bluuebunny/crossref_metadata_2025 huggingface dataset:
(Energy Technology Division Graduate Student Award Address) Advanced Water Management in Fuel Cells Using Engineered Gas Diffusion Layers with Patterned Wettability: From Concept to Fuel Cell Application
Authors: Forner-Cuenca Antoni , Manzi-Orezzoli Victoria , Biesdorf Johannes , Gubler Lorenz , Schmidt Thomas J. , Boillat Pierre
Published: February 2020

The water management in PEFCs is a rather complex issue. On one hand side, some water is needed in order to hydrate a proton conductive membrane and ionomer in the catalyst layers. Therefore, humidified gases are fed into the cell. On the other hand, excessive amounts of water in the porous layers lead to blockage of available pores for gas transport and consequently increased mass transfer limitations, especially at high current densities when large amounts of water are produced. The gas diffusion layers (GDLs) are highly porous carbon fiber materials which are sandwiched between electrodes and flow fields and provide several functionalities: conduction of electricity and heat, mechanical integrity of the membrane, distribution of reactant gases and removal of the liquid water produced. These functions imply a triple set of contradictory requirements: high diffusivity of the gas phase, high permeability of the water phase, and high thermal and electrical conductivity of the solid phase.

The creation of artificial pathways for water removal within the porous material would permit the development of advanced water management strategies; however none of the existing approaches proposed a method to produce such materials in a way compatible with mass productions. To tackle this issue, we invented a method to produce GDLs with patterned wettability based on radiation grafting [1]. The method permits creating hydrophilic patterns throughout the complete material thickness while the remaining areas remain hydrophobic [2]. The first part of the talk will focus on the synthetic method details [3] and particularly on the effect that electron beam energy has on the achievable resolution of the hydrophilic patterns [4].

In the second part, the capillary pressure characteristic of the modified materials will be shown and the influence of various material parameters (substrate type, pattern width, coating load, etc.) will be discussed. The water distribution was imaged at various capillary pressures using neutron radiography (NR) and X-ray tomographic microscopy [5]. Finally, electrochemical characterization of operando cells combined with NR will demonstrate the potential of these materials to improve power density at various conditions [6].

[1] P. Boillat et al., 2014
European Patent 15165515.6.

[2] A. Forner-Cuenca et al., Adv. Mater.
2015, 27, 6317-6322.

[3] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163 (8), F788-F801.

[4] A. Forner-Cuenca et al., Radiat.
Phys. Chem., Submitted.

[5] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163(9), F1038-F1048.

[6] A. Forner-Cuenca et al., J. Electrochem.
Soc. 2016, 163 (13), F1389-F1398.
Oxygen-Reduction Active Carbon Supports for Pt Cathode Catalysts in Polymer Electrolyte Fuel Cells
Authors: Wu Gang
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely considered one of environmentally friendly and highly efficient electric power sources for a wide variety of power applications ranging from portable and stationary power supplies to transportation. However, some of the most critical barriers to their commercialization are the intrinsic high cost and insufficient long-term performance durability. Among others, the spherical carbon black particle support used for Pt catalyst in MEAs have a number of intrinsic structural disadvantage. It is partially responsible for current insufficient performance and durability of MEAs. They include (1) inefficient O2 transport due to significant tortuosity in carbon black-based cathode, (2) non-uniform distribution of ionomer due to significant microporosity of carbon blacks, (3) catastrophic corrosion during start-up/shut-down events due to low corrosion resistance, (4) low electrical conductivity, and (5) weak binding sites with Pt nanoparticles.

University at Buffalo, SUNY has developed a new type of high-surface areas (up to 850 m2/g) and large size nitrogen-diped graphene tubes (NGT) in a highly controlled manner and at high yields. The diameters of these graphene tubes can be tuned from 50 to 500 nm, which is much larger than conventiona carbon nanotubes (20 nm). It should be noted that the graphene tube is low cost using inexpensive dicyandiamide as precursors ($1-2/kg) and the synthesis method is easily scaled up. Apart from the obvious advantage of high electronic conductivity and enhanced corrosion resistance, the large tube size provided better Pt nanoparticle dispersion and more facil mass transfer including O2 and H2O. Importantly, the NGT exhibited oxygen reduction reaction (ORR) activity in acidic media comparable with state of the art PGM-free catalsyts. Thus, the novel ORR active nitrogen-doped graphene tubes are able to not only offer remarkable support effects by geometrically and electronically modifying the deposited Pt nanoparticles, but also provide a large amount of complementary nonprecious ORR active sites, thereby significantly improving the overall activity and durability of the Pt catalysts. Thus, relative to conventional carbon blacks, the highly graphitized and active N-GT is an ideal support for low-PGM catalysts for high-performance MEAs with enhanced mass transport and durability along with ideal interfaces with ionomer.
Pd-Monolayer Catalysts for CO2 Electrochemical Reduction
Authors: Liang Zhixiu , Vukmirovic Miomir B , Adzic Radoslav R
Published: February 2020

The ever increasing consumption of fossil-fuels for transportation causes climate change by emitting large amounts of CO2, a green-house gas, and a growing concern about future availability of fossil-fuels as energy sources due to their limited reserves. The concept of ‘CO2 neutral fuels’ based energy cycle can reduce our dependence on fossil-fuels and eliminate the detrimental effects of fossil-fuel consumption on environment. The principle of ‘CO2 neutral fuels’ based energy cycle is that the energy from renewable energy sources would be used to synthesize carbon based fuels from captured CO2 and such fuels are then used to power vehicles.

One of the products of CO2 electrochemical reduction is formic acid, which is used as fine chemical and a fuel in direct formic acid fuel cell. Therefore, efficient production of formic acid attracts a lot of attention in recent years [1]. It was reported that palladium and palladium based catalysts are very promising towards such process for lowered overpotential and improved selectivity as well as durability [2, 3]. Here we report high performance Pd monolayer catalysts for CO2 electrochemical reduction to formic acid. Pd monolayer catalysts were chosen in order to manipulate its activity toward formic acid production by their electronic interaction with the supporting core material. Cores with high electron affinity metal, the CO-Pd bond can be weaken thus to enhance the reaction kinetics.

Pd monolayer catalysts were prepared via Cu-UPD followed by Pd galvanic replacement [4]. Au@Pd/C and Pt@Pd/C showed improved activity and CO poisoning resistance compared to Pd/C catalyst via final product NMR analysis and CO-stripping experiment respectively. More detailed discussion on the origin of such improvement will be given on the presentation. Our work demonstrates the great potential of Pd-monolayer catalyst for CO2 electrochemical reduction reaction.

Acknowledgements

This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

References

R. Kortlever, I. Peters, S. Koper, and M. T. M. Koper, ACS Catalysis,
5
, 3916 (2015).

J. J. L. Humphrey, D. Plana, V. Celorrio, S. Sadasivan, R. P. Tooze, P. Rodríguez, D. J. Fermín, ChemCatChem, 8, 952 (2016).

X. Min and M. W. Kanan, J. Am. Chem. Soc., 137
, 4701 (2015).

M. H. Shao , T. Huang , P. Liu , J. Zhang , K. Sasaki , M. B. Vukmirovic , and R. R. Adzic, Langmuir,
22
, 10409 (2006).

Figure 1
Epitaxial CaTi5O11 and TiO2-B Thin Films for High Rate Lithium-Ion Batteries
Authors: Pan Xiaoqing
Published: February 2020

The bronze polymorph of titanium dioxide (TiO2-B) is interesting for many applications including high rate energy storage, solar cells, photocatalysis, thermoelectrics and sensing, owing to its uniquely layered structure and highly asymmetric unit cell. Although known to have advantages over anatase or rutile, high quality bronze phase TiO2-B specimens that demonstrate good electrochemical properties thus far have exclusively been nano-structured powders prepared by hydrothermal methods. We have recently discovered that Ca can stabilize the bronze structure, forming a variant phase CaTi5O11, which has then been successfully synthesized in epitaxial single-crystalline thin films by pulsed laser deposition (PLD), a completely waterless process. Due to the near-perfect lattice match, the CaTi5O11 film can be used as a template layer to grow high quality, water-free TiO2-B films on top, which facilitates the synthesis and application of both materials on a wide variety of substrates, including SrTiO3, Nb:SrTiO3, LaAlO3, LSAT and SrTiO3 buffered Si.

Lithium ion transport in the bronze structure is highly anisotropic. By utilizing substrates with a different orientation to align the more open channels with out-of-plane directions, extremely high rates of lithium ion transport, up to 600C (1C=335 mA g-1), with extraordinary structural stability has been achieved. In a battery half-cell using metallic lithium as counter electrode, the orientation-engineered CaTi5O11 film discharged to 155 mA h g-1 at a rate of 60C, corresponding to a time of 60 s to fully discharge the capacity, at the 100th cycle, delivering specific power of ~20 kW kg-1. Post-mortem examinations by x-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that both the TiO2-B and CaTi5O11 structures were essentially unchanged after aggressively cycling for more than 60 days. The film microstructure and interfacial atomic structure were characterized by atomic resolution transmission electron microscopy. In addition, we have employed novel in situ TEM to study the Li-intercalation of the films. Revealed by TEM of electrochemical lithiation in TiO2-B, many defects were induced by strain relaxation upon Li-induced TiO2-B lattice expansion. Depending on Li intercalation direction in the crystal structure, either high-symmetry structural transformation or plain shears was generated. These results provide the basic knowledge needed to realize and utilize TiO2-B single crystals, while also supporting theoretical studies with determinate experimental data.
Metal-Free Oxygen Reduction Electrocatalysts in the Membrane Electrode Assemblies for Anion Exchange Membrane Fuel Cells: Pore Size and Doping-Site Position Effects
Authors: Lee Seonggyu , Lee Jinwoo
Published: February 2020

Low temperature fuel cells have been developed as next-generation, clean energy conversion devices. Oxygen reduction reaction (ORR), which is one of the biggest barrier in low temperature fuel cells, is more facile in alkaline media than acidic media. Therefore, anion exchange membrane fuel cells (AEMFCs) have been garnering attention. In AEMFCs, it could be possible that the use of less-expensive ORR electrocatalysts such as metal-free catalysts based on heteroatom doped carbon materials. To realize the feasibility of metal-free catalysts, studies based on membrane electrode assemblies (MEA) are important but most of previous studies are focused on kinetic activities in half-cell measurement systems. Herein, we report the effects of pore size and doping site Position of metal-free ORR electrocatalysts in MEAs using well-defined ordered mesoporous materials. Pore size and doping-site position were precisely controlled via using different templates and size of doping precursors, separately. They affect the accessibility of reactants to reaction sites, which influences mass-transport properties and the utilization of doping-sites. As a result, remarkable on-set potential and maximum power density were obtained by the MEA using a large pore sized- N, P co-doped ordered mesoporous carbon with controlled doping-site position as a cathode catalyst. It is expected that the effective design strategy of electrocatalysts developed in this work could be widely applied to various electrocatalytic systems in addition to AEMFCs.
High Performance Pd-CeO2-Nanorods/G Catalyst for the ORR and Its Application in a Microbial Fuel Cell
Authors: Carrillo-Rodriguez J.C. , Alonso-Lemus I.L , Pérez-Hernández R. , Ochoa-Lara M.T. , Espinosa-Magaña F. , Rodriguez-Varela F.J.
Published: February 2020

Nanostructured Pd-CeO2-NR/G, synthesized with NaBH4 as reducing agent, was evaluated as cathode catalyst for the Oxygen Reduction Reaction (ORR) in 0.5 M KOH and in a Microbial Fuel Cell (MFC) with pH=9.6. Previously, ceria nanorods (CeO2-NR) were synthesized by a hydrothermal method, while graphene (G) was obtained by mechanical milling. Morphological characterization showed agglomerated Pd nanoparticles and CeO2-NR dispersed over graphene. Evaluation of catalytic activity for the ORR in half cell showed a higher mass activity of Pd-CeO2-NR/G relative to Pd/C. The MFC was of the two-chamber type, separated by a Nafion(R) 117 membrane. In the anode, residual water directly from a pharmaceutical company (pH=9.6) was the electrolyte with an anode containing commercial Pt/C. The Bacilus Subtilis microorganism was used to form a biofilm over Pt/C and promote the bioelectrochemical reactions in N2 atmosphere. In the cathode chamber, KOH with pH=9.6 was the electrolyte, which was saturated with O2. The polarization curves from the MFC demonstrated a higher catalytic activity of Pd-CeO2-NR/G than Pd/C. The former delivered an open circuit voltage of 0.26 V and a maximum power density of 12.47 mW m-2.
Effect of Valency of Sn in Sn-Modified Pt-Ru Catalyst on CO Tolerance and HOR Activity for PEFC
Authors: Takeguchi Tatsuya , Sirinutsomboon Bunpot , Wongsawa Thidarat , Ui Koichi
Published: February 2020

Introduction Pt-Ru on the carbon support has been regarded as a bimetallic catalyst with high CO tolerance for polymer electrolyte fuel cells (PEFCs). The addition of metal oxides such as SnO2 into the carbon support has also been reported to further enhance the CO tolerance1)-2). We have investigated the effect of valency of Sn in Sn-modified Pt-Ru catalyst on CO tolerance and HOR activity.

Experimental Sn in Sn-modified Pt-Ru catalysts was obtained by a rapid quenching method3). Pt-Ru-Sn/C and Ru/SnO2/C catalysts were treated in H2 and He at 800 oC, respectively. The catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Hydrogen oxidation reaction (HOR) activities of the catalysts were determined by single cell tests.

Results and Discussion The TEM analysis, as shown in Fig. 1, indicates that the particle sizes of Pt-Ru/SnO2/C and Pt-Ru-Sn/C are around 2.5 nm, which are slightly smaller than commercial Pt-Ru/C (TKK, TEC61E54). Since the particle sizes of SnO­­2 are less than 2 nm, the interaction between Pt-Ru and SnO2 is expected. Without the CO contamination, the terminal voltage of the cell using Pt-Ru-Sn/C is 752 mV at the current density of 0.2 A cm-2, which is 18 mV lower than those using Pt-Ru/SnO2/C and Pt-Ru/C (TKK, TEC61E54), as shown in Fig. 2. For Pt-Ru-Sn/C, the heat treatment in H2­ at 800 oC possibly triggers the formation of the trimetallic Pt-Ru-Sn alloy by the reaction Pt-Ru + SnO2 + 2H2 → Pt-Ru-Sn + 2H2O. HOR activities are suppressed by the formation of the trimetallic alloy. On the other hand, the terminal voltage of the cell using Pt-Ru/SnO2/C is as high as 599 mV even in the presence of 1000-ppm CO contamination, which is 27 and 128 mV higher than those using Pt-Ru-Sn/C and Pt-Ru/C (TKK, TEC61E54), respectively. Modification with Sn clearly enhances the CO tolerance. From the above, it is concluded that Sn in the Pt-Ru-Sn alloy reduces the HOR activity, while SnO2 does not. Both of metallic Sn in the Pt-Ru-Sn alloy and SnO2 encourage the CO tolerance.

References

1) T. Takeguchi et al., Catal. Sci. Technol.,
6, 3214-3219 (2016).

2) G. Wang et al., J. Electrochem. Soc.,
156, B862-B869 (2009).

3) T. Takeguchi et al., J. Am. Chem. Soc., 134, No. 35, 14508-14512 (2012).

Acknowledgements

This research was partially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Figure 1
Exploring Novel Dopants in Graphene: Unique Properties, Group Trends, and New Insights from DFT for Electrocatalytic Applications
Authors: Ocon Joey Duran , Serraon Ace Christian , Futalan Wilbert James , Geronia Reynaldo Marcelino , del Rosario Julie Anne Dalmacio , Padama Allan Abraham Bustria
Published: February 2020

Although platinum and platinum alloys (e.g. PtNi and PtCo) are widely regarded as the best catalysts for ORR at present, they are expensive and still suffer from technical drawbacks. Recently, the exploration of Pt-free or even metal-free ORR catalysts including heteroatom-doped carbon nanomaterials is very active in the electrochemistry and carbon research communities. Previous investigations have employed five main dopant elements (i.e. nitrogen, boron, phosporus, sufur, and selenium), with majority of these studies concluding that nitrogen, especially when doped in a specific manner, shows the most positive effect in improving the catalytic activity of carbon. In this study, we explore a new set of dopant atoms (alkali, alkaline earth, and halogen atoms) for the two-dimensional graphene structure (both in the buckled and planar configurations) and look at the changes in the geometric and electronic structures via density functional theory (DFT) calculations. We also qualify and quantify the stability and nature of the substitional doping on graphene and observe the trends for various properties for each elemental group. For instance, the doping of alkaline-earth atoms on the graphene structure, which has been unexplored so far, modifies the electronic properties and consequently the oxygen adsorption energetics. We found that novel properties such as semi-metallic properties emerge after substitutional doping except with beryllium, pointing to the possibility that these doped materials can be used not just in electrochemical but also in catalytic and electronic applications.

Figure 1
Unravelling the Degradation Mechanisms of Metal-Based Carbon-Supported Electrocatalysts in Alkaline Medium: Similarities and Differences Compared to Acidic Medium
Authors: Dubau Laetitia , Zadick Anicet , Lafforgue Clémence , Chatenet Marian
Published: February 2020

Direct liquid alkaline fuel cells (DLAFC), e.g. using performant anion-exchange polymers [1], may viably compete with H2-fed proton-exchange membrane fuel cells for the powering of portable or automotive devices: non-Pt electrodes can be used without detrimental loss of performances and liquid fuel storage is easy versus compressed H2 gas. The common belief considers that AFC electrocatalysts are stable in alkaline environment, owing to the better thermodynamics stability of many metal and oxides at high pH [2]. However, this belief does not apply to carbon-supported Pt nanoparticles (NPs), which undergo massive degradations even for a very mild potential cycling procedure in 0.1 M NaOH [3]. Identical-location transmission electron microscopy (ILTEM) experiments demonstrate that the very pronounced loss of electrochemical surface area (ECSA) is linked to the detachment of the Pt NPs from the carbon support; surprisingly, the latter does not undergo any consequent corrosion, and the Pt NPs seem very stable from a dissolution/redeposition view point (Ostwald ripening). Similar ILTEM experiments demonstrate that carbon-supported palladium NPs (Pd/C) are more stable than Pt/C but still suffer NP detachment from the carbon [4]. The degradation of Pd/C NP is slightly larger when the alkaline electrolyte contains strong reducing species (e.g. hydrogen or hydrazine borane), and this effect is enhanced for small Pd/C NP than for large ones. In contrast with acidic medium, this set of results suggests that the propensity of the metal NPs to be reduced (nobleness) enhances their instability. This hypothesis was further confirmed for non-noble Ni3Co/C NPs, which are more durable than Ni3Ag/C, Ni3Pd/C, Pd/C and Pt/C ones: the link between the carbon support and the NPs is more easily destroyed in liquid alkaline electrolytes when the NPs are containing a noble metal.

References

[1] E.H. Yu, X. Wang, U. Krewer, L. Li, K. Scott, Direct oxidation alkaline fuel cells: from materials to systems, Energy Environ. Sci., 5, 5668, 2012.

[2] M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, in, National Association of Corrosion Engineers, Houston, pp. 453, 1979.

[3] A. Zadick, L. Dubau, N. Sergent, G. Berthomé, M. Chatenet, Huge Instability of Pt/C Catalysts in Alkaline Medium, ACS Catal., 5, 4819, 2015.

[4] A. Zadick, L. Dubau, U.B. Demirci, M. Chatenet, Effects of Pd Nanoparticle Size and Solution Reducer Strength on Pd/C Electrocatalyst Stability in Alkaline Electrolyte, J. Electrochem. Soc., 163, F781, 2016.
Photo/ Catalytic Activation of Carbon Dioxide through Implementation of Plasmonic Metal Nanoparticles
Authors: Solarska Renata , Bienkowski Krzysztof
Published: February 2020

Investigations of the photo-induced phenomena enabling to improve and understand fundamental processes involved in CO2 reduction includes co-assembly of plasmonic and catalytic metal nanoparticles to the build-up of a semiconductor photocathode. Combination of the nanostructures of plasmonic metals, such as silver or gold with other metal electrocatalysts will substantially decrease the energy barriers of the CO2 reduction process through interaction of photo-excited surface plasmon states with adsorbed reaction intermediates. The significance to investigate reduction of CO2 at gold, silver and copper surfaces enhanced by the extra activation of the process provided by the illuminated, incorporated plasmonic metallic nanostructures is supported by the occurrence of the photo-emission process associated with the decay of photo-excited surface plasmons. Of particular interest will be a strong influence of the Ag/FTO electrode roughness upon the photo-emissive cathodic currents of electro-reduction of CO2 dissolved in aqueous solution. Actually, two metals Ag and Au, the nanostructures of which exhibit strong excitation of surface plasmon resonance through interaction with near UV and visible photons are also catalytically active toward electro-reduction of CO2. Besides the photo-emission, another property of plasmonic NPs – heat generation resulting from the absorption of incident photons and their influence on the reduction of CO2 at composite cathodes will be the objectives of this presentation.
(Invited) Photocatalysis Based on Plasmon-Induced Charge Separation
Authors: Tatsuma Tetsu , Kao Kun-Che , Wu Ling , Kuroiwa Yoshinori , Nishi Hiroyasu
Published: February 2020

Plasmon-induced charge separation (PICS) occurs at the interface between plasmonic nanostructures of gold, silver, or copper and a semiconductor (typically titanium oxide),1-3 on the basis of carrier transfer from the nanostructure to the semiconductor due to external photoelectric effects including hot carrier injection, or interfacial electron transition.4 We reported PICS for the first time more than 10 years ago1-3 and studied its mechanisms3-7 and applications.1,3,8,9 The applications of PICS include photocatalysis, in particular hydrogen evolution from water. We also work on photocatalytic hydrogen evolution based on PICS by using some different systems including gold nanoparticle/titanium oxide systems and gold halfshell/titanium oxide systems.10

1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

2. Y. Tian and T. Tatsuma, Chem. Commun., 2004, 1810.

3. T. Tatsuma, Bull. Chem. Soc. Jpn., 86, 1 (2013) [account].

4. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014).

5. E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011).

6. H. Nishi and T. Tatsuma, Angew. Chem. Int. Ed., 55, 10771 (2016).

7. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).

8. Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nat. Mater.,
2, 29 (2003).

9. Y. Takahashi and T. Tatsuma, Appl. Phys. Lett., 99, 182110 (2011).

10. L. Wu, H. Nishi, and T. Tatsuma, APL Mater., 3, 104406 (2015).
Interplay Between Chemical and Optoelectronic Properties of III/V-Water Interfaces from Ab Initio Simulations
Authors: Wood Brandon C. , Pham Tuan Anh , Ogitsu Tadashi
Published: February 2020

Photoelectrochemical cells promise sustainable production of hydrogen fuel from water using sunlight, mimicking natural photosynthetic processes. However, finding light-absorbing semiconductor photoelectrode materials that are suitably efficient and also durable under operation has proven challenging. This is largely because electrode durability and efficiency are extremely sensitive to the chemistry at the interface between liquid water and the semiconductor, which is often extraordinarily difficult to probe under operating conditions. In this talk, I will illustrate how ab initio methods have been applied to understand the complex chemistry active at the interface of water with III-V semiconductor photocathodes (GaP, InP, and GaInP2), which offer among the highest solar-to-hydrogen conversion efficiencies but suffer from durability shortcomings. I will show how large-scale ab initio molecular dynamics simulations have assisted in determining the dependence of the available chemical pathways on the surface structure and composition of these materials. I will also show how dynamics simulations can be coupled to many-body perturbation theory to directly probe the link between macroscopic optoelectronic properties and local interfacial chemistry, which is necessary for devising meaningful interface optimization strategies. Finally, I will discuss how combining X-ray photoelectron spectroscopy (XPS) simulations with near-ambient-pressure XPS experiments can identify interfacial chemical speciation under operating conditions. Key differences between InP and GaP will be highlighted, including how different chemistry and mass transport behavior at the interface with water impact relative stability and efficiency. Specific implications for understanding the performance and durability of III-V photocathodes will be discussed, along with some general insights for engineering photoelectrochemical interfaces.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Solar-to-Hydrogen Efficiency: Shining Light on Photoelectrochemical Device Performance
Authors: Young James L , Döscher Henning , Geisz John F , Turner John A , Deutsch Todd G
Published: February 2020

Direct photoelectrochemical (PEC) hydrogen production aims to provide a clean and cost-effective solar fuel. Solar-to-hydrogen (STH) conversion efficiency is central to evaluating and comparing research results, and it largely establishes the prospect for successfully introducing commercial solar water-splitting systems. Present measurement practices do not follow well-defined standards, and common methods potentially impact research results and their implications. We demonstrate underestimated influence factors and experimental strategies for improved accuracy[1].

Our focus is tandem devices that have the prospect for greater STH efficiency[2], but increased complexity that requires more careful consideration of characterization practices. We perform measurements on an advanced version of the classical GaInP/GaAs design[3] while considering (i) calibration and adjustment of the illumination light-source; (ii) confirmation of the consistency of results by incident photon-to-current efficiency (IPCE), and (iii) definition and confinement of the active area of the device.

We propose applying the following standards for future PEC performance reporting: (i) traceable disclosure of the illumination-source configuration (lamp, filters, optics, PEC configuration) and/or its measured spectral distribution; (ii) thorough device-area definition including confinement of the illumination area and avoidance of indirect light paths; (iii) complementary IPCE confirmation of the solar-generation potential; (iv) proper consideration of faradaic efficiency. We will also give a brief overview of the PEC measurements and capabilities available at NREL to support academic and industry research.

[1] H. Döscher, J. L. Young, J. F. Geisz, J. A. Turner, and T. G. Deutsch, “Solar to hydrogen efficiency: Shining light on phoelectrochemical device performance,” Energy Environ. Sci. 2015.

[2] H. Döscher, J. F. Geisz, T. G. Deutsch, and J. A. Turner, “Sunlight absorption in water – efficiency and design implications for photoelectrochemical devices,” Energy Environ. Sci. 2014.

[3] O. Khaselev and J. A. Turner, “A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting,” Science. 1998.
Light Guided Placement of Platinum Catalysts on Silicon Microwire Array Photocathodes
Authors: Kempler Paul Andrew , Carim Azhar I , Lewis Nathan S
Published: February 2020

Silicon microwire arrays decorated with catalyst particles are a promising design for photoelectrochemical conversion of water and sunlight to hydrogen fuel. This device geometry reduces the material quality requirements for the semiconductor due to its tolerance of short carrier diffusion lengths and allows for direct integration within flexible polymer membranes which are required for product separation. In a water splitting photocathode, electrons generated within the microwires are collected at catalyst sites to electrochemically reduce water to hydrogen gas. When highly active catalysts such as platinum are utilized, the collection efficiency of electrons at catalyst sites can become a limiting factor in device performance. Because the carrier generation rate within silicon microwires is non-uniform, determining the optimal distribution of catalyst particles is a challenge. Controlled photoelectrodeposition of metals on silicon microwires can be used to localize catalysts near regions where carrier generation is highest. To demonstrate this concept, silicon microwire arrays were decorated with platinum via controlled photoelectrodeposition. The illumination wavelength during photoelectrodeposition was varied to control the location of platinum catalysts on the microwire arrays. The influence of the distribution of catalyst on the performance of hydrogen evolving microwire array photocathodes was investigated.
Evaluation of Material Properties and Performance of Zinc Ferrite (ZnFe2O4) for Photoelectrochemical Water-Splitting
Authors: Bright Joeseph , Wu Nianqiang
Published: February 2020

With greenhouse gases such as methane and carbon dioxide contributing significantly to global climate change, sustainable, carbon-neutral fuels are needed to replace fossil fuels for meeting society’s energy needs. A possible replacement for fossil fuels for energy is hydrogen gas derived from photoelectrochemical (PEC) water-splitting. However, existing materials capable of driving photoelectrochemical water-splitting have several problems not limited to poor light absorption at visible wavelengths that compromise the sunlight, poor charge transport within the material, and/or poor photo-stability in aqueous electrolyte solutions. Therefore, new materials must be developed or efforts must be made to solve the issues of existing materials for PEC water-splitting.

Zinc ferrite (ZnFe2O4) is a n-type, narrow bandgap (Eg = 1.9 eV) semiconductor with a sufficiently positive valence band to drive PEC water-splitting as a photoanode. However, ZnFe2O4 suffers from multiple issues that lower its performance for PEC water-splitting such as extremely poor conductivity, poor light absorption despite its narrow bandgap due to the bandgap’s indirect nature, and poor surface catalytic activity. This work fundamentally studies ZnFe2O4 by quantifying its optical, electrical, and catalytic properties and comparing these properties to other established materials for PEC water-splitting. Based on this study, the critical limiting factors for ZnFe2O4’s implementation as a photoanode for PEC water-splitting will be discussed.
(Invited) Atomic-Scale Surface Science Investigations for Understanding and Producing Electrochemical Interfaces
Authors: Diebold Ulrike
Published: February 2020

Key ingredients in solid-state electrochemistry are charge transfer to, and adsorption/reaction of molecules, both heavily influenced by the availability of charge carriers and O vacancies. Surface science techniques, in particular Scanning Tunneling Microscopy (STM) in combination with surface spectroscopy, can help unravel how these processes happen at the atomic scale. The talk will showcase several examples of STM studies of adsorption and reaction of O2 and H2O on titania and selected perovskite materials. It will also exemplify how STM can be used to judiciously steer thin film growth in in Pulsed Laser Deposition (PLD) towards fabricating model electrodes with a desired surface structure, which could help increasing functionality in electrochemical devices.
(Invited) Cationic, Anionic & Electronic Disorder on Perovskite Oxide Surface for (Electro)Catalysis
Authors: Chueh William C
Published: February 2020

Transition-metal perovskite oxides are being investigated as catalysts and electrocatalysts for reactions such as aqueous oxygen evolution and elevated-temperature oxygen incorporation. These oxides are characterized by their tendency to exhibit cationic, anionic and electronic disorder, such as Schottky defect pairs, oxygen vacancies, and small polarons, respectively. When present in significant concentrations, these defects alter the phase stability of the near-surface region, reactivity, and carrier transport. We have investigated a range of Ti, Co, and Fe-based materials using high-resolution transmission electron microscopy, in-situ X-ray photoemission spectroscopy and X-ray absorption spectroscopy. In this talk, I will discuss the role of these lattice disorder in catalysis and electrocatalysis involving oxygen molecules.
Importance of the Formation of Dy4+ in BaZr0.9Dy0.1O3-δ proton-Conducting Ceramics in Oxidizing Atmospheres
Authors: Ricote Sandrine , Hudish Grant , Beedle Christopher , Tsoi Stanislas , Owrutsky Jeffrey C. , O Brien James
Published: February 2020

Yttrium doped barium zirconate, BaZr1-xYxO3-δ, has been one of the most studied high temperature proton conductors for the last two decades [1]. Several research groups focused on the choice of the trivalent dopant, which is necessary to create the oxygen vacancies required for the hydration of the material. Han et al. studied for example Sc, Sm, Eu and Dy dopants [2-4] and reported the presence of Dy4+in oxidizing atmospheres.

In this work, we are interested in the comparison of structural and electrical properties between the well-known BZY10 (BaZr0.9Y0.1O3-δ) and BZDy10 (BaZr0.9Dy0.1O3-δ). A wide combination of experiments was used to confirm the presence of Dy4+ in oxidizing atmosphere, including high temperature X-ray diffraction, Raman spectroscopy, SQUID magnetometry and electron spin resonance (ESR or EPR). Figure 1 summarizes the BZDy10 lattice parameter in dry oxidizing atmosphere as a function of temperature and shows a decrease in the lattice parameter when increasing the oxygen partial pressure. This is explained by the difference in Dy radii in VI coordination: 0.78 Å and 0.912 Å for Dy4+ and Dy3+respectively.

Conductivity measurements as a function of pO2in dry and moist conditions were performed for both BZY10 and BZDy10. The two materials behaved quite similarly in moist reducing atmosphere (i.e., pure ionic conduction), while significant differences were noticed in oxidizing atmospheres.

[1] Fabbri E., Pergolesi D. and Traversa E., “Materials challenges toward proton-conducting oxide fuel cells: a critical review ”, Chem. Soc. Rev 39, 4355-4369 (2010)

[2] D. Han, K. Shinoda, T. Uda, Dopant site occupancy and chemical expansion in rare earth-doped barium zirconate, J. Am. Ceram. Soc. 97 (2014) 643-650

[3] D. Han, T. Uda, Y. Nose, T. Okajima, H. Murata, I. Tanaka and K. Shinoda, Tetravalent Dysprosium in a Perovskite-Type Oxide, Advanced Materials 24 (2012) 2051-2053

[4] D. Han, K. Shinoda, S. Sato, M. Majima, T. Uda, Correlation between electroncutive and structural properties of proton conductive acceptor doped barium zirconate, J. Mater. Chem. A, 13 (2015) 1243-1250

Figure 1
(Invited) Sr and Mn Doped LaFeO3 Perovskite Oxide As Active Cathode for High Temperature Electrolysis
Authors: Ishihara Tatsumi , Wu Kuan-Ting , Wang Shijing
Published: February 2020

Solid oxide electrolysis cells (SOECs) for converting CO2 to more useful chemical species are attracting considerable attention because of their high electrolytic efficiency, offering the possibility of direct conversion of CO2 to CO (CO2 → CO + 1/2O2). In addition, recently, high temperature electrolysis of steam to H2 is also attracing much interest. Heat energy supplied to SOECs can maximize electrolysis efficiency, offering both thermodynamic and kinetic advantages. The generated CO can be used as a fuel gas, converted into syngas via reaction with H2, or to reduce iron oxide to pure iron in the iron-making process. The application of SOECs and related technologies can contribute to a more sustainable economy. For the electrolyte in SOECs, ZrO2 doped with 8 mol% of Y2O3 (YSZ) has always been used because of its chemical stability and mechanical strength. However, an electrolyte for CO2 or H2O electrolysis with lower internal resistance and increased efficiency is highly desirable. LaGaO3-based electrolytes have higher oxide-ion conductivities and transport numbers, which can lead to higher energy conversion efficiency; hence, a doped-LaGaO3 electrolyte (La0.9Sr0.1Ga0.8Mg0.2O3, LSGM) has been tested in this study. For CO2 and H2O electrolysis, another drawbacks is durability since electrode is easily aggregated and deactivated.

Although metals, particularly Ni, are widely used as cathodes in CO2 electrolysis cells, we found that a LaFeO3−δ-based perovskite cathode (La0.6Sr0.4Fe0.8Mn0.2O3−δ, LSFM6482) showed the highest activity for CO2 and H2O electrolysis among the examined oxides Among the cells using a La0.6Sr0.4Fe0.9M0.1O3−δ-based oxide cathode (M = Mn, Co, Ni, or Cu) for CO2 electrolysis at 1073K. Mn was the most effective Fe replacement on the B site, and the La0.6Sr0.4Fe0.9Mn0.1O3−δ cathode showed the highest activity and current density for CO2 electrolysis of this set of cathodes. Among the tested dopants, Mn and Co have ionic sizes most similar to Fe and a smaller size mismatch between the host and dopant cations in the perovskite structure, which should suppress dopant segregation and minimize detrimental effects of cation segregation. Overall, among the examined cations, Mn was the best dopant for the B site of the LaFeO3 cathode. A cell consisting of BLC64/LSGM/LSFM6482 exhibited the highest CO2 electrolysis activity (a current density of 0.52 A/cm2 at 1.6 V and 1173 K) of all cathodes investigated in this study and reduced CO2 at a rate of 153 μmol/cm2•min at 1173 K and 1.6 V with negligible carbon formation. In this study, change in internal resistance during electrolysis is also discussed based on impedance measurement.
Influence of the Activation Catalyst on the Polarization Resistance of Electroless Cu Electrodes on BaCe0.1Zr0.8Y0.1O3-δ proton-Conducting Ceramics
Authors: Ricote Sandrine , Patki Neil , Way James Douglas
Published: February 2020

Copper (Cu) electrodes appear as potential methane dehydroaromatization (MDA) electrodes on BaCexZr0.9-xY0.1O3- δ (BCZY) proton-conducting ceramics [1]. When applied from paste, the electrodes suffer from poor adhesion, and therefore high polarization resistance. In this work, 1 micron thin Cu electrodes were deposited onto BaCe0.1Zr0.8Y0.1O3-d (BCZY18) specimens by electroless plating, using three different activation catalysts: Pd, Ru and Cu [2].

Impedance spectra were recorded on electrolyte based symmetric cells Cu/BCZY/Cu in the temperature range 750-600°C, in dry and moist reducing atmospheres. The area specific resistances (ASR) of these three electrodes were found to be lower in moist gases and were two orders of magnitude lower than that measured on painted Cu electrodes (see figure) . At 700°C, in 3% moist forming gas, ASR of 2.9, 3.8 and 22.7 Ω∙cm2 were calculated on the Cu electrodes with the Pd, Ru and Cu activation catalyst respectively.

The microstructure of the electrodes was evaluated before and after electrochemical testing. In all cases, nano-pores were present on the as-deposited electrodes. After exposure to dry and moist reducing atmosphere at high temperatures, the microstructure of the Pd/Cu and Ru/Cu did not change significantly while major reorganisation was observed for the Cu/Cu electrode.

[1] Morejudo SH, Zanón R, Escolástico S, Yuste-Tirados I, Malerød-Fjeld H, Vestre PK, et al. Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science 2016;353:563–566

[2] Patki N, Ricote S, Way JD, Fabrication of reducing atmosphere electrodes (fuel electrodes) by electroless plating of copper on BaZr0.9-xCexY0.1O3-δ – a proton-conducting ceramic, submitted to International Journal of Hydrogen Energy in November 2016

Figure 1
(Invited) The Effect of Heat-Treatment on Mechanical Property and Wetting Behavior of α-LiAlO2
Authors: Gao Liangjuan , Selman J. Robert , Nash Philip
Published: February 2020

α-LiAlO2 is widely used as membrane structural material to support electrolyte in molten carbonate fuel cell (MCFC) stacks. The α-LiAlO2 electrolyte matrix always experiences mechanical and thermal stress during the initial start-up and operation (550-650oC) due to (1) insufficient mechanical strength of non-sintered α-LiAlO2, (2) thermal expansion coefficient difference between the α-LiAlO2 matrix and carbonate electrolyte, and (3) high capillary force, which may cause cracking of the matrix. A non-sintered/heat-treated pure α-LiAlO2 matrix has low mechanical strength. In this study, heat-treatment was used to enhance the mechanical strength of the α-LiAlO2 matrix. It has been found that the mechanical strength of the α-LiAlO2 matrix was increased four folds (2.72MPa) after heat-treated at 800oC for 5h to that of pure α-LiAlO2 matrix (0.57MPa). The porosity of those matrices was not changed significantly after the heat-treatment. The XRD results showed that the crystal structure of α-LiAlO2 did not change during the heat-treatment at 800oC. The wetting behavior and carbonate electrolyte distribution of those pure α-LiAlO2 matrix and heat-treated α-LiAlO2 matrix was investigated. Non-heat-treated and heat-treated α-LiAlO2 matrices were all completely wetted by liquid carbonate electrolyte. Non-heat-treated α-LiAlO2 sample cracked during the melting and wetting process of carbonate electrolyte, however, the heat-treated α-LiAlO2 matrices did not crack due to enhanced mechanical strength.
(Invited) The Electrocat (Electrocatalysis) Consortium
Authors: Wilson Adria R , Papageorgopoulos Dimitrios C , Myers Deborah J , Zelenay Piotr , Dinh Huyen N , More Karren L.
Published: February 2020

Catalysts are key cost components for both automotive and stationary polymer electrolyte membrane fuel cells (PEMFCs), and as such represent a materials problem ripe to be addressed through the President’s Materials Genome Initiative (MGI). The ElectroCat (Electrocatalysis) Consortium was formed at DOE as part of the Energy Materials Network in early 2016 to expedite the development of next-generation catalysts and electrodes for fuel cells that are free of the precious platinum group metals (PGMs) currently required for good fuel cell performance. Addressing this barrier is key to meeting DOE’s ultimate fuel cell cost target of $30/kW. It is also a critical step in increasing U.S. competitiveness in manufacturing fuel cell electric vehicles (FCEVs) and other fuel cell energy conversion devices. ElectroCat helps universities and companies to accelerate their PGM-free catalyst research by providing access to high-throughput combinatorial methods, multi-scale modeling techniques and PGM-free catalyst expertise at the national labs and by providing a public-facing data repository to document the findings of the Consortium. The ElectroCat Consortium will be discussed.
(Invited) An Overview of the Hydrogen Materials - Advanced Research Consortium (HyMARC), a DOE Energy Materials Network Consortium, to Accelerate Development of Hydrogen Storage Materials
Authors: Stetson Ned T , Allendorf Mark D. , Adams Jesse , Hulvey Zeric , Randolph Katie
Published: February 2020

The DOE launched the Hydrogen Materials – Advance Research Consortium (HyMARC) to address the key barriers impeding the development of hydrogen storage materials that meet the demands of transportation applications. The consortium is composed of a national laboratory core team, and individual materials development projects selected from academia, industry and other Federally Funded Research and Development Centers.

The goal of the DOE Hydrogen Storage Program is to enable the widespread commercialization of hydrogen and fuel cell technologies through the development of advanced hydrogen storage technologies that meet the onboard storage demands. Commercial fuel cell electric vehicles are being released today that use high-pressure 700 bar hydrogen storage onboard, and the hydrogen fuel infrastructure is being installed to support fast fueling of 700 bar onboard hydrogen storage. The high-pressure tanks are significantly more expensive, larger and heavier than conventional gasoline or diesel fuel tanks. Additionally high pressure delivery to the vehicle adds significantly to the cost of fuel and creates reliability issues at the station. Materials-based storage offers an opportunity to enable storage at high density in a compact container at lower pressures, providing the potential to decrease the cost of the onboard hydrogen storage system and the fueling infrastructure.

The HyMARC national laboratory core team, composed of Sandia (SNL) - lead, Lawrence Livermore (LLNL), and Lawrence Berkeley National Laboratories (LBNL), is tasked with carrying out foundational research to understand the interaction of hydrogen with materials in relation to the formation and release of hydrogen from hydrogen storage materials. This effort includes the development of computational material design tools, synthetic and characterization methodologies, and online databases of hydrogen storage materials properties and computational data that will accelerate materials discovery and development for on-board hydrogen storage applications. Individual materials development projects are selected to work with the national laboratory core team to apply the tools and accelerate the development of materials tailored to meet the needs for transportation hydrogen storage applications.