bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of in-Situ 57 Fe Mössbauer Spectroscopic Data for Differently Prepared Fe-N-C Catalysts
Authors: Ni Lingmei , Gallenkamp Charlotte , Wagner Stephan , Wallace David , Paul Stephen , Kübler Markus , Krewald Vera , Kramm Ulrike Ingrid
Published: February 2020

Electrochemical energy conversion in proton exchange fuel cells (PEFCs) is very promising device for world-wide energy demand, especially in the transportation sector [1]. Fe-N-C catalysts are promising materials as alternative for platinum-based catalyst because of the low cost and high activities especially for the ORR. However, a fundamental understanding of the nature of active site structures and the ORR reaction mechanism is missing. Especially also considering the question, to what extent differently prepared catalysts obtain similar trends or not.

57Fe Mössbauer Spectroscopy (MS) is a very good technique in distinguishing FeN4 centers with changing local coordination environment [2,3]. So far, the electronic and geometric structure have been investigated under in-situ / operando conditions by spectroscopic techniques, like XAS [4], XES [5]. However, only once Mössbauer spectroscopy was applied quasi in-situ by Bouwkamp-Wijnoltz et al. on frozen electrodes [6] and there are only a rare number of publications on carbon supported macrocycles [7,8].

In this work, we have designed a feasible electrochemical cell for in-situ Mössbauer spectroscopy. Two different types of Fe-N-C catalysts were studied under in-situ conditions and we will present the structural changes induced by the effect of applied potential. By comparing different catalysts, we are able to show to what extent Mössbauer sites remain the same, independent of the preparation route or are changing. The data will be correlated with selectivity measurements of the catalysts. Based on this, further fundamental insights on the nature of the active site structure in Fe-N-C catalysts can be gained which could guide the preparation for highly active non precious metal catalyst for commercialization.

References:

[1] Debe, M. K., Nature., 486 (2012), 43−51.

[2] Kramm, U.I. et al., J. Am. Chem. Soc.
136 (2014), 978-985.

[3] Kramm, U. I. et al., Phys. Chem.Chem.Phys.
14 (2012), 11673-11688.

[4] Zitolo, A. et al., Nat Mater 14 (2015), 937-942.

[5] Niwa, H. et al.,
Electrochemistry Communications
35 (2013), 57-60.

[6] Bouwkamp-Wijnoltz et al., J. Phys.
Chem. B, 106, (2002), 12993-13001.

[7] Blomquist, J.et al., Electrochimica Acta, 1982, 27(10), 1445-1451.

[8] Scherson. D.A. et al., J. Electroanal. Chem.,
184 (1985), 419-426.
Non-PGM Electrocatalysts for Oxygen Reduction Reaction Inspired By Metalloenzyme Active Sites
Authors: Kato Masaru , Fujibayashi Natsuki , Matsubara Naohiro , Muto Marika , Murotani Takeshi , Yagi Ichizo
Published: February 2020

Oxygen reduction reaction (ORR) is a key reaction in future energy generation devices such as polymer electrolyte fuel cells (PEFCs) and metal–air batteries. To drive the ORR in state-of-the-art PEFCs, platinum group metal (PGM) alloys have been used. Since platinum is rare and expensive, there is a need to develop highly active PGM-free ORR electrocatalysts for wide spread applications of PEFCs. In nature, catalytic active sites based on 3d transition metals are widely utilized as catalytic reaction centers in metalloenzymes: for example, laccases and cytochrome c oxidases are known to catalyze the ORR with almost no energy loss at the active sites of multinuclear metal complexes.[1,2]

We present ORR electrocatalysts with multinuclear copper active sites incorporated in nitrogen-doped carbon nanosheets, which were inspired by the active site of laccases. Our copper-based electrocatalyst exhibited high ORR activity in alkaline aqueous solution. Physicochemical measurements including in situ X-ray absorption spectroscopy[3] revealed that multinuclear copper sites were embedded in nitrogen-doped carbon nanosheets and worked as the catalytic active center.[4] We also prepared a Fe–Cu-codoped carbon electrocatalyst inspired by the active site of cytochrome c oxidase.[5] Optimization of synthetic conditions and doping ratios of Fe to Cu into carbon resulted in the improvement of the ORR activity in acidic media. The electrocatalyst codoped with Fe and Cu showed higher ORR activity than those with Fe or Cu. Our bioinspired approaches will offer guidance for developing non-PGM ORR electrocatalysts with high activity.

References

[1] N. Mano, V. Soukharev, A. Heller, J. Phys. Chem. B, 110, 11180 (2016).

[2] C. H. Kjaergaard, J. Rossmeisl, J. K. Nørskov, Inorg. Chem. 49, 3567 (2010).

[3] M. Kato, K. Kimijima, M. Shibata, H. Notsu, K. Ogino, K. Inokuma, N. Ohta, H. Uehara, Y. Uemura, N. Oyaizu, T. Ohba, S. Takakusagi, K. Asakura, I. Yagi, Phys. Chem. Chem. Phys., 17, 8638 (2015).

[4] M. Kato, M. Muto, N. Matsubara, Y. Uemura, Y. Wakisaka, T. Yoneuchi, D. Matsumura, T. Ishihara, T. Tokushima, S. Noro, S. Takakusagi, K. Asakura, I. Yagi, ACS Appl. Energy Mater., 1, 2358 (2018).

[5] M. Kato, T. Murotani, I. Yagi, Chem. Lett., 45, 1213 (2016).
Generalized Silica-Coating-Mediated Synthesis Toward Enhancing the Catalytic Activity of Fe−N/C Oxygen Reduction Electrocatalysts
Authors: Woo Jinwoo , Sa Young Jin , Joo Sang Hoon
Published: February 2020

Iron and nitrogen codoped carbon (Fe−N/C) catalysts have emerged as promising substitutes for the Pt-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells, owing to their high ORR activity among nonprecious metal catalysts. This high ORR activity originates from the atomically dispersed Fe coordinated with nitrogen atoms (Fe−Nx site). However, the rational design that can create abundant active Fe−Nx site remains an important challenge. In this work, we demonstrate that a silica-coating-mediated synthetic strategy enables the preparation of Fe−N/C catalysts enriched with active Fe−N
x
sites while mitigating the formation of less active Fe and Fe3C species. The silica coating-mediated strategy was generally applicable to various types of Fe and N precursors, including iron porphyrin, iron acetate/1,10-phenanthroline, and iron chloride/polyaniline. This strategy was also effective in the preparation of Fe−N/C catalysts with various carbon supports and with a wide range of Fe contents and pyrolysis temperatures. The strategy could be further extended to S- or P-doped Fe−N/C catalysts, in which the formation of inactive FeS and Fe2P species was suppressed. Significantly, the S-doped Fe−N/C catalyst exhibited very high ORR activity with half-wave potential at 0.91 V (vs. RHE) in alkaline media. In anion-exchange membrane fuel cell tests, the S-doped Fe−N/C based cathode showed a current density of 977 mA cm−2 at 0.6 V, which is the highest performance among reported AMEFCs with NPMC-based cathodes. The S-doped Fe−N/C-based cathode also demonstrated promising volumetric current density in an acidic proton exchange membrane fuel cell. Thus, the silica-coating-mediated strategy is generally effective in preparing atomically dispersed catalytic entities and may be applicable to other catalytic reactions whereby atomically dispersed catalysts exhibit high catalytic activities.
New Insights of Hydrogen Oxidation Reaction Mechanism of Platinum-Based Bimetallic Catalysts in Alkaline
Authors: Liu Ershuai , Mukerjee Sanjeev , Jia Qingying
Published: February 2020

As one of the key reactions of electrocatalysis, hydrogen oxidation reaction (HOR) has been extensively investigated to understand its sluggish kinetics in alkaline. Elucidation of the mechanism of HOR in alkaline can not only deepen our understandings of alkaline electrochemistry, but also help to rationalize the design of highly active catalysts for alkaline fuel cells. Recent research of bimetallic catalysts for the HOR shed some light on the HOR mechanism in alkaline1. It was shown that alloying Pt with oxophilic metals (Ni, Ru, Ir) or depositing those metals on Pt surface can largely accelerate the HOR kinetics of Pt2. However, the beneficial roles of the second metals are under extensive debate. Herein, we investigate the HOR kinetics of Pt-M bimetallic catalysts by using electrochemical characterization and in situx-ray absorption spectroscopy. We propose that the oxidation state of the second surface metal is the governing factor for the hydroxide transportation between the surface and the bulk solution in alkaline, thereby controlling the HOR kinetics of Pt-M bimetallic catalysts.

Liu E, Li J, Jiao L, Doan HT, Liu Z, Zhao Z, Huang Y, Abraham KM, Mukerjee S, Jia Q. Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation. Journal of the American Chemical Society. 2019 Feb 20.

Strmcnik D, Uchimura M, Wang C, Subbaraman R, Danilovic N, Van Der Vliet D, Paulikas AP, Stamenkovic VR, Markovic NM. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nature chemistry. 2013 Apr;5(4):300.
A Universal Picture of the HER/HOR Kinetics of Pt in Alkaline Solution
Authors: Liu Ershuai , Jiao Li , Mukerjee Sanjeev , Jia Qingying
Published: February 2020

Some progress has been recently made in understanding the sluggish kinetics of hydrogen evolution and oxidation reactions (HER/HOR) of Pt in alkaline solutions. The pH dependence of the HER/HOR activity of Pt was reasonably accounted for by the potential of zero free charge (pzfc) theory.1 We lately proposed the 2B theory to account for the alkali cation effects on the HER/HOR activity of Pt and the beneficial roles of the second metal such as the Ni on the HER/HOR activity of Pt.2,3 Meanwhile, the Ru-induced improvement of the HOR activity of Pt was ascribed to the bifunctional mechanism4,5 or the hydrogen binding energy.6,7 However, these different theories often conflict with each other, and have not been unified into a coherent picture depicting the kinetics of HER/HOR in alkaline solutions. Herein, we propose a new theory to account for the Ni and Ru induced improvement of the HOR activity of Pt in alkaline solutions, on the basis of combined electrochemical and in situ spectroscopic data. The combination of this new theory with the pzfc and 2B theories appears to give a coherent picture of the HER/HOR kinetics of Pt in alkaline solutions.

Acknowledgements

This work was supported by the Office of Naval Research (ONR) under award number N00014-18-1-2155. The authors declare no competing financial interests. Use of Beamline ISS 8-ID of the National Synchrotron Light Source (NSLS) II was supported by the NSLS-II, Brookhaven National Laboratory, under U.S. DOE Contract No. DE-SC0012704. Use of beamline 5-BM-D at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31–109-Eng-38. Jia acknowledged the help from Eli Stavitski, Klaus Attenkofer from ISS, NSLS-II; Qing Ma from DND-CAT, APS at ANL; and Todd E Miller, Lynne LaRochelle Richard from Northeastern University on the XAS data collection.

References

(1) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M., Nat. Energy
2017, 2, 17031.

(2) Liu, E.; Li, J.; Jiao, L.; Doan, H. T. T.; Liu, Z.; Zhao, Z.; Huang, Y.; Abraham, K. M.; Mukerjee, S.; Jia, Q., J. Am. Chem. Soc.
2019, 141, 3232.

(3) Jia, Q.; Liu, E.; Jiao, L.; Li, J.; Mukerjee, S., Current Opinion in Electrochemistry
2018, 12, 209.

(4) Li, J.; Ghoshal, S.; Bates, M. K.; Miller, T. E.; Davies, V.; Stavitski, E.; Attenkofer, K.; Mukerjee, S.; Ma, Z.-F.; Jia, Q., Angew. Chem. Int. Ed.
2017, 56, 15594.

(5) Strmcnik, D.; Uchimura, M.; Wang, C.; Subbaraman, R.; Danilovic, N.; Van Der Vliet, D.; Paulikas, A. P.; Stamenkovic, V. R.; Markovic, N. M., Nat. Chem.
2013, 5, 300.

(6) Schwämmlein, J. N.; Stühmeier, B. M.; Wagenbauer, K.; Dietz, H.; Tileli, V.; Gasteiger, H. A.; El-Sayed, H. A., J. Electrochem. Soc.
2018, 165, H229.

(7) Wang, Y.; Wang, G.; Li, G.; Huang, B.; Pan, J.; Liu, Q.; Han, J.; Xiao, L.; Lu, J.; Zhuang, L., Energy Environ. Sci.
2015, 8, 177.
Heteroatom-Doped Graphdiynes: Enhanced Oxygen Reduction/Evolution Reaction Electrocatalytic Activity
Authors: Gu Jinxing , Magagula Saneliswa , Zhao Jingxiang , Chen Zhongfang
Published: February 2020

Metal-free catalysts with controllable compositions are quite attractive for ORR/OER applications in fuel cells due to their low cost, high stability and high efficiency. Nitrogen-doped graphdiynes have recently emerged as such a promising metal-free ORR catalyst, with excellent catalytic performances compatible to Pt/C. Considering the mechanism of their outstanding activities, the debate still goes on whether the sp-hybridized or pyridinic nitrogen dopants paly the crucial role. Moreover, will other heteroatoms doping into graphdiynes lead to the enhanced ORR/OER activity? To solve the debate and answer the question, we studied the electrocatalytic activities of X-doped graphdiynes (X = B, N, P, S) toward ORR/OER by means of density functional theory (DFT) computations. In total, 15 models were constructed for X-doped graphdiynes, including one for pristine graphdiyne (Gdy), five for N-doped graphdiynes, and three for each B-, P- and S-doped graphdiynes. We revealed that the sp-N-doped graphdiyne, the graphitic S-doped and the graphitic P-doped graphdiyne exhibit comparable or even better catalytic activities compared with Pt/C (η = 0.44 V) or RuO2 (the most active OER catalyst so far, η = 0.37 V). Among N-doped graphdiynes, the sp-N-doped graphdiyne is most active for both ORR (η = 0.49 V) and OER (η = 0.40 V), respectively. Among all heteroatom (B, N, P and S) doped graphdiynes, the graphitic S-doped graphdiyne is the best ORR catalyst (η = 0.42 V), while the graphitic P-doped graphdiyne is the best OER catalyst (η = 0.35 V). This study not only gains deep insights into the catalytic activity of N-doped graphdiyne for ORR, but also guides the developing of graphdiyne-based catalysts beyond N doping.
Alkaline Stability and Fuel Cell Performance of Piperidinium-Based Anion Exchange Membranes
Authors: Wang Zhongyang , Zhao Yang , Ramani Vijay
Published: February 2020

There is a growing interest in using anion exchange membranes (AEMs) as separators in alkaline membrane fuel cells (AMFCs) and in other energy conversion and storage systems such as redox flow batteries (RFBs), alkaline water electrolyzers (AWEs) and reverse electrodialysis (RED) cells. The most commonly used cation group in AEMs is the benzyl trimethylammonium cation. However, it had been shown that quaternary ammonium-based AEMs are sensitive towards Hofmann elimination [1] and direct nucleophilic elimination reactions [2] that result in loss of ion exchange capacity (IEC) and ionic conductivity. To solve the alkaline stability issue inherent to quaternary-ammonium-group-containing AEMs, alternative cations such as piperidinium-based cations has been proposed and investigated.

The piperidinium-based AEM was able to maintain its ca. 90% of its initial IEC after immersion into 1M KOH at 80 ºC for 30 days. Such piperidinium-based AEMs showed higher alkaline stability than benzyl-trimethylammonium-based AEM (ca. 20% degradation in 1M KOH at 60 ºC for 30 days) [3]. The improved alkaline stability was mainly attributed to the avoidance of attaching quaternary ammonium onto benzylic position. The planar structure of piperidinium-based cation slows down the β-elimination phenomenon. Also, there is no ether linkage with the polymer backbone and hence, the stability of polymer backbone is superior. The chloride ion conductivity of the piperidinium-based AEM was 65 mS/cm at 80 ºC under an IEC of 2.26 mmol/g. An AEMFC was assembled using our piperidinium-based AEM with Pt/C catalysts used for both anode and cathode. A peak power density of 700 mW/cm2 with 2 A/cm2 current density was obtained at 70 ºC without any backpressure.

References

[1] C.G. Arges, L. Wang, J. Parrondo, V. Ramani, Journal of The Electrochemical Society, 160 (2013) F1258-F1274.

[2] S. Chempath, J.M. Boncella, L.R. Pratt, N. Henson, B.S. Pivovar, The Journal of Physical Chemistry C, 114 (2010) 11977-11983.

[3] Z. Wang, J. Parrondo, V. Ramani, Journal of The Electrochemical Society, 164 (2017) F1216-F1225.
Synthesis and Characterization of Composite Anion Exchange Membranes (AEM) Using Layered Double Hydroxides (LDH) with Ionic Liquids (IL) and Metal Organic Framework (MOF)
Authors: Narducci Riccardo , Di Vona Maria Luisa
Published: February 2020

Anion Exchange Membranes (AEM) are used in alkaline fuel cells, electrolysers and redox-flow batteries. The main disadvantage of AEM is the degradation of the ionomer in basic conditions and high temperature. The formation of composite offers several advantages, such as enhanced hydrolytic stability and improved mechanical properties. The composite anion-conducting membranes were made by dispersion of Mg/Al layered double hydroxide (LDH) in the polymeric matrix made by polysulfone (PSU) grafted with trimethylamine (TMA) and 1,4-diazabicyclo[2.2.2]octane (DABCO) [1]. They presented a reduced swelling and the mechanical properties in fully humidified conditions were enhanced. Furthermore, the membranes can be treated in alkaline conditions at 60 °C without losing their properties. The Zn/Al and Mg/Al LDH were also modified by adding ionic liquids (IL) in the inter-lamellar space showing an improved ionic conductivity (Figure 1) [2]. The LDH-IL fillers were added to PSU-DABCO and poly(2,6-dimethyl-1,4-phenylene)oxide DABCO (PPO-DABCO) membranes, the resulting properties were studied. For the composite with metal organic frameworks (MOF) we used UiO-66 [3], consisting of a cluster of [Zr6O4(OH)4] and 1,4-benzodicarboxylic-NH2, preliminary studies were achieved.

Figure 1: Schematic of PSU-DABCO-LDH-IL (ZnAl-
1-butyl-3-methylimidazolium hydrogen sulphate).

References

[1] M.L. Di Vona, M. Casciola, A. Donnadio, L. Pasquini, R. Narducci, P. Knauth, International Journal of Hydrogen Energy, 42 (2017) 3197-3205

[2] R. Pizzoferrato, E. Ciotta, I.V. Ferrari, R. Narducci, L. Pasquini, A. Varrone, M. Richetta, S. Antonaroli, M. Braglia, P. Knauth, M.L. Di Vona, ChemElectroChem, 5 19 (2018) 2081-2088

[3] J. Escorihuela, R. Narducci, V. Compañ and F. Costantino, Advanced Materials Interfaces, 6 2 (2019) 1801146

Figure 1
Properties and Parameters of Importance for Enhanced Performance and Performance Stability of Anion Exchange Membrane Fuel Cells – a Modeling Study
Authors: Brandon Simon , Yassin Karam , Rasin Igal G , Dekel Dario R.
Published: February 2020

Research and development of anion exchange membrane fuel cells (AEMFCs) has placed a large focus on cell performance. For example, one of the main goals of anion exchange membrane (AEM) materials development has been the increase of their hydroxide conductivity, which directly enhances AEMFC performance. Although crucially important, achieving high performance is not enough since robust AEMFCs must exhibit both high performance AND high performance stability (i.e. longevity).

In this contribution we present results from one-and-three dimensional modeling studies aimed at elucidating the impact of a number of key AEM material properties, as well as AEMFC design and operating parameters, both on performance and on performance stability.

Using a one-dimensional model of AEMFC operation [1], which includes AEM chemical degradation analysis capabilities [2], we discuss the relative importance of membrane conductivity, membrane thickness and membrane water diffusivity. In particular, we demonstrate that although conductivity is an important AEM property where cell performance is concerned, its impact on longevity is minimal. Thus developing an AEM which promotes enhanced cell performance and cell performance stability requires a focus both on conductivity and on other properties and/or parameters which do impact stability. Our results show that one of these is AEM water diffusivity which strongly influences AEMFC performance stability and should therefore (in addition to conductivity) be on the list of important properties and parameters to be tailored in the next generation of AEMs.

In addition to our one-dimensional analysis, we employ a full three-dimensional model of an AEMFC to explore additional properties and parameters of importance. In particular, we discuss the impact of system geometry (flow field patterns) as well as gas flow rates (gas stoichiometry) on performance, and propose possible related routes to process improvement.

References:

R. Dekel, I.G. Rasin, M. Page, S. Brandon, J. Power Sources 375 (2018) 191

R. Dekel, I.G. Rasin, S. Brandon, J. Power Sources 420 (2019) 118
Electrolysis Cell Performance and Durability - a Contradiction in Terms?
Authors: Bensmann Boris , Suermann Michel , Trinke Patrick , Immerz Christoph , Broda Agata , Hanke-Rauschenbach Richard
Published: February 2020

In the current stage the focus of PEM water electrolysis cells development is on improving durability and reliability. Over the next decade growing attention has to be paid to reduce capital and operating cost as well as to increase flexible operation in order to fulfil the needs of the costumers, e.g. reducing the systems total cost of ownership (TCO). In most cases, however, achieving the desired cost reduction and higher flexibility contradicts durability and reliability expectations as well as performance requirements.

TCO reductions can be achieved by changing the operating conditions, e.g. increasing temperature, current density, operating pressure or load flexibility, but also by e.g. reducing the catalyst loading or membrane thickness. With respect to the operating conditions, it seems problematic as the different parameters also act as stressors for certain degradation phenomena in the system. On the other hand, reducing the so far oversized materials used, increases the vulnerability of the components with regard to degradation and thus limits the durability and reliability of the system.

This contribution discusses this described interplay between performance and durability in more detail. First, stressors (e.g. high compartment pressures) are attributed to certain degradation effects (e.g. voltage increase) appearing in the cell. Concerning such a general analysis, there is much information available about the response of the electrochemical cell to certain stressors and the relations are well known. However, only less can be said about the origin of this measureable effects. But to achieve the required performance while maintaining or even increasing the durability, a deeper understanding of the underlying degradation phenomenon (e.g. loss of ionic conductivity) is required. It is shown on the example of the membrane as critical component in electrolysis cells that standard electrochemical characterization methods, if evaluated properly, can already provide important information about the origin of such measured effects.

Starting from this, new materials can be developed or adequate mitigation strategies can be implemented to suppress degradation. It is also shown that additionally applied comprehensive modelling of electrolysis cells can support these efforts and can potentially be used for optimized cell design, considering performance and durability requirements.
Effect of Microscopic Oxygen Bubbles on Measured OER Catalyst Stability - a Comparative Study between RDE and MEA Measurements
Authors: El-Sayed Hany A , Tovini Mohammad Fathi , Weiß Alexandra , Gasteiger Hubert A.
Published: February 2020

Fast screening of OER catalysts for their intrinsic activity and stability is pivotal for the development of PEM electrolyzers.1 With respect to OER activity, catalyst screening is very well-established using different measurement techniques such as rotating disk electrode (RDE), flow-channel methods, or full cell measurements in an electrolyzer, where comparable activities are obtained. On the other hand, accelerated stability testing of OER catalysts has been reported to result in different stability lifetimes based on the testing method. For example, stability tests using the RDE technique result in magnificently shorter catalyst lifetimes than those using an electrolyzer.2

We have recently discovered that the use of an RDE-based galvanostatic test is not reliable to investigate the OER catalyst stability as the “apparent” catalyst degradation associated with this test is mostly due to a measurement artefact.3 During the OER galvanostatic test, oxygen gas bubbles form and accumulate in the pores of the catalyst layer, shielding the active surface area of the catalyst, therefore resulting in an increasing potential, mistakenly interpreted in the literature as catalyst degradation.4, 5

In this contribution, we present a comprehensive study in which we demonstrate how the accumulation of microscopic oxygen bubbles in the pores of the electrocatalyst layer during the OER results in an artefact that falsifies the estimated catalyst lifetime. We will show that this artefact exists in all RDE-based stability tests including galvanostatic, potentiostatic, and potential cycling techniques. Furthermore, we will show that the same artefact also exists during the stability test carried out using a membrane electrode assembly (MEA) in an electrolyzer, but to a much lesser extent compared to that associated with the RDE technique. We will also discuss how to mitigate this accumulation of gas bubbles in an MEA, and discuss possible protocols that enable the OER catalyst stability testing using RDE-based techniques.

References

L. Wang, F. Song, G. Ozouf, D. Geiger, T. Morawietz, M. Handl, P. Gazdzicki, C. Beauger, U. Kaiser, R. Hiesgen, A. S. Gago and K. A. Friedrich, J. Mater. Chem. A,
5(7), 3172–3178 (2017).

S. Cherevko, Current Opinion in Electrochemistry,
8, 118–125 (2018).

Hany A. El-Sayed, Alexandra Weiß, Lorenz F. Olbrich, Garin P. Putro, and Hubert A. Gasteiger, Journal of the Electrochemical Society,
166(8), F1-F7 (2019).

H.-S. Oh, H. N. Nong, T. Reier, M. Gliech and P. Strasser, Chem. Sci.,
6(6), 3321–3328 (2015).

H.-S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Araújo, E. Willinger, R. Schlögl, D. Teschner and P. Strasser, J. Am. Chem. Soc.,
138(38), 12552–12563 (2016).
Operando Sub-Second Neutron Imaging of Cationic Species Migration in a Proton Exchange Membrane Water Electrolyzer
Authors: Zlobinski Mateusz , Babic Ugljesa , Gubler Lorenz , Schmidt Thomas J. , Boillat Pierre
Published: February 2020

In recent years, it became clear that implementing energy storage on a large scale is a necessary route for the power production sector to maintain a stable and sustainable grid with increasing share of intermittent renewable sources of energy. Proton exchange membrane water electrolyzers show promise especially because of their suitability to be coupled to renewables in remote areas decentralizing the energy grid. There are, however, some challenges, which have to be tackled before market penetration can occur. One of the most pressing issues is the susceptibility of the proton exchange membrane to feed water impurities in form of cations [1], [2]. Titanium porous transport layers, piping and other system components will introduce slight amounts of cations during normal operation (Fe, Na, Cu, Ca, Ti), which over a longer period will become the cause of significant overpotential [3]. It is therefore necessary to understand the contamination mechanism of proton exchange membranes and its impact on the electrochemical performance of the cell.

Motivated by the fact that the reversible degradation is one of the key factors which dictate the operability of an electrolyzer, we carried out experiments which bring further insights into the influence and behavior of the cationic species in the proton exchange membrane water electrolyzer under operation and standby conditions. Neutron imaging techniques were employed to observe the model contaminant in form of Gd3+, which is a perfect fit due to its large neutron cross-section. We found that under the effect of the electric field the cations migrate and accumulate near cathode catalyst layer/porous transport layer interface. A sub-second imaging setup enabled us to correlate the position of cations within the membrane with electrochemical data. Subsequently we regenerated the cell by operating it with diluted sulfuric acid (below 1mMol/L) injected into cathode compartment during the neutron imaging. Influence of the accumulation of the cations near the cathode catalyst layer on the electrolyzer performance and optimal operando regeneration procedures will be discussed.

[1] S. Sun, Z. Shao, H. Yu, G. Li, and B. Yi, “Investigations on degradation of the long-term proton exchange membrane water electrolysis stack,” J. Power Sources, vol. 267, pp. 515–520, 2014.

[2] X. Wang, L. Zhang, G. Li, G. Zhang, Z. G. Shao, and B. Yi, “The influence of Ferric ion contamination on the solid polymer electrolyte water electrolysis performance,” Electrochim. Acta, vol. 158, pp. 253–257, 2015.

[3] U. Babic, M. Suermann, F. N. Büchi, L. Gubler, and T. J. Schmidt, “Critical Review—Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development,” J. Electrochem. Soc., vol. 164, no. 4, pp. F387–F399, 2017.

Figure 1
In-plane Mass Transport in Polymer Electrolyte Membrane Electrolyzer Porous Transport Layers with Through Pores
Authors: Kim Pascal Junseob , Lee ChungHyuk , Lee Jason Keonhag , Fahy Kieran F. , Bazylak Aimy
Published: February 2020

The porous transport layer (PTL) is a key component in the polymer electrolyte membrane (PEM) electrolyzer for transporting reactant liquid water to the active sites while facilitating oxygen gas removal. Most current PTL designs use an expanded foam structure with uniform porosity. The interactions between the PTL and flow fields typically leads to non-uniform reactant and product distributions due to the necessarily open and closed regions (channels and lands in the flow fields). These non-uniform distributions hinder performance in the cell; therefore, structures tailored to particular flow field geometries would benefit the technology and be of significant interest to the field.

Mesh-type PTLs are promising for their ease of fabrication with controllable structures at low manufacturing costs, yet the nature of two-phase flow within the mesh-type PTLs is not well understood in the literature. Furthermore, mesh structures have not been optimized to be used with conventional flow fields. In this study, the effect of mesh structures on the mass transport properties of a PEM electrolyzer is investigated through customized porous transport layers and synchrotron X-ray imaging. Two porous transport layers were compared: a PTL with straight pores under the channel and the land and another PTL with straight pores under only the channel (Figure 1). The pores under the land were inaccessible for both liquid water and gas, and as a result, reactions were localised under the channel regions. Moreover, the presence of pores under the land region led to a reduced electrical contact area, thereby contributing to increased ohmic resistance. We observed that pores under the land resulted in higher mass transport resistances exhibited by an increase in gas volume in the pores under the channel. Overall, the PTL with pores only under the channel exhibited relatively superior electrochemical performance; thus, we recommend that mesh PTL should be designed with minimal pores under the land.

Figure 1: Schematic of the anode half of PEM electrolyzers installed with a mesh PTL with a) pores under the channel and land regions, and b) pores under only the channel region of the flow fields.

Figure 1
Effects of Catalyst and Electrode Composition on Performance of Unitized Regenerative Fuel Cells
Authors: Rhodes Christopher P. , Godinez-Salomon Fernando , Adame Solorio Jesus
Published: February 2020

A unitized regenerative fuel cell (URFC) that uses a single cell that functions in electrolysis or fuel cell mode provides potential advantages including lower cost, mass, and volume compared with discrete electrolyzer and fuel cell systems. However, significant challenges for URFCs include lower performance, lower round-trip efficiency, and higher stability/degradation issues compared with separate systems. The lower performance and enhanced degradation of URFCs results from a combination of factors including catalyst degradation and water management issues that result from switching between electrolyzer and fuel cell modes. To address these challenges and improve performance of proton-exchange membrane (PEM) URFCs in both fuel cell and electrolyzer modes, we evaluated the effects of catalyst and electrode composition of the bifunctional oxygen electrode. To improve catalyst activity and efficiency of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), we explored using bifunctional oxygen catalysts composed of bimetallic nanoframes derived from our prior studies.1,2 Electrochemical testing using a rotating disk electrode configuration showed that the nanoframe bifunctional oxygen electrocatalysts have higher ORR mass activity, OER mass activity, and round-trip efficiency and reasonable stability compared with baseline Pt-IrO2 catalysts. URFC membrane electrode assemblies (MEAs) were fabricated and tested to determine the effect of the composition of the oxygen electrode on fuel cell and electrolyzer performance and evaluate the effect of switching between operating in fuel cell and electrolyzer modes. Performance comparisons were made with MEAs composed of baseline commercial Pt black-IrO2 catalysts.

References

Godinez-Salomon, F.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Jose-Yacaman, M.; Rhodes, C. P., Metallic Two-Dimensional Nanoframes: Unsupported Hierarchical Nickel-Platinum Alloy Nanoarchitectures with Enhanced Electrochemical Oxygen Reduction Activity and Stability. ACS Appl. Mater. Interfaces
2017, 9, 18660-18674. DOI: 10.1021/acsami.7b00043

Godínez-Salomón, F.; Albiter, L.; Alia, S. M.; Pivovar, B. S.; Camacho-Forero, L. E.; Balbuena, P. B.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Rhodes, C. P., Self-Supported Hydrous Iridium–Nickel Oxide Two-Dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catal.
2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171
Investigation of the Microstructure and Rheology of Iridium Oxide Catalyst Inks for Low-Temperature Polymer-Electrolyte-Membrane Water Electrolyzers
Authors: Khandavalli Sunilkumar , Park Jaehyung , Kariuki Nancy N. , Myers Deborah J. , Ulsh Michael , Mauger Scott A
Published: February 2020

Low-temperature polymer electrolyte membrane water electrolyzers (PEMWE) are an attractive clean energy technology to produce hydrogen (H2) as an energy carrier for several applications such as transportation and grid-scale energy storage and distribution (as supported by the US Department of Energy’s H2@Scale initiative). A critical component of PEMWE membrane electrode assemblies (MEA) is the catalyst layer (CL), where the electrochemical reactions occur. The microstructure of the CL plays a key role in MEA performance by affecting porosity, connectivity, etc. The CL microstructure is formed by the catalyst particles and an ionomer - which acts both as a binder for catalyst particles and as a proton conducting medium. The interactions between the ink components (catalyst-ionomer-solvent), and the ionomer concentration in the ink, which dictates the ink microstructure and the processing behavior during coating and drying, play a critical role in the formation of the CL microstructure.

In this talk, an investigation of catalyst-ionomer interactions, microstructure and rheological behavior of the catalyst inks will be presented. The ink consists of iridium oxide (IrO2) catalyst particles and Nafion ionomer dispersed in a mixture of 1-propanol and water. A combination of rheology, ultra-small/small angle x-ray scattering, dynamic light scattering, and electrophoretic mobility were used to understand inter-particle and particle-ionomer interactions and characterize microstructure. Our results show that iridium catalyst dispersions in the absence of ionomer are agglomerated. When ionomer is added to the dispersion it adsorbs to the surface of IrO2 and provides stabilization through both electrostatic and steric mechanisms. As the ionomer content increases, we see increasing interparticle interactions. The stability and microstructure evolution as a function of ionomer concentration in the ink will be discussed. As well as their relation to device performance.
Catalyst Effects on Gas Phase HCl Oxidation in PEM Electrolyzer
Authors: Likit-anurak Kris , Lopata Joseph Steven , Shimpalee Sirivatch , Weidner John W. , Khunatorn Yottana , Meekins Benjamin Highsmith
Published: February 2020

Electrolysis of HCl exhibits promise for large-scale production of hydrogen with the additional benefit of converting a low-value byproduct (HCl) into a more valuable feedstock (Cl2). However, most of the available publications in literature use aqueous phase HCl as the electrolyte [1-3]. Previously, gas phase hydrogen bromide (HBr) was shown to electrolyze at current densities an order of magnitude greater than that of aqueous HBr [4]. Aqueous HBr electrolysis was limited by slow diffusion in the liquid phase. We show here that gas phase HCl also exhibits higher reactions rates, as reflected by higher current densities, when compared to aqueous phase.

The purpose of this work was to study the efficiency and durability of the anode catalyst (RuO2 and IrRuO2), the role of the polymer membrane (Nafion vs. polybenzimidazole), and the operating parameters (temperature, HCl flow rate, and current density) in a proton exchange membrane (PEM) electrolyzer. We found that crossing over of chorine from anode to cathode can poison the catalyst at the cathode, resulting in less durability and shorter lifetime of the electrolyzer. We also discuss how operating temperature, HCl flow rate, and hydration affect the performance of the electrolyzer.

References:

Huskinson, J. Rugolo, S.K. Mondal, M.J. Aziz, Energy & Environmental Science. 5 (2012) 8690.

Mohammadi , S.N. Ashrafizadehb, A. Sattari, Chemical Engineering Journal 155 (2009) 757–762.

Barmashenko and J. Jo"Rissen, Journal of Applied Electrochemistry 35 (2005) 1311–1319

Sivasubramanian, R.P. Ramasamya, F.J. Freireb, C.E. Hollanda, J.W. Weidner, International Journal of Hydrogen Energy 32(4) (2007) 463-468.
(Invited) The Evolution of Membrane Electrode Assemblies for Automotive Applications
Authors: Martinez Alex
Published: February 2020

Membrane Electrode Assemblies (MEAs) have evolved significantly in recent years to become a complex piece of technology. Currently, MEAs incorporate a variety of catalyst types and supports which need to be integrated into layers for both anode and cathode electrodes. In addition, the additives used in the membrane have also become more complex, to mitigate gas crossover and degradation that can be caused by metal ion impurities, thus enabling the deployment of thinner membranes (<15 mm). Further, different approaches to maximising the power per cost lead to different power density requirements. For example, the performance target set by the US-DOE is 1.0 W/cm2, whereas in EU funded program GAIA1 the target is a demanding 1.8 W/cm2. This forces MEA developers to carefully design each component to enable mass commercialization.

This presentation will document recent advances at JM in the design of MEAs for the transportation industry, with an emphasis on the integration of scaled-up alloy catalysts in cathode layers. Results from advanced catalyst characterisation using state of the art TEM and XPS facilities will be provided; these results have helped identify the mechanisms that compromise catalyst stability and activity and have allowed the synthesis of new materials and layers that will enable thrifting of Pt to levels that will help mass commercialization. In addition, with the help of 1D testing and the use of simulation tools such as OpenFCST, insights will be provided into proton and oxygen transport limitations at high current densities. Finally, a detailed analysis will also be provided that highlights the importance of understanding catalyst and ionomer surface compositions to give high kinetic activity whilst also enabling high performance at high current densities in H2/Air, in order to reach 1.8 W/cm2.

References

GAIA, Grant Agreement Number 826097, http://www.gaia-fuelcell.eu/

Acknowledgements

The GAIA project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 826097. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research.
Perovskite Solar Cells Using Tin Oxide As Electron Transport Layer
Authors: Workman Maniell , Chen Zhi David , Sarvari Hojjat , Liu Guoduan , Graham Kenneth , Park So Min
Published: February 2020

Abstract

Solar Energy has many challenges and disadvantages preventing its widespread use and implementation. Current silicon solar panel technology is still more expensive than coal and oil. The need for alternative energy sources has driven research for high efficiency and low-cost solar cells. The previous electron transport material (ETL) is TiO2, which needs high processing temperature (~400°C), which limits many applications using flexible substrates. Tin oxide layer can be processed at low temperatures (<200°C). It is promising for applications for flexible substrates.

My research is focused on perovskite solar cells utilizing tin oxide nanoparticle as ETL. Tin oxide layer was spin coated and annealed in order to create a conductive electron transport material. In this study, we will compare two precursor materials: SnCl4 nanoparticles in ethanol solution and SnO2 nanoparticles in aqueous solution. We found that the ETL using SnCl4 nanoparticles results in much poorer performance of solar cells with a power conversion efficiency (PCE) of 12.32% (Figure 1) and the ETL using SnO2 nanoparticles results in much better solar cells with PCE of approximately 18.13% (Figure 2). Therefore, SnO2 nanoparticle is a promising ETL material for high efficiency perovskite solar cells.

a)b)

Figure 1: a) I-V curves of a solar cell with SnO2 ETL using SnCl4 precursor. Poor performance (12% PCE) and large hysteresis observed. b) I-V curves of a solar cell with SnO2 ELT using SnO2 nanoparticle precursor. Lower hysteresis and higher PCE (18%) observed.

Figure 1
Earth-Abundant Semiconductors Based Electric Power Window
Authors: Patel Malkeshkumar , Ban Dong-Kyun , Nguyen Thanh Tai , Kim Joondong
Published: February 2020

Earth-abundant semiconductors and scalable fabrication of the photovoltaic device are the cornerstones to realize the net-zero emission energy-eco system. Metal oxides have a high energy bandgap and pass light to the vision to enlighten the vision to the human eyes. This study demonstrates all-transparent photovoltaic framework by various heterostructures, for example, ZnO/NiO and TiO2/Co3O4. The large area (> 1-inch square) sputtering grown these heterostructures exhibits high power conversion efficiency with outstanding stability under the UV light portion of Sunlight, and visible light transmittance more than 50%. This study revealed the high-work-function of p-type metal oxide played a vital role to achieve photovoltage >0.7 V under low-intensity light illumination. We studied the various aspect that includes the effect of metal work-function, transient optoelectronics, and back surface field. The optoelectronic performances of these heterostructures demonstrate their potential in the ultraviolet photodetector, transparent solar cells, and transparent electronics.
Adherent Light-Induced Al Plating on Si for Substitution of Ag in Si Solar Cells
Authors: Ricci Lewis , Tseng Mao-Feng , Shin Woo Jung , Tao Meng , Liu Yunyu , Jiang Fangdan , Xing Guoqiang
Published: February 2020

Silver (Ag) is one of the most expensive materials used in the manufacture of silicon (Si) solar cells today as the front electrode. The current Si cell manufacturing cost from Si wafers is ~$0.10 per cell and Ag accounts for about half of that cost. Another key issue is the limited reserve of Ag on our planet, with a US Geological Survey estimated amount of 530,000 metric tons [1]. Even if the entire Ag reserve was used for cell manufacturing, we could only supply ~5% of the 2100 global energy demand [2]. Based on material cost, abundance, and resistivity, only two suitable replacements for Ag exist, Cu and Al. Al bears the advantage over Cu since it eliminates the need for a barrier layer such as Ni. Al is also less prone to oxidization often experienced by Cu. We reported light-induced Al electroplating on Si solar cells using a Lewis acidic chloroaluminate ionic liquid [3], demonstrating direct Al plating on Si without a seed layer.

This talk focuses on surface preparation and Al plating processes to promote strong adhesion and low contact resistance between plated Al and cell emitter. Sheet resistance and surface morphology of the emitter were monitored as a function of laser power for SiNx removal. Electrochemical capacitance-voltage profiling determined the laser power at which the emitter surface dopant profiles were preserved. A process to remove laser damage and clean the Si surface after laser patterning was developed by etching Si in 1 wt% NaOH. It was found by atomic force microscopy that ~23 s was the minimum time to completely remove the original Si surface which was damaged and contaminated. Al deposits on substrates prepared by this surface cleaning process showed strong adherence in the Scotch tape test. Al plating was performed at different temperatures. The resulting film thickness and morphology were investigated with scanning electron microscopy. The lowest film resistivity was less than 8 µΩ-cm which was obtained at a plating temperature of 50°C and showed a grain size of 2–5 µm.

[1] U.S. Geological Survey, Mineral Commodity Summaries (2017).

[2] M. Tao, Terawatt Solar Photovoltaics: Roadblocks and Opportunities (Springer, London, 2014).

[3] L. Wang, W.-H. Huang, W. J. Shin, M. Tao, B. Deng, and D. Wang, J. Electrochem. Soc., 165, D381 (2018).
A Novel Technique to Analyze the Electrolyte Wetting Rate through Li-Ion Battery Electrodes
Authors: Davoodabadi Ali , Li Jianlin , Wood David L. , Jin Congrui
Published: February 2020

The electrolyte wetting step is one of the most critical processes in lithium-ion battery (LIB) manufacturing that typically requires a long period of time. Rapid and complete electrolyte wetting is extremely beneficial for reducing the wetting time, hence eliminating the bottleneck and saving substantial capital cost in battery production plant.

The wetting balance technique has been conventionally used to measure the electrolyte imbibition rate in electrodes, however, it suffers from several drawbacks and has limited accuracy. We presented a combined experimental and theoretical investigation of the dynamics of electrolyte imbibition through electrodes. We proposed a novel method to accurately measure the electrolyte imbibition rate. Excellent agreement between the experimental data and the developed analytical model is obtained, which demonstrates the robustness and accuracy of the proposed technique. The coefficient of penetrance (COP) and the solid permeability coefficient (SPC) are identified as important parameters, i.e., the electrolyte with higher COP value wets faster into an electrode, whereas for an electrolyte, the electrode with greater SPC is more amenable to impregnation. We utilized this technique to study the effect of different LIB parameters on electrolyte wetting rate. For example, as shown in Fig. 1 [1], the imbibition coefficient (D) that represents the electrolyte wetting rate decreases by increasing the electrolyte salt concentration. Electrolyte solvent, and calendering extent are among other factors that their effects on imbibition rate have been investigated. Such results can greatly help optimize electrolyte formulation and electrode design to achieve rapid and complete wetting, potentially leading to reduced battery production costs and improved product quality.

[1] A. Davoodabadi, J Li, Y Liang, DL Wood III, TJ Singler, C Jin; “Analysis of electrolyte imbibition through lithium-ion battery electrodes”, Journal of Power Sources, 424, 193-203 (2019)

Figure 1