Spontaneous Redox Reaction Research Articles

Li/graphene oxide primary battery system and mechanism

AbstractA novel type of Li/graphene oxide (Li/GO) battery based on a spontaneous redox reaction between Li metal and GO cathode is introduced as an alternative viable primary battery system. Here, we present an efficient synthesis of GO by the modified Hummers method and focus on a comprehensive study of the reduction mechanism. The Li/GO battery was thoroughly analyzed by various physical and electrochemical methods. GO rich in oxygen‐bearing functional groups on graphene layers provided lithium storage sites and delivered a high discharge capacity of around 720 mAh/g at 12 mA/g. Products formed on the surface during reduction were analyzed, and a mechanism was proposed. The results uncovered the reasons underlying the improved electrochemical properties and the contribution of the irreversible capacity of reduced GO in graphene‐based composite electrode materials for metal‐ion batteries. The Li/GO concept is expected to shed light on the design of similar M/GO batteries based on other active metal anodes (e.g., M = Na, Mg, Al, Zn).

In situ synthesis of PEDOT:PSS-Ag nanoparticle composites without acid catalysts

This paper reports in-situ synthesis of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate silver nanoparticle (PEDOT:PSS-AgNP) composites without an acid catalyst via a spontaneous redox reaction between silver nitrate (AgNO3) and 3,4-ethylenedioxythiophene (EDOT). To investigate the effect of solvent on the formation of PEDOT:PSS and AgNP, nitric acid, distilled water, and acetonitrile were prepared as solvent. PEDOT:PSS-AgNPs were produced successfully, regardless of solvent; however, high-quality PEDOT:PSS-AgNPs were formed in an organic solvent; acetonitrile. The effects of polymer additives, polystyrene sulfonate ions, and polyvinylpyrrolidone (PVP) on the synthesis of PEDOT:PSS-AgNP nanocomposites were also investigated. Chemical and morphological analyses revealed that low weight ratio of PVP promoted AgNP nucleation, resulting in a size reduction and enhanced distribution of AgNPs. In addition, PVP reduced the binding energy, thus enhancing S-Ag bonding and PEDOT:PSS at the surface of AgNPs. Our results demonstrate that PEDOT:PSS-AgNP nanocomposites can be fabricated without an acid catalyst. A mechanism for the synthesis process is also proposed.

A fast self-charging and temperature adaptive electrochromic energy storage device

ECESDs exhibit a wide operating temperature range. They can be chemically self-charged through a spontaneous redox reaction and the energy status could be estimated by the naked eye according to the obvious color during the charge/discharge process.

Room-temperature chemical looping hydrogen production mediated by electrochemically induced heterogeneous Cu(I)/Cu(II) redox

The chemical looping process is a promising technology for high-purity hydrogen production. However, this process is operated at high temperature (e.g., >600°C), leading to rigorous requirements in the aspects of reactor design and oxygen carriers. Here, we develop a room-temperature electrocatalytic chemical looping hydrogen production system using Cu(OH) 2 as the oxygen carrier and ascorbate as the fuel. The electrolyzer is assembled by coupling cathodic hydrogen evolution and anodic Cu 2 O electro-oxidation. Ascorbate acts as the reducible fuel to reduce the resultant Cu(OH) 2 into Cu 2 O and completes the redox loop. The assembled electrolyzer achieves a current density of 100 mA cm −2 at 0.94 V. The required electricity input per cubic hydrogen produced is 2.57 kWh Nm −3 H 2 , almost half of that for conventional water electrolysis (4.83 kWh Nm −3 H 2 ). This work not only provides a new approach for hydrogen production but also facilitates the development of an innovative catalytic process. • A room-temperature electrocatalytic chemical looping H 2 production system was reported • Operando methods revealed that RTECL works on the basis of Cu(OH) 2 /Cu 2 O redox • The electricity input for hydrogen produced is merely 2.57 kWh Nm 3 H 2 for RTECL As an ideal hydrogen production method, water electrolysis is limited by its high energy consumption because of oxygen evolution reaction with sluggish kinetics. A room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system using Cu(OH) 2 as the oxygen carrier was reported. A two-step indirect process was demonstrated, including an electrocatalytic-driven catalyst oxidation reaction from Cu 2 O to Cu(OH) 2 and spontaneous redox reaction between Cu(OH) 2 and ascorbate to form Cu 2 O and dehydroascorbic acid. The assembled RETCL hydrogen production system needs only 0.94 V to drive 100 mA cm −2 and realizes electricity consumption as low as 2.23 kWh Nm −3 H 2 (half of that of sole water electrolysis). Ultra-low electricity consumption for hydrogen production was achieved based on a room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system. A two-step, Cu(OH) 2 -mediated indirect process was proved for the RETCL system that the pivotal specie Cu(OH) 2 is generated by the electrically driven oxidation of Cu 2 O and spontaneously undergoes redox reaction with ascorbate to reform Cu 2 O, achieving electricity consumption of 2.23 kWh Nm −3 H 2 .

Phenoxy Radical‐Induced Formation of Dual‐Layered Protection Film for High‐Rate and Dendrite‐Free Lithium‐Metal Anodes

The uncontrollable dendrite growth of Li metal anode leads to poor cycle stability and safety concerns, hindering its utilization in high energy density batteries. Herein, a phenoxy radical Spiro-O8 is proposed as an artificial protection film for Li metal anode owing to its excellent film-forming capability and remarkable ionic conductivity. A spontaneous redox reaction between the Spiro-O8 and Li metal results in the formation of a uniform and highly ionic conductive organic film in the bottom. Meanwhile, the phenoxy radicals on surface of Spiro-O8 facilitate the decomposition of Li salt upon exposed to the ether electrolyte and lead the formation of LiF film on the top. Arising from the synergistic effects of inner high ionic conductive film and outer rigid film, stable Li plating/stripping can be realized at a high current density (4000 cycles at 10 mA cm-2 ) and a high areal capacity of 5 mAh cm-2 for 550 h with an ultrahigh Li utilization rate of 54.6 %. As a proof of concept, this work shows a facile strategy to rationally fabricate dual-layered interfaces for Li metal anodes.

Phenoxy Radical‐Induced Formation of Dual‐Layered Protection Film for High‐Rate and Dendrite‐Free Lithium‐Metal Anodes

AbstractThe uncontrollable dendrite growth of Li metal anode leads to poor cycle stability and safety concerns, hindering its utilization in high energy density batteries. Herein, a phenoxy radical Spiro‐O8 is proposed as an artificial protection film for Li metal anode owing to its excellent film‐forming capability and remarkable ionic conductivity. A spontaneous redox reaction between the Spiro‐O8 and Li metal results in the formation of a uniform and highly ionic conductive organic film in the bottom. Meanwhile, the phenoxy radicals on surface of Spiro‐O8 facilitate the decomposition of Li salt upon exposed to the ether electrolyte and lead the formation of LiF film on the top. Arising from the synergistic effects of inner high ionic conductive film and outer rigid film, stable Li plating/stripping can be realized at a high current density (4000 cycles at 10 mA cm−2) and a high areal capacity of 5 mAh cm−2 for 550 h with an ultrahigh Li utilization rate of 54.6 %. As a proof of concept, this work shows a facile strategy to rationally fabricate dual‐layered interfaces for Li metal anodes.

In-situ construction of a NaF-rich cathode–electrolyte interface on Prussian blue toward a 3000-cycle-life sodium-ion battery

As a kind of high-voltage cathode for sodium-ion batteries (SIBs), the instability of a cathode–electrolyte interface (CEI) of Prussian blue (PB) results in the consumption of electrolyte and poor cycling life. Herein, an artificial NaF-rich CEI is in-situ designed on a PB cathode via a chemically presodiated strategy to remarkably prolong the cycling life of SIBs. Based on a spontaneous redox reaction between a chemical presodiation solvent and a polyvinylidene fluoride (PVDF) binder, a homogeneous, thin, and NaF-rich CEI is conformally coated on the surface of PB, forming CEI@PB. The components of CEI within CEI@PB mainly comprise inorganic Na-salts (NaF, Na2CO3, and NaHCO3) and organic Na-based species (R-O-Na, R–CO–Na, and R–O2CO–Na), which can ensure the rapid transport of Na+ ions while effectively preventing CEI@PB against the attack of organic solvent and improving its cycling stability. Besides, density functional theory calculations also reveal that NaF is a good electronic insulator and ionic conductor, which is suitable as a stable CEI. Benefiting from the aforementioned merits, the CEI@PB cathode with a high areal capacity of 0.61 mAh cm−2 delivers an ultra-long cycling life of 3000 cycles. More importantly, the concept of in-situ CEI can be extended to other cathodes beyond Na batteries discussed herein.

Spontaneous Deposition of Uniformly Distributed Ruthenium Nanoparticles on Graphitic Carbon Nitride for Quantifying Electrochemically Accumulated H2O2

Main observation and conclusionHighly dispersed ultrasmall ruthenium nanoparticles with a clean surface are deposited onto graphitic carbon nitride (C3N4‐Ru) through spontaneous redox reaction between the C3N4 sheets and Ru salt without the use of any reductant. The as‐prepared C3N4‐Ru exhibits distinct peroxidase‐like activity. A nanozyme based method is successfully developed for detecting the H2O2 generated in‐situ by the two‐electron oxygen reduction strategy. The C3N4‐Ru nanozyme can realize the detection of H2O2 with a wide linear range and a low detection limit. The testing results are also compared with the conventional modified titration method, and show greater possibility for the practical detection of H2O2 produced via the electrochemical oxygen reduction for its higher selectivity.

Surface reconstruction on silver nanoparticles decorated trimetallic hydroxide nanosheets to generate highly active oxygen-deficient (oxy)hydroxide layer for high-efficient water oxidation

The transition-metal (oxy)hydroxides have been considered as one of the promising electrocatalysts for oxygen evolution reaction (OER). Therefore, it is necessary to have in-depth study on the origin behind their favorable inherent OER activity and further improve their catalytic performance. Herein, nickel–cobalt-vanadium trimetallic (oxy)hydroxide nanosheets decorated with silver nanoparticles (Ag NPs) (Ag@NiV0.2Co0.2) are fabricated for OER by a simple spontaneous redox reaction. The Ag@NiV0.2Co0.2 can deliver an overpotential of only 255 mV at 10 mA cm−2 and a small Tafel slope of 38.3 mV dec-1 in alkaline solution. We accredit the outstanding catalytic performance to the following aspects: (1) the active (oxy)hydroxide layer on the surface of Ag@NiV0.2Co0.2 generated through the surface reconstruction, (2) the optimal local coordination induced by the interaction between Ag NPs and trimetallic system, (3) the extensively exposed active sites, and (4) the significantly improved charge-transfer ability due to the incorporation of Ag NPs. Our findings may provide deep understanding on the mechanism of OER and offers a novel strategy to design electrocatalysts with superior OER activity.

Spontaneously engineering heterogeneous interface of silver nanoparticles on α-Co(OH)2 for boosting electrochemical oxygen evolution

Highly-efficient electrocatalysts for oxygen evolution reaction, especially for metal nanoparticles supported on layered double hydroxides (LDHs) are very desirable and highly challenge able in modern water splitting and metal air batteries. Herein, this work applies a novel and simple spontaneous redox reaction to fabricate a heterogeneous structure by depositing silver nanoparticles on MoO2-4 intercalating α-Co(OH)2 support in a quite quick manner (5 min). The as-constructed heterostructural interface endows the hybrid α-Co(OH)2/Ag with electronic interaction between Ag and α-Co(OH)2, modulated electronic structure, and synergistic effect. Furthermore, the spontaneously engineering interface also promotes the water adsorption and the valence state regulation and enhances the intrinsic activity of the catalytically active site. Benefitting from the above collective merits, the optimal heterostructural electrocatalyst (α-Co(OH)2/Ag-0.01) can drive a current density of 10 mA cm−2 at the overpotential of only 270 mV, outperforming the bare α-Co(OH)2 and even commercial benchmark RuO2. This work opens up a new avenue towards advanced OER electrocatalysts by cheap metal nanoparticles engaged interface engineering, also showing significant potential for other energy-related electrocatalysis.

Localized Surface Plasmon Enhanced Laser Reduction of Graphene Oxide for Wearable Strain Sensor

AbstractLaser reduced graphene has been increasingly attracting broad attention owing to its unique properties and potential applications in energy conversion and storage, flexible electronics, optoelectronics, and nanocomposites. In this study, graphene sheets decorated with Au nanoparticles are fabricated in situ using milliwatt femtosecond laser reduction. The findings reveal an enhancement in both the reduction of graphene oxide sheets and the nucleation and growth of the Au nanoparticles during the in situ laser treatment. Three stages of reactions are considered, namely, (i) the spontaneous redox reaction between HAuCl4 and graphene oxide, (ii) the laser‐induced decomposition of HAuCl4 and reduction of graphene oxide, and (iii) the localized surface plasmon resonance enhanced photoreduction in the presence of Au particles. Moreover, the Au nanoparticles form densely and evenly distributed square‐lattice‐like microcrack networks that ensure a linear resistance change over the tested strain range. This microcrack network architecture enables the development of flexible graphene/Au strain sensors with gauge factors up to 52.5, and linear behaviour up to 25.4% strain. This strain sensor is demonstrated to effectively monitor human motions. The findings leverage the resistive properties of graphene/metal nanoparticle composites with fundamental mechanisms, laying a critical step toward highly functional, low‐cost, flexible, and wearable graphene‐based electronics.

Effect of the external metal on the electrochemical behavior of M3[Co(CN)6]2 (M: Co, Ni, Cu, Zn), towards their use as anodes in potassium ion batteries

A series of crystalline-cubic Prussian blue analogues (PBA) M3[Co(CN)6]2 (M=Co, Ni, Cu, Zn) were straightforwardly synthesized via the coprecipitation method as confirmed by X-ray diffraction and FTIR spectroscopy. These transition metal hexacyanocobaltates show electrochemical activity related to reversible K-ion storage between 0.05-2.6 V vs Ko/K+, that makes them suitable as anode-materials in K-ion batteries. The non-steady open circuit potential (OCP) observed in cells containing Cu3[Co(CN)6]2 and Zn3[Co(CN)6]2 electrodes suggests the presence of spontaneous redox reactions at the electrolyte/PBA interface, which leads to the loss of electrochemical activity with the time. On the other hand, the Co3[Co(CN)6]2 and Ni3[Co(CN)6] show extended -stability periods and multiple reduction/oxidation reactions which lead to the reversible charge storage mechanism. From an in-depth electrochemical study on the Co3[Co(CN)6]2-PBA, used as reference, an improvement on capacity retention is observed when the electrode is discharged at high negative potentials, 0.2 V vs Ko/K+, possibly due to the beneficial effect of a different electrochemical reaction on the PBA surface. The Ni3[Co(CN)6]2-PBA does not follow this trend, suggesting a different kinetics for this reaction on the particle surface, avoiding to observe its favorable effect as in the case of the Co3[Co(CN)6]2. This is the first time that transition metal-modified hexacyanocobaltates are reported as anode materials for K-ion batteries; particularly the Ni3[Co(CN)6]2-PBA exhibits specific capacities as high as ~ 310 mA h g−1 in the first discharge making it a promising material for applications in novel energy-storage technologies as K-ion batteries.

Soft X-ray absorption spectroscopic investigation of MnO2/graphene nanocomposites used in supercapacitor

Electrochemistry and X-ray absorption spectroscopy (XAS) of MnO2/reduced graphene oxide (RGO) were made to evaluate capacitive performance and electronic structure as a supercapacitor. MnO2 was deposited on the surface of RGO by a spontaneous redox reaction. At low current density (1 A g−1), the specific capacitance of MnO2/RGO (MRGO) greatly increased with increasing growth time from 281 to 462 F g−1. Electrochemical results show that the specific capacitance of RGO and MRGO arises from the combined contributions of electrochemical double-layer capacitance (EDLC) and pseudo-capacitance. To gain insights into the charge storage mechanism of RGO and MRGO, it was characterized using ex-situ soft XAS techniques at Mn L-edge and C, O K-edges in the charging/discharging process. The ex-situ soft XAS results provide evidence that the contribution of RGO to specific capacitance involves an oxygen-functionality-related contribution of pseudocapacitance and EDLC. In addition, the specific capacitance of MRGO reveals pseudocapacitive contributions from the redox processes that involve the Mn(III)/Mn(IV) redox reaction in MnO2. This work utilizes electrochemical and ex-situ XAS techniques to elucidate charge storage mechanism for supercapacitor applications.

High chlorine evolution performance of electrochemically reduced TiO2 nanotube array coated with a thin RuO2 layer by the self-synthetic method.

Recently, reduced TiO2 nanotube arrays via electrochemical self-doping (r-TiO2) are emerging as a good alternative to conventional dimensionally stable anodes (DSAs) due to their comparable performance and low-cost. However, compared with conventional DSAs, they suffer from poor stability, low current efficiency, and high energy consumption. Therefore, this study aims to advance the electrochemical performances in the chlorine evolution of r-TiO2 with a thin RuO2 layer coating on the nanotube structure (RuO2@r-TiO2). The RuO2 thin layer was successfully coated on the surface of r-TiO2. This was accomplished with a self-synthesized layer of ruthenium precursor originating from a spontaneous redox reaction between Ti3+ and metal ions on the r-TiO2 surface and thermal treatment. The thickness of the thin RuO2 layer was approximately 30 nm on the nanotube surface of RuO2@r-TiO2 without severe pore blocking. In chlorine production, RuO2@r-TiO2 exhibited higher current efficiency (∼81.0%) and lower energy consumption (∼3.0 W h g−1) than the r-TiO2 (current efficiency of ∼64.7% of and energy consumption of ∼5.2 W h g−1). In addition, the stability (ca. 22 h) was around 20-fold enhancement in RuO2@r-TiO2 compared with r-TiO2 (ca. 1.2 h). The results suggest a new route to provide a thin layer coating on r-TiO2 and to synthesize a high performance oxidant-generating anode.

Surface-controlled galvanic replacement for the development of Pt-Ag nanoplates with concave surface substructures

Galvanic replacement, a spontaneous redox reaction arising from contact between a nanotemplate and a replacing ion, has been widely used for its convenience, stability, and ability to form various complex nanostructures. In this study, the two-dimensional nanosurface adsorption of polymeric micelles is performed for substructure formation through advanced galvanic replacement strategies. Polymeric micelles adsorbed on the nanotemplate surface form a nano-array structure of hydrophobic and hydrophilic domains, resulting in surface controlled galvanic replacement and the formation of concave surface substructures. The hydrophobic domain formation and blockage region expansion due to nanotemplate curvature and solvent composition contributes greatly to the surface substructure formations. The results can be summarized as a successful attempt to design the nanostructure by coordinating all potential factors involved in conventional galvanic replacement to create an unprecedented high-complexity nanostructure. Manufactured Pt-Ag nanoplates with concave surface substructures exhibited the successful hydrogen evolution electrocatalytic efficiency as demonstration. The Pt-Ag nanoplates with concave surface substructures exhibit the enhanced HER activity in strong acidic solutions with a low Tafel slope. The enhancement of the HER performance can be attributed to concave surface substructures, which greatly improve the edge sites and defects, resulting in a high density of exposed active sites. The galvanic replacement-based material design strategy demonstrated here exemplifies a novel and versatile approach to developing electrocatalysts with high activity and durability for advanced electrochemical water-splitting systems.

Morphology-Retained Conversion of Neutral to Mixed Valence Tetrathiafulvalene Crystals through a Spontaneous Redox Reaction

Solid-state conversion by the spontaneous redox reaction between tetrathiafulvalene (TTF) and ferric ion is employed to obtain morphology-retained TTF mixed valence (MV) salt crystals. Radical spec...

Spontaneous Formation of a ZnO Monolayer by the Redox Reaction of Zn on Graphene Oxide.

Graphene-based two-dimensional heterostructures are of substantial interest both for fundamental studies and their various potential applications. Particularly interesting are atomically thin semiconducting oxides on graphene, which uniquely combine a wide band gap and optical transparency. Here, we report the atomic-scale investigation of a novel self-formation of a ZnO monolayer from the Zn metal on a graphene oxide substrate. The spontaneous oxidation of the ultrathin Zn metal occurs by a reaction with oxygen supplied from the graphene oxide substrate, and graphene oxide is deoxygenated by a transfer of oxygen from O-containing functional groups to the zinc metal. The ZnO monolayer formed by this spontaneous redox reaction shows a graphene-like structure and a band gap of about 4 eV. This study demonstrates a unique and straightforward synthetic route to atomically thin two-dimensional heterostructures made from a two-dimensional metal oxide and graphene, formed by the spontaneous redox reaction of a very thin metal layer directly deposited on graphene oxide.

In situ green growth of uniform and naked Ag nanoparticles on graphene oxide at room temperature and its enhanced catalytic performance

In situ growth of naked Ag nanoparticles on graphene oxide was achieved following a simple, green, and environment-friendly one-step stirring method. In the absence of extra reductant and stabilizer, the naked Ag nanoparticles formed on the surface of GO via a spontaneous redox reaction between Ag+ and GO at room temperature. The morphology and microstructure of the resultant heterogeneous nanostructures were characterized by various spectroscopic and microscopic techniques systematically. The characterization results showed that the naked metallic Ag nanoparticles with an average diameter of 4.31 ± 0.13 nm distribute homogeneously and tend to “stand” in line on GO. The well-known catalytic hydrogenation of 4-nitrophenol by NaBH4 was carried out to investigate the potential catalytic activity of the obtained heterogeneous Ag/GO nanocomposite. The obtained Ag/GO nanocomposite exhibited high catalytic ability with the apparent kinetics constant of 1.856 min−1 and high turnover frequency of 2131.6 h−1 and high structural and performance stability. It is believed that the small size and naked surface of the Ag nanoparticles, which provide abundant exposed catalytically active sites, facilitate greatly in improving the catalytic performance of Ag/GO. It is anticipated that the proposed green method is extendible to prepare other efficient noble-metal/GO nanocatalyst.

A chemically self-charging aqueous zinc-ion battery

Self-charging power systems integrating energy harvesting technologies and batteries are attracting extensive attention in energy technologies. However, the conventional integrated systems are highly dependent on the availability of the energy sources and generally possess complicated configuration. Herein, we develop chemically self-charging aqueous zinc-ion batteries with a simplified two-electrode configuration based on CaV6O16·3H2O electrode. Such system possesses the capability of energy harvesting, conversion and storage simultaneously. It can be chemically self-recharged by the spontaneous redox reaction between the discharged cathode and oxygen from the ambient environment. Chemically self-recharged zinc-ion batteries display an initial open-circuit voltage of about 1.05 V and a considerable discharge capacity of about 239 mAh g−1, indicating the excellent self-rechargeability. Impressively, such chemically self-charging zinc-ion batteries can also work well at chemical or/and galvanostatic charging hybrid modes. This work not only provides a route to design chemically self-charging energy storage, but also broadens the horizons of aqueous zinc-ion batteries.

Spontaneous Synthesis of Silver‐Nanoparticle‐Decorated Transition‐Metal Hydroxides for Enhanced Oxygen Evolution Reaction

AbstractThe fabrication of metal‐supported hybrid structures with enhanced properties typically requires external energy input, such as pyrolysis, photolysis, and electrodeposition. In this study, silver‐nanoparticle‐decorated transition‐metal hydroxide (TMH) composites were synthesized by an approach based on a spontaneous redox reaction (SRR) at room temperature. The SRR between silver ions and TMH provides a simple and facile route to establish effective and stable heterostructures that can enhance the oxygen evolution reaction (OER) activity. Ag@Co(OH)x grown on carbon cloth exhibits outstanding OER activity and durability, even superior to IrO2 and many previously reported OER electrocatalysts. Experimental and theoretical analysis demonstrates that the strong electronic interaction between Ag and Co(OH)2 activates the silver clusters as catalytically OER active sites, effectively optimizing the binding energies with reacted intermediates and facilitating the OER kinetics.