bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chromium Nitride/ N-Doped Carbon Heterostructure As Oxygen Reduction Electrocatalyst
Authors: Sarkar Bidushi , Nanda Karuna Kar 
Published: July 2021

One of the major challenges for the widespread application of clean energy technologies like fuel cells and metal air batteries is the development of an efficient Pt-free electrocatalyst for the cathodic oxygen reduction reaction (ORR). Further, the ORR activity is largely dependent on the pH of the electrolyte. To use a single catalyst for anion exchange membrane fuel cell, cation exchange membrane fuel cells and direct methanol fuel cells, the catalyst should be ORR active in alkaline as well as in acidic media and should be methanol tolerant.
In this regard, we synthesised chromium nitride (CrN) nanoparticles anchored onto N-doped graphitic carbon (CrN@NG) as a wide pH ORR catalyst active in alkaline as well as acidic media. The synthetic route offers a drastic development over traditionally used methods like nitridation, nanopatterning, etc by omitting the use of toxic ammonia and any expensive machinery. The CrN@NG catalyst is synthesized using simple precursors using single step pyrolysis. The CrN catalysts are reported to be used as ORR catalyst in alkaline media but the usage in acidic media is still restricted. Herein, the CrN@NG catalyst can potentially replacw Pt/C catalyst in alkaline and acidic media with comparable E1/2, Eonset and better durability. The close adherence of CrN nanoparticles and NG support plays a major role in enhancing the ORR activity. We believe that the simplistic method reported can be expanded to other metal nitrides as well.
Effects of Effluent Stream Composition and Competing Reactions Effect on Wastewater Nitrate Reduction in a Photoelectrochemical Device
Authors: Barrera Luisa , Bala Chandran Rohini 
Published: July 2021

More than 80% of nitrogen-contaminants are present in the form of nitrates in point sources of wastewater, including municipal wastewater effluents, ion-exchange brines, low-level nuclear wastes and in power generation. Wastewater nitrates represent an untapped source for the recovery of nutrients, value-added chemicals, and energy. Nitrates can be reduced to form ammonia, which can be used as a fertilizer or fuel, and nitrous oxide, which is a powerful oxidizer for the combustion and supercharging applications. Depending upon the source of the wastewater, the concentration of nitrates present in these streams can vary significantly. Ion-exchange brines and low-level nuclear wastes have large nitrate concentrations, on the order of > 0.1 M, whereas municipal and power generation effluents are more dilute (0.1 mM). However, the effect of varying contaminant concentrations and the competing redox reactions have not been quantified for these systems.
In this study, a photoelectrochemical device is proposed to transform wastewater nitrates into ammonia, coupled with water oxidation. We expand on a previously developed numerical model to include the effects of the reacting nitrate species concentrations and the competing redox reactions on the solar-to-chemical efficiencies and nitrogen-removal rates. Notably, we implemented an equivalent circuit modeling approach to account for the influences of the competing reactions and the concentration-dependent mass-transfer limiting current densities. Model results predict that for a single light-absorber and a nitrate concentration of 100 mM, the optimal solar-to-chemical efficiency is 7% and the nitrogen recovery rate (as NH3) is 260 gN m-2 day-1. Oxygen reduction is more dominant as a competing reaction than hydrogen reduction at the cathode. However, this reduction is mass-transfer limited even while assuming an air-saturated (1 atm) device and therefore didn’t impact the performance significantly. Modeling results are complemented by experimental measurements of the effects of nitrate concentrations on the operating current densities and the rates of product formation with copper and platinum electrodes at the cathode and anode respectively.
(Invited) Multi-Scale Photocorrosion Modeling in Photoelectrodes and Photoelectrochemical Devices
Authors: Haussener Sophia 
Published: July 2021

The development of a sustainable energy economy based on renewable, carbon-neutral energy is a necessary and urgent task. Photo-electrochemical (PEC) approaches to solar fuels and materials are interesting, provided they can be efficiently, stably, scalably, and sustainably implemented.
While significant progress on the development of earth abundant materials and on high-efficiency demonstrations has been achieved, there is relatively little known about the behavior of materials and devices under more realistic, varying conditions and on the implication of degradation on the performance and lifetime.
Here, I will first discuss multi-scale numerical modeling approaches to investigate and quantify the effect of photocorrosion on the performance evolution. I will show how important the local reaction environment is for the stability of a component, and how heterogeneity in the operating variables (current density, species concentration, temperature, etc.) affect degradation. Furthermore, I will comment on the importance of device design on device stability.
Second, I will then transition towards discussing material, device and system performance as a function of varying, non-design-point operation. I will show how these dynamics can affect the performance, show how multi-physical transport can help in controlling and smoothing some of the observed variations, and generally highlight synergistic effects. I will end with providing general guidelines on operating materials, devices and systems under more realistic conditions.
Modeling Photocatalysts and Reactors for Solar Hydrogen Production through Particle-Based Water Splitting
Authors: Savant Sangram Ashok , Haussener Sophia 
Published: July 2021

Hydrogen as an energy carrier has by far the highest gravimetric energy density, which, when produced by a renewable pathway would go a long in achieving the goal of carbon neutral and responsible economy. Photocatalytic water splitting is a promising approach for the production of solar hydrogen. The technological potential of this approach is unclear and it is not known how the choice of the components (semiconducting particles, electrolyte, mediator, etc.), the design of the system, and the operating conditions affect the performance of the system.
Firstly, we present a steady 1-dimensional model of a single photocatalyst particle which couples semiconductor physics to account for the charge carrier generation and transport with the electrochemical kinetics governed by the butler-volmer equation. We account for the solar absorption and the charge carrier generation with Lambert-Beer’s law. We then solve for the carrier transport and conservation with Poisson’s equations and the hole and electron transport by drift diffusion currents. We assume the recombination in the particle to be a Shockley-Reed-Hall trap recombination. The semiconductor electrolyte interface is treated as an ideal Schottky contact. We show the effect of intrinsic parameters like doping concentration, electron affinity (band positions), relative permittivity on the operating current density. We also present the effect of particle size on the operating current density.
Secondly, we present a transient 0-dimensional model, which accounts for ideal solar absorption, ideal charge generation and transport, and the kinetic characteristics at the catalytic sites for two sets of photocatalyst semiconductor particles. We solve for species transport (mediator species and protons) and conservation in the one or two reactor compartments separated by a semipermeable membrane. We evaluate this 0-dimensional model on a reactor level as well, comparing three different reactor types, these three types include: i) a single photocatalyst reactor, ii) a membrane-separated dual compartment reactor and iii) a membrane-separated dual compartment reactor with wire and two auxiliary electrodes. We put forth a theoretically limiting efficiency which considers no overpotentials and a realistic case which accounts for losses for each type of reactor. For these reactor designs, we establish a link between the thermodynamic limits and materials requirements, changes in material requirements when more realistic operation and losses are considered, and compare the three reactor designs.
Conclusively, the steady 1-dimensional particle model allows us to evaluate the effect of intrinsic material properties of a single photocatalyst on the operating current density, and the transient 0-dimensional model giving us a broader evaluation on a reactor design level with respect to the employed photocatalysts and redox mediators.
Tunable Heterostructured Nanomaterials for Efficient Hydrogenation Reactions at Intermediate Temperatures
Authors: Li Meng , Hua Bin , Wang Lucun , Wu Wei , Ding Dong 
Published: July 2021

To address rising environmental concerns and energy challenges, it is highly desirable to develop green technologies for a sustainable future. Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds. Electrochemical CO2 and N2 hydrogenation using renewable electricity is considered one of the most promising pathways to reach the environmental economics. Among various electrochemical devices, a solid state electrolyzer working at intermediate temperatures has the advantages of high reaction rates and low overpotentials. As CO2 and N2 molecules are quite stable, it is critical to develop electrocatalysts with high activity to reduce electricity engagement. Also, CO2 hydrogenation has multiple pathways which normally results in low selectivity for a target product. A tunable electrocatalyst with high selectivity to different products is desirable for CO2 hydrogenations. Heterostructured nanomaterials attracts great attentions in electrochemical systems. With careful design, they can show very high activity and selectivity towards an electrochemical reaction. In this work, we combine theoretical simulations, including density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations, with experimental methods (characterizations and electrochemical measurements) for rational design of highly efficient heterostructured nanomaterials for CO2 and N2 hydrogenations.
We studied the strong metal-support interaction (SMSI) in a doped CeO2 supported noble metal nanoparticles (NPs) system using theoretical calculations. The results indicate that SMSI largely depends on chemical conditions of the support and particle size of dispersed metal NPs. By tuning the SMSI, we can successfully change the catalytic activity and selectivity towards CO2 and N2 hydrogenation reactions. Based on these findings, we designed tunable heterostructured nanomaterials for efficient hydrogenation reactions at intermediate temperatures. These predictions were further confirmed by experimental method. By using a combination of high-throughput theoretical calculations and electrochemical measurements, we developed highly active catalysts for electrochemical CO2 and N2 hydrogenation reactions. This framework is also applicable to other electrochemical systems using heterostructured materials.
(Invited) Conjugated Semiconductors for Photoelectrochemical and Photocatalytic Hydrogen Production Via Water Splitting
Authors: Sivula Kevin 
Published: July 2021

The application of pi-conjugated polymeric semiconductors toward direct solar-to-fuel energy conversion by photoelectrochemical (PEC) or heterogeneous photocatalytic (PC) approaches is an emerging trend.[1] While these materials offer impressive tunability of energy levels and light absorption, their long-term robustness under the harsh conditions of PEC or PC water splitting is a major concern.[2] In this presentation critical factors that influence the operational stability of donor:acceptor bulk heterojunction photoelectrodes[3] for solar hydrogen production are discussed and routes to significantly advance their performance under long term operation are presented. An outlook on employing organic based semiconductor systems in comparison to their inorganic counterparts will be presented with respect to the possible economic viability of this technology.
[1] Adv. Energy Mater.
2018, 8, 1802585.
[2] ACS Energy Lett. 2020, 5, 1970.
[3] J. Am. Chem. Soc. 2020
, 142, 7795.
Understanding and Controlling the Efficiency of Au24
m(SR)18 Nanoclusters As Singlet-Oxygen Photosensitizers
Authors: Agrachev Mikhail , Fei Wenwen , Antonello Sabrina , Bonacchi Sara , Dainese Tiziano , Zoleo Alfonso , Ruzzi Marco , Maran Flavio 
Published: July 2021

Singlet oxygen, 1O2, is an excited oxygen species [1] that can be efficiently generated by photosensitizers. These are molecules that upon photoexcitation eventually generate a triplet excited state that can be quenched by the ground state oxygen triplet, 3O2, to form 1O2 [1]. The latter finds uses in many applications, especially organic synthesis, photocatalysis, and photodynamic therapy [2-4]. On the other hand, its possible use depends on its effective lifetime, as 1O2 is a very reactive species that decays via quenching by the solvent and/or interactions with other molecules in solution [1]. This is the case of the photosensitizers themselves, and this may result in a serious drawback for efficient applications of 1O2. In this area, the use of monolayer-protected metal nanoclusters as photosensitizers is limited. We carried out a systematic study on the photosensitizer behavior of a series of molecular Au24M(SR)18 clusters [5,6], where the R group and the doping metal M were varied. Electrochemical characterization allowed us to select the best R/M combinations to test a sufficiently large oxidation-potential range. 1O2 detection was carried out by time-resolved electron paramagnetic resonance [7], which allowed us to determine 1O2 lifetimes spanning more than one order of magnitude (on the microsecond time scale), depending on the specific cluster employed. Among the main results, we found that: (i) a more positive potential for the oxidation of the cluster is matched by a (beneficial) longer 1O2 lifetime; (ii) proper design of the electrochemical properties of the cluster yields the same results as those of reference photosensitizers, despite the unprecedented low oxidation potentials exhibited by these clusters; (iii) kinetic analysis based on the Marcus theory provides important insights into the mechanism of the quenching of 1O2 by gold nanoclusters, how to control it, and why properly doped gold nanoclusters may perform very well in 1O2 photosensitization [8]. Further effects, detected by electrochemistry, are under investigation.
References
[1] Bregnhoj, M.; Westberg, M.; Minaev, B. F.; Ogilby, P. R. Acc. Chem. Res.
2017, 50, 1920.
[2] Turro, N. J.; Ramamurthy, V.; Scaiano, J. C. Molecular Oxygen and Organic Photochemistry. In Modern Molecular Photochemistry of Organic Molecules; University Science Books: Sausalito, CA, 2010; Ch. 14.
[3] Ghogare, A. A.; Greer, A. Chem. Rev.
2016, 116, 9994.
[4] Nosaka, Y.; Nosaka, A. Y. Chem. Rev.
2017, 117, 11302.
[5] Antonello, S.; Maran, F. Curr. Opin. Electrochem.
2017, 2, 18.
[6] Fei, W.; Antonello, S.; Dainese, T.; Dolmella, A.; Lahtinen, M.; Rissanen, K.; Venzo, A.; Maran, F. J. Am. Chem. Soc.
2019, 141, 16033.
[7] Agrachev, M.; Ruzzi, M.; Venzo, A.; Maran, F. Acc. Chem. Res. 2019, 52, 44.
[8] Agrachev, M.; Fei, W.; Antonello, S.; Bonacchi, S.; Dainese, T.; Zoleo, A.; Ruzzi, M.; Maran, F. Chem. Sci.
2020, 11, 3427.
A New Approach to Selectivity in a Preparative Electrochemical Reaction
Authors: Jing Qiwei , Feng Enqi , Moeller Kevin D 
Published: July 2021

We have been trying to introduce new selectivity into electrochemical reactions by modifying the surface of an electrode and then confining chemical reactions to the region of the reaction close to that surface. The goal is to translate the extremely high levels of site-selectivity seen in chemical reactions on a microelectrode array into a tool for preparative synthetic reactions. As a proof-of-principle experiment, we have coated a Pt-anode with a diblock copolymer that is known to have an affinity for pyrene groups. The electrode is then used in the oxidation of two alcohol substrates; one having the pyrene group and one not having a pyrene group (Scheme 1). The oxidation reactions are mediated by a TEMPO-derived oxidant. The oxidant can be confined to the region immediately surrounding the electrode with the use of methyl-α-D-glucopyranoside which is known to undergo fast oxidations with the TEMPO derived oxidant.
In the experiment, we found that a competition study between the two substrate led to a 1:1 mixture of the two aldehydes when a bare Pt-electrode was used, a 2:1 mixture (4:3) of the two aldehydes when the Pt electrode was modified with the diblock copolymer, and a 20:1 ratio (4:3) of the two aldehydes when the modified electrode was used in conjunction with the confining agent. From this experiment it was clear that a molecular recognition event on the surface of the electrode could be used to control the selectivity of the reaction in the reaction was confined to the surface of the electrode.
The origin of the selectivity in this reaction and its implications for future synthetic transformations will be discussed.

Figure 1
Electrochemical Oxidation of Phenol-Based Analogues Towards C-C Bond Formation
Authors: Gao Stephanie , Lewis Tyra , Dobson Breenna , Martic Sanela 
Published: July 2021

The use of phenolic compounds range from the industrial sector and agriculture to pharmaceuticals. These compounds may serve as a phenolic precursor to produce raw materials in a wide range of applications. The selective electrochemical oxidation of bulky phenols was recently achieved [1]. Herein, the 2,2-dihydroxybiphenyl (DHBP) was characterized in an aprotic environment using cyclic voltammetry, square-wave voltammetry, and UV-vis spectroscopy. The DHBP was characterized with an irreversible oxidation. The electrooxidation of DHBP by CV and chronoamperometry resulted in the solution colour change and the formation of new products. The product formation was monitored by UV-vis and fluorescence spectroscopy and characterized by mass spectrometry.
[1] Zabik, N. L.; Virca, C. N.; McCormick, T. M.; Martic-Milne, S. Selective Electrochemical versus Chemical Oxidation of Bulky Phenol. J. Phys. Chem. B
2016, 120 (34), 8914–8924. https://doi.org/10.1021/acs.jpcb.6b06135.
(Invited) Electrochemical Hydrodefluorination of Trifluoromethyl Groups
Authors: Lennox Alastair J. J. 
Published: July 2021

The difluoromethyl group (CF2H) has attracted significant recent attention in medicinal chemistry. This complements the well-documented importance of fluorine in small-molecule pharmaceuticals that impact bioavailability, potency and pharmacokinetics. This is exemplified by 28% of FDA-approved drugs containing one or more fluorine atom. The CF2H group is an H-bond donor that is also lipophilic, which is a unique combination, and is thus becoming an increasingly valuable tool within drug discovery. Current methods to prepare them are limited either by a limited scope or by the prohibitively expensive reagents that are required.
We have developed methods to form these important difluoromethyl groups from readily installed trifluoromethyl groups using an electrochemical reductive approach. This reaction requires “deeply-reductive” potentials, which poses several problems, including functional group intolerance and low charge efficiencies. We have developed conditions that overcome these problems to produce a single-step process that can be applied to a wide scope of substrates, including those containing reductively sensitive functionality. Details of our studies into the electrochemical hydrodefluorination at highly reductive potentials will be presented.
(Invited) Chiral Lewis Acid-Catalyzed Asymmetric Electrochemical Reactions
Authors: Guo Chang 
Published: July 2021

Although the field of electrochemical synthesis has been developed rapidly, it is still highly desirable to develop the asymmetric electrochemical transformation as a general strategy for controlling the reactivity and enantioselectivity.1 More importantly, the routine application of asymmetric electrosynthesis to pursue the total synthesis of bioactive molecules remains an unsolved challenge in organic chemistry. Our goal was to provide an attractive and sustainable alternative for the distinctive activation of bond connections in a highly asymmetric fashion. We apply a reliable chiral Lewis acid-catalytic strategy in the asymmetric electrochemical transformations.2

Reference:
(1) Chang, X.; Zhang, Q.; Guo, C.* Angew. Chem. Int. Ed.
2020, 132, 12612-12622.
(2) a) Zhang, Q.; Chang, X.; Peng, L.; Guo, C.* Angew. Chem. Int. Ed.
2019, 131, 7073-7077; b) Chang, X.; Zhang, J.; Zhang, Q.; Guo, C.* Angew. Chem. Int. Ed. 2020, 132, 18658-18662.

Figure 1
(Student Battery Slam Best Presentation Award Winner) Enhancing the Stability of the Electrode/Electrolyte Interface in Solid State Li-Ion Batteries
Authors: Gogia Ashish , Estevez Luis , Subramanyam Guru , Kumar Jitendra 
Published: July 2021

All-solid-state Lithium-ion batteries (LIBs) based on solid ceramic electrolytes are a promising next-generation energy storage technology for high energy density and enhanced cycle life. A key requirement for such batteries is packing high energy in low form factor (i.e. in thin-film form) to increase both the gravimetric and volumetric energy densities. Lithium superionic conducting (LISICON) solid electrolytes are prominent candidates among liquid, gel, polymer and solid electrolytes that can enable safety and optimum performance in a high energy density battery with thin-film cell components. One particular LISICON material, lithium aluminum germanium phosphate (LAGP), is a promising solid-electrolyte due to its high ionic conductivity (~ 5 mS/cm at 23 °C), high electrochemical stability window (> 5V), and single Li+ ion conduction (high transference number, low porosity mitigating dendrite propagation), enabling a high energy battery and mitigating safety and packaging issues of conventional LIBs. However, most solid electrolytes, suffer from low chemical stability with the lithium (Li) anode. This is especially true for LAGP, with such chemical instability invariably leading to the formation of a highly resistive electrode/electrolyte interface which is detrimental for high power and cell longevity. Therefore, despite the promise of solid ceramic electrolytes for next-generation solid-state LIBs, if they are to be practical for use in solid-state LIBs with Li metal anodes, it is very important to design a chemically stable interface with kinetically efficient charge transport processes (i.e. Li+ transport).
In order to enhance the chemical stability of the electrode/electrolyte interface, we identified lithium compatible materials (such as thin film of lithium phosphorus oxynitride (LIPON), gold (Au), carbon nanotube (CNT) layer, aluminium oxide (Al2O3) and suitable methods to apply them at the Li metal/LAGP interface. The evolution of the interfacial resistance as a function of time was monitored using Electrochemical Impedance Spectroscopy (EIS). We will present data showing that the application of the lithium-compatible, thin film interfacial layer, results in enhanced stability and a significant reduction in resistance compared with the unmodified Li metal/LAGP interface, offering an interfacial engineering approach for improved performance of an all-solid-state LIB.