bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Mass Transport and Electrocatalysis: Experimental Techniques for Determining the Performance of Low Temperature Fuel Cell Electrocatalysts
Authors: Kucernak Anthony R. J.
Published: February 2020

Gases are important reactants in low temperature fuel cells, comprising both the fuel (hydrogen) in many systems and the oxidant (oxygen in air) in most systems. The fast transport of these reactants through the gas phase provides a problem in accurately assessing the performance of electrocatalysts over the relevant potential range of operation. This comes about because most electrochemical methods involve provision of reactant dissolved in an electrolyte, and mass transport through a condensed phase is orders of magnitude slower than through the gaseous phase. In this paper, we consider the different approaches that can be used to determine the electrocatalytic performance of test fuel cell catalysts using liquid electrolytes, and assess how closely the different approaches mimic the mass transport conditions in a low temperature PEFC. In principle, we can adopt two different approaches, we can either (a) change (in a defined way) the electron transfer kinetics of our electrochemical reaction through changing the temperature, or poisoning our catalysts; or (b) we can increase mass transport of reactant to the electrode. In the latter case, our choices include either decreasing our measurement time (fast voltammetry); increasing convection in our system (Rotating disk, Wall-Jet, channel flow, etc); or change the geometry of our system (e.g. ultra microelectrode, floating electrode etc). There is a tradeoff between accuracy of results and ease of use,  leading to some significant discrepancies in the literature.
Ordered Mesoporous Porphyrinic Carbons for Oxygen Reduction Reaction: Pt-like Activity in Acidic Media and Active Site
Authors: Joo Sang Hoon
Published: February 2020

The high cost of polymer electrolyte fuel cell (PEFC) systems, predominantly dictated by the platinum-based cathode catalysts for the oxygen reduction reaction (ORR), has critically impeded the widespread application of PEFCs. Therefore, the quest for low-cost yet high-performance non-precious metal catalysts has been of prime importance in recent years. We present a new class of self-supported, transition metal-doped ordered mesoporous porphyrinic carbon (M-OMPC; M=transition metal) catalysts, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors [1]. The preparation of M-OMPC catalysts is simple, tunable, scalable, and highly reproducible. Among the M-OMPC catalysts, FeCo-OMPC exhibits a very high ORR activity in an acidic medium, which is one of the best performances among the non-precious M/N/C catalysts, and outperformed the carbon-supported commercial Pt/C catalyst. Furthermore, the FeCo-OMPC showed superior long-term durability in ORR, compared to Pt/C; after cycling 10,000 times under O2 bubbling, the FeCo-OMPC exhibited 6-fold higher ORR activity than the Pt/C. The weakening of the interaction between oxygen atom and the FeCo-OMPC compared to Pt/C as well as high surface area of the former could be responsible for its significantly high ORR activity. We also systematically investigated the potential active sites for the ORR in the FeCo-OMPC catalysts, and could correlate the local coordination structure around metal centers and corresponding ORR activities [2]. The M-OMPC catalysts could suggest a new concept for future design of non-precious metal-based high-performing ORR catalysts.

[1] J. Y. Cheon, T. Kim, Y. Choi, H. Y. Jeong, M. G. Kim, Y. J. Sa, J. Kim, Z. Lee, T.-H. Yang, K. Kwon, O. Terasaki, G.-G. Park, R. R. Adzic, S. H. Joo, Scientific Reports 3, 2715 (2013).

[2] J. Y. Cheon, M. G. Kim, G.-G. Park, S. H. Joo, manuscript in preparation.
Electrochemical Stress Development during CO and NO Oxidation on Pt
Authors: Ha Yeyoung , Cohen Yair , Gewirth Andrew A.
Published: February 2020

The adsorption and oxidation of CO on Pt electrodes is among the most studied electrochemical reactions due to its fundamental importance as a simple model system and practical importance as CO is a well-known poison in fuel cells.1 We use in situ electrochemical surface stress measurements to monitor the surface stress development during the oxidation of CO on Pt electrodes where adsorbed CO reacts with oxygen-containing species on the surface via Langmuir-Hinshelwood mechanism.1-2 The nature of adsorbed CO layer and the role of oxygenated species are studied in both acid and alkaline media. Further, the effect of dissolved CO is examined. Another strong adsorbate, NO, is oxidized on Pt surface and the surface stress change is monitored. Despite the similarity in the electronic structure, the oxidation of NO follows a different mechanism where the complete oxidation of adsorbed NO is very difficult due to surface oxide formation.3The different role of oxygenated species on the surface can be seen from the surface stress response.

References

 1.             Garcia, G.; Koper, M. T., Carbon monoxide oxidation on Pt single crystal electrodes: understanding the catalysis for low temperature fuel cells. Chemphyschem : a European journal of chemical physics and physical chemistry
2011,
12(11), 2064-72.

2.             Arenz, M.; Mayrhofer, K. J. J.; Stamenkovic, V.; Blizanac, B. B.; Tomoyuki, T.; Ross, P. N.; Markovic, N. M., The Effect of the Particle Size on the Kinetics of CO Electrooxidation on High Surface Area Pt Catalysts. J. Am. Chem. Soc.
2005,
127(18), 6819-6829.

3.             de Vooys, A. C. A.; Beltramo, G. L.; van Riet, B.; van Veen, J. A. R.; Koper, M. T. M., Mechanisms of electrochemical reduction and oxidation of nitric oxide. Electrochim. Acta
2004,
49 (8), 1307-1314.
Voltage Asssisted Photocatalytic Flow through Cell for Inactivation of Biological Pathogens Using Titania Nanotube Arrays
Authors: Carlson Krista , Huber Jeff , Misra Mano , Mohanty Swomitra K.
Published: February 2020

Diseases stemming from pathogen contaminated water kills 3.4 million people annually; despite our centralized water treatment facilities in the US, we are not immune to tainted drinking water.   Aging infrastructure and natural disasters can cause limited access to potable water, making point-of-use (POU) disinfection devices critical for survival.

In this work, a POU device using a voltage assisted photocatalytic flow through cell, was designed and built for the disinfection of water under various conditions.  Anodically formed titania nanotube arrays (TNAs) were used as the photocatalytic component of the cell.  The TNAs were characterized via x-ray diffraction, scanning electron microscopy and photoelectrochemical measurements.  Voltage assisted inactivation was examined under different light intensities, water chemistries and applied biases. Complete biocide (a 10-log reduction) of Escherichia coli (E. Coli) W3110, was achieved in 15 s of contact time under 25 mW/cm2 insolation and an anodic bais of 3 V. The presence of chloride ions was found to enhance disinfection as chlorine radicals participate in bacterial inactivation; however, sulfate and nitrate ions were found to inhibit inactivation.  It was also determined that TNAs annealed in a reducing atmosphere performed significantly better than those annealed in air.  Overall, this voltage assisted photocatalysis methodology proved to be highly effective in complete inactivation of E. Coli.

Figure 1
4A-Zeolite Enhanced Electrocatalytic Activity of Pt/C for Electrooxidation of Methanol in Alkaline Medium
Authors: Zhang Guangli , Feng Wanru , He Ping , Zhang Susu
Published: February 2020

Pt-based electrocatalyst is considered to be the most efficient materials in direct methanol fuel cells [1].  However, the high cost of noble metals inhibits their application in fuel cells on a large scale.  Therefore, the effort to finding out an abundant, inexpensive and efficient electrocatalytic material is of great significance.  Zeolite, composed of silicon-aluminum oxides, is well known for its ion exchange property, adsorption with of acidic protonic entities and porosity on its surface, making it more hydrophilic and facilitating the diffusion of analytes into the film of electrode surface as well as the enhancement of active area [2,3].  Furthermore, the lower resistance and less ohmic power losses can be obtained when zeolite is used as electrode materials.

In this study, Pt/C catalyst was prepared by reducing H2PtCl6 with NaBH4 as reducer, and subsequently co-mixed with the porosity structured 4A-zeolite for the purpose of enhancing of the specific activity and reducing of the dosage of noble metal.  The corresponding electrocatalytic activity for electrooxidation of methanol was evaluated in alkaline medium by cyclic voltammetry.  It was shown that the electrocatalytic activity of the 4A-zeolite modified Pt/C catalyst was much better than that of Pt/C catalyst (Figure 1).  This increased electrocatalytic activity could be attributed to that the micrometer 4A-zeolite with porosity structure could significantly increase the effective electrode surface and facilitate the diffusion of analytes into the film of electrode surface.

References

[1] Ziwu Liu, Qianqian Shi, Rufan Zhang, Quande Wang, Guojun Kang, Feng Peng. Phosphorus-doped carbon nanotubes supported low Pt loading catalyst for the oxygen reduction reaction in acidic fuel cells. Journal of Power Sources. 2014, 268: 171-175

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

[3] Ping He, Wei Wang, Licheng Du, Faqin Dong, Yuequan Deng, Tinghong Zhang. Zeolite A functionalized with copper nanoparticles and graphene oxide for simultaneous electrochemical determination of dopamine and ascorbic acid. Analytica Chimica Acta. 2012, 739: 25-30

Figure 1
Intrinsic Relationship Between Enhanced Oxygen Reduction Reaction Activity and Nanoscale Work Function of Doped Carbons
Authors: Cheon Jae Yeong , Kim Jong Hoon , Kim Jae Hyung , Park Jeong Young , Joo Sang Hoon
Published: February 2020

Nanostructured carbon materials doped with a variety of heteroatoms have shown promising electrocatalytic activity for the oxygen reduction reaction (ORR). However, understanding of the working principles that underpin the superior ORR activity observed with doped nanocarbons is still limited to theoretical calculations-based predictions. In the present work, we demonstrate, for the first time, that the enhanced ORR activity in doped nanocarbons can be correlated with the variation in their nanoscale work function. A series of doped ordered mesoporous carbons (OMCs) were prepared using N, S, and O as dopants; the triple-doped, N,S,O-OMC displayed superior ORR activity and four-electron selectivity compared to the dual-doped (N,O-OMC and S,O-OMC) and the monodoped (O-OMC) OMCs. Significantly, the work functions of these heteroatom-doped OMCs, measured by Kelvin probe force microscopy, display a strong correlation with the activity and reaction kinetics for the ORR. This unprecedented experimental insight can be used to provide an explanation for the enhanced ORR activity of heteroatom-doped carbon materials.
Thermochromic Smart Windows for Energy Saving and Comfort in Buildings and Vehicles
Authors: Jin Ping
Published: February 2020

Thermochromic materials are such being able to change their optical properties in response to temperature change. Nano-scaled thermochromic material can result in novel properties and widen applications. Vanadium dioxide is one of the most useful thermochromic materials, characteristic of a reversible semiconductor-to-metal phase transition at a temperature near the ambient. We have been studied this unique material for over 20 years to develop a thermochromic “smart window” for energy saving and comfort for buildings and vehicles. Multiple approaches have been achieved to fulfill the goal: 1) multifunctional structure using thermochromic VO2 and photocatalytical TiO2 was deposited on float glass by magnetron sputtering, which shows excellent solar control and self-cleaning performance; 2) a polymer-aided deposition method has been established with the performance even superior to the best film by sputtering; 3) mass production of high quality VO2-based nano-particles have recently been established in Japan (AIST) and China (SICCAS), and thermochromic polymer foil was produced for the first time. Optimization of the VO2 nanoparticle/polymer foil system was done using the effective medium theory, which demonstrates an ever high energy modulation. This talk will present a review to the state-of-the-art of smart windows, with focus mostly on thermochromic ones both in China and Japan.
Self-Powered Electrochromic Smart Window Driven By Transparent Triboelectric Nanogenerators Via Harvesting Wind and Rain Energies
Authors: Yeh Min-Hsin , Lin Long , Yang Po-Kang , Wang Zhong Lin
Published: February 2020

Self-powered system is one of promising electronic concepts in upcoming future due to its independent and sustainable operations without a battery. To realize this idea, triboelectric nanogenerator (TENG) was recently invented that could effectively convert the ambient mechanical energy into electricity to power up portable electronics. In this work, the concept of self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by wind blowing and raindrops The ECD consisted of Prussian blue and zinc hexacyanoferrate as the electrochromic material and the ion storage layer, respectively. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD displays reversible variations due to electrochemical redox reactions. The maximum transmittance change can reach up to 32.4% at 695 nm which is comparable to that operated by conventional electrochemical potentialstation (32.5%). This research is a substantial advancement towards the practical application of nanogenerators and self-powered systems, and it paves the way for the development of fully independent smart windows or high-performance displays.
Solution Phase Electrochromic Materials and Devices
Authors: Byker Harlan
Published: February 2020

The “Smart Glass” market was recently estimated to be worth about 1.6 billion dollars US for the year 2013 by an organization called “Markets and Markets”. A significant portion of this dollar amount is believed to be the result of the sale of electrochromic rearview mirrors for motor vehicles. Electrochromic devices may involve inorganic, metal-organic or organic materials and they may involve surface confined, electrodeposition or solution phase type electrochemical systems or essentially any combination of materials or systems from these six categories since most devices involve an anode and a cathode. Out of all of these possible combinations only completely solution phase electrochromic devices have enjoyed true commercial success. The history of solution phase electrochromic materials will be reviewed and chemistry and device characteristics of these electrochromic systems will be described.
High-Throughput Screening for Color in Electrochromic Devices
Authors: Sotzing Gregory
Published: February 2020

Color selection for the transition between two color states within an electrochromic device can be a difficult and drawn out process involving careful molecular design of the chromophore, synthesis, and purification, followed by reiteration of this procedure should the desired color not be achieved.  Here, we present a technique in which high-throughput screening of color for conjugated polymer electrochromics inside an electrochromic device.   The techique involves co-diffusion of a monomer that would produce a high bandgap conjugated polymer with a monomer that would produce a low bandgap conjugated polymer within a polyelectrolyte to generate a diffusional gradient of both monomers between their points of introduction.  This diffusional gradient of monomers is then converted to a gradient of random copolymers via an electrochemical oxidation producing nearly the entire subtractive spectrum of colors that can then be switched to a colorless state.  Perpendicular orientation of this gradient to the electrochromic device allows for achievement of neutral coloration, important for tinting applications.  Electrochromic devices of 171 cm2 active switch area have been optimized through optimization of the polyelectrolyte, and monomer choice for our solid-state conversion process of monomers to conjugated polymers to result in photopic contrasts as high as 58% without any substrate corrections.  Photopic contrasts of 41% have been achieved for devices meeting military neutrality standards.  As a further demonstration of our solid-state conversion, we have prepared all-spandex electrochromic devices in which the electrochromic device can be stretched during the color-change process.  The spandex devices have the feel of spandex and could find applications in wearable displays and/or adaptive camouflage.
Spectroelectrochemical Study of the Role of Pyridinium in Carbon Dioxide Reduction
Authors: Lucio Anthony J , Shaw Scott K
Published: February 2020

Pyridinium (pyrH+) has been studied for its potential catalytic role in the electrochemical reduction of carbon dioxide (CO2) to methanol. We report electrochemical analysis of the pyrH+ + CO2 interaction on metallic electrodes, independently of the hydrogen evolution reaction. Present results show that gold electrodes exhibit unique pyrH+ and CO2 electrochemistry compared with previous work on platinum electrodes or photochemical systems. Analysis of the electrochemical data show multi-layer adsorption of pyridine, an irreversible reduction wave associated with pyrH+ as the pH approaches the pKa of pyrH+, and a small but significant catalytic activity (0.15 mA/cm2) for CO2 reduction in the presence of pyrH+ at -1.0 V vs. Ag/AgCl.

The present work aims to discern the electroreduction mechanism by analyzing the proposed pyrH+ reduction process in inert purge gas environments using electrochemical and in situ infrared and Raman spectroscopic techniques. This information will guide the analogous exploration under CO2 environments to determine the nature of the enhanced current response. Possible products from the pyrH+ + CO2 electroreduction will be discussed.
In Situ UV-Vis Differential Reflectance Spectroscopy Study of Polycrystalline Platinum Oxidation in Aqueous Solutions
Authors: Xu Jing , Scherson Daniel
Published: February 2020

A primitive model involving the combined use of coulometric and in situ differential reflectance spectroscopy data collected simultaneously1 has been applied to examine oxide formation on the surface of Pt(poly) electrodes in aqueous 0.1M HClO4 as a function of the applied potential. Analysis of experimental data assumed sequential formation of two different kinds of oxides, PtOH in the low and PtO, in the high potential regions, denoted as Ox1 and Ox2, respectively. The potential dependence of the coverages of each of these species, thetaOx1 and thetaOx2, was obtained by solving the following set of coupled equations:

The symbol thetabare   in Eq.(1) represents the coverage of the bare, i.e. non-oxidized surface sites, Qn, is the charge determined from the integration of the oxide reduction peak following the method reported by Novak2 and the factor 2 in Eq.(2) accounts for the stoichiometry of the oxide. Lastly the symbol -deltaR/R =-[R(Eref)-R(Esam)]/R[Eref], R(Eref) and R(Esam) are the reflectance values recorded at the reference potential, Eref, set at 0.05 V, and at any arbitrary sampling potential, Esam, respectively3 represents the differential reflectance, where A(E), B(E) and C(E) are coefficients that account for changes in the optical signal of each of the types of sites induced by the applied potential.1

Shown in jagged line in Fig. 1 is a plot of -deltaR/R vs potential, E, for Pt(Poly) in 0.1M HClO4 recorded at a scan rate of 10 mV/s.  The solid smooth line in this figure was obtained from the analysis of the model specified above which yielded values of thetaOx1, thetaOx2, and thetabare vs E, for Pt(poly) in 0.1M HClO4 in Fig. 2.

REFERENCES

A. J. J. Jebaraj, D. Scherson, Anal. Chem.,  86, 4241, (2014).

D. M. Novak, B. Conway, J. Chem. Soc. Faraday Trans. 77, 234, (1981).

J. Xu, D. Scherson, Anal. Chem., 85, 2795, (2013).

Figure 1
Separation of Enantiomers of Alanine from Racemic Mixture By Polycrystalline Metal Surfaces- a Spectroelectrochemical Approach
Authors: Kumar Deepak , Pal Samanwita , Chhabbra Meenu , Harinipriya S
Published: February 2020

ABSTRACT:Spectroelectrochemicalinvestigation of racemic alanine on polycrystalline metal surfaces was studied in 1M LiClO4 medium, to achieve cost effective separation of biologically important molecules from the racemic mixture. Analysis of the FTIR spectrum of racemic alanine in 1M LiClO4 indicated degradation of the same. Upon prolonged exposure in LiClO4, byproducts from degradation of alanine increasedin concentration as also observed from UV-Vis spectroscopy. Cyclic Voltammetry studies unraveled different adsorption behaviors on different metal surfaces for the racemic and the enantiomeric solution of alanine. Further FTIR analysis of the alanine solution after Cyclic Voltammetry revealed possible presence of cyanide (-C≡N) and terminal alkyne as byproducts. As predicted by Monte Carlo simulations earlier, Circular Dichroism implied the dextro rotation ofthe racemic alanine solution after Cyclic Voltammetry. These results support the preferential adsorption of L-alanine over D-alanine from racemic mixture that could be attributed to the umbrella inversion of the molecule after adsorption on the metal surface in presence of applied electric field in the LiClO4 environment. A plausible mechanism for the formation of terminal alkyne and -C≡N byproducts had also been attempted.
(Invited) Activity Trends and Design Principles for Multi-Transition-Metal (Oxy)Hydroxide Oxygen Evolution Catalysts
Authors: Boettcher Shannon Wachter
Published: February 2020

Oxygen evolution reaction (OER) catalysis limits the efficiency of H2 production through water electrolysis/photoelectrolysis, a route to large-scale energy storage. The factors governing the activity of OER catalysts are not well understood. We found Ni-Fe oxyhydroxides are the fastest known water oxidation catalysts under basic conditions when compared to others using a quantitative electrochemical-microbalance approach. In-situ electrical, photoelectron spectroscopy, x-ray diffraction, and electrochemical analyses on Ni1–x
Fe
x
OOH films show that the reaction mechanism relies on the local electronic structure of a Ni-O(H)-Fe active site. Experiments with rigorous exclusion of Fe electrolyte impurities reveal that, contrary to common belief, pure NiOOH is a poor OER catalyst. FeOOH was found to be a poor electrical conductor, explaining its low apparent OER activity. Measurements on Co1–x
Fe
x
OOH support the hypothesis that NiOOH and CoOOH provide a conductive host for the Fe-related active sites. In sum, these results establish a new activity trend for OER catalysts, opposite to previous ones, that informs catalyst design.

(1) Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. Solution-cast metal oxide thin film electrocatalysts for oxygen evolution. J. Am. Chem. Soc.
2012, 134, 17253.

(2) Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S. W. Nickel–iron oxyhydroxide oxygen-evolution electrocatalysts: The role of intentional and incidental iron incorporation. J. Am. Chem. Soc.
2014, 136, 6744.

(3) Burke, M. S.; Kast, M.; Trotochaud, L.; Smith, A.; Boettcher, S. W. Cobalt-iron (oxy)hydroxide oxygen evolution electrocatalysts: The role of structure and composition on activity, stability and catalytic mechanism. To be submitted
2014.
Structural Dynamism in Manganese Oxides in the Potential Regime for Water Oxidation: A SERS Study
Authors: Ranjan Chinmoy
Published: February 2020

Non noble metal "earth abundant" electrocatalysts will significantly reduce the costs and make it possible to use electrochemical water splitting (electrolysis) on a very large scale. Non noble metal catalysts can be an effective replacement even if their electrochemical activities are a fraction of their noble metal counterparts. If these catalysts can be developed to an extent where their operational lifetime would become comparable to their noble metal counterparts, a large part of the problem would be solved. MnO2 is earth abundant and well known for catalyzing oxygen evolution. A form of MnOx cluster is known to catalyze water oxidation in photosynthesis. These catalysts although with immense potential remain a long way from successful implementation within electrolysers. In order to understand the limitations of this catalyst under the operational conditions, it is important to study this material in situ. Setup for in situ Surface Enhanced Raman Spectroscopy is used for tracking the structural changes of hydrous MnOx. Electrodeposition of MnOx on the surface of Au was achieved by passing an anodic current of 50 mC/cm2 at 1,6V.

The resulting MnO2 phase could be termed as the alpha/MnO2 phase. The structural integrity of the MnOx was studied by following the Mn-O-Mn stretching various potential ranges in various electrolytes. Onset of phase changes and corrosion could be clearly established. Beside this, other methods such as XRD, SEM, TEM were applied to study these thin films. Depending upon the nature of electrolyte the catalyst acquired a specific structure.

Figure 1
Perovskite Oxides Electrodes for Alkaline Oxygen Evolution Reaction
Authors: Sljukic Biljana , Martins Marta , Santos Diogo M.F. , Amaral Luis , Sousa Nuno , Sequeira Cesar A.C. , Figueiredo Filipe M
Published: February 2020

Designing electrode materials for oxygen evolution reaction (OER) and for oxygen reduction reaction (ORR) is crucial for the development of renewable energy technology devices, such as water electrolyzers and fuel cells [1]. Alkaline water electrolysis is seen as an eco-friendly process for large-scale production of hydrogen required for hydrogen economy. However, the efficiency of water electrolysis in practice is limited by the large overpotential necessary to drive OER, resulting in high cost of the process and produced hydrogen.

There are few literature reports on OER at perovskite-based electrodes where different carbon supporting materials were often used for increase of active surface area and conductivity [1-3]. The aim of this study was to examine the intrinsic activity of perovskite materials.

Therefore, six different perovskite oxides were used for preparation of electrodes with no carbon support, to be studied for OER in alkaline media. These were La0.8Sr0.2Fe0.8Co0.2O3, La0.7Sr0.3MnO3, La2NiO4, La1.9Pr0.1CuO4, La1.8Pr0.2NiO4 and La1.9Sr0.1NiO4. OER studies were performed using cyclic voltammetry (CV) and linear scan voltammetry (LSV) in potassium hydroxide (KOH) solution. Main reaction parameters, namely Tafel slopes, charge transfer coefficients, exchange current densities, and activation energies were determined from the LSV data. Influence of operating parameters, specifically electrolyte composition and temperature, was also investigated.

First results indicated the highest activity of La1.9Sr0.1NiO4 for the OER in the studied temperature range (25 – 85 ºC).

References

[1] M. Risch, K. A. Stoerzinger, S. Maruyama, W. T. Hong, I. Takeuchi, Y. Shao-Horn, J. Am. Chem. Soc. 136 (2014) 5229 − 5232.

[2] C. Jin, X. Cao, L. Zhang, C. Zhang, R. Yang, J. Power Sources 241 (2013) 225 – 230.

[3] R. A. Rinc, E. Ventosa, F. Tietz, J. Masa, S. Seisel, V. Kuznetsov, W. Schuhmann, ChemPhysChem 15 (2014) 2810 – 2816.
Nanoengineering of MoS2 Electrocatalysts for Efficient Hydrogen Evolution Reactions
Authors: Gao Qingsheng , Liu Ning
Published: February 2020

Advanced catalysts with element-abundance, economic-cost and stability are desired for electrochemical hydrogen evolution reaction (HER) to scale-up the promising clean energy of hydrogen.[1] The discoveries in the (de)hydrogenation of petroleum chemicals have inspired several efficient and economic catalysts of metal non-oxides towards HER, such as Mo-based sulfides and carbides.[2] MoS2 possesses a layered structure exposing Mo- and S- edges, which are highly active for HER due to the moderate hydrogen bonding energy (ΔGH*).[3] However, its performance is still limited by the poor conductivity and the uncontrolled properties of active-sites.

In our recent work, efforts have been made to synergically enhance the conductivity and active-site abundance of MoS2, achieving the high current densities and low onset overpotentials for HER.[4-6] For example, we proposed a new route to confine MoS2 growth within an in-situ formed polysaccharide matrix from glucose condensation during hydrothermal processes, and after the following carbonization, MoS2/C nanocomposites evenly integrating ultrathin MoS2 nanosheets (2 ~ 4 nm) with conducting carbon were successfully harvested (Fig. 1a).[6] The MoS2/C exhibited an excellent HER activity characterized by higher current densities and lower onset overpotentials than the conventional MoS2. In particular, the MoS2/C with a suitable MoS2 content of 14.8% showed a small onset overpotential of ~80 mV, a high current density of 88 mA cm-2 at η = 200 mV, which are ascribed to the abundant rim-sites on ultrathin MoS2 nanosheets and the improved conductivity by carbon. On the other hand, a facile microwave-assisted hydrothermal method was further introduced to fabricated active-site enriched MoS2 nanosheets employing reactant self-shelter, in which the excessive S source (e.g., thiourea) would cover the highly-active Mo-sites during MoS2 formation, and then be removed by following treatment with H2SO4, resulting in abundant active sites on MoS2. The electrocatalytic test well-confirmed the significantly improved active-sites (~3 orders) and conductivity as compared with the traditionally prepared MoS2. Thanks to the facile synthesis and outstanding electrochemical behaviors, our effort is expected to pave the way for earth-abundant, economic and efficient electrocatalysts used in energy conversion and storage.

References:

[1] A. B. Laursen, S. Kegnaes, S. Dahl, I. Chorkendorff, Energy Environ. Sci., 2012, 5, 5577.

[2] C. G. Morales-Guio, L. Stern and X. L. Hu, Chem. Soc. Rev., 2014, 43, 6555.

[3] T. F. Jaramillo, K. P. Jorgensen, J. Bonde, J. H. Nielsen, S. Horch, I. Chorkendorff, Science, 2007 317, 100-102.

[4] L. C. Yang, S. N. Wang, J. J. Mao, J. W. Deng, Q. S. Gao, Y. Tang, O. G. Schmidt , Adv. Mater., 2013, 25, 1180.

[5] Q. S. Gao, N. Liu, S. N. Wang, Y. Tang, Nanoscale, 2014, 6, 14106.

[6] N. Liu, L. C. Yang, S. N. Wang, Z. W. Zhong, S. N. He, X. Y. Yang, Q. S. Gao, Y. Tang, J. Power Source, 2015, 275, 588.

Figure 1
Water Splitting Using Gallium Nitride Based Working Electrodes for Hydrogen Generation without Applying Bias
Authors: Chen Yen Yu , Sheu Jinn Kong , Lai Wei Chi , Lee Ming Lun
Published: February 2020

In this study, we demonstrated photoelectrochemical(PEC) hydrogen generation using InGaN-based semiconductors as the working electrode for water splitting under solar illumination. For a working electrode made of n-type semiconductor, the holes drive the oxidation of water on the photoelectrode, and the electrons transport within semiconductor and in turn move to the cathode electrode leading to the reduction reaction. Although GaN is potentially resistant to aqueous solution and its energy band is suitable for water photoeletrolysis, GaN only absorbs UV light which is about 5% of the solar spectrum. The bandgap energy of the InxGa1-xN can be tuned from 0.7eV to 3.4eV by changing the Indium content to fit the most of the terrestrial solar spectrum. Therefore, InGaN-based working electrodes for water splitting are expected to be more efficient than the GaN working electrodes.

　　The working electrodes used in this study featuring meshed metal contacts with SiO2 protection layer were immersed in electrolyte to enhance the collection efficiency of photogenerated carriers. On the other hand, the generation rate of hydrogen could be improved by applying external bias onto the working electrodes to enhance the separation of photogenerated electron-hole pairs in the semiconductor and the charge transfer at the interface between semiconductor and electrolyte during the PEC water splitting process. However, the external bias on PEC water splitting requires extra input power except light illumination. In this study, InGaN-based semiconductors associated with meshed metal contacts were served as working electrodes without external bias to conduct the PEC water splitting process under the light illumination.

　　Instead of using an external bias provided by power supply, a solar cell was used to raise the driving force to increase the rate of hydrogen production. The solar cell was connected in series between the InGaN-based working electrode and the platinum (Pt) counter electrode to bias the PEC cell. In principle, the water splitting for generating hydrogen involves two mechanisms during the light illumination if the solar cell supplies bias voltage larger than 1.23 V. The mechanisms are photoelectrolysis and electrolysis of water splitting. To solely evaluate the efficiency of photoelectrolysis or electrolysis of water splitting, the output voltage of solar cell was varied through changing the type of solar cell to allow the PEC cell with bias less or larger than 1.23 V. The preliminary results indicated that the hybrid working electrodes exhibited a marked improvement in the efficiency of hydrogen generation.

　　The detailed results will be presented in the forthcoming conference.

Figure 1
Carbon Nanotubes/Heteroatom-Doped Carbon Core-Sheath Nanostructures As Highly Active Bifunctional Oxygen Reduction and Oxygen Evolution Electrocatalysts
Authors: Sa Young Jin , Park Chiyoung , Jeong Hu Young , Park Seok-Hee , Park Gu-Gon , Joo Sang Hoon
Published: February 2020

An ionic liquid (IL)-driven, facile, scalable route to new carbon nanostructures comprising pure carbon nanotube cores and heteroatom-doped carbon sheath layers (CNT/HDC) has been developed. The design of the CNT/HDC nanocomposites allows for combining electrical conductivity derived from the CNTs with the catalytic activity of the heteroatom-containing HDC sheath layers. The CNT/HDC nanostructures showed excellent electrocatalytic activity for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in an alkaline medium. The ORR activity of CNT/HDC nanostructures is one of the best performances among the heteroatom-doped nanocarbon catalysts in terms of half-wave potential and kinetic current density. The kinetic parameters of the CNT/HDC nanostructures, including 4-electron transfer selectivity and exchange current density, compared favorably with those of a Pt/C catalyst. The CNT/HDC nanostructures also exhibited superior long-term durability and poison-tolerance relative to Pt/C. Bifunctional oxygen electrocatalytic activity of CNT/HDC was comparable to that of Ir/C and better than that of Pt/C. In addition, the CNT/HDC nanostructures showed high current and power densities when employed as a cathode catalyst in alkaline fuel cell, which sheds light on their practical applicability.
(Energy Technology Division Graduate Student Award) Plasmonic Light Absorption Enhancement Mechanisms in Semiconductors Above and below the Band Edge
Authors: Cushing Scott Kevin , Li Jiangtian , Bristow Alan D. , Wu Nianqiang
Published: February 2020

Plasmonics can manipulate light by controlling scattering, absorbing light to create hot electrons, and through the intense local electromagnetic field, making it ideal for recovering light otherwise lost by a semiconductor in solar energy conversion. However the link between each of the plasmon’s unique properties and the corresponding enhancement routes remains unclear. In this presentation systematic sample design is combined with transient absorption and action spectrum/IPCE analysis to isolate the plasmonic enhancement mechanisms. Systematic control of energy alignment, metal to semiconductor distance, and spectral overlap through sample design reveals the transfer mechanisms. Additionally, ultrafast optics connects the initial plasmon-mediated charge creation to long time scale device performance, identifying key losses. The efficiency of scattering, hot electrons, and the local field in enhancing light absorption above and below the band gap is explored, with guidelines given as to how plasmonics can best be used in enhancing solar energy conversion.
Organophotocatalyst Films and Their Multilayerization That Efficiently Utilize Natural Sunlight
Authors: Nagai Keiji , Abe Toshiyuki , Iyoda Tomokazu
Published: February 2020

A full-spectrum visible-light-responsive organophotocatalyst membrane array is designed and employed for a one-pass-flow water purification system.  Whereas previous photocatalyst systems required strong light source, the present design manages with natural sunlight intensity, owing to multi-layerization of a newly optimized low-absorbance organophotocatalyst.  The design of the system is to utilize natural-sunlight-equivalent visible light with 1 m2 of irradiation area to process 1 ton/day of water.  A 1/3300 scale module of the system was constructed and experimentally demonstrated its viability.  The reactor part of the flow system contains 24 stacked layers of organic-semiconductor-laminated Nafion film.  The organic semiconductor is a bilayer of metal-free phthalocyanine (H2Pc, p-type semiconductor) and 3,4,9,10-perylenetertacarboxylic-bisbenzimidazole (PTCBI, n-type semiconductor).  Transparent Nafion functions as mechanical support and absorbent of trimethylamine, which was chosen as a typical contaminant of underground water in coastal areas.  The reactor was irradiated for only 1 h/day by visible light (10 mW/cm2).  The light intensity at the bottom layer was estimated to be 0.1 mW/cm2, which was sufficient intensity (Internal quantum efficiency was 0.15.) for the photocatalytic reaction, due to the optimized absorbance and photocatalytic quantum efficiency of each layer.  The inlet TMA concentration was 3 ppm, while that of the outlet was less than 0.03 ppm for the first day of the operation of the system with and without the bilayer.   Without the bilayer, the TMA concentration of the outlet flow increased after the 20 days.  With the bilayer, the TMA concentration of the outlet flow remained at less than 0.03 ppm for the 40-day experimental period due to its photocatalysis.  The turnover number of photocatalytic reaction was calculated to be 1.8×104.

References: [1] K. Nagai et al, ACS Sus. Eng. Chem. 1, 1033 (2013).  [2] K. Nagai et al, ChemSusChem. 4, 727 (2011).  [3]  T. Abe et al., Chem. Commun, 50, 1950, (2014).
Prospects for Future Photoelectrolysis Devices: New Oxide Semiconductors and Electrode Structures
Authors: Parkinson Bruce A
Published: February 2020

The full potential of solar energy cannot be realized unless there is method to store it and use it as fuel.   In this talk I will give both a brief historical look at the past efforts to solve this problem and provide some options and opinions about the way forward.  It is clear that materials that are stable and have the proper band gaps for an efficient photoelectrochemical water splitting device are currently unknown.  In addition these materials need to be catalytic for water oxidation or reduction reactions or have catalyst layers deposited on their surfaces.  I will discuss combinatorial methods for discovering new oxide semiconductors and solid-state catalysts that might be further optimized to be useful in a solar water splitting device.  Researchers need to focus on quickly evaluating the many new materials that will emerge from the combinatorial searches to identify a few that have the potential to be stable, efficient and inexpensive.  An example of a new semiconducting oxide containing earth abundant iron, chromium and aluminum that was discovered by an undergraduate researcher participating in the Solar Hydrogen Activity research Kit (SHArK) project will be given. Thie photoelectrochemical behaviour of this material was followed up in our laboratory and found, after optimization of the stoichiometry,  to have a high open circuit voltage for water reduction. An example of collaborations between my laboratory and other laboratories to quickly evaluate the potential of this material will be given as an example.
Role of Surface Amorphization in CuO-Cu2o Core-Shell Nanowire Array for Photoelectrochemical Water Splitting
Authors: Wu Fei , Banerjee Sriya , Myung Yoon , Banerjee Parag
Published: February 2020

We demonstrate spatial (i.e., where) and stoichiometric (i.e., how much) control of dense CuO core - Cu2O shell nanowires (NWs). These NWs are then used as photocathodes for water splitting. CuO has a narrower band gap (1.53 eV) and a higher conduction band edge compared to Cu2O (2.0 eV), thus enabling an efficient way to absorb light and convert solar energy.

Thermally grown CuO NWs under carbothermal reduction conditions lose oxygen from the surface.[1] The out-diffusion of oxygen makes single crystalline CuO transform to Cu2O. However, a 2 to 3 nm transition, amorphous Cu2O layer on the surface is formed. This transition, surface amorphous Cu2O layer crystallizes under longer reduction time. We tune the CuO core/Cu2O shell ratio by controlling the temperature and time of reduction to study the CuO NW phase transformation kinetics. We examine the phase transformation (oxygen loss) in the NWs using Raman spectroscopy and model it within the framework of the Johnson-Mehl-Avrami equation. The nature of the transformation under oxygen loss conditions in narrow 1D NWs will be presented.

The as-synthesized CuO-Cu2O core-shell NW array is systematically used to examine water splitting performance. The maximum photocurrent density measured is 2.69 mA/cm2 at 0.6 V vs. Ag/AgCl for the CuO-Cu2O core-shell NW structure with a 2-3 nm transition, surface amorphous Cu2O layer. Once the amorphous layer crystallizes, photocurrent density decreases to 0.3-0.4 mA/cm2 range. This data indicates that amorphous protection layers can improve the photocathodic performance CuO NWs.

[1] Wu, F. Myung, Y. Banerjee, P. Cryst. Growth Des.
2014,
10.1021/cg500784y.
Au Nanoparticle-Enhanced Photocatalysis: Beyond Plasmonic Effect
Authors: Li Jiangtian , Cushing Scott Kevin , Wu Nianqiang
Published: February 2020

Plasmonic metal nanostructures have strong, tunable absorption and scattering band. Coupling semiconductors with metal nanoparticles can apparently increase their photocatalytic activity. Besides the plasmonic effect, gold nanoparticles may bring other beneficial effects in the metal-semiconductor composite photocatalyst system. Herein we show that Au nanoparticles sandwiched between the quantum dots (QDs) and the TiO2 nanorod array photoelectrode can act as an electron relay to facilitate the charge transfer. In another case, Au nanoparticles are deposited on the surface of semiconductor photoelectrode, which can also facilitate the charge transfer. A better understanding of different effects of gold nanoparticles will help develop effective metal-semiconductor device for solar fuel generation.
Unexpected Hydrogen Production of α-Fe2O3 Nanorings
Authors: Wender Heberton , Gonçalves Rentao
Published: February 2020

The production of hydrogen from water using only a catalyst and solar energy, water photolysis, is one of the most challenging and promising outlets for the generation of clean and renewable energy. [1] Semiconductor photocatalysts for hydrogen production by water photolysis must employ stable, non-toxic, abundant and inexpensive visible-light absorbers capable of harvesting light photons with adequate potential to reduce water. Herein, we will present a-Fe2O3 nanorings (IONRs) and show that they can carry out hydrogen efficiently from water/methanol solution without applying any external bias. Our results indicate that IONRs could fill the requirements to split water due to a possible upward shift of the conduction band edge compared to bulk hematite [2], vary similar to that recently observed for CoO nanoparticles. [3] Understanding the underlying mechanisms for hydrogen evolution is currently being investigated in more details since the band gap, as measured by UV-Vis diffuse reflectance spectroscopy, is identical to bulk hematite removing the possibility of quantum confinement effect as observed elsewhere. [4] In addition, by depositing Co(OH)2 nanoparticles (NPs) of ~ 6 nm diameter in the NRs with a H2 evolution rate of 546 mmols.h-1.g-1 could be obtained, increasing by 35% the evolution of hydrogen. Both nanoparticle-coated and uncoated NRs displayed superior photocatalytic activity for hydrogen evolution when compared with P25-TiO2nanoparticles, showing themselves to be promising materials for water-splitting using only solar light.

References

H. Wender et al, Nanoscale
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C. X. Kronawitter, et al, Energy Environ. Sci.
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Longb Liao, et al,

Nature Nanotechnology
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L. Vayssieres, et al, Adv. Mater.
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Decoupling Ion and Proton Transport from Structural Relaxation in Polymers and Ionic Liquids
Authors: Sokolov Alexei
Published: February 2020

Classical theory relates the rate of ion transport to viscosity or rate of structural relaxation in a liquid electrolyte. We present here an overview of the relationship between ion and proton transport and structural relaxation in ionic liquids (IL) and polymer electrolyte. We demonstrate that in contrast to most of ILs, there is a strong decoupling of ionic conductivity from structural dynamics in many polymers, including polymerized ionic liquids (polyIL). This decoupling is caused by frustration in packing of relatively rigid polymer chains. As a result, ions retain high mobility even when structural dynamics is very slow or completely frozen. To provide a systematic picture of ionic conductivity we employ the so-called Walden plot. Application of this analysis to different classes of polymer electrolytes and polyILs helps to identify ‘superionic’ behavior for many polymers. We present several examples of promising polymers with conductivity approaching 10-4 S/cm at room temperature. Similar ideas can be applied to proton conductivity. We demonstrate significant decoupling of proton mobility from structural relaxation and/or viscosity in a series of protic ionic liquids. Mechanism of enhanced proton conductivity is discussed at the end.
Ion-Conduction within the Fibrous Framework of an Electrospun PEO Gel Electrolyte
Authors: Moore Robert B
Published: February 2020

Poly(ethylene oxide) (PEO) containing pentaerythritol triacrylate (PETA) was electrospun to yield fiber mats that were subsequently crosslinked by exposure to UV irradiation.  These mats were then supplemented with lithium perchlorate and swollen with ethylene/dimethyl carbonates to generate a structured polymer-gel electrolyte for Li-polymer battery applications.  The fibrous mats were found to be composed of a nonwoven collection of ca. 1μm diameter PEO fibers with up to 85% porosity. Prior to UV exposure, the mats were completely soluble in polar solvents.  However, following UV exposure, the mats were rendered insoluble by chemical crosslinking, yielding gel fractions in excess of 80%.  Upon incorporation of a liquid lithium ion electrolyte, the swollen mats were shown to maintain the fiberous framework and exhibit conductivities as high as 1.2 × 10-2 S/cm at room temperature.  In contrast, a control mat of electrospun poly(vinylidene fluoride) containing fibers of comparable dimensions and identical electrolyte loading was found to yield a conductivity of only 5 × 10-3 S/cm. NMR methods to probe further details of the transport properties of these new electrolytes will also be expored.