bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Versatility of Soluble Redox Active Polymers
Authors: Montoto Elena C. , Rodriguez-Lopez Joaquin
Published: February 2020

Organic redox-active materials offer advantages of material tunability while maintaining high performance for next-generation energy storage and conversion solutions. Macromolecular architectures such as polymers, colloids, and oligomers have recently gained interest for their size-exclusion capabilities. Redox Active Polymers (RAPs) have traditionally been electrochemically studied as films or composites [1], with few examples of solution-phase studies until recent years [2]. Soluble RAPs have begun emerging as viable active materials for energy storage solutions such as size-exclusion flow batteries [3-4]. Our laboratories have introduced several redox active motifs used as pendants on these soluble RAPs in recent years [3]. Their introduction into the field of energy storage as fluid energy carriers has elucidated some of their reactivity and applicability, yet detailed characterization of their complex charge transfer mechanisms and their interactions in solution and with catalytic and photocatalytic interfaces has not been fully addressed.

In this talk, I will highlight advances in characterizing the redox activity of these polymers and their behavior at electrode interfaces with the aim of using them as versatile redox fluids. I will also describe how their charge transfer mechanisms make them ideal for varied energy storage applications beyond size-exclusion redox flow batteries. The RAPs are evaluated using analytical techniques such as potential-controlled electrolysis, spectro-electrochemistry, and voltammetric methods including transient and steady-state methods. Additionally, comparisons to the small molecule counterparts of the RAP active units aid to understand the differences observed when redox active centers are tethered to a chain containing hundreds of pendants. I will discuss how this new type of soluble RAPs interact with energy conversion electrodes and how charge transfer and transport within RAP particles facilitates catalytic processes associated with energy storage.

[1] J. Am. Chem. Soc. 1978, 100, 4248.

[2] J. Am. Chem. Soc. 2018, 140, 2093.

[3] Acc. Chem. Res. 2016, 49, 2649.

[4] J. Am. Chem. Soc. 2014, 136, 16309.
Chromium Oxynitride Electrocatalysts for Electrochemical Synthesis of Ammonia Under Ambient Conditions
Authors: Yao Yao , Feng Qi , Li Jiadong , Zhu Shangqian , Yao Yuze , Wang Yajun , Wang Qi , Gu Meng , Wang Haijiang , Li Hui , Shao Minhua
Published: February 2020

The electrochemical synthesis of ammonia via N2 reduction reaction (NRR) has received much attention in recent years due to its promising advantages of being more environmentally friendly and less energy consuming than conventional chemical synthesis. However, as the theoretical potentials of hydrogen evolution reaction (HER) and NRR are very close on most catalysts, H2 is the dominant product due to the much faster reaction kinetics of HER, leading to low NRR Faradaic efficiency and ammonia formation rate. The DFT calculation indicates that the transition metal nitrides, such as VN, CrN, and ZrN, are promising candidates for NRR electrocatalysts.1-2

In this study, chromium oxynitride (CrO0.66N0.56) was synthesized and its NRR performance was evaluated in a proton exchange membrane electrolyzer (PEMEL) under ambient conditions. The schematic illustration of the PEMEL employed in this study is shown in Figure 1a. The highest ammonia formation rate of 8.9×10-11 mol s-1 cm-2 and Faradic efficiency of 6.7% were achieved, shown in Figure 1b, which is so far the best result reported among the non-noble metal-based electrocatalysts under similar conditions. Its performance is even higher than that of Pt/C and Pd/C.

Figure 1. a) The schematic illustration of the PEMEL device for the electrochemical synthesis of ammonia. b) The ammonia production rate and faradaic efficiency of chromium oxynitride at various potentials in a PEMEL device with ammonia water pretreated under room conditions.

References

(1) Abghoui, Y.; Skulason, E., J. Phys. Chem. C
2017, 121, 6141-6151.

(2) Abghoui, Y.; Garden, A. L.; Hlynsson, V. F.; Björgvinsdóttir, S.; Ólafsdóttir, H.; Skúlason, E., Phys. Chem. Chem. Phys.
2015, 17, 4909-4918.

Figure 1
Twisty Pd-Au Nanowires for Highly Selective and Active CO2 electrochemical Reduction
Authors: Zhu Shangqian , Shao Minhua
Published: February 2020

The continuous increase of CO­2 concentration in the atmosphere would potentially bring catastrophic global climate changes, which is one of the most urgent issues of the society. CO2 electrochemical reduction (CO2RR) is promising in simultaneously controlling the CO2 concentration and store renewable energy. However, selectively producing valuable chemicals and fuels with reasonable low overpotentials is quite difficult.

In this study, Pd and Pd-Au nanowires with a varied composition were synthesized. The nanowires have a twisty morphology with a lot of grain boundaries. For the first time, highly selective CO2-to-CO electrocatalytic conversion with low overpotentials was achieved on Pd-based nanocatalysts. All the synthesized nanowires exhibited significantly improved CO selectivity as compared to commercial Pd nanoparticles (Figure 1). At -0.6 V, a maximum faradaic efficiency over 94% can be obtained on Pd0.8Au nanowires. CO can also be detected with a faradaic efficiency of 8.5% at an overpotential of merely 90 mV. The Pd-Au nanowires have superior mass and specific activities, which are highly dependent on the composition. In situ infrared spectroscopic studies with an attenuated total reflection configuration (ATR-IR) was conducted to reveal the combined structure and composition impacts on the activity. It was found that *CO could be more easily generated at much lower overpotentials on nanowires as compared to that on particles. Additionally, the alloying between Pd and Au would generate more linearly-bonded *CO, which is more facile to desorb and results in an improved reaction rate.

Figure 1. Faradaic efficiency of CO measured on Pd/C, synthesized Pd and Pd0.8Au nanowires.

Figure 1
Enhancement of Electrocatalytic Reduction of Carbon Dioxide at Electrodes Modified with Highly-Acidic Mixed-Metal-Oxide Films
Authors: Rutkowska Iwona Agnieszka , Kulesza Pawel J.
Published: February 2020

Electroreduction of carbon dioxide to simple organic fuels and chemicals is a topic of growing scientific and technological interest. The reaction provides means for both reducing emissions of CO2 into atmosphere and storing renewable energy. The presentation will address low-temperature CO2-conversion processes based on electrocatalytic and photoelectrochemical approaches. Among important issues are choice of the catalytic or semiconducting materials, their morphology and operating conditions including temperature, solvent, electrolyte, pH etc. There is a need to improve the reaction dynamics and selectivity toward specific products. In practical electrolysis cells, the CO2-reduction (at cathode) is accompanied by water oxidation (at anode or photoanode).

Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. It is often postulated that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. In this respect, the proton availability and its mobility at the photo(electro)chemical interface has to be addressed. On the other hand, competition between such parallel processes as hydrogen evolution and carbon dioxide reduction has also to be considered.

Recently, mixed oxide systems stabilized through Zr-O-W bonds have been demonstrated to be very attractive acid catalysts exhibiting high catalytic activities and good stabilities in many demanding industrial reactions. The mixed WO3/ZrO2 systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Cu electrocatalytic nanoparticles over, under or within, such active WO3/ZrO2 matrices, the electrocatalytic activities of the respective systems toward the reduction of carbon dioxide have been significantly enhanced even at decreased loadings in acid media. The enhancement effects should be attributed to features of the mixed metal oxide support such as porosity and high population of hydroxyl groups (due to presence of ZrO2), high Broensted acidity of sites formed on mixed WO3/ZrO2, fast electron transfers coupled to unimpeded proton displacements (e.g. in HxWO3), as well as strong metal-support interactions between nanosized metals (Cu) and the metal (W,Zr) oxo species.

Application of the hybrid system composed of both above-mentioned oxides resulted in high current densities originating from electroreduction of carbon dioxide mostly to methanol (CH3OH) as demonstrated upon identification of final products.
Kinetic Monte Carlo Simulation of CO2 Electroreduction Cascade
Authors: Chavan Kanchan Suklal , Matanovic Ivana , Calabrese Barton Scott
Published: February 2020

Capture of CO2 and conversion into useful chemicals can alleviate atmospheric buildup and provide an alternative source of chemical building blocks. CO2 can be reduced electrochemically to small chain carbon molecules (C1-C3) like CO, ethylene, formic acid, methane and alcohols.1 Integrating multiple catalytic sites on an electrode surface enables further reduction to higher value hydrocarbons.

In this work, we describe kinetic Monte Carlo (kMC) simulations of CO2 reduction to ethane on an integrated catalytic electrode surface. Electrode surface incorporates two catalyst sites, which may include molecular catalytic structures or tethered metal complexes.2 The catalytic mechanism at each active site, as well as adsorption and transport of intermediates between sites, is considered in the overall model. Monte Carlo simulation allows inclusion of both kinetic and transport events whose time scales span multiple orders of magnitude.3 Channeling of intermediate transport between active sites via Van Der Waals, electrostatic, and ligand-exchange interactions is considered. We predict the effect of catalyst loading and composition on overall cascade efficiency, a defined by ethane yield.

References

R. J. Lim, M. Xie, M. A. Sk, J.-M. Lee, A. Fisher, X. Wang, and K. H. Lim, Catal. Today, 233, 169–180 (2014) doi:10.1016/J.CATTOD.2013.11.037.

A. S. Varela, N. Ranjbar Sahraie, J. Steinberg, W. Ju, H.-S. Oh, and P. Strasser, Angew. Chemie Int. Ed., 54, 10758–10762 (2015) doi:10.1002/anie.201502099.

M. Stamatakis and D. G. Vlachos, ACS Catal., 2, 2648–2663 (2012) doi:10.1021/cs3005709.
Electrodeposition of Graded Metal Coatings on Spherical Mandrels
Authors: Peters Vanessa N. , Horwood Corie , Bhandarkar Neal , Stadermann Michael , Bunn Thomas
Published: February 2020

Inertial confinement fusion energy research at the National Ignition Facility (NIF) requires the fabrication of hollow metal spherical capsules for the laser-driven fusion reaction. These sub-millimeter diameter capsules must have perfect coating uniformity and a specific gradient density, achieved by plating two metal elements with graded composition. We are investigating electrodeposition to produce hollow metal spheres as opposed to other deposition techniques (i.e. physical vapor deposition, film casting, etc.), because electrodeposition coats faster, more smoothly, with good thickness uniformity, and better grain size control.

Electroplating metals on spheres presents its own specific challenges; the spherical samples must make contact with the electrified cathode, but must also remain in motion during plating to ensure an even coating. Additionally, electroplating on hollow spheres also involves the challenge of keeping the sphere submerged in the electrolyte. These issues were mitigated by enclosing the mandrel in an electrified cage which the electrolyte is flown through, resulting in intermittent contact of the mandrel with the cathode and a continuous flow of fresh electrolyte to the mandrel surface while plating.

We have developed several approaches for electroplating alloys[1] and density gradients on metal spherical mandrels. We will present results from a parametric study that improved coating uniformity, obtained desired thickness, and achieved the required density gradients during electrodeposition.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM Release Number: LLNL-ABS-748349

[1] C. Horwood, M. Stadermann, T.L. Bunn, Metal Alloy ICF Capsules Created by Electrodeposition, Fusion Sci. Technol. 73 (2018) 335–343. doi:10.1080/15361055.2017.1387458.
Electrochemical Evidence of Formation of the Quinizarin-β Cyclodextrin Complex in Aqueous Solution
Authors: Guzmán-Hernández Dafne Sarahia , Rivas-Sanchez Alma Karina , Romero-Romo Mario Alberto , Palomar-Pardavé Manuel , Corona-Avendaño Silvia , Ramirez-Silva Maria Teresa
Published: February 2020

Quinizarin (Qz) is 1,4-dihydroxy-9,10-anthraquinone, exhibiting important potential applications in medicine. However, this molecule typically exhibits low water solubility at room temperature. Recently, the supramolecular host–guest interactions have been the subject of very active research due to their wide spread applications in various areas like pharmaceuticals, sensors, etc. Cyclodextrins (CDs) have been the most extensively investigated due to their higher solubility in aqueous medium. This work proposes the use of β-cyclodextrin (β-CD) to increase the Qz´s solubility through a study carried out via cyclic voltammetry recorded over a carbon paste electrode (CPE) vs Ag/AgCl: the potential sweep started at −0.1 V in the anodic direction at 0.1 Vs−1 rate. The switching potential was recorded in −0.980 V at pH 12.794, in the CPE/66 µM Qz system. Quinizarin (Qz) cyclic voltammetry presented a sharp reduction peak at −0.756 V, with increasing β-CD concentration that evidences the formation of second reduction peak in such a way that the Qz now presents two sharp reduction peaks at −0.895 V and −0.683 V. The formation of a second reduction peak and the potential shift to more positive values is indicative of the of formation of the quinizarin-β cyclodextrin complex in aqueous solution.
Electrochemical Deposition of Alkaline-Earth Elements (Sr and Ba) into Liquid Metals in Molten LiCl-KCl-SrCl2-BaCl2 salt
Authors: Kim Hojong , Lichtenstein Timothy , Smith Nathan
Published: February 2020

Electrochemical deposition of Sr and Ba into liquid metals (Bi and Sb) was investigated in LiCl-KCl-SrCl2-BaCl2 electrolytes at 500–650 °C as a means to separate stable alkaline-earth ions from the molten salts (eutectic LiCl-KCl) utilized for recycling used nuclear fuel. Considering the higher stability of Sr and Ba ions relative to the Li and K ions in the chloride system, it would seem impractical to deposit Sr and Ba from the molten chloride solutions by electrochemical means; however, this work will present that the deposition of Sr and Ba into liquid metal electrodes becomes thermodynamically feasible by leveraging the strong chemical interactions between alkali/alkaline-earth metals and liquid metals.

The thermodynamic properties of four binary alkaline earth-liquid metal alloys, (Sr, Ba)-(Bi, Sb), were determined by electromotive force (emf) measurements using solid-state electrolytes to examine the degree of chemical interactions (activity) between alkaline-earth metals and liquid metals. Using a pure alkaline-earth metal A (A = Sr or Ba) as the reference electrode and binary A-B alloys (B = Bi or Sb) as working electrodes in solid-state binary CaF2-AF2 electrolyte, emf measurements were conducted over a temperature range of 450–850 °C in 25 °C increments. Reproducible emf values were obtained within ±5 mV accuracy during cooling-heating cycle at alloy mole fractions up to x
A(in B) = 0.40. Based on the experimentally determined emf values of alkaline-earths in liquid Bi and Sb electrodes, the electrode reactions involving Sr and Ba elements were found to be thermodynamically feasible due to substantially larger emf values of Sr and Ba in Bi, compared to those of Li and K in Bi. Namely, the chemical interactions of liquid metals (Bi and Sb) were stronger for alkaline-earths (Sr and Ba) than for alkali (Li and K) metals.

Based on thermodynamic measurements, the liquid metal electrodes were subjected to cathodic discharge at a constant current density of 50 mA cm–2 in eutectic LiCl-KCl with the addition of 5–10 mol% of SrCl2 and/or BaCl2. As shown in Figure 1, the use of liquid metals (Bi and Sb) resulted in the deposition of Ba in LiCl-KCl-10mol%BaCl2 electrolyte. Further study in LiCl-KCl-SrCl2-BaCl2 electrolytes also indicated that the use of strongly interacting liquid metal electrodes could result in the co-deposition of Sr and Ba in addition to Li. The results of this work show that alkaline-earth fission products (Sr2+ and Ba2+) accumulated in molten salts can be recovered into liquid metals by electrochemical separation, which could be employed as a critical step for recycling the process salt (LiCl-KCl) in order to minimize the generation of additional nuclear wastes.

Figure 1. Cross-section analyses of Bi (discharged at 510 °C) and Sb (discharged at 650 °C) electrodes under constant current density at 50 mA cm–
2 in LiCl-KCl-10mol%BaCl2 electrolyte, using SEM and elemental X-ray mapping.

Figure 1
Water and Proton Concentration Affects the Electrocatalytic Conversion of Carbon Dioxide in Ionic Liquids
Authors: Shaw Scott K , Hailu Amanuel
Published: February 2020

We report efforts to carry out the reduction of CO2 in mixtures of imidazolium based RTIL in water (H2O) as functions IL:H2O solution ratio and solution pH. IL electrolytes are expensive (relative to water) and many are hydroscopic. Development of CO2 reduction methods based on electrolytes tolerant of significant amounts of water is desirable for large-scale processes. Further, optimization of solution conditions will allow reduced over-potentials, suppression of the competing hydrogen evolution reaction (HER), increases in diffusion rate of dissolved carbon dioxide, and overall improved current efficiencies. In this work we discuss the varying concentration and source of protons in the context of results obtained by carrying out the CO2 reduction in aqueous/IL solutions at various pH values.
Electrochemical Synthesis of Chromium Borides in Halide-Oxide Melts
Authors: Ashinova Oksana , Kushkhov Hasbi , Ligidova Marina , Shogenova Madina
Published: February 2020

The work is devoted to investigation of electrochemical synthesis of chromium borides from halide-oxide melts. In this paper results of synthesis of chromium borides from halide-oxide melts is presented. Cyclic voltammetry and potentiostatic electrolysis were chosen by method of investigation of chromium and boron-ions electroreduction processes. Electrochemical synthesis of chromium borids by joint electroreductioon of chromium and a boron ions in halide –oxidie melts NaCl-KCl-K2Cr2O7-KBF4 melt is carried out.

Investigation of a mechanism of bichromate ions electroreduction in NaCl-KCl-K2Cr2O7 melt have been conducted by method of a cyclic voltamperometriya at different concentration of potassium bichromate. The optimal parameters of electrolysis process is established: electrolysis potential, temperature of process, duration of electrolysis. Syntheses powders of chromium borides were identified by X-Ray methods.
Ionic Liquids As Property Modifiers in Additive Manufacturing
Authors: Etheredge A W , Ellett T R , Poole G M , Reichert William Matthew
Published: February 2020

In recent years, the popularity of additive manufacturing, also known as 3-D printing, has grown exponentially. One research path in this field is the ability to change the properties on the “printed” object beyond those of the original polymer. Therefore, a means to control the properties of these materials is needed. Ionic liquids can provide this means. With the ability to tune the properties of an ionic liquid to meet process requirements, one can create uniquely functionalized materials or improve the properties of the polymer. For instance, previous work in combining polymer chemistry with ionic liquids has shown that ionic liquids can contribute to the various properties of polymeric materials, whether as plasticizers, thermal properties modifiers, or as co-polymers.1,2,3 By combining ionic liquids with current stereo-lithography (SLA) printing techniques, one can create materials with a wide range of thermal and tensile properties. In this presentation, we will discuss our work on using ionic liquids as modifiers in additive manufacturing using stereo-lithography techniques, including their effects on the physical properties, such as tensile strength and flame resistance, and the chemical properties, such as reactivity, of the “printed” materials. We will also discuss the use of ionic liquids as co-polymers in SLA printing and the properties of these co-polymeric materials. The composition, properties, and performance of these materials will be evaluated by SEM, tensile testing, DSC, TGA, IR spectroscopy, and mass spectrometry. With the increasing interest in 3-D printing, this work highlights the impact ionic liquids can have on this emerging technology.

Scott, M. P.; Brazel, C. S.; Benton, M. G.; Mays, J. W.; Holbrey, J. D.; Rogers, R. D. Chem. Commun.
2002, 1370.

Rahman, M.; Brazel, C. S. Polymer Degradation and Stability
2006, 91, 3371.

Hong, K.; Zhang, H.; Mays, J. W.; Visser, A. E.; Brazel, C. S.; Holbrey, J. D.; Reichert, W. M.; Rogers, R. D. Chem. Commun.
2002, 1368.
Investigating Processes Occurring in Acoustically Levitated Ionic Liquid Droplets
Authors: Duranty Edward R. , Jacoby Seth A. , Davis James H.
Published: February 2020

Chemical processes that occur in small volume containers have many benefits that have only recently become apparent. Containers such as thin films, compartments within microfluidic systems, and droplets require small amounts of solvent and therefore provide an inherently green alternative to reactions that take place in typical laboratory containers. Additionally, reactions that take place in small volumes seem to improve the rates of processes ranging from simple syntheses to protein folding. This increase in rate is attributed to increased surface area availability, rapid reagent mixing times, and increased heat transport properties as compared to the bulk. Acoustic levitation is a popular technique for the suspension of small volumes, most commonly droplets, in a “contact-free” container that preserves the large droplet surface area, a leading contributor to increased chemical activity.

In our laboratory we are coupling acoustic levitation and droplet chemistry with ionic liquids which are rapidly becoming the solvent of choice for many systems. This increased popularity is primarily due to their unique “tunability” and their low vapor pressures. Thus far we have reproducibly levitated 10μL droplets of deionized water, aqueous calcium hydroxide, toluene, and most interestingly the ionic liquid 1-butyl-1methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-BTI) using an acoustic levitation device reported in the literature as a “TinyLev.” We have currently measured droplet lifetimes for aqueous solutions near 30 minutes, 15 minutes for toluene, and approximately 2 weeks for BMP-BTI. These preliminary results suggest that ionic liquids may be suitable acoustically-levitated droplets and we are currently working to develop a technique for probing the interactions and structure of solutes within an ionic liquid solvent via laser light scattering.

Figure 1
Understanding the Doping Effects on the Co Oxides for the Water Oxidation
Authors: Kim Byunghoon , Park Inchul , Kang Kisuk
Published: February 2020

Electrochemical water splitting provides sustainable means of generating hydrogen fuel, a carbon-free alternative for fossil fuels. The bottleneck in proceeding water splitting reaction is the sluggish kinetics of the oxygen evolution reaction (OER), resulted from its complex four-electron pathway. While precious metal oxide-based materials such as IrO2 and RuO2 deliver superior catalytic activity toward OER, their scarcity and high cost is not appropriate for the large-scale commercialization. In this respect, earth-abundant, first-row (3d) transition metal oxides have been of recent interest.1 As an effective strategy to enhance the activity of 3d metal based catalysts, great efforts have been dedicated to multi-metal systems. Exploiting large diversity of metal compositions, various multi-metal oxides-based catalysts have been reported, including Ni-Fe, Co-Fe, Ni-Co, and ternary oxides/oxyhydroxides.2 Among them, Fe-containing Co and Ni based oxide-based catalysts have known to be most active toward OER in alkaline electrolyte.3 Despite the substantial research efforts to unveil the origin of improved activity of Fe-containing Co and Ni oxide-based catalysts, one of the most important task that still remains unsolved is the accurate determination of catalytic active sites and their reaction mechanism at the atomistic scale.

In this work, we present a theoretical study on the electrocatalytic properties of pristine and transition metal (Fe, Ni, and Mn)-substituted Co oxides. Through the exhaustive consideration of oxygen sites in the vicinity of dopants, the prediction of the active sites and reaction mechanism is provided. The OER mechanisms estimated for the terminal sites of dopant and neighboring Co cations, and for the bridge site are introduced in detail. Notably, it is demonstrated that the bridge site which has been generally considered inactive for OER can be activated by Fe incorporation. We further investigate the structural properties of the relevant intermediates. With the structural analyses, we propose that the modulation of hydrogen bonding distance induced by the Jahn-teller active Fe(IV) cation leads to the activation of the bridge site. Finally, with the comprehensive view of estimated OER thermodynamics, we suggest an origin of improved OER performance of the Fe-containing Co oxide-based catalysts. We believe that our findings establish theoretical deign rule of Co based multi-metal oxide-based catalysts, and propose a viable strategy to resuscitate catalytic activity of inert sites by the structural modulation through cation doping.

Reference

P. et al. Energy Environ. Sci. 5, 6012 (2012).

N.T. et al. Chem. Soc. Rev.
46, 337 (2017).

C.L. et al. J. Am. Chem. Soc.
137, 4347 (2015).
(Invited) The Benefits of Nanoscale Metal Oxide Films to Solar Fuels Research
Authors: Steier Ludmilla , Durrant James
Published: February 2020

Though the field of photoelectrochemical (PEC) solar fuel production focuses on a broad variety of materials, metal oxides are probably the most commonly employed materials in state-of-the-art photoelectrodes. Metal oxides such as bismuth vanadate and hematite are currently intensely studied as photoanode materials in our group and by the PEC water oxidation community.1-4 Stable metal oxides such as TiO2 have been successfully employed as protection layers in, for example, Cu2O photocathodes and are now advancing the field of organic photocathodes for hydrogen evolution.5, 6 Especially metal oxides grown by atomic layer deposition (ALD) offer many benefits to solar fuel research such as i) precise growth control on the atomic scale ii) conformal and pinhole-free coatings and ii) formation of high-quality interfaces. In our studies of recombination losses, we benefit from high-quality ALD hematite films and are able to gain new insights from electrochemical impedance spectroscopy that will be reported here. Furthermore, we could demonstrate stable organic photocathodes for hydrogen evolution and will report on new organic photocathode designs employing ALD TiO2 electron selective layers.6 Finally, I will discuss the importance of ALD surface treatments in the science of CO2 reduction.7

Le Formal, F.; Pastor, E.; Tilley, S. D.; Mesa, C. A.; Pendlebury, S. R.; Gratzel, M.; Durrant, J. R. Rate Law Analysis of Water Oxidation on a Hematite Surface. Journal of the American Chemical Society
2015, 137, 6629-6637.

Mesa, C. A.; Kafizas, A.; Francas, L.; Pendlebury, S. R.; Pastor, E.; Ma, Y. M.; Le Formal, F.; Mayer, M. T.; Gratzel, M.; Durrant, J. R. Kinetics of Photoelectrochemical Oxidation of Methanol on Hematite Photoanodes. Journal of the American Chemical Society
2017, 139, 11537-11543.

Ma, Y. M.; Mesa, C. A.; Pastor, E.; Kafizas, A.; Francas, L.; Le Formal, F.; Pendlebury, S. R.; Durrant, J. R. Rate Law Analysis of Water Oxidation and Hole Scavenging on a Bivo4 Photoanode. Acs Energy Letters
2016, 1, 618-623.

Ma, Y. M.; Kafizas, A.; Pendlebury, S. R.; Le Formal, F.; Durrant, J. R. Photoinduced Absorption Spectroscopy of Copi on Bivo4: The Function of Copi During Water Oxidation. Advanced Functional Materials
2016, 26, 4951-4960.

Luo, J. S.; Steier, L.; Son, M. K.; Schreier, M.; Mayer, M. T.; Gratzel, M. Cu2o Nanowire Photocathodes for Efficient and Durable Solar Water Splitting. Nano Letters
2016, 16, 1848-1857.

Steier, L.; Bellani, S.; Rojas, H. C.; Pan, L. F.; Laitinen, M.; Sajavaara, T.; Di Fonzo, F.; Gratzel, M.; Antognazza, M. R.; Mayer, M. T. Stabilizing Organic Photocathodes by Low-Temperature Atomic Layer Deposition of Tio2. Sustainable Energy & Fuels
2017, 1, 1915-1920.

Schreier, M.; Heroguel, F.; Steier, L.; Ahmad, S.; Luterbacher, J. S.; Mayer, M. T.; Luo, J. S.; Gratzel, M. Solar Conversion of Co2 to Co Using Earth-Abundant Electrocatalysts Prepared by Atomic Layer Modification of Cuo. Nature Energy
2017, 2.
Enhanced Perovskite Electrocatalysis By Cation Deficiency and Strain Control
Authors: Choi Min-Ju , Jang Ho Won
Published: February 2020

Increasing energy demand, fossil fuel depletion, and environmental issues require sustainable and efficient energy sources. Hydrogen produced by water splitting is one of the promissing candidates, and electrocatalysts can help to reduce overpotential of the reaction. Electrocatalytic activity can be improved by increasing number of active sites and intrinsic activity. Tuning cation deficiency and strain can enhance intrinsic activity. Here, we explore how cation deficiency and strain can affect electrocatalysis.

Noble metals are representative electrocatalysts, but they are expensive and unstable during oxygen evolution reaction (OER) in alkaline solution. Therefore, new materials for water splitting such as transition metal oxides are needed. Perovskite oxides have been actively studied because of their excellent catalytic activity, attractive physical-chemical properties, low cost, and non-toxicity.

To investigate the effect of La-site deficiency, epitaxial La1-xNiO3-δ (x=0, 0.05, 0.1, 0.15) thin films were deposited on NdGaO3 substrates by pulsed laser deposition (PLD) method. The structural information of each film was verified by X-ray diffraction peaks in θ-2θ scans, Raman spectroscopy and X-ray linear dichroism (XAD) measurements. Each of La-site deficient samples were electrochemically characterized. To compare the effect of La-site deficiency and strain, which can induce eg orbital polarization, an epitaxial La0.95NiO3-δ thin films were grown on a different lattice parameter substrates ranging in lattice parameter from 3.69 to 3.947 Å. They were also characterized physically and electrochemically. Based on experimental results, cation deficiency and strain can cause the eg orbital polarization. Both can control the metal-oxygen bond strenth and improve catalytic activity.
(Invited) Metal-Organic Framework-Metal Oxide Composite for Solar Water Splitting
Authors: Yang Hui , Wu Nianqiang
Published: February 2020

The metal-organic framework (MOF) has been deposited on metal oxide surface layer-by-layer. The synthesis of MOF-inorganic oxide composite has been optimized. The optimized MOF-oxide composite has been used in a photoelectrochemical cell for solar water splitting. The composite shows much higher photocurrent density than the metal oxide alone.
(Invited) Rationally Designed Metal Nanoclusters for Electrocatalytic Hydrogen Production
Authors: Lee Dongil
Published: February 2020

The theoretically predicted volcano plot for hydrogen production shows the best catalyst as the one that ensures that the hydrogen binding step is thermodynamically neutral. However, the experimental realization of this concept has suffered from the inherent surface heterogeneity of solid catalysts. It is even more challenging for molecular catalysts because of their complex chemical environment. In this presentation, I report that the thermoneutral catalyst can be prepared by simple doping of a platinum atom into atomically precise gold nanoclusters such as Au25(SR)18 and Au38(SR)24, where SR is a thiolate ligand. The catalytic activity of the resulting bimetallic nanocluster for the hydrogen production is found to be significantly higher than reported catalysts. It is even better than the benchmarking platinum catalyst. The bimetallic metal nanoclusters represent a new class of catalysts that bridge homogeneous and heterogeneous catalysis and provide a platform for the discovery of finely tuned catalysts for hydrogen production from water. Studies of electrocatalysis by the bimetallic nanoclusters provide many important design principles for the development of electrocatalysts with tailored cluster structure and adsorption energy. These principles are illustrated with nanocluster-based electrocatalysts for water splitting and CO2 conversion.
Anodized Hematite Nanostructures and Their Electrochemical Properties for Photoelectrochemical Water Splitting
Authors: Rosas-Barrera Kevin Leandro , Pedraza Julio Andrés , Reguera Edilso , Acevedo-Peña Prospero
Published: February 2020

Photoelectrochemical (PEC) water splitting using semiconductor electrodes has received much attention in the last decades. In this sense, hematite photoanode has appeared as a good candidate due to it is synthetized from cheap and abundant elements, non-toxicity and has a band gap of 2.1 eV that permits the absorption of visible light (Sivula, Le Formal, & Grätzel, 2011). However, their transport properties change drastically depending of synthesis method employed and the different morphologies obtained (Horiz et al., 2016). In this study, we report the electrochemical growth of hematite (α-Fe2O3) nanostructures by anodization process of carbon steel substrates in an ethylene glycol based medium. The influence of experimental parameters including the NH4F concentration, anodization time and applied voltage were systematically investigated to study their electrochemical properties. The obtained films were heat treated to 500 ºC to obtain the hematite crystalline phase. The crystalline phase was determined using an X-ray diffraction and Raman spectroscopy. FE-SEM images of the hematite nanostructures films provided morphological parameters. Photoelectrochemical characterization was achieved through OCP, LSV, CA and EIS procedures. A hard dependence between the synthesis variables and their photoelectrochemical properties for water splitting reaction was observed.

Horiz, N., Tamirat, A. G., Rick, J., Dubale, A. A., Su, W.-N., & Hwang, B.-J. (2016). Using hematite for photoelectrochemical water splitting: a review of current progress and challenges. Nanoscale Horizons, 1, 243–267. https://doi.org/10.1039/c5nh00098j

Sivula, K., Le Formal, F., & Grätzel, M. (2011). Solar water splitting: Progress using hematite (α-Fe2O3) photoelectrodes. ChemSusChem, 4(4), 432–449. https://doi.org/10.1002/cssc.201000416
TiO2-RuO2 Based Photoanodes for Photoelectrochemical Applications Using Visible Light
Authors: Carrera-Crespo J. Edgar , Vázquez-Arenas Jorge G. , Romero-Ibarra Issis
Published: February 2020

TiO2 nanotube arrays (TNTs) are interesting photoanodes with potential use in photoelectrochemical applications, such as hydrogen production and degradation of water pollutants, due to its low fabrication cost, chemical stability, high specific surface area, photosensitivity, and catalytic potential. Moreover, high ordered nanotubular structures can be obtained through anodization process of a titanium film. This 1-D geometry facilitates the unidirectional transport of photogenerated charge carriers, diminishing the recombination of electron-hole pairs. However, the major drawback for the practical use of TiO2 is its wide band gap (3.2 and 3.0 eV for anatase and rutile phase, respectively), making it only sensitive to UV light, which carries about 4% power of sunlight. For expanding the sensitivity of the TiO2 nanotubes towards the visible region, which is the 45% of the solar spectrum, several strategies have been carried out such as surface modification with narrow band gap semiconductors. Moreover, the methodology used to synthesize the semiconductor on the TNTs has a great impact in the photoelectrochemical performance of the photoelectrode. For this reason, in this work the modification of TNTs with RuO2 employing a hybrid strategy is proposed, consisting in the electrodeposition of Ru and its subsequent thermal oxidation. The characterization of the semiconductor, electrical and optical properties, as well as photoelectrochemical evaluation of the TNTs-RuO2 are in progress.
Metal-Free Dyes Based on Piperidine-Substituted Perylene-Monoanhydride Derivatives As Sensitizers in ZnO-Based DSSCs
Authors: Canto Aguilar Esdras Josué , Guitiérrez Moreno David , Sastre-Santos Ángela , Fernández-Lázaro Fernando , Mori Shogo , Oskam Gerko
Published: February 2020

The dye sensitized solar cell (DSSC) is a third generation photovoltaic technology with conversion efficiencies as high as 14 %, which has been achieved through the optimization of the cell components and a better understanding of the mechanisms of charge generation and recombination processes involved in the solar cell functioning. The selection of the most promising components (e.g., the film material, the dye and the redox couple) related with their single properties is the starting point in the efficiency improvement process. Based on this observation, ZnO is one of the most promising alternatives to replace TiO2 as electron transporting material in the DSSCs, this due to its higher electron mobility (comparing with TiO2), where the ZnO-organic dyes combination promises an increase in the overall efficiency of the solar device.

Poor chemical stability of ZnO (compared to TiO2) during the sensitization process has been reported as an important efficiency-limiting factor in ZnO-based DSSCs, related to the "acidic" character of the groups through which the molecule binds to the surface of the material. Piperidine-substituted perylene-monoanhydride derivatives not only show light absorption in a wide range of the electromagnetic spectra and high molar extinction coefficients, making them attractive molecular absorbers for this application, but also show to be a factible route to overcome the stability issue associated to the ZnO, anchoring the molecule at the semiconductor surface through the rupture of the anhydride moiety. In this work we study the suitability of sensitizers based on piperidine-substituted perylene-monoanhydride derivatives to interact with ZnO (evaluating their ability to show "aggregation"), and their performance in photovoltaic devices related to the optical and energetic features of these molecules, determined by spectroscopic and electrochemical techniques.
Photocatalytic Oxigen Production Using Nitroprussides Derived Materials
Authors: Diaz Lujan Alfredo , Reguera Edilso , Acevedo-Peña Prospero
Published: February 2020

Energy and environmental concerns related to the use of fossil fuels have forced researchers to seek renewable and clean energy resources. The demand of this energy encourages to study artificial photosynthesis, in which high-energy compounds are produced from water as an electron donor, by utilizing solar energy [1,2,5]. In a quest to develop sustainable energy conversion processes, many research groups have attempted water splitting using sunlight, which occurs in two processes: water oxidation or oxygen evolution reaction (OER) and water reduction or hydrogen evolution reaction (HER). However, oxidation of water to produce O2 is challenging from both thermodynamic and kinetic points of view, and thus, this process is considered too important for water splitting [3,4]. It is important to study the catalytic activity of different catalysts, especially when using sustainable and cheaper semiconductors for the oxidation of photoactivated water.

This work presents the synthesis, characterization of catalysts derived from nitroprussides as new materials for photocatalytic for oxygen evolution reaction [5]. Our attempts to use electrocatalysts derived from Nitroprussides (Np) M[Fe(CN)5NO] where M = Fe2+, Mn2+, Co2+ and Ni2+, in photocatalytic water oxidation (pH 7.2) using [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a sensitizer and Na2S2O8 as an electron acceptor [2], will be discussed in this presentation.

References:

[1] Mohammad Mahdi Najafpour, Spideh Madadkhani, Mojtaba Tavahodi, Manganese oxides supported on nano-sized metal oxides as water-oxidizing catalysts for water-splithing systems: 3-Electrochemical studies, International Journal of Hydrogen Energy 42 (2017) 60-67.

[2] Yusuke Yamada, Kohei Oyama, Rachel Gates, and Shunichi Fukuzumi. High Catalytic Activity of Heteropolynuclear Cyanide Complexes Containing Cobalt and Platinum Ions: Visible-Light Driven Water Oxidation. Angew. Chem. Int. Ed. 2015, 54, 5613 –5617.

[3] Mingxing Chen, Yizhen Wu, Yongzhen Han, Xiaohuan Lin, Junliang Sun, Wei Zhang and Rui Cao. An Iron-based Film for Highly Efficient Electrocatalytic Oxygen Evolution from Neutral Aqueous Solution. ACS Appl. Mater. Interfaces 2015, 7, 21852−21859.

[4] Sara Goberna-Ferroń, WillintonY.Hernańdez, BarbaraRodríguez-García, and José Ramoń Galań-Mascaroś. Light-Driven Water Oxidation with Metal Hexacyanometallate Heterogeneous Catalysts. ACS Catal. 2014, 4, 1637−1641.

[5] L. Reguera, J. Balmaseda, C.P. Krap, and E. Reguera, Hydrogen Storage in Porous Transition Metals Nitroprussides, J. Phys. Chem. C2008, 112, 10490-10501.
(Invited) Redox-Active Organic Electrode Materials for Safe Energy Storage
Authors: Yao Yan
Published: February 2020

The rapidly growing markets of electric vehicles (EVs) and grid integration of renewable energy sources have triggered demand for batteries with unprecedentedly low cost, high specific energy, and good safety. Organic electrode materials (OEMs) feature sufficiently high energy, Earth-abundant elements, and unique electrolyte-dictated properties. In this talk we start with the charge storage mechanism of modern OEMs with an emphasis on comparison with those of intercalation inorganic compounds and previous-generation OEMs (conducting polymers). The storage mechanism determines the reaction reversibility, redox potential, and specific capacity of modern OEMs. We then perform a head-to-head comparison of selected OEMs and classes of inorganic materials intensively studied to target high-energy EV batteries. An analysis of the synthesis of state-of-the-art OEMs from possible biomass and petrochemicals follows to assess the short-/long-term resource availability. Finally, we present recent examples where the structural versatility and suitable redox potentials allow OEMs to be custom-designed for aqueous and all-solid-state batteries and achieve unprecedented cycling stability and high specific energy.
Application of Cyclic Thermal-Oxidized IrOx Electrode in pH Detection of Interface Region of Zn/Steel Galvanic Process
Authors: Huang Feifei , Bi Peng , Wang Qingrui , Jin Ying , Wen Lei , Yan Songtao
Published: February 2020

Previously, a cyclic heating and quenching process for developing IrOx electrodes is proposed. The fabricated IrOx electrodes show excellent comprehensive properties including wide E-pH range, near Nernst pH sensitivity, fast response rate, and long term stability etc. In this work, the IrOx electrodes are applied in the detection of surface pH changes during galvanic corrosion process of Zn/Steel couple in thin electrolyte film and bulk solution respectively. This detection is realized by integrating the self-fabricated IrOx pH sensor and self-built moving platform together. Before the application of the IrOx electrode, the appropriate way of scanning the surface of the Zn/steel galvanic couple is discussed. Comparing with the case in bulk solution, the Zn/steel couple corrodes faster in 1mm electrolyte layer, the surface pH of which increases to a high value after corrosion begins for 20~40min, and the low pH region exists on the zinc surface and the region adjacent to border area of the steel surface, whereas the pH value of the steel surface away from the border area is relative high. It is demonstrated that the IrOx electrode could detect the pH distribution effectively in surface region during metal corrosion, which could help the understanding of corrosion process under different situations.
(Invited) Design of Nanomaterial-Based Electrochemical Sensor for Sensitive Detection of Nitric Oxide
Authors: Chen Aicheng , Liu Zhonggang , Khaper Neelam
Published: February 2020

Nitric oxide (NO) plays important roles in myriad biological processes and is considered as a biomarker of cardiovascular disease, hypertension, symptoms of vaginitis, and cancer. Sensitive detection of NO molecules is vital toward the understanding of cell functionality and pathology as well as to the diagnosis of disease, drug discovery, and biological research [1-4]. Here, we report on the development of high-performance NO electrochemical sensors based on the nanocomposite of reduced graphene oxide (rGO) and AuPt bimetallic nanoparticles (rGO-AuPt) and the nanoporous Au microelectrode.

The rGO-AuPt nanocomposites were formed a glassy carbon electrode (GCE) using an electrochemical method. The prepared nanocomposites were tested for the electrochemical detection of NO using differential pulse voltammetry (DPV) and amperometric methods. The dependence of AuPt molar ratios on the electrochemical performance was investigated. Through the combination of the advantages of the high conductivity from rGO and highly electrocatalytic activity from AuPt bimetallic nanoparticles, the rGO-AuPt based NO sensor exhibited a high sensitivity of 7.35 µA µM-1 and a low detection limit of 2.88 nM. Additionally, negligible interference from common ions or organic molecules was observed, and the r-GO-AuPt modified electrode demonstrated excellent stability. Moreover, this optimized electrochemical sensor was practicable for efficiently monitoring the NO released from rat cardiac cells, which were stimulated by L-arginine (L-arg), showing that stressed cells generated over 10 times more NO than normal cells.

The nanoporous gold microelectrode was fabricated via an electrochemical alloying/dealloying method. It exhibited a high electrochemically active surface area and excellent performance for the detection of NO with high stability. Based on DPV and amperometric techniques, extremely high sensitivities (21.9 μA μM-1 cm-2 and 14.3 μA μM-1 cm-2) with very low detection limits of 17.0 nM and 1.43 nM, respectively, have been achieved. Moreover, the developed nanoporous Au microelectrode provides a new approach to monitor NO release from different cells, revealing that a significant differential amount of NO can be generated from the normal and stressed rat cardiac cells as well as from the untreated and treated breast cancer cells, promising for the elucidation of cellular stress responses and medical diagnostics.

References

[1] Z.G. Liu, H. Forsyth, N.Khaper, A. Chen. Analyst 141 (2016) 4074-4083.

[2] M. Govindhan, A. Chen. Microchim. Acta 183 (2016) 2879-2887

[3] M. Govindhan, Z. Liu, A. Chen. Nanomater. 6 (2016) 211.

[4] Z Liu, A Nemec-Bakk, N Khaper, A Chen. Anal. Chem. 89 (2017) 8036-8043