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Ionic diodes have emerged repeatedly in the literature for gel interfaces, for nanopores and channels, for nano-/micro-fluidic systems, and for asymmetrically ionomer-covered microholes. Concentration polarisation is likely to be the key to understanding the diode function and the diode time constant diode, i.e. the time for approaching steady state following a potential/polarity switch. For frequencies higher than diode = 2f = (diode)-1, the polarization mechanism is too slow for ion current rectification. Below the frequency associated with the diode time constant, irreversibility in ion flow is induced and the diode switches between two resistive states at opposite potentials (“open” and “closed”). The irreversible flow of ions allows energy conversion from electrical to electrochemical. For energy conversion, two coupled ionic diodes are necessary driven by alternating current (AC) electricity to minimise driver electrode electrolysis and energy losses. Opportunities for AC-desalination and for electroosmotic water harvesting with coupled ionic diodes are discussed.

Urine citrate analysis is relevant in the screening and monitoring of patients with prostate cancer and calcium nephrolithiasis. A sensitive, fast, easy, and low-maintenance electrochemiluminescence (ECL) method with conductivity detection for the analysis of citrate in urine is developed and validated by employing polymer of intrinsic microporosity-1 nanoparticles/nitrogen-doped carbon quantum dots (nano-PIM-1/N-CQDs). Using optimum conditions, the sensor was applied in ECL experiments in the presence of different concentrations of citrate ions. The ECL signals were quenched gradually by the increasing citrate concentration. The linear range of the relationship between the logarithm of the citrate concentration and ΔECL (ECL of blank − ECL of sample) was obtained between 1.0 × 10−7 M and 5.0 × 10−4 M. The limit of detection (LOD) was calculated to be 2.2 × 10−8 M (S/N = 3). The sensor was successfully applied in real samples such as human serum and patient urine. Graphical abstract: [Figure not available: see fulltext.].

A modified glassy carbon electrode (GCE) was developed based on a synthesized graphene oxide (GO) gold nanorod (AuNR) decorated composite (GO/AuNR) for sensitive electrochemical sensing of uric acid (UA). The electrochemical performance of GO/AuNR/GCE for UA detection was investigated employing the differential pulse voltammetry (DPV) technique. Central composite design (CCD) was applied to obtain the optimum composition of the GO and AuNR composite, which provide the highest possible UA oxidation peak current. The optimum composition was obtained at a GO concentration of 5 mg mL

A bio-derived polyester has been crosslinked into flexible films for solid polymer electrolyte applications in Li+-ion batteries, with ionic conductivity around 10−5 S cm−1 at 60 °C, high Li+ transference number (0.84), and hydrolytic degradability.

This review throws light on the development and emerging electrocatalytic applications of potentially important 2D material MXene with specific references to oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER).

Conductive polymeric microneedle (MN) arrays as biointerface materials show promise for the minimally invasive monitoring of analytes in biodevices and wearables. There is increasing interest in microneedles as electrodes for biosensing, but efforts have been limited to metallic substrates, which lack biological stability and are associated with high manufacturing costs and laborious fabrication methods, which create translational barriers. In this work, additive manufacturing, which provides the user with design flexibility and upscale manufacturing, is employed to fabricate acrylic-based microneedle devices. These microneedle devices are used as platforms to produce intrinsically-conductive, polymer-based surfaces based on polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). These entirely polymer-based solid microneedle arrays act as dry conductive electrodes while omitting the requirement of a metallic seed layer. Two distinct coating methods of 3D-printed solid microneedles, in situ polymerization and drop casting, enable conductive functionality. The microneedle arrays penetrate ex vivo porcine skin grafts without compromising conductivity or microneedle morphology and demonstrate coating durability over multiple penetration cycles. The non-cytotoxic nature of the conductive microneedles is evaluated using human fibroblast cells. The proposed fabrication strategy offers a compelling approach to manufacturing polymer-based conductive microneedle surfaces that can be further exploited as platforms for biosensing.

A blue light mediated photochemical process using solid graphitic carbon nitride (g-C3N4) in ambient air/isopropanol vapour is suggested to be linked to “nanophase” water inclusions and is shown to produce...

A highly selective electrochemical sensor based on a molecularly imprinted polymer (MIP) to be developed for uric acid detection in the presence of dopamine as an interference molecule was demonstrated in this study. This non-enzymatic uric acid sensor was developed by electropolymerizing poly-pyrrole onto a composite of electrochemically reduced graphene oxide (ErGO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on a glassy carbon electrode (GCE) to give MIP/ErGO/PEDOT:PSS electrodes. The structural properties, surface morphology, and electrochemical interface of this fabricated uric acid sensor was then characterized using infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and electrochemical impedance spectroscopy. This fabricated non-enzymatic electrochemical sensor (MIP/ErGO/PEDOT:PSS modified GCE) also showed excellent analytical performance at the optimum ratio of monomer/template concentration and optimized electropolymerization conditions, for example in the low concentration range of 0.1-100 μM with a detection limit of 0.05 μM towards uric acid detection in the presence of dopamine. Furthermore, this fabricated uric acid sensor also exhibited good reproducibility and stability for uric acid measurements in the presence of dopamine for 5 consecutive days. In addition, this sensor demonstrates highly selective detection of uric acid in the presence of several interfering species such as dopamine, urea, glucose, magnesium ions, and ascorbic acid. This fabricated uric acid sensor ultimately showed satisfactory uric acid measurement in samples of human urine and is expected to be used in early-stage disease diagnosis.

In order to prevent the microwave leakage and mutual interference, more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation. In this work, we have successfully prepared MoS2/TiO2/Ti3C2Tx hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties. Supported by comprehensive characterizations, MoS2 nanosheets were proved to be anchored on the surface and interlayer of Ti3C2Tx through a hydrothermal process. Additionally, TiO2 nanoparticles were obtained in situ. Due to these hierarchical structures, the MoS2/TiO2/Ti3C2Tx composites showed greatly enhanced microwave absorbing performance. The MoS2/TiO2/Ti3C2Tx composites exhibit a maximum reflection loss value of −33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1 GHz (13.9–17 GHz) at the thickness of 1.0 mm, implying the features of wide frequency and light weight. This work in the hierarchical structure of MoS2/TiO2/Ti3C2Tx composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.

This study examines the role of defects in structure–property relationships in spinel LiMn1.5Ni0.5O4 (LMNO) cathode materials, especially in terms of Mn3+ content, degree of disorder, and impurity phase, without the use of the traditional high-temperature annealing (≥700 °C used for making disordered LMNO). Two different phases of LMNO (i.e., highly P4332-ordered and highly Fd3̅m-disordered) have been prepared from two different β-MnO2−δ precursors obtained from an argon-rich atmosphere (β-MnO2−δ (Ar)) and a hydrogen-rich atmosphere [β-MnO2−δ (H2)]. The LMNO samples and their corresponding β-MnO2−δ precursors are thoroughly characterized using different techniques including high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman spectroscopy, powder neutron diffraction, X-ray photoelectron spectroscopy, synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy, and electrochemistry. LMNO from β-MnO2−δ (H2) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO2−δ (Ar). For the first time, defective β-MnO2−δ has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn3+ content, and impurity contents without the need for conventional methods of doping with metal ions, high synthetic temperature, use of organic compounds, postannealing, microwave, or modification of the temperature-cooling profiles. The results show that the oxygen vacancy changes concurrently with the degree of disorder and Mn3+ content, and the best electrochemical performance is only obtained at 850 °C for LMNO-(Ar). The findings in this work present unique opportunities that allow the use of β-MnO2−δ as viable precursors for manipulating the structure–property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.

Stainless steels typically feature high toughness and good corrosion resistance. However, pitting corrosion can easily occur on stainless steel and the passivation film tends to be vulnerable under pressure or in brine environments. Metal corrosion is a long-standing challenge for the steel industry, forging a path to net-zero. Herein, by successive growth of a series of quantum confined nanocrystals such as quantum dots and nanorods with gradient band energy level alignment, high-performance photoelectrochemical cathodic protection for steel is demonstrated with remarkable mechanical and electrochemical stability. Under simulated solar light illumination, effective photoinduced protection can be realized for 304 stainless steel which enables long-term corrosion resistance in a 3.5 wt% NaCl solution. Unique nanotree-like structures and the quaternary material combination can store excess charges and release them gradually, enabling time-delay protection for metals after light excitation. Various promising functionalities as unique photoelectrodes can be envisioned arising from the proposed 3D nanotree morphology.

Commercial resin microbeads are widely applied in ion exchange and extraction. Here, a single anion-selective and phosphate binding resin microbead (FerrIX™) is mounted into an epoxy membrane and investigated by 4-electrode membrane voltammetry and membrane impedance spectroscopy. Anion transport properties are observed to dominate associated with three distinct potential domains: (I) a low bias ohmic potential domain (dominant at high electrolyte concentration), (II) a concentration polarisation potential domain, and (III) an over-limiting potential domain. Voltammetric responses show transient diffusion-migration features at higher scan rates and quasi-steady state features at lower scan rates. Inherent microbead conductivity is shown to be linked to two resistive elements, electrolyte concentration dependent and independent, in series. The effects of phosphate binding are revealed as transient pattern in impedance spectroscopy data. Preliminary data suggest phosphate concentration-dependent peak features in the imaginary impedance versus frequency plot due to phosphate binding into the microbead. Graphical abstract

Ionic rectifier membranes or devices generate uni-directional ion transport to convert an alternating current (AC) ion current input into stored energy or direct current (DC) in the form of ion/salt gradients. Electrochemical experiments 80 years ago were conducted on biological membrane rectifier systems, but today a plethora of artificial ionic rectifier types has been developed and electroanalytical tools are employed to explore mechanisms and performance. This overview focuses on microscale ionic rectifiers with a comparison to nano- and macroscale ionic rectifiers. The potential is surveyed for applications in electrochemical analysis, desalination, energy harvesting, electrochemical synthesis, and in selective ion extraction.

The discovery of electrochemical switching of the Lα phase of chlorpromazine hydrochloride in water is reported. The phase is characterized using polarizing microscopy, X-ray scattering, rheological measurements, and microelectrode voltammetry. Fast, heterogeneous oxidation of the lyotropic liquid crystal is shown to cause a phase change resulting from the disordering of the structural order in a stepwise process. The underlying molecular dynamics is considered to be a cooperative effect of both increasing electrostatic interactions and an unfolding of the monomers from “butterfly”-shaped in the reduced form to planar in the oxidized form.

Here we report the development of a new scalable and transferable plasma assisted atomic layer deposition (PEALD) process for the production of uniform, conformal and pinhole free NiO with sub-nanometre control on a commercial ALD reactor. In this work we use the readily available nickel precursor nickelocene in conjunction with O2 plasma as a co-reagent (100 W) over a temperature range of 75–325 °C. An optimised growth per cycle of 0.036 nm was obtained at 250 °C with uniform thickness and coverage on scale-up to and including an 6 inch Si wafer (with a 200 nm thermal SiO2 top layer). The bulk characteristics of the NiO thin films were comprehensively interrogated by PXRD, Raman spectroscopy, UV-vis spectroscopy and XPS. The new NiO process was subsequently used to fabricate a 3D nanostructured NiO/TiO2/FTO heterojunction by depositing 20 nm of NiO onto pre-fashioned TiO2 nanorods at 250 °C for application in the photo-electrolysis of water in a photoelectrochemical cell (PEC). The NiO/TiO2 3D array was shown to possess a peak current of 0.38 mA cm−2 at 1.23 VRHE when stimulated with a one sun lamp.

Microporous polymer materials based on molecularly “stiff” structures provide intrinsic microporosity, typical micropore sizes of 0.5 nm to 1.5 nm, and the ability to bind guest species. The polyamine PIM-EA-TB contains abundant tertiary amine sites to interact via hydrogen bonding to guest species in micropores. Here, quercetin and catechin are demonstrated to bind and accumulate into PIM-EA-TB. Voltammetric data suggest apparent Langmuirian binding constants for catechin of 550 (± 50) × 103 M-1 in acidic solution at pH 2 (PIM-EA-TB is protonated) and 130 (± 13) × 103 M-1 in neutral solution at pH 6 (PIM-EA-TB is not protonated). The binding capacity is typically 1:1 (guest : host polymer repeat unit), but higher loadings are readily achieved by host/guest co-deposition from tetrahydrofuran solution. In the rigid polymer environment, bound ortho-quinol guest species exhibit 2-electron 2-proton redox transformation to the corresponding quinones, but only in a thin mono-layer film close to the electrode surface. Release of guest molecules occurs depending on the level of loading and on the type of guest either spontaneously or with electrochemical stimuli.

Graphitic carbon nitride (g-C

Water splitting by photocatalysis, for example employing seawater or wastewater, has the potential to make a substantial contribution to a future hydrogen economy. New types of 3D metal-wire substrates in woven form or brushes for photoelectrochemical processes are desirable to replace flat semiconductor-coated surfaces. In this report, titanium microwires (100 m diameter; pre-passivated) are employed to produce high surface area photoanodes with a TiO2 (rutile) nanocrystal array coating that was grown hydrothermally. A photo-active electrode is obtained with nanocrystal TiO2 rods of adjustable length from 1.67 µm up to 7.38 µm. Saturation of the photoelectrochemical response occurs at an intermediate length of approx. 3.19 µm with a photocurrent density of approximately 4.4 mA cm-2 at 1.0 V vs. Ag/AgCl (3M) in aqueous 1 M Na2SO4 under 100 mW cm-2 385 nm LED illumination. The effectiveness of vacuum annealing for enhancing TiO2 photochemical processes is demonstrated. The formation of oxygen in aqueous 1 M Na2SO4 electrolyte media (with/without chloride) is assessed using Clark probe measurements. Co-evolution of chlorine was evident in 1 M KCl. This work demonstrates that microwire photoelectrodes for woven form or brush structures are entirely feasible, and that pre-passivated titanium metal can be readily coated with titania nanocrystals via hydrothermal synthesis.

Photo-generated high-energy surface states can help to produce chlorine in aqueous environments. Here, aligned rutile (TiO2) nanocrystal arrays are grown onto fluorine-doped tin oxide (FTO) substrates and activated either by hydrothermal Sr/Ba surface doping and/or by vacuum-annealing. With vacuum-annealing, highly photoactive films are obtained with photocurrents of typically 8 mA cm−2 at 1.0 V vs. SCE in 1 M KCl (LED illumination with λ = 385 nm and approx. 100 mW cm−2). Photoelectrochemical chlorine production is demonstrated at proof-of-concept scale in 4 M NaCl and suggested to be linked mainly to the production of Ti(III) surface species by vacuum-annealing, as detected by post-catalysis XPS, rather than to Sr/Ba doping at the rutile surface. The vacuum-annealing treatment is proposed to beneficially affect (i) bulk semiconductor TiO2 nanocrystal properties and electron harvesting, (ii) surface TiO2 reactivity towards chloride adsorption and oxidation, and (iii) FTO substrate performance.

Nicked-based metal–organic framework-derived carbon (Ni/MOFDC) and its acid-treated counterpart (AT-Ni/MOFDC) have been prepared as supports for palladium nanoparticle electrocatalysts (Pd/Ni/MOFDC...

In this work, 2D-layered Ti3C2/TiO2 hybrids derived from Ti3C2 MXenes were calcined at different temperature for 2 h with a ramping rate of 5 °C/min to adjust the electromagnetic wave absorption performance, and the static dielectric properties of the Ti3C2 and anatase TiO2 were studied by density functional theory calculations to illustrate the contribution to dielectric loss of TiO2 and Ti3C2 MXenes. The 2D-layered Ti3C2/TiO2 Hybrids exhibit a minimum reflection loss of −40.07 dB at 19.2 GHz with a relative thin thickness of 1.1 mm, and the effective bandwidth with reflection loss less than −10 dB reaches more than 3.6 GHz. The calculated results display higher e ' and e ' ' of Ti3C2 MXenes than that of anatase TiO2 in the measured range of frequency, which is in accordance with the experiments. The 2D-layered Ti3C2/TiO2 hybrids are expected to exhibit the enhanced electromagnetic wave absorption performance thanks to the appropriate complex permittivity, matching impendence and high dielectric loss.

The transformation of solar energy into chemical energy stored as hydrogen fuel underlies the water splitting process into O2 and H2 in photo-electrochemical (PEC) cells. This a potentially promising technology to generate renewable and clean energy. To make this technology commercially viable, the engineering of appropriate low-cost and robust photo-electrode materials and substrates is needed. In this study, we introduce BiVO4-photoelectrodes grown on conductive bulk SnO2–Sb2O5 ceramics acting as porous substrate. For these photoelectrodes, the value of photocurrent density of 1.1 mA/cm2 was achieved in 0.1 M NaOH electrolyte at 1.23 V vs. RHE (reversible hydrogen electrode) under LED light (λ = 455 nm). This PEC performance of these BiVO4 photoelectrodes is reached in spite of using a simple and low-cost deposition technique, where the BiVO4-precursor is delivered to the bulk porous ceramic substrate as a nebulized aerosol in air-flow at room temperature. The high porosity of the ceramic substrate permits some permeation of the aerogel into the pores to a depth of several micrometers to provide a 3D-growth of the BiVO4-coating on conductive SnO2 grains. The film thickness of the BiVO4 on individual grains is approximately 100 nm. This construction of the photoelectrode leads to an effective interface with good absorption of solar radiation and good electron harvesting. The bulk ceramics assure favorable conditions for electron collection and charge transport, which results in a good PEC performance with this type of photoanode.

Hydrogen permeation through a pure palladium film (25 μm thickness, optically dense) is employed to trigger electron transfer (hydrogen-driven) reactions at the external palladium | aqueous electrolyte interface of a two-compartment electrochemical cell. Two systems are investigated to demonstrate feasibility for (i) indirect hydrogen-mediated silver electrodeposition with externally applied potential and (ii) indirect hydrogen-mediated silver electrodeposition driven by external formic acid decomposition. In both cases, porous metal deposits form as observed by optical and electron microscopies. Processes are self-limited as metal deposition blocks the palladium surface and thereby slows down further hydrogen permeation. The proposed methods could be employed for a wider range of metals, and they could provide an alternative (non-electrochemical or indirect) procedure for metal removal or metal recovery processes or for indirect metal sensing.

Voltammetric analysis is often dependent on pH and on the addition of buffer reagents to optimise the analytical procedure. This approach is not always possible for in situ analytical measurements, for example when studying biological fluids or ingredients in food. Therefore, a method is proposed herein, which employs a working electrode to do both, that is, to locally modulate the pH value and to measure the analytical response. As a model system, thiamine (vitamin B1) is detected in aqueous KCl with a pH modulation brought about with negative potentials applied to the working electrode. Interferences from ascorbic acid and uric acid are considered. Exploratory data are presented and methods for improving the detection limit are suggested. Their potential for applications in electroanalysis (and in a broader range of processes) is discussed and the detection of thiamine in rice is demonstrated.

Membrane materials with semipermeability for anions or for cations are of interest in electrochemical and nanofluidic separation and purification technologies. In this study, partially hydrolyzed polyacrylonitrile (phPAN) is investigated as a pH-switchable anion/cation conductor. When switching from anionic to cationic semipermeability, also the ionic current rectification effect switches for phPAN materials deposited asymmetrically onto a 5, 10, 20, or 40 μm diameter microhole in a 6 μm thick polyethylene-terephthalate (PET) film substrate. Therefore, ionic rectifier behavior can be tuned and used to monitor and characterize semipermeability. Effects of electrolyte type and concentration and pH (relative to the zeta potential at approximately 3.1) are investigated by voltammetry, chronoamperometry, and impedance spectroscopy. A computational model provides good qualitative agreement with the observed electrolyte concentration data. High rectification effects are observed for both cations (pH > 3.1) and anions (pH < 3.1) but only at relatively low ionic strengths.