Iodine Reduction Reaction Research Articles

Thermodynamically and Dynamically Boosted Electrocatalytic Iodine Conversion with Hydroxyl Groups for High-Efficiency Zinc-Iodine Batteries.

Rechargeable zinc-iodine (Zn-I2) batteries have shown immense potential for grid-scale energy storage applications, but there remain challenges of improving efficiency and cycling stability due to the sluggish iodine reduction reaction (IRR) kinetics and serious shuttle problem of polyiodides. We herein demonstrate an efficient metal-free hydroxyl (-OH)-functionalized carbon catalyst that effectively boosts the performance of Zn-I2 batteries. It has been found that the obtained electrocatalytic performance is strongly correlated with the surface oxygen chemical environment in the carbon matrix. Both theoretical calculations and experimental measurements have uncovered that the -OH group, rather than carbonyl (-C═O) and carboxyl (-COOH), provides the active electrocatalytic site for IRR, improves the iodine redox kinetics and the electrochemical reversibility, and facilitates I2 nucleation. As confirmed by a series of in situ and ex situ spectroscopy techniques, due to the favorable reaction thermodynamics and the lowered energy barrier for I3- dissociation, the O-H···I channels can effectively trigger the direct transformation of I2/I- and avoid the formation of stable polyiodides. As a result, the as-assembled battery of I2/oxygen-functionalized carbon cloth (I2/OCC-2)//Zn exhibits a high capacity of 2.27 mA h cm-2 at 1 mA cm-2, outstanding rate capability with 89.0% capacity retention at 20 mA cm-2, and long-term stability of 10,000 cycles.

Highly transparent and efficient Pt/CeOx counter electrodes for bifacial dye-sensitized solar cells

In this research, we introduce a pioneering approach for enhancing the electrocatalytic performance of counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) by synthesizing Pt/CeOx hybrid nanocatalysts through a refined polyol reduction technique. This method facilitates the accurate production of Pt nanoparticles supported on ceria, leveraging their strong metal-oxide interactions. X-ray photoelectron spectroscopy (XPS) was employed to confirm the co-presence of both metallic and oxidized states of Pt, as well as the mixed valence states of ceria within these nanostructures. The electrocatalytic behavior of these nanocatalysts was rigorously evaluated using cyclic voltammetry (CV), Tafel polarization analyses, and electrochemical impedance spectroscopy (EIS). We identified an optimal Pt/Ce ratio of 1:0.1, which significantly enhanced the kinetics of the iodine reduction reaction (IRR), a crucial factor for efficient DSSC operation. Photovoltaic testing under one-sun AM 1.5 G conditions demonstrated that DSSCs with the optimized Pt/CeOx CEs exhibited a 10 % increase in power conversion efficiency (PCE) comparted to control cells. This study highlights the effectiveness of Pt/CeOx hybrid nanocatalysts in improving bifacial DSSC performance, combining the catalytic strengths of platinum with the unique properties of ceria.

High-Performance Zn-I2 Batteries Enabled by a Metal-Free Defect-Rich Carbon Cathode Catalyst.

Aqueous iodine-zinc (Zn-I2) batteries based on I2 conversion reaction are one of the promising energy storage devices due to their high safety, low-cost zinc metal anode, and abundant I2 sources. However, the performance of Zn-I2 batteries is limited by the sluggish I2 conversion reaction kinetics, leading to poor rate capability and cycle performance. Herein, we develop a defect-rich carbon as a high-performance cathode catalyst for I2 loading and conversion, which exhibits excellent iodine reduction reaction (IRR) activity with a high reduction potential of 1.248 V (vs Zn/Zn2+) and a high peak current density of 20.74 mA cm-2, superior to a nitrogen-doped carbon. The I2-loaded defect-rich carbon (DG1100/I2) cathode achieves a large specific capacity of 261.4 mA h g-1 at 1.0 A g-1, a high rate capability of 131.9 mA h g-1 at 10 A g-1, and long-term stability with a high retention of 88.1% over 3500 cycles. Density functional theory calculations indicated that the carbon seven-membered ring (C7) defect site possesses the lowest adsorption energies for iodine species among several defect sites, which contributes to the high catalytic activity for IRR and the corresponding electrochemical performance of Zn-I2 batteries. This work offers a defect engineering strategy for boosting the performance of Zn-I2 batteries.

The Structural Design of Dual‐Element‐Doped Graphene for Iodine Reduction Reaction: Density Functional Theory Study

AbstractDual‐element‐doped graphene has been widely used in the counter electrode due to its enhanced catalytic activity. However, experiments lack a fundamental understanding of the doping effects accounting for the enhanced catalytic activity of dual‐element‐doped graphene. Here, we selected heteroatoms with different electronegativity (e. g., N: 3.0, P: 2.1, Se: 2.4, O: 3.5) based on the C atom with electronegativity of 2.5, then N atoms and heteroatoms co‐doped graphene (N/X‐G, X=P, Se, O) were constructed to investigate the effects of the electronegativity, the doping configuration and position of heteroatoms, the edge structure of graphene on iodine reduction reaction by density functional theory. After a detailed analysis of the electronic structure of N/X‐G, it revealed that the doping of dual‐element could lead to more electrons transfer to the area near heteroatoms, and thus providing more electrons for iodine species. The results of this study indicated that the effects of the dual‐element doping could be divided into three categories, and these principles provide theoretical guidance for further design of the dual‐element‐doped graphene.

Reduction-Induced Crystallization-Driven Self-Assembly of Main-Chain-Type Alternating Copolymers: Transformation from 1D Lines to 2D Platelets

In recent years, crystalline-driven self-assembly (CDSA) has received enormous attention, but almost only for block copolymers (BCPs). Herein, we introduced perfluorocarbon chains into main-chain-type liquid crystalline alternating copolymers (ACPs) to obtain perfluoroalkane-containing ACPs with periodic C-I bonds in polymer backbones via step transfer-addition and radical-termination (START) polymerization, followed by an iodine reduction reaction of C-I bonds to induce CDSA of ACPs and put forward a novel concept of "reduction-induced crystallization-driven self-assembly" (RI-CDSA) of main-chain-type ACPs for the first time. Finally, we proposed the folded-chain model and mechanism to explain the novel RI-CDSA behavior, and its rationality has been proved by the corresponding experimental results.

Electrocatalytic Iodine Reduction Reaction Enabled by Aqueous Zinc‐Iodine Battery with Improved Power and Energy Densities

AbstractProposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I− conversion kinetics of the I2 reduction reaction, and free up 1/3 I− from I3−. Co[Co1/4Fe3/4(CN)6] exhibits a low energy barrier (0.47 kJ mol−1) and low Tafel slope (76.74 mV dec−1). Accordingly, the Co[Co1/4Fe3/4(CN)6]/I2//Zn battery delivers a capacity of 236.8 mAh g−1 at 0.1 A g−1 and a rate performance with 151.4 mAh g−1 achieved even at 20 A g−1. The battery delivers both high energy density and high‐power density of 305.5 Wh kg−1 and 109.1 kW kg−1, higher than I2//Zn batteries reported to date. Furthermore, solid‐state flexible batteries were constructed. A 100 mAh high capacity solid‐state I2//Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles.

Electrocatalytic Iodine Reduction Reaction Enabled by Aqueous Zinc-Iodine Battery with Improved Power and Energy Densities.

Proposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I- conversion kinetics of the I2 reduction reaction, and free up 1/3 I- from I3 - . Co[Co1/4 Fe3/4 (CN)6 ] exhibits a low energy barrier (0.47 kJ mol-1 ) and low Tafel slope (76.74 mV dec-1 ). Accordingly, the Co[Co1/4 Fe3/4 (CN)6 ]/I2 //Zn battery delivers a capacity of 236.8 mAh g-1 at 0.1 A g-1 and a rate performance with 151.4 mAh g-1 achieved even at 20 A g-1 . The battery delivers both high energy density and high-power density of 305.5 Wh kg-1 and 109.1 kW kg-1 , higher than I2 //Zn batteries reported to date. Furthermore, solid-state flexible batteries were constructed. A 100 mAh high capacity solid-state I2 //Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles.

Unraveling the controversy over a catalytic reaction mechanism using a new theoretical methodology: One probe and non-equilibrium surface Green's function

We propose a new methodology called “one probe and non-equilibrium surface Green's function (OPNS)” to elucidate the longstanding controversial issue of a catalytic reaction mechanism, especially iodine reduction reaction (IRR) mechanisms. With aid of OPNS overcoming the limitations of conventional approach based on the free energy diagram and theoretical slab model, we clearly elucidate that the IRR follows a consecutive mechanism where the configurational preference of approaching I2 molecules depending on the external electric field governs the IRR mechanism. Under reductive potential, I2 molecules prefer a vertical configuration (I2V) rather than a parallel configuration (I2P), which leads to the consecutive mechanism where I atoms are sequentially reduced due to asymmetric charge accumulation on a single I atom that is subsequently desorbed. In addition, we provide new convincing descriptors for catalytic activity evaluation, the slope of the linear relation between the reductive process and the electric field strength representing the ability of the partial reduction and the threshold electric field of minimum required potential for the complete reduction.

Edge-terminated few-layer MoS2 nanoflakes supported on TNAs@C with enhanced electrocatalysis activity for iodine reduction reaction

Construction of hierarchical structures composed of edge-terminated MoS2 with abundant active sites is challenging but yet desirable for many practical applications. Herein, the edge-terminated few-layer MoS2 nanoflakes are synthesized on carbon nanofilm–coated TiO2 nanorod arrays (TNAs@C) to form vertically aligned TNAs@C-MoS2 core-shell nanostructure. This TNAs@C-MoS2 nanomaterial exhibits a large number of MoS2 active sites and possesses fast electron transport ability. When evaluated as an electrocatalyst for the triiodide reduction in a dye-sensitized solar cell, the TNAs@C-MoS2 shows higher power conversion efficiency (7.98%) than that (7.16%) of Pt. This structure engineering synthesis offers a facile and general way of manipulating the relevant device structures and provides a promising approach for producing other transition-metal dichalcogenides materials with unique properties.

Guiding Principles for Designing Highly Efficient Metal-Free Carbon Catalysts.

Carbon nanomaterials are promising metal-free catalysts for energy conversion and storage, but the catalysts are usually developed via traditional trial-and-error methods. To rationally design and accelerate the search for the highly efficient catalysts, it is necessary to establish design principles for the carbon-based catalysts. Here, theoretical analysis and material design of metal-free carbon nanomaterials as efficient photo-/electrocatalysts to facilitate the critical chemical reactions in clean and sustainable energy technologies are reviewed. These reactions include the oxygen reduction reaction in fuel cells, the oxygen evolution reaction in metal-air batteries, the iodine reduction reaction in dye-sensitized solar cells, the hydrogen evolution reaction in water splitting, and the carbon dioxide reduction in artificial photosynthesis. Basic catalytic principles, computationally guided design approaches and intrinsic descriptors, catalytic material design strategies, and future directions are discussed for the rational design and synthesis of highly efficient carbon-based catalysts for clean energy technologies.

Sulfur-doped cobalt oxide nanowires as efficient electrocatalysts for iodine reduction reaction

Sulfur-doped cobalt oxide (S-Co3O4) crystals exhibit excellent catalytic activities towards multiple useful reactions, however, the impact of the structural properties on the resultant catalytic activities has been overlooked in the past. We demonstrate a facile vapor-phase hydrothermal (VPH) doping approach to effectively create electrocatalytically active surface sulfur species on the chemical bath deposited polycrystalline Co3O4 nanowires for iodine reduction reaction (IRR). The dye-sensitized solar cells (DSSCs) equipped with the S-Co3O4 nanowire film as the counter electrode (CE) achieve a best energy conversion efficiency of 6.78%, which is comparable to those of DSSCs with commercial Pt CE (7.36%). The impact of film structure, VPH temperature and VPH duration on the resultant structures as well as the electrocatalytic activities has been comprehensively studied. More importantly, our results manifest a close correlation between the surface sulfur dopant level and the key electrocatalytic activity indicators. The VPH approach could be further extended to the fabrication of low-cost, high-performance nanomaterials for energy conversion applications.

From two-dimensional graphene oxide to three-dimensional honeycomb-like Ni3S2@graphene oxide composite: insight into structure and electrocatalytic properties.

Three-dimensional (3D) graphene composites have drawn increasing attention in energy storage/conversion applications due to their unique structures and properties. Herein, we synthesized 3D honeycomb-like Ni3S2@graphene oxide composite (3D honeycomb-like Ni3S2@GO) by a one-pot hydrothermal method. We found that positive charges of Ni2+ and negative charges of NO3− in Ni(NO3)2 induced a transformation of graphene oxide with smooth surface into graphene oxide with wrinkled surface (w-GO). The w-GO in the mixing solution of Ni(NO3)2/thioacetamide/H2O evolved into 3D honeycomb-like Ni3S2@GO in solvothermal process. The GO effectively inhibited the aggregation of Ni3S2 nanoparticles. Photoelectrochemical cells based on 3D Ni3S2@GO synthesized at 60 mM l−1 Ni(NO3)2 exhibited the best energy conversion efficiency. 3D Ni3S2@GO had smaller charge transfer resistance and larger exchange current density than pure Ni3S2 for iodine reduction reaction. The cyclic stability of 3D honeycomb-like Ni3S2@GO was good in the iodine electrolyte. Results are of great interest for fundamental research and practical applications of 3D GO and its composites in solar water-splitting, artificial photoelectrochemical cells, electrocatalysts and Li-S or Na-S batteries.

Back Cover: Solar RRL 3‐4∕2017

Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. This is the back cover of Solar RRL 3-4∕2017 with an image relating to the article Sulfur-Doped Graphene with Iron Pyrite (FeS 2 ) as an Efficient and Stable Electrocatalyst for the Iodine Reduction Reaction in Dye-Sensitized Solar Cells (https://dspace.lboro.ac.uk/2134/24841)

Sulfur‐Doped Graphene with Iron Pyrite (FeS2) as an Efficient and Stable Electrocatalyst for the Iodine Reduction Reaction in Dye‐Sensitized Solar Cells

As an alternative to platinum (Pt), hybrid electrocatalysts based on sulfur‐doped graphene with FeS2 microspheres (SGN‐FeS2) were used as a counter electrode (CE) in dye‐sensitized solar cells (DSSCs). Benefiting from the high conductivity of SGN and excellent electrocatalytic activity of the FeS2, the bifunctional hybrid electrocatalyst‐based device displays a power conversion efficiency (PCE) of 8.1%, which is comparable to that (8.3%) of traditional Pt CE‐based DSSC, while also exhibiting excellent stability in ambient conditions. These characteristics, in addition to its low‐cost and facile preparation, make the SGN–FeS2 hybrid an ideal CE material for DSSCs.

CoNi alloy incorporated, N doped porous carbon as efficient counter electrode for dye-sensitized solar cell

Abstract The design of efficient non-Pt counter electrode (CE) materials is highly desired in field of dye sensitized solar cell (DSC). Herein, by combining the catalytic features of N doped carbon (NC) and CoNi alloy, CoNi alloy incorporated porous N doped carbon hybrid (CoNi-NC) is synthesized for application as catalytic CE of DSC. Benefiting from the proper meso-/macroporosity with high electroactive surface area, the CoNi-NC electrode demonstrates apparently higher electrocatalytic activity for iodine reduction reaction (IRR) over pyrolyzed Pt electrode. As a consequence, the DSC based on CoNi-NC CE yields a power conversion efficiency ( PCE ) of 7.6%, which is superior over that of Pt CE based cell (7.2%), highlighting the bright potential of CoNi-NC in efficient and economical CE of DSC.

Theoretical design and experimental synthesis of counter electrode for dye-sensitized solar cells: Amino-functionalized graphene

For some specific catalytic reaction, how to construct active sites on two dimensional materials is of great scientific significance. Dye-sensitized solar cells (DSCs) can be viewed as one representative photovoltaics because in which liquid electrolyte with triiodide/iodide (I3−/I−) as redox couples are involved. In this study, amino-functionalized graphene (AFG) has been designed according to theoretically analyzing iodine reduction reaction (IRR) processes and rationally screening the volcanic plot. Then, such AFG has been successfully synthesized by a simple hydrothermal method and shows high electrocatalytic activity towards IRR when serving as counter electrode in DSCs. Finally, a high conversion efficiency of 7.39% by AFG-based DSCs was obtained, which is close to that using Pt as counter electrode.

Edge-selenated graphene nanoplatelets as durable metal-free catalysts for iodine reduction reaction in dye-sensitized solar cells.

Metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) are sufficiently active in Co(II)/Co(III) electrolytes but are not satisfactory in the most commonly used iodide/triiodide (I(-)/I3 (-)) electrolytes. Thus, developing active and stable metal-free electrocatalysts in both electrolytes is one of the most important issues in DSSC research. We report the synthesis of edge-selenated graphene nanoplatelets (SeGnPs) prepared by a simple mechanochemical reaction between graphite and selenium (Se) powders, and their application to the counter electrode (CE) for DSSCs in both I(-)/I3 (-) and Co(II)/Co(III) electrolytes. The edge-selective doping and the preservation of the pristine graphene basal plane in the SeGnPs were confirmed by various analytical techniques, including atomic-resolution transmission electron microscopy. Tested as the DSSC CE in both Co(bpy)3 (2+/3+) (bpy = 2,2'-bipyridine) and I(-)/I3 (-) electrolytes, the SeGnP-CEs exhibited outstanding electrocatalytic performance with ultimately high stability. The SeGnP-CE-based DSSCs displayed a higher photovoltaic performance than did the Pt-CE-based DSSCs in both SM315 sensitizer with Co(bpy)3 (2+/3+) and N719 sensitizer with I(-)/I3 (-) electrolytes. Furthermore, the I3 (-) reduction mechanism, which has not been fully understood in carbon-based CE materials to date, was clarified by an electrochemical kinetics study combined with density functional theory and nonequilibrium Green's function calculations.

Unique ZnS nanobuns decorated with reduced graphene oxide as an efficient and low-cost counter electrode for dye-sensitized solar cells

Unique ZnS nanobuns decorated with reduced graphene oxide (RGO) was synthesized and found to exhibit a synergetic effect as a highly efficient and low-cost counter electrode (CE) in dye-sensitized solar cells (DSCs). Using this ZnS-RGO CE, a power conversion efficiency (PCE) of 7.03% was achieved. This value was 53% and 41% higher than those of pure ZnS and RGO CEs, respectively. The ZnS-RGO nanocomposite is indeed an efficient and cost-effective Pt-like alternative for iodine reduction reaction.

Standardization of the reducing power of zero-valent iron using iodine

Because iron-based materials that are used for the permeable reactive barrier systems come in various shapes, sizes, and with various surface properties depending on the manufacturing sources, their reductive powers vary in a wide spectrum. A new experimental procedure to evaluate the reductive power of iron material was developed in this study. Tri-iodide (I3 −) was used as the representative oxidizing agent that reacts with zero-valent iron (ZVI). Three iron-based materials (two scraps, two powders) and four chlorinated chemicals [perchloroethene (PCE), trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and pentachlorophenol (PCP)] were used in this study. Redox reactions were conducted in glass vials containing aqueous solutions of chlorinated compounds or tri-iodide with known masses of iron material. After a predetermined reaction time each vial was opened and the solution was analyzed for the concentration of reduced compound. The apparent rate contant (ki obs ) of iodine reduction reaction with ZVIs was found to be proportional to that (kc obs ) of chlorinated contaminant. The surface area-normalized reduction rate constants (kc nor ) for contaminants and tri-iodide (ki nor ) were also proportional to each other. The ratio of rate constants, Knor (= kc nor /ki nor ) was estimated for each contaminant; 3.29 × 10−7, 5.86 × 10−7, 6.70 × 10−7, and 7.87 × 10−10 M, for PCE, TCE, TCA, and PCP, respectively. The results of this study suggest that the reductive power of ZVI materials can be standardized using tri-iodide, and thus, can provide a good reference for the quantitative assessment of the reactivity of metallic reducing agents of environmental interest including ZVIs.