bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Mechanism of Synergistic ORR in Pt@PGM-Free Catalyst
Authors: Liu Di-Jia , Chong Lina
Published: February 2020

Maximizing the platinum utilization represents a critical research area in the commercial PEM fuel cell development. This is particularly true at the fuel cell cathode where to promote sluggish oxygen reduction reaction (ORR) requires three to four times more Pt in the catalyst than its counterpart in anode. In the electrode, Pt should be highly dispersed to be fully accessible by the reactants. This becomes more important at the high fuel cell current density domain where a large influx of O2 must be converted. By simply dispersing platinum to smaller nanoparticles (NPs) has its limitation. Past studies indicate that the ideal NPs should have dimension in between 4 nm to 6 nm to balance the needs between high Pt exposure and low dissolution rate. At ultralow cathode loading of 0.03 mgPt/cm2 to 0.06 mgPt/cm2 in the PEM fuel cell, such size requirement adds a significant constraint to the available number of NPs for the effective oxygen conversion.

At Argonne National Laboratory, we recently developed a new type of ORR catalyst by integrating ultralow loading of Pt (~3 wt.%) over PGM-free catalytically active support derived from the zeolitic imidazolate frameworks. [1] The new catalyst not only demonstrated excellent platinum mass activity and polarization current density in PEM fuel cell test at the cathodic Pt loading < 0.04 mg/cm2, but also showed very good durability during multiple fuel cell voltage cycling in the accelerated stress test (AST). Various characterization tools including XPS, XRD, XAS, TEM have identified the new catalyst containing highly strained Pt-Co core-shell NPs over hig-density and uniformly distributed Co/N/C and Co@graphene PGM-free active support. DFT calculation found two ORR catalytic routes over Pt and PGM-free active site with a crossover path at the formation of hydrogen peroxide, leading to synergistic catalysis.

In this presentation, I will discuss the synergistic catalysis from the catalyst design perspective, supported by our recent experimental observation. I will also share our thoughts on the new research direction of this approach.

Acknowledgement: This work is supported by U. S. Department of Energy, Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials, an U.S. Department of Energy Office of Science User Facility, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

[1] L. Chong, J. Wen, J. Kubal, F. G. Sen, J. Zou, J. Greeley, M. Chan, H. Barkholtz, W. Ding, and D.-J. Liu, “Ultralow-loading Platinum-Cobalt Fuel Cell Catalysts Derived from Imidazolate Frameworks,” Science 362, 1276 (2018).
Development of Combined Small-Angle X-Ray Scattering and Fluorescence Yield X-Ray Absorption Spectroscopy Measurement Systems for Characterization of Structural and Chemical Information of Pt Alloy Nanoparticle Catalyst
Authors: Watanabe Takeshi , Hiraoka Yuji , Suda Kohei , Kawamoto Teppei , Yano Hiroshi , Inukai Junji , Hirosawa Ichiro
Published: February 2020

The understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate the properties of Pt catalysts. Recently, Povia et al developed a powerful tool by combining the SAXS and XAS measurements for the characterization of the Pt nanoparticle catalysts [1]. However, this technique is difficult to investigate the chemical states of the low-concentrated catalysts. In this study, we developed the combined SAXS and the fluorescence-yield (FY) XAS measurement systems to investigate the structural and the chemical properties of low-concentrated catalysts.

The combined SAXS-FYXAS measurement system was developed at BL19B2 in SPring-8. For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a single-element Ge solid state detector were used to obtain the FYXAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LⅢ absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M). The PtCo alloy nanoparticle for the oxygen reduction reaction was used as the sample in this experiment.

As the result, we could demonstrate the combined SAXS-FYXAS measurement systems. We will discuss the degradation mechanism of the PtCo alloy nanoparticle catalyst from both SAXS and FYXAS data.

[1] M. Povia et al. ACS. Catal., 8, 7000 (2018).
Effect of Hydrogen Sulphide Contamination on Platinum Catalyst Degradation in Polymer Electrolyte Membrane Fuel Cells
Authors: Dushina Anastasia , Wagner Peter , Dyck Alexander
Published: February 2020

Platinum catalysts are widely used as electrocatalysts in polymer electrolyte membrane fuel cells (PEMFC). However, there are many factors that may lead to their degradation in PEMFC and one of them are impurities, which can penetrate the cell together with the feeding gases and then poison the catalyst [1]. Sulfur contaminants are strong undesirable poisons for the fuel cell even though they are usually present at very low levels (up to 5 ppm) in both fuel and air streams [2]. Hydrogen sulfide can adsorb onto platinum and affect the catalyst performance causing the loss of mass activity [3].

In this work the influence of H2S contamination on commercially available Pt catalyst with carbon support was studied by means of rotating ring-disk electrode experiments in perchloric acid. Accelerated stress testing (AST) was performed in terms of potential cycling up to 10.000 cycles in the absence of contaminants and in the presence of H2S for comparison. Cyclic voltammetry technique in terms of hydrogen under potential deposition (HUPD) and CO stripping was employed in order to determine the electrochemical surface area (ECSA). Oxygen reduction reaction (ORR) was used to identify kinetic parameters including kinetic limited current, Tafel slopes, mass and specific activity of the catalyst before and after degradation.

After AST the platinum degradation was observed in the presence of the contaminant as well as in the absence of H2S. Highly reproducible measurements showed that derived from HUPD and CO methods ECSA in the presence of poisoning species was slightly higher in comparison to the ECSA obtained in the absence of contamination. In contrast, the calculated catalyst activity after stress test in the presence of contaminations dropped more significantly compared to the test without poisoning species. This fact may be attributed to the sulfur adsorption on the catalyst layer leading to morphology changes [3]. Moreover, the increased Tafel slopes after AST may be an indication of the changes of the ORR mechanism from a four electron reaction to a two electron process reaction.

[1] R. Borup, Chemical Reviews 107 (2007) 3904–3951.

[2] Fuel Cell Handbook, US Department of Energy (2008).

[3] R. Mohtadi et al., Electrochemical and Solid-State Letters 6 (2003) A272–A274.

Figure 1
Understanding the Fundamental Drivers for Performance Losses in Operating AEMFCS in the Presence of CO2
Authors: Zheng Yiwei , Omasta Travis J , Varcoe John R. , Pivovar Bryan S. , Mustain William E.
Published: February 2020

Anion exchange membrane fuel cells (AEMFCs) have recently received significant attention as a future high efficiency, environmentally energy conversion device. This attention is due to the potential advantages that AEMFCs can offer compared the much more common, and commercialized, proton exchange membrane fuel cells (PEMFCs) – most notably lower cost. However, there are several remaining roadblocks for the AEMFC technology to be widely adopted, such as: i) the stability of the anion exchange membranes (AEMs) and anion exchange ionomer (AEIs); ii) the development of highly active low-platinum group metal (PGM) for non-PGM catalysts; iii) the discovery of water management strategies to prevent from electrodes flooding or drying out; and iv) reducing the negative effect of CO2 on the AEMFC performance. In an AEMFC operating on ambient air, CO2 reacts with the OH- anions created from the oxygen reduction reaction at the cathode, forming HCO3- and CO3
2-. These carbonates are transported from the cathode to the anode during operation. The presence of carbonate anions has multiple impacts on the operating AEMFC; carbonates decrease the conductivity and water uptake of AEM, introduce additional charge transfer resistance at the hydrogen oxidation anode and change the anode pH (resulting in a thermodynamic decrease in the cell operating voltage). In total, the CO2-related overpotential can be up to 400 mV, which is unacceptable from a practical perspective. Unfortunately, to date, only very few (especially experimental) studies have focused on quantifying the effect of CO2 on AEMFC performance. This poster will present an extensive array of experiments that deconvolutes the fundamental electrochemical mechanism for carbonate “poisoning” in AEMFCs. We also investigate the dynamics of CO2 uptake and removal and dynamics in these systems – with a particular focus on the impact of CO2 concentration in the reacting gas, temperature, AEM thickness and AEM chemistry. Finally, strategies to reduce the CO2 related overpotential below 100 mV will be shown.
Biocarbon from Sewage Sludge As Anode Catalyst for the Production of Bioelectricity in an MFC
Authors: García-Mayagoitia S. , Fernández-Luqueño F. , Morales-Acosta Diana , López-Valdez Fernando , Alonso-Lemus Ivonne Liliana , Escobar-Morales Beatriz , de la Torre Saenz Luis , Rodríguez-Varela F.J.
Published: February 2020

Over the last few years, the use of novel anode carbon catalysts from biomass as raw materials in Microbial Fuel Cells (MFC) has been increasingly investigated due to their catalytic properties and low cost compared to noble metals such as Pt. Nevertheless, it is acknowledged that the use of a catalyst in an MFC is not sufficient to generate bioenergy. A biofilm of electroactive bacteria must be grown on the catalyst surface, forming a bioanode. The combination of catalyst and biofilm oxidizes organic matter contained in substrate, promotes the electron transfer kinetics and thus enhances the generation of bioelectricity.

In this work, a biosolid from waste water sewage sludge from the food industry has been pyrolyzed and activated with KOH in N2 atmosphere in order to obtain a biocarbon. The biocarbon has been further functionalized with methanol in different concentrations (0.15, 0.5 and 1.0 M) aiming to enhance its biocompatibility with electroactive Bacillus subtilis (B. subtilis), used as microorganism. With these components, bioanodes have been fabricated using gas diffusion carbon cloths on which a catalytic layer containing the biocarbon have been painted using the brush method, followed by the growth of a biofilm of B. subtilis for 6 days in broth media.

The biocarbon was physicochemically characterized by XRD, SEM-EDS and FESEM. XRD patterns indicate that the material is amorphous in nature with a broad (002) peak attributed to graphitic structures. Some reflections attributed to crystalline phases are also observed. EDS analysis shows the presence of C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti and Fe in the biocarbon. On this matter, the biosolid shows a composition of 72.0, 18.96, 2.96 and 0.22 (wt. %) of C, O, Si and K, respectively. The biocarbon has a reduction in C content (29.23 wt. %), with an increase in O (23.54 wt. %) and K (17.29 wt. %), attributed to the activation with KOH.

Moreover, the biocarbon shows biocompatibility with B. subtilis as indicated by morphology analysis by FESEM. The biocarbon + B. subtilis bioanodes have been characterized in a half-cell with pharmaceutical waste water (PWW, pH= 6.1) as the electrolyte. The cyclic voltammograms (CVs) show their biocatalytic activity, generating a high current density from the PWW compared with the electrodes without biofilm.

The results indicate that biocarbons from waste water sewage sludge are promising catalysts for MFC anode applications, due to their biocompatibility with bacteria and because their chemical composition may enhance the microbial metabolism mechanism, enhancing the performance of the bioelectrochemical device.
A Non-Negligible Interface Effect for Alkaline Hydrogen Oxidation Reaction
Authors: Zhao Tonghui , Gong Mingxing , Wang Deli
Published: February 2020

In alkaline medium, the slow kinetics of the anodic hydrogen oxidation reaction (HOR) hinders the development of alkaline membrane fuel cells (AMFCs). Therefore, it is of great significance to explore the mechanism of HOR from establishing the "structure-activity relationship" and researching the main factor influencing the activity of the catalyst. Generally accepted viewpoint is the hydrogen binding energy (HBE) theory, a main descriptor of the catalytic activity, and regulation of the binding energy usually could be achieved by controlling the lattice strain. In our research, by taking advantage of the difference in the atomic radius of the 3d transition metals, a trimetal model (Pd3M@Pt (M=Fe, Co, Cu) core-shell structure) is constructed to study the HOR through the tuning of stress shrink degrees. By step-by-step electrochemical monitoring method and surface-controlled technology, the phase changes in the cycle were regulated and analyzed. Interestingly, it shows that the low-valence M(OH)x species formed in the electrochemical cycle obviously influenced the HOR activity rather than the HBE change caused by lattice shrink, mainly ascribed to strengthen the adsorption of OHad species and accelerate the Volmer step (Had+OH-→H2O+e-+*, rate-determined step, RDS). Meanwhile, It's worth noting the mass activity (MA) and specific activity (SA) of Pd3Co@Pt are significantly improved compared with Pt/C, close to 4 and 2 times. This Pd3M@Pt core-shell structure also improves the utilization of Pt and facilitates the design of efficient HOR catalyst.

Figure 1. a) Schematic diagram of the mechanism exploration for HOR with the model of Pd3M@Pt (M=Fe, Co, Cu); b) CV curves of four core-shell structure catalysts

Keywords: Hydrogen Oxidation Reaction, Pd3M@Pt core-shell structure, low-valence M(OH)x species, interface effect

References:

Strmcnik D, Uchimura M, Wang C, et al. Nat. Chem., 2013, 5(4): 300.

Lu S, Zhuang Z. J. Am. Chem. Soc., 2017, 139(14): 5156-5163.

Li J, Ghoshal S, Bates M K, et al. Angew. Chem. Int. Edit., 2017, 56(49): 15594-15598.

Figure 1
Understanding the Mass Transfer and Diffusion Effects of Carbon-Dioxide Absorption with Reaction in an Anion Exchange Membrane
Authors: Divekar Ashutosh G , Antunes Christopher M , Yang-Neyerlin Ami C. , Pivovar Bryan S. , Herring Andrew M.
Published: February 2020

Anion exchange membranes for fuel cell are a promising technology for stationary applications. The technology still needs to overcome certain challenges before they can be applied to vehicular applications. These challenges include enhancing the durability of the cell performance and a solution to carbon-dioxide poisoning problem. This work will focus on the carbon-dioxide issue. In the past couple of years, a lot of emphasis has been placed on understanding the effect of carbon-dioxide on the material or electrochemical characteristics of the membrane.1-3 We have investigated the effect of carbon-dioxide on ionic concentrations, conductivity and the morphological characteristics of the membrane. We have also studied the equilibrium carbonate-bicarbonate concentration at different temperatures.2 However, we haven’t investigated the physical quantities of carbon-dioxide absorption like mass-transfer coefficient and diffusivity of the CO2 through the membrane. Researchers have tried to assume classical mass transfer absorption models in their simulation works however no one has attempted to experimentally investigate these crucial properties.4 Therefore, this work will discuss absorption phenomenon from a chemical engineering point to shed more light on the CO2 problem. Here we have used CO2 sensors to track the absorption of CO2 at different conditions. We have also conducted segmented cell tests to spatially understand the spatial effects of CO2 absorption on current density and voltage in-situ fuel cell test. The data will be fit to models to better predict the CO2 absorption with chemical reaction.5, 6 Ultimately this would be very useful to modelers so they can incorporate these absorption models and come up with better ways to operate the fuel cell using ambient air(400 ppm CO2).

References:

H. Yanagi and K. Fukuta, ECS Transactions, 2008, 16, 257-262.

A. G. Divekar, B. S. Pivovar and A. M. Herring, ECS Transactions, 2018, 86, 643-648.

A. G. Divekar, A. M. Park, Z. R. Owczarczyk, S. Seifert, B. S. Pivovar and A. M. Herring, ECS Transactions, 2017, 80, 1005-1011.

J. A. Wrubel, A. A. Peracchio, B. N. Cassenti, T. D. Myles, K. N. Grew and W. K. S. Chiu, Journal of The Electrochemical Society, 2017, 164, F1063-F1073.

V. A. Juvekar and M. M. Sharma, Chemical Engineering Science, 1973, 28, 825-837.

P. Danckwerts, Gas-liquid reactions, McGraw-Hill Book Co., 1970.
(Invited) Characterizing Performance Losses over Time in an Alkaline Exchange Membrane-Electrode Assembly By Electrochemical Impedance Spectroscopy
Authors: Amel Alina , Ashdot Aviv , Page Miles , Tal-Gutelmacher Ervin
Published: February 2020

Anion exchange membrane fuel cells (AEMFC) are getting more and more attention in the last decade, due to their great potential as low cost electrochemical energy conversion systems. In the last years, great advancement were made in the performance of anion exchange membrane fuel cells.

With recent advances especially beginning-of-life power density showing that direct competition with proton exchange membrane fuel cell technology is indeed feasible, the durability of the alkaline Membrane-Electrode Assemblies (MEAs), which had been largely set aside in the community, comes into focus as perhaps the definitive remaining challenge of the technology .

In order to understand AEMFC performance losses, most of the characterization methods presented in the literature use ex-situ tools for post-mortem characterization, which are very effective especially in selecting material components (durability of membranes and membrane/ionomer chemistry, choice of Gas Diffusion Layers, mechanical stability of catalyst particles and catalyst layer morphologies, delamination, etc. However, the need for in-operando methods to follow performance losses in real time, and in real fuel cell hardware, can be satisfied using in-situ electrochemical impedance spectroscopy (EIS).

In this study we will present EIS measurements coupled with polarization curves collected during stability tests, while modifying operation parameters specially chosen to interrogate selected limitations, and study their evolution with time in fuel cell durability tests.

We focus especially on the influence of two features of the AEMFC: Mass transport loss modes, of which three are available: hydrogen, oxygen and – uniquely to the alkaline polymer electrolyte system – water, which is a reactant in the AEMFC cathode. Second, we examine the role of PtRu, by now a widely used alkaline HOR electrocatalyst that demonstrates high activity, but in some cases can be subject to activity loss via partial surface oxidation. This work demonstrates the opportunity to use EIS as a real time characterization tool towards improved understanding of AEMFC stability challenges.
A Novel Water Oxidation Catalyst Made By the Facile Deposition of Ruthenium on Graphene Oxide
Authors: Fruehwald Holly M , Moghaddam Reza B. , Zenkina Olena V , Easton E. Bradley
Published: February 2020

As populations grow worldwide, there is an ever-increasing need for sustainable and renewable energy sources to keep up with the high demand of energy. One promising technology is electrochemical water-splitting, which creates hydrogen and oxygen at the cathode and anode, respectively. Developing viable, stable catalysts for water splitting is critical since this reaction is truly a green, sustainable method to generate hydrogen fuel.

However, more active electrocatalysts for the water oxidation reaction (WOR) are needed to improve the viability of this technology. Currently, these catalysts are most often composed of rare and expensive earth metals such as iridium. More sustainable materials such as those based on ruthenium have been recently investigated as alternatives to the rare metal systems. Ruthenium-based materials are an ideal choice as Ru offers multiple available oxidation states to help facilitate the water-splitting reaction and possibly lower overpotentials[1]. However, many ruthenium-based materials are prone to stability issues in acidic media at high over potentials. In addition, sluggish kinetics are often observed [2].

In this work we synthesized graphene oxide, via a simple and low-cost method, and utilized it as a support for the Ru oxide nanocatalyst[3]. We used graphene oxide due it high mechanical strength, favorable electronic properties, and the ease at which it can be doped with metals[4]. Ruthenium oxide nanoparticles were deposited on the surface of the graphene oxide at a 5wt% metal loading by a facile method. The materials were examined electrochemically in acidic media for the water oxidation reaction, where we observed low overpotentials and high stability during prolonged testing. This simple preparation method could be used to efficiently synthesize active and highly stable water-oxidation catalysts that are more cost-effective. This novel ruthenium stabilized on graphene catalyst could aid in the future development of more sustainable materials for the future of renewable energy technology.

References

[1] Kamdar, J.M.; Grotjahn, D.B. Molecules
2019, 24, 494.

[2] Haschke, S.; Pankin, D.; Mikhailovskii, V.; Barr, M. K. S.; Both-Engel, A.; Manshina, A.; Bachmann, J. Beilstein J. Nanotechnol.
2019,
10, 157–167

[3] Liu, J.; Poh C. K.; Zhan, D.; Lai, L; Lim, S. H.; Wang, L.; Liu, X.; Sahoo, N. G.; Li, C.; Shen, Z.; Lin, J. Nano Energy. 2013, 3, 377-386

[4] Tu, W.; Lei, J.; Zhang, S.; Ju, H. Chemistry – A European Journal. 2010,
16, 10771-10777.

Figure 1
Ruthenium-Metal Nanostructures for High Activity and Stability Acidic Oxygen Evolution Electrocatalysts
Authors: Adame Solorio Jesus , Godinez-Salomon Fernando , Rhodes Christopher P.
Published: February 2020

Oxygen evolution electrocatalysts with high activity, extended durability, and lower costs are needed to further the development of proton-exchange membrane (PEM) electrolyzers. Tuning the interaction of metals within bimetallic alloys allows the surface atomic and electronic structure to be altered and provides an approach to obtain acidic oxygen evolution reaction (OER) electrocatalysts with increased activity and stability. Our group has recently explored unsupported metallic Ni-Ir alloy nanoarchitectures which show significantly higher OER activities compared with baseline IrO2 catalysts, however lower relative stability was also obtained.1 Compared with iridium-based catalysts, ruthenium-based catalysts (metallic Ru and RuOx) have shown the highest reported activities of any acidic OER catalysts. In addition, ruthenium has lower cost and higher supply compared with iridium. However, Ru-based catalysts show significant instability with substantial dissolution that leads to catalyst degradation. We have investigated Ru-metal nanostructures as a route to obtain OER catalysts with high activity and stability. Bimetallic nanostructures were synthesized using sol-gel chemistry routes and subsequent thermal treatments under reducing conditions. The structure and morphology were determined by X-ray diffraction and scanning electron microscopy. Cyclic voltammetry was used to investigate the surface structure and the effect of anodic potentials on the surface. Rotating disk electrode measurements were used to evaluate the electrochemical oxygen evolution activity and stability of the bimetallic nanostructures which were compared with baseline ruthenium OER catalysts.

References

1. Godínez-Salomón, F.; Albiter, L.; Alia, S. M.; Pivovar, B. S.; Camacho-Forero, L. E.; Balbuena, P. B.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Rhodes, C. P., Self-Supported Hydrous Iridium–Nickel Oxide Two-Dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catal.
2018, 8, 10498-10520.
Effect of Inner Catalyst Layer with PTFE Binder on Performance of High Temperature Polymer Electrolyte Membrane Fuel Cells
Authors: Lee Eunae , Kim Do-Hyung , Pak Chanho
Published: February 2020

Recently, high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have attracted much attention due to their tolerance to carbon monoxide and simple water management in the system level. HT-PEMFCs mostly use polybenzimidazole membrane doped with phosphoric acid (PA) as electrolyte. Therefore, uniform distribution of PA through a whole MEA plays a critical role in determining fuel cell performance. Distribution of PA in a MEA does not only depend only on properties of membrane such as a doping level of PA in membrane but also on gas diffusion layer(GDE) characteristics, especially the structure of the catalyst layer (CL). At present, the CL for HT-PEMFCs is typically composed of platinum catalyst and a polymeric binder. The polymeric binder maintaining the integrity of CL has an influence on mechanical stability of CL and the PA distribution within MEA. There have been many studies to explore the characteristics of different binders such as polytetrafluoroethylene(PTFE), polybenzimidazole(PBI) and polyvinylidenefluoride(PVDF). As previously described by Huaneng Su et al., PVDF has a good affinity with PA which leads to quick distribution of PA, on the other hand hydrophobic PTFE reduce PA leaching.[1] In this study, dual structured CLs with two different binders(PVDF and PTFE) by controlling the contents in catalyst layer are fabricated to investigate the influence of the wettability of CL surface in terms of fuel cell perfoemance. The properties of these CL were evaluated by structure characterization and electrochemical analysis. At ambient pressure and 150oC, the GDEs with PTFE binder exhibit the highest power density (383mW/cm2) with H2/air which may result from highly hydrophobic CL, leading to improved mass transport. It was suggested that the change in ratio of two binders with different wettabilities respectively had an impact on small arc on EIS.

Keywords

:high temperature proton exchange membrane fuel cell, catalyst layer, Membrane electrode assembly, poly(2,5-benzimidazole), hydrophobicity, Pt loading, gas diffusion electrode

References

S. Huaneng, J. Power Sources, 246, 63 (2014).
(Invited) U.S. Department of Energy’s Low Temperature Electrolysis R&D Activities
Authors: Peterson David , Miller Eric L. , Randolph Katie
Published: February 2020

The U.S. Department of Energy (DOE) is supporting a wide range of research and development efforts that fall under the umbrella of low temperature electrolysis (LTE). These efforts range from early stage R&D on cell components to demonstrating the effectiveness of integrating MW-scale electrolyzer systems with the electric grid to provide ancillary services. LTE is included in multiple initiatives led by the Fuel Cell Technologies Office (FCTO) at DOE’s Office of Energy Efficiency and Renewable Energy (EERE). Low temperature electrolysis is one of four pathways being supported under DOE’s HydroGEN Energy Materials Network (EMN) Consortium on Advanced Water Splitting Materials (AWSM) for H2 production. The HydroGEN EMN offers an extensive collection of materials research capabilities at 6 core national laboratories for addressing AWSM R&D challenges in efficiency, durability, and cost. The LTE work supported under HydroGEN includes early stage R&D in membranes and catalysts for both PEM and AEM electrolysis. Low temperature electrolysis also has a role in DOE’s H2@Scale energy system vision. This initiative is bringing together diverse stakeholders to advance affordable wide-scale hydrogen production, transport, storage, and utilization to unlock revenue potential and value across multiple sectors. The use of low-cost electricity to affordably split water into hydrogen and oxygen is central to implementation of the H2@Scale concept. Work is also being carried out on electrolyzer manufacturing, benchmarking, protocol development, and technoeconomic analysis. An overview of FCTO-supported activities related to these initiatives and topics, and the role of LTE in them, will be provided.
Understanding Interfaces of PEM Electrolyzers with Operando Synchrotron X-Ray Computed Tomography and Radiography
Authors: Leonard Emily , Shum Andrew , Sabarirajan Dinesh C , Capuano Christopher B , Ayers Katherine E. , Danilovic Nemanja , Pant Lalit M. , Weber Adam Z. , Xiao Xianghui , Parkinson Dilworth Y. , Zenyuk Iryna V.
Published: February 2020

Polymer electrolyte membrane (PEM) electrolyzers are electrochemical energy-conversion devices that convert electricity into hydrogen fuel at high efficiencies. The state-of-the-art systems use high IrOx loading (~2-3 mg/cm2), largely due to a lack of stable electrocatalyst supports that can effectively disperse the catalyst particles. Currently, the catalyst layers are made of IrOx and ionomer without an additional support. Without micro-porous layers (MPLs), the rough contact between the porous transport layer (PTL) and catalyst layer presents a challenge.

In this study we use operando x-ray computed tomography (CT) and x-ray radiography to visualize operation of PEM electrolyzer under two current densities: 500 and 800 mA/cm2. First, we compare performance of electrolyzer with catalyst-coated membrane (CCM) and that with porous transport electrode (PTE) and correlate polarization curves to morphology of the interfaces observed with x-ray CT. At 1 A/cm2, the micro-CT CCM electrolyzer showed 200 mV improvement in potential primarily due to better contact between the electrocatalyst, membrane, and PTL. From the nano-CT imaging we discovered non-homogeneous distribution of IrOx electrocatalsyt and from the images it is also not clear whether the larger IrOx agglomerates are electrically connected via a percolating conductive network of nanoparticles. The modeling study shows that the primary reason for performance loss in PTE configuration is low connectivity of catalyst particles with membrane. This causes bottlenecks in proton transport and results in high potential losses in anode.

We also compared the polarization behavior and morphology of cells with CCMs but two types of PTLs. One was made with sintered Ti and the other with Ti fiber. The Ti fiber PTL showed higher porosity and lower tortuosities, both in-plane and thru-plane. However these better morphological properties did not necessarily translate into lower potentials, as 1 A/cm2 was not a high enough current density to resolve differences attributable to improved two phase flow. This was also confirmed by radiography study, where oxygen residence fraction in the channels showed similar fractions for both types of the PTLs.
Modeling Electrolyte Composition Effects on Anion-Exchange-Membrane Water Electrolyzer Performance
Authors: Stanislaw Lauren N. , Gerhardt Michael R. , Weber Adam Z.
Published: February 2020

Anion-exchange membrane (AEM) electrolyzers are an attractive alternative for hydrogen production due to the potential stability and activity of non-precious metal catalysts in alkaline environments. Recently, AEM electrolyzers have been demonstrated using various membranes, ionomers, porous-transport layers, and catalysts (1). The influence of these materials and their properties on AEM electrolyzer performance, however, is underdeveloped. Furthermore, recent studies have shown (2) and hydrogen-evolution reaction kinetics (3), offering additional routes to decreasing cost and reducing operating voltage.

In this work, we use a coupled, nonisothermal, multiphase model of an AEM electrolyzer to understand the role of material properties, transport phenomena, and reaction kinetics in improving device pformance. We use the model to identify performance bottlenecks through applied voltage breakdowns (AVBs) and provide guidance for next-generation electrolyzer materials and designs by evaluating sensitivity to membrane and catalyst-layer properties. Finally, we explore the effects of various electrolyte solution feeds and operating paradigms on cell performance, with a particular interest in the influence of ion transport on reaction kinetics.

Acknowledgements

This work was funded under the HydroGEN Consortium, by the Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internship (SULI) program. This work was also supported in part by Workforce Development & Education at Berkeley Lab. We thank Sanjeev Mukerjee, Ian Kendrick, Yu Seung Kim, and Dongguo Li for helpful discussions.

References

I. Vincent and D. Bessarabov, Renewable and Sustainable Energy Reviews, 81, 1690 (2018).

H. Ito, N. Kawaguchi, S. Someya, T. Munakata, N. Miyazaki, M. Ishida and A. Nakano, International Journal of Hydrogen Energy, 43, 17030 (2018).

Q. Jia, E. Liu, L. Jiao, J. Li and S. Mukerjee, Current Opinion in Electrochemistry, 12, 209 (2018).
Highly Active and Durable Perovskite OER Catalyst for Pure Water Anion Exchange Membrane Electrolysis
Authors: Chung Hoon T , Li Dongguo , Lee Albert S , Fujimoto Cy , Kim Yu Seung
Published: February 2020

Anion exchange membrane (AEM) water electrolysis can afford cheaper hydrogen (H2) production compared to the current state-of-the-art of proton exchange membrane (PEM) electrolysis. In AEM electrolysis, i.e., in alkaline environment, platinum group metal (PGM)-free catalysts can be adopted as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, contrary to the PEM electrolysis in which PGM-catalysts should be used. Furthermore, expensive titanium flow-field that is indispensable in acidic PEM electrolyzer can be replaced by inexpensive stainless flow-field. These advantages of AEM electrolysis make AEM electrolysis attractive technology to produce H2 in low cost. However currently performance of AEM electrolysis is much lower than that of PEM electrolysis. Therefore to make the AEM electrolysis technology viable, significant advancement in AEM electrolysis technology is needed.

Many PGM-free OER catalysts measured in aqueous alkaline electrolytes, such as 0.1 M KOH or NaOH, have demonstrated as high activities as that of PGM IrO2 OER catalysts measured in an aqueous acid electrolytes in an electrochemical cell test. This implies that the low AEM electrolysis performance is possibly caused by some detrimental effect of AEM/anion exchange ionomer (AEI) onto catalysts. In this work we exploited different types of catalysts and AEIs to investigate the effect of catalyst-AEI interaction on AEM electrolysis performance. We observed that catalyst-AEI interaction substantially affects the AEM water electrolysis performance. The higher activity and durability of perovskite oxide OER catalyst than IrO2 OER catalyst in AEM water electrolysis can be explained by this catalyst-AEI interaction.

In this talk, we will discuss the causes for low AEM electrolysis and possible pathways to improve AEM water electrolysis performance.

Acknowledgements

The authors gratefully acknowledge research support from the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office.
Balancing Reactant Transport and PTL-CL Contact in PEM Electrolyzers by Optimizing PTL Design Parameters via Stochastic Pore Network Modeling
Authors: Lee Jason Keonhag , Bazylak Aimy
Published: February 2020

Optimizing the porous transport layer (PTL) structure is crucial for high current density operation of polymer electrolyte membrane (PEM) electrolyzers. Previous studies from the literature demonstrated that PTL structures, mainly porosity and titanium powder diameter, can be strategically chosen to improve the performance (1-3). However, transport mechanisms in the PTL can be further explained from the perspective of mass transport. In this work, we employed modelling approaches to investigate the effect of porosity and titanium particle size of the sintered titanium powder based PTL on mass transport. PTLs were numerically generated using a stochastic model (Figure 1) with three titanium powder diameters, 25 µm, 50 µm, and 75 µm, and three porosities, 26.5%, 40.5%, and 63.5%. Pore network modelling was used to calculate the gas saturation and the permeability of liquid water in the presence of oxygen gas. We observed that all simulated PTLs exhibited similar gas saturation profiles and relative permeabilities, yet the PTLs with higher porosities had significantly higher liquid water permeabilities. For a constant powder diameter of 25 μm, increasing the porosity from 26.5% to 63.5% led to an increase in the average surface roughness from 8.9 μm to 38.6 μm. For a constant porosity of 26.5%, increasing the powder size from 25 μm to 75 μm resulted in an increase in the average surface roughness from 8.9 μm to 18.3 μm. Larger open pore spaces were acquired for PTLs with higher surface roughness, resulting in higher liquid water permeabilities (two-phase permeability). Therefore, PTLs with higher porosities and larger particle sizes provide superior liquid water permeation and gas removal.

Figure 1. The 3D reconstruction of the PTL generated with titanium powder diameter of (a) 25 µm, (b) 50 µm, and (c) 75 µm at overall porosity of 40.5%.

References

S. A. Grigoriev, P. Millet, S. A. Volobuev and V. N. Fateev, Int J Hydrogen Energy,
34, 11, p. 4968-4973 (2009).

J. O. Majasan, F. Iacoviello, P. R. Shearing and D. J. Brett, Energy Procedia,
151 (2018).

L. Zielke, A. Fallisch, N. Paust, R. Zengerle and S. Thiele, Royal Society of Chemistry Advances,
4, p. 58888-58894 (2014).

Figure 1
The Synthesis of Zirfon-Type Porous Separator with Reduced Gas Crossover for Pressurized Alkaline Water Electrolyzer
Authors: Cho Won-Chul , Cho Hyun-Seok , Kim Sangkyung , Kim Chang Hee
Published: February 2020

Alkaline water electrolysis is one of the most efficient ways to produce hydrogen in a large scale with mature technique. It employs porous separators to provide the ionic conductivity of alkaline electrolyte between the electrodes, while separating the evolved gases. Zirconia nanoparticles and polysulfone composite separator exhibits satisfactory performance of high bubble point (2.5 bar) and low area resistance (~0.3 Ωcm2). However, the alkaline water electrolysis shows the efficiency loss in the lower partial load mainly due to the gas crossover through the separator. Therefore, detailed characterization and its effects on bubble point, resistance, and gas crossover are investigated.

In this study, we synthesized a porous ZrO2/polysulfone composite separator varying the amount of ZrO2 (70-85 wt.%) via film casting method. Scanning electron microscopy and thermogravimetric analysis show that the increased amount of ZrO2 reduces the bubble point and area resistance and increases the gas crossover, mainly due to the instability of the composite separator. 80wt.% ZrO2/20wt.% polysulfone composite separator shows a bubble point of 2.1 bar, low area resistance (~0.2 Ωcm2) and reduced hydrogen permeability (<2 E-11 mol cm-1 bar-1 sec-1) compared to the Zirfon PERL® separator. The enhanced performance is attributed to large portion of small size pore (< 100 nm from Hg porosimetry) and increased concentration of ZrO2 nanoparticles on the skin surface (XPS analysis), resulting in the high wettability. This experimental study suggests the various characterization methods that determine the performance of the composite separator for alkaline water electrolysis coupled with the renewable energy sources.
(Invited) Scalable Roll-to-Roll and Sheet-to-Sheet Processing for Perovskite Photovoltaics
Authors: van Hest Maikel
Published: February 2020

Metal halide perovskites have emerged as a highly promising solar cell technology with high light to electric power conversion efficiency and low processing cost due to their solution processability. However, to make perovskite solar cells commercially viable, particularly to compete with or build upon the traditional silicon dominated photovoltaic market, substantial progress is needed in improving their process techniques and scalability. Fabricating perovskite devices and modules in a roll-to-roll process on flexible substrates will enable high throughput manufacturing, and it will also allow the application space to be extended beyond what is available to rigid geometries. We developed chemistries, contact and absorber layers, that can be deposited in a roll-to-roll fashion using scalable slot-die coating. Progress of scaling up perovskites to larger area, sheet-to-sheet and roll-to-roll, on flexible substrates will be reported. Insight will be given in module performance and the stability of such modules.
(Invited) Critical Parameters for GW Scale Perovskite PV Manufacturing
Authors: DeLuca Stephan J , Tombs Thomas
Published: February 2020

A recent NREL white paper proposing a new US Perovskite Energy Consortium states “Fulfilling the world’s demand for PV requires continued exponential growth of production capacity without exponential growth in capital expenditure and remains a major challenge due to the inadequate capital efficiency of PV using existing technologies. There is an opportunity and a need for disruptive and fundamentally profitable technologies to supplement the ongoing growth of the PV manufacturing industry”.

Perovskite technology promises high conversion efficiency, low manufacturing cost, and low capital expense (CapEx) to build manufacturing capacity. Fulfilling that promise requires a manufacturing process with a very high throughput. The ability to fabricate perovskite films using low-temperature, solution based methods has been touted as a path to low cost and low CapEx manufacturing, however fast deposition of the perovskite layer alone is not sufficient to create the throughput that transforms the PV manufacturing landscape; an in-line process that integrates the deposition of all the functional layers of the device, as well as cell interconnects and module lamination, is required. Any slow vacuum deposition step (e.g., sputtering ITO for the transparent conductor) or long thermal annealing step (e.g., forming a charge transport barrier by forming a compact TiO2 layer) commonly used in lab-scale perovskite device fabrication must be avoided.

Our cost modeling shows that the throughput of a single line needed to get to disruptive CapEx and manufacturing cost will be on the order of 45 m2/min. That results in over 3GW/year production capacity at conservative uptime and yield values. An integrated in-line roll-to-roll (RtR) process with a 1.5m wide web would require all deposition steps to run at 30 m/min; much faster than processes cited in the academic literature for lab scale devices. That line speed is not taxing to most commercially available RtR systems, but practical limitations on oven size means a tight window for drying and annealing steps of all solution coated layers. The challenges of creating high performance transparent conductors, inorganic charge transport and barrier layers, perovskite layers and cell interconnects at those speeds will be discussed. The implied TAKT time is less than 3 seconds for 2m2 modules coming off of a single production line. The final assembly and test operations take much longer for each module, so methods of dealing with the mismatch must be implemented. We will also describe the practical considerations, including material sourcing and process requirements for production at GW scale.
Scalable Hole Transport Materials for Roll-to-Roll Perovskite Photovoltaic Modules
Authors: Martin Blake , Ghahremani Amir Hossein , Druffel Thad
Published: February 2020

Toxicity, stability, and scalability of perovskite solar cells are the three main challenges hindering commercialization of the technology. Multiple coating and printing techniques have been used to produce high-throughput solution-based perovskite photovoltaics, but there are unique challenges and opportunities that arise in upscale from a laboratory scale (<1 cm2) to an industrial scale (>1 m2). One limit of scale is the difficulty of deposition and cost of hole-transport materials (HTMs) in a perovskite solar cell (PSC). 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD) is the most commonly used HTM; however, the cost per gram of this material makes large scale production practically impossible. Additionally, transition metal oxides have shown promise as HTMs, but they require high temperature annealing, which is not compatible with the perovskite material. This work is an attempt to replace the current HTMs with a less expensive material that can be annealed at low temperatures. This study can aid in the commercialization and development of high-throughput solution-based perovskite photovoltaic modules.
Hole Transporting Layers in Solar Cells: Stabilizing NiO Perovskite Inks with Organic Capping Agents
Authors: Armstrong Peter , Ghahremani Amir , Druffel Thad , Buchanan Robert , Grapperhaus Craig
Published: February 2020

Increasing global demand for inexpensive energy has stimulated the development of sustainable alternative energy sources. One approach is the development of artificial water splitting electrocatalysts based on solid state materials, such as utilizing solar energy generated by perovskites for efficient O2 and H2 production from water. Perovskite solar cells is a growing field of efficient and affordable photovoltaic devises. Current systems use expensive organic poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) for hole transporting layers when constructed in the nip configuration. NiO is potentially an efficient alternative to PEDOT:PSS but cannot be used directly because its solubility in various solvent is similar to perovskites. Previous work has shown that capping agents can be added to NiO during in situ synthesis. Addition of organic capping agents to NiO should improve its solubility in alternative organic solvents enabling deposition on perovskite surfaces. NiO coated perovskite inks are cheaper than the PEDOT:PSS materials currently used and are ideal for mass production of perovskite solar cells. In this study, we will demonstrate a process for adding capping agents to pre-synthesized NiO particles. Earlier capping agents included long chain carboxylic acids and xanthates. Herein, we evaluated the effect of chain length reduction on the conductivity of NiO materials. In addition, we will demonstrate using PXRD, IR, and SEM that the addition of these capping agents maintains the NiO crystallinity and conductivity.