bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanistic Insights into Electrochemical Oxidation of Small Alcohol Molecules
Authors: Dewan Shalaka , Raciti David , Wang Chao
Published: February 2020

Small alcohol molecules such as methanol and ethanol represent promising fuels to power fuel cells for mobile electronic devices, transportation and stationary applications. Ethanol is of particular interest due to its renewability by generation from biomass feedstocks, large energy density and compatibility with existing infrastructures for fuel storage and delivery. Although substantial progress has been made in the recent years for the development of direct ethanol fuel cell (DEFC) technology, obstacles are still present for the practical implication, largely in the lack of efficient and selective electrocatalysts for complete oxidation of ethanol to CO2.

Platinum (Pt) is commonly used as electrocatalyst in fuel cells, including DEFCs. However, ethanol oxidation on Pt is found to be incomplete and produces undesired partial oxidation products such as acetaldehyde and acetic acid. It is thereby considered that Pt itself cannot cleave the C-C bond in ethanol molecules and a second transition metal such as Rh and Ir is needed to facilitate this rate- and selectivity-limiting step. However, evidences are also present in the literature for the formation of strongly binding adsorbates, such as -CO and -CH
x
, at low potentials (<0.5 V vs. RHE), from both in situ molecular spectroscopy (e.g., Infrared (IR) and surface enhanced Raman spectroscopy (SERS)) and differential electrochemical mass spectroscopy (DEMS) studies. These results suggest that oxidative removal of these C1 species, instead of C-C bond cleavage, is the sole rate-limiting factor on Pt catalysts.

In attempt to resolve this controversy, we have performed systematic studies of methanol, ethanol and ethylene glycol oxidation on polycrystalline Pt electrodes. In particular, surface-specific sum frequency generation (SFG) spectroscopy is combined with electrochemistry to determine the reaction intermediates and evaluate their dependence on electrode potentials. It is found that C1 adsorbates form at low potentials, and the coverages increase as the electrode potential is raised from 0.1 V to ~0.4 V. While the -CO feature drops above 0.4 V for methanol and ethylene glycol oxidation, it persists up to 0.5 V and then drops for ethanol oxidation. Our results confirm the presence of active Pt sites for C-C bond cleavage and underline the role of -CH
x
species generated from the β-carbon in governing the kinetics of alcohol oxidation reactions. It is proposed that the slow transition from -CH
x
to -CO gives rise to the higher overpotentials for ethanol oxidation compared to methanol and ethylene glycol oxidation.
Experimental Elucidation of the Oxygen Reduction Volcano in Base on a Pt Alloy Single Crystal
Authors: Jensen Kim Degn , Tymoczko Jakub , Bandarenka Aliaksandr S , Chorkendorff Ib , Escudero-Escribano María , Stephens Ifan E. L.
Published: February 2020

It is of fundamental importance to understand the factors controlling trends in activity for electrocatalytic reactions as a function of pH. In the case of the oxygen reduction reaction, numerous reports suggest significant divergences between noble metals surface catalytic performances in acid and base.[1,2]

In our earlier studies, we mapped out the experimental Sabatier volcano for the oxygen reduction reaction in 0.1 M HClO4 using the Cu/Pt(111) near-surface alloy system, see Figure 1 for near-surface alloy schematic.[3,4]

In this study, as those of [3,4], we found that by changing the subsurface coverage of Cu we could tune the surface binding of the key reaction intermediate, OH; we thus monitored the OH binding energy shift through the observable shifts in the base voltammograms in both acidic and alkaline media.

Further, we elucidate the experimental oxygen reduction volcano in 0.1 M KOH for the Cu/Pt(111) near-surface alloy system. Remarkably, we observe that the same trend persists between OH binding shifts and Cu/Pt(111) oxygen reduction activities between acid and alkaline electrolyte, with the optimum catalyst in alkaline exhibiting an 8-fold improvement in activity, relative to Pt(111). However, all surfaces show a ~4 fold improvement in activity in 0.1 M KOH, relative to the same surface in 0.1 M HClO4. At the peak of the volcano the surface exhibits an exceptionally high specific activity of 90 mA/cm2 at 0.9 V with respect to the reversible hydrogen electrode. Thus, our results confirm that OH binding energy is the key descriptor in both alkaline and acid electrolytes.

[1] R. Rizo, E. Herrero, J. M. Feliu, Phys. Chem. Chem. Phys. 2013, 15, 15416–25.

[2] J. Staszak-Jirkovský, R. Subbaraman, D. Strmcnik, K. L. Harrison, C. E. Diesendruck, R. Assary, O. Frank, L. Kobr, G. K. H. Wiberg, B. Genorio, et al., ACS Catal. 2015, 5, 6600–6607.

[3] I. E. L. Stephens, A. S. Bondarenko, F. J. Perez-alonso, F. Calle-vallejo, L. Bech, T. P. Johansson, A. K. Jepsen, R. Frydendal, B. P. Knudsen, J. Rossmeisl, et al., 2011, 5485–5491.

[4] A. S. Bondarenko, I. E. L. Stephens, I. Chorkendorff, Electrochem. commun. 2012, 23, 33–36.

Figure 1
Highly Efficient Nitrogen and Sulfur Co-Doped Three-Dimensional Graphene-Based Nanocatalysts for the ORR
Authors: Wang Jie , Wu Min , Wu Zexing , Xin Huolin L. , Wang Deli
Published: February 2020

a, Key Laboratory of Material Chemistry for Energy Conversion and Storage (Huazhong University of Science and Technology), Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P.R. China. *Email: wangdl81125@hust.edu.cn

b, Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA

Graphene, a single-atom-thick hexagonally arrayed sp2 carbon atoms bonded sheet, has attracted tremendous interest in renewable energy conversion and storage devices due to its extraordinary properties, especially ultrahigh specific surface area and predominant electron conductivity1. However, graphene based two-dimensional catalysts suffer from an irreversible re-stacking of the nanosheets due to the strong π-interaction during thermal annealing process and electrochemical measurements which would result in a lower surface area, limiting the mass transfer rate and even decreasing the catalytic activity as well as electrochemical stability.

Figure 1 (a) TEM image of NSGCB; (b) ORR activity of NSGCB and the corresponding comparative catalysts; (c) TEM image of NSCNT-3; (d) ORR activity of NSCNT-3 and the corresponding comparative catalysts.

Herein, we report two strategies for the synthesis of nitrogen and sulfur co-doped three-dimensional graphene intercalated structure nanomaterials as electro-catalysts for ORR in alkaline medium. One is the insertion of Vulcan XC-72 carbon spheres into the graphene layer, forming a graphene-Vulcan XC-72- grapheme “sandwich-like” structure2. The other way is partially unzipping of multi-walled carbon nanotubes to form a graphene nanoribbon-carbon nanotube-graphene nanoribbon structure. Both of the prepared three-dimensional structured nanocomposites were experienced to nitrogen and sulfur co-doping process, and moreover, the resulting doped electro-catalysts exhibited outstanding ORR performance.

Acknowledgements

This work was supported by the National Natural Science Foundation (21306060, 21573083), the Program for New Century Excellent Talents in Universities of China (NCET-13-0237), the Doctoral Fund of Ministry of Education of China (20130142120039).

References

(1) Li, Y., Zhao, Y., Cheng, H., Hu, Y., Shi, G., Dai, L., & Qu, L. Nitrogen-doped graphene quantum dots with oxygen-rich functional groups. Journal of the American Chemical Society, 2011, 134, 15-18.

(2) Wu, M., Wang, J., Wu, Z., Xin, H. L., & Wang, D. Synergistic enhancement of nitrogen and sulfur co-doped graphene with carbon nanosphere insertion for the electrocatalytic oxygen reduction reaction. Journal of Materials Chemistry A, 2015, 3, 7727-7731.

Figure 1
(Invited) Durable Nanoparticle for Fuel Cell Electrocatalyst
Authors: Sung Yung-Eun , Chung Dong Young
Published: February 2020

Demand on the practical synthetic approach to the high performance electrocatalyst is rapidly increasing for the fuel cell commercialization. However, sluggish kinetics hindered high performance. Therefore methods to improve the activity of catalysts that facilitate reaction kinetic have been and continue to be a popular area of research. Since electrocatalytic reactions occur on the catalyst surface, nanoparticles (NPs) with high surface area are promising candidates to overcome problems. However, their low stability at harsh operating condition impedes nanoparticle utilization. Here we present a synthesis of highly durable and active nanoparticle based electrocatalyst for fuel cell electrocatalyst. One example is ordered intermetallic face-centered tetragonal (fct)-PtFe NPs encapsulated by thin-layer carbon shell. Only few nanometers of carbon shells which is in situ formed from dopamine coating could effectively prevent the coalescence of NPs. This carbon shell also protects the NPs from detachment and agglomeration as well as dissolution throughout the harsh fuel cell operating conditions. The other is carbon encapsulated metal phosphide NPs for robust hydrogen evolution reaction. Anti-oxidative carbon shell prevent surface oxidation of NPs, leading exceptionally long-term durability. We believe that thin-layer carbon shell encapsulation of NPs can open a new possibility for the development of highly active and durable electrocatalyst in near future.
Mimicking Active Pt3ni (111) Surface on Pt3ni Icosahedron for Oxygen Reduction
Authors: Xing Wei , Zhu Jianbing , Xiao Meiling , Li Songtao , Ge Junjie , Liu Changpeng
Published: February 2020

The oxygen reduction reaction (ORR) is a corner stone for energy conversion techniques such as fuel cells and metal-air batteries[1]. The use of Pt unfortunately generate a number of obstacles including the high cost, scarcity and readily poisoning by impurity and the cross-over of fuel9. Shaped bimetallic nanocrystals (NCs) with precisely controlled structure and composition at the atomic level, e.g. PtxNi1−x alloy NCs[2], intermetallic PtCo core–shell nanoparticles[3] and Pt3Ni nanoframes[4], represent a class of exciting and promising ORR catalysts.

Herein, we demonstrate a one-pot protocol for the controlled synthesis of icosahedral Pt3M nanocrystal with twenty active Pt3M (111) facets using glucosamine as both reducing and structure-directing agent. Among the investigated catalysts, the Pt3Ni icosahedral with nano-segregated Pt-skin displays the unexpected 32-fold enhancement in specific activity and 12-fold improvement in mass activity relative to state-of-the-art Pt/C catalyst. Besides, the catalyst was found ultra-robust during 20,000 potential cycling tests. The Pt3Ni icosahedral thus represents one class of the most efficient ORR electrocatalysts ever reported and demonstrates an effect technique in mimicing the active extended surface in nano-scale.

Fig.1 (a) TEM image of the typical icosahedral Pt3Ni nanocrystal, (b) HRTEM micrograph showing the twin boundaries of five-fold symmetry, (c) the (111) and (200) planes, (d)cyclic voltammetry curves of Pt/C, Pt NI/C and Pt3Ni/C catalysts, (e) ORR polarization curves for Pt/C, Pt NI/C and Pt3Ni/C catalysts in O2-saturated 0.1M HClO4, (f) comparative ORR activities of Pt/C and Pt3Ni/C catalysts before and after 20,000 potential cycles.

Acknowledgments

The study was financed by the National Basic Research Program of China (973 Program, 2012CB215500), the National Natural Science Foundation of China (21373199, 21433003) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA09030104). 

References

[1] Stamenkovic, V.R., B. Fowler, B.S. Mun, G. Wang, P.N. Ross, C.A. Lucas, and N.M. Marković, Science, 315(5811), 493-497,(2007).

[2] Zhang, C., S.Y. Hwang, A. Trout, and Z. Peng, Journal of the American Chemical Society, 136(22), 7805-7808,(2014).

[3] Wang, D., H.L. Xin, R. Hovden, H. Wang, Y. Yu, D.A. Muller, F.J. DiSalvo, and H.D. Abruña, Nat Mater, 12(1), 81-87,(2013).

[4] Chen, C., Y. Kang, Z. Huo, Z. Zhu, W. Huang, H.L. Xin, J.D. Snyder, D. Li, J.A. Herron, M. Mavrikakis, M. Chi, K.L. More, Y. Li, N.M. Markovic, G.A. Somorjai, P. Yang, and V.R. Stamenkovic, Science, 343(6177), 1339-1343,(2014).

 

Figure 1
Performance of Platinum-Nickel Nanowires in a PEMFC
Authors: Mauger Scott A , Neyerlin K.C. , Alia Shaun M , Hurst Katherine , Shulda Sarah , Ngo Chilan , Weker Johanna Nelson , Pylypenko Svitlana , Pivovar Bryan S
Published: February 2020

Platinum-coated nickel nanowire (PtNiNW) catalysts have shown high mass activity, specific activity, and exceptionally high surface areas in oxygen-reduction reaction (ORR) rotating disc-electrode experiments, all several times higher than platinum on carbon and well above DOE targets.1,2 However, their subsequent incorporation into proton exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEA) has been exceedingly difficult, resulting in substantially lower mass and specific activities and lower than anticipated electrochemical areas (ECAs).2 This presentation will focus on the challenges associated with the incorporation of extended surface Pt alloys in PEMFC MEAs, the ensuing conditioning protocols and the large discrepancy between RDE and MEA data. It is found that soaking the MEA in dilute sulfuric acid to remove nickel and increase the platinum weight fraction increases cell performance metrics such as open-circuit voltage, mass activity, and specific activity, as shown in Figure 1. Decreases in membrane resistance are also observed. The effects of ionomer, carbon and unsupported electrocatalyst ratios on MEA performance will also be discussed. Scanning transmission electron microscopy (STEM) and transmission x-ray microscopy (TXM) tomography will be examined as tools to elucidate the relationship between electrocatalyst/electrode structure and MEA performance.

1. Alia, S. M. et al. Platinum-Coated Nickel Nanowires as Oxygen-Reducing Electrocatalysts. ACS Catal.
4,1114–1119 (2014).

2. Pivovar, B. S. Extended, Continuous Pt Nanostructures in Thick, Dispersed Electrodes. 2015 DOE Hydrogen and Fuel Cells Program Review (2015).

Figure 1
The Impact of Fuel Impurities on Pemfcs Using a Hydrogen Fuel Re-Circulation System
Authors: Rockward Tommy , Valdez Jacob , Mukundan Rangachary
Published: February 2020

Research has shown that contaminants in the hydrogen fuel stream have an impact on Polymer Electrolyte Membrane Fuel Cells (PEMFCs) performance that is influenced by the platinum loading, membrane thickness, the impurity, its concentration and PEMFC operating conditions such as cell temperature, relative humidity, and back pressure. A significant portion of previous reported results were conducted with the fuel cell being operated in single-pass mode where the exhaust hydrogen is vented from the fuel cell. While these findings have proven useful in improving the fundamental understanding of the poisoning mechanisms of non-hydrogen species (contaminants) in operating single fuel cells; the question remains whether or not these findings correlate to PEMFC systems that use a re-circulating fuel stream as being designed by the OEMs. Some advantages of re-circulating the anode exhaust gas back into the anode inlet are: 1) the anode outlet water is returned into the dry H2 fuel stream to obtain proper humidification and also 2) the excess H2 fuel is returned to enhance fuel utilization. While these advantages are attractive, there are some inherent challenges that are introduced in fuel re-circulation mode. Two of the more notable drawbacks involve inert gas build-up due to crossover and the accumulation of contaminants in the anode. In this study, we focus our efforts on correlating the impact of CO and H2S on fuel cell performance in H2 single-pass versus H2 re-circulation mode using the SAE J27191 and ISO 14687-2 Hydrogen Fuel Product Specification2
limits (4 ppb H2S and 200 ppb CO). This study was conducted on Membrane Electrode Assemblies (MEAs) at the 2015 DOE target loadings for platinum (anode: 0.05 mg/cm2 and cathode: 0.1 mg/cm2).

References:

SAE J2719: Hydrogen Fuel Quality for Fuel Cell Vehicles, www.sae.org

ISO 14687-2, Hydrogen Fuel – Product Specification, Part 2: PEM fuel cell applications for road vehicles, http://www.iso.org/iso/catalogue_detail.htm?csnumber=55083

Acknowledgements:

The authors gratefully acknowledge the financial support of the DOE Fuel Cell Technologies Office and the support of Technology Development Manager, Charles (Will) James, Jr.
Characterization of Water Cluster Connectivity and Fluid Transport in PEFC Gas Diffusion Layers
Authors: Eller Jens , Büchi Felix N
Published: February 2020

Polymer electrolyte fuel cells (PEFC) require an effective water management to operate efficiently, especially at high current densities which are needed to reach system cost targets [1]. The description of the complicated two-phase water transport remains a challenge in PEFC models and requires experimental validation on various length scales. In this work, operando X-ray tomographic microscopy (XTM) with scan times of 10 s was used to depict the liquid water at defined differential conditions at the technically relevant cell temperature of 80 °C at the TOMCAT beamline of the Swiss Light Source.

Cells with Toray TGP-H060 GDL with MPL were operated at high feed gas humidity (0.75 A/cm2, 108 % rH, H2/Air) or high current density (3.0 A/cm2, 78 % rH, H2/O2) conditions. The liquid water in the cathode GDL was analysed in terms of the local and average saturation, water cluster sizes, connectivity of the water clusters and the permeability of the water filled GDL pores. While fully through-plane connected water clusters contribute to the transport of water in the liquid phase, only partly connected water clusters do not (see Figure 1a). The majority of liquid water volume (> 80 %) is found in a limited number of fully through-plane connected water clusters (< 20 %) (see Figure 1b). Even though the water phase occupies in average the larger pores of the GDL, as reported earlier [2], still some large pores and percolation paths remain liquid free. Nevertheless, the available fully through-plane liquid paths provide liquid permeabilities that result in no noteworthy pressure losses to drain the product water of today's and upcoming current densities.

As research in industry and academia strive for the separation of the transport paths of the liquid and the vapour phase [3], the effect of the presence or absence of the partly connected water clusters on the gas phase transport parameters (permeability & effective diffusivity) of the GDL is discussed as well.

References

[1] O. Gröger et al., J. Electrochem. Soc. 162 (2015), A2605-A2622.

[2] T. Rosén et al., J. Electrochem. Soc. 159 (2012), F536-F544.

[3] A. Forner et al., Advanced Materials 27 (2015), 6317-6322.

Figure 1: a) Sketch of the different cluster types that can be found in the GDL domain; blue: full connected water clusters (FC); green: top connected (TC); red: bottom connected (BC); purple: non connected (NC). b) Volume and cluster number fractions of the different cluster types for the high humidity condition.

Figure 1
Iron-Based Spinel Oxide Nanoparticles for Electrocatalysis of Oxygen Evolution Reaction
Authors: Liu Weiyan , Fan Shaoxun , Li Jia , Gan Lin
Published: February 2020

The design of cost-effective and highly active, durable electrocatalysts for the sluggish oxygen evolution reaction (OER) is critical for promoting various energy conversion process such as water splitting and rechargeable metal-air batteries. Due to a wider selection of earth-abundance and low cost catalyst candidates (e.g., mixed 3d-transition metal oxides), OER in alkaline environment has attracted considerable interests during past years. Besides the recently developed Ni-Fe layered double hydroxides (LDH) catalysts, spinel phase transition metal oxides have also drawn particular interests owing to their well-defined rigid structure and thus potentially high stability during electrocatalysis. While improved OER activities have been demonstrated, currently most spinel transition metal oxides (mainly Co-based spinel oxides) still underperformed the state-of-the-art benchmark OER catalyst IrO2and the Ni-Fe LDH catalysts. Moreover, atomic insights into the surface structure that governs their OER reactivities and stabilities still remain very limited.

We report here the exploration of iron-based spinel oxide nanoparticles (MxFe3-xO4, M= Mn, Fe, Co, Ni, Cu) as a new class of alkaline OER electrocatalysts with potentially both high electrocatalytic activity and high stability. Emphasis will be placed on atomistic understanding on the surface cation chemistry and surface atomic structures of the spinel oxide nanoparticles and their correlations with OER activities and stabilities. This will be achieved by comparative microscopic and spectroscopic studies of the nanoparticle surfaces before and after OER electrocatalysis using high-resolution (scanning) transmission electron microscopy, electron energy loss spectroscopy and X-ray photon spectroscopy, which will be further complemented by density functional theory calculations. The results will provide important insights into the structure-activity-stability relations of spinel phase transition metal oxides as well as other mixed metal oxides for OER electrocatalysts.
PEMFC Stack Diagnostics Using EIS
Authors: Smon Araya Samuel , Jeppesen Christian , Kær Søren Knudsen
Published: February 2020

One way of improving the durability and reliability of a fuel cell stack or system is to isolate faults within the fuel cell and perform targeted condition-based maintenance on the affected components, to remove or limit the conditions that caused the fault. This can be done by on-line monitoring of the fuel cell system's state of health to locate and isolate faults and prevent sudden failures before they occur and correcting faulty conditions to prolong the lifetime of the fuel cell. This paper presents electrochemical impedance spectroscopy (EIS) results obtained on PEMFC stacks, with the aim of investigating the fuel cell stacks’ response to different faults, for a possible use of EIS as an advanced monitoring and diagnostics tool. The stacks used in this study are from Dantherm Power A/S, intended for stationary microCHP application. Four different faults were considered; change in fuel composition, air starvation, fuel starvation and water management, both for flooding and drying. Each fault simulation was performed in a separate fuel cell stack to avoid the mixing of the impedance signatures of the different faults. The same continuous, steady state operations under nominal condition were recorded prior to fault simulations as healthy-state references. Then the different faults were induced at varying current densities and varying fault levels.
Morphology of Elastomeric Anion Exchange Membranes: A Dissipative Particle Dynamics Study
Authors: Sepehr Fatemeh , Paddison Stephen J.
Published: February 2020

The design and optimization of stable and highly conductive anion exchange membranes (AEMs) is essential to the development of energy and conversion technologies.1
,
2 There has been an increased interest and research to address the low stability and ionic conductivity of polymeric AEMs. However, a fundamental understanding of stability and transport in AEMs is still in its infancy3 and the effects of the choice of the cationic functional group and polymer architecture are still not known. Recently developed elastomeric AEMs4 exhibiting satisfactory chemical stability are investigated in this study. These AEMs are based on the elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), that are functionalized with various cationic groups.

Dissipative particle dynamics (DPD) is a meso-scale simulation technique5
,
6 which enables the simulation of large time- and length-scales with reasonable computational expense has been selected to investigate the morphology and dynamical behavior of such systems. The system of hydrated AEM is coarse-grained to a degree that the consideration of both chemical distinction and fine structural variants are satisfied. The structures of the DPD beads were optimized using first principles electronic structure calculations and the interaction parameters were determined using a recently developed methodology.7

The effects of several microstructural parameters including the length of the tether chains, type of the cationic group (trimethylammonium [(CH3)3NH]+; dimethylimidazolium [DMIm+]; and triphenylphosphonium [(C6H5)3PH]+ ), and the polymer architecture on the morphology and transport of anions in the aforementioned elastomeric AEMs were investigated. The effect of water content in the membrane and the effect of ion exchange capacity (IEC) were also studied. The results are compared with the widely studied proton exchange membrane Nafion.

References:

1. G. Couture, A. Alaaeddine, F. Boschet and B. Ameduri, Prog Polym Sci, 2011, 36, 1521-1557.

2. J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. W. Xu and L. Zhuang, Energ Environ Sci, 2014, 7, 3135-3191.

3. M. G. Marino, J. P. Melchior, A. Wohlfarth and K. D. Kreuer, J Membrane Sci, 2014, 464, 61-71.

4. A. D. Mohanty, C. Y. Ryu, Y. S. Kim and C. Bae, Macromolecules, 2015, 48, 7085-7095.

5. P. Espanol and P. B. Warren, Europhys Lett, 1995, 30, 191-196.

6. R. D. Groot and P. B. Warren, J Chem Phys, 1997, 107, 4423-4435.

7. F. Sepehr and S. J. Paddison, Chem Phys Lett, 2016, 645, 20-26.
(Invited) Recent Progress in Analysis Methods of PEFCs: From Catalysts to Meas
Authors: Imai Hideto
Published: February 2020

Understanding the relationship between structures and properties in PEFC materials and/or components are essential in designing better PEFCs and their materials. Recent progress in analysis methods point toward this direction: combination of basic and advanced structure analyses and imaging methods using x-rays and electron probes, as well as computational simulations correlate structural information and electrode properties.

Quick overview of x-ray and electron beam analysis methods using various physical phenomena, such as, diffraction, scattering, x-ray absorption, x-ray photo-emission, and latest challenges of their application to the catalyst and catalyst-layer developments for both platinum-based and non-platinum catalysts will be presented.
Ultra-Low Pt Decorated Porphyrinic Carbon Based Hybrid Electrocatalysts for Oxygen Reduction Reaction
Authors: Hwang Sun-Mi , Choi YongMan , Joo Sang Hoon , Yim Sung-Dae , PARK Gu-Gon
Published: February 2020

As the fuel cell market has been growing, the price competitiveness of polymer electrolyte fuel cell (PEFC) became the most important factor for its commercialization. In particular, the production of membrane-electrode assembly (MEA) consisting of Pt-based electrocatalyst is a critical hurdle for the cost reduction of PEFCs. Therefore, many researchers have veen focusing on the development of cost effective electrocatalysts such as non-precious metal based catalysts (NPMCs) or low content platinum based catalysts to minimize Pt loading by morphological and structural tunings with inexpensive transition metals. Recently, we reported the M-N doped ordered mesoporous porphyrinic carbon (M-OMPC, M=Fe, Co) which showed a comparable ORR activity to that of Pt/C in an acid medium. However, an inferior MEA performance of M-OMPC is a practical barrier because of high mass transport resistance and electrical resistance, which mainly comes from the thicker electrode of M-OMPC. In this study, we proposed a new approach for enhanced ORR activity as well as reduction of noble metal loading content via adding a trace of platinum nanoclusters on M-OMPC. The Pt/M-OMPC (Pt~5 wt%) hybrid catalyst showed an increased Pt based mass activity and specific activity by a factor of 7, compared to that of Pt/C (5 wt%) at 0.85 V RHE.
Towards Understanding of the Anode Catalyst Layer Structure for Extended Reversal Tolerance: An Advanced Characterization Approach
Authors: Susac Darija , Jankovic Jasna , Ash Arash , Putz Andreas Michael Vincent , Lei Chao , Zhang Hao , Lee Wendy , Stumper Jürgen
Published: February 2020

Proton exchange membrane fuel cells for automotive applications (PEMFC) frequently experience transient conditions such as start-up/shut-down, freeze start-up and local fuel starvation at the anode catalyst layer (ACL) that are responsible for the loss of performance and durability as a result of irreversible carbon corrosion [1].

 

To mitigate such degradation, oxygen evolution catalysts have been incorporated into ACL and studied for effects on membrane electrode assembly (MEA) performance and reversal tolerance. Ru and Ir oxides are among the most studied catalysts for oxygen evolution reaction (OER) in both PEMFCs and water electrolyzers [2-5]. Although comparative measurements have been performed to investigate the OER activity trends, systematic studies focusing on effects of particle/agglomerate size and distribution within ACL on PEMFC MEA reversal tolerance have not yet been reported. 

 

In order to be able to design anode catalyst layer structures that meet the performance and reversal tolerance requirements, it is necessary to obtain a better understanding of structure versus performance relationships. This requires the capability to fabricate different anode catalyst layer structures, as well as efforts in development of methodologies to characterize the spatial distribution of all components within the catalyst layers. The ultimate goal is to use the experimentally measured structural parameters as inputs for the development of models for understanding of the relationship between anode structures and reversal tolerance. The objective of this work is to present the methodology for structural characterization of anode catalyst layers containing OER materials. Structural parameters correlating with the extended reversal tolerance will be discussed.

 

References

S. Enz, T.A. Dao, M. Messerschmidt and J. Scholta, Investigation of degradation effects in polymer electrolyte fuel cells under automotive-related operating conditions, J. Power Sources, 274 (2015) 521-535

E. Antolini, Ir as catalyst and cocatalyst for oxygen evolution/reduction in acidic polymer electrolyte membrane electrolyzers and fuel cells, ACS Catal. 4 (2014) 1426-1440

T. Reier, M. Oezaslan and P. Strasser, Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir and Pt catalysts: a comparative study of nanoparticles and bulk materials, ACS Catal. 2 (2012) 1765-1772

S. Cherevko, T. Reier, A.R. Zeradjanin, Z. Pavolek, P. Strasser and K.J.J. Mayrhofer, Stability of nanostructure iridium oxide electrocatalysts during oxygen evolution reaction in acidic environment, Electrochem. Commun. 48 (2014) 81-85

M. Bernicke, E. Ortel, T. Reier, A. Bergmann, J.F. de Araujo, P. Strasser and R. Kraerhnet, Iridium oxide coatings with template porosity as highly active oxygen evolution catalysts: structure-activity relationship, ChemSusChem, 8 (2015) 1908-1915
Effect of Water Balance in Ionomer Solution for Novel Membrane Electrode Assembly of Polymer Electrolyte Membrane Fuel Cells
Authors: Park Seok-Hee , Woo Seunghee , Yim Sung-Dae
Published: February 2020

The performance of membrane electrode assemblies (MEA) is considerably affected by water balance or content in ionomer solution. The three-dimensional structure of the ionomer in electrode is very important for getting higher current density in MEA. In this study, some representative water-based and alcohol-based commercial ionomers were compared for getting higher MEA performance under different humidity level. The contact angle of the catalyst layer was measured to determine the variation in wetting properties with different ionomer solution. Various MEAs with different electrode combination were tested in single cell station. And some electrochemical techniques were applied to this MEA such as polarization curve, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The results show that a MEA of water-based ionomer as anode and alcohol-based ionomer as cathode exhibits higher performance at most humidity levels.
Hydrogen Oxidation Reaction Activity of RuO2 Nanosheets Modified Pt−Ru / C
Authors: Ohnishi Tomohiro , Takimoto Daisuke , Ayato Yusuke , Mochizuki Dai , Sugimoto Wataru
Published: February 2020

Carbon supported Pt-Ru systems such as PtRu/C and Pt2Ru3/C have been investigated as anode catalysts of polymer electrolyte membrane fuel cells. However, hydrogen oxidation reaction (HOR) activity for Pt-Ru/C is significantly degraded due to adsorption of carbon monoxide (CO) on the active Pt sites and dissolution of Ru. The addition of metal oxide nanosheets enables to enhance the performance of catalysts. We have reported that RuO2 nanosheets [1] as an additive to Pt/C (RuO2ns-Pt/C) and PtRu/C (RuO2ns-PtRu/C) enhances CO tolerance at room temperature [2]. The HOR current of RuO2ns-Pt/C was improved by 25% compared to Pt/C. RuO2ns-PtRu/C had higher HOR activity and enhanced CO tolerance. Thus, CO poisoning is suppressed by the addition of RuO2 nanosheets. However, it is necessary to measure the performances at higher temperature near actual operating of PEFC. In this study, we report the addition effect of RuO2 nanosheets to PtRu/C and Pt2Ru3/C at 25◦C as well as 70◦C.

Chronoamperograms (CA) of commercial and RuO2 nanosheests modified catalysts at 25 and 70◦C are shown in Figures A and B. At 25◦C (Fig. A), the addition of RuO2 nanosheets increased the initial HOR activity and the activity after accelerated durability tests (ADT) in 300 ppm CO containing H2 (CO/H2) as well as pure H2. The current was enhanced in the entire range of CA. The addition of RuO2 nanosheets slightly enhanced CO tolerance and durability which were represented by ratio of density current j (in H2) divided by j (initial in CO/H2) and j (initial in CO/H2) divided by j (after ADT in CO/H2), respectively. This behavior is similar to the previous result of comparing RuO2ns-PtRu/C and PtRu/C [2].

The HOR current at 70◦C showed the different behavior compared to 25◦C (Fig. B). At 70◦C, there was a difference of HOR current between composite and commercial catalysts in CO/H2 while HOR activity of the catalysts was almost the same in pure H2. Thus, the decline in HOR current of composite catalysts was slower than non-modified catalysts. Therefore, the composite catalysts suppresses CO adsorption. In particular, the durability of RuO2ns-Pt2Ru3/C at 70◦C shows higher (93%) than the other catalysts (78~86%).

This work was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO), Japan

[1] W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, and Y. Takasu, Angew.
Chem. Int. Ed., 42, 4092 (2003).

[2] D. Takimoto, T. Ohnishi, and W. Sugimoto, ECS Electrochem. Lett., 4(5), F35-F37 (2015).

Figure 1
Preparation of Ultrathin Palladium Nanosheet and Its Application in Pd@Pt Core-Shell Catalyst for Oxygen Reduction Reaction
Authors: Shen Zhongrong , Takimoto Daisuke , Nutariya Jeerapat , Ayato Yusuke , Mochizuki Dai , Sugimoto Wataru
Published: February 2020

High cost, sluggish kinetics, and poor durability of Pt catalysts predominantly hinder the wide-spread commercialization of fuel cells. Pt-based core-shell nanosheet catalyst may resolve　these problems listed above because of the following 3 advantages. 1) The Pt content can be greatly reduced via core−shell nanostructures consisting of a Pt shell on appropriate monometallic or alloy cores; 2) Nanosheets have high surface-to-volume ratio and terrace sites. The active sites for the oxygen reduction reaction (ORR) have been suggested to be located on the terrace sites of the nanocrystals.[1] 3) Nanosheets should dramatically reduce Pt dissolution due to few edges and corners with their low coordinate sites. Terraced facets have been reported to be more stable than edges and corners.[2]

Here, we present a novel method to synthesize palladium (Pd) nanosheets by a wet-chemical preparation at room temperature (Fig.A). The Pd precursor (Pd(acac)2) is reduced by CO in the presence of decylamine (DA). The protection agent (DA) was easily removed by washing with acetic acid. Using this nanostructure as a core, Pd@Pt core-shell nanosheets were prepared by surface limited redox replacement (SLRR). AFM indicates Pd nanosheets are synthesized with a thickness around 0.9 nm to 1.6 nm and lateral size from tens to several hundred nanometers (Fig.B). After dispersing the Pd nanosheet on a carbon support, Pd@Pt core-shell nanosheets with different Pt shell thickness were prepared, i.e. Pd6.0ML@Pt2.7ML, Pd6.0ML@Pt4.4ML, and Pd6.0ML@Pt5.9ML. The electrochemically active surface area (ECSA) of Pd@Pt nanosheets are 56, 48, 60 m2/g-PGM (90, 66, 77 m2/g-Pt), respectively (Fig. C). The linear sweep voltammetry is applied by using a rotating disc electrode (RDE) in 0.1 M HClO4 at room temperature. The ORR activity is evaluated from jk values at 0.9 V (vs RHE) estimated from Koutecky-Levich Plots. The Pd@Pt nanosheets demonstrated mass activity of 364, 685, 598 A/g-Pt (227, 501, and 492 A/g-PGM), which is much higher than the benchmark Pt/C catalyst (177 A/g-Pt) for the oxygen reduction (Fig. D).

This research was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Fig. A) TEM of Pd@DA nanosheets; B) AFM image of Pd nanosheets; C) CV profiles of the Pd@Pt nanosheets recorded in N2-saturated 0.1 M HClO4 solution at a sweep rate of 50 mV/s; and D) The mass activity of Pd@Pt nanosheets and commercial Pt/C.

Reference

F. J. Perez-Alonso, D. N. McCarthy, A. Nierhoff, P. Hernandez-Fernandez, C. Strebel, I. E. L. Stephens, J. H. Nielsen, I. Chorkendorff, Angew. Chem. Int. Ed.
2012, 51, 4641–4643.

F. N. Büchi, M. Inaba, T. J. Schmidt, Polymer Electrolyte Fuel Cell Durability, Springer Science+ Business Media, New York, 2009.

Figure 1
Synthesis of Two-Dimensional Nanosheets Catalyst with Ru-Core@Pt-Shell Towards Oxygen Reduction Reaction
Authors: Takimoto Daisuke , Ohnishi Tomohiro , Nutariya Jeerapat , Shen Zhongrong , Ayato Yusuke , Mochizuki Dai , Demortiere Arnaud , Boulineau Adrien , Sugimoto Wataru
Published: February 2020

Improvement in the activity and durability of electrocatalysts for the oxygen reduction reaction (ORR) is an essential issue for wide-spread commercialization of polymer electrolyte fuel cells. Nanoparticle catalysts with alloy, skin, and/or core-shell structures have been developed to improve the activity and durability. However, these nanoparticle catalysts often suffer from degradation under harsh conditions. On the other hand, extended surfaces including thin-films possess high durability; however, the surface area is lower than that of nanoparticles due to low surface area.

Nanosheets with atomic thickness have large specific surface area and two dimensionally extended surface. We previously reported the synthesis of metallic ruthenium nanosheets with monoatomic thickness via thermal reduction of RuO2 nanosheets.1,2In this study, we demonstrate the synthesis of Ru-core@Pt-shell nanosheets and the catalytic performance towards the oxygen reduction reaction.

Metallic Ru nanosheets supported on carbon composite was prepared via thermal reduction.3 Pt shell was successively formed on metallic Ru nanosheets supported on carbon via galvanic displacement reaction between Cu and Pt2+. The electrochemically active Pt surface area of Ru-core@Pt-shell nanosheets with 3.5 monolayer Pt-shell (Ru@Pt-3.5ML(ns)/C) was 148 m2 (g-Pt)‒1and showed 4.5 times higher activity than benchmark commercial Pt/C catalyst for the oxygen reduction reaction. In addition, the activity retention of Ru@Pt-3.5ML(ns)/C after durability test (0.6-1.0 V and 1.0-1.5 V for 5000 cycles) was higher than that of Pt/C. The high activity could be attributed to the core-shell structure, and the durability originates from the extended surface structure.

This research was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

1) W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, and Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003).

2) K. Fukuda and K. Kumagai, e-Journal Surf. Sci. Nanotechnol., 12, 97 (2014).

3) D. Takimoto, T. Ohnishi, Y. Ayato, D. Mochizuki, and W. Sugimoto, J. Electrochem. Soc., 163, F367 (2016).

Figure 1
A Development of the Nanostructured Conducting Carbon/Polymer Composites As a Stable Electrode for Polymer Electrolyte Membrane Fuel Cells
Authors: Song Youjung , Lee JuHee
Published: February 2020

One of the main issues restricting wide-spread commercialization of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) is the gradual decline in their performance during operation, primarily due to degradation of cathode catalyst layer by sintering, dissolution and re-deposition of Pt and corrosion of carbon support. Development of durable carbon-based supports for PEMFC electrodes can be beneficial for improving catalytic activity and stability of the electrocatalysts. Accordingly, various carbons (carbon blacks, carbon nanotubes, carbon nanofibers, and graphenes) as well as metal oxides are extensively explored as support materials. Among them, mesoporous carbon (MC) is highly attractive from the viewpoint of pore structure and pore-size distribution desired for mass-transport and enhanced Pt-utilization, which enables encountering problems inherent with microporous carbon black support (i.e., Vulcan XC-72R). On top of that, improvement of catalytic performance can be obtained by modifications in both surface chemistry and pore structure of MC. Therefore, in situ polymerization of 3,4-ethylenedioxythiophene(EDOT) with mesoporous carbon is prepared as catalyst support for platinum nanoparticles by sol-gel method. This conducting polymer was chosen owing to its characteristics such as high chemical, thermal stability, and high electrical conductivity of Poly(3,4-ethylenedioxythiophene)(PEDOT). Pt nanoparticles are then impregnated onto the MC-PEDOT composite using conventional formaldehyde reduction method. Resulting Pt supported MC-PEDOT composite exhibits promising electrocatalytic activity toward oxygen reduction reaction (ORR), which make it attractive for use as electrode material for fuel cell application. The morphology and nanosturcture of Pt supported MC-PEDOT was confirmed by several analysis equipment including SEM, TEM, BET and FT-IR. Electrochemical techniques such as cyclic voltammetry (CV) and impedance measurements are also used to evaluate the extent of degradation in the catalyst layer.
Understanding Pt Nanoparticle Anchoring on Graphene Supports through Surface Functionalization
Authors: Xin Le , Rasouli Somaye , Yang Fan , Uzunoglu Aytekin , Sun Cheng-Jun , Ferreira Paulo Jorge , Liu Yuzi , Stanciu Lia , Xie Jian
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) that use hydrogen as fuel to produce electricity have attracted extensive interests over the past decades.[1] The high efficiency and zero carbon- emission make PEMFCs promising candidates for viable propulsion systems in electric vehicels.[2] One of major challenges that hinder the commercialization of PEMFCs vehicles is the poor stability of Pt nanoparticles on carbon supports, which is mainly due to (1) the dissolution and re-deposition of Pt and (2) migration of Pt nanoparticles over carbon supports.[3],[4] Both of them will cause the agglomeration of Pt nanoparticles, resulting in loss of Pt electrochemical surface area (ECSA) and the increasing of activation over-potential. In this regard, the enhancement of Pt nanoparticle anchoring strength and dispersion on carbon supports is highly desirable in PEMFCs as well as in other catalysis processes.

Presented here is a comprehensive study of the interaction between catalyst nanoparticles and carbon supports in terms of the electronic structure change and its effects on the electrocatalytic performance of supported catalysts. Graphene was chosen as an ideal model system for catalyst support because the unique 2-D structure allows the direct investigation of the interaction with supported metal nanoparticles at their interface. We developed a facile strategy to covalently graft p-phenyl SO3H or p-phenyl NH2 groups onto the graphene surface. The functional groups were found to not only facilitate the homogeneous distribution of Pt nanoparticles over the surface of graphene supports and reduce the Pt average particle size but also strengthen the interaction of the Pt atoms with the functional groups and, consequently, minimize the migration/coalescence of the Pt nanoparticles in the course of accelerated durability tests. The experimental results from both X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) demonstrate the electron density shift from Pt to graphene supports with the strength of the Pt−graphene interaction following the trend of Pt/p-phenyl NH2-graphene > Pt/p-phenyl SO3H-graphene > Pt/graphene. This study will shed light on strategies to improve not only the durability but also the activity of the metal nanoparticles via the functionalization of the catalyst supports in the catalysis field

(1) Gasteiger, H. A.; Markovic, N. M. Science 2009, 324, 48.

(2) Debe, M. K. Nature 2012, 486, 43.

(3) Xie, J.; Wood, D. L.; More, K. L.; Atanassov, P.; Borup, R. L. Journal of The Electrochemical Society 2005, 152, A1011.