Nanoporous Electrodes Research Articles

A high-performance amperometric sensor based on amonodisperse Pt-Au bimetallic nanoporous electrode for determination of hydrogen peroxide released from living cells.

A neotype electrochemical sensor based on a three-dimensional nanoporous gold (3D-NPG) electrode decorated with ultra-thin platinum nanoparticles (Pt NPs) was fabricated for high-performance electrocatalysis and sensitive determination of hydrogen peroxide (H2O2) released from pheochromocytoma (PC12) cells. The monodisperse Pt-Au bimetallic nanoporous (Pt-Au-BNP) electrode prepared by cyclic voltammetry electrodepositing monolayer Pt NPs on the surface ofthe 3D-NPG electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive spectroscopy (EDS). Amperometric response for H2O2 measurement was chosen at an applied potential of - 0.4V. Upon optimal conditions, the wide linear range for the amperometric determination of H2O2 was from 0.05μM to 7.37mM, with a limitof detection (S/N = 3) of 1.5 × 10-8mol/L and a high sensitivity of 1.125μAμM-1cm-2, certifying the largeelectrocatalytic actionof the Pt-Au-BNP electrode. Theproposed sensor has been successfully applied tothe dynamic determination of H2O2 released from PC12 cells (from which the H2O2 generated by each cell was about 52.5amol) with negligible interference. Thus, the proposed new electrochemical sensor displays potential applications for the dynamic, real-time monitoring of key small molecules secreted by living cells, further deepening theunderstanding of cell behavior stimulated by foreign materials. Graphical Abstract .

Unraveling the reaction mechanism of co-reactant free in-situ cathodic solid state ECL of Ru(bpy)32+ molecule immobilized on Nafion coated nanoporous gold electrode

The electrochemiluminescence (ECL) of Ru(bpy)32+ molecule which is immobilized on Nafion coated nanoporous gold electrode (Ru(bpy)32+/Nafion/NPG) is investigated without involving any additional co-reactant in 0.1 M phosphate buffer solution (PBS) at pH 7.4 and the observed results are compared with Ru(bpy)32+ molecule immobilized on Nafion coated polycrystalline gold (Ru(bpy)32+/Nafion/pc-Au). Because of high surface area volume ratio and more active sites on NPG, the obtained co-reactant free unusual cathodic ECL signal at less cathodic potentials (0.1 V vs Ag/AgCl) showed 40 times higher intensity on Ru(bpy)32+/Nafion/NPG when compared with Ru(bpy)32+/Nafion/pc-Au in PBS (pH 7.4). Interestingly, this kind of ECL signal is not observed in the case of Ru(bpy)32+ molecule which is immobilized on Nafion coated glassy carbon (GC) and polycrystalline platinum (pc-Pt) electrodes. Based on the detailed experiments on effect of different pH, various direction of scanning potential and in-situ spectroelectrochemical studies, we proposed a new reaction mechanism for the unusual cathodic ECL on Ru(bpy)32+/Nafion/NPG. Upon electrochemical oxidation on Ru(bpy)32+/Nafion/NPG at higher potential, the stored Ru(bpy)32+ is converted into Ru(bpy)33+ at the same time generated reactive intermediate species like OH radical from the conversion of Au(OH)3 to Au0 during the reduction process leads energetic electron transfer reaction to proceed the excited state of Ru(bpy)32+ and then emits light. Unlike the conventional ECL system, this kind of co-reactant free in-situ generated solid state ECL approach offers to the scope in various bio analytical applications.

Impact of chloride surface treatment on nano-porous GaN structure for enhanced water-splitting efficiency

Photoelectrochemical devices equipped with semiconductor electrodes could be used for economically feasible hydrogen generation from water and sunlight energy. The bottleneck is in designing efficiently operating photoelectrodes, in particular with practical nano-architectures maximizing the extraction of the generated charge carriers for the water splitting reaction. In this work, using conventional electrochemical wet etching, we fabricated a nano-porous GaN structure and demonstrated its excellent functionality as a photoelectrode applicable for the water splitting. In particular, using a conventional analysis, we confirmed the water splitting efficiencies of 0.12% and 0.31%, comparing the planar and the nano-porous photoelectrode architectures, respectively. The major advantage of the porosity was in the increased fraction of the space charge region allowing for radically more efficient extraction of photo-generated charge carriers. The water splitting performance of the nano-porous electrodes was further improved by chloride treatment of the samples. This improvement was attributed to the surface chemical bonds reconstruction and/or electronic traps filling, resulting in additional ~20% water splitting efficiency improvement employing the nano-porous photoelectrode architecture. Altogether, we conclude that chloride treated nano-porous GaN photoelectrodes has a great potential for the use in the photoelectrochemical water splitting devices.

Structural Anomalies and Electronic Properties of an Ionic Liquid under Nanoscale Confinement.

Ionic liquids (ILs) promise far greater electrochemical performance compared to aqueous systems, yet key physicochemical properties governing their assembly at interfaces within commonly used graphitic nanopores remain poorly understood. In this work, we combine synchrotron X-ray scattering with first-principles molecular dynamics simulations to unravel key structural characteristics of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([TFSI]-) ionic liquids confined in carbon slit pores. X-ray scattering reveals selective pore filling due to size exclusion, while filled pores exhibit disruption in the IL intermolecular structure, the extent of which increases for narrower slit pores. First-principles simulations corroborate this finding and quantitatively describe how perturbations in the local IL structure, particularly the hydrogen-bond network, depend strongly on the degree of confinement. Despite significant deviations in structure under confinement, electrochemical stability remains intact, which is important for energy storage based on nanoporous carbon electrodes (e.g., supercapacitors).

High-performance supercapacitor based on MOF derived porous NiCo2O4 nanoparticle

Transition metal oxide is a promising candidate for future supercapacitors due to its pronounced electrical properties and low cost. Unfortunately, the poor cycle stability and low capacitance due to the small lattice spacing and strong volume expansion in dense transition metal oxide impede its practical applications seriously. Herein, a nanoporous electrode of metal oxide has been prepared via the solvothermal and subsequent calcination process of MOF-74 (MOF=metal-organic framework), which shows outstanding cycle reversibility, excellent capacitance. Because of large surface areas with a nanoporous structure which is beneficial to the ion transport and relief to volume expansion. Three samples with different divalent metals (MOF-74-Ni, MOF-74-NiCo2 and MOF-74-Co) were prepared by hydrothermal method. After a facile annealing process, the NiO, NiCo2O4 and Co3O4 with the large surface area and porous structure were easily obtained and further the electrochemical properties were investigated. As a result, the NiCo2O4 electrode exhibits obviously high specific capacity (684 F/g) and excellent cycling stability (86% retention after 3000 cycles) compared with the monometallic oxides.

Chain length matters: Structural transition and capacitance of room temperature ionic liquids in nanoporous electrodes

Room-temperature ionic liquids (RTILs) have shown great potential in promoting the widespread application of energy storage devices. The relationship between the electrical double layer (EDL) structure and capacitive performance of different RTILs is vital to the rational design of novel RTIL electrolytes. Herein, we have investigated the microscopic structures of three types of RTILs containing cations with varying tail lengths in nanopores, their charging behaviors, and their EDL capacitances using classical density functional theory (CDFT). The results show that the interfacial structure changes from a monolayer to a bilayer as the neutral chain length of the cations increases, which is in agreement with previous experimental results (Smith et al., 2013). Moreover, the RTILs containing cations with longer chains can significantly enhance the capacitance in nearly neutral pores, while they dampen capacitance under negative electrical potential and show little disadvantage when positive potential is applied.

Molecular aspects, electrochemical properties and water oxidation catalysis on a nanoporous TiO2 electrode anchoring a mononuclear ruthenium(II) aquo complex

A mononuclear Ru aquo complex, [Ru(C8Otpy)(H2dcbpy)(OH2)]2+ (C8Otpy = 4′-octyloxy-2,2′:6′,2′′-terpyridine, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) was stably adsorbed on a nanoporous TiO2 surface to afford a TiO2 electrode anchoring the complex. The adsorption isothermal of the complex on the TiO2 surface was analyzed by the Langmuir adsorption model to provide a maximum coverage of Гmax = 4.4 × 10−8 mol cm−2 and an adsorption equilibrium constant of Kads = 1.1 × 104 M−1, suggesting that the monolayer of the complex is formed on the TiO2 surface. The cyclic voltammetry measurement of the complex on the TiO2 surface suggested the diffusion-controlled charge transport via electron hopping between the complexes through the TiO2 layer. Pourbaix diagram showed that the complex undergoes a non-H+-coupled 1e- redox reaction of a RuIIOH/RuIIIOH pair of the complex on the TiO2 electrode due to pH buffering ability of the TiO2 surface in a range of pH 5−11. Bulk electrolysis at 1.7 V vs Ag/AgCl using the complex-anchoring TiO2 electrode provided a high and steady catalytic current density of 0.39 mA cm−2 with 83 % Faradaic efficiency for O2 evolution during 1 h electrolysis. However, we presume that the complex is transformed to RuOx nanoparticles on the TiO2 electrode during the electrocatalysis, on the basis of our earlier report on the complex / mesoporous ITO electrode system (Dalton Trans., 2020, 49, 1416−1423.). The RuOH/TiO2 electrode is the efficient anode for water oxidation under the acidic conditions, irrespective of the molecular catalyst of RuOH and the alternative catalysts formed via its oxidative transformation.

Dealloyed nanoporous materials for rechargeable lithium batteries

Dealloying has been recognized as a universal strategy to fabricate various functional electrode materials with open networks, nanoscale ligaments, tunable pore sizes and rich surface chemistry, all of which are very attractive characteristics for rechargeable lithium batteries. In particular, lithium ion insertion/extraction in metal anodes is naturally associated with the alloying/dealloying mechanism. The past decade has witnessed rapid growth of this research field with enormous progress. In this review article, we first summarize the recent development and microstructural regulation of dealloyed materials. Next, we focus on the rational design of nanoporous electrodes for rechargeable lithium batteries and related structure-performance correlations. Finally, some critical issues and perspectives are presented to guide the future development directions of such promising technology for high-energy batteries. This review systematically summarizes the recent progress of dealloyed nanoporous materials and their application in rechargeable lithium batteries.

Fitting the porous texture of carbon electrodes to a binary ionic liquid electrolyte for the realization of low temperature EDLCs

We report on electrical double-layer capacitors (EDLCs) operating effectively at low temperature (down to −40 °C) while implementing nanoporous carbon electrodes and an ionic liquid (IL) electrolyte. For this purpose, the binary mixture of [EMIm][FSI] and [EMIm][BF4] in 1:1 mol ratio has been selected, since it has been previously shown that it remains liquid down to its vitrification at −97 °C, unlike the parent ILs with melting points of −13 °C and 14 °C, respectively. To enhance the mass transport of the IL ions, especially at a low temperature, where the IL electrolyte exhibits a high viscosity, carbon electrode materials with a substantial share of mesopores serving as passageways for bulky ions were selected. These were a carbon black (SC2A) with a broad range of interparticle mesopores in addition to a reasonable amount of micropores, as well as a home-made templated carbon (MP98B) with hierarchical porous texture made of interconnected micropores and well-defined mesopores. From 20 to −40 °C, the capacitor with MP98B electrodes displayed greater specific capacitance, energy and power as well as better charge propagation than the cell with SC2A, whereas on volumetric basis its performance was inferior due to lower electrode density. Advanced SCMP composite electrodes of intermediate density were formulated by mixing these two carbons in the 1:1 mass ratio and harnessed to realize EDLCs with enhanced both specific and volumetric energy. Owing to the adjusted electrode properties, the performance of SCMP-based EDLCs surpassed literature data obtained with analogous constructions based on IL electrolytes and lightweight mesoporous materials, which suffered from poor volumetric metrics.

Electrochemical Detection Using Nanoporous Structures

Nanoporous electrodes are a unique class of nanostructured electrodes for promising electrochemical sensor applications because of a range of important attributes which include but are not limited to: high surface area, interesting catalytic properties, fast mass transport and low Ohmic resistance drops, potentially low cost and good fouling tolerance [1, 2]. In addition to the conventional concept of enlarged surface area, nanoporous structures provide a unique environment for reactive molecules. Once a reactant molecule enters a nanopore, the probability of interaction between the nanoporous electrode surface and the molecule is increased compared with that on a flat electrode. The molecule involved in a sluggish electrochemical reaction can enter deep into the nanopore, leading to longer penetration depth. Consequently, the heterogeneous charge transfer gets facilitated and the amperometric response of sluggish faradaic reactions can be selectively enhanced. This will selective amperometric detection, in which the selectivity and sensitivity could be tuned by the depth, shape, and interconnectivity of the nanopores. In addition, the nanoporous structures resulted nano-confinement effects can prevent reactive intermediates from escaping back to the bulk solution. Expedited by the rapid advance of nanomaterial engineering and manipulating technology, nanoporous electrodes will be a strong impetus to a wide range of emerging areas such as in-situ and remote monitoring and controls [3, 4].In this presentation, we will introduce the structural effects of nanoporous materials including discriminative electrokinetics, the nano-confinement effect and electrical double layer overlapping, the fabrication nanoporous microelectrodes, the characterization of their porous structures, and their nanopore-induced enhanced electrochemical responses to several interesting molecules such as nitrate, nitrite, and chlorides.

Block-Copolymer Derived Nanoporous Thin Films for the Development of a L-BMAA Aptamer-Based Electrochemical Biosensor

Produced by diverse cyanobacteria, b-N-methylamino-l-alanine (L-BMAA) is a non-protein neurotoxic cyanotoxin that has been linked to an elevated incidence of neurodegenerative diseases such Parkinson’s and Alzheimer’s disease and Multiple Lateral Sclerosis. The continuing rising of water temperatures and eutrophication of the water bodies propitiate the increment and size of harmful algal blooms, subsequently increasing the production of L-BMAA and other cyanotoxins. This toxin is known to bioaccumulate in plants, animals and humans. Currently, the detection of L-BMAA in water is limited by its hydrophilicity, absence of ultraviolet and fluorescent properties, and the isomers that cause false positives. Given the threat that this cyanotoxin could represent to the long-term human health, it is imperative to develop new analytical techniques for its detection in water. Therefore, this project proposes the development of an impedimetric aptamer-based biosensor, using block-copolymer (BCP’s) derived nanoporous thin films as the electrode, for the detection of L-BMAA. Our hypothesis is that the development of such aptasensor will lead to the advancement of an innovative device for a sensitive, portable, economic and flexible way to achieve the detection of the cyanotoxin in water. To achieve this, we used BCP polystyrene-poly(methylmethacrylate) (PS-b-PMMA), known to form cylinder-like structures, to create recessed nanodisk-array electrodes (RNEs). These cylindrical nanostructures provide primary mass transport pathways for ionic and redox active species which changes upon analyte binding, making them ideal to use in biosensing applications. The nanoporous electrodes were prepared by spin-coating a PS-b-PMMA solution in toluene over gold-coated silicon wafers, followed by thermal annealing and UV etching. Different annealing times, temperatures and UV exposure has been used in order to produce the alignment of the cylindrical polymer microdomains in a vertical fashion over the surface of the electrode. The prepared films were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), to confirm the formation of RNE’s. Under specific sets of conditions, CV data shows sigmoidal curves at high scan rates characteristic of RNE’s, suggesting the formation of this type of nanopores with a sufficiently large distance among them to attain radial diffusion. Atomic force microscopy (AFM) images of the samples evidence the formation of vertical nanopores but mixed with horizontal alignments. Furthermore, grazing incident small angle x-ray scattering (GISAXS)11 suggests that the polymer was well-dispersed among the surface although the expected scattering profile for RNEs is missing. Future work includes the optimization of the electrode preparation methods and the selection of a L-BMAA specific aptamer through graphene oxide-assisted selection evolution of ligands by exponential enrichment (GO-SELEX).

Structure and Na Ion Transport in NaPF6/Carbonate Electrolyte inside Carbon Nanopores: A Molecular Dynamics Study

Sodium-ion batteries (NIBs) are in the spotlight as highly promising energy storage applications due to the low cost and wide availability of Na sources. To date, computational studies of Na storage and transport in carbon electrodes have been carried out without considering the realistic structural and dynamic properties of a carbon anode - electrolyte, which could be critical to battery performance. Using combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we describe the behavior of a Na-based electrolyte, consisting of sodium hexafluorophosphate (NaPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC), near the confined structures of nanoporous carbon electrodes. In our simulation, nanoporous carbons with an average pore size of 8.9 Å were first generated using the Mimetic porous carbon model by quench MD simulation. We also adopted the constant potential method (CPM) to model the electrode carbon to account for the fluctuation of the local charges that are characteristic of realistic battery systems. We investigated the distribution of electrolyte molecules and their microstructures at 0 V and 2 V potentials to provide molecular insights on properties such as solvent packing, degree of confinement (DoC), preferential adsorption sites, and solvation sheath structure. Under the influence of applied potential, we report a good wettability of the electrode by electrolyte molecules as a result of the interconnectivity of nanopores, with the accumulation of electrolyte compounds at the electrode/electrolyte interface as they diffuse into the nanopores. Also, Na+ intercalates into highly confined carbon structures while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. We show that nanoporous carbon structures reduce the adsorption distance of Na+ by ~29 % compared to planar electrodes and consequently identify a hydrogen-terminated edge of porous carbon as a preferential adsorption site for Na+ of favorable adsorption energy of -0.27 eV compared to the adsorption energy of 0.02 eV for Na+ insertion onto a basal surface. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.

A Molecular Dynamics Study of Na Ion Transport and Storage inside Nanoporous Carbon Electrode for Na-Ion Batteries

Hard carbon has emerged as an attractive anode material for sodium ion batteries (NIBs) because of its low cost, high initial coulombic efficiency, high specific capacity, and steady cycling performance. Based on combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we present an atomistic description of the electrolyte-electrode interaction of sodium hexafluorophosphate (NaPF6) in mixed ethylene (EC) and dimethyl carbonate (DMC) electrolyte inside nanoporous carbon electrode. We investigate the microstructure of electrolyte in carbon nanopores with an average pore size of 8.9 Å and a specific surface area of 1794 m2g-1 at 0 V and 2 V to gain molecular insight into electrolyte behavior such as solvent packing, preferential adsorption sites, and solvation structure. Our simulation suggests good accessibility of carbon nanopores by electrolyte molecules upon charging. At 2 V, Na+ is desolvated and intercalates into highly confined carbon structures as a result of the strong interaction between Na+ and charged carbon atoms while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. Also, we examined the various levels of confinement of electrolyte components using a degree of confinement (DoC) analysis, and present the effects of confinement on electrolyte properties. Our calculations show a 29 % reduction in Na+ adsorption distance for a nanoporous structure compared to a planar structure of carbon, and the preferential adsorption of Na+ at a hydrogen-terminated edge of porous carbon with an adsorption energy of -0.27 eV compared to a basal site with a higher adsorption energy of 0.02 eV. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.

Sintering-resistant platinum electrode achieved through atomic layer deposition for thin-film solid oxide fuel cells

Abstract Thin-film solid oxide fuel cells (TF-SOFCs) using a dense and thin electrolyte have attracted much attention as a promising portable power generator because they can lower the operating temperature of devices, which is a key issue related to conventional SOFCs, to below 500 °C and are compatible with several microfabrication processes. Highly porous interconnected Pt thin films are now widely used as oxygen electrodes, but their poor thermal stability seriously hampers the sustainable operation of TF-SOFCs. Here, we demonstrate how Al2O3 layers coated through atomic layer deposition effectively suppress the degradation of nanoporous Pt thin-film electrodes. Although Al2O3 is an electrical insulator, the selection of an appropriate overcoat thickness ensures stable electrochemical reaction sites of the Pt electrode at high temperatures even without serious current collection or gas flow issues. As a result, a 3.6-nm-thick Al2O3 layer maintains the high specific surface area morphology of Pt thin films at 450 °C and improves the electrode activity by more than twofold compared to an uncoated sample. These results suggest that a simple and scalable coating strategy enables the implementation of TF-SOFCs with ideal performance and durability outcomes.

Observation of Ion Electrosorption in Metal–Organic Framework Micropores with In Operando Small‐Angle Neutron Scattering

AbstractA molecular‐level understanding of transport and adsorption mechanisms of electrolyte ions in nanoporous electrodes under applied potentials is essential to control the performance of double‐layer capacitors. Here, in operando small‐angle neutron scattering (SANS) is used to directly detect ion movements into the nanopores of a conductive metal–organic framework (MOF) electrode under operating conditions. Neutron‐scattering data reveals that most of the void space within the MOF is accessible to the solvent. Upon the addition of the electrolyte sodium triflate (NaOTf), the ions are adsorbed on the outer surface of the protrusions to form a 30 Å layer instead of entering the ionophobic pores in the absence of an applied charging potential. The changes in scattering intensity when potentials are applied suggests the ion rearrangement in the micropores following different mechanisms depending on the electrode polarization. These observations shed insights on ion electrosorption in electrode materials.

Observation of Ion Electrosorption in Metal-Organic Framework Micropores with In Operando Small-Angle Neutron Scattering.

A molecular-level understanding of transport and adsorption mechanisms of electrolyte ions in nanoporous electrodes under applied potentials is essential to control the performance of double-layer capacitors. Here, in operando small-angle neutron scattering (SANS) is used to directly detect ion movements into the nanopores of a conductive metal-organic framework (MOF) electrode under operating conditions. Neutron-scattering data reveals that most of the void space within the MOF is accessible to the solvent. Upon the addition of the electrolyte sodium triflate (NaOTf), the ions are adsorbed on the outer surface of the protrusions to form a 30 Å layer instead of entering the ionophobic pores in the absence of an applied charging potential. The changes in scattering intensity when potentials are applied suggests the ion rearrangement in the micropores following different mechanisms depending on the electrode polarization. These observations shed insights on ion electrosorption in electrode materials.

Fabrication and characterization of transparent Cr-decorated TiO2 nanoporous electrode for enhanced photo-electrocatalytic performance

A Cr-decorated TiO2 nanoporous transparent electrode was fabricated by DC sputtering, anodization, and thermal evaporation methods, respectively. Ti films were deposited on fluorine-doped tin oxide (FTO) coated glass and anodized to obtain a transparent TiO2 nanoporous film (TN). The fabricated electrodes were characterized using a field emission scanning electron microscope (FESEM), atomic force microscope (AFM) and X-Ray diffraction (XRD). Photoelectrochemical activity of prepared films was investigated by photo-electrocatalytic degradation of RhB dye under constant voltage and UVA light irradiation. The Cr-decorated TiO2 nanoporous film (CTN) served as an electrode and exhibited better photo-electrocatalytic performance than a TN electrode. Results show that Cr decoration increased photoelectrochemical activity significantly due to more efficient charge separation and lower recombination rate.

Electrowetting-Mediated Transport to Produce Electrochemical Transistor Action in Nanopore Electrode Arrays.

Understanding water behavior in confined volumes is important in applications ranging from water purification to healthcare devices. Especially relevant are wetting and dewetting phenomena which can be switched by external stimuli, such as light and electric fields. Here, these behaviors are exploited for electrochemical processing by voltage-directed ion transport in nanochannels contained within nanopore arrays in which each nanopore presents three electrodes. The top and middle electrodes (TE and ME) are in direct contact with the nanopore volume, but the bottom electrode (BE) is buried beneath a 70 nm silicon nitride (SiNx ) insulating layer. Electrochemical transistor operation is realized when small, defect-mediated channels are opened in the SiNx . These defect channels exhibit voltage-driven wetting that mediates the mass transport of redox species to/from the BE. When BE is held at a potential maintaining the defect channels in the wetted state, setting the potential of ME at either positive or negative overpotential results in strong electrochemical rectification with rectification factors up to 440. By directing the voltage-induced electrowetting of defect channels, these three-electrode nanopore structures can achieve precise gating and ion/molecule separation, and, as such, may be useful for applications such as water purification and drug delivery.

Ion Dynamics of Water‐in‐Salt Electrolyte with Organic Solvents in Nanoporous Supercapacitor Electrodes

AbstractWater‐in‐salt electrolytes blended with organics solvents, that is, organic solvent/water mixed electrolytes, are promising for applications in next‐generation energy storage devices vitally needed for industrial electrification and decarbonization. However, the electrolyte ion diffusion behaviors within nanoporous supercapacitor electrodes are poorly understood. Here a systematic investigation into supercapacitor resistances and ion kinetics is carried out experimentally and with numerical simulations. The electrochemical results on the nanoporous electrodes reveal a nonmonotonic (decreasing, increasing, and then decreasing) trend of supercapacitor resistances with increasing solvent mobility, challenging the long‐held views that supercapacitor resistances decrease with elevated mobility of organic solvent. The abnormal trend is examined by numerical molecular dynamics simulations of electrolyte ion diffusion within 0.95 nm nanochannels. The electrolyte conductivity is related to cation–anion interactions within nanochannels. We further confirm the crucial interplay of the van der Waals sizes of solvent molecules and channel width in determining electrolyte conductivity in nanoporous electrodes.

Nanoporous carbon-fiber microelectrodes for sensitive detection of H2O2 and dopamine

In this study, sensitive electrochemical detection of H2O2 and dopamine (DA) was demonstrated using a nanoporous carbon fiber electrode (CFE). SEM images confirmed the surface modification and elemental composition analysis demonstrated an increase in the C/O ratio favoring higher conductivity and electron-transfer rate. Nanoporous CFEs were first used for electrochemical oxidation and reduction of H2O2 and results were compared with those of unmodified CFEs. Oxidation current drastically increased with heat treatment and unlike unmodified CFEs, nanoporous CFEs demonstrated a concentration-dependent current change for the reduction of H2O2. Next, the performance of nanoporous CFEs was assessed for DA detection in comparison to unmodified CFEs and they showed remarkable electrocatalytic activity in terms of both sensitivity and selectivity. The nanoporous CFEs have great potential to be used in various applications ranging from measurements in localized volumes to tissue analysis.