bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Study to Improve O → OH Reactions in the Fuel Cell ORR
Authors: Yu Ted H. , Torres Randy , Goddard William A 
Published: February 2020

Using density functional theory (DFT), Pt sandwich catalysts1 are studied to improve the oxygen reduction reaction (ORR) in fuel cells. The ORR can occur through six different reactions, in which the oxygen hydration2 (Oad + H2Oad → 2OHad) reaction was determined to be the rate determining step. A sandwich catalyst consists of Pt on the surface layer, a different metal in the second, and Pt in the bulk. The catalysts have been shown to display unique properties that improve the sluggish ORR in fuel cells.
Twenty-eight different transition metals were tested as the middle sandwich layer. We found that the correlation of these special catalysts with the electronic d-band center is different from what was previously thought. For the 28 catalysts tested, the d-band center fits best linearly with a new index that measures non-correlated binding energy of Oad and OHad. This value is related to the exothermicity of a reaction with Oad as reactant and OHad as product. Thus, Pt sandwich catalysts with large d-band centers calculated using nudged elastic band (NEB) perform exceptionally well for reactions that convert Oad to OHad.
Breaking down the ORR into three basic steps, we categorize the catalytic property that can best improve each step:
Step I) O2Activation: High O binding Energy.
Step II) OH Formation: High Index
Step III) OH Consumption: Low OH binding Energy.
While previous models based on binding energy can predict relatively well a catalystic reaction for Step I and Step III, improving Step II of the ORR was difficult to characterize due to the correlated binding energy of O and OH. Improving this new index was found to be a new strategy to improve Step II ORR reactions. Studying the density of state, we explain why the d-band center is related to this index in Pt sandwich catalysts to give theoretical insights.
Figure 1: Binding energy of 28 different Pt sandwich catalysts. The line in the middle describes the general correlated binding energy of pure metal catalysts between O and OH. The perpendicular distance for each catalyst from the middle line is the new index, in which, Pt-W-Pt is the highest, while Pt-Ag-Pt is the lowest.
References:
1. C. A. Menning, H. H. Hwu and J. G. G. Chen, J Phys Chem B 110(31), 15471-15477 (2006).
2. Y. Sha, T. H. Yu, B. V. Merinov, P. Shirvanian and W. A. Goddard, Journal of Physical Chemistry Letters 2 (6), 572-576 (2011).

Figure 1
Mechanistic Study of Palladium Based Electrocatalysts for Direct Borohydride Oxidation
Authors: Grimmer Christoph , Grandi Maximilian , Zacharias Robert , Friedrich Theo , Woisetschläger Dieter , Mayer Nicole , Koncar Michael , Kalb Roland , Hacker Viktor 
Published: February 2020

The direct borohydride fuel cell (DBFC) is one of several promising direct liquid fuel cells due to easy fuel handling and high energy storage density [1]. DBFCs are still in an early stage of development and further improvements of anode catalyst materials and MEA design are necessary for widespread application.
Herein we present an extensive study of Palladium based catalysts for the anode reaction of DBFCs (see reaction 1) including several electrochemical experiments supported by 11B-NMR and FTIR measurements.
BH4
- + 8OH- → BO2
- + 6H2O + 8e- (1)
(E0 = -1.24 V vs. SHE)
Palladium based electrocatalysts nanodispersed on high surface area carbon are prepared by reduction of precursor salts in an aqueous dispersion of the support material. The catalyst is characterized by transition electron microscopy (TEM).
Rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) experiments with subsequent analysis of reaction products by 11B-NMR are conducted. Fig. 1 shows a typical result of Pd/C on a RDE with a borohydride concentration of 5 mM. Additionally mechanistic aspects on Palladium are investigated employing in-situ FTIR spectroscopy [2].
By combining all results obtained from the experiments mentioned above a substantial proposition of ongoing mechanisms of BH4
--electrooxidation on Palladium is presented.
[1] J. Ma, N. a. Choudhury, Y. Sahai, Renew. Sustain. Energy Rev. 14 (2010) 183.
[2] B.M. Concha, M. Chatenet, C. Coutanceau, F. Hahn, Electrochem. Commun. 11 (2009) 223.
Caption Figure 1:
RDE experiments of Pd/C catalyst at rotation rates of 0-2000 rpm (anodic sweeps) in 1M NaOH with 5 mM NaBH4, insert: according Levich-plot at 0.830 V.

Figure 1
Enhancement of the Oxygen Reduction on Nitride Stabilized Pt-M (M = Fe, Co and Ni) Core-Shell Nanoparticle Electrocatalysts
Authors: Kuttiyiel Kurian A , Sasaki Kotaro , Park Gu-Gon , Choi YongMan , Hwang Sun-Mi , Yang Tae-Hyun , Su Dong , Liu Ping , Adzic Radoslav 
Published: February 2020

Given the harsh operating conditions in hydrogen/oxygen fuel cells, there has been considerable efforts to make Pt(M) alloy nanoparticles as a stable oxygen reduction reaction (ORR) catalyst that have had a marginal success. Core-shell catalysts have unique properties of reducing the precious metal for the reaction and at the same time increasing the ORR activity by combined geometrical and electronic effects. Multiple mechanism has been proposed to explain the enhanced ORR activity of Pt(M) alloys. Watanabe et al. had explained the enhanced ORR activity based on the lattice parameter changes by alloying non-precious metals to Pt. Their results showed that the ORR activity increased in the order of PtFe/C > PtCo/C > PtNi/C, whereas the calculated lattice parameter decreased in the order of PtFe/C < PtCo/C < PtNi/C. Mukerjee et al. investigated the enhancement mechanism on some PtM alloys for the ORR by using XANES and EXAFS. Based on the d-band calculations that decreased in the order of PtFe/C < PtCo/C < PtNi/C, the ORR activity increased in the order of PtFe/C > PtCo/C > PtNi/C. So overall the trend in ORR activity for Pt(M) alloy nanoparticles have been in the order of PtFe/C > PtCo/C > PtNi/C.
Here we report on a new class of catalyst consisting of nitride metal cores enclosed by thin Pt shells that can be easily synthesized. Our theoretical analysis and the experimental data indicate that metal nitride nanoparticle cores could significantly enhance the ORR activity as well as the durability of the core-shell catalysts as a consequence of combined geometrical, electronic and segregation effects on the Pt shells. Adding nitride metal in the core increases the ORR activity in the order of PtNiN/C > PtFeN/C > PtCoN/C. DFT calculations have shown a volcano type behavior with PtNiN/C at the top of the curve revealing the fact that, among the catalysts investigated, it has the best combination of both the surface strain and d-band center shifts.

Figure 1
Understanding the Superior ORR Activity of the Fe-N2+2 to That of the Fe-N4 Site
Authors: Jia Qingying , Strickland Kara , Hafiz Hasnain , Bernardo Barbiellini-Amidei , Mukerjee Sanjeev , Ramaswamy Nagappan , Tylus Urszula 
Published: February 2020

Despite recent progress made in the development of M–Nx–C catalysts, the exact nature of the active sites formed during pyrolysis, as well as the reaction mechanisms remains unclear. Herein, in situ
x-ray absorption spectroscopy (XAS) measurements were performed on representative iron–based catalysts [1-3] to identify the nature of the active sites in these catalysts. XAS offers unique insights into electrode processes by providing simultaneous electronic and structural information on the electrode materials under actual in situ cell operating conditions [4]. In particular, Δμ technique, which has evolved into a powerful tool for elucidating surface adsorbed species in electrocatalysis, was utilized to probe the local structure of the active sites and their interactions with reaction intermediates [3-5]. In addition, density function theory calculations were conducted to correlate the structure to the ORR activity.
We showed that the original macrocycle (denoted as Fe-N4), in which the N is pyrolylic type can be differentiated from the active sites formed upon high temperature pyrolysis (denoted as Fe–N2+2), in which the N is pyridinic type by using Δµ. Combined EXAFS and XANES showed that the central Fe in Fe–N2+2 is off the N4–plane and in high spin state, whereas the central Fe in Fe–N4 is precisely in the N4-plane and in intermediate spin state. Upon the adsorption of ORR intermediates at high potential region, the displacement, the oxidation state, and the spin state of the central Fe change in different ways between Fe–N4 and Fe–N2+2 sites. DFT calculations showed that this different Fe–N switching behavior accounts for the superior ORR activity of Fe–N2+2 to Fe–N4.

Acknowledgements:
The PANI-derived catalysts were prepared and provided by Gang Wu and Piotr Zelenay (Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545). Use of the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL), was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was made possible by the Center for Synchrotron Biosciences grant, P30-EB-009998, from the National Institute of Biomedical Imaging and Bioengineering (NBIB). Support from beamline personnel Dr. Erik Farquhar and Mark Chance (X3B) are gratefully acknowledged.

References

(1) Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. Science
2011, 332, 443-447.
(2) Tylus, U.; Ramaswamy, N.; Jia, Q.; Mukerjee, S. Meeting Abstracts
2012, 225-225.
(3) Ramaswamy, N.; Mukerjee, S. Advances in Physical Chemistry
2012, 2012, 17.
(4) Roth, C.; Benker, N.; Buhrmester, T.; Mazurek, M.; Loster, M.; Fuess, H.; Koningsberger, D. C.; Ramaker, D. E. J. Am. Chem. Soc.
2005, 127, 14607-14615.
(5) Jia, Q.; Ramaker, D. E.; Ziegelbauer, J. M.; Ramaswamy, N.; Halder, A.; Mukerjee, S. The Journal of

Physical Chemistry C
2013, 117, 4585-4596.
Study of Non-PGM ORR Catalyst Degradation Using Synchrotron Techniques
Authors: Tylus Urszula , Chung Hoon T , Higgins Drew C , Myers Deborah J , Nordlund Dennis , Segre Carlo U , Zelenay Piotr 
Published: February 2020

Several recent reports on the development of oxygen reduction reaction (ORR) non-platinum group metal (non-PGM) catalysts have shown an impressive progress towards high ORR activity [1-2]. By now, in RDE testing, these catalysts are quite routinely reaching E½
values of 0.8 V versus reversed hydrogen electrode [1]. The high initial performance notwithstanding, truly durable non-PGM catalysts, capable of maintaining ORR activity for hundreds or thousands of hours at low pH values of the polymer electrolyte fuel cell (PEFC), are yet to be developed. The development of such catalysts must involve a carefully thought-out experimental design and the use of reliable multiple techniques to provide answers to the quarter-of-a-century-old questions about the structure of the ORR active site(s) in metal-nitrogen-carbon (M-N-C) catalysts.
According to some previous in-situ XAS studies [3-4], a vast majority of non-PGM catalysts consist of two forms of transition metal, iron coordinated by nitrogen species (Fe-Nx) and non-coordinated iron nanoparticles (FeNP). While the existence of these species has been detected using different methods, the in-situ XAS reviled a specific redox behavior accompanied with spin switching behavior of the Fe-Nx species when subjected to potential bias simulating PEFC environment [2-4]. There is still a large ambiguity, however, about the actual nature of the M-N-C active sites and their degradation modes. Among many challenges facing this research, it is important to take a closer look at other elements present in such catalysts, such as nitrogen and carbon. This is especially needed for non-PGM catalysts without nitrogen-coordinated Fe (e.g. FeNP) with very high activity [5].
Herein, we present a study of a Fe-based non-PGM catalyst derived from multiple nitrogen precursors. The study has been performed using synchrotron X-ray absorption techniques coupled with standard electrochemical methods, including RRDE and MEA testing. We look at the structures involving all elements in the catalyst by employing high-energy photons at Argonne National Laboratory (to monitor in-situ Fe-containing species) and low-energy photons at Stanford Synchrotron Lightsource to monitor carbon and nitrogen species (C and N K-edge), claimed to play an important part in the ORR active site sites. With better understanding of the structure-to-function relationship in Fe-N-C species as the main objective, we study the effect of durability cycling (Figure1) on the catalyst performance and structural changes involving all elements in Fe-N-C species.

Figure 1
Model Non-Precious Metal Catalysts for Oxygen Reduction Reaction: A Bottom-up Approach
Authors: Martinez Ulises , Williamson Todd L , Artyushkova Kateryna , Hoffbauer Mark A , Purdy Geraldine M , Dumont Joseph H , Dattelbaum Andrew M , Mohite Aditya , Gupta Gautam , Zelenay Piotr 
Published: February 2020

Further development of non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements (C, N, transition metal) continues to be challenged by the lack of understanding of the origin of the oxygen reduction reaction (ORR) activity from such complex materials. Current state-of-the-art synthesis methods for NPMCs involve intricate pyrolysis steps producing highly heterogeneous catalytic systems (1, 2). Therefore, a systematic bottom-up approach using model carbon systems needs to be developed for the better understanding of the formation of active sites and the active site identification.
Recently, we have reported a novel approach for the incorporation of nitrogen heteroatoms into the graphitic carbon structure of liquid-phase exfoliated graphite (3). This approach utilizes high-flux energetic neutral atom beam technology (ENABLE) to incorporate nitrogen heteroatoms via direct chemical activation overcoming thermal activation barriers. Our preliminary results have identified a relationship between the type of nitrogen species doped and the substrate temperature (Figure 1). However, although improved onset potential for the ORR was observed from thin films doped with 13 at.% nitrogen (87% graphitic), the electrocatalytic activity in acid electrolyte is still poor. The work to be presented in this talk represents the continuation of our efforts to understand the role of each component in NPMCs, this time with the addition of transition metals, Fe and/or Co, prior to nitrogen doping. Electrochemical studies will be performed in both acid and alkaline electrolytes to better understand the different reaction mechanism in both environments.

References:

1. G. Wu, K. L. More, C. M. Johnston and P. Zelenay, Science (New York, N.Y.), 332, 443 (2011).
2. E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J. Herranz and J.-P. Dodelet, Nature Communications, 2, 416 (2011).
3. U. Martinez, T. L. Williamson, K. Artyushkova, N. Mack, G. M. Purdy, J. H. Dumont, D. Kelly, W. Gao, A. M. Dattelbaum, A. Mohite, G. Gupta and P. Zelenay, ECS Transactions, 64, 293 (2014).

Figure 1
(Physical and Analytical Electrochemistry Division David C. Grahame Award) Kinetics of the Hydrogen Oxidation in Alkaline and Acid Electrolytes
Authors: Gasteiger Hubert A , Durst Julien , Herranz Juan , Siebel Armin , Hasché Frédéric , Rheinländer Philipp Jan , Simon Christoph 
Published: February 2020

The development of fuel cells based on alkaline membranes (AMFCs) is one of the options to reduce the required amount of platinum, whereby the strong CO2sensitivity of alkaline membranes is a significant challenge. However, while there are several non-noble metal catalysts for the oxygen reduction reaction in alkaline electrolytes which match the activity of platinum, the only currently known hydrogen oxidation catalysts are based on platinum or palladium. Furthermore, the activity of platinum is orders of magnitude lower than in acidic electrolytes [1,2,3], so that ultra-low platinum loading anodes which can be used in acidic electrolytes (PEMFC) are not feasible in alkaline electrolytes. Therefore, the challenge to catalysis research for alkaline membrane fuel cells is to develop more active hydrogen oxidation catalysts.
In our presentation, we will compare the kinetics of the H2 oxidation/evolution reaction (HOR/HER) on carbon supported platinum-group metal electrocatalysts in alkaline and acid electrolytes, determined by rotating disk electrode measurements in liquid electrolytes and hydrogen-pump measurements in fuel cells. The so far proposed causes for the »100-fold lower HOR/HER kinetics in alkaline electrolyte are an increased H/metal bond strength [1,4], a change of the reaction mechanism from H+ to H2O activation requiring more oxophilic catalyst surfaces [5], and/or a change of the water configuration at the metal/electrolyte interface [6]. The consistency of these hypotheses with the HOR/HER kinetics on different metal electrodes will be discussed.
References:
[1] J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz, H.A. Gasteiger, Energy Environ. Sci.
7(2014) 2255.
[2] J. Durst, C. Simon, A. Siebel, P.J. Rheinländer, T. Schuler, M. Hanzlik, J. Herranz, F. Hasché, H.A. Gasteiger, ECS Trans. 64(3)(2014) 1069.
[3] C.M. Zalitis, D. Kramer, A.R. Kucernak, Phys. Chem. Chem. Phys. 15 (2013) 4329.
[4] Y. Wang, G. Wang., G. Li, B. Huang, J. Pan, Q. Liu, J. Han, L. Xiao, J. Lu, L. Zhuang, Energy Environ. Sci.(2014), DOI: 10.1039/c4ee02564d.
[5] D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, D. Van der Vilet, A.P. Paulikas, V. Stamenkovic, N. Markovic, Nat. Chem. 5 (2013) 300.
[6] J. Rossmeisl, K. Chan, R. Ahmed, V. Tripkovic, M. Bjorketun, Phys.
Chem. Chem. Phys. 15 (2013) 10321.
(Invited) A Central Aspect of Electrocatalysis: Generation of Active Sites By Potential-Driven Surface Processes (Part 2)
Authors: Gottesfeld Shimshon 
Published: February 2020

This talk will open with presentation of a general aspect of electrocatalysis which has not been fully recognized, particularly so when it comes to theoretical derivations of the dependence of the rate of electrocatalystic processes on the electrode potential. Description of this prevalent and important pattern of potential-generated active sites in electrocatalysis, will be followed by specific examples of ORR and HOR electrocatalysts in acid and in alkaline fuel cells , including the case of bifunctional HOR catalysts in alkaline membrane fuel cells.
A wide variety of electrocatalytic processes taking place at either functionalized surfaces or “metal” surfaces, are all , in fact, surface redox mediated . This means that the electrode potential defines the steady state population of active sites and suggests that the role of the potential in active site generation must be incorporated in the pre-exponential factor of the overall rate expression. In fact, the potential driven active site generation serves to “ignite” the faradaic process. This explains why the E0
redoc

system of M/Mox , or MOX+n/MOX+n+m surface couples , must be as close as possible to E0
cell process , to enable high conversion efficiency as well as higher rates at low overpotentials.
In acid systems, strong proximity of E0
redoc

system to E0
cell process , is difficult to implementfor the ORR , because the reduced form of the relevant redox mediator must also serve as stabilizer of the intermediate,OOHads, requiring significant oxygen affinity of the reduced form of the redox system ( e.g., Pt metal) The coinage metals are active ORR catalysts at high pH apparently because a different early step in the faradaic process results in full highlighting of the benefit of active site generation at the lowest possible overpotential.
Bifunctional metal catalysts have been recognized as key to high HOR activity in alkaline membrane fuel cells. The last part of this talk will analyze this observation in terms of the wide principle of potential generated active sites.
(Invited) Water As Promoter and Catalyst in Dioxygen Electrochemistry at Aqueous and Organic Electrified Interfaces
Authors: Markovic Nenad M 
Published: February 2020

Water and di-oxygen are the most important and pervasive chemicals that influence all areas of science, from physics to biology to chemistry, and are particularly important in governing phenomena occurring at solid-liquid interfaces in electrochemical environments. One property that sets aqueous-based electrochemical interfaces apart from all other interfaces is the unique arrangements of water molecules within the distinctive interactions between metal surfaces and hydrated ions. These interactions are complex, involving molecular and dissociative adsorption, as well as van der Waals forces both between water molecules and neighboring ions in the compact part of the double layer (i.e. solvation) and between water and covalently-bonded co-adsorbates (e.g. adsorbed hydroxyl species, OHad). Despite the enormous fundamental and technological significance in unfolding these complexities, previous work has treated the water molecule itself simply as a reactant needed to satisfy the stoichiometry of electrochemical reactions, rather than a vital hydrogen-/hydroxyl-donor molecule that can promote the rates of transformation of reaction intermediates to final products. The prime example of such an “incomplete” treatment of water is the oxygen reduction reaction (ORR) in “proton”-O2 fuel cell systems and in lithium-O2 battery systems. Current models guiding the development of new materials for these systems rely on a single descriptor - the binding energy of oxygen intermediates – that cannot explain many “anomalous” phenomena.
Here, we introduce a new model in which water itself plays a critical role in determining the reaction kinetics in dioxygen electrochemistry. The model is based on the formation of HOad···H2O (aqueous solutions), and LiO2···H2O (organic solvents) complexes that place water in a configurationally favorable position for proton transfer to weakly adsorbed intermediates. We found that water plays a dual role, acting as a key promoter in both environments as well as a catalyst in Li-O2 systems