Ionic Strength-Controlled Virtual Area of Mesoporous Platinum Electrode

Emerging Frontiers in Multichannel Membrane Capacitive Deionization: Recent Advances and Future Prospects

Capacitive deionization (CDI) has emerged as a promising desalination technology and recently promoted the development of multichannel membrane capacitive deionization (MC-MCDI). In MC-MCDI, the independent control of multiflow channels, including the feed and electrolyte channels, enables the optimization of electrode operation in various modes, such as concentration gradients and reverse voltage discharge, facilitating semicontinuous operation. Moreover, the integration of redox couples into MC-MCDI has led to advancements in redox-mediated desalination. Specifically, the introduction of redox-active species helps enhance the ion removal efficiency and reduce energy consumption during desalination. This systematic approach, combining principles from CDI and electrodialysis, results in more sustainable and efficient desalination. These advancements have contributed to improved desalination performance and practical feasibility, rendering MC-MCDI an increasingly attractive option for addressing water scarcity challenges. Despite the considerable interest in and potential of this process, there is currently no comprehensive review available that covers the operational features and applications of MC-MCDI. Therefore, this Review provides an overview of recent research progress, focusing on the unique cell configuration, vital operation principles, and potential advantages over conventional CDI. Additionally, innovative applications of MC-MCDI are discussed. The Review concludes with insights into future research directions, potential opportunities in industrial desalination technology, and the fundamental and practical challenges for successful implementation.

Two-dimensional mesoporous metals: a new era for designing functional electrocatalysts

Two-dimensional (2D) mesoporous metals contribute a unique class of electrocatalyst materials for electrochemical applications. The penetrated mesopores of 2D mesoporous metals expose abundant accessible undercoordinated metal sites, while their 2D nanostructures accelerate the transport of electrons and reactants. Therefore, 2D mesoporous metals have exhibited add-in structural functions with great potential in electrocatalysis that not only enhance electrocatalytic activity and stability but also optimize electrocatalytic selectivity. In this Perspective, we summarize recent progress in the design, synthesis, and electrocatalytic performance of 2D mesoporous metals. Four main strategies for synthesizing 2D mesoporous metals, named the CO (and CO container) induced route, halide ion-oriented route, interfacial growth route, and metal oxide atomic reconstruction route, are presented in detail. Moreover, electrocatalytic applications in several important reactions are summarized to highlight the add-in structural functions of 2D mesoporous metals in enhancing electrochemical activity, stability, and selectivity. Finally, current challenges and future directions are discussed in this area. This Perspective offers some important insights into both fundamental investigations and practical applications of novel high-performance functional electrocatalysts.

Electrochemical flow injection analysis for the rapid determination of reducing sugars in potatoes

Non-enzymatic electrochemical sensors for the monitoring of reducing sugars in foods has great potential as a rapid in-situ detection method. This development involved the assembly of a nanoporous platinum structure on a screen-printed carbon electrode (SPCE). The modified electrode was then employed as an amperometric sensing element in a flow injection analysis (FIA) manifold. The system was successfully applied to the rapid detection of reducing sugars in potatoes, without the need for sample preparation. Optimal signals were achieved in phosphate buffer (pH 7.4) at a flow rate of 0.5 mL min^-1 and an applied potential of 0.6 V. Experimental results demonstrated the sensor's long-term stability and high selectivity for reducing sugars. This method provides high sample throughput due to a rapid response time of less than five seconds. Reducing sugar values determined were in good agreement with those recorded using a commercially available enzymatic assay kit.

Hexagonally Packed Macroporous Molecularly Imprinted Polymers for Chemosensing of Follicle-Stimulating Hormone Protein

Homogenous nanostructuration of molecularly imprinted polymer (MIP) films for follicle-stimulating hormone (FSH)-sensing was achieved by using optimized colloidal crystals as a hard mold. Introduction of a heating step after assembling colloidal crystals of silica beads promoted their adhesion. Thus, precise assembling of beads was not disturbed during further multisteps of surface imprinting, and crack-free hexagonal packing was maintained. Scanning electron microscopy imaging confirmed hexagonal packing of silica colloidal crystals as well as homogenous nanostructuration in MIP films. FSH immobilization over silica beads and later its derivatization with electroactive functional monomers was confirmed by X-ray photoelectron spectroscopy analysis. The nanostructured molecular recognition films prepared in this way were combined with an electrochemical transducer in order to design a capacitive impedimetry-based chemosensing system. It was tested for the determination of FSH in the range from 0.1 fM to 100 pM in 10 mM 2-(N-morpholino) ethane sulfonic acid buffer (pH = 4.2). The detection limit of the chemosensor was 0.1 fM, showing a high selectivity with respect to common protein interferences as well as other protein hormones of the gonadotropin family.

Electrochemical CO2 reduction on nanostructured metal electrodes: fact or defect?

Electrochemical CO2 reduction has received an increased amount of interest in the last decade as a promising avenue for storing renewable electricity in chemical bonds. Despite considerable progress on catalyst performance using nanostructured electrodes, the sensitivity of the reaction to process conditions has led to debate on the origin of the activity and high selectivity. Additionally, this raises questions on the transferability of the performance and knowledge to other electrochemical systems. At its core, the discrepancy is primarily a result of the highly porous nature of nanostructured electrodes, which are vulnerable to both mass transport effects and structural changes during the electrolysis. Both effects are not straightforward to identify and difficult to decouple. Despite the susceptibility of nanostructured electrodes to mass transfer limitations, we highlight that nanostructured silver electrodes exhibit considerably higher activity when normalized to the electrochemically active surface in contrast to gold and copper electrodes. Alongside, we provide a discussion on how active surface area and thickness of the catalytic layer itself can influence the onset potential, selectivity, stability, activity and mass transfer inside and outside of the three dimensional catalyst layer. Key parameters and potential solutions are highlighted to decouple mass transfer effects from the measured activity in electrochemical cells utilizing CO2 saturated aqueous solutions.

Electro-deposited Nanoporous Platinum Electrode for EEG Monitoring

BACKGROUND

One of the key issues in electroencephalogram (EEG) monitoring is accurate signal acquisition with less cumbersome electrodes. In this study, the L2 phase electro-deposited nanoporous platinum (L2-ePt) electrode is introduced, which is a new type of electrode that utilizes a stable nanoporous platinum surface to reduce the skin-electrode impedance.

METHODS

L2-ePt electrodes were fabricated using electro-deposition technique. Then, the effect of the nanoporous surface on the surface roughness and the electrode impedance were observed from the L2-ePt electrodes and the flat platinum (FlatPt) electrode. The skin-electrode impedances of the L2-ePt electrodes, a gold cup electrode, and the FlatPt electrode were evaluated when placed on the hairy occipital area of the head in ten subjects. For the validation of using the L2-ePt electrode, a correlational analysis of the alpha rhythms was performed in the same subjects for simultaneous EEG recordings using the L2-ePt and clinically-used EEG electrodes.

RESULTS

The results indicated that the L2-ePt electrode with a roughness factor of 200 had the lowest mean impedance performance. Moreover, the proposed L2-ePt electrode showed a significantly lower mean skin-electrode impedance than the FlatPt electrode. Finally, the EEG signal quality recorded by the L2-ePt electrode (r = 0.94) was comparable to that of the clinically-used gold cup electrode.

CONCLUSION

Based on these results, the proposed L2-ePt electrode is suitable for use in various high-quality EEG applications.

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

Tailoring of pore structure in mesoporous carbon for favourable flavin mediated interfacial electron transfer in microbial fuel cells

Mesoporous carbon (MC) is supposed to be a good candidate for microbial fuel cell (MFC) anodes as it possesses a large specific area for the redox reaction of the electron shuttles and should deliver high power density. However, the power generation performance of MC anodes is often un-satisfying. It seems that a large portion of the pore surface is not available for anodic redox reaction but the reason is not clear. Here, three MCs with different pore sizes and pore shapes were fabricated and used to explore the effect of the pore structure on the bioelectrocatalysis in Shewanella putrefaciens CN32 MFCs. It is interesting that MC with 40–60 nm spheric pores (MC-III) possesses superior bio-electrocatalytic performance to the CMK-3 (MC-I with 3 nm channel like pores) and the one with 14 nm spheric pores (MC-II) although the specific surface area of MC-III is lower than MC-II and MC-I. The reason might be that the MC-III provides a more favorable pore structure than the other two MCs for flavin based redox reaction at the interface between the biofilm and the electrode. As a result, the MC-III anode delivered the highest power density at around 1700 mW m⁻², which is 1.6 fold higher than that of the MC-I anode. A possible mechanism for the pore shape/size dependent interfacial electron transfer process has also been proposed. This work reveals that spheric mesopores with large pore width could be more favorable than the narrow channel-like pores for flavin based interfacial electron transfer in biofilm anodes, which will provide some insights for the design of the mesoporous anode in MFCs.

Spherical mesopores with large pore width are more favorable to flavin mediated interfacial electron transfer in microbial fuel cells.

Hollow Carbon Nanopolyhedra for Enhanced Electrocatalysis via Confined Hierarchical Porosity

A novel strategy for the fabrication of hollow Co and N-codoped carbon nanopolyhedra (H-CoNC) from metal-organic framework (MOF) using in situ evaporation of ZnO nanosphere templates is proposed. The excess Zn supply during the pyrolysis process is found beneficial in terms of high nitrogen (≈9.75 at%), relatively homogenous CoN bonding, and the electrochemically accessible hierarchical porous system. Compared with other reported "solid" CoNC of identical surface areas, the newly developed H-CoNC shows enhanced kinetic current in 0.1 m KOH electrolyte and elevated oxygen reduction reaction (ORR) performance in 6 m KOH. The latter exceeds results obtained with the benchmark 20 wt% Pt/C, which is related to the strong confinement of O₂ molecules in the H-CoNC hierarchical porous system. Furthermore, the H-CoNC displays great tolerance toward the methanol crossover and KSCN poisoning. Finally, the assembled Zn-air batteries with H-CoNC yield a record open circuit potential (1.59 V vs Zn, stabilized at 1.52 V), high power density (331.0 mW cm^-2 ), and promising rate performance. This work provides a new guideline for the design of MOF-derived carbon materials, as well as novel insights into spatial confinement effect toward the ORR activity.

Interfacial double layer mediated electrochemical growth of thin-walled platinum nanotubes

This work demonstrates that thin-walled platinum nanotubes can be readily synthesized by controlling the interfacial double layer in alumina nanochannels. The gradient distribution of ions in nanochannels enables the creation of Pt nanotubes with walls as thin as 5 nm at the top end when using a solution containing polyvinylpyrrolidone (PVP) and chloroplatinic acid (H₂PtCl₆) under the influence of an electric potential in nanochannels. The highly efficient formation of thin-walled Pt nanotubes is a result of the concentration gradient of [Formula: see text] and a thick double layer, which was caused by the low concentration of Pt precursors and the enhanced surface charge density induced by protonated PVP steric adsorption. This well-controlled synthesis reveals that the interfacial double layer is a useful tool to tailor the structure of nanomaterials in a nanoscale space, and holds promise in the construction of more complex functional nanostructures.

Dynamic manipulation of the local pH within a nanopore triggered by surface-induced phase transition

Manipulating the local pH within nanopores is essential in nanofluidics technology and its applications.

Densely charged polyelectrolyte-stuffed nanochannel arrays for power generation from salinity gradient

We devised anodized aluminium oxide (AAO) frame-supported polyelectrolytic ion-exchange membranes for the application of electrical power generation systems where salinity differences are present. A series of polyelectrolytic AAO membranes (PAMs) were fabricated as a function of concentration of monomers and cross-linkers. Of the ion-selective PAMs as made, the membranes from the most concentrated monomers and cross-linkers, C-PAM100 and A-PAM100, showed the highest area resistances and permselectivities (the resistances were 4.9 and 2.9 Ω · cm(2), the permseletivities for C-PAM100 and A-PAM100 were 99 and 89%, respectively). The measured resistances and permselectivities allowed the power density to be estimated for C-PAM100 and A-PAM100, 3.5 W/m(2), and experimentally obtained power density using a reverse electrodialysis (RED) stack was 17.3 mW/m(2). In addition, we investigated the influence of an AAO framework on a membrane resistance by comparing the PAMs with polyelectrolyte-stuffed capillaries, revealing that the resistance of the PAM has plenty of potential to be further reduced by optimizing the AAO pore spaces.

CuO nanowire/microflower/nanowire modified Cu electrode with enhanced electrochemical performance for non-enzymatic glucose sensing

CuO nanowire/microflower structure on Cu foil is synthesized by annealing a Cu(OH)2 nanowire/CuO microflower structure at 250 °C in air. The nanowire/microflower structure with its large surface area leads to an efficient catalysis and charge transfer in glucose detection, achieving a high sensitivity of 1943 μA mM(-1) cm(-2), a wide linear range up to 4 mM and a low detection limit of 4 μM for amperometric glucose sensing in alkaline solution. With a second consecutive growth of CuO nanowires on the microflowers, the sensitivity of the obtained CuO nanowire/microflower/nanowire structure further increases to 2424 μA mM(-1) cm(-2), benefiting from an increased number of electrochemically active sites. The enhanced electrocatalytic performance of the CuO nanowire/microflower/nanowire electrode compared to the CuO nanowire/microflower electrode, CuO nanowire electrode and CuxO film electrode provides evidence for the significant role of available surface area for electrocatalysis. The rational combination of CuO nanowire and microflower nanostructures into a nanowire supporting microflower branching nanowires structure makes it a promising composite nanostructure for use in CuO based electrochemical sensors with promising analytical properties.

Nanoporous CuO layer modified Cu electrode for high performance enzymatic and non-enzymatic glucose sensing

Nanoporous CuO layer on Cu foil with a thick Cu2O interlayer is synthesized via post annealing of previously fabricated Cu(OH)2 nanowires at 500 °C under an oxygen flow. The formation of the thick sandwiched Cu2O layer is realized through the outward diffusion of Cu ions and subsequent oxidation. An O2 pressure above the dissociation pressure of CuO is used to form a CuO layer at the outer surface of the structure, thus realizing a low cost structure having a porous and high isoelectric point layer. The Cu/Cu2O/CuO structure is used as an efficient electrode for glucose sensing. Sensitivities of [Formula: see text] at 0.8 V versus Ag/AgCl and 1066 μA mM(-1) cm(-2) at 0.6 V versus Ag/AgCl are achieved in an enzymatic and non-enzymatic glucose sensing schemes, respectively. The improved electrochemical sensing ability might be attributed to the efficient electrocatalytic reaction on the high crystal quality CuO layer and the porous structure.

Nanoparticles of Pt loaded on a vertically aligned TiO2 nanotube bed: synthesis and evaluation of electrocatalytic activity

Pt nano particle loaded TiO₂ nanotube (TiNT) electrode with excellent electrocatalytic activity was synthesized via seed mediated hydrothermal reduction method on self-aligned TiNT bed.

Facile preparation of a highly sensitive nonenzymatic glucose sensor based on multi-walled carbon nanotubes decorated with electrodeposited metals

Preparation of Ni/CuAg/MWCNT hybrid composite modified electrode: (a) bare, (b) MWCNT, (c) CuAg/MWCNT, and (d) Ni/CuAg/MWCNT modified electrodes.

Enhanced charge storage of ultrathin polythiophene films within porous nanostructures

In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance.

Electrochemical control of ion transport through a mesoporous carbon membrane

We report a carbon-based, three-dimensional nanofluidic transport membrane that enables gated, or on/off, control of the transport of organic molecular species and metal ions using an applied electrical potential. In the absence of an applied potential, both cationic and anionic molecules freely diffuse across the membrane via a concentration gradient. However, when an electrochemical potential is applied, the transport of ions through the membrane is inhibited.

Nonenzymatic amperometric sensor for ascorbic acid based on hollow gold/ruthenium nanoshells

We report a new nonenzymatic amperometric detection of ascorbic acid (AA) using a glassy carbon (GC) disk electrode modified with hollow gold/ruthenium (hAu-Ru) nanoshells, which exhibited decent sensing characteristics. The hAu-Ru nanoshells were prepared by the incorporation of Ru on hollow gold (hAu) nanoshells from Co nanoparticle templates, which enabled AA selectivity against glucose without aid of enzyme or membrane. The structure and electrocatalytic activities of the hAu-Ru catalysts were characterized by spectroscopic and electrochemical techniques. The hAu-Ru loaded on GC electrode (hAu-Ru/GC) showed sensitivity of 426 μA mM(-1) cm(-2) (normalized to the GC disk area) for the linear dynamic range of <5 μM to 2 mM AA at physiological pH. The response time and detection limit were 1.6 s and 2.2 μM, respectively. Furthermore, the hAu-Ru/GC electrode displayed remarkable selectivity for ascorbic acid over all potential biological interferents, including glucose, uric acid (UA), dopamine (DA), 4-acetamidophenol (AP), and nicotinamide adenine dinucleotide (NADH), which could be especially good for biological sensing.

Differential pulse voltammetry detection of dopamine and ascorbic acid by permselective silica mesochannels vertically attached to the electrode surface

Silica mesochannels vertically aligned on the electrode surface have been employed for permselective detection of dopamine and ascorbic acid.

Simple and robust strategy for potentiometric detection of glucose using fluorinated phenylboronic acid self-assembled monolayer

BACKGROUND

Field effect transistor (FET) based signal-transduction (Bio-FET) is an emerging technique for label-free and real-time basis biosensors for a wide range of targets. Glucose has constantly been of interest due to its clinical relevance. Use of glucose oxidase (GOD) and a lectin protein Concanavalin A are two common strategies to generate glucose-dependent electrochemical events. However, these protein-based materials are intolerant of long-term usage and storage due to their inevitable denaturing.

METHODS

A phenylboronic acid (PBA) modified self-assembled monolayer (SAM) on a gold electrode with an optimized disassociation constant of PBA, that is, 3-fluoro-4-carbamoyl-PBA possessing its pKa of 7.1, was prepared and utilized as an extended gate electrode for Bio-FET.

RESULTS

The prepared electrode showed a glucose-dependent change in the surface potential under physiological conditions, thus providing a remarkably simple rationale for the glyco-sensitive Bio-FET. Importantly, the PBA modified electrode showed tolerance to relatively severe heat and drying treatments; conditions under which protein based materials would surely be denatured.

CONCLUSIONS

A PBA modified SAM with optimized disassociation constant (pKa) can exhibit a glucose-dependent change in the surface potential under physiological conditions, providing a remarkably simple but robust method for the glyco-sensing.

GENERAL SIGNIFICANCE

This protein-free, totally synthetic glyco-sensing strategy may offer cheap, robust and easily accessible platform that may be useful in developing countries. This article is part of a Special Issue entitled Organic Bioelectronics-Novel Applications in Biomedicine.

Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry

Nanoporous gold prepared by dealloying Au:Ag alloys has recently become an attractive material in the field of analytical chemistry. This conductive material has an open, 3D porous framework consisting of nanosized pores and ligaments with surface areas that are 10s to 100s of times larger than planar gold of an equivalent geometric area. The high surface area coupled with an open pore network makes nanoporous gold an ideal support for the development of chemical sensors. Important attributes include conductivity, high surface area, ease of preparation and modification, tunable pore size, and a bicontinuous open pore network. In this paper, the fabrication, characterization, and applications of nanoporous gold in chemical sensing are reviewed specifically as they relate to the development of immunosensors, enzyme-based biosensors, DNA sensors, Raman sensors, and small molecule sensors.

Hierarchically driven IrO2 nanowire electrocatalysts for direct sensing of biomolecules

Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO(2)) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H(2)O(2)) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules.