape of an onion. Its development begins with the use of nano-diamonds, a carbon material of strong structure which it forms in a very violent environment. The nano-diamonds are taken to a furnace at a temperature of 1650°C to finally obtain the CNO. Janus particles are receiving increasing attention because of their dual properties, where each side can be functionalized to have distinctive characteristics. The modifications on the surface of these nanoparticles can provide different chemical and physical properties. The interesting properties of Janus nanoparticles are that they have different sizes and shapes which have now been able to be studied in more detail. The purpose of this project is to use asymmetrically modified CNO as a support for metal nanoparticles to avoid agglomeration and, thus, increase their surface area and efficiency. Janus nanoparticles will be designed by a wax-paraffin Pickering emulsion process using CNO on its surface. The deposition of Platinum (Pt) was carried out by a chemical process using sodium borohydride. The removal process of the paraffin involves the dispersion of the wax-paraffin/CNO-Pt particles in Chloroform and rinse with isopropanol to finally obtain the amphiphilic nanoparticle. The differences on the surface of the particles before and after removing the paraffin were observed by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and Raman Spectroscopy. Cyclic Voltammetry was used to characterize the proposed catalyst and comparison with the commercial catalyst Pt/Vulcan providing information about their catalytic behavior. It was possible to confirm the deposition of Pt on the surface of the CNO by TEM. The Pt-CNO/CNO catalyst was tested for ORR using the Rotating Ring Disk Electrode (RRDE) and compared its performance with Pt/Vulcan. Thermogravimetric Analysis was used as a characterization technique to corroborate percent of Pt on these particles.
Effect of the Pore Structure of the Gas Diffusion Electrode on the Power Generation and Mass Transport Properties of Direct Formic Acid Fuel Cell
Authors: Tsujiguchi Takuya , Osaka Yugo , Kodama Akio
Published: December 2020

Direct Formic Acid Fuel Cell has been attracted match attention due to its higher power density and lower crossover. In order to improve their performance, we have tried to improve the mass transport in the anode electrode since a large amount of carbon dioxide is emitted by the electrochemical reaction.

For the anode electrode, diffusion layer, such as carbon cloth and carbon paper used in the polymer electrolyte fuel cell, is commonly used in direct formic acid fuel cell. These diffusion layers were suitable for the gas supplying; however, it is not clear that these diffusion layers were also suitable for direct liquid fuel cell using liquid fuel. Moreover, the suitable pore structure of diffusion layer for the direct liquid fuel cell is also unknown. In this context, we fabricated the gas diffusion layer having different pore diameter, thickness and porosity using same manner and material in order to evaluate the effect of the pore structure of diffusion layers on the power generation characteristics and mass transport properties in direct formic acid fuel cell.

The diffusion layers having 0.03-0.1 mm in average pore diameter, 60-90% in porosity, and 0.1-0.3 mm in thickness could be successfully fabricated using the purchased carbon fiber. The direct formic acid fuel cells using different diffusion layers for anode were fabricated and evaluated the i-V performance and crossover flux. It was found that the big pore can enhance the fuel feed rate to the anode catalyst layer under low current density (low CO2 emission), on the other hands, it did not contribute to the improvement of the fuel feed rate to the catalyst layer under higher current regions (high CO2 emissions). Small pore showed the counter trend. These results implies that the liquid feed and CO2 emissions is closely related the pore properties of diffusion layers, therefore, it is suggested that diffusion layer having suitable pore properties for direct liquid fuel cell is desired.
Effect of Varying Carbon Supports on Pt Based HOR Electrocatalysts for Alkaline Media Synthesized By CVD
Authors: Williams Stefan T. D. , Rockward Tommy , Martinez Ulises , Zawodzinski Thomas A.
Published: December 2020

The synthesis of electrocatalysts for the chemical reactions of hydrogen systems (e.g. fuel cells and electrolyzer systems) continues to be a significant area of research in the renewable energy community. The kinetics of hydrogen reactions decrease by two orders of magnitude in alkaline environments compared to acidic, which has rendered significant challenges in the development as catalysts of alkaline fuel cell systems[1,2]. Chemical vapor deposition (CVD) is a conventional synthesis process applied to manufacture electrocatalysts[3,4]. In this study, a modified form known as “Poor Man’s” CVD (PMCVD) is utilized, to further its impact in electrochemical catalyst development. This work assesses the deposition mechanism as well as its ability to develop tuneable catalysts for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) for alkaline media.

In our last efforts, we showed Pt based catalysts synthesized using the PMCVD method exhibited higher activities for the HOR/HER in alkaline media than commercially available catalysts[5]. The performance was attributed to the tunability of crystallite size by varying the temperature and pressure of the PMCVD process. In an effort to further understand the deposition mechanism of this processes, we investigated Pt catalysts on various carbon supports. In doing so, Pt was deposited on three supports: XC-72, Acetylene Black, and Graphitized Nanoplatelets with 30% Pt by weight. The carbons varied in both surface areas and degree of graphitization. This work will summarize the HOR/HER activities of these three Pt/C catalysts in alkaline media. It will also help elucidate the impact of the deposition mechanism as a function of each support based on their material properties.

[1] Durst, J. et al. New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energ. Environ. Sci. 7, 2255–2260 (2014).

[2] Sheng, W. et al. Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes.” Electrochem. Soc. 2010 volume 157, issue 11, B1529-B1536

[3] Garcia, Vargas, et al., “Chemical Vapor Deposition of Iridium, platinum, Rhodium, and Palladium.” Materials Transactions, Vol. 44, No. 9 (2003) pp. 1717 to 1728

[4] Serp, Philppe, et. al., “Chemical Vapor Deposition Methods for the Controlled Preparation of Supported Catalytic Materials.” Chem. Rev. 2002, 102, 3085−3128

[5] Williams, S. et. al. “Synthesis and Characterization of Electrocatalysts for the Hydrogen Evolution Reaction in Alkaline Environment.” ECS Abstract Fall 2019.

Figure 1
Nitrogen-Doped Carbide-Derived Carbon/Carbon Nanotube Composites As Cathode Catalysts for Anion Exchange Membrane Fuel Cell Application
Authors: Lilloja Jaana , Kibena-Poldsepp Elo , Sarapuu Ave , Kikas Arvo , Kisand Vambola , Käärik Maike , Merisalu Maido , Treshchalov Alexey , Leis Jaan , Sammelselg Väino , Wei Qiliang , Holdcroft Steven , Tammeveski Kaido
Published: December 2020

Due to the increasing energy consumption, there is a need for renewable energy production devices. Low temperature fuel cells are among the possible options, but their performance is limited by the sluggish kinetics of the electrochemical oxygen reduction reaction (ORR) at the cathode. The most efficient electrocatalysts for the ORR are based on expensive and scarce noble metals, mainly platinum. As more sustainable replacements, various non-precious metal or entirely metal-free catalysts could be used. The latter ones include heteroatom-doped nanocarbons.1,2

Herein, a composite of carbide-derived carbon and carbon nanotubes (CDC/CNT) is doped with nitrogen by pyrolyzing of a mixture containing CDC, CNT and a nitrogen precursor at 800 °C. A composite of carbons were chosen on the premise of obtaining a feasible structure with both micro- and mesopores, which should be beneficial in the anion exchange membrane fuel cell (AEMFC) application. Four different precursors of nitrogen (cyanamide, dicyandiamide, urea or melamine) were used and compared in order to find the most suitable one.3

For the physico-chemical characterization of the catalysts SEM, XPS, Raman spectroscopy and N2 adsorption studies were applied. These proved indeed that a novel carbon structure was formed and the doping with nitrogen was successful with all four precursors (≥3 at% of N). The electrocatalytic activity of the four N-doped catalyst materials was studied in 0.1 M KOH using RDE and RRDE methods. The four N-CDC/CNT catalyst materials exhibited virtually the same and good activity toward the ORR. In order to assess the possible application of the N-CDC/CNT material, it was employed as a cathode catalyst in AEMFC together with a HMT-PMBI4 membrane. The tests were conducted at different conditions and the best performance with peak power density of 310 mW cm–2 was obtained at 70 °C with 1 bar back pressure (Figure 1). This good performance shows that the metal-free N-CDC/CNT materials are promising cathode catalysts for the AEMFC application.3

References

A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, J. Mater. Chem. A, 6, 776-804 (2018).

C.Z. Zhu, H. Li, S.F. Fu, D. Du, and Y.H. Lin, Chem. Soc. Rev., 45, 517-531 (2016)

J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, A. Kikas, V. Kisand, M. Käärik, M. Merisalu, A. Treshchalov, M. Rähn, J. Leis, V. Sammelselg, Q. Wei, S. Holdcroft, and K. Tammeveski, Appl. Catal., B, 272, 119012 (2020).

A.G. Wright, J.T. Fan, B. Britton, T. Weissbach, H.F. Lee, E.A. Kitching, T.J. Peckham, and S. Holdcroft, Energy Environ. Sci., 9, 2130-2142 (2016).

Figure 1
Redox Tuning-Induced Modulation of in-Situ Dynamic Surface Reconstruction Activates Superior Electrochemical Water Oxidation
Authors: Wang Jian , Lim Jongwoo
Published: December 2020

Surface reconstruction of electrocatalysts has been widely observed during the water electrolysis. However, the rational control of surface reconstruction for efficient electrocatalysts remains a tremendous challenge. In this contribution, a cationic redox-tuning method was reported to modulate the in situ dynamic surface reconstruction ofa layered transition metal oxide, i.e., LiCoO2, for the oxygen evolution reaction (OER). Partial chlorination modified the redox transitions during the OER from Co3+/Co4+ in LiCoO2 to Co2+/Co3+ in Cl-doped LiCoO2,as detected by operando X-ray absorption spectroscopy. This redox change led to a self-terminated amorphous (oxy)hydroxide surface phase. In contrast, pristine LiCoO2 required higher electrochemical potentials to initiating the surface reconstruction and longer cycles for stabilizing it, generating spinel-type Li1-xCoO2 surface species. Cl-doped LiCoO2 with restructured surface showed an OER activity ~two orders of magnitude higher than that of benchmark RuO2 and sustained this high activity for 500 h without degradation. This work contributes to the modulation of surface restructuring and provides new opportunities to design OER electrocatalysts via tuning the redox.
Polymer-Ceramic Composite Diaphragm for Reducing Dissolved Hydrogen Permeability in Alkaline Water Electrolysis
Authors: Lee Hae In , Cho Hyun-Seok , Kim Sang Kyung , Kim MinJoong , Kim Chang-Hee , Cho Won-Chul , Rhee Young Woo
Published: December 2020

The porous diaphragm is a typical separator used in an alkaline water electrolyser. Gas crossover through the diaphragm during electrolysis depends upon the different evolution quantity of hydrogen and oxygen gas which consequently develop the differential pressure between cathode and anode side. This phenomenon limits the cell efficiency and develops safety concerns. In this study, diaphragm was prepared by film casting, which consists of mixing, casting and extraction. We measured the hydrogen flux density of commercial diaphragm (Zirfon PERL) and the prepared diaphragm during the operation. For this purpose, the diaphragm was mounted in a zero-gap design unit cell with Ni foam as electrodes and operated in 30wt% KOH solution at 60oC with atmospheric differential pressure between 0.1 ~ 0.3 bar (cathode side – anode side) controlled by a back-pressure regulator. Results showed that the anodic hydrogen content of commercial diaphragm was up to 2% during the operation but prepared diaphragm was negligible. This is due to the smaller pore size in the prepared diaphragm as compared to the commercial diaphragm confirmed by morphological and surface area analysis.

Fig 1. (a) The anodic hydrogen contents as a function of current density and differential pressure and (b) polarization curves at 60oC and 30wt% KOH solution of conventional and prepared diaphragm with nickel foam as electrode

Figure 1
Does Power Ultrasound (26 kHz) Affect the Hydrogen Evolution Reaction (HER) on Pt Polycrystalline Electrode in a Mild Acidic Electrolyte?
Authors: Pollet Bruno G. , Foroughi Faranak , Faid Alaa , Emberson David R. , Islam Md Hujjatul
Published: December 2020

In this study, we investigated the effects of power ultrasound (26 kHz, up to ~75 W/cm2, up to 100% acoustic amplitude, ultrasonic horn) on the hydrogen evolution reaction (HER) on a platinum (Pt) polycrystalline disc electrode in 0.5 M H2SO4 by cyclic and linear sweep voltammetry at 298 K. We also studied the formation of molecular hydrogen (H2) bubbles on a Pt wire in the absence and presence of power ultrasound using ultra-fast camera imaging. It was found that ultrasound significantly increases currents towards the HER i.e. a ~250% increase in current density was achieved at maximum ultrasonic power. The potential at a current density of -10 mA/cm2 under silent conditions was found to be -46 mV and decreased to -27 mV at 100% acoustic amplitude i.e. a DE shift of ~+20 mV, indicating the influence of ultrasound on improving the HER activity. A nearly 100% increase in the exchange current density (j
o) and a 30% decrease in the Tafel slope (b) at maximum ultrasonic power, was observed in the low overpotential region, although in the high overpotential region, the Tafel slopes (b) were not significantly affected when compared to silent conditions. In our conditions, ultrasound did not greatly affect the “real” surface area (A
r) and roughness factor (R) i.e. the microscopic surface area available for electron transfer. Overall, it was found that ultrasound did not dramatically change the mechanism of HER but instead, increased currents at the Pt surface area through effective hydrogen bubble removal.
Structural Engineering of Highly Accessible Edge Sites and Electronic Optimization of N-MoS2 for Efficient Hydrogen Evolution
Authors: Wang Hao , Gao Lijun
Published: December 2020

Superior HER performance of MoS2 electrocatalyst has been demonstrated due to the low free energy of hydrogen adsorption, electrochemical stability and cost-effectiveness. However, experimental and theoretical studies reveal that the HER activity of MoS2 remains unsatisfactory due to the inactive basal planes, low intrinsic electronic conductivity and restacking of 2D layered nanosheets. To overcome these challenges, maximizing the accessible active sites and enhancing the conductivity of MoS2 are critical to boost its HER performance. Herein, we perform structural engineering of MoS2 electrocatalyst by developing a self-template strategy realizing a “0D/3D” nanostructure of N-doped MoS2 nanocrystals anchored on carbon network (N-MoS2/CN). As-prepared N-MoS2/CN could address the above-mentioned issues: 1) N dopants in MoS2 could simultaneously boost HER activity of the edge and enhance electronic conductivity of the basal plane; 2) The ultrasmall size of N-MoS2 nanocrystals largely enriches the density of active edge sites; 3) The 3D hierarchically porous structure of the carbon substrate delivers the accessibility of H3O+ ions from electrolyte to active sites on MoS2 and also facilitates the charge transfer during the HER process. Consequently, N-MoS2/CN exhibits an onset potential of -30 mV vs. RHE, an overpotential of 114 mV at a current density of 10 mA cm-2 and a Tafel slope of 46.8 mV dec-1, demonstrating one of the best HER performance among various nanostructured MoS2 electrocatalysts.
Atomic Pillar Effect in PdxNbS2 to Boost Basal Plane Activity for Stable Hydrogen Evolution
Authors: Wang Xin , Huang Chong , Wang Dong , Zhao Wei , Bu Kejun , Xu Jijian , Huang Xieyi , Bi Qingyuan , Huang Jian , Huang Fuqiang
Published: December 2020

Exploring novel electrocatalysts with prominent performance is highly demanded for electrochemical hydrogen evolution. As one family member of layered transition-metal dichalcogenides (TMDs), metallic niobium disulfide (NbS2) with intrinsic basal plane activity might be a promising candidate once its electrical and structural characteristics are optimized. Here, we develop novel electrocatalysts by incorporating palladium (Pd) atoms into the van der Waals gaps of NbS2 to form new compounds PdxNbS2 (x = 0−0.23). On the basis of single crystal structure refinement and theoretical calculations, the Pd atoms act as atomic pillars to expand the interlayer spacing of NbS2 and boost the basal plane activity with a drop of Gibbs free energy for hydrogen adsorption to 0.06 eV on neighboring S atoms, resulting in more protons to adsorb and react. In addition, pillared Pd stabilizes the crystal structure by connecting the NbS2 interlayers with [PdS6] octahedra. All these merits endow Pd0.23NbS2 with superior electrochemical activity and durability, achieving 10 mA cm−2 at a low overpotential of 157 mV with a negligible change in 12 h. This unique atomic pillar effect for optimizing the electrocatalytic performance of PdxNbS2 demonstrates a functional and powerful strategy to develop efficient TMD-based electrocatalysts.
New Strategies to Strongly Coupled Ni-Molybdenum Carbide Grafted N-Doped Carbon Architectures for Efficient Electrocatalysis
Authors: Das Debanjan , Santra Saswati , Nanda Karuna Kar
Published: December 2020

Despite the recent promise of transition metal carbides as non-precious catalysts for hydrogen evolution reaction (HER), their extension to oxygen evolution reaction (OER) in order to achieve the goal of overall water splitting remains a significant challenge. Herein, a new Ni/MoxC (MoC, Mo2C) nanoparticles supported N-doped graphene/CNT hybrid (NC) catalyst is developed via a facile, one-step integrated strategy which can catalyze both the HER and OER in an efficient and robust manner. The catalyst affords low overpotentials of 162 and 328 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively, in an alkaline medium which either compares favourably or exceeds most of the Mo-based catalysts documented in the literature. The electronic synergistic effect between MoxC, Ni and NC are responsible for the higher electrocatalytic activity wherein, a tandem electron transfer process yields both excellent HER and OER activity. [1]

Unfortunately, however, the synergy among the components was curtailed on account of large spatial separation. To mitigate this problem, we pyrolyzed a PANI/NiMoO4 nanowire hybrid which brought the individual components closer as compared to the previously adopted method resulting in improved catalytic activity. To further enhance the intimacy in these multi-component catalysts, a MOF-confined synthesis method was developed which resulted in the best activity among all the catalysts developed in the series.

[1] D.Das, S.Santra and K.K Nanda, ACS Appl. Mater. Interfaces, 2018, 10, 35025−35038
Perfluorinated Anion Exchange Membranes for Alkaline Water Electrolysis
Authors: Nguyen Quynh-Mai , Jung Sung Yoon , Hwang Jin Pyo , Ahn Juhee , Lim Jun Hyun , Jang Wongi , Lee Chang Hyun
Published: December 2020

The anion exchange membranes (AEMs) contain positively charged functional groups in their polymeric matrices to selectively transport anions including hydroxide ion. The desirable AEMs should satisfy high chemical resistance and excellent anion conductivity. Commercially available AEMs are vulnerable to thermo-chemical attacks at the alkaline conditions and undesirable to anion transport owing to their hydrocarbon matrices’ characteristics. On the other hand, the use of perfluorinated backbones as AEM matrices can provide a route to avoid these negative issues, since the perfluorinated materials have excellent chemical resistance to alkaline atmospheres and well-developed morphologies. In this study, perfluorinated AEMs were synthesized via stepwise chemical substitution reactions of a perfluorinated sulfonic acid precursor membrane. The resulting membranes were evaluated as polymer electrolytes for alkaline water electrolysis.
Thermo-Chemically Durable Perfluorinated Anion-Conducting Ionomer Membranes for Advanced Alkaline Water Electrolysis
Authors: Nguyen Quynh-Mai , Jung SungYoon , Hwang Jin Pyo , Jang Wongi , Lee Chang Hyun
Published: December 2020

The state-of-the-art membrane for alkaline water electrolysis is porous Zirfon®. Unfortunately, Zirfon® has been suffering from the crossover of hydrogen gas permeated through the pores, inducing safety issues including explosion. To date, there have been approaches to solve this problem. One good example is to use anion-conducting ionomer membranes with dense structures. Generally, the membranes, which are made up of hydrocarbon matrices, experience severe degradation, when they are exposed under strong basic conditions at the temperatures higher than 50 oC for high electrochemical performances. In this study, perfluorinated ionomer membranes with extremely high thermo-chemical resistances are developed via the combination of architectural design and supercritical dispersion.

References

[1] Zirfon perl separator for alkaline water electrolysis, AGFA, April (2016)

[2] C. Y Ahn, J, Ahn, S. Y. Kang, O. H. Kim, D. W. Lee, J. H. Lee, J. G. Shim, C. H. Lee, Y. H. Cho, Y. E. Sung, Sci Adv
6, 1-9 (2020)

Keywords: Alkaline water electrolysis, Perfluorinated ionomers, Anion conductivity, Thermo-chemical stability, Membrane
Visualization of Bubble Behavior on Hydrophobic Coated CL in PEM Water Electrolysis Cell
Authors: Wani Kodai , Araki Takuto , Nagasawa Kensaku , Mitsushima Shigenori
Published: December 2020

Due to the need for a new energy infrastructure, water electrolysis technology is receiving increased attention (1), (2). One of the serious problems is management of generated oxygen bubbles which inhibit water supply to the CL. Therefore, bubble behavior was observed on three types of CL with hydrophilic and hydrophobic surface by using a high-speed camera. A single cell, shown in Fig. 1, was used for observing oxygen bubble behavior. Nafion-117 was used as PEM, and IrOx and Pt/C was used anode and cathode catalyst, respectively. Sinterd Ti with Pt plating was used for anode porous transport layer (PTL). Three types of PTFE coated CL were prepared: (a) no coating, (b) coated all and (c) coated half. High-speed camera (Redlake MASD, HS-1), magnifying glass (Hirox, cx-10c) and objective lens (Hirox, OL-35) were used. Electrochemical measurement system (Bio-Logic, SP-240) was used for applying voltage, and the voltage sweep was performed at a rate of 4 mV/s until the cell voltage turned from 0 V to 2.5 V. The current density at voltage of 2.5 V was about 4200 mA/cm2 for CL (a), 1200 mA/cm2 for CL (b) and 3700 mA/cm2 for CL (c). A big bubble covering entire PTL hole was visualized in Fig. 2 (b). In Fig. 2 (c), smaller bubbles appeared from left PTFE uncoated area were merged into a bigger bubble, which stayed on right PTFE coated area. The size of bubbles staying on the edge of PTL-holl in Fig. 2 (a) was smaller than those of (b, c). The results may suggest that the CL (b) deteriorated the cell performance because of the bubble covering entire reaction area. From this experiment, we could control stagnation of bubbles on CL by PTFE treatment. There may be some possibilities that controlling bubble stagnation make some differences on cell performance.

Acknowledgements: This study was based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Reference:

(1) G. Bender, et al, Int. J. Hydrogen Energy, 44 (2019), 9174-9187

(2) S. Mitsushima et al, ECS Meeting Abstracts, MA2019-02 (2019), 1715.

Figure 1
Direct Roll-to-Roll Coating of Catalyst-Coated Membranes for Low-Cost PEM Water Electrolyzers
Authors: Park Janghoon , Kang Zhenye , Bender Guido , Ulsh Michael , Mauger Scott A
Published: December 2020

Low temperature polymer electrolyte membrane (PEM) water electrolysis is a technology capable of producing hydrogen, which has been in the spotlight with the recent worldwide efforts to improve energy system sustainability and security. As the drive toward megawatt-scale hydrogen production intensifies, the production rate of PEM water electrolyzers is becoming an important issue. Catalyst-coated membranes (CCM) are a key component of water electrolyzers. However, existing spray coating and decal transfer methods have several limitations with regards to large-area production of the CCMs, such as, slow production speeds and multiple process steps.

In this talk, high-throughput and large-area CCM production based on roll-to-roll (R2R) slot-die coating of IrO2 catalyst inks directly onto the membrane will be discussed. In order to minimize phenomena such as swelling and solvent permeation during direct coating of the ink onto the membrane, ink compositions with various catalyst contents, types of organic solvents, and water-to-solvent ratios are investigated. The results show that alcohol-rich inks may lead to improved particle dispersion and wetting onto the substrate, but have shown poor coating qualities (e.g. cracks and high thickness deviation) due to larger ink-membrane interaction and faster drying rate. In-situ results of R2R-processed CCMs using optimized inks will be presented that indicate comparable electrochemical performance to a lab-scale sample fabricated with the standard ultrasonic spray coating technique. Considering that the R2R-processed CCM has achieved a throughput of several hundred times greater than the lab scale sample (on an area/time basis), it is expected that this manufacturing approach can contribute to a significantly reduced capital cost of PEM water electrolyzers.

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Hydrogen and Fuel Cells Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.