Integrated Photoelectrochemical Solar Energy Conversion and Organic Redox Flow Battery Devices

Building on regenerative photoelectrochemical solar cells and emerging electrochemical redox flow batteries (RFBs), more efficient, scalable, compact, and cost‐effective hybrid energy conversion and storage devices could be realized. An integrated photoelectrochemical solar energy conversion and electrochemical storage device is developed by integrating regenerative silicon solar cells and 9,10‐anthraquinone‐2,7‐disulfonic acid (AQDS)/1,2‐benzoquinone‐3,5‐disulfonic acid (BQDS) RFBs. The device can be directly charged by solar light without external bias, and discharged like normal RFBs with an energy storage density of 1.15 Wh L^?1 and a solar‐to‐output electricity efficiency (SOEE) of 1.7 % over many cycles. The concept exploits a previously undeveloped design connecting two major energy technologies and promises a general approach for storing solar energy electrochemically with high theoretical storage capacity and efficiency.     

Thermodynamics,Charge Transfer and Practical Considerations of Solid Boosters in Redox Flow Batteries

Solid boosters are an emerging concept for improving the performance and especially the energy storage density of the redox flow batteries, but thermodynamical and practical considerations of these systems are missing, scarce or scattered in the literature. In this paper we will formulate how these systems work from the point of view of thermodynamics. We describe possible pathways for charge transfer, estimate the overpotentials required for these reactions in realistic conditions, and illustrate the range of energy storage densities achievable considering different redox electrolyte concentrations, solid volume fractions and solid charge storage densities. Approximately 80% of charge storage capacity of the solid can be accessed if redox electrolyte and redox solid have matching redox potentials. 100 times higher active areas are required from the solid boosters in the tank to reach overpotentials of <10 mV.     

Prediction of Redox Potentials and Isomer Distribution Yields for Reductive Dechlorination of Chlorobenzenes

Abstract

Gibbs free energies of reductive dechlorination processes of chlorobenzenes are calculated from thermodynamic data. The results are utilized to predict redox potentials and isomer distribution yields.

The model predicts a standard redox potential of 0.680 V for the reduction of hexachlorobenzene to pentachlorobenzene, tapering off to 0.535 V for the reduction of monochlorobenzene to benzene. It is shown that under anaerobic conditions, reductive dechlorination is more likely to occur, while aerobic conditions favour the formation of chlorophenols.

An isomer distribution yield is predicted for each of the reductive dechlorination processes of chlorobenzenes. Predicted yields correspond to experimental values within 10%. The model includes a possibility to establish a temperature dependence of the relative isomer yields.     

On the Use of Thermodynamic Cycles for the Calculation of Standard Potentials for the Oxidation of Solid Metals in Solution

The performance of a thermodynamic cycle for the calculation of the standard reduction potential (SRP) of a series of metals is examined. It is found that the introduction of simple entropic corrections substantially improves the agreement with experimental data. The accuracy of the estimations is in the range of 0.04 V, which opens the possibility to calculate the SRP for metals in non-aqueous solvents or other unusual situations.     

Structure and electrochemical properties for complexes of nitrocompounds with inorganic ions: A theoretical approach

Reduction and oxidation (redox) reactions are widely used for removal of nitrocompounds from contaminated soil and water. Structures and redox properties for complexes of nitrocompounds, such as 2,4,6‐trinitrotoluene (TNT), 2,4‐dinitrotoluene (DNT), 2,4‐dinitroanisole (DNAN), and 5‐nitro‐2,4‐dihydro‐3H?1,2,4‐triazol‐3‐one (NTO), with common inorganic ions (Na⁺, Cl^?, ) were investigated at the SMD(Pauling)/PCM(Pauling)/MPWB1K/TZVP level of theory. Atoms in molecules (AIM) theory was applied to analyze the topological properties of the bond critical points involved in the interactions between the nitrocompounds and the ions. Topological analyses show that intermolecular interactions of the types O(N)…Na⁺, C‐H…Cl^?( ), and C…Cl^?( ) may be discussed as noncovalent closed‐shell interactions, while N‐H···Cl^?( ) hydrogen bonds are partially covalent in nature. Complexation causes significant decrease of redox activity of the nitrocompounds. Analysis of the reduction potentials of the complexes obtained through application of the Pourbaix diagram of an iron/water system revealed that sodium complexes of NTO might be reduced by metallic iron. © 2016 Wiley Periodicals, Inc.     

Direct Solar Charging of an Organic–Inorganic,Stable, and Aqueous Alkaline Redox Flow Battery with a Hematite Photoanode

The intermittent nature of the sunlight and its increasing contribution to electricity generation is fostering the energy storage research. Direct solar charging of an auspicious type of redox flow battery could make solar energy directly and efficiently dispatchable. The first solar aqueous alkaline redox flow battery using low cost and environmentally safe materials is demonstrated. The electrolytes consist of the redox couples ferrocyanide and anthraquinone‐2,7‐disulphonate in sodium hydroxide solution, yielding a standard cell potential of 0.74 V. Photovoltage enhancement strategies are demonstrated for the ferrocyanide‐hematite junction by employing an annealing treatment and growing a layer of a conductive polyaniline polymer on the electrode surface, which decreases electron–hole recombination.     

Novel,Stable Catholyte for Aqueous Organic Redox Flow Batteries: Symmetric Cell Study of Hydroquinones with High Accessible Capacity

Owing to their broad range of redox potential, quinones/hydroquinones can be utilized for energy storage in redox flow batteries. In terms of stability, organic catholytes are more challenging than anolytes. The two-electron transfer feature adds value when building all-quinone flow battery systems. However, the dimerization of quinones/hydroquinones usually makes it difficult to achieve a full two-electron transfer in practical redox flow battery applications. In this work, we designed and synthesized four new hydroquinone derivatives bearing morpholinomethylene and/or methyl groups in different positions on the benzene ring to probe molecular stability upon battery cycling. The redox potential of the four molecules were investigated, followed by long-term stability tests using different supporting electrolytes and cell cycling methods in a symmetric flow cell. The derivative with two unoccupied ortho positions was found highly unstable, the cell of which exhibited a capacity decay rate of ~50% per day. Fully substituted hydroquinones turned out to be more stable. In particular, 2,6-dimethyl-3,5-bis(morpholinomethylene)benzene-1,4-diol (asym-O-5) displayed a capacity decay of only 0.45%/day with four-week potentiostatic cycling at 0.1 M in 1 M H₃PO₄. In addition, the three fully substituted hydroquinones displayed good accessible capacity of over 82%, much higher than those of conventional quinone derivatives.     

Computational Prediction for the Slopes of AL-type Phase Solubility Curves of Organic Compounds Complexed With α-, β-, or γ-cyclodextrins Based on Monte Carlo Docking Simulations

A Monte Carlo (MC) docking method was introduced in order to predict the aqueous solubility of inclusion complexes composed of small organic compounds and various cyclodextrins. The slope (S) of the A_L-type phase solubility curve was accurately predicted by a combination of the interaction energy and nonpolar solvation free energy for each of the docked complexes. The regression equation for S, the slope of the phase solubility curve gives a fine correlation coefficient, r ², of 0.913 and standard error of 0.028 for the 63 organic compounds complexed with cyclodextrins.     

Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible Fe^III/IV and Fe^IV/V anodic transitions, the formal reduction potentials (E°′) for which are observed in the ranges 0.4–1.2 and 1.4–1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°′(IV/V) against E°′(III/IV) plot suggests that the TAML ligand system plays a bigger role in the Fe^III/IV transition, whereas the second electron transfer is to a larger extent an iron-centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°′(III/IV) and E°′(IV V⁻¹) correlate 1) with the pK_a values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern–Volmer constants K_SV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of Fe^III and Fe^IV TAMLs; and 4) with rate constants k_I and k_II for the oxidation of the resting iron(III) TAML state by H₂O₂ and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log k_II versus E°′(III/IV) plots are lower for fast-to-oxidize S than for slow-to-oxidize S. The log k_I versus E°′(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H₂O₂ as a horseradish peroxidase enzyme.     

第一性原理方法预测水相核酸碱基及其代谢物的氧化还原电动势

氧化还原电动势是了解核酸中电荷/电子转移过程以及设计具有新型氧化还原活性的碱基类化合物的重要参数. 本文对82个芳香化合物的氧化还原电动势进行理论预测, 通过计算值和实验值的比较发现: 气相采用B3LYP/6-311++G(2df,2p)//B3LYP/6-31+G(d)方法, 液相采用HF-COSMORS/UAHF方法, 对运用HF- CPCM/UAHF方法在水相重新优化的构型计算溶剂化能, 能有效预测芳香化合物水相氧化还原电动势, 该理论方法计算的绝对均方根误差(RMSD)为0.124 V. 运用该理论方法成功预测了属于芳香化合物的核酸碱基及其代谢物的水相氧化还原电动势. 根据预测结果, 讨论了核酸中电荷/电子转移过程以及结构改变对设计具有新型氧化还原活性的核酸碱基类化合物的影响. 本文为设计具有氧化还原活性的新型核酸碱基类化合物提供了一种理论方法.     

First Principles Neural Network Potentials for Reactive Simulations of Large Molecular and Condensed Systems

Modern simulation techniques have reached a level of maturity which allows a wide range of problems in chemistry and materials science to be addressed. Unfortunately, the application of first principles methods with predictive power is still limited to rather small systems, and despite the rapid evolution of computer hardware no fundamental change in this situation can be expected. Consequently, the development of more efficient but equally reliable atomistic potentials to reach an atomic level understanding of complex systems has received considerable attention in recent years. A promising new development has been the introduction of machine learning (ML) methods to describe the atomic interactions. Once trained with electronic structure data, ML potentials can accelerate computer simulations by several orders of magnitude, while preserving quantum mechanical accuracy. This Review considers the methodology of an important class of ML potentials that employs artificial neural networks.     

Thiocyanate‐free ruthenium(II) tetrabenzoporphyrin sensitizers for photoelectrochemical cell: A DFT/TD‐DFT probe for stability of axial donor ligands

Although previously studied [(HOOC)₄(TBPor)Ru(NCS)₂]^2– ( A ; TBPor = tetrabenzoporphrin) avoided the intrinsic π‐stacking aggregation of planar metallophorphryins via incorporating two axial ligands, these isothiocyanato groups are believed to be the weakest part of the sensitizer while operating in dye‐sensitized solar cells (DSSCs). In this work, a series of thiocyanate‐free ruthenium porphyrin complexes featuring with phenyl/substituted‐phenyl axial groups, [(HOOC)₄(TBPor)Ru(L′)₂]^2– (L′ = Ph ( 1 ), PhF₂ ( 2 ), PhCl₂ ( 3 ), PhBr₂ ( 4 ), and PhI₂ ( 5 )), have been examined using density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Both analyses of electronic structures and calculations of interaction energies demonstrate that the Ru‐L′ interaction in 1 – 5 is significantly enhanced relative to the Ru‐NCS in A , which will raise chemical stability of the former in DSSCs. Single‐electron oxidation mechanism has been proposed. Oxidation potentials (E⁰) are increased by 0.2–0.6 V when changing axial groups from NCS to Ph/PhX₂. The spin‐orbit coupling (SOC) relativistic effects can be negligible in computing E⁰ values. TD‐DFT calculations show that 1 – 5 have more intense Q band in the visible region than A does. Taken together, high chemical stability, suitable oxidation potential and expanding absorption spectra would allow for potential applications of the thiocyanate‐free sensitizers in DSSCs. © 2016 Wiley Periodicals, Inc.     

A Cation and Anion Dual Doping Strategy for the Elevation of Titanium Redox Potential for High-Power Sodium-Ion Batteries

Titanium-based polyanions have been intensively investigated for sodium-ion batteries owing to their superior structural stability and thermal safety. However, their low working potential hindered further applications. Now, a cation and anion dual doping strategy is used to boost the redox potential of Ti-based cathodes of Na₃Ti_0.5V_0.5(PO₃)₃N as a new cathode material for sodium ion batteries. Both the Ti³⁺/Ti⁴⁺ and V³⁺/V⁴⁺ redox couples are reversibly accessed, leading to two distinctive voltage platforms at ca. 3.3 V and ca. 3.8 V, respectively. The remarkably improved cycling stability (86.3 %, 3000 cycles) can be ascribed to the near-zero volume strain in this unusual cubic symmetry, which has been demonstrated by in situ synchrotron-based X-ray diffraction. First-principles calculations reveal its well-interconnected 3D Na diffusion pathways with low energy barriers, and the two-sodium-extracted intermediate NaTi_0.5V_0.5(PO₃)₃N is also a stable phase according to formation energy calculations.     

Experimental and Computational Analysis of the Solvent‐Dependent O2/Li+‐O2− Redox Couple: Standard Potentials,Coupling Strength,and Implications for Lithium–Oxygen Batteries

Understanding and controlling the kinetics of O₂ reduction in the presence of Li⁺‐containing aprotic solvents, to either Li⁺‐O₂^? by one‐electron reduction or Li₂O₂ by two‐electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li‐O₂ batteries. Standard potentials of O₂/Li⁺‐O₂^? and O₂/O₂^? were experimentally measured and computed using a mixed cluster‐continuum model of ion solvation. Increasing combined solvation of Li⁺ and O₂^? was found to lower the coupling of Li⁺‐O₂^? and the difference between O₂/Li⁺‐O₂^? and O₂/O₂^? potentials. The solvation energy of Li⁺ trended with donor number (DN), and varied greater than that of O₂^? ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li⁺‐O₂^? solubility and DN. These results highlight the importance of the interplay between ion–solvent and ion–ion interactions for manipulating the energetics of intermediate species produced in aprotic metal–oxygen batteries.     

CAST: A new program package for the accurate characterization of large and flexible molecular systems

The presented program package, Conformational Analysis and Search Tool (CAST) allows the accurate treatment of large and flexible (macro) molecular systems. For the determination of thermally accessible minima CAST offers the newly developed TabuSearch algorithm, but algorithms such as Monte Carlo (MC), MC with minimization, and molecular dynamics are implemented as well. For the determination of reaction paths, CAST provides the PathOpt, the Nudge Elastic band, and the umbrella sampling approach. Access to free energies is possible through the free energy perturbation approach. Along with a number of standard force fields, a newly developed symmetry‐adapted perturbation theory‐based force field is included. Semiempirical computations are possible through DFTB+ and MOPAC interfaces. For calculations based on density functional theory, a Message Passing Interface (MPI) interface to the Graphics Processing Unit (GPU)‐accelerated TeraChem program is available. The program is available on request. © 2014 Wiley Periodicals, Inc.     

A Cation and Anion Dual Doping Strategy for the Elevation of Titanium Redox Potential for High‐Power Sodium‐Ion Batteries

Titanium‐based polyanions have been intensively investigated for sodium‐ion batteries owing to their superior structural stability and thermal safety. However, their low working potential hindered further applications. Now, a cation and anion dual doping strategy is used to boost the redox potential of Ti‐based cathodes of Na₃Ti_0.5V_0.5(PO₃)₃N as a new cathode material for sodium ion batteries. Both the Ti³⁺/Ti⁴⁺ and V³⁺/V⁴⁺ redox couples are reversibly accessed, leading to two distinctive voltage platforms at ca. 3.3 V and ca. 3.8 V, respectively. The remarkably improved cycling stability (86.3 %, 3000 cycles) can be ascribed to the near‐zero volume strain in this unusual cubic symmetry, which has been demonstrated by in situ synchrotron‐based X‐ray diffraction. First‐principles calculations reveal its well‐interconnected 3D Na diffusion pathways with low energy barriers, and the two‐sodium‐extracted intermediate NaTi_0.5V_0.5(PO₃)₃N is also a stable phase according to formation energy calculations.     

A Very Useful Redox Initiator for Aqueous RAFT Polymerization of N‐Isopropylacrylamide and Acrylamide at Room Temperature

Reversible addition fragmentation chain transfer (RAFT) polymerizations of N‐isopropylacrylamide (NIPAM), and acrylamide (AM) were successfully performed in aqueous media at ambient temperature using a redox initiator, potassium persulfate (K₂S₂O₈), and sodium thiosulfate (Na₂S₂O₃). The molecular weight of the polymers obtained increases linearly with monomer conversion, molecular weight distribution is narrow even at high conversion (>90%), and a linear relationship exists between ln([M]₀/[M]) and polymerization time. Moreover, self‐chain extension reaction also proceeded successfully. All the results demonstrate that K₂S₂O₈–Na₂S₂O₃ is a very efficient initiating system for the RAFT polymerizations of NIPAM and AM in aqueous media at room temperature.

     

Interesting properties of Thomas–Fermi kinetic and Parr electron–electron‐repulsion DFT energy functional generated compact one‐electron density approximation for ground‐state electronic energy of molecular systems

The reduction of the electronic Schrodinger equation or its calculating algorithm from 4N‐dimensions to a (nonlinear, approximate) density functional of three spatial dimension one‐electron density for an N‐electron system, which is tractable in the practice, is a long desired goal in electronic structure calculation. If the Thomas‐Fermi kinetic energy (～∫ρ^5/3d r ₁) and Parr electron–electron repulsion energy (～∫ρ^4/3d r ₁) main‐term functionals are accepted, and they should, the later described, compact one‐electron density approximation for calculating ground state electronic energy from the 2nd Hohenberg–Kohn theorem is also noticeable, because it is a certain consequence of the aforementioned two basic functionals. Its two parameters have been fitted to neutral and ionic atoms, which are transferable to molecules when one uses it for estimating ground‐state electronic energy. The convergence is proportional to the number of nuclei (M) needing low disc space usage and numerical integration. Its properties are discussed and compared with known ab initio methods, and for energy differences (here atomic ionization potentials) it is comparable or sometimes gives better result than those. It does not reach the chemical accuracy for total electronic energy, but beside its amusing simplicity, it is interesting in theoretical point of view, and can serve as generator function for more accurate one‐electron density models. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

A genetic algorithm encoded with the structural information of amino acids and dipeptides for efficient conformational searches of oligopeptides

The genetic algorithm (GA) is an intelligent approach for finding minima in a highly dimensional parametric space. However, the success of GA searches for low energy conformations of biomolecules is rather limited so far. Herein an improved GA scheme is proposed for the conformational search of oligopeptides. A systematic analysis of the backbone dihedral angles of conformations of amino acids (AAs) and dipeptides is performed. The structural information is used to design a new encoding scheme to improve the efficiency of GA search. Local geometry optimizations based on the energy calculations by the density functional theory are employed to safeguard the quality and reliability of the GA structures. The GA scheme is applied to the conformational searches of Lys, Arg, Met‐Gly, Lys‐Gly, and Phe‐Gly‐Gly representative of AAs, dipeptides, and tripeptides with complicated side chains. Comparison with the best literature results shows that the new GA method is both highly efficient and reliable by providing the most complete set of the low energy conformations. Moreover, the computational cost of the GA method increases only moderately with the complexity of the molecule. The GA scheme is valuable for the study of the conformations and properties of oligopeptides. © 2016 Wiley Periodicals, Inc.