bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Uncovering the Role of Alkaline Pretreatment for Hydroxide Exchange Membrane Fuel Cells
Authors: Shi Lin , Setzler Brian , Weiss Catherine M. , Matz Stephanie , Xue Yanrong , Xu Zhiyuan , Zhuang Zhongbin , Gottesfeld Shimshon , Yan Yushan 
Published: December 2020

As an emerging alternative to proton exchange membrane fuel cells, hydroxide exchange membrane fuel cells (HEMFCs) can use more cost-effective platinum-group-metal-free (PGM-free) catalysts, bipolar plates, and other components.1 Taking advantage of the recent significant progress in hydroxide exchange membranes (HEMs) and optimized electrodes based on hydroxide exchange membrane ionomers (HEIs), HEMFCs achieved unprecedented performance and the record of peak power density was updated frequently in the past few years. Interestingly, nearly all membrane electrode assemblies (MEAs) with satisfactory performances reported in the literature were pretreated with alkaline solutions such as KOH before cell assembly.
Here we show that the most crucial role of the alkaline soak is to remove carboxylates that are generated from the oxidation of primary alcohols, used as solvents for ionomers and/or catalyst inks, by platinum/palladium catalysts during membrane electrode assembly fabrication. These carboxylates are difficult or impossible to eliminate by self-purging processes. We also show that bicarbonates are an adequate replacement for the most frequently used strong bases for the pretreatment. As shown in Figure 1, the pretreatment effect can be seen in the shape of polarization curves. And Figure 2 depicts the electrochemical purging process in HEMFCs for acetate and carbonate/bicarbonate, respectively. As a result, alkaline pretreatment is unnecessary for catalysts that do not oxidize primary alcohols. In fact, membrane electrode assemblies with Pt/Pd-free catalysts deliver a better performance without the alkaline pretreatment: a voltage of 0.64 V at 1.0 A/cm2 and a peak power density of 0.69 W/cm2 in H2/O2.

References

B. P. Setzler, Z. Zhuang, J. A. Wittkopf, and Y. Yan, Nat Nanotechnol, 11 (12), 1020-1025 (2016).

Figure 1
(Invited) Carbon Coatings for Components in Anion Exchange Membrane Electrochemical Energy Conversion
Authors: Proch Sebastian Karl , Bexell Ulf , Moffatt Claire , Jansson Anna , Stenström Mikael , Bernuy-Lopez Carlos , Westlinder Jörgen 
Published: December 2020

We at SMT are committed to using engineering and innovation to advance the world towards more sustainable business. We also understand the need to make the shift to new business models and new thinking in line with the UN’s Sustainable Development Goals and the Paris Climate Agreement. We are, moreover, fully aware that the intermittency of renewables poses significant challenges, but we believe that long-term energy storage by power-to-gas (e.g., the “Hydrogen Economy”) is an important pillar in overcoming those challenges. We imagine carbon as (almost) ideal (coating) material for low-temperature electrochemical energy conversion due to its sustainability, conductivity, low cost, and the fact that, unlike most metals and alloys, it does not form thick oxide layers increasing its contact resistance (CR). Therefore, we have evaluated a selection of materials (Ti, [carbon-coated] stainless steels, stainless nickel) towards its compatibility with alkaline environments in terms of contact resistance and dissolution properties. The outcome clearly demonstrates the superiority of the carbon-coated material at intermediate pH values (< 11) [1]. Finally, at SMT we have long outgrown the research stage and offer, today, graphite-like roll-to-roll coatings on metal substrates, like stainless steel, as convenient low-cost material for bipolar plates in all types of low-temperature electrochemical energy conversion devices.
[1] Proch S, Stenström M, Eriksson L, Andersson J, Sjöblom G, Jansson A, et al. Coated stainless steel as bipolar plate material for anion exchange membrane fuel cells (AEMFCs). Int J Hydrogen Energy. 2020;45:1313-24.
Determination of Oxygen Transport Resistance through Limiting Current Analysis in Hydroxide Exchange Membrane Fuel Cells
Authors: Weiss Catherine M. , Setzler Brian , Shi Lin , Matz Stephanie , Gottesfeld Shimshon , Yan Yushan 
Published: December 2020

Development of Hydroxide Exchange Membrane Fuel Cells (HEMFC) is motivated by the promise of significantly reduced overall module costs compared to Proton Exchange Membrane Fuel Cells (PEMFC). By transitioning from a low-pH to a high-pH environment, less expensive materials become stable1. Specifically, platinum-group metal loading can be greatly reduced or potentially eliminated from the catalyst formulations2, and the bipolar plates can be manufactured more cost effectively. However, HEMFCs are currently in the early stages of development, and improvements in performance and durability are needed.
A key challenge in the design of PEM and HEM fuel cells is maximizing O2 transport from the inlet air stream to the triple phase boundary in the cathode catalyst layer. O2 transport resistance causes voltage losses at high current densities, limiting maximum power density. Limiting current analysis has been used extensively to experimentally determine O2 transport resistance in PEMFCs, and we demonstrate that this technique is valid for HEMFCs and produces similar results. Our analysis quantifies the individual O2 transport resistance contributions from several factors: molecular diffusion through the gas diffusion layer (GDL), Knudsen diffusion through the microporous layer (MPL) and catalyst layer, and diffusion through ionomer in the catalyst layer. Importantly, PEMFC and HEMFC have a different water balance. In PEMFC, an MPL is added to relieve the cathode GDL of flooding but also contributes to O2 transport losses. Conversely, in HEMFCs, the cathode dries-out and the anode floods; therefore, the MPL is an unnecessary component on the cathode GDL3. We report that the elimination of the MPL significantly decreases the O2 transport resistance and improves the performance under air, especially at high current density.
References

Setzler, B. P., Zhuang, Z., Wittkopf, J. A. & Yan, Y. Activity targets for nanostructured platinum-group-metal-free catalysts in hydroxide exchange membrane fuel cells. Nat. Nanotechnol.
11, 1020–1025 (2016).

Wang, J. et al. Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells. Nat. Energy
4, 392–398 (2019).

Kaspar, R. B., Wittkopf, J. A., Woodroof, M. D., Armstrong, M. J. & Yan, Y. Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells. J. Electrochem. Soc.
163, F377–F383 (2016).

Figure 1
Clarification of Active Sites for Oxygen Reduction Reaction on Silver and Nitrogen Co-Doped Carbon Materials
Authors: Kruusenberg Ivar , Kuzmin Anton , Shainyan Bagrat A. , Hu Jin-Song , Macdonald Digby D. 
Published: December 2020

The oxygen reduction reaction (ORR) is one of the most important reactions in both fuel cells and metal-air batteries [1]. ORR needs catalysis to lower the electrochemical overpotential for high-voltage output for these technologies and, so far, platinum (Pt) has been the main catalyst of choice. However, as the expensive, traditional Pt/C catalysts are not viable in the long term, much effort has been focused on heteroatom doped and non-precious metal catalysts [2]. Metal-nitrogen co-doped carbon materials have emerged as the main candidates for replacing the platinum-based catalysts. Among these materials, silver and nitrogen co-doped catalysts have proven to exhibit high electrocatalytic activity for the ORR in alkaline media. However, no clear understanding exists about the exact catalytic mechanism and rational design of these catalysts.
In this work, we synthesized model catalyst of silver and nitrogen co-doped carbon (Ag-N-C) by using simple precursors. Silver phthalocyanine and multi-walled carbon nanotubes have been used for the one-pot synthesis of Ag-N-C material. The morphology of the catalyst was studied by the transmission electron microscopy and the surface elemental composition was examined with X-ray photoelectron spectroscopy (XPS). The catalysts‘ activity towards ORR in 0.1 M KOH is assessed using the rotating disk electrode (RDE) method and the results are compared to those of commercial Pt/C catalysts (Figure 1). The created Ag-N-C model catalyst reveal a highly enhanced activity via the synergistic, doubly beneficial effects of the support material and formed catalytic centers, which were studied by density functional theory (DFT). Our theoretical calculations, which matched with the experimental findings, provide necessary hints on ORR mechanistic issues on the developed Ag-N-C model catalyst and will guide how to design and prepare better active non-Pt catalyst materials for fuel cell and metal-air battery electrodes, as well as providing deeper insight into the ORR mechanism occurring on this type of catalysts.

References

[1] M. Shao, Q. Chang, J.P. Dodelet, R. Chenitz, Recent Advances in Electrocatalysts for Oxygen Reduction Reaction, Chem. Rev. 116 (2016) 3594-3657.
[2] K.M. Villemson, K. Kaare, R. Raudsepp, T. Käämbre, K. Šmits, P. Wang, A.V. Kuzmin, A. Šutka, B.A. Shainyan, I. Kruusenberg. J. Phys. Chem. C 123 (2019) 16065-16074.

Figure 1
Template Synthesis of Ag@Fe-N-Doped Carbon Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media
Authors: Gong Chong , Wang Zhihuan , Chen Xing , Chen Yingjie , Yu Liyan , Dong Lifeng 
Published: December 2020

With the development of fuel cells, it is critical to find suitable oxygen reduction reaction (ORR) catalyst materials to replace current commercial Pt/C catalysts. On the one hand, atomically dispersed Fe-N-C with highly active Fe-Nx centers has been proved to be one of the best ORR catalysts comparable to the Pt/C. In addition, structural effects and strong metal-carrier interactions greatly improve performance. Therefore, various templates have been used for controlling the structure of Fe-N-C catalysts. For instance, polypyrrole is widely utilized as a nitrogen-rich carbon precursor, and hollow porous Fe3O4 microspheres with polypyrrole (PPy) encapsulated on the surface were pyrolyzed to obtain Fe-N-doped double-shell hollow carbon microspheres. Also, silica balls were applied as templates to fabricate hollow Fe-N-C carbon using a nano-casting method. These hollow structural Fe-N-C materials showed efficient ORR catalytic activities. On the other hand, Ag-based catalysts are also considered as possible candidates for ORR in alkaline medium due to their comparatively low cost and good CO tolerance capability. For example, Janus nanostructured Ag@N-C synthesized by pyrolyzing core-shell Ag@PPy demonstrated comparable ORR activity to the Pt/C, which was largely attributed to the synergistic effect between Ag nanoparticles and carbonized PPy shell. Therefore, rational design of porous Fe-N-C structure with Ag nanoparticles would achieve excellent ORR electrocatalysts.
Herein, Ag@Fe3O4 nanoparticles were synthesized by a solvothermal method and utilized as templates, and PPy enveloped on the template surface functioned as nitrogen and carbon sources. After pyrolysis, hollow porous Fe-N-C was decorated with Ag nanoparticles, which demonstrated excellent ORR catalytic activity and durability in alkaline medium. Therefore, this study provides a new simple method for preparing Ag@Fe-N-C hybrid catalysts.
Fabrication of Iron Phosphide Nanoparticle/Carbon Paper Electrodes Via Electrophoretic Deposition for HER Catalysis
Authors: Park Yoonsu , Kang Hyeri , Hong Yun-kun , Ha Don-Hyung 
Published: December 2020

As a renewable energy source to replace traditional fossil fuels, hydrogen is a promising sustainable energy carrier due to its eco-friendly nature and high energy density. Although Pt-based materials are widely used as catalysts for generating hydrogen through water electrolysis because of their high catalytic activity, Pt is expensive, and its scarcity hinders the commercialization of large-scale hydrogen production. The development of alternative low-cost materials with low hydrogen evolution reaction (HER) overpotential is the key to achieve low price and highly efficient hydrogen generators such as proton-exchange membrane water electrolysis (PEMWE). Among the numerous candidates of earth-abundant materials, transition metal-based phosphides (TMPs) are suitable for HER applications due to their low toxicity, high electrical conductivity, and catalytic activity. Especially, FeP is in the spotlight as a HER catalyst due to its high catalytic activity in solutions with a wide pH range, and this is a competitive material for large-scale commercial production of hydrogen, since Fe is one of the most abundant elements on earth.
In this study, we synthesized the colloidal FeP nanoparticles (NPs) via a hot injection process, so that the pre-synthesized Fe NPs can be converted to FeP NPs through the phosphorization reactions by various phosphorus sources (trioctylphosphine, triphenylphosphite (TPP), tris(diethylamino)phosphine, and tri-n-butylphosphine). Different HER activities were induced by the phase transformation of NPs over the controlled reaction time for the NP samples synthesized with each phosphorus precursor. The FeP synthesized using TPP achieved excellent HER activity with an overpotential of 76 mV at 10 mA cm-2 in 0.5 M H2SO4 as measured by drop casting the catalyst on Ti foil. In terms of the fabrication for the efficient HER electrode, the prepared FeP NPs were deposited on the carbon paper (CP) via electrophoretic deposition (EPD), which is a suitable method for the fabrication of NP films that can be used for various electronic applications. Different morphologies and catalytic activities of the FeP/CP samples were derived by controlling EPD parameters such as mixing ratio of solvents, NP concentration, and deposition voltage. The optimized EPD process lead to excellent HER activity of the FeP/CP with an overpotential of 38 mV and 91 mV at 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively. The maximum activity of the catalyst was mainly attributed to the large active surface area and low charge transfer resistance due to the strong contact between the NPs and CP. A PEMWE single cell with the FeP/CP cathode achieved 1.2 A cm-2 at cell voltage of 2.0 V. This study of the EPD procedure for fabricating the NP film from the colloidal NP catalysts contributes to advance manufacturing of HER electrodes for efficient hydrogen generation through water electrolysis.
New Synthesis Strategies for Transition-Metal Phosphide Based Water Splitting Electrocatalysts
Authors: Das Debanjan , Nanda Karuna Kar 
Published: December 2020

Transition metal phosphides (TMPs) have emerged as an intriguing class of efficient electrocatalyst finding widespread application in hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Currently adopted wet chemistry and solid-gas synthesis techniques rely on the use of surfactants/ toxic organic solvents or toxic gas which restricts facile fabrication of TMPs. Moreover, hybridizing TMPs with suitable carbon support (graphene, carbon nanotubes etc.) favorably optimizes the electrochemical activity of TMPs. However, this is often achieved via post-synthesis modification further complicating the synthesis procedure.
In an attempt to overcome these limitations, we have recently developed a solid state, phosphine free method to fabricate Co2P nanoparticles encapsulated N, P co-doped CNTs. These as prepared catalysts were applied as a bi-functional electrocatalyst for HER and OER. In order to increase the surface area and loading of Co2P nanoparticles, we next designed Co2P encapsulated CNTs grafted N, P co-doped hollow spheres via MOF-templated strategy with superior catalytic activity compared to Co2P@CNTs.[1] [2]
We then introduced sub-2nm IrP2 nanoparticles encapsulated bilayer N, P co-doped graphene as a novel electrocatalyst which exhibits better HER activity than benchmark Pt/C in acid, neutral as well as the alkaline medium. Interestingly, careful tuning of the reaction parameters also enables the synthesis of phase pure Ir2P.
In conclusion, the versatile strategy developed here can be extended to fabricate a variety of TMPs with widely varied applications.
[1] D. Das and K.K. Nanda, Nano Energy, 2017, 30, 303-311
[2] D. Das, A.Das, M.Reghunath and K.K Nanda, Green Chemistry, 2017,19, 1327-1335
(Invited) High Efficiency PEM Water Electrolysis Enabled By Advanced Catalysts, Membranes and Processes
Authors: Capuano Christopher , Ayers Kathy , Manco Judith , Wiles Luke , Errico Shaina , Zenyuk Iryna V. , Weber Adam Z. , Kusoglu Ahmet , Danilovic Nemanja , Ulsh Michael , Mauger Scott A , Pfeilsticker Jason , Alia Shaun M 
Published: December 2020

Commercial water electrolysis technologies, including proton exchange membrane electrolysis (PEMWE), are the only renewable hydrogen generation technologies that can achieve the U.S. Department of Energy (DOE) cost targets within the next ten years at the required scale, based on the supply chain maturity and materials performance. In particular, membrane and electrode modifications have enabled the use of advanced electrolysis membranes to achieve the efficiency targets, while nanoengineered alloy catalyst layers (CLs) have been pursued to meet the cost and efficiency targets. These advancements have been achieved by building the basic understanding to allow the successful technical development and include: (1) Mechanical and chemical understanding of membranes in liquid water below 90oC; (2) Characterization of as-deposited electrodes and MEAs after operation; (3) Water management in the anode catalyst layer, dependence on catalyst loading and porous transport layer form factor; and (4) Long-term degradation rate and stability of engineered alloy Ru-Ir alloy nanocatalysts in well-defined anode catalyst layers.
Nel Hydrogen’s pathway to meet these DOE goals is through the i) use of 50-75% thinner membranes that operate at 80-90 oC, while controlling mechanical creep and gas crossover; ii) reducing the catalyst loading to 1/10th the current value on both electrodes, while controlling water distribution and the porous transport layer/catalyst layer (PTL/CL) electrochemical interface; iii) incorporation of a less stable but more active Ru containing catalyst managed on the anode side of the cell, which is achievable with lower voltage operation (accomplished via low ohmic drop in the anode catalyst layer, thinner membranes, and higher temperature operation); and iv) fabricating a membrane electrode assembly (MEA) integrating all of these characteristics.
In this talk, some of the advancements achieved and how these have impacted the cost of hydrogen will be discussed, as well as the longer-term targets that need to be reached to provide the robustness required for commercial applications. Additionally, cost models will be compared along with sensitivity analysis to show how the impact of operating parameters, with regard to the capital and operational expense for the PEM electrolysis technology cost, show the critical areas to focus on to provide the largest impact towards meeting cost target goals and what is required to go beyond.

Figure 1
Investigating the Interface of TiOx/PGM Coating of Porous Transport Layers Used in PEM Electrolyzers By Surface Analysis
Authors: Liu Chang , Shviro Meital , Zaccarine Sarah F , Gago Aldo Saul , Gazdzicki Pawel , Morawietz Tobias , Biswas Indro , Schierholz Roland , Pylypenko Svitlana , Lehnert Werner , Carmo Marcelo 
Published: December 2020

Titanium porous transport layer (PTL) situating at the anode side of a PEM electrolyzer is subjected to harsh oxidizing conditions such as high anode overpotential, low pH, and oxygen evolution [1, 2]. Under these conditions, titanium (Ti0) changes its oxidation state over time, which induces the formation of a thin but continuously growing layer of passivated titanium (TiOx). Consequently, the electrical conductivity of the titanium fibers is adversely affected, fatally decreasing cell performance and durability [3, 4].
Here, we demonstrate a scalable and simple approach to using iridium or platinum as a protective layer for titanium-based PTLs. In this work, 4000 hour stable durability profiles are achieved when PTLs are coated with only 0.1 mg·cm-2 platinum or iridium (10 times reduction of Au or Pt typically used in current commercial electrolyzers). The real morphology of the TiOx/PGM (platinum group metal) coating interface of PTL is shown by different surface analysis methods. We found that the thickness of TiOx layer of iridium coated PTL did not further increase after the long-term operation. The results of this work show how the interface of a well-protected titanium fiber behaves against passivation after a long-term operation under real electrolysis conditions.

Reference

[1] M. Carmo, D.L. Fritz, J. Merge, and D. Stolten, A comprehensive review on PEM water electrolysis. International Journal of Hydrogen Energy, 2013. 38(12): p. 4901-4934.
[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar, and M. Bornstein, Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale, in Annual Review of Chemical and Biomolecular Engineering, Vol 10, J.M. Prausnitz, Editor. 2019, Annual Reviews: Palo Alto. p. 219-239.
[3] C. Rakousky, U. Reimer, K. Wippermann, M. Carmo, W. Lueke, and D. Stolten, An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis. Journal of Power Sources, 2016. 326: p. 120-128.
[4] C. Liu, M. Carmo, G. Bender, A. Everwand, T. Lickert, J.L. Young, T. Smolinka, D. Stolten, and W. Lehnert, Performance enhancement of PEM electrolyzers through iridium-coated titanium porous transport layers. Electrochemistry Communications, 2018. 97: p. 96-99.
Separation of Polarizations Using Shifted Electrode Arrangement in Proton Exchange Membrane Water Electrolysis
Authors: Watanabe Konosuke , Araki Takuto , Nagasawa Kensaku , Kuroda Yoshiyuki , Mitsushima Shigenori 
Published: December 2020

Proton exchange membrane water electrolysis (PEMWE) has attracted much attention because of its advantages such as the ability to downsize the equipment and produce high-purity hydrogen. For further improvement of the efficiency and durability of PEMWE, it is necessary to separate and examine polarizations. However, it is difficult to separate the anodic and cathodic polarizations by the AC impedance method. Also, it is difficult to separate resistance polarizations by using the reference poles with normal electrodes as shown in Figure 1 (a). Therefore, we are developing a device in which the electrode arrangement of both poles is deliberately shifted and a reference electrode is placed on each of the anode and cathode, as shown in Figure 1 (a) [1]. Since the phenomena in PEMWE are complicated due to the mutual influence of material/electric charge transport and reaction distribution, a multiphysical numerical analysis considering the potential distribution in the shifted electrode structure have been performed using COMSOL Multiphysics 5.4. Ohm's law was solved for the ionic charge transport in the electrolyte and the ionomer of the catalyst layer and also applied to the contact resistance between the electrode and the current collector. Butler-Volmer's equation was used for the activation overpotential at both poles. Figure 1(b) shows the electrolyte potential distribution when the electrode arrangement is shifted, and the potential distribution was completely changed from the (a). Figure 2 shows the relationship between the shift amount of electrode and the potential difference between both reference electrodes. The potential difference between both reference electrodes increases as the shift amount of electrode increases, and the rate of change of the potential difference decreases as the shift amount increases. Design and data processing based on these numerical results will lead to the development of devices that can perform more accurate separation of polarizations.
Reference
1) S. Mitsushima, H. Kashiwagi, K.Nagasawa, and Y. Kuroda, ECS Meet. Abstr., MA2019-02, 1715 (2019).

Figure 1