bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogen Oxidation Reaction on Metal@Pt Core-Shell Catalysts in Alkaline Electrolyte
Authors: Hu Jue , Zhang Chengxu 
Published: February 2020

Hydrogen oxidation reaction (HOR) as the key reaction in hydrogen-oxygen fuel cell has been widely investigated, and ultra low loading Pt (≤0.05 mg cm–2) is required for HOR in proton exchange membrane fuel cells.(1, 2) However, the HOR kinetics becomes sluggish in base, which is at least two orders of magnitude slower than that in acid.(3) The sluggish HOR kinetics in alkaline electrolyte hinders the development of alkaline exchange membrane fuel cell, which is more commercially viable because of the potential to forego noble metal catalysts and less serious corrosion.(4) To obtain the catalysts with high HOR activity in alkaline environment, it is essential to understand the reason for this puzzling difference of HOR kinetics in acid and base. The understanding of the sluggish hydrogen oxidation reaction (HOR) kinetics in alkaline electrolyte is crucial for designing high performance electrocatalysts. Here, we report a clear and convincing result on this problem by investigating the relationship between the HOR kinetics and Pt-adsorbate energetics. Using electrochemical analysis for well-modified Pt surfaces with distinct Pt-adsorbate interactions, we establish a clear trend in activity for HOR in alkaline electrolyte, that is, the activity changes in the order Au@Pt < Pt < Pd@Pt < Ru@Pt (Figure 1a). A decisive role of Pt－Had energetics in the HOR kinetics on Pt surfaces is determined, while no favorable effects of Pt－OHad energetics in the HOR kinetics were found (Figure 1b). The in-situ XANES analysis demonstrated a higher Had coverage on the pure Pt surface than that on the Pt surface with Ru core due to more strongly bonded Had on pure Pt surface (Figure 1c,d). These findings provide us a novel aspect to understand the HOR kinetics on Pt surfaces and also provides fundamental insights into the influence of the Pt－Had interaction on the HOR mechanism.
Figure Caption
Figure 1. (a) HOR polarization curves normalized to the limiting current density. (b) Trend in the exchange current density for HOR in alkaline solution as a function of the Hupd coverage. Error bars stand for the variation of at least two sets of experimental repeats. (c) Magnified XANES from Pt L
3 edge of commercial Pt/C in 0.1 M KOH solution at different potentials. (d) Comparison of the relative changes in the intensity of absorption peaks for Ru@Pt/C and commercial Pt/C shown in the XANES spectra.

References

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486, 43-51 (2012).

H. A. Gasteiger, S. S. Kocha, B. Sompalli, F. T. Wagner, Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs. Appl. Catal. B: Environ.
56, 9-35 (2005).

J. Durst et al., New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energy Environ. Sci.
7, 2255-2260 (2014).

J. R. Varcoe, R. C. T. Slade, Prospects for alkaline anion-exchange membranes in low temperature fuel cells. Fuel Cells
5, 187-200 (2005).

Figure 1
Bipolar Membrane Development for Fuel Cells and Electrolyzers
Authors: Chen Yingying , Klein Ellis , Deutsch Todd G , Neyerlin K C 
Published: February 2020

Bipolar membranes (BPMs) are composed of a cation exchange layer (CEL), an anion exchange layer (AEL), and a nanometer scale bipolar junction (Fig 1). At reverse bias polarization the potential drop within both the AEL and CEL are almost negligible when compared to the potential drop within the junction. This large potential drop within the bipolar junction results in a high electric field, which, in combination with water dissociation catalyst, allow BPMs to facilitate water dissociation (into H+ and OH- ions) at a rate seven orders of magnitude greater than the rate in bulk water [1].
BPMs have been studied at the laboratory and pilot scale for a wide variety of applications, including: electrodialysis for water treatment [2], CO2 reduction [3], solar water splitting [4], and fuel cells [5]. Despite the commercial availability of BPMs, significant hurdles exist both in the fundamental understanding of limiting processes and their subsequent incorporation into electrochemical devices. The main technological challenges for BPMs at present include: i) low membrane stability, ii) insufficient water transport at high current densities, and iii) high membrane resistance.
Here we will discuss the optimization of BPM junctions and related water management issues. An example of the improved interfacial charge transfer for BPMs fabricated using 3-D electrospun junctions is shown in Fig 2. The AC impedance spectra shown in Fig 2, highlights both the similarity in the high frequency resistance (membrane + electrolyte resistance) of the two samples, along with the significantly different low frequency (membrane + electrolyte + interfacial charge transfer) resistance. The experimental results from both 4-electrode and membrane electrode assembly (MEA) level operando testing of BPM junctions fabricated using 2-D and 3-D approaches both with and without water dissociation promoters will be shown.

Reference

[1] Strathmann, H., Krol, J. J., Rapp, H. J., & Eigenberger, G. (1997). Limiting current density and water dissociation in bipolar membranes. Journal of Membrane Science, 125(1), 123-142.
[2] Reig, M., Valderrama, C., Gibert, O., & Cortina, J. L. (2016). Selectrodialysis and bipolar membrane electrodialysis combination for industrial process brines treatment: Monovalent-divalent ions separation and acid and base production. Desalination, 399, 88-95.
[3] Li, Y. C., Zhou, D., Yan, Z., Gonçalves, R. H., Salvatore, D. A., Berlinguette, C. P., & Mallouk, T. E. (2016). Electrolysis of CO2 to syngas in bipolar membrane-based electrochemical cells. ACS Energy Letters, 1(6), 1149-1153.
[4] Luo, J., Vermaas, D. A., Bi, D., Hagfeldt, A., Smith, W. A., & Grätzel, M. (2016). Bipolar Membrane‐Assisted Solar Water Splitting in Optimal pH. Advanced Energy Materials, 6(13), 1600100.
[5] Peng, S., Xu, X., Lu, S., Sui, P. C., Djilali, N., & Xiang, Y. (2015). A self-humidifying acidic–alkaline bipolar membrane fuel cell. Journal of Power Sources, 299, 273-279.

Figure 1
Caveat of High Temperature Accelerated Stability Test for Anion Exchange Membranes
Authors: Park Eun Joo , Maurya Sandip , Hibbs Michael , Fujimoto Cy , Kim Yu Seung 
Published: February 2020

Alkaline stability of hydroxide-conducting anion exchange membranes (AEMs) is a significant requirement for practical applications of alkaline membrane fuel cells. Recently, quaternized aryl ether-free polyaromatics with alkaline stable polymer backbone structure have been receiving much attention as promising materials for AEMs.1 Since a prolonged stability test (≥1000 h) is time-consuming and costly, a harsher test condition at more elevated temperature and higher alkaline concentration to push the limit of AEM stability was advised for degradation and durability studies of such membranes.
In this study, we investigate alkaline stability of aryl ether-free Diels-Alder polyphenylene (DAPP) with a trimethylammonium cation attached to an electron-donating hexamethylene spacer2 under low and high temperature (80, 120 and 160 °C) alkaline stability test conditions. Although high temperature stability testing may seem to be a useful tool to measure alkaline stability in a short time period, we observed different phenomena when DAPP AEM was subjected to the extreme test conditions in a pressure vessel. Even though DAPP AEM did not show any structural change or significant decrease in ion exchange capacity or hydroxide conductivity in 4 M NaOH at 80 °C after 3000 h, at the elevated temperature of 160 °C, the membrane underwent instant crosslinking resulted in insolubility of the membrane and sharp decrease in water uptake and swelling degree. The source of crosslinking is the low concentration of residual alkyl bromide from the incomplete quaternization process, which often causes initial conductivity decrease of AEMs. The crosslinked membrane did not show any further change in their properties, exhibiting consistent ion exchange capacity and hydroxide conductivity during the follow-up alkaline stability test (4 M NaOH, 80 °C, 1000 h). In this presentation, structural analysis and membrane properties including ion exchange capacity, water uptake, swelling degree, solubility, mechanical properties and hydroxide conductivity of DAPP AEMs after different temperature alkaline stability testing will be discussed to elucidate the unexpected consequence of high temperature accelerated stability test.

References

E. J. Park, Y. S. Kim. J. Mater. Chem. A, 2018, 6, 15456–15477.

M. R. Hibbs. J. Polym. Sci., Part B: Polym. Phys., 2013, 51, 1736–1742.
Modelling Anion-Exchange Membrane-Electrode Assembly Systems for CO2 Reduction
Authors: Weng Lien-Chun , Bell Alexis T. , Weber Adam Z. 
Published: February 2020

Gas diffusion electrodes (GDEs) have drastically increased the achievable CO2 reduction (CO2R) current density by overcoming the significant mass transport limitations observed in aqueous planar electrodes.1-3 The thin diffusion layer in GDEs, typically in the order of 10-100 nm, also allows operation of CO2R in alkaline conditions, which have been shown to suppress the side reaction, hydrogen evolution reaction (HER), and reduce the onset potentials of CO2R products such as CO and C2H4.4-7

With this increase in total current density, conventional cell designs for planar electrodes become severely limited by the ohmic drop across the cell, making membrane-electrode assemblies (MEAs) an attractive alternative. MEAs have smaller cell resistances as they do not have aqueous electrolyte compartments and can greatly reduce the distance between the two electrodes.
In this talk, we explore the mechanisms and limitations through multiphysics modeling of two MEA designs: one with gaseous feeds at both the anode and cathode (full-MEA); the other with an aqueous anode feed (KHCO­3 or KOH exchange solution) and a gaseous cathode feed (exchange-MEA). We discuss important cell design considerations such as the distribution of the applied voltage, water management, and CO2 utilization efficiencies. Finally, we examine the effects of temperature and the trade-off between CO2 solubility and water supply for a full-MEA.

R. L. Cook, R. C. Macduff and A. F. Sammells, J. Electrochem. Soc., 1990, 137, 607-608.

B. Kim, S. Ma, H.-R. Molly Jhong and P. J. A. Kenis, Electrochim. Acta, 2015, 166, 271-276.

L. C. Weng, A. T. Bell and A. Z. Weber, Phys. Chem. Chem. Phys., 2018, 20, 16973-16984.

S. Verma, X. Lu, S. Ma, R. I. Masel and P. J. Kenis, Phys. Chem. Chem. Phys., 2016, 18, 7075-7084.

C. T. Dinh, T. Burdyny, M. G. Kibria, A. Seifitokaldani, C. M. Gabardo, F. P. G. de Arquer, A. Kiani, J. P. Edwards, P. De Luna, O. S. Bushuyev, C. Q. Zou, R. Quintero-Bermudez, Y. J. Pang, D. Sinton and E. H. Sargent, Science, 2018, 360, 783-787.

C.-T. Dinh, F. P. García de Arquer, D. Sinton and E. H. Sargent, ACS Energy Lett., 2018, 3, 2835-2840.

D. Raciti, M. Mao, J. H. Park and C. Wang, J. Electrochem. Soc., 2018, 165, F799-F804.
(Invited) Electronic Tuning of Photo-Electro-Catalytic Processes By Intermediate-Band Oxides
Authors: Hu Shu 
Published: February 2020

Intermediate-band oxides possess tunable transport energy levels: they can serve as chemically-stable, transparent conductive protective layers for durable photo- and electro-catalytic processes. They have initially shown to promote charge separation, practically interfacing the otherwise unstable light absorbers and protecting them against corrosion. The initial re-discovery of “leaky” TiO2 coatings utilize their Ti3+- defect bands to stabilize an entire class of Si, GaP, GaAs, CdTe, BiVO4 semiconductors, as well as structured Si pillars and GaAs wires for 1000s-hour operation under sunlight. Recently, a ternary protective coating of manganese-alloyed titanium oxide, (Ti,Mn)Ox, had achieved the incorporation of transition metal cation impurities, e.g. Mn3+, into an otherwise insulating TiO2 coating. Here, Mn compositions can reach as high as 70% for a 150°C growth, which cannot be achieved by any method other than ALD.
The individual redox of the Mn3+ composes a continuous Mn-impurity band. On the one hand, this intermediate band induced electronic interactions between ALD coatings and underlying electro-catalysts, for boosting the hydrogen evolution activity of such buried interfaces. On the other hand, these oxide coatings have further shown to confine charge transport to specific electrochemical potentials and confine charge transfer to specific surface-attached intermediates, thus promoting product selectivity. To summarize, the tunable electronic structures of intermediate-band oxides enabled new strategies for controlling charge separation and charge transfer at liquid interfaces.
(Invited) Efficient Charge Ggeneration Dynamics in Hematite Photoanodes Decorated with Gold Nanostructures
Authors: Furube Akihiro , Okazaki Masahiro , Chen Liang-Yih 
Published: February 2020

Photochemical water splitting offers a useful solution for efficient energy conversion into hydrogen gas. Hematite has been focused on this purpose due to the advantage of low-cost, chemical stability, and suitable band gap. This photocatalytic ability, however, is limited by the short-lived carriers, the poor conductivity, and the short hole diffusion length. As one solution, combination with noble metal can enhance the photocatalytic performance. In particular, gold nanoparticles (AuNP) indicate characteristic absorption in the visible region and injection of electrons into the semiconductor. In this study, a hybrid material of hematite photoanodes with gold nanostructures was fabricated and the carrier dynamics was elucidated by femtosecond transient absorption (TA) spectroscopy.
The hybrid material was prepared by immersing the photoanode into the AuNP solution for 16 h, followed by heating at 400℃ for 4 h to remove the organic matter. Femtosecond pump-probe TA spectroscopy was carried out with a Ti:sapphire laser (800 nm wavelength, 130 fs fwhm pulse width, 0.7 mJ/pulse intensity, 1 kHz repetition; Spectra Physics, Hurricane) using pump pulses at 400 nm and probe pulses in the Vis/NIR region.
FE-SEM images of hematite and hematite decorated with AuNP (Au/Hematite) indicated that 40 nm AuNPs were decorated on the hematite surface. TA signal of hematite exhibited the positive absorption peak at the 585 nm, while the signal of Au/Hematite did bleaching at 580-620 nm overlapping with broad absorption whose apparent peak shifts from 670 nm towards 580 nm with time. The negative signal at the plasmon band indicates heat generation within the time resolution and cooling in the picosecond timescale. The observed strong positive absorption is induced by the increased electron density in the hematite due to electron transfer from AuNP, demonstrating efficient charge carrier generation in hematite by the decorated gold nanostructure.
(Invited) Single-Source Precursors for Gas Phase Deposition of Catalytic Coatings for Water Splitting Applications
Authors: Mathur Sanjay , Jürgensen Lasse , Fischer Thomas , Leduc Jennifer , Möllmann Alexander 
Published: February 2020

Keywords:
Single-source precursor, CVD, nanostructured films, catalytic water splitting
Investigation of the interplay of metal-organic chemistry will enrich the state-of-the-art of CVD and ALD technology and open new possibilities for the applications of new Ir-based materials. Therefore new heteroleptic Janus-typed compounds exhibiting high volatility and defined thermal decomposition under CVD and ALD conditions are reported to elaborate the precursor chemistry – materials synthesis – functional property chain. The new precursors unify both reactivity and sufficient stability through its heteroleptic constitution to provide a precise control over compositional purity in CVD and ALD deposits. CVD- and ALD-grown materials were tested towards their (electro)catalytic applications, particular in the oxygen evolution reactions. In this work functional characterization of deposited materials will be reported and their catalytic behavior is examined. The deposition on various substrate materials without the need of additional reactant gases underlines the potential of heteroleptic precursor class for CVD and ALD of metallic thin films. The presented CVD data opens new possibilities in the vapor phase synthesis of materials facilitating the application of such films, for example, as electro- or photocatalyst in OER and ORR.

Figure 1
(Invited) New Mixed-Anion Photocatalysts for Water Splitting and CO2 Fixation
Authors: Maeda Kazuhiko 
Published: February 2020

Water splitting and CO2 fixation using semiconductor photocatalysts are important reactions from the viewpoint of solar-to-fuel energy conversion toward artificial photosynthesis. Mixed-anion compounds containing more than one anionic species in a single-phase have attracted attention as visible-light-driven photocatalysts, since as compared to oxygen 2p orbital, p orbitals of less electronegative anion can form a valence band that possesses more negative potential. In this talk, recent progress on the development of new mixed-anion photocatalysts that are applicable to water splitting and CO2 fixation will be given.
We developed Ta and N-codoped rutile TiO2 for visible-light-driven water oxidation. TiO2:Ta,N powders modified with a RuO2 cocatalyst were active under visible light up to 540 nm for water oxidation to produce O2 in the presence of reversible electron acceptors (IO3
– or Fe3+), while TiO2:N exhibited negligible activity. Results of time-resolved infrared absorption spectroscopy revealed that the codoping Ta with N into TiO2 prolonged the lifetime of photogenerated free electrons, leading to high photocatalytic activity. Overall water splitting into H2 and O2 was achieved using TiO2:Ta,N, in combination with a H2-evolution photocatalyst of SrTiO3:Rh and an Fe3+/Fe2+ or IO3
–/I– redox couple even under simulated sunlight (AM1.5G). A similar result was obtained with rutile TiO2 codoped with N and F.
TiO2:Ta,N also served as a very stable photoanode to oxidize water under visible light, and could be coupled to not only a H2 evolution cathode but also a molecular photocathode for CO2 reduction. A photoelectrochemical cell constructed with RuO2/TiO2:Ta,N photoanode and Ru(II)–Re(I) supramolecular photocathode was capable of reducing CO2 into CO using water as the electron source upon visible light, with stoichiometric production of CO and O2.
Another interesting example of mixed-anion photocatalyst is an oxyfluoride pyrochlore Pb2Ti2O5.4F1.2. It had been believed that oxyfluorides are unsuitable as visible-light-responsive photocatalysts because of the highest electronegativity of fluorine. Surprisingly, Pb2Ti2O5.4F1.2 had an unprecedented small band gap of ca. 2.4 eV, and worked as a stable photocatalyst for visible-light H2 evolution and CO2 reduction when modified with suitable promoters. Density functional theory calculations indicated that the unprecedented visible-light-response of Pb2Ti2O5.4F1.2 originates from strong interaction between Pb-6s and O-2p orbitals, which is enabled by a short Pb–O bond in the pyrochlore lattice due to the fluorine substitution.
Charge Carrier Dynamics in Metal-Oxide/Nanocarbon Hybrid Photoelectrodes
Authors: Kormányos Attila , Honarfar Alireza , Pullerits Tönu , Janáky Csaba 
Published: February 2020

One of the most critical challenges of the 21st century is the shift in energy use from fossil fuels to renewable sources. Photoelectrochemical solar energy conversion, as a potentially attractive candidate, has gained an increased momentum during the recent years. Although both water-splitting (hydrogen evolution) and carbon dioxide reduction are promising avenues, they both have substantial shortcomings to be addressed. A common virtue of these two processes is that a good photoelectrode has to concurrently fulfill many attributes to drive these reactions efficiently. One of the most important is the efficient charge carrier transport, which ensures that most of the photogenerated charge carriers can be extracted both toward the electrode/electrolyte junction and toward the back contact. Numerous promising photoelectrode material showed poor performance due to extensive charge carrier recombination both in the bulk and at the surface. A well-known example is α-Fe2O3 (hematite), in which the hole-diffusion length is only 2-4 nm.1 One possible way to improve charge carrier transport properties is to deposit the metal-oxide on an interconnected nanocarbon network (e.g., carbon nanotubes or graphene). These highly conductive nanoscaffolds can improve the transport of the photogenerated charge carriers, which in turn, results in an enhanced photoelectrochemical performance.2

In my presentation, I am going to discuss how charge carrier dynamics of various hematite and hematite/nanocarbon composites is affected by the composition of the nanohybrids and by the applied bias. Hematite/nanocarbon photoelectrodes were synthesized by a two-step method: first the nanocarbon layer was spray-coated on the surface of the substrate electrode, and the nanostructured metal-oxide component was electrodeposited in a subsequent step. The metal-oxide/nanocarbon ratio was precisely controlled by the deposition charge density. To investigate charge carrier dynamics on a timescale ranging from seconds to femtoseconds three different techniques were employed: (i) transient absorption spectroscopy, employing a fs pump-probe setup, (ii) intensity-modulated photocurrent spectroscopy, and finally (iii) fast chronoamperometry. By covering this broad timescale, it was possible to study charge carrier transport, trapping and recombination processes, which were greatly affected by both the applied potential and the presence of the nanocarbons.
1 Energy Environ. Sci., 2016, 9, 2744—2775.
2 J. Am. Chem. Soc. 2017, 139, 6682−6692.