bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Phase Dependence on HER Water Splitting Performance of Earth-Abundant Electrocatalysts
Authors: Rodene Dylan Daniel , Eladgham Ebtesam H. , Arachchige Indika , Gupta Ram B. 
Published: February 2020

Economical hydrogen production via renewable-energy-powered water splitting is only feasible with earth-abundant low over-potential (<150 mV @ 10 mA/cm2) electrocatalysts. Nickel-molybdenum alloys, as earth-abundant electrocatalysts, have been reported to show competitive performance characteristics over past years. Herein, we will present stoichiometric ratios that result in multiple crystal phases and alkaline hydrogen evolution reaction (HER) over-potentials. In particular, the performance of specific transition metal crystal phases in alkaline media were evaluated for HER performance with general knowledge of that alkaline media leads to higher stabilities over acidic media. Typically, alkaline media also limits low over-potentials. In our case, specific phases of NixMo showed competitive over-potentials regardless of electrolyte.
Colloidal nanocrystals were synthesized and drop-casted onto titanium foil to form fashioned single crystal phase electrodes. Electrodepositing, contrary to drop-casting, films might result in good electrode stability and performance but cannot easily provide experimental elucidation of crystal phase dependence on HER over-potential. A more robust method is needed to differentiate long-term stability differences for fashioned electrodes in 2M KOH.
Structural crystal phase differences between different colloidal nanocrystal alloy compositions will be presented as x-ray photoelectron spectroscopy (XPS) and x-ray powder diffraction (XRD) data. Electrochemical data, including polarization curves and Tafel plots, will be presented. Specific insights into over-potential differences of alloys with similar elemental composition was gained and a discussion linking metal oxidation states to over-potential performance will take place.
Design of a Solar Device to Transform Wastewater Nitrates to Nitrogen-Species Coupled with Energy and Nutrient Recovery
Authors: Barrera Luisa , Bala Chandran Rohini 
Published: February 2020

Excessive anthropogenic production of nitrogen fertilizers combined with rapid industrialization has disrupted the natural balance of the nitrogen cycle leading to increased concentrations of reactive-nitrogen/nutrient species including nitrates (NO3
-), nitrites (NO2
-), and ammonium (NH4
+) in groundwater, rivers and lakes1,2. These nutrient imbalances can lead to health risks to human beings by causing methemoglobinemia in infants, also known as “blue baby syndrome,” and negatively impact the environment by causing acid rain and algal blooms. Despite the chemical energy that is stored in common dissolved contaminants in water, wastewater treatment poses the challenge of being a highly energy intensive process. In this study we propose a photoelectrochemical approach to oxidize water and reduce nitrates (NO3
-) to various nitrogen-species including N2, and other value-added products such as NH3 and N2O. An ion-exchange membrane attenuates gas crossover while facilitating species transport. NH3 can be directly used as a fuel and/or for fertilizer production, and N2O is a powerful oxidant in combustion reactions (used as “nitrox” to supercharge engines of high performance vehicles); in the combustion of methane (CH4), N2O increases the heat released in the reaction by 37% as compared to when O2 is used as an oxidant. Thermodynamic analyses is first performed to predict the solar energy conversion efficiencies for the various product species. Furthermore, a one-dimensional, coupled species transport and reaction kinetics model is developed for a batch reactor to predict overall rates of product formation. Specifically, the model developed is applied to investigate the influences of device-design, competing reactions and mass transport on the rates and the selectivity of product formation. Thermodynamic predictions show that N2O could be a more promising value-added NO3
- reduction product compared to NH3 due to the increased aqueous solubility of the latter, which leads to significant crossover losses.
References:

Falkowski, P. et al. The Global Carbon Cycle : A Test of Our Knowledge of Earth as a System. Science (80).
290, 291–297 (2000).

Duca, M. & Koper, M. T. M. Powering denitrification: the perspectives of electrocatalytic nitrate reduction. Energy Environ. Sci.
5, 9726 (2012).

Figure 1
Photoelectrochemical Hydrogen Generation Using a Bis-Chelating Nickel PNP Catalyst Tethered to Band-Edge Modified Si(111)|TiO2
Authors: Gurrentz Joseph Martin , Boucher Dylan G , Rose Michael J 
Published: February 2020

We report the generation of a novel “bis-bidentate” chelating nickel phosphine electrocatalyst functionalized with pendant amines. Two PNP appended donor moieties are tethered to a single surface-tethering anchor, with the intention of leveraging the chelate effect to increase the kinetic stability of the bound nickel ion upon surface immobilization. The carboxylic acid moiety of this bis-bidentate PNP catalyst allows for adsorption to band-edge modified p-silicon(111) photoelectrodes coated with amorphous TiO2 for photogeneration of dihydrogen under illumination and negative applied bias. The synthesis of this ligand also allows for variability in metal oxide binding groups and phosphine R-groups.
The band-edge modification of p-silicon(111) is achieved with a mixed monolayer of phenyl-3,5-bismethoxytriethylene glycol and methyl units, which also enhances electron transport through the interface. An ultrathin film (20Å) of amorphous titania further passivates the semiconductor from the generation of surface defects, acts as an electron selective layer, and allows for adsorption of the metal complex to the electrode.
Cyclic voltammetry and XPS were used in conjunction to estimate catalyst loading, evaluate photoelectrochemical performance of these devices, and investigate different mechanisms of activity loss such as via loss of the nickel or desorption of the ligand. Different modes of device construction, such as via adsorption of the PNP ligand to the TiO2-coated photoelectrodes followed by treatment with a solution of [Ni(MeCN)6]·2ClO4 and via deposition of the fully constructed, metalated complex were evaluated for differences in Ni loading and device performance. Both the adsorbed catalyst as well as non-specifically adsorbed Ni2+ on TiO2 were shown to be active for proton reduction, albeit at different potentials. Efforts were therefore made to isolate the activity of the nickel phosphine catalyst and prevent convolution of the electrochemical response.
Rapid One-Pot Synthesis of Α- and Β-Cu2V2O7 and Their Use in Photoelectrochemical Water Splitting
Authors: Hossain mohammad Kabir , Rajeshwar Krishnan 
Published: February 2020

Photoelectrochemical (PEC) water splitting is a promising strategy to make high density chemical fuels via utilization of solar energy using semiconductor materials. Oxide semiconductors, especially transition metal oxide semiconductors, offer various advantages such as stability, Earth-abundance and easy fabrication. A twin-photoelectrode tandem cell approach appears to be the most viable route to high solar-to-hydrogen conversion (STH) efficiency. In this configuration, the optimual energy bandgap for the semiconductor photoanode has been estimated to be ~ 2 eV. Ternary copper vanadates fulfill this criterion. The compound, Cu2V2O7 exists in two stable polymorphs at room temperature: orthorhombic α-Cu2V2O7 (Blossite) and monoclinic β-Cu2V2O7 (Ziesite). There are limited reports on the PEC behavior of β-Cu2V2O7, however, no corresponding reports on α-Cu2V2O7 are available.
In this present work, we report the synthesis of these two polymorphs using a rapid and simple one-pot solution combustion synthesis and document their PEC behavior. The effect of various synthetic parameters were investigated and thus enabled to identify the optimum growth conditions to achieve phase-pure samples. Rietveld refinements along with powder X-ray diffraction confirmed the phase purity of the two polymorphs. The bandgap values of these oxides were estimated employing two different methods: Tauc plot from diffuse reflectance spectroscopy and surface photovoltage spectroscopy. These values agreed with those derived from density functional theory (DFT) calculations. Fermi level energies were quantified from contact potential difference (CPD) measurements which positioned them close to the conduction band minima (CBM) and thereby confirmed their n-type conductivity. The β-Cu2V2O7 phase showed higher photoactivity at lower applied bias; however, both phases showed similar photoactivity toward water splitting at higher applied bias.
Photocatalytic Overall Water Splitting: Observing H2 and O2 Transients with Ni/NiOx-Modified Mg:SrTiO3
Authors: Mei Bastian Timo , Han Kai , Mul Guido 
Published: February 2020

SrTiO3 is a promising semiconductor driving photocatalytic overall water splitting (POWS) under UV light illumination. Improving the performance of SrTiO3 in decomposing water into H2 and O2 can be achieved by introducing feasible co-catalyst, such as Pt or Ni/NiOx. Though co-catalysts are employed in heterogeneous photocatalysis engineering of semiconductor/co-catalysts interfaces is rarely reported in literature [1]. In addition, limited attention has been paid to structural/electronic changes of co-catalysts during illumination/reaction and transients occurring in hydrogen and/or oxygen evolution are barely discussed.
In this contribution the photocatalytic performance of SrTiO3-based systems will be analyzed using a Continuously Stirred Tank Reactor (CSTR) connected to a micro GC-PDD (Pulsed Discharge Detector). Due to the favorable time-resolution of the GC-PDD transients in the evolution of H2 and O2, especially in the initial stages of testing, can be easily revealed. We will highlight the following recent observations:

For Ni/NiOx-modified SrTiO3, severe changes in the oxidation state of NiOx assigned to the transformation of Ni(OH)2 to NiOOH leading to an active photocatalyst/co-catalyst material in agreement with transient H2 evolution will be discussed [2];

Electronic modification of SrTiO3 by Mg incorporation into the perovskite structure can be obtained by a simple solid-state preparation [3]. While significant improvements in the steady state photocatalytic efficiency are obtained (Fig. 1), we also observed drastic changes in the initial transients caused by the interaction of Mg and Ni/NiOx;

Finally, it will be highlighted that stabilization of the Ni/NiOx-modified Mg:SrTiO3 photocatalyst is obtained by photodeposition of CrOx from Cr(VI) containing solutions [4]. Enhanced stability is probably caused by electronic modification of Ni/NiOx as a severe influence of the back reaction of H2 and O2 was not observed for the process conditions used.

Finally, the general stability of SrTiO3 in aqueous environment will be discussed.

Thus, using state-of-the-art micro-GC analysis we were able to design a stable composite photocatalyst and improve the efficiency of the system (AQE) from 0.6% to >40%.
References
[1] B. Mei, K. Han, G. Mul, ACS Catal., 2018, 8, 9154-9164; [2] K. Han, T. Kreuger, B. Mei, G. Mul, ACS Catal., 2017, 7, 1610-1614; [3] K. Han, Y. Lin, C. Yang, R. Jong, G. Mul, B. Mei, ChemSusChem, 2017, 10, 4510 – 4516. [4] K. Han, B. Mei, et al., to be submitted
Pt-Zn Nanocube for Enhanced Mass and Specific Activities in Ammonia Electro-Oxidation Reaction (AOR)
Authors: Shao Minhua , Chan Yat Tung 
Published: February 2020

Many studies have revealed that only platinum and iridium can selectively oxidize ammonia to nitrogen, as the two combines a good dehydrogenation capacity with a sufficiently low affinity for the poison Nads [1]. While platinum is expensive, one effective approach to reduce platinum loading and increase catalytic activity is alloying platinum with other metals and forming binary or ternary alloys. In one research, Jiang [2] introduced zinc into platinum and iridium electrode by electrodeposition and demonstrated an increase of ammonia electro-oxidation reaction (AOR) catalytic activity.
In this study, Pt-Zn cubic nanoparticles were synthesized and loaded onto carbon black. The shape of Pt-Zn nanoparticles was mostly cubic illustrated by TEM images and the atomic ratio of Pt to Zn was around 4 to 1 according to ICP-OES. These Pt-Zn nanoparticles exhibited an improvement in AOR activity compared with cubic Pt nanoparticles and commercial Pt nanoparticles normalized to ECSA, termed specific activity, as shown in figure 1. The AOR peak current of Pt-Zn nanoparticles specific activity was 2.15*10-3 A/cm2 which is 1.1 and 17.1 times higher than cubic Pt and commercial Pt nanoparticles respectively. The possible reasons for increase of AOR activity will be discussed in detail.
Reference
[1] A. C. A. de Vooys, M. T. M. Koper, R. A. Van Santen and J. A. R. Van Veen, J. Electroanal. Chem., 2001, 506, 127–137.
[2] J. Jiang, Electrochemistry Communications, 75 (2017) 52-55.

Figure 1
(Invited) Development of High Performance Non-PGM Electrocatalysts and Electrodes for the Oxygen Reduction Reaction in Aemfcs
Authors: Peng Xiong , Kashyap Varchaswal , Kurungot Sreekumar , Mustain William E. 
Published: February 2020

Anion exchange membrane fuel cells (AEMFCs) have received significant attention in recent years as a potentially lower cost electrochemical energy conversion device compared to proton exchange membrane fuel cells (PEMFCs) [1]. In the past few years, several achievements have been made in terms of single cell performance, including power densities comparable to PEMFCs (~ 1.9 W cm-2)[2–4], and stability over hundreds of hours of operation[5,4], which are critical to the development and future deployment of AEMFCs. However, to make AEMFCs more economically competitive, or even favorable, with PEMFCs, it is crucial to discover non-PGM electrocatalysts for both the oxygen reduction reaction (ORR) and hydrogen oxidation reaction in AEMFCs that are able to achieve high power densities and long term operation.
Over the last decade, significant progress has been made in finding PGM-free catalysts for the ORR in alkaline media. However, an overwhelming majority of the tests with these materials have been done ex-situ using rotating disk electrodes (RDE), and these measurements and are not typically representative of the in-cell performance due to more complicated mass transport and reacting conditions. Hence, many highly active ex-situ catalysts have shown limited performance in operating AEMFCs. In this work, we studied two types of non-PGM electrocatalysts, including CoOx embedded in nitrogen-doped carbon (CoOx-N-C)[6] and classical Fe-N-C, for the ORR in AEMFCs. Not only was the ORR activity fully characterized using RDE and RRDE measurements, with both catalyst exhibiting excellent half-cell activity, but they were also incorporated into gas diffusion electrodes and studied in 5 cm-2 single cell AEMFCs. This study was able to show that PGM-free electrodes are able to support high performance (> 1.0 W cm-2), achievable current density and stability (>100 h). This work demonstrates a significant improvement in non-PGM electrocatalysts development and performance than previous work.

Reference:

[1] J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, et al., Energy Environ. Sci.
2014, 7, 3135–3191.
[2] L. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-González, R. Bance-Souahli, R. C. T. Slade, et al., Green Chem.
2017, 19, 831–843.
[3] T. J. Omasta, L. Wang, X. Peng, C. A. Lewis, J. R. Varcoe, W. E. Mustain, J. Power Sources
2018, 375, 205–213.
[4] T. J. Omasta, A. M. Park, J. M. LaManna, Y. Zhang, X. Peng, L. Wang, D. L. Jacobson, J. R. Varcoe, D. S. Hussey, B. S. Pivovar, et al., Energy Environ. Sci.
2018, 11, 551–558.
[5] W. E. Mustain, Curr. Opin. Electrochem.
2018, 1–7.
[6] xiong peng, T. J. Omasta, E. Magliocca, L. Wang, J. R. Varcoe, W. E. Mustain, Angew. Chemie Int. Ed.
2018, 1–7.
(Invited) Precious Metal-Free Electrocatalysis: Accomplishments and Challenges
Authors: Zelenay Piotr 
Published: February 2020

In this short presentation, we will concentrate on entirely precious metal-free electrocatalysts as potential alternatives to the incumbent platinum group metal (PGM) materials for electrochemical reactions occurring in acidic, relevant to the energy conversion and storage: (i) oxygen reduction reaction (ORR), (ii) hydrogen evolution reaction (HER) and, time permitted, (iii) hydrogen peroxide generation (“two-electron ORR”). In the first part of this presentation, we will offer a summary of the development of non-precious metal ORR catalysts, emphasizing in particular the approaches that aim at improving the ORR active-site density and understanding of the origins of electrocatalytic activity of non-precious metal catalysts in oxygen reduction as a prerequisite for further development of this class of catalysts. We will focus on metal-nitrogen-carbon (M-N-C) catalysts obtained via the high-temperature treatment of organic precursors of carbon and nitrogen and inorganic precursors of a transition metal, which have been under development at Los Alamos for over a decade and have consistently exhibited the highest ORR activity in both electrochemical-cell and fuel cell testing to date.
The second part of this presentation will be devoted to less frequently studied electrocatalysts based on small organic molecules as materials for hydrogen evolution reaction and hydrogen peroxide generation in a two-electron ORR. Unlike the oxygen reduction reaction catalysts in the first part of the talk, these HER/two-electron ORR catalysts are entirely metal-free and have been obtained by a low-temperature synthesis route. In addition to exhibiting a promising activity in electrochemical testing these catalysts show good performance durability over several days of continuous operation. The density functional theory (DFT) calculations have been performed to gain an insight into the reaction mechanisms of HER and two-electron ORR on various conformations of one selected organic molecule. The calculations have revealed thermodynamically favorable reaction pathways and structure-activity relationships, which can guide future synthesis of this new class of electrocatalysts.

Acknowledgements

Financial support of this research by the U.S. Department of Energy via Fuel Cell Technologies Office (FCTO) and by Los Alamos National Laboratory via Laboratory Directed Research and Development (LDRD) program is gratefully acknowledged.
(Invited) Shape-Controlled Multimetallic Nanoparticle Electrocatalysts
Authors: Roldan Cuenya Beatriz 
Published: February 2020

Alternatives to fossil fuels are actively being sought for the sustainable generation of energy with minimum environmental impact. Direct alcohol fuel cells are among the most promising clean energy supply devices. Nevertheless, the high cost and the low efficiency of the electrocatalysts difficult the commercialization of such devices. Thus, the replacement of Pt-based materials in fuel cells has received increasing attention over the past years.
In this talk I will describe the rational design of highly active and selective mono and multimetallic nanoparticle (NP) electrocatalysts with tunable exposed facets and composition. Examples include spherical Au NPs for 2-propanol oxidation, cubic Pt-Sn-Co NPs for ethanol oxidation and Pd cubes decorated with Cu and Sn for methanol and ethanol oxidation. Valuable mechanistic insights were obtained by combining different in situ spectro-electrochemical techniques and operando synchrotron methods, such as differential electrochemical mass spectrometry, Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption fine-structure spectroscopy.
(Invited) Materials/System Tradeoffs for Automotive Fuel Cell Applications
Authors: Gittleman Craig S , Kongkanand Anusorn 
Published: February 2020

Recent focus on materials R&D for proton exchange membrane fuel cells for automotive applications has been on lower cost materials such as non-PGM catalysts and non-fluorinated membranes. Other areas of focus have been on materials that can withstand specific failure modes, such as non-carbon supports that can withstand elevated potentials experienced during non-mitigated start-stop conditions. These materials, in nearly all cases, do not perform as well as Pt or Pt-alloy catalysts supported on high surface area carbons with perfluorinated membranes. This could lead to the incorporation of larger stacks, and therefore, more expensive systems.
This talk will focus on the system materials trade-offs that OEMs must consider when developing automotive FC systems. When designing a system, all high-level requirements including cost, performance, durability and robustness, must be considered. Performance metrics must include power density, efficiency and heat rejection. Power density and heat rejection and driven by high current density performance whereas efficiency is driven more by low current density performance. Durability issues include voltage degradation as well as failures that prevent a system from operating safely such as severe membrane crossover. Some of these metrics can be directly translated into cost. For example, power density and voltage degradation can be combined into an end-of-life power density requirement. This requirement can often be “bought” by adding more Pt. Other metrics, such as efficiency, time to membrane failure and robustness are less easy to “buy”.
This talk will discuss the materials trade-offs to optimize automotive fuel cell system requirements. We will discuss the how to determine the optimum Pt loading to minimize system cost. We will also discuss the trajectory and potential for non-PGM catalysts to reduce automotive fuel cell system costs. We will discuss the trade-offs regarding membrane thickness, where thinner membranes promote higher power density but reduced efficiency due to greater H2 crossover. We will discuss the tradeoffs for corrosion resistance catalyst supports, which are being developed to prevent degradation during start-start environments, but due to their inherent lower surface area and electrical conductivity ultimately limit fuel cell performance. There are system mitigation strategies that can be employed that may be less expensive than the added cost of a larger stack required to meet power density requirements. We will also discuss how all of these materials developments impact durability.