Multistep Electron Transfer Research Articles

Effect of metal doping on multi-step electron transfer and oxygen species of silicon-based nanocomposite aerogel supported Pd catalysts in oxidative carbonylation of phenol

A series of new metal/silicon-based nanocomposite aerogel supported Pd catalysts were prepared using ambient pressure drying method with low energy consumption, which was applied in the synthesis of diphenyl carbonate (DPC) by oxidative carbonylation. New PS-MnCe nanocomposite areogel catalyst with better activity and stability than traditional metal oxide, which the single pass yield of DPC reached 34.2% with selectivity above 99.2% and TOF (turnover frequency) 100.6 molDPC/molPd h−1. The regeneration of the catalyst maintained the yield 16.6% in the third run with selectivity 97.9%. The prepared nanocomposite areogel catalysts were characterized by power X-ray diffraction pattern, FTIR spectrum, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller and Transmission electron microscopy, in order to make clear the effects of metal doping on multi-step electron transfer, oxygen species and active Pd2+ in the oxidative carbonylation of phenol by as-prepared nanocomposite aerogel supported Pd catalysts. The results showed that this kind of catalyst had a typical structure of aerogel stereoscopic three-dimensional network with high specific surface area and high metal dispersion, which effectively increased the number of active site (Pd2+). Different kinds of metal complexes can adjust the ratio of oxygen species, raise the efficiency of multi-step electron transfer and improve the performance of oxidation properties at low temperatures of the catalyst. The strong SMSI effect between the active center Pd and the support can effectively promote the recycling of Pd2+ so as to improve the activity and stability of the catalyst which may suite for industrial experiments in fixed-bed reactor in future.

Critical Hammett Electron-Donating Ability of Substituent Groups for Efficient Water Oxidation Catalysis by Mononuclear Ruthenium Aquo Complexes.

[Ru(Rtpy)(bpy)(H2O)]2+ (1R; bpy = 2,2'-bipyridine, and Rtpy = 2,2':6',2″-terpyridine derivatives) complexes with a variety of 4'-substituent groups on Rtpy were synthesized and characterized to reveal the effects of substituents on their structures, physicochemical properties, and catalytic activities for water oxidation. The geometric structures of 1R are not considerably influenced by the electron-donating ability of the 4'-substituent groups on Rtpy. Similar multistep proton-coupled electron transfer reactions were observed for 1R, and the redox potentials for each oxidation step tended to decrease with an increase in the electron-donating ability of the substituent, which is explained by the increased electron density on the Ru center by electron-donating groups, stabilizing the positive charge that builds up upon oxidation. This is consistent with the red-shift of the absorption bands around 480 nm assigned to the metal-to-ligand charge transfer transition for 1R due to the increased d orbital energy level of the Ru center. The turnover frequency (kO2) of 1R for water oxidation catalysis, however, depended greatly on the Rtpy ligands, varying from 0.05 × 10-2 to 44 × 10-2 s-1 (as the highest kO2 was observed for R = ethoxy) by a factor of 880. A critical electron-donating ability of the 4'-substituent groups with a narrow range of Hammett constants (σp = -0.27 to -0.24) found for the highest kO2 values is valuable for understanding the great difficulty in the search for efficient water oxidation catalysts. On another front, the kO2 values increased with a decrease in the redox potentials of RuIV═O/RuV═O for 1R, indicating that the potential of formation of RuV═O species for 1R is crucial for water oxidation catalysis under the employed conditions.

CeO2 nanocrystal-modified layered MoS2/g-C3N4 as 0D/2D ternary composite for visible-light photocatalytic hydrogen evolution: Interfacial consecutive multi-step electron transfer and enhanced H2O reactant adsorption

Developing low-cost and high-performance catalysts is significant to solar-to-fuel conversion. Here, the synthesis of zero-dimensional (0D) CeO2 nanocrystal-decorated two-dimensional (2D) layered hybrids of MoS2/g-C3N4 was reported for the first time. In the absence of noble-metal cocatalyst, the optimized ternary CeO2@MoS2/g-C3N4 still manifested high photocatalytic activity toward H2 generation, with a rate of 65.4 μmol/h, which is approximately 8.3 and 17.5-fold greater than g-C3N4 and CeO2, respectively. The corresponding apparent external quantum efficiency reached 10.35% at a wavelength of 420 nm. The superior photocatalytic behavior of CeO2@MoS2/g-C3N4 heterojunction could be ascribed to the positive synergetic effects of well-matched energy-level positions and effective charge separation arose from the multi-step electron transfer processes between Ce4+/Ce3+ reversibility pairs and heterostructures. Furthermore, the adsorption ability of reactant H2O molecules on CeO2@MoS2/g-C3N4 was investigated. Due to the interfacial electronic interaction and Ce3+ species, CeO2@MoS2/g-C3N4 presented more reaction active sites with enhanced adsorption capacity and decreased energy barrier for reactant H2O molecules adsorption, which collaboratively promoted photocatalytic water splitting. This study provides new insights into the rational design of inexpensive ternary photocatalyst with multilevel electron transfer for efficiently converting solar energy into hydrogen without noble metals.

Anion–Cation Double Doped Co3O4 Microtube Architecture to Promote High-Valence Co Species Formation for Enhanced Oxygen Evolution Reaction

A method for efficiently catalyzing the oxygen evolution reaction (OER) represents a top priority for water electrolysis due to its multistep electron transfer pathway and sluggish kinetics. The OE...

Highly Conductive Catalyst with Advanced Manufacturing for Efficient Oxygen Evolution Reaction

The electrochemical water electrolysis is a convenient technique to store intermittent, sustainable energies, such as solar and wind, into high-purity hydrogen. The state-of-the-art electrocatalysts for oxygen evolution reaction (OER) are Ir/Ru-based materials. However, their scarcity and high costs hamper the industrialization of water electrolysis. In addition, the low electrical conductivity (~ 1000 Ω/□) of those catalysts and the sluggish multistep proton-coupled electron transfer of OERs significantly reduce the reaction sites and performances of water splitting. To overcome those problems, this research will present a highly conductive multi-layer catalyst fabricated with advanced manufacturing methods. We employ spray printing, sputter coating, and inkjet printing to produce nafion layers, gold nanolayers (AuNL), and IrO2 catalyst layers, respectively. The mesoporous AuNLs provide the catalyst layer with not only excellent electrical conductivity (0.5 Ω/□) but also good proton permeability. Furthermore, the novel structure of the multi-layer catalyst in the electrolyser cell helps to directly investigate the influence of conductivity on OER kinetics by visualizing the generated oxygen bubbles, which enables the establishment of correlation between the conductivity and reaction sites. Most importantly, the faster OER kinetics can be achieved even with a much lower loading of IrO2 catalysts (as low as 0.1 mg/cm2) than the conventional IrO2 catalyst layer in pure water, acidic, and alkaline solutions. The novel multi-layer catalyst provides a new way to enhance the performance and reduce the usage of noble catalysts in energy conversion and storage devices. Keywords: Inkjet printing, mesopores, high conductivity, ultra-low catalyst loading, water electrolysis.

Synergistic action of adsorption and reductive properties of ash derived from distilled Mentha piperita plant waste in removal of Cr(VI) from aqueous solution

Adsorption behavior of Mentha Plant Ash (MPA) in removal of Cr(VI) from aqueous solution was analyzed as a function of different pH (3.0–8.0), different concentration of Cr(VI) (10–50 mg L−1), contact time (0–90 min) and doses of adsorbent (0.1–0.5 g/100 mL). Adsorption of Cr(VI) onto MPA was found to be dependent on pH condition of the solution and showed maximum removal of Cr(VI) at pH 3.0. The study of adsorption kinetics on Cr(VI) removal by MPA showed that pseudo-second order kinetic model was more suitable to describe the Cr(VI) removal by adsorption onto MPA. Results on Cyclic Voltammetry study of MPA treated with Cr(VI) solution revealed the reduction of Cr(VI) to Cr(III) and Cr(II) by MPA particles through multi-step electron transfer reactions. A combined effect of adsorption and reduction properties of MPA was particularly responsible for removal and transformation of Cr(VI). These attributes of MPA were contributed by many active Cr(VI) binding and electron donating ligands present on the MPA surface as evident from FTIR and XPS analysis of MPA.

Photoelectrochemical bioanalysis of antibiotics on rGO-Bi2WO6-Au based on branched hybridization chain reaction

Herein a versatile photoelectrochemical (PEC) bioanalysis platform for sensitive and specific screening of low-abundance antibiotics (kanamycin, Kana, used in this case) was innovatively designed using rGO-Bi2WO6-Au as photoactive matrix and target-induced branched hybridization chain reaction (t-bHCR) for efficient signal amplification. To realize the high-performance of our PEC bioanalysis system, rational introduction of reduced graphene oxide (rGO) and Au nanoparticles (Au NPs) greatly accelerated the electron transfer and enhances photoactivity. As expected, the ternary nanocomposite (i.e., rGO-Bi2WO6-Au) system with cascade energy level exhibited intense PEC signal responses thanks to multistep electron-transfer (MET) mechanism. Upon sensing the target Kana, t-bHCR is readily implemented, thus resulting in the assembly of numerous CuS nanoparticle (CuS NP). As a result, the loading CuS NPs from hyper-branched structure boosted the electron donors (ascorbic acid) consumption and enhanced the steric hindrance, synergistically decrease the photoelectric response. Under the optimized testing conditions, the t-bHCR-based PEC bioanalysis exhibited superior analytical performance with a linear range of 1 pM to 5 nM target Kana and limit of detection down to 0.78 pM. Additionally, favorable stability, great anti-interference ability and satisfactory accuracy for the analysis of actual samples were acquired. Impressively, the concept of t-bHCR-mediated provides an alternative to construct PEC bioanalysis and inspire more interest in the design of advanced PEC bioanalysis through nucleic acid-related signal amplification.

The Energy Level Regulation of CoMo Carbonate Hydroxide for the Enhanced Oxygen Evolution Reaction Activity

The oxygen evolution reaction (OER) accompanied by multistep proton-coupled electron transfer is the decisive step of electrochemical water splitting due to the sluggish kinetics process. Enhancing the efficiency of water splitting indispensably requires stable and high-efficiency electrocatalysts for OER. The OER activity of electrocatalysts can be largely heightened by well adjusting their energy level and active sites. Herein, the amorphous iron cobalt molybdenum carbonate hydroxide core–shell microspheres (FeCoMo/CoMo) offer significant opportunities to improve the OER activity in both thermodynamics and kinetics due to the appropriate matching of the energy level with the equilibrium potential of OER and the abundant active sites.The well-designed Fe0.25–CoMoCH/NF sample exhibits prominent activity toward OER with an overpotential as low as 232 mV to deliver a current density of 10 mA cm–2, a small Tafel slope of 46 mV dec–1, and excellent stability in alkaline solution. Mechanistic studies using a r...

Engineering the Interface of Carbon Electrocatalysts at the Triple Point for Enhanced Oxygen Reduction Reaction

The aqueous oxygen reduction reaction (ORR) has recently received increased attention due to its critical role in clean and sustainable energy-generation technologies, such as proton exchange membranes (PEM) fuel cells, alkaline fuel cells and Zn-air batteries. The sluggish kinetics associated with ORR result from multistep electron-transfer process. The slow kinetics are partially related to the O2 adsorption process onto the catalyst, which happens at the triple-phase boundary (TPB) of the electrocatalyst-electrolyte-oxygen interface. Hence, tremendous efforts have been devoted to improving the intrinsic properties of electrocatalysts such as active sites, electrical conductivity and porosity. Engineering the electrocatalyst's interfacial properties is another critical issue in ORR, however less described in the literature. The surface of the catalyst provides the microenvironment for the triple boundary interface reaction, which directly influences its electrocatalytic activity and the kinetics. This Minireview is a summary of the existing literature on manipulating the interfacial surface of non-precious metal catalysts at the triple point between the solid catalyst, the aqueous electrolyte and the O2 gas with the aim of improving the ORR efficiency. Various approaches towards improving the wettability and nanostructuring the catalyst surface to boost the activity of the surface-active sites and provide improved stability are discussed.

Multistep and multiscale electron transfer and localization dynamics at a model electrolyte/metal interface.

The lifetime, coupling, and localization dynamics of electronic states in molecular films near metal electrodes fundamentally determine their propensity to act as precursors or reactants in chemical reactions, crucial for a detailed understanding of charge transport and degradation mechanisms in batteries. In the current study, we investigate the formation dynamics of small polarons and their role as intermediate electronic states in thin films of dimethyl sulfoxide (DMSO) on Cu(111) using time- and angle-resolved two-photon photoemission spectroscopy. Upon photoexcitation, a delocalized DMSO electronic state is initially populated two monolayers from the Cu surface, becoming a small polaron on a 200 fs time scale, consistent with localization due to vibrational dynamics of the DMSO film. The small polaron is a precursor state for an extremely long-lived and weakly coupled multilayer electronic state, with a lifetime of several seconds, thirteen orders of magnitude longer than the small polaron. Although the small polaron in DMSO has a lifetime of 140 fs, its role as a precursor state for long-lived electronic states could make it an important intermediate in multistep battery reactivity.

(Invited) Electrochemistry of Solid-State Inorganic Polymer Electrolyte

Electrochemistry explores the charge transfer reaction across the interfaces, such as solid/liquid interface, liquid/liquid interface and also solid/solid interface. Most reported charge transfer behaviours across the “solid/solid” interface are involved liquid electrolyte. For example, in the lithium-ion batteries, the redox of cobalt-based active material is coupled by the heterogeneous intercalation/deintercalation of Li+ ions, which is existed in the electrolyte solution. In another words, the electron transfer occurs at the solid/solid interface while the ion transfer occurs at the solid/electrolyte solution. We employ SECM to construct the solid-solid interface and to study the electron transfer phenomena therein. That means there is no liquid electrolyte environment. When the electron transfer occurs at the solid/solid interface, the counterion transfer will occur in the crystal due to the crystalline defects. For example, we cultured the NaCl microcrystals, which are doped with iron oxides, between the pair electrodes on a microchip. The multi-step electron transfer processes of iron from Fe(0) to Fe(VI) through Fe(II) and Fe(III) were observed. The solid-state electrolyte solution just like an inorganic polymer. The electron transfer is wired through hopping between the neighboring redox lattice sites, coupling with the counterion transfer in the crystalline defects. The electrochemical behavior in the solid-state inorganic “polymer” electrolyte will be discussed in this presentation.

A 3D electrode of core@shell branched nanowire TiN@Ni0.27Co2.73O4 arrays for enhanced oxygen evolution reaction

The combination of highly active materials with judicious nanostructures is crucial to develop high-performance electrocatalysts for oxygen evolution reaction (OER), which involves sluggish multistep electron transfer processes. Herein, TiN nanowire arrays are used as conductive trunks to support active Ni-doped Co3O4 (Ni0.27Co2.73O4) nanosheets to construct a binder-free three-dimensional (3D) electrode for OER. In the core@shell configuration, the TiN nanowire arrays possess a single-crystal-like structure favoring charge migration and the ultrathin Ni0.27Co2.73O4 nanosheets have a mesoporous structure providing more active sites. The hierarchically branched morphology, high conductivity and large surface area can be achieved simultaneously by the optimization in composition and nanostructure, which contributes to excellent electrochemical performances. The TiN@Ni0.27Co2.73O4 electrode shows much better OER activity than the Ni-doped Co3O4 nanosheets deposited on planar Ti substrate and low conductive TiO2 nanowire arrays.

Light as Trigger for Biocatalysis: Photonic Wiring of Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase to Quantum Dot-Sensitized Inverse Opal TiO2 Architectures via Redox Polymers

The functional coupling of photoactive nanostructures with enzymes creates a strategy for the design of light-triggered biocatalysts. This study highlights the efficient wiring of flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (FAD-GDH) to PbS quantum dot (QD)-sensitized inverse opal TiO2 electrodes (IO-TiO2) by means of an Os-complex-containing redox polymer for the light-driven glucose oxidation. For the construction of IO-TiO2 scaffolds, a template approach has been developed, enabling the tunability of the surface area and a high loading capacity for the integration of QDs, redox polymer, and enzyme. The biohybrid signal chain can be switched on with light, generating charge carriers within the QDs, triggering a multistep electron-transfer cascade from the enzyme toward the redox polymer via the QDs and finally to the IO-TiO2 electrode. The resulting anodic photocurrent can be modulated by the potential, the excitation intensity, and the glucose concentration, providing a new degree...

(Invited) Visible Light-Driven Water Oxidation with Porphyrin Sensitizers and Water Oxidation Catalysts

Exporing renewable energy sources is an important task in making our society sustainable. In this regard, use of sunlight as an infinite energy source is fascinating. Specifically, realizing artificial photosynthesis, i.e., integration of light-harvesting, multi-step electron and proton transfer, and water oxidation for the efficient production of solar fuels, is a great challenge in chemistry. For the purpose, dye-sensitized photoelectrosynthesis cells (DSPSC) have been investigated, as the heterogeneous water splitting on inorganic semiconductors is promising for the upcoming large scale device operation. In DSPSC a molecular sensitizer adsorbed on a semiconducting electrode harvests visible light and injects an electron from the excited-state of the sensitizer (S*) to a conduction band (CB) of the electrode. Then, the sensitizer radical cation (S• +) extracts an electron from a water oxidation catalyst (WOC) to regenerate the sensitizer and one-electron oxidized WOC. After reiterating the cycle, high oxidation states of the WOC are produced, eventually transforming two water molecules into four protons and one oxygen molecule. As the sensitizer bis(2,2’-bipyridine)(4,4’-diphosphonato-2,2’-bipyridine)ruthenium(II) (RuP) has been frequently employed for the construction of molecule-based artificial photosynthetic systems, owing to its sufficient first oxidation potential for water oxidation and a long lifetime of its excited state for electron injection. However, the light-harvesting ability of RuP is rather low in visible region beyond 500 nm. Considering that yellow to red photons mainly shower down on the earth from sun, use of photons in visible region is essential for efficient chemical conversion by sunlight. In this context, porphyrins are attractive as the sensitizer due to their excellent light-harvesting in visible region and facile tuning of their excited-states and redox properties by their chemical functionalization. Nevertheless, molecule-based artificial photosynthetic systems with porphyrins as the sensitizer have been very limited as the result of their poor performance. One plausible reason is the occurrence of fast charge recombination (CR) between the electron injected into the CB of TiO2 (denoted as TiO2(e−)) and S• +. CR from TiO2(e−) to the oxidized WOC would also take place within a few microsecond. Undesirable CR from TiO2(e−) to water is indicated. Thus, to overcome the disadvantages, it is crucial to optimize the electron transfer (ET) processes at the interfaces. In this talk, I will give an overview of our recent initiatives on visible light-driven water oxidation with novel porphyrin sensitizers and water oxidation catalysts. [1] M. Yamamoto, L. Wang, F. Li, T. Fukushima, K. Tanaka, L. Sun and H. Imahori, Chem. Sci., 7, 1430-1439 (2016). [2] M. Yamamoto, Y. Nishizawa, P. Chábera, F. Li, T. Pascher, V. Sundström, L. Sun, and H. Imahori, Chem. Commun., 52, 13702-13705 (2016). [3] M. Yamamoto, J. Föhlinger, J. Petersson, L. Hammarström, and H. Imahori, Angew. Chem. Int. Ed., 56, 3329-3333 (2017).

Photoinduced electron-transfer reactions of tris(2,2′-bipyridine)ruthenium(II)-based carbonic anhydrase inhibitors tethering plural binding sites

AbstractTris(2,2′‐bipyridine)ruthenium(II) complex‐based carbonic anhydrase (CA) inhibitors, [Ru(bpy)2(bpydbs)]2+ {bpy = 2,2′‐bipyridine and bpydbs = 2,2′‐bipyridinyl‐4,4′‐dicarboxilic acid bis[(2‐{2‐[2‐(4‐sulfamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide]} and [Ru(bpydbs)3]2+, tethering plural benzenesulfonamide groups have been prepared. The CA catalytic activity was effectively suppressed by these synthetic [Ru(bpy)2(bpydbs)]2+ and [Ru(bpydbs)3]2+ inhibitors, and their dissociation constants at pH = 7.2 and at 25°C were determined to be KI = 0.93 ± 0.02 μM and KI = 0.24 ± 0.03 μM, respectively. Next, 2 photoinduced electron‐transfer (ET) systems comprising a Ru2+‐CA complex and an electron acceptor, such as chloropentaamminecobalt(III) ([CoCl(NH3)5]2+) or methylviologen (MV2+) were studied. In the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of 3([Ru(II)]2+)* was quenched through an intermolecular photoinduced ET mechanism. In case of the [Ru(bpydbs)3]2+‐CA‐MV2+ system, the photoexcited triplet state of 3([Ru(bpydbs)3]2+)* was quenched by sacrificial quencher through an intermolecular photoinduced ET mechanism, giving the oxidized [Ru(bpydbs)3]3+. Then the following intramolecular ET from the amino acid residue, Tyr6, near the active site of CA proceeded. We observed a transient absorption around at 410 nm, arising from the formation of a Tyr•+ in the [Ru(bpydbs)3]2+‐CA‐MV2+ system. These artificial Ru(II)‐CA systems may clearly demonstrate both intermolecular and intramolecular photoinduced ET reactions of protein and could be one of the interesting models of the ET proteins. Their photophysical properties and the detailed ET mechanisms are discussed in order to clarify the multistep ET reactions.

Multiscale Principles To Boost Reactivity in Gas-Involving Energy Electrocatalysis.

Various gas-involving energy electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), has witnessed increasing concerns recently for the sake of clean, renewable, and efficient energy technologies. However, these heterogeneous reactions exhibit sluggish kinetics due to multistep electron transfer and only occur at triple-phase boundary regions. Up to now, tremendous attention has been attracted to develop cost-effective and high-performance electrocatalysts to boost the electrocatalytic activities as promising alternatives to noble metal counterparts. In addition to the prolific achievements in materials science, the advances in interface chemistry are also very critical in consideration of the complex phenomena proceeded at triple-phase boundary regions, such as mass diffusion, electron transfer, and surface reaction. Therefore, insightful principles and effective strategies for a comprehensive optimization, ranging from active sites to electrochemical interface, are necessary to fully enhance the electrocatalytic performance aiming at practical device applications. In this Account, we give an overview of our recent attempts toward efficient gas-involving electrocatalysis with multiscale principles from the respect of electronic structure, hierarchical morphology, and electrode interface step by step. It is widely accepted that the intrinsic activity of individual active sites is directly influenced by their electronic structure. Heteroatom doping and topological defects are demonstrated to be the most effective strategies for metal-free nanocarbon materials, while the cationic (e.g., Ni, Fe, Co, Sn) and anionic (e.g., O, S, OH) regulation is revealed to be a promising method for transition metal compounds, to alter the electronic structure and generate high activity. Additionally, the apparent activity of the whole electrocatalyst is significantly impacted by its hierarchical morphology. The active sites of nanocarbon materials are expected to be enriched on the surface for a full exposure and utilization; the hybridization of other active components with nanocarbon materials should achieve a uniform dispersion in nanoscale and a strongly coupled interface, thereby ensuring the electron transfer and boosting the activity. Furthermore, steady and favorable electrochemical interfaces are strongly anticipated in working electrodes for optimal reaction conditions. The powdery electrocatalysts are suggested to be constructed into self-supported electrodes for more efficient and stable catalysis integrally, while the local microenvironment can be versatilely modified by ionic liquids with more beneficial gas solubility and hydrophobicity. Collectively, with the all-round regulation of the electronic structure, hierarchical morphology, and electrode interface, the electrocatalytic performances are demonstrated to be comprehensively facilitated. Such multiscale principles stemmed from the in-depth insights on the structure-activity relationship and heterogeneous reaction characteristics will no doubt pave the way for the future development of gas-involving energy electrocatalysis, and also afford constructive inspirations in a broad range of research including CO2 reduction reaction, hydrogen peroxide production, nitrogen reduction reaction, and other important electrocatalytic activation of small molecules.

Artificial Photosynthesis for Formaldehyde Production with 85% of Faradaic Efficiency by Tuning the Reduction Potential

In the present study, artificial photosynthesis by CO2 reduction in NaCl is studied for solar fuel production. C1 fuels are evolved from various photoelectrochemical reactions at different reduction potentials depending on the multistep electron-transfer processes to CO2. The (040) facet engineered BiVO4 (040-BVO)|NaCl|Cu system is illuminated with solar light, and the external bias potential is tuned from 0.7 V to 1.5 (vs RHE) for the CO2 reduction reaction. Integrating the applied external bias potential into the conduction band minimum of 040-BVO enables the CO2 molecules to be converted into valuable chemical fuels. This thermodynamic control leads to product selectivity and increased faradaic efficiency. We observed that the selectivity and yield of the products depend on the magnitude of the CO2 reduction potential. Its products were obtained by tuning the appropriate reduction potential, leading to faradaic efficiencies of 62% for formic acid, 85% for formaldehyde, 8% for MeOH and 6% for EtOH at di...

Mechanistic modeling of electrochemical charge transfer in HT-PEM fuel cells

An electrochemical model for H2 oxidation and O2 reduction in HT-PEM fuel cells derived from multi-step single electron transfer elementary reactions is presented. The exchange current density expressions are free from arbitrary order dependency with respect to the concentration of reactants and products. The reaction mechanism also considers CO adsorption and desorption, which enables the prediction of cell performance drop due to CO poisoning. The electrochemical model is coupled with a quasi two dimensional model of the cell, which resolves the flow channel in the axial direction and the electrodes along its length and thickness. A 3 cm long cell is simulated and the results are compared with experimental measurements. Very good agreement is obtained between the model predictions and experimental measurements for cell operating on pure H2 and with 1–16% CO in the temperature range of 150–200 °C.

Behaviors of the Interfacial Consecutive Multistep Electron Transfer Controlled by Varied Transition Metal Ions in Porphyrin Cores.

Almost all life activities involve the process of multistep electron transfer (ET) which occurs on biomembrane. Metalloporphyrins (MTPPs) are a class of molecules which are closely related to life course. Here, the n-step (n = 1, 2) ET behaviors controlled by different metal ions in porphyrin cores were investigated by thin-layer cyclic voltammetry (TLCV). The bimolecular ET was reacted between the MTPP (M = Fe, Zn, Co, Cu, Ni) and Fe(CN)64- in nitrobenzene and aqueous phase, respectively, and the interface between nitrobenzene and aqueous phase was considered as a bionic membrane. The thin-layer theory, which has been revised, was used to calculate the kinetic constants for each step electron transfer reactions. It was shown that the kinetic data were affected dramatically by the different coordinated ions in porphyrin complexes.

Model of multistep electron transfer in a single-mode polar medium

A mathematical model of multistep photoinduced electron transfer (PET) in a polar medium with a single relaxation time (Debye solvent) is developed. The model includes the polarization nonequilibrity formed in the vicinity of the donor–acceptor molecular system at the initial steps of photoreaction and its influence on the subsequent steps of PET. It is established that the results from numerical simulation of transient luminescence spectra of photoexcited donor–acceptor complexes (DAC) conform to calculated data obtained on the basis of the familiar experimental technique used to measure the relaxation function of solvent polarization in the vicinity of DAC in the picosecond and subpicosecond ranges.