bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in the Molten Carbonate Electrolysis Cell (MCEC)
Authors: Hu Lan , Lindbergh Göran , Lagergren Carina
Published: February 2020

There is a growing interest in electrolysis cell technology for producing hydrogen that is today considered as an important fuel in the future systems. Electrolysis in molten carbonate salts at high temperature is a promising method for hydrogen- and/or syngas (H2+CO2) production. Due to the favorable thermodynamic and kinetic conditions, high-temperature electrolysis will gain higher overall efficiency and require lower applied voltage when compared to low-temperature electrolysis. Electrolysis in molten carbonates has been investigated by some authors mainly by converting CO2into CO [1-3]. In our previous study, the feasibility of running the molten carbonate fuel cell reversibly with conventional state-of-the-art cell components is evidenced [4]. However, the Ni hydrogen electrode shows slightly higher polarization losses in water electrolysis than in hydrogen oxidation. For the development of molten carbonate electrolysis cells it is important to figure out the activity of the Ni electrode for water electrolysis in molten carbonates.    

In the present study the kinetics and reaction mechanism of hydrogen production in the Ni porous electrode in a molten carbonate electrolysis cell is investigated. For this purpose the electrochemical reaction orders of hydrogen, carbon dioxide and water were determined on basis of the steady-state polarization data. Within the temperature range of 600-650 °C the electrochemical reaction order of hydrogen is not constant; the value was found to be 0.49-0.44 at lower H2 concentration, while increasing to 0.79-0.94 when containing 25-50% H2, i.e. not strongly depending on the temperature. On the other hand the partial pressure dependence of CO2 exhibits a larger influence by temperature increasing from 0.62 to 0.86 when the temperature rose from 600 to 650 °C. The reversed water-gas shift reaction has little or almost no impact on the electrochemical reaction order of hydrogen and carbon dioxide. The electrochemical reaction order of water shows two cases as does hydrogen. At lower water concentration, 10-30%, the reaction order is in the range of 0.47-0.67 while it increases to 0.83-1.07 with 30-50% water at 600-650 °C. When taking the shift equilibrium into account, the reaction order of water is constant and the value is approaching to that of higher water content. The activation energy of the Ni porous electrode for hydrogen production is in the range of 55-100 kJ·mol-1, which indicates that the Ni electrode is under mixed-control.

Reference

[1] W.H.A. Peelen, K. Hemmes, and J. H. W. De Wit, Electrochim. Acta, 43, 763 (1997).

[2] V. Kaplan, E. Wachtel, K. Gartsman, Y. Feldman, and I. Lubomirsky, J. Electrochem. Soc., 157, B552 (2010).

[3] D. Chery, V. Albin, V. Lair, and M. Cassir, Int. J. Hydrogen Energy, 39, 12330 (2014).

[4] L. Hu, I. Rexed, G. Lindbergh, and C. Lagergen, Int. J. Hydrogen Energy, 39, 12323 (2014).
Stability Enhancement of the Interaction Between Pt Nanoparticles and Carbon Supports through Carbon Surface Functionalization
Authors: Xin Le , Yang Fan , Li Zhe-Fei , Sun Chengjun , Stanciu Lia , Xie Jian
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) that use hydrogen and oxygen in air as fuels to produce electricity have attracted extensive interests over the past decades.1 The high efficiency and zero emission make PEMFCs promising candidates for viable propulsive systems in electric automobiles.2 One of the major challenges that hinder the commercialization of PEMFCs vehicles is the poor stability of Pt nanoparticles on carbon supports, which mainly due to the dissolution and re-deposition of Pt and migration of Pt over carbon supports.3
4Both of them will cause the agglomeration of Pt nanoparticles, resulting in loss of Pt electrochemical surface area (ECSA) and the increasing of activation overpotentials.  

Aiming to minimize the growth of Pt nanoparticles due to the Pt migration on carbon supports, fundamental understanding of their interaction is required, so as to modify the carbon supports to enhance the binding energy between Pt and carbons. In our recent work, Pt of 3% to 5% loading was deposited on XC-72 carbon black, graphene, functionalized XC-72 carbon black and functionalized graphene, where the Pt clusters or islands of about 3-6 atoms thickness on different supports can be achieved by a general two step method. The dispersion and morphology of Pt on pristine graphene, SO3H-graphene and NH2-graphene were then characterized by high resolution transmission electron microscopy (HRTEM). It is clearly shown that spherical Pt nanoparticles of very small size were uniformed dispersed on functionalized graphene, whereas on pristine graphene, some rod-like Pt crystals were observed. It indicates that the presence of functional groups prevents the migration of Pt nuclei on the two-dimentional graphene sheet during the synthetic process. X-ray absorption near edge structure (XANES) of Pt L-edge and C K-edge were performed to further characterize the interaction between Pt and different supports. The increasing of the intensity of the Pt L-edge adsorption peak compared with unsupported Pt suggests electron withdrawn from Pt to carbon supports might exists between Pt and carbon supports and the interaction strength follows the order of Pt/SO3H-Graphene > Pt/SO3H-XC72 carbon black > Pt/Graphene > Pt/XC72 carbon black. On the other hand, the shift of Pt L-edge adsorption peak to higher photon energy also indicates the possible increase of oxidation state of Pt due to the Pt-C interaction. This study will shed light on the strategy to improve not only the durability but also activity of Pt based catalysts in fuel cells.

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

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

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

(4)          Shao-Horn, Y.; Sheng, W. C.; Chen, S.; Ferreira, P. J.; Holby, E. F.; Morgan, D. Topics in Catalysis
2007, 46, 285.
PEM Water Electrolysis - Durability Under Heavily Reduced Anode Catalyst Loading
Authors: Rakousky Christoph , Carmo Marcelo , Maier Wiebke , Stolten Detlef
Published: February 2020

When coupled to renewable but nonetheless intermittent power sources such as wind or solar, polymer electrolyte membrane (PEM) electrolyzers are intended to be in operation for tens of thousands of hours1. Hence, the long term behavior of membrane electrode assemblies (MEAs) under these power operating characteristics is of great importance. At moderate conditions (25 cell stack, around 50°C and 1.3 A/cm²)2, commercial PEM electrolyzers show little to no significant degradation (< 4 µVh) after 55,000 h2. However the anode catalyst loading in commercial systems is generally high (> 2 mg/cm²)3 and the state-of-the-art catalyst material, iridium, is expensive and rare. A reduced catalyst loading will contribute to reduce the costs of electrolyzer stacks, but to this date the effect of anode catalyst loading on the durability of PEM electrolysis has not yet been thoroughly investigated in literature.

This study aims to show the durability of PEM electrolysis single cells under reduced anodic catalyst loadings. As shown in Fig. 1 (top), with IrO2 loadings as low as 0.6 mg/cm² we were able to reach identical performance when compared to our standard catalyst loading of 2.25 mg/cm² IrO2. Moreover, stable cell performances over 680 h in an initial life time test were obtained (Fig. 1 bottom). Further reductions in catalyst loading show deteriorating cell performances in 1000 h long term testing. In this study the performance degradation data of MEAs with lower anode loadings were shown and the degradation effects differentiated. The degradation characteristics were also partially localized using electrochemical impedance spectroscopy and reference electrode measurements4 in order to separate cathodic and anodic overvoltages.

We aim to contribute to the understanding of the degradation mechanisms and to possible cost reductions of MEAs for PEM electrolysis by showing the relation between anode loading and long term stability. This information shall assist in making PEM water electrolysis both cost effective and durable.

Fig. 1: Top: single cell performance under a heavily reduced anode loading of 0,60 mg/cm² IrO2. We were able to obtain similar cell performances as for the regular loadings of 2,25 mg/cm² IrO2 and stable cell performances over time (bottom).

References:

1. M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013)

2. K. Ayers, PEM Electrolysis R&D Webinar, presented at the DOE Fuel Cell Technologies Program Webinar, May 23 (2011)

3. Debe, M. K.; Hendricks, S. M.; Vernstrom, G. D.; Meyers, M.; Brostrom, M.; Stephens, M. et al.:. In: J. Electrochem. Soc. 159 (6) (2012)

4. Jung, Myunghee; van Zee, John W., 216th ECS Meeting, 1585–1593 (2009)

Figure 1
First Principles Investigation on the Phase Change Induced By Delithiation of Li2Fe0.5Mn0.5SiO4
Authors: Yi Tiancheng , Li Yunsong , Cheng Xuan , Zhang Ying
Published: February 2020

In this work, the phase change induced by the delithiation of Li2Fe0.5Mn0.5SiO4 compound is investigated via the First Principles calculations. Three delithiated states are selected to calculate their formation energies and crystal structures. The calculated results reveal that there is a significant difference in phase structures between the LiFe0.5Mn0.5SiO4 and Li0.5Fe0.5Mn0.5SiO4 compounds with severe volume variation. It is found that the local structures of Li2Fe0.5Mn0.5SiO4 compound is transformed from the corner-sharing tetrahedrons centered by Fe and Mn into the deformed hexahedrons in which Mn and Fe ions are connected to five O ions. The accompanied redox couples are Fe2+/Fe3+, Mn2+/Mn3+, and Mn3+/Mn4+ for the delithiation of Li2Fe0.5Mn0.5SiO4 to Li1.5Fe0.5Mn0.5SiO4, LiFe0.5Mn0.5SiO4, and Li0.5Fe0.5Mn0.5SiO4, respectively.
Novel Hyperbranched Polymer-Based Anion-Exchange Membranes
Authors: Movil-Cabrera Omar , Frank Logan , Staser John A
Published: February 2020

Anion-exchange membranes (AEMs) are promising materials for a wide variety of applications including among others, fuel cells, electrolyzers, and membrane separation processes. However, development of AEMs with improved hydroxyl conductivity and selectivity as well as excellent thermo-mechanical stability, remains an absolute necessity, now more urgent than ever, due to the global climate change and energy crisis.

The main objective of the present study is to synthesize novel AEMs with excellent hydroxyl conductivity and mechanical stability from hyperbranched polyester polymers. More specifically, poly (vinyl pyridine) (PVP) was grafted onto bis-MPA polyester-64-hydroxyl via graft copolymerization and subsequently quaternized using different alkylating agents. The effects of some variables such as grafting degree and alkylating agent on the morphology as well as on the materials properties of these new-developed membranes were evaluated. The cation stability in alkaline media and the water uptake of these AEMs were also investigated. Some characterization techniques such as NMR, SAXS, FTIR, TEM, TGA, DSC and impedance spectroscopy were used to assess the materials properties of these membranes.
Potential Distributions and the Corresponding Driving Forces for Transport in Cathodes of Solid Oxide Fuel Cells
Authors: Liu Xingbo , Li Wenyuan
Published: February 2020

The mixed ion-electron conductive (MIEC) cathode materials with extended reaction zone have been attracting increasing interest due to their superior performance than the conventional cathode with active three-phase boundary. In the MIEC cathode, a complete electrode process consists of gas diffusion, surface reaction, surface or bulk diffusion and interface exchange. The relevant potentials controlling those processes include electrostatic potential, electrochemical potential of electron and ion. The distributions of those potentials and resultant influence on electrode processes are treated with Nernst and drift diffusion equations. The correlation between those potentials and the measured electrochemical impedance spectra are also discussed. It is found that the change of oxygen electrochemical potential determines the impedance of the processes whichever involves oxygen species, even though the electron electrochemical potential determines the impedance response directly. The assumption of electroneutrality in electrode is disproven and the resultant electrostatic gradient is established in the dense electrode model due to the uneven distributions of ions and electrons. Besides the concentration gradient, electrical field force produced by the electrostatic potential is proposed for the first time as one of the driving forces in the ion diffusion in electrode.
(Invited) How Surface Ionic & Electronic Point Defects Control Oxygen Exchange Reactions
Authors: Chueh William C
Published: February 2020

Surface electrochemical reactions are ubiquitous in many energy conversion systems. Of immense interests are solid-state electrochemical reactions that occur at the solid/gas interface in oxide electro-catalysts, such as those in oxygen-ion-conducting solid-oxide fuel cells and electrolyzers. Unlike their liquid counterparts, these electrochemical reactions involve the simultaneous transfer of ions and electrons between the solid and the gas. As such, the electro-catalysts need to catalyze both the oxygen-ion-insertion and electron-transfer reactions.

Under reaction conditions, perovskite oxides such as lanthanum ferrites and fluorite oxides such as cerium oxides gain and lose significant amounts of oxygen. It is well known that oxygen nonstoichiometry control a vast number of properties in oxides, such as magnetism, the formation of 2-D electron gas at heterojunction, and catalysis. Yet, the role of surface oxygen nonstoichiometry in electrochemical reactions remains largely a mystery due to difficulties in controlling and quantifying oxygen and valence electrons on the surface.

The fundamental question here is how does the surface oxygen nonstoichiometry control the electro-catalytic activity of oxides. In this talk, I will present operando spectroscopic investigations of cerium oxide and transition metal perovskite oxide surfaces using X-rays. We directly probed occupied and unoccupied electronic states using surface sensitive techniques under reaction conditions, that is, under high temperature, pressure and bias.
Anode-Supported Solid Oxide Fuel Cells Fabricated By Single-Step Reduced-Temperature Co-Firing
Authors: Wang Hongqian , Gao Zhan , Jakus Adam E , Shah Ramille N , Barnett Scott A
Published: February 2020

Anode-supported solid oxide fuel cells (SOFCs) consisting of NiO-Y0.16Zr0.92O2-δ (YSZ) anode support layer, NiO-YSZ anode functional layer, YSZ electrolyte and (La0.8Sr0.2)0.98MnO3-δ (LSM)-YSZ cathode were successfully fabricated by single-step co-firing at 1250oC, 150oC lower than the usual 1400oC, with the addition of 1mol% Fe2O3 as sintering aid. Two different ceramic processing strategies - tape casting and colloidal deposition - were utilized for the fabrication. For the colloidally deposited cells, open-circuit voltages (OCVs) were near theoretical values for all cells. The cell yields maximum power density of 975 mW/cm2 and area specific resistance of 0.34 Wcm2 at 800oC.  For the tape casted cells, a replica technique utilizing a graphite layer was incorporated to protect the cell during lamination, which improved the cell performance with maximum power density from 325 mW/cm2 to 650 mW/cm2 at 800oC. The effect of oxygen partial pressures on the cathode performance and hydrogen partial pressures on the anode performance was investigated using electrochemical impedance spectroscopy (EIS), and the results on the main limiting mechanisms will be discussed. Scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS) showed no element transport between each layer during sintering process. The correlation between electrode microstructure and cell performance will be discussed.

Single-step firing is interesting in general to reduce the number of cell processing steps, but is also interesting for fabricating entire stack structures that can be co-fired together. Preliminary results will be presented on single-step reduced-temperature co-firing of stack structures fabricated by a combination of tape casting and direct ink write three-dimensional (3-D) printing.
In Situ X-Ray Absorption Spectroscopy for Batteries: Discovery of New Mechanisms and Materials
Authors: Segre Carlo U , Katsoudas John P. , Timofeeva Elena V. , Ramani Vijay K , Singh Dileep , Pelliccione Christopher J. , Ding Yujia , Aryal Shankar , Beaver Nathaniel M. , Li Yue , Sen Sujat
Published: February 2020

Development of transformational electrochemical energy storage technologies is an imperative for enabling sustainable technologies such as vehicle electrification and renewable energy generation. Major advances in these technologies are made possible by developing the ability to predict how structural changes correlate with the functionality of new materials.

Characterization by x-ray absorption spectroscopy (XAS) is an important tool in developing a better understanding of the structure-function relationship in battery materials, including structural changes upon cycling and aging mechanisms. XAS is commonly used to study electrochemical reactions in situ and is particularly valuable when working with nanomaterials or highly disordered or doped crystalline systems. A successful in situ XAS experiment on battery materials requires a careful choice of experimental conditions including design of the in situ cell, choice of beamline, energy scan mode, and detectors. An overview of these considerations for various types of battery materials will be presented along with results which illustrate the pitfalls inherent in these experiments.

Results will be presented on a variety of Li-ion battery cathode and anode materials, including metals and metal oxides where there is a high capacity but rapid aging due to severe swelling of the anode material upon lithiation. Our results have identified the structural signature of metal-Li bonds and their persistence upon discharge, which imply a loss of electrical contact as the primary failure mode of these materials. In situ results on aqueous battery materials such as Fe2O3 and NiOOH will also be presented and discussed with particular emphasis on the comparison between nanoparticles in solid state electrodes and in nanofluid suspension electrodes known as nanoelectrofuel (NEF). NEF are stable dispersions of battery active nanoparticles in electrolyte that effectively charge/discharge as they are pumped through custom-designed flow cell(s) and represent a high-energy-density rechargeable, renewable, and recyclable electrochemical fuel.
(Invited) Enabling Oxygen Electrocatalysis for Sustainable Energy
Authors: Shao-Horn Yang
Published: February 2020

The development of sustainable energy is one of the most important scientific challenges in the 21st century. A critical element for sustainable energy implementation is to have efficient energy conversion and storage. Oxygen electrocatalysis is central to enable photoelectrochemical and electrolytic water-splitting, fuel cells, and metal-air batteries.  Probing a fundamental catalyst “design” principle” that links surface structure and chemistry to the catalytic activity can guide the search for highly active catalysts that are cost effective and abundant in nature.  While such a design concept exists for metal catalysts, little is known about the design principles for oxygen electrocatalysis on oxides. Recent advances in identifying the design principles and activity descriptors of transition metal oxides will be presented. We will show that these fundamental concepts can be used to tune transition metal oxide surfaces with much enhanced catalytic activities. Moreover, we will discuss how oxide bulk electronic structures can influence the catalytic activities of oxides, from which two different reaction mechanisms are proposed. Lastly, connecting bulk to surface electronic structures is challenging but much needed to provide mechanistic insights, and some in-situ synchrotron X-ray measurements to this end will be discussed.
(La,Sr)CoO3-Rgo Hybrid Oxygen Reduction Reaction/Oxygen Evolution Reaction Bifunctional Catalyst
Authors: Chung Hoon T , Gao Wei , Higgins Drew Christopher , Martinez Ulises , Mukundan Rangachary , Tylus Urszula , Dumont Joseph H , Purdy Geraldine M , Dattelbaum Andrew M , Zelenay Piotr
Published: February 2020

A bifunctional oxygen reduction reaction (ORR)/ oxygen evolution reaction (OER) catalyst is essential for rechargeable metal-air batteries and regenerative fuel cells. Platinum (Pt) and iridium oxide (IrO2) are the state-of-the-art ORR and OER catalysts, respectively. However the high price and scarcity of these platinum group metals (PGMs) has been an obstacle for wide spread application of these catalysts. Recently, in alkaline media, carbon based ORR and perovskite OER catalysts have demonstrated similar or even better catalytic activities compared to the counterpart PGM catalysts [1, 2]. Therefore, if we combine these two non-PGM catalysts, a non-PGM bifunctional ORR/OER catalyst can be obtained. A hindrance in this approach is the vulnerability of carbon-based ORR catalysts to oxidation in the OER potential range, i.e., potentials > 1.5 V vs. RHE. Thus development of robust ORR catalysts under practical OER conditions is a key to realize this kind of bifunctional catalysts.

 The carbon support used in our ORR catalysts was black pearl (BP) 2000 [1]. In preliminary tests, however, we found that BP 2000 undergoes oxidization at potentials around ca. 1.2 V vs. RHE and above (data not shown). In this work, we used reduced graphene oxide (rGO) as an alternative support to synthesize oxidation resistant ORR catalysts. The OER catalyst we chose was a perovskite (La1-xSrx)CoO3-δ (LSC). Pre-synthesized LSC was added into the initial solution of the rGO based ORR catalyst synthesis process, and after drying and heat-treatment, bifunctional (LSC + rGO) catalysts were obtained. In measuring the OER activity of the LSC catalyst, acetylene black (AB) carbon was added to the LSC (LSC + AB) to increase the electrical conductivity. Fig. 1 shows the comparison of ORR/OER activities between (LSC + AB) and (LSC + rGO). As expected, the ORR activity of (LSC + rGO) is greatly improved by ca. 200 mV in terms of E½
, in comparison to that of (LSC + AB). Interestingly even the OER activity of (LSC + rGO) becomes higher than that of (LSC + AB). Thanks to the enhancement of both ORR and OER activities with (LSC + rGO), highly active bifunctional catalysts are obtained. In this talk, material analysis results and diverse electrochemical performances of the (LSC + rGO) catalysts will be presented.

Acknowledgements

Support from the Directed Research of the Los Alamos National Laboratory’s Laboratory Directed Research & Development (LDRD-DR) is greatly acknowledged.

References

Chung et al., Nat. Commun. 4, 1922 (2013).

Suntivich et al., Science, 334, 1383 (2011).

Figure 1
Enhanced Electrocatalytic Activity of Sm2O3-doped Ni-Co Coating Electrode for Hydrogen Evolution Reaction
Authors: Ding Shuangshuang , He Ping , Feng Wanru , Zhang Guangli , Zhang Susu
Published: February 2020

Direct electrochemical splitting of water is an attractive method to generate the renewable energy carrier hydrogen [1].  Low-cost catalyst for hydrogen evolution reaction (HER) is one key step in this process [2].  So far, there are no other pure metals except for noble elements really showing high activities for HER, and many efforts have been made to look for highly catalytic activated transition metal based alloys for HER [3,4].

In this work, HER was investigated on Ni-Co alloy electrode and Ni-Co-Sm2O3 composite electrode in 0.50 M Na2SO4 + 0.10 M H2SO4 solution.  It was indicated that Sm2O3 particles promoted the formation of an amorphous structure of Ni-Co alloy coating, which was benefit for HER.  The surface of Ni-Co-Sm2O3 composites was more coarse and grainy compared with that of Ni-Co alloy layer (Fig. 1).  Steady-state polarization curves (Fig. 2) showed that the hydrogen evolution potential of Ni-Co-Sm2O3 composite electrode positively moved by about 240 mV at 8.0 mA cm-2 compared with that of Ni-Co alloy electrode, indicating that the embedded Sm2O3 particles enhanced the electrocatalytic activity of Ni-Co coating for HER.  Furthermore, Ni-Co-Sm2O3 composite electrode has considerably lower charge transfer resistance and higher exchange current density.

 

References

[1] C. Lupi, A. Dell’Era, M. Pasquali. In situ activation with Mo of Ni-Co alloys for hydrogen evolution reaction. International Journal of Hydrogen Energy, 2014, 39: 1932-1940

[2] Wei Cui, Chenjiao Ge, Zhicai Xing, Abdullah M. Asiri, Xuping Sun. NixSy-MoS2 hybrid microspheres: One-pot hydrothermal  synthesis and  their application as a  novel hydrogen evolution reaction electrocatalyst  with enhanced activity. Electrochimica Acta, 2014, 137: 504–510

[3] Zhengwei Xie, Ping He, Licheng Du, Faqin Dong, Ke Dai, Tinghong Zhang. Comparison of four nickel-based electrodes for hydrogen evolution reaction. Electrochimica Acta, 2013, 88: 390-394

[4] Ping He, Xiaofang Yi, Yongjun Ma, Wei Wang, Faqin Dong, Licheng Du, Hongtao Liu. Effect of Gd2O3 on the hydrogen evolution property of nickel-cobalt coatings electrodeposited on titanium substrate, Journal of Physics and Chemistry of Solids, 2011, 72: 1261-1264

Figure 1
First-Principles Study of Structure Property Relationships of Monolayer (Hydroxy)Oxide-Metal Bifunctional Electrocatalysts
Authors: Zeng Zhenhua , Kubal Joseph , Greeley Jeff
Published: February 2020

In the present study, on the basis of detailed density functional theory (DFT) calculations, and using Ni hydroxy(oxide) films on Pt(111) and Au(111) electrodes as model systems, we describe a detailed structural and electrocatalytic analysis of hydrogen evolution (HER) at three-phase boundaries under alkaline electrochemical conditions. We demonstrate that the structure and oxidation state of the films can be systematically tuned by changing the applied electrode potential and/or the nature of substrates. Structural features determined from the theoretical calculations provide a wealth of information that is inaccessible by purely experimental means, and these structures, in turn, strongly suggest that a bifunctional reaction mechanism for alkaline HER will be operative at the interface between the films, the metal substrates, and the surrounding aqueous medium. This bifunctionality produces important changes in the calculated barriers of key elementary reaction steps, including water activation and dissociation, as compared to traditional monofunctional Pt surfaces.

The successful identification of the structures of thin metal films and three-phase boundary catalysts is not only an important step towards accurate identification and prediction of a variety of oxide/electrode interfacial structure-properties relationships, but also provides the foundation for rational design and control of ‘targeted active phases’ at catalytic interfaces. The successful design of bifunctional electrocatalysts that exploit these structures, in turn, could ultimately lead to advances in the development of alkaline fuel cells.

References

1Surnev, S.; Fortunelli, A.; Netzer, F. P. Chem Rev 2012, 113, 4314.

2Shaikhutdinov, S.; Freund, H.-J. Annu. Rev. Phys. Chem. 2012, 63, 619.

3Subbaraman, R.; Stamenkovic, V.; Markovic, N. et al, Science 2011, 334, 1256.

4Subbaraman, R.; Greeley, J.; Stamenkovic, V.; Markovic, N. et al, Nat Mater
2012, 11, 550

5Strmcnik, D; Stamenkovic, V. R.; Markovic, N. et al, Nat Chem 2013, 5, 300.
Low-Cost High-Throughput Photoelectrochemical Hydrogen Production
Authors: Schwartz David Eric , Deutsch Todd G
Published: February 2020

Hydrogen production via photoelectrochemical (PEC) water splitting has promise for storage of solar energy in a clean fuel for vehicular and grid applications. However, PEC technologies with high solar-to-hydrogen (STH) efficiency have high materials and processing costs, and less expensive alternatives have not achieved high efficiencies. Here we discuss a systems-level approach to improving utilization of high-efficiency III-V PEC cells using optical concentration factors much higher than have been previously considered. Full system and cost analyses are presented, indicating the potential of this approach to reduce the cost per kilogram of hydrogen produced to significantly lower than that of a photovoltaic-plus-electrolyzer solution.
Materials for Efficient Photoelectrochemical Water Splitting: The PEC Working Group
Authors: Wang Heli , Jaramillo Thomas F , Miller Eric Lars
Published: February 2020

The development of durable photoelectrochemical (PEC) water splitting systems with high solar-to-hydrogen (STH) conversion efficiency has been a significant challenge. Critical requirements on semiconductor materials’ band gap, energetics, efficiency, and stability must be satisfied simultaneously.

Metal oxides can be stable and earth-abundant, and different tandem cell configurations have been developed to address the band-edges mismatch. More focus is needed on overcoming the efficiency limitations due to absorption, charge mobility, recombination, interfacial kinetics, etc. With suitable band gaps and optoelectronic quality, high efficient PV semiconductors, like III-V, offer alternative pathway to efficient STH conversion by addressing the band edge mismatch using monolithic PEC/PV tandem cell design. Stability, however, remains a key issue. NREL, working with other members of the PEC working group have been investigating the corrosion of III-V materials and interfaces with a goal to develop surface modification methods for mitigating the corrosion issue. Approaches include coatings, ion bombardment, surface nitridation as well as electrolyte treatments.

Significant materials challenges remain, and effective usage of resources is needed. The PEC Working Group facilitates progress by bringing together diverse PEC researchers with common interests and goals, promoting collaborative activities, resource sharing, and joint publications.
BiVO4 Photoelectrodes for Use in Solar Water Splitting
Authors: Choi Kyoung-Shin
Published: February 2020

Many recent efforts have focused on the development of n-type semiconductors that can serve as efficient photoanodes for solar water oxidation.  Desirable photoanodes should have a small bandgap to utilize a significant portion of visible light, and a valence band (VB) edge that is positive enough to provide sufficient overpotential for the water oxidation reaction.  The position of the conduction band (CB) edge or the flatband potential of the photoanode is also important because it determines the potential of the photoexcited electrons that will be used for the cathode reaction (i.e., water reduction).  If these electrons do not have sufficient overpotential to reduce water, an external bias needs to be provided, effectively reducing the cell efficiency.  Bismuth vanadate (BiVO4) has recently emerged as a promising material for use as a photoanode in water splitting photoelectrochemical cells.  It is because it absorbs a substantial portion of the visible spectrum (bandgap energy, ca. 2.4 eV) and has a favorable conduction band (CB) edge position very near the thermodynamic H2 evolution potential.  Significant advancement in the understanding and construction of efficient BiVO4-based photoanode systems has been made within a short period of time owing to various newly developed ideas and approaches.  In this presentation, we will discuss our recent efforts in improving the photoelectrochemical properties of BiVO4 photoanodes, which include an enhancement in photon absorption and charge transport properties.  These efforts resulted in an applied bias photon-to-current efficiency (ABPE) for water splitting higher than 2% using all oxide-based electrodes.
Catalyst Modified Ternary Oxide Photoanodes for Photoelectrochemical Water Splitting
Authors: Pilli Satyananda Kishore , Furtak Thomas E. , Chidambaram Dev , Deutsch Todd G , Turner John A , Herring Andrew M
Published: February 2020

Recently, BiVO4 with moderate band gap of 2.4-2.6 eV and conduction band edge at 0 V vs. NHE at pH 0, has emerged as a promising water oxidation photoanode. However, water oxidation activity of BiVO4 is relatively low compared to the theoretical efficiency that could be achieved with this material. Poor charge carrier separation characteristics, relatively low electron transport properties and slow charge transfer at electrode-electrolyte interface are attributed to the poor performance characteristics of BiVO4 photoelectrode. However, recent advances in the material science and the development of efficient water oxidation electrocatalysts have assisted to design BiVO4 photoelectrodes with enhanced efficiencies. For this instance, various strategic approaches that were intended towards the enhancement of charge carrier separation, light absorption and charge injection characteristics of BiVO4 photoelectrodes and recent studies on application of these modified BiVO4 electrodes for solar energy conversion are presented in this talk.
Photoelectrochemical Ion Pumping with Dye-Functionalized Polymer Membranes
Authors: Sanborn Christopher D. , Ardo Shane
Published: February 2020

Artificial photosynthesis could be a cost-effective and sustainable means of converting sunlight energy into usable energy. Most artificial photosynthetic systems mimic nature’s properties of light absorption, electronic charge separation, and electronic charge collection, where ultimately electrons make and break chemical bonds. However, nature also transduces photon energy into proton gradients whose electric potential also drives chemical-bond formation. In my presentation I will report on my research group’s progress toward mimicking nature in function, by using light to drive endergonic proton transfer, ultimately converting photon energy into ionic current. The applicability and practicality of this material as a membrane in solar fuels devices and as a separate ionic photoelectrochemical device will also be discussed.

My research group’s near-term goal is to provide a proof-of-concept demonstration of an artificial proton pump where light-driven ion transport results in photovoltaic action. For an initial model system we utilized a conical nanopore etched in a polyethylene terephthalate plastic sheet. This pore was formed via swift heavy ion bombardment followed by alkaline chemical etching which resulted in a pore lined with fixed anionic functional groups. Then, using peptide coupling chemistries, the pore was asymmetrically functionalized with novel photoacids to generate a region containing fixed cationic dyes. This ordered distribution of interfacial charge was intended to mimic a solid-state semiconductor pn-junction and be used to separate photogenerated charges. We demonstrated that under visible-light illumination and a small reverse bias, excitation of the photoacid molecules resulted in an ionic photocurrent. We are currently expanding this initial research and successful demonstration of an artificial light-driven ion pump to other polymeric materials with hopes of generating ionic power through sunlight absorption and incorporating these materials as ion-exchange membranes in solar fuels devices.
Using Protection Layers for a 2-Photon Water Splitting Device
Authors: Seger Brian , Mei Bastian Timo , Frydendal Rasmus , Permyakova Anastatia , Bae Dowon , Pedersen Thomas , Castelli Ivano , Malacrida Paolo , Vesborg Peter C. K. , Stephens Ifan E. L. , Hansen Ole , Jacobsen Karsten , Chorkendorff Ib
Published: February 2020

The 2-photon tandem device for photocatalytic water splitting has been theoretically shown to provide a higher efficiency than a single photon device(1). This increased efficiency can be achieved by having one material optimized to absorb high energy photons (large bandgap) and another material optimized to absorb low energy photons (small bandgap).    

  To a large degree this approach has been hindered by corrosion issues.  In this talk I will first discuss how our computational screening of 2,400 materials showed that very few materials can efficiently absorb light without corroding in water splitting conditions.(2)  I will follow this up by discussing how protection layers bypass the corrosion issue by creating a buffer layer.(3) Finally I will show how we integrated a photocatalyst/protection layer/(co-catalyst) scheme to produce highly efficient H2 evolution photocathodes and O2 evolution photoanodes.(3, 4)

1.  A. B. Laursen, S. Kegnaes, S. Dahl and I. Chorkendorff, Energy & Environmental Science, 5 (2012).

2.  B. Seger, I. E. Castelli, P. C. K. Vesborg, K. W. Jacobsen, O. Hansen and I. Chorkendorff, Energy & Environmental Science, 7, 2397 (2014).

3.  B. Seger, T. Pedersen, A. B. Laursen, P. C. K. Vesborg, O. Hansen and I. Chorkendorff, Journal of the American Chemical Society, 135, 1057 (2013).

4.  B. Mei, A. A. Permyakova, R. Frydendal, D. Bae, T. Pedersen, P. Malacrida, O. Hansen, I. E. L. Stephens, P. C. K. Vesborg, B. Seger and I. Chorkendorff, The Journal of Physical Chemistry Letters, 5, 3456 (2014).

Figure 1
Stable Solar-Driven Water Oxidation to O2(g) By Multifunctional Electrocatalysts Coated Small Band Gap Semiconductors
Authors: Sun Ke , Lewis Nathan S.
Published: February 2020

Technologically important small band gap (<2 eV) semiconductors must be stabilized against corrosion or passivation in aqueous electrolytes before they can be used as photoelectrodes that directly produce fuels from sunlight.  In addition, incorporation of electrocatalysts on the surface of the photoelectrodes is required for efficient oxidation of H2O to O2(g) and reduction of H2O or H2O and CO2 to fuels. Stabilization of technologically important semiconductors against photocorrosion and photopassivation would have a significant impact on photoelectrochemical energy conversion, and could enable the development of a new generation of robust integrated devices for efficient solar-driven water splitting and solar-driven CO2 reduction. Previous efforts have been extensively dedicated on elongating the lifetime of semiconductors under harsh fuel forming reaction conditions especially during the water oxidation half reaction. To date, the energy conversion performances and stability were limited on these systems, obscuring the realization of integrated solar fuel devices. In this work, we presented our recent effort on preparation of a multifunctional coating using Ni oxide, which provides multiple important functions on semiconductor photoelectrodes surfaces, including chemical/corrosion protection, electrically conducting, optical transparent/antireflective, and inherent electrocatalytic activity. The combination of the extraordinary film properties has resulted benchmark performances and stability on Si photoanodes, as well as other group II-VI and group III-V semiconductors that have never been able to be protected in relevant water oxidation conditions before. Results presented here indicated a viable strategy that is a promising approach to achieve the long-term stability of semiconducting photoanodes for use in solar fuel applications.
Efficient Photoelectrochemical Hydrogen Evolution of Amorphous Group VI Metal Chalcogenides on Si Micropyramids
Authors: Ding Qi , Zhang Xingwang , Zhai Jianyuan , Shearer Melinda J. , Caban Miguel , Meng Fei , He Jr-Hau , Hamers Robert J. , Jin Song
Published: February 2020

Hydrogen, a clean, storable, and high-energy density energy carrier, is a promising sustainable alternative for meeting the global energy demand and achieving an environmentally friendly fuel economy. Utilizing an integrated photoelectrochemical (PEC) system to directly convert solar to hydrogen via water splitting is one of the most promising approaches. Platinum and other noble metals remain the best catalysts for solar-driven hydrogen evolution reaction (HER), but the high cost and scarcity greatly limit their large scale deployment. In this work, we synthesized efficient yet low-cost HER electrocatalysts, amorphous MoSxCly and MoSexCly, via a facial chemical vapor deposition (CVD) method, and discovered when these catalysts were coupled with light absorber planar p-Si could make efficient and robust photocathodes for solar-driven HER. Moreover, by utilizing a special designed n+p Si micropyramid structure, we were able to further improve the photocurrent density, onset voltage, as well as the overall power conversion efficiency. This superior performance is originated from the significant improvement in light harvesting properties from Si nanostructuring as well as the optimized interface between the catalysts and Si substrate via the direct CVD growth. Outstanding stability was also demonstrated over long-term operation, suggesting these heterostructures are promising earth-abundant alternatives to photocathodes based on noble metal catalysts for solar-driven hydrogen production.
New Photocatalyst for the Generation of Environmentally Friendly Fuel Using Visible Solar Spectrum
Authors: Akter Tahmina , Saupe Geoffrey B.
Published: February 2020

Wide band gap semiconductor photocatalysts, such as titanium dioxide, along with a metal co-catalyst have been used to generate hydrogen fuel from water. However, ultraviolet light is required, which limits their utility in solar energy conversion. Modification of these types of semiconductors can sensitize them to visible light, providing a promising way to create clean, renewable hydrogen fuel.  Many photocatalysts suffer from poor hydrogen production efficiencies under visible light, due to inadequate visible light absorption. In this research, co-precipitating [Ru(bpy)3]2+ sensitizer dye molecules into nanosheet agglomerates provides a new way to modify porous oxide (POX) photocatalysts. A series of dye-sensitized POX materials have been synthesized from KTiNbO5, KNb3O8 and K4Nb6O17. These materials were characterized by XRD, TEM, SEM and EDS and water photolysis.
Novel Hybrid 1-D Structure of PEDOT/TiO2 Nanotubes As the Pt-Free Catalyst of Counter Electrodes in Dye-Sensitized Solar Cells
Authors: Chen WeiChieh , Yeh Min-Hsin , Peng Jia-De , Lin Lu-Yin , Ho KuoChuan
Published: February 2020

Due to its outstanding electrocatalytic ability and reliable stability under severe circumstances, Pt is one of promising catalysts in electrochemical applications. However, cost issue and delicate process is inevitable for this kind of precious metals. How to provide a dependable material is an interesting issue. Hence, in this study, novel one-dimensional (1-D) hybrid structure of poly(3,4-ethylenedioxythiophene) (PEDOT) supported with TiO2 nanotubes (PEDOT/TNTs) were successfully synthesized and further applied as catalysts of counter electrodes (CEs) for dye–sensitized solar cells (DSSCs). PEDOT/TNTs were formed with electropolymerization of 3,4-ethylenedioxythiophene onto TiO2 nanotubes (TNTs) by the pulse current process, in which TNTs were obtained by anodization of Ti foils. After optimizing the sintering temperature of TNTs and electropolymerizing charge density of PEDOT, a high solar–to–electricity conversion efficiency (η) of 8.82% is achieved for a DSSC containing the CE of PEDOT/TNTs, with the optimized sintering temperature of 400 oC for TNTs and electropolymerizing charge density of 400 mC/cm2 for PEDOT deposited onto TNTs (PEDOT/TNTs-400 mC/cm2); a η is higher than those of the cells with the CEs of flat PEDOT (6.50%) and Pt (8.24%). Cyclic voltammetry (CV), symmetric electrochemical impedance spectra (s–EIS) and Tafel polarization plots reveal that the highest h of the cell with PEDOT/TNTs is due to the higher electrocatalytic ability of the CE for the reduction of triiodide ions (I3
–) and lower charge transfer resistance (R
ct) at the interface between the CE and the electrolyte. Incident photon–to–current conversion efficiency (IPCE) spectra are used to substantiate the explanations on the photovoltaic parameters of the cells.
The Relationship Between Segmental Motions, Hydration and Overall Mass Transport in Pfsas
Authors: Zawodzinski Thomas A. , Elgammal Ramez A. , Bai Yujia
Published: February 2020

A great many membranes have been studied for use in fuel cells and other electrochemical devices. Prominent amongst these are the perfluorosulfonic acids, including Nafion as an archetype and materials prepared by Dow (later others) and 3M presented over time.  Generally, similar mass transport (conductivity and water transport) phenomena have been observed, with high transport rates closely tied to high levels of hydration. However, maintaining high hydration of the membrane by maintaining an environment of high relative humidity requires system level measures that represent parasitic losses.

Achieving high conductivity with less hydration requires more substantial understanding and then control of the transport mechanisms involved at low water content.  There are clear differences in the behavior of materials at low and high hydration, with a line of demarcation at hydration levels of ca. 5 or 6 waters per sulfonate.  Above this level, the water in the membrane is more continuous across multiple pores and protons move in an environment that increasing resembles that in aqueous solutions as hydration levels increase.  Below this level, such factors as the acidity of the sulfonic acid, the mobility of water within the first or second hydration spheres of the sulfonate and proton and possibly sidechain movements in the polymer all have been suggested to play roles in the transport processes.

In this contribution, we will explore various processes in the low water content regime.  For a series of PFSAs, we will gather experimental information to reveal the approximate rate of side chain motion, use vibrational spectroscopy and related methods to provide an in-depth view into the hydration of ions and water interactions in the membrane and present information on the energetics of hydration.  These will be synthesized into an experimentally supported picture allowing us to assess the relative importance of the motions of anions, cations and water molecules in determining transport in PFSAs at RH < 50% under different conditions.
Hybrid Polymer Electrolytes Based on Linear Siloxane Networks and Crosslinked Polyether Domains: Interplay Between Composition and Properties
Authors: Boaretto Nicola , Brinkmann Christine , Vezzù Keti , Di Noto Vito , Lorrmann Henning
Published: February 2020

In this study, a new class of hybrid polymer electrolytes was prepared and characterized. The materials consisted of a matrix based on linear oligosiloxane networks and partially crosslinked polyether domains, doped with Lithium bis(trifluorosulfonyl)imide (LiTFSI). These materials are characterized by a maximum conductivity of 8∙10-5 S/cm at 30 °C, and high thermo-mechanical stability, with decomposition temperature of 250 °C and a storage shear modulus of almost 105 Pa at 100 °C. Compositional parameters such as salt, cross-linker concentration, and polyether chain length were varied, and the materials were characterized by several analytical techniques. Vibrational spectroscopy provided details of the hybrid structure and the effect of salt doping. The thermo-mechanical properties were studied by thermogravimetric analysis, differential scanning calorimetry and rheological analysis. Finally, the transport properties were analyzed by means of broadband electric spectroscopy. The study made it possible to describe the relationships between composition, morphology, thermo-mechanical and transport properties of the synthesized hybrid electrolytes, with particular emphasis on the interplay between polymer dynamics and conduction mechanism.

Figure 1