bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Activity-Stability Relationships for Water Electrolysis Electrocatalysis
Authors: Lopes Pietro Papa , Strmcnik Dusan , Stamenkovic Vojislav , Markovic Nenad M
Published: February 2020

Dihydrogen, the chemical fuel with the highest specific energy, is the ideal energy carrier for our transition to renewable energy society. The successful implementation of the so-called "Hydrogen Economy" relies on cost-effective, high performance production of H2 in water electrolyzers and its energy efficient consumption in fuel cells. While fuel cell technology have developed tremendously over the past 20 years, with fuel cell automobiles commercially available nowadays, such as the Toyota Mirai and the Honda Clarity, electrolyzer technology is still heavily based on cell and stack designs dating back 40 years ago. This proven H2 technology does not provide a cost effective solution for large scale deployment due extensive use of noble metals such as Ir and Pt that are required to drive both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), respectively. Together with kinetic limitations, the challenges facing water electrolyzers also include poor electrode stability and losses associated with limited electronic conductivity of metal oxides in the anodes. Overall, then, the design of materials for water electrolysis requires understanding the at atomic scale what are the fundamental limitations behind catalytic activity for both OER and HER, how does activity and stability are interconnected, and based on this knowledge, how can we effectively design new electrochemical interfaces and tailored 3D electrode morphology that will be at the core of the next generation water electrolyzer technology.
Theoretical and Experimental Investigations in Metal−N−C Composites for Oxygen Reduction Reaction and Hydrogen Evolution Reaction at Universal Phs
Authors: Qin Xueping , Zhang Lulu , Shao Minhua
Published: February 2020

During the development of platinum group metal (PGM)-free electrocatalysts for both polymer electrolyte membrane fuel cells and electrolyzers, non-precious metal and nitrogen co-doped carbon (denoted as Me-N-C) has been widely investigated as a promising catalyst for oxygen reduction reactions (ORR)1-3 and hydrogen evolution reactions (HER)4. However, these studies were conducted by different groups under various experimental conditions and most of the experiments were focused on a certain kind of reaction (ORR or HER) in either acid or alkaline media. In addition, current understanding can not explain well the activity discrepancy between Fe-N-C and Co-N-C. For instance, the former is much active than the latter for ORR, while the trend is reversed for HER4. This study aims to solve this dilemma by a first-principles density functional theory (DFT) approach.

In the theoretical simulations, the catalytic activities on Fe-N-C and Co-N-C were studied for ORR and HER in both acid and alkaline solutions by constructing the free energy diagrams. Meanwhile, the effect of applied potential on the activity was also included. Figure 1 shows the free energy diagrams of ORR for Fe-N-C and Co-N-C at low pH at 0 V (Fig. 1a) and 0.80 V (Fig. 1b), respectively. At 0 V, all elementary reaction steps are downhill for Fe-N-C (blue line) and Co-N-C (red line), indicating that both catalysts have good ORR activity in acid media; however, when the potential increases to 0.80 V, the OOH* and O* formation steps become uphill for Co-N-C while the Fe-N-C still possesses the downhill trend, illustrating the latter one has a better activity at low overpotentials. Similarly, the free energy diagrams based on the elementary reaction steps were constructed for ORR in alkaline media as well as the HER, from which the comparison between the Fe-N-C and Co-N-C regarding the ORR and HER activities at universal pHs could be obtained.

Our DFT calculation results demonstrateed that Fe-N-C had the better ORR activity than Co-N-C in both acid and alkaline media but a completely different trend was found for HER. These theoretical findings were also verified by our experimental results.

References

(1) Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. Science
2011, 332, 443.

(2) Shao, M.; Chang, Q.; Dodelet, J.-P.; Chenitz, R. Chemical reviews
2016, 116, 3594.

(3) Lefèvre, M.; Proietti, E.; Jaouen, F.; Dodelet, J.-P. science
2009, 324, 71.

(4) Zhang, L.; Liu, W.; Dou, Y.; Du, Z.; Shao, M. The Journal of Physical Chemistry C
2016, 120, 29047.

Figure 1. Gibbs free energy diagrams for ORR in acid media for Fe-N-C (blue) and Co-N-C (red) at 0 V (a) and 0.80 V (b).

Figure 1
Transition-Metal-Doped TiO2 Decorated Nife Layered Double Hydroxide Catalyst in Alkaline Oxygen Evolution Reaction
Authors: Tsai Meng-Che , Hwang Bing-Joe , Lin Xiang-De , Su Wei-Nien
Published: February 2020

Efficient and earth abundant electrocatalysts for high-performance oxygen evolution reaction (OER) are essential for the development of sustainable energy conversion technologies. Here, the 3d transition-metal-doped TiO2 were synthesized and used the catalysts for alkaline oxygen evolution reaction. Commercial catalyst usually uses carbon as support such as Ir/C and Ru/C. But during oxygen evolution reaction, carbon will be corroded seriously. So, catalyst will detach from carbon support cause efficiency of catalyst to decay very quickly. In order to overcome these problems, we develop TiO2 as a support because TiO2 is a very durable material in high potential region and high concentration alkaline electrolyte. However, TiO2 is not a good catalyst for oxygen evolution reaction and suffer from its poor conductivity. To solve these drawbacks, we synthesized different 3d transition metal doping TiO2 in this work. After electrochemical tests, we choose (Ni, Fe) dual doped TiO2 was chosen because of its potential for oxygen evolution reaction.

First of all, different different doping compositions of Ni and Fe were investigated, and it was found that Ni:Fe in molar ratio 3:1 showed the best oxygen evolution reaction performance. Next, different doping amounts of Ni to Fe, from 6:2, 3:1 to 1.5:0.5 were also evaluated, where Ni:Fe in 6:2 was the best composition for alkaline oxygen evoution.

Furthermore, we modified catalyst by adding long chain anion, hydrogen treatment and loading NiFe LDH on (Ni, Fe) dual doped TiO2. Finally, NiFe/TiNiFe perform better oxygen evolution reaction than pure NiFe LDH. At the current density reach 10 mA/cm2, the required potential of NiFe/TiNiFe was 10 mV less than for pure NiFe LDH. After chronopotentiometric stability test for 48 hours, NiFe/TiNiFe showed almost no decay during reaction and is more superior than NiFe LDH. Our work successfully solves activity and stability issue at the same time by an excessive dual doping approach.
Activity and Stability Relations on Oxygen Evolution Electrocatalysis
Authors: Chung Dong Young , Lopes Pietro Papa , Strmcnik Dusan , Stamenkovic Vojislav , Markovic Nenad M
Published: February 2020

Due to the vigorous demanding of renewable energy, it is important to develop efficient electrocatalyst with high stability and activity .The importance of Water electrolysis, energy storage concept from electricity to hydrogen and oxygen, is highly accentuated to achieve hydrogen-based energy cycles. In oxygen evolution reaction (OER), which is anode reaction of water electrolysis, low stability and sluggish kinetics are considered as major problems. Various candidates have recently been proposed including transition metal analogues (oxide, hydroxide, phosphide and nitride, etc.), however in-detail analysis of reaction mechanism and activity-stability relations are still under debate. In this talk, we will discuss about activity-stability trend of OER catalyst and suggest which factor is important for designing durable and active electrocatalyst.
Ni- and Co-Based Heterogeneous Nanosheet Array As Efficient Electrocatalysts for Oxygen Evolution Reaction from Water
Authors: Li Yong , Zhang Weiran , Liu Mengjie , Lee Lawrence Yoon Suk
Published: February 2020

Efficient oxygen evolution reaction (OER) catalysts composed of earth-abundant elements are crucial to the development of practical and environmental-friendly water splitting system. Herein, we present the synthesis of Ni- and Co-based heterogeneous composites and their application in electrocatalytic OER. Using a straightforward two step reaction, the NiCoO2/CoO/Ni3N nanosheet arrays (NiCoON NSAs/NF) are fabricated in situ on the 3D nickel foam. We have controlled the ratio of two metal sources, reaction temperature, and the annealing time to optimize the active surface species, as well as the morphology. In the alkaline solution, the NiCoON nanocomposite has excellent catalytic OER properties such as a small overpotential of 247 mV (at 10 mA cm−2) and Tafel slope of 35 mV dec−1, which are better than those of NixCo3-xO4 and most Ni- and Co-based electrocatalysts. There are more active sites with oxygen vacancies on NiCoON NSAs after the treatment with NH3 and the face-centered cubic NiCoO2 facilitates the formation of active Ni-Co layered hydroxide/oxyhydroxide species (NiOOH) in comparison with spinal NixCo3-xO4 during the electrochemical process. In addition, the Ni3+-rich surface together with Co incorporation has been shown to favor the formation of β-NiOOH over γ-NiOOH. Our study reveals that the precise control of active species on NiCoON NSAs/NF leads to high activity and stability in OER catalysis.
Cups Ultrafine Nanoparticles Anchored into N-Doped Carbon Framework for Bifunctional Water Splitting
Authors: Yu Jing
Published: February 2020

Hydrogen has been considered as the green energy carrier to substitute gradually depleted fossil fuels due to its virtues holding high energy density and zero environmental discharge. Electrocatalytic water splitting is one of the most effective approach to generate hydrogen fuel, which involves two half reactions, namely hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The design of efficient and low-cost electrocatalysts to reduce the large energy barriers of water splitting is challenging. Nanosizing of the electrocatalysts could provide new insight into understanding the catalytic reaction at nanoscale and even molecular level. Here, a novel ultrafine CuPS nanoparticles anchored into N-doped carbon framework (CuPS/NC) was proposed as advanced electrocatalyst for full water splitting. Density functional theory calculations revealed the synergistic electronic interaction between S and P, leading to optimal electronic structure and hydrogen adsorption free energy, thus facilitating HER kinetics. The highly open yet interconnected 3D framework creates a large surface area, exposing abundant active sites and providing convenient charge and ionic diffusion pathway. The ultrafine CuPS nanoparticles enable to fully utilize accessible edge sites. As a result, the obtained CuPS/NC exhibits relatively low overpotentials and small Tafel slopes for both HER and OER, as well as superior performance toward full water splitting.
A Conical Nanogenerator Consisted of Multi-Walled Carbon Nanotubes
Authors: Dao Van-Duong , Jeong Youngsoon , Yoon Ilsun , Choi Ho-Suk
Published: February 2020

The shift to an industrial ecosystem that operates with abundant water and sunlight on the earth is essential to the sustainability of mankind. One effort to do this is to produce freshwater utilizing solar energy, called solar steam generation. Here, we develop a dual-function ecosystem of the 3-dimensional conical structure consisted of multi-walled carbon nanotubes (MWNTs), which utilizes the solar energy to produce the fresh water from any pollutated water or saline water at the massive production rate and to generate the high electric power of hundreds mW·m-2 using evaporation-enhanced capillary water stream of the structure under ambient daylight conditions. Since this cone-shaped fluidic nanogenerator (CFN) acquires all energy required from the environment, it will find immediate applications in providing electricity and freshwater for living and system maintenance in water-abundant isolated locations such as islands or wetlands. The CFN of MWNTs has advantages in solar steam generation because it can be more exposed to the environment due to its high surface curvature and because it can be thermally isolated from the cold water by the inside air-pocket. A single CFN of which vertical projection area is 0.64 cm2 can show high water evaporation rate of 1.6 kg·m-2·h at 20 °C. Multilayers of functionalized MWNTs can have advantages in fluidic nanogenerator which can harvest large electric power with high open-circuit voltage (Voc) and current density (Jsc) by the double layer interaction of MWNTs with ions flowing in the evaporation-induced capillary water stream. The CFN of MWNTs can produce strong electric power due to the capillary water stream induced by the solar steam under 1 sun irradiation (1 kW·m-2) and the single CFN produces electric powers of 120.7 mW·m-2 (Voc: 0.5V, Jsc: 0.12 mA·cm-2) at the saline water and of 505.69 mW·m-2 (Voc:0.64 V, Jsc: 0.59 mA·cm-2) at the 0.6 M KCl aqueous solution.
(Industrial Electrochemistry and Electrochemical Engineering Division New Electrochemical Technology (NET) Award Address) Development and Commercialization of Large Scale PEM Water Electrolysis
Authors: Abouatallah Rami , Joos Nathaniel Ian , Wang Rainey Yu , Sinanan Anson
Published: February 2020

Keywords: PEM Electrolyzer, Power to Gas, Mega Watt (MW)

In future energy systems with high percentages of fluctuating renewable energy generation, electricity storage will become increasingly important for the utilization of surplus energy. Among several electricity storage options, the Power to Gas technology is one promising option for solving the challenge of long-term electricity storage [1]. In this approach, excess renewable energy is converted via water electrolysis to hydrogen and used directly as an energy storage medium or it can go thru further conversion to methane [2]. To fully utilize the potential of Power to Gas, large-scale technology implementation should be accelerated so the costs are driven down. PEM electrolyzers need to become quickly available on multi-mega watt (MW) scale [3].

Hydrogenics has been developing water electrolysis technology based on proton exchange membrane (PEM) since the late 1990s. Driven by Power to Gas applications and corresponding cost modeling, Hydrogenics increased the scale of its PEM water electrolysis stack and launched its new MW scale electrolysis platform in 2014. This MW scale platform is still the most compact, highest capacity PEM electrolyzer cell stack in the world and capable of absorbing 3 MW of electricity with a single stack.

To date, Hydrogenics has delivered numerous MW systems globally, with the majority of them in Power to Gas, renewable energy storage and grid balancing applications. Hydrogenics is developing the next-generation systems with continuing focus on cost reduction through technology innovation and scale up. With the market introduction of a single 3 MW stack, Hydrogenics continues to demonstrate that its hydrogen-based energy storage technology will transform the energy sector by providing ancillary and grid balancing services to grid operators while converting large scale renewable energy at a utility scale.

References:

Jentscha, T. Trosta, M. Sternerb, Optimal Use of Power-to-Gas Energy Storage Systems in an 85% Renewable Energy Scenario, Energy Procedia
46 ( 2014 ) 254 – 261

Power-to-Gas: The Case for Hydrogen White Paper, Califonia Hydrogen Business Council, 2015

Schulze, J. Holstein, A. Noort and J. Knijp, Power-to-gas in a Decarbonized European Energy System Based on Renewable Energy Sources, European Power to Gas White Paper
(Energy Technology Division Supramaniam Srinivasan Young Investigator Award Address) Towards Deterministic Electrode Design: Elucidating the Role of Surface Chemistry and Microstructure on Flow Battery Performance
Authors: Brushett Fikile R.
Published: February 2020

Redox flow batteries (RFBs) are promising for energy-intensive grid storage applications, but further improvements are needed for universal adoption.1,2 While research efforts have primarily focused on molecular engineering of redox couples as a means of reducing system cost, advances in other critical systems components also hold significant cost reduction potential. Of particular importance are the porous electrodes which are responsible for multiple critical functions in the flow cell related to thermodynamics, kinetics, and transport including providing surfaces for electrochemical reactions, enabling uniform liquid electrolyte distribution with low hydraulic resistance, as well as conducting electrons and heat. However, there is limited knowledge on how to systematically design and implement these materials in emerging RFB applications, forcing the repurposing of available materials that are not tailored for this electrochemical system. Moreover, current generation materials, which are typically developed via empirical approaches, lack control of surface chemistry (e.g., compositional heterogeneity) and morphology (e.g., broad pore size distribution). This fundamentally limits the performance, durability and, consequently, the cost of resultant systems. In this talk, I will discuss methods for disaggregating and quantifying resistive losses in various porous electrodes using model redox couples, diagnostic flow cells, and electrochemical modeling.3,4 When applied in combination with suitable spectroscopy and microscopy techniques, structure-performance relations can be elucidated5,6 which may eventually lead to design rules that enable the fabrication of chemistry-specific electrodes based solely on the knowledge of the physical and electrochemical properties of the redox active electrolyte.

References

1. I. Gyuk, M. Johnson, J. Vetrano, K. Lynn, W. Parks, R. Handa, L. Kannberg, S. Hearne, K. Waldrip, R. Braccio, Grid Energy Storage, US Department of Energy, 2013

2. R.M. Darling, K.G. Gallagher, J.A. Kowalski, S. Ha, F.R. Brushett, Energy & Environmental Science, 2014, 7, 3459

3. J.D. Milshtein, J.L. Barton, R.M. Darling, F.R. Brushett, Journal of Power Sources, 2016, 327, 151

4. J.D. Milshtein, K.M. Tenny, J.L. Barton, J. Drake, R.M. Darling, F.R. Brushett, Journal of the Electrochemical Society, 2017, 164(11), E3265

5. K.V. Greco, A. Forner-Cuenca, A. Mularczyk, J. Eller, F.R. Brushett, ACS Applied Materials & Interfaces, 2018, 10(51), 44430

6. A. Forner-Cuenca, E. Penn, A. Oliveira, F.R. Brushett, in preparation
Metal Complexing Agents for Low-Cost Flow Battery Electrolytes
Authors: Marshak Michael P.
Published: February 2020

Redox flow batteries provide a compelling engineering framework for grid-scale energy storage; however there is a need for advanced electrolyte chemistry that can drive down the cost of long-duration energy storage. This presentation describes the design strategy and implementation of new metal complexing agents that can enable high-voltage and high-performance aqueous flow batteries. This approach enables low-cost electrolyte formulations in excess of 1.6 volts with over 99% Coulombic efficiency during cycling.
(Invited) Understanding Benzothiadiazole Based Anolyte Materials for Nonaqueous Redox Flow Cells
Authors: Zhang Lu , Zhang Jingjing , Wei Xiaoliang , Brushett Fikile R. , Shkrob Ilya A
Published: February 2020

Redox-active organic materials (ROMs) have shown great promise for redox flow battery applications but generally encounter limited cycling efficiency and stability at relevant redox material concentrations in nonaqueous systems. In this talk, a new family of heterocyclic organic anolyte molecules, 2,1,3-benzothiadiazole (BZNSN) and derivatives,1-2 will be discussed, which demonstrated high solubility, low redox potential, and fast electrochemical kinetics. By coupling BZNSN with a benchmark catholyte ROM (DBMMB), the nonaqueous organic flow battery delivered significant improvement in cyclable redox material concentrations and cell efficiencies compared to the state-of-the-art nonaqueous systems. In order to obtain an insightful understanding of this family of molecules, a series of derivatives have been developed by varying the 5-position substitutions with tunable electronic accepting/withdrawing features. The substituent effects on their properties of interest have been examined, including redox potentials, calendar lives of charged ROMs in an electrolyte, and the flow cell cycling performance. While the calendar life of energized fluids can be tuned in a predictable fashion over a wide range, the improvements in the calendar life do not directly translate into the enhanced cycling performance. This finding strongly indicates the significant role of structural engineering in achieving improvement of radical ion stability, suggesting a generic guidance for developing long-cycling ROM-based flow cells.

Figure 1 Structures and cyclic voltammogram of benzothiadiazole derivatives and the correlation of the half-decay lifetime of the radical anions with the redox potentials. Mind the logarithmic vertical scale.

Duan, W.; Huang, J.; Kowalski, J. A.; Shkrob, I. A.; Vijayakumar, M.; Walter, E.; Pan, B.; Yang, Z.; Milshtein, J. D.; Li, B.; Liao, C.; Zhang, Z.; Wang, W.; Liu, J.; Moore, J. S.; Brushett, F. R.; Zhang, L.; Wei, X.,. ACS Energy Letters
2017,
2(5), 1156-1161.

2. Huang, J.; Duan, W.; Zhang, J.; Shkrob, I. A.; Assary, R. S.; Pan, B.; Liao, C.; Zhang, Z.; Wei, X.; Zhang, L..Journal of Materials Chemistry A
2018,
6 (15), 6251-6254.

Figure 1
Lock-in Thermography As a Diagnostic Tool for Water Detection and Quantification in Polymer Electrolyte Fuel Cells (PEFCs)
Authors: Rasha Lara , Brett Dan J.L , Shearing Paul R. , Cho Jason I.S
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are among the most promising energy conversion technologies for a broad range of applications and in recent years has shown tremendous advancements in terms of performance and durability, with wide-scale commercialisation imminent. However, new techniques are sought to optimise performance by understanding the internal workings of these devices. Understanding aspects of thermal and water management is of particular interest as they have a profound effect on both PEFC performance and durability, especially under dynamic load changes when used as power sources in automotive vehicles.

Neutron imaging is a powerful technique for probing water distribution in PEFCs; however, beam-time access is limited, expensive and only available in a few sites worldwide. This work looks to develop a new diagnostic technique that is able to image water distribution in PEFCs in-operando using lab-based equipment. This non-invasive and non-destructive technique requires a thermal imaging camera and a periodic heat stimulus imposed on the fuel cell. By locking-in the camera to the frequency of the heat source stimulus, it is possible to isolate heat travelling through a fuel cell from the source. The internal fuel cell features (including presence of water) affect heat transfer properties and can consequently be detected by the camera. Furthermore, if the technique is applied over a range of perturbation frequencies, it can determine the spatial location and amount of liquid water within the fuel cell (figure attached).

Figure 1
Pore Morphology Effects of Liquid/Gas Diffusion Layers in Proton Exchange Membrane Electrolyzer Cells
Authors: Yu Shule , Yang Gaoqiang , Li Yifan , Canfield Brian , Terekhov Alexander , Davis Lloyd , Zhang Feng-Yuan
Published: February 2020

Hydrogen is now considered the most preferred medium for storing energyout of renewable, intermittent power sources because of its great advantages such as high energy density, low weight, environmental friendliness, etc. Water electrolysis is the most accessible hydrogen production method. Proton exchange membrane (PEM) water electrolysis is attracting much attention with its high efficiency. In a PEM electrolyzer cell (PEMEC), liquid/gas diffusion layers (LGDLs) are porous layers whose main functions are conducting electrons and heat and transporting reactants/products to and from the reaction sites. To achieve high efficiency, a PEMEC demands LGDLs with minimum intrinsic ohmic, thermal, and mass diffusion losses and also low interfacial contact resistances with other components. Thus, the morphologies and surface properties of LGDLs can greatly affect the cell performance.

In this research, anode LGDLs featuring pore sizes of approximately ten microns are fabricated by pulsed-laser micromachining (PLM). The effects of pore morphologies, including porosities and pore sizes, are characterized comprehensively ex-situ and in-situ. Electrochemical
impedance
spectroscopy (EIS) analysis is also carried out to investigate the impact of LGDL pore morphologies on the PEMEC performance. Results from this research can help the community better understand the relationship between LGDL morphology and PEMEC performance. A prediction of the performance at the design stage should also be available based on the morphology of an anode LGDL. Furthermore, an optimal design for anode LGDLs may be acquired.
(Invited) Earth-Abundant Transition Metal Single Atom Electrocatalysts for Selective CO2 Reduction in Water
Authors: Wang Haotian
Published: February 2020

The development of highly selective and earth-abundant electrocatalysts for CO2 reduction is becoming increasingly important for renewable energy applications. The challenge here is the strong competition from water reduction, as well as the low selectivity towards a desired product. In this talk I will introduce the rational tuning of electronic properties of catalytic materials for their significantly improved CO2 reduction performance. By dispersing transition metals into isolated single atoms with electronic structures significantly different from their bulk counterparts, we can dramatically suppress the competing hydrogen evolution and deliver an ultra-high CO2 reduction selectivity of more than 99% under ambient conditions in water.
Alkaline Fuel Cell Performance of Saturated N-Heterocyclic Cationic Multiblock Polymers
Authors: Hwang Monica , Willis Carl , Elabd Yossef A
Published: February 2020

Alkaline fuel cells (AFCs) have attracted attention as low-cost alternatives to proton exchange membrane fuel cells (PEMFCs) because of their ability to produce high power densities without the use of non-precious metal catalysts. However, long-lasting AFCs require highly hydroxide conductive solid-state anion exchange membranes (AEMs) (or separators) and ionomers (for use in the catalyst layer) that are highly chemically stable at high pH. Recent results have shown that polymers with covalently attached saturated N-heterocyclic cations possess high alkaline chemical stability (ex situ), however their performance and durability as AEMs and ionomers in AFCs (in situ or in operando) have yet to be explored. In this study, the AFC performance of a multiblock polymer containing saturated N-heterocyclic cations (methylpyrrolidinium) as both the AEM and ionomer was explored. Both high power density and durability (i.e., constant power density or voltage over time) were demonstrated. AFC performance will be presented as a function of membrane electrode assembly processing conditions (ionomer content, casting solvents, cell assembly pressure) and AFC operating conditions (cell temperature, humidity). These results demonstrate the possibility to produce high power density, long-lasting, low-cost AFCs.
Low Temperature Performance of MnOx@Carbon Nanofoam-Based Ecs with Neutral pH-Based Aqueous Electrolytes
Authors: Sassin Megan B. , Brant Kaylin , Pitman Catherine L. , Wallace Jean , Long Jeffrey W.
Published: February 2020

Electrochemical capacitors (ECs) comprising high-surface-area carbon electrodes and nonaqueous electrolytes offer many attractive performance attributes including long cycle life and the ability to operate at low temperatures (–40⁰C), yet their energy density is ultimately limited by reliance on the double-layer charge-storage mechanism. Asymmetric EC configurations that include pseudocapacitive materials (e.g., transition metal oxides) offer the opportunity to increase energy density while also using safer and cheaper aqueous electrolytes. We have shown that with the appropriate electrode structure and electrolyte additives, the additional charge stored via pseudocapacitance is delivered at EC-like rates over 1000 cycles with minimal capacitance fade. To further prove the practical feasibility of such aqueous-electrolyte ECs, we turned our attention to low-temperature performance, focusing on aqueous electrolyte compositions containing lithium or sodium cations and sulfate or nitrate anions. We characterized pertinent bulk properties (e.g., freezing point and ionic conductivity) of down-selected electrolytes and found that the anion dominates the freezing point, with sulfate-based electrolytes having a freezing point of –45oC, while nitrate-based electrolytes have a freezing point of –35oC. The ionic conductivities ranged from 63 to 136 mS cm-1 at 20oC, conductive enough to support high-rate operation. To assess the impact of temperature on performance as a function of electrolyte composition, we fabricated symmetric pouch cells comprised of MnOx@carbon nanofoam electrodes, evaluating the resulting devices via cyclic voltammetry and electrochemical impedance spectroscopy over a wide temperature range (25⁰C to –45⁰C). All ECs exhibited a gradual decrease in capacitance as the temperature decreased; however, capacitance was recovered upon warming to 25°C for all electrolyte compositions. We found that ECs with Li2SO4-based electrolytes (neat or mixed composition) were operational at temperatures as low as –35°C, revealing that these electrolytes are competitive with the nonaqueous electrolytes used in conventional double layer capacitors.
Enhanced Anodic Reaction of Dimethyl Ether (DME) on Ptpdsn Based Catalysts for High Power Low Temperature Fuel Cells
Authors: Schechter Alex , Teller Hanan , Kashyap Diwakar
Published: February 2020

Dimethyl ether (DME) was recently proposed as an alternative fuel for fuel cells, due to its high energy density (8 kWh kg−1), low boiling point (-24 °C) which enables to supply it as fumes to the cell, and the lower crossover of DME molecules through the membrane compared to methanol, enabling the use of thin membranes. Yet, the state of the art DME oxidation catalysts such as PtRu, do not prove to be highly has slower oxidation kinetic and lower durability. Fuel cells utilizing Pt based catalysts requires high anode loading (above 2-4 mg of Pt), pressure and temperature which are relatively high (1.4 - 3.0 bar and 80 ֯C) to produce power output of 60- 200 mW cm-2.

We present herein a study of our patented ternary PtPdSn\C catalyst. The catalyst was optimized in terms of synthesis conditions and composition for DME oxidation in liquid electrolyte. Comparison with Pt\C, Pd\C and PtPd\C catalysts was done to explore the role of the different metals in the oxidation process over PtPdSn. Online FTIR and mass spectrometry measurements applied towards the identification of DME oxidation products, which included methanol, formic acid and methyl formate. The high electrto-activity in DME oxidation was maintained even after prolonged cycling 0.5 M H2SO4, in contrary to state of the art commercial PtRu catalyst. Polymer electrolyte fuel cell implementing PtPdSn/C catalyst produces peak power density of 150 mW cm-2 with a loading of only 1.2 mg/cm2 of active platinum group metal (PGM) at 70 ֯C and ambient pressure, which is significantly higher than reported power density values with PtRu under more demanding conditions. Analytical analysis of the DME oxidation product formed under selected anode operation conditions was carried out by on line mass spectrometry and on line FTIR showed formic acid as the main partial oxidation product at water stichometry lower than 3, whereas at full hydration above 3 moles of water per mole of DME, the main product other than CO2 was methanol resulting from hydrolysis reaction of the ether bond. The above mentioned results suggest that DME feed directly to a acidic PEMFC structure device has the potential of becoming a viable alternative to compressed hydrogen in PEMFC system in wide spectrum of applications.
Effect of Heat Treatment and Bath Compositions on the Performance of Co-Ni-Mo-P Electrocatalysts for Ethanol Electro-Oxidation
Authors: Kalu Egwu Eric , Chaitree Wasu
Published: February 2020

As-deposited (ASD) Co-Ni-Mo-P electrocatalyst on carbon support was investigated for the ethanol electro-oxidation. Electrocatalysts were prepared by electroless deposition method on carbon substrate support (CCS) made active for electroless deposition with Pd-ink. The reaction performances for all electrodes were investigated using cyclic voltammetry (CV). An effect of electroless bath compositions was studied. The result showed that the current density tended to increase with increasing Co, Ni, and Mo contents, suggesting that they contributed to the catalytic activity. The optimum molar ratio of NiSO4, CoSO4, and Na2MoO4 was 1:1.8:0.6 for the catalyst without heat treatment. In addition, after the electrocatalysts were treated thermally for 2h under H2/Ar gas at different temperatures, an optimal temperature of 400°C was identified for which the current density was higher than any other annealing temperature including that of the ASD electrocatalyst. The result is attributed to the effect of crystallinity and particle sizes. Above and below this optimal temperature, the current density decreased, indicating that the crystalline structures at these conditions are not appropriate for optimal performance. Moreover, the active surface area decreased after the heat treatment because the catalyst lost its amorphous structure. Additionally, the stability of the ASD and thermally treated electrocatalysts will be discussed.

Figure 1
Oxygen Reduction Reaction, Catalyst Development
Authors: Siahrostami Samira
Published: February 2020

The sluggish oxygen reduction reaction (ORR) is the main bottleneck for development of highly efficient fuel cells. It has been a long-standing goal to develop and identify efficient and cost-effective electrocatalysts with high activity towards this reaction. In this talk, I will give an overview of our recent developments in catalyst discovery effort for ORR. 1–3

References

(1) Kulkarni, A.; Siahrostami, S.; Anjli, P.; Norskov, J. K. Chem. Rev. 2018, 118 (5), 2302-2312.

(2) Abroshan, H.; Bothra, P.; Back, S.; Kulkarni, A.; Nørskov, J. K.; Siahrostami, S. J. Phys. Chem. C 2018, 122 (9), 4783–4791.

(3) Back, Seoin; Kulkarni, Ambarish; Siahrostami, S. ChemCatChem 2018, 10 (14), 3034-3039.
Electrochemical and Ultra-Small Angle X-Ray Scattering Study of Ionomer Adsorption on Catalytic Sites in PEFC Electrodes
Authors: Farghaly Ahmed A. , Kariuki Nancy N. , Park Jaehyung , Myers Deborah J.
Published: February 2020

The composition of the catalyst ink has a crucial impact on the electrode performance in the polymer electrolyte fuel cells (PEFCs). The presence of the perfluorosulfonic acid (PFSA) ionomer in the membrane electrode assembly (MEA) catalyst layer results in a sluggish oxygen reduction reaction (ORR) kinetics compared with an ionomer-free catalyst layer. Moreover, recently it has been shown that a thin film with high resistance to oxygen transport is formed around the catalyst particles due to its interaction with the ionomer.1 In order to improve the performance of the catalyst layer and eliminate or minimize the loss in both the ionic conductivity and electronic conductivity due to the ionomer-catalyst particles interaction in the next generation fuel cells new encased platinum group metal catalysts have been designed. Nanoporous materials have a wide range of technological applications2-6 and are potential candidates to improve the performance of the PEFC catalysts. Ordered inorganic nanoporous structures with well-defined and uniform pores are used to host the catalyst nanoparticles and block the access of the ionomer aggregates to the catalyst surface. In order to validate this assumption a series of catalyst inks with different ionomer: catalyst ratios (I/C) in isopropyl alcohol aqueous solvent were prepared. The ORR activity of the catalysts in thin film electrodes formed from these inks has been determined. The activity measurements are complemented by ultra-small-angle X-ray scattering (USAXS) studies on the inks and electrodes to determine the effect ionomer on the microstructure of the catalyst aggregates.

References

C. Cetinbas, R. K. Ahluwalia, N. N. Kariuki, and D.J. Myers, J. Electrochem. Soc.,
165(13), F1051 (2018).

A. Farghaly, R. K. Khan, and M. M. Collinson, ACS Appl. Mater. Interfaces, 10(25), 21103 (2018).

Demir, A. A. Farghaly, M. J. Decuir, M. M. Collinson, and R. B. Gupta, Mater. Chem. Phys., 216, 508 (2018).

Nahar, A. A. Farghaly, R. J. A. Esteves, and I. U. Arachchige, Chem. Mater., 29(18),7704 (2017).

A. Farghaly and M. M. Collinson, Langmuir, 32(23), 5925 (2016).

A. Farghaly, M. Lam, C. J. Freeman, B. Uppalapati, and M. M. Collinson, J. Electrochem. Soc., 163(4) H3083 (2016).

Acknowledgements

This work was supported by the United States Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office. This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.
Reduced Graphene Oxide / Polyaniline (rGO/PANI) Composite As Pt Support for Oxygen Reduction Reaction: Effect of PANI Content
Authors: Sánchez-Padilla N.M. , Méndez V. , Fernández Tavizón Salvador , Benavides Roberto , Morales-Acosta Diana
Published: February 2020

In order to enhance the activity for oxygen reduction reaction by improving dispersion and distribution of platinum nanoparticles (Pt NPs), three composite materials were prepared and evaluated as cathode catalysts for fuel cells applications. Composite materials consisted on polyaniline grafted with reduce graphene oxide in three different compositions (rGO90-PANI10, rGO50-PANI50 and rGO10-PANI90). Graphene oxide (GO) was obtained by modified Hummer’s method using graphite as precursor and subsequently hybrid materials through in situ oxidative polymerization of aniline in presence of GO. Finally, deposition of Pt NPs was carried out by the polyol method. For comparative purpose a Pt/rGO material was prepared and evaluated under the same conditions. Materials were physicochemically characterized by X-Ray diffraction (XRD), infrared spectroscopy (FT-IR), transmission electronic microscopy (TEM) and thermogravimetric analysis (TGA) and evaluated by cyclic voltammetry for oxygen reduction reaction (RRO) in acid media. Characterization results demonstrated the formation of composite materials by the grafting of PANI. It was also observed that the amount of PANI leads to a higher dispersion and a low particle size, being of 1.5 nm for Pt/rGO10-PANI90 and 2.6 nm for Pt/rGO90-PANI10 which were lower compared to Pt/rGO (3.5 nm). The effect of PANI amount on the activity during evaluation of ORR was as follow: for lower amount of PANI a higher current density (j) and onset potential (E0) was observed, being the higher activity for Pt/rGO90-PANI10 with E0 = 0.85 V and j= 3.9 mA cm-1, which is even higher than Pt/rGO (0.77 V and 2.9 mA cm-1). The higher activity of Pt/rGO90-PANI10 is due to an optimum particle size, distribution and dispersion achieved with the composite support (rGO90-PANI10).
Thickness Dependence Impact on Proton Transport Proton Properties of Nafion® Thin-Film on Platinum Model Electrode
Authors: Uchiyama Tomoki , Gao Xiao , Yamamoto Kentaro , Takao Naoki , Matsumoto Masashi , Imai Hideto , Sugawara Seiho , Shinohara Kazuhiko , Uchimoto Yoshiharu
Published: February 2020

Introduction

Improving oxygen reduction reaction (ORR) activity of cathode catalyst is required for wide spread of polymer electrolyte fuel cells. Because ORR occurs at the three-phase-boundary among the cathode catalyst, ionomer and oxygen gas, understanding the impact the ionomer on the cathode catalyst is important to achieve the high performance PEFCs. Especially, the structure of the ionomer on the cathode is strongly influenced by humidity, thickness, annealing treatment [1-3]. In this study, we examined the proton conductivity the Nafion® thin-film with various thickness from 5 to 200 nm. The correlation between structure and proton conductivity of the Nafion on Pt electrode was discussed.

Experimental

For proton conductivity measurements, Nafion thin-films were prepared on interdigitated array of gold electrodes on SiO2 substrate by soaking the electrode on Nafion dispersion. For GISAXS measurements, Nafion thin-films were prepared on Pt sputtered P doped-silicon substrates by spin casting of Nafion dispersion. Proton conductivity under humidity was measured by applying an alternating potential of amplitude 100 mV over a frequency 7 MHz to 0.01 Hz. GISAXS measurements were performed under humidity in beamline BL40B2 at SPring-8, Japan.

Results and Discussion

In the Nafion thin-films with thickness more than 50 nm, EIS results indicated that the hydrophilic domains grew gradually as the thickness increases. In contrast, the hydrophilic domains, which works as the protonic path, grows larger with increase of the thickness, leading to reduce the activation energy of proton conductivity. According to GISAXS, the hydrophilic domain disappears in the Nafion thin-film with thickness less than 50 nm. These results indicate that the structure of Nafion thin-film drastically changes with the thickness. It is anticipated that the proton conductivity of the in-plane in the Nafion film is larger than that of the out-of-plane because the hydrophilic domain of the in-plane grows larger than that of the out-of-plane. The anisotropy of the ordered structure in the Nafion thin-film is enhanced by the interaction between the ionomer and substrate. These results indicate that the proton conductivity in the Nafion is largely influenced by the amount of the hydrophobic domain.

Acknowledgments

This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Reference:

[1] A. Kusoglu, D. Kushner, D. K. Paul, D. Karan, M. Hickner, A. Weber, Adv. Funct. Mater., 24, 4763 (2014)

[2] D. K. Paul, H. K. Shim, J. B. Giorgi, K. Karan, J. Polym. Sci. B Polym. Phys., 54, 1267 (2016)

[3] D. K. Paul, R. McCreery, K. Karan, J. Electrochem. Soc., 161, F1395 (2014)
Mesoporous Semiconductors: A New Model to Assess Accessible Surface Area and Increased Photocatalytic Activity
Authors: Marschall Roland
Published: February 2020

Mesoporous photocatalysts have gained great attention in the last decade by demonstrating that increased surface area and porosity can strongly improve their performance. In fact, all reports on mesoporous semiconductors support this scenario. But is it possible to quantify and compare the reported advantages of the mesopores and the increased surface area between different works? In this contribution, we present a model that can evaluate the improvements in photocatalytic activity achieved by the introduction of mesoporosity independent on synthetic or test conditions. We exemplify this methodology focusing on photocatalytic hydrogen/oxygen evolution with sacrificial reagents, but also include examples of CO2 reduction and electrocatalysis. By correlating the relative increase in surface area to the relative increase in activity – in comparison to non-porous counterparts – we show that the origin of mesoporosity can have a pronounced influence on the activity enhancement, and that different semiconductor materials behave quite differently. Our model can serve as a starting point for the community to extract and compare key information on mesoporous photocatalysts, to put results into context of existing data, and to compare the performances of various catalytic systems much better.
(Invited) Plasmon Excitation-Driven Reduction and Coupling of Carbon Dioxide Molecules
Authors: Jain Prashant K
Published: February 2020

To mimic natural photosynthesis, one requires a synthetic photocatalyst that can absorb sunlight and direct that energy to the conversion of CO2 into energy-dense hydrocarbons. My talk will make the case that plasmonic metal nanostructures may be well-suited to this task. With Au, Ag, and Cu nanostructures, it is possible to pair strong light-matter interactions with the ability of these metals to activate CO2. We have found that plasmonically excited Au nanoparticle catalysts drive kinetically challenging, multi-electron, multi-proton reduction of CO2 to hydrocarbons under visible-light excitation. The product selectivity is dependent on the nature of the exciting light. Unlike electrochemical CO2 reduction on Au, C-C coupling appears to be prevalent in this light-driven scheme, which suggests that unique reaction pathways are possible under plasmonic excitation.
(Invited) Separations in Solar Fuels Systems
Authors: Houle Frances A
Published: February 2020

Solar fuels generators produce mixtures of products – O2 and H2 in the case of water splitting, and O2, H2 and carbon-containing products in the case of CO2 reduction. Membrane separators included as integral parts of the (photo)electrochemical generation system serve the dual purpose of transporting ions between anode and cathode and product blocking, thus preventing back reactions of products. In the case of water splitting current commercial membranes have reasonably efficient performance, but this is not the case for CO2 reduction where crossover can be significant. Moreover, mixtures of reduced products must still be separated from the electrolyte and each other. In this talk, computational and experimental projects in the Joint Center for Artificial Photosynthesis to understand membrane performance, how membranes interact with CO2 and reaction products, and the characteristics of membrane transport under diurnal generation conditions will be described. The energy cost of separating mixtures of products and its implications for the sustainability of solar fuels generation will be discussed.
Crystal Phase Dependence on HER Water Splitting Performance of Earth-Abundant Electrocatalysts
Authors: Rodene Dylan Daniel , Eladgham Ebtesam H. , Arachchige Indika , Gupta Ram B.
Published: February 2020

Economical hydrogen production via renewable-energy-powered water splitting is only feasible with earth-abundant low over-potential (<150 mV @ 10 mA/cm2) electrocatalysts. Nickel-molybdenum alloys, as earth-abundant electrocatalysts, have been reported to show competitive performance characteristics over past years. Herein, we will present stoichiometric ratios that result in multiple crystal phases and alkaline hydrogen evolution reaction (HER) over-potentials. In particular, the performance of specific transition metal crystal phases in alkaline media were evaluated for HER performance with general knowledge of that alkaline media leads to higher stabilities over acidic media. Typically, alkaline media also limits low over-potentials. In our case, specific phases of NixMo showed competitive over-potentials regardless of electrolyte.

Colloidal nanocrystals were synthesized and drop-casted onto titanium foil to form fashioned single crystal phase electrodes. Electrodepositing, contrary to drop-casting, films might result in good electrode stability and performance but cannot easily provide experimental elucidation of crystal phase dependence on HER over-potential. A more robust method is needed to differentiate long-term stability differences for fashioned electrodes in 2M KOH.

Structural crystal phase differences between different colloidal nanocrystal alloy compositions will be presented as x-ray photoelectron spectroscopy (XPS) and x-ray powder diffraction (XRD) data. Electrochemical data, including polarization curves and Tafel plots, will be presented. Specific insights into over-potential differences of alloys with similar elemental composition was gained and a discussion linking metal oxidation states to over-potential performance will take place.