A photoelectrochemical sensor based on nickel hydroxyl-oxide modified n-silicon electrode for hydrogen peroxide detection in an alkaline solution

Characterizing and understanding the photovoltage in n-Si/Au light-addressable electrochemical sensors

Here, we characterize the photovoltage of n-Si/Au light-addressable electrodes (LAEs) over a range of solution potentials from ca. -1 to +1 V. We find that the n-Si/Au photoelectrodes show photovoltages consistent with a semiconductor/liquid junction in contrast to a buried junction, which opposes our previous understanding of how photovoltage originates in these sensors.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing

As an important compound in many industrial and biological processes, hydrogen peroxide (H₂O₂) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H₂O₂ detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe₂O₃) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe₂O₃ displays the relatively wide linear range from 1 to 2000 μM with a high sensitivity of 132.0 μA mM^-1 cm^-2 and a low detection limit of 0.04 μM (S/N ≥ 3) for PEC detection of H₂O₂, which is superior to other similar α-Fe₂O₃-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe₂O₃ toward H₂O₂. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe₂O₃, but also could act as trapping centers for holes and followed by as active sites for H₂O₂ oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

A Disposable Screen Printed Electrodes with Hexagonal Ni(OH)2 Nanoplates Embedded Chitosan Layer for the Detection of Depression Biomarker

Serotonin (5-hydroxytryptamine (5-HT)) is one of the important neurotransmitters which is released from the endocrine system. An abnormal level of this biomarker leads to several neurological diseases. The accurate assessment of serotonin is the utmost option to start treatment in the early stages of the disease. The current work is focused on the development of a disposable, screen-printed electrochemical sensor for the depression biomarker, serotonin in the physiological pH medium (pH 7.4) with the aid of a hexagonal, Ni(OH)₂-nanoplate (NH-HNP)-embedded chitosan (Chit) and modified, screen-printed carbon electrode (SPCE). Initially, hexagonal nanoplates of Ni(OH)₂ were synthesized by an eco-friendly and simple hydrothermal method. The prepared materials were well characterized by advanced analytical techniques to examine the physicochemical properties of the synthesized Ni(OH)₂ hexagonal nanoplates. From the cyclic voltametric (CV) analysis, it was found that the oxidative current response of 5-HT at a NH-HNP-modified SPCE has about fivefold higher current values than over bare SPCE. The scan rate studies of NH-HNP-Chit/SPCE electrodes revealed that the oxidation mechanism of 5-HT is controlled by the diffusion behavior of the analyte. Differential pulse voltammetric tests of the NH-HNP-Chit/SPCE electrode exhibited a linear response in the dynamic concentration range of 0.1 to 30 µM, with a detection limit of about 60 nM. The sensor response is very reproducible from electrode to electrode, and the deactivation or surface-fouling of the sensor was not observed within the several experimental measurements. The sensor exhibited excellent storage stability over a period of twenty days. Finally, the fabricated, disposable SPCE sensor has shown respectable activity for the detection of depression biomarker 5-HT from synthetic urine and saliva samples.

Excellent performance supercapacitors with the compounding of Ni(OH)2 and ZIF-67 derived Co-C-N nanosheets as flexible electrode materials

Owing to the advantages of high theoretical capacity, low cost, and excellent chemical stability, Ni(OH)₂ is considered as a potential candidate for electrode materials of supercapacitors. However, its further applications are limited by its adverse surface chemical properties. In this paper, a composite material consisting of ZIF-67 derived Co-C-N nanosheets and Ni(OH)₂ was synthesized facilely on carbon cloth in situ, and based on the collective advantages of the various components, excellent electrochemical performance could be achieved when used as a flexible electrode material of supercapacitors. In detail, the as-obtained sample Ni(OH)₂/Co-C-N/CC exhibits an ultrahigh specific capacitance of 2100 F g^-1 at a current density of 1 A g^-1. Moreover, the further assembled asymmetric supercapacitor device exhibits a maximum energy density of 78.6 W h kg^-1 at a power density of 749.4 W kg^-1. Furthermore, the device also shows outstanding cycling stability with 90.2% capacitance retention after 5000 cycles of charge-discharge. Basically, the remarkable performance can be attributed to the well-developed structure, abundant active sites, complex beneficial components, and their intrinsic properties. Significantly, rational design can broaden the research directions of corresponding electrode materials.

Introducing visible-light sensitivity into photocatalytic CeO2 nanoparticles by hybrid particle preparation exploiting plasmonic properties of gold: enhanced photoelectrocatalysis exemplified for hydrogen peroxide sensing

In this report we combine the catalytic properties of CeO₂ nanoparticles with their transduction ability for photoelectrochemical sensing. This study highlights the usage of CeO₂ providing catalytic activity towards H₂O₂, but only with a limited excitation range in the UV for the construction of a sensing system. In order to improve the photoelectrocatalysis of CeO₂ nanoparticles by extending their excitation to visible light, Au/CeO₂ core/shell hybrid nanoparticles have been synthesized. The hybrid nanoparticles are fixed on electrodes, allowing for the generation of photocurrents, the direction of which can be controlled by the electrode potential (without bias). The application of the hybrid nanoparticles results in an enhanced photocurrent amplitude under white light illumination as compared to the pure CeO₂ nanoparticles. Wavelength-dependent measurements confirm the participation of the Au core in the signal transduction. This can be explained by improved charge carrier generation within the hybrid particles. Thus, by using a plasmonic element the photoelectochemical response of a catalytic nanoparticle (i.e. CeO₂) has been spectrally extended. The effect can be exploited for sensorial hydrogen peroxide detection. Here higher photocatalytic current responses have been found for the hybrid particles fixed to gold electrodes although the catalytic reduction has been comparable for both types of nanoparticles. Thus, it can be demonstrated that Au/CeO₂ core-shell nanoparticles allow the utilization of visible light for photoelectrochemical hydrogen peroxide (H₂O₂) detection with improved sensitivity under white light illumination or application of such particles with only visible light excitation, which is not possible for pure CeO₂. With help of the layer-by-layer (LbL) technique for nanoparticle immobilization, the electrode response can be adjusted and with a 5 layers electrode a low detection limit of about 3 μM H₂O₂ with a linear detection range up to 2000 μM is obtained.

Synthesis of Cu(OH)F microspheres using atmospheric dielectric barrier discharge microplasma: a high-performance non-enzymatic electrochemical sensor

Cu(OH)F microspheres were in situ synthetized using microplasma and were employed as an electrochemical sensor for glucose, hydrogen peroxide and formaldehyde.

Controlling the Size and Pattern Pitch of Ni(OH)2 Nanoclusters Using Dip-Pen Nanolithography to Improve Water Oxidation

We use dip-pen nanolithography to accurately pattern Ni(OH)₂ nanoclusters on a metachemical surface with an exceptionally large surface area. The distance between the nanoclusters can be manipulated to control the oxygen-evolution reaction current and overpotential, thereby improving the efficiency of the water-splitting process while using minute amounts of the catalyst.

Carbon-dot wrapped ZnO nanoparticle-based photoelectrochemical sensor for selective monitoring of H2O2 released from cancer cells

This study reports on a simple approach for the fabrication of an electrode modified with biocompatible C-dot wrapped ZnO nanoparticles for selective photoelectrochemical monitoring of H₂O₂ released from living cells. The biocompatibility of the ZnO nanoparticles was confirmed through in-vitro cellular testing using the MTT assay on Huh7 cell lines. The ZnO nanoparticles wrapped with dopamine-derived C-dots possess numerous catalytically active sites, excessive surface defects, good electrical conductivity, and efficient separation ability of photo-induced electrons and holes. These properties offer highly sensitive and selective non-enzymatic photo-electrochemical monitoring of H₂O₂ released from HeLa cells after stimulation with N-formylmethionyl-leucyl-phenylalanine. The sensor has a wide linear range (20-800 nM), low detection limit (2.4 nM), and reliable reproducibility, this implying its suitability for biological and biomedical applications. Graphical abstract Schematic of the fabrication of ZnO nanoparticles by using a plant extract as a reducing agent. Wrapping of ZnO with C-dots enhances the photoelectrocatalytic efficacy. Sensitive and selective photoelectrochemical monitoring of H₂O₂ released from cancer cells is demonstrated.

Enhancing Oxygen Evolution Electrocatalysis via the Intimate Hydroxide-Oxide Interface

The development of electrocatalysts with high activity and stability for oxygen evolution reaction (OER) is critically important, the one being regarded as the bottleneck process of overall water splitting. Herein, we fulfill significant OER improvement in both activity and stability by constructing a class of Ni(OH)₂-CeO₂ supported on carbon paper (Ni _xCe _y@CP) with an intimate hydroxide (Ni(OH)₂)-oxide (CeO₂) interface. Such interface largely promotes the OER activity with a low overpotential of 220 mV at 10 mA cm^-2 and a small Tafel slope of 81.9 mV dec^-1 in 1 M KOH. X-ray photoelectron spectroscopy analysis shows that the intimate interface induced by the strong electronic interactions between Ni(OH)₂ and CeO₂ involves the modulation of binding strength between intermediates and catalysts, making a great contribution to the OER enhancement. Importantly, such intimate interface structures can be largely maintained even after a long-time stability test. We have further demonstrated that, when pairing the Ni₄Ce₁@CP after phosphorization (P-Ni₄Ce₁@CP), the Ni₄Ce₁@CP and P-Ni₄Ce₁@CP assembly is highly active and stable for overall water splitting with a low voltage of 1.68 V at 25 mA cm^-2 and negligible stability delay over 30 h of continuous operation, which are much better than the commercial Ir/C and Pt/C.

Interface engineering of a CeO2-Cu3P nanoarray for efficient alkaline hydrogen evolution

It is of great importance to design and develop highly active electrocatalysts for the hydrogen evolution reaction (HER) under alkaline conditions. In this work, we report the development of a CeO₂-Cu₃P nanoarray supported on nickel foam (CeO₂-Cu₃P/NF) as an excellent HER catalyst with the demand of an overpotential of only 148 mV to deliver a geometrical catalytic current density of 20 mA cm^-2 in 1.0 M KOH. Remarkably, this catalyst also shows strong long-term electrochemical durability for at least 100 h with nearly 100% Faradaic efficiency. Density functional theory calculations reveal that the CeO₂-Cu₃P/NF hybrid has a lower water dissociation energy and a more thermo-neutral hydrogen adsorption free energy.

Cobalt Phosphide Double-Shelled Nanocages: Broadband Light-Harvesting Nanostructures for Efficient Photothermal Therapy and Self-Powered Photoelectrochemical Biosensing

Ultra-broadband light-absorbing materials are highly desired for effective solar-energy harvesting. Herein, novel cobalt phosphide double-shelled nanocages (CoP-NCs) are synthesized. Uniquely, these CoP-NCs are able to nonselectively absorb light spanning the full solar spectrum, benefiting from its electronic properties and hollow nanostructure. They promise a wide range of applications involving solar energy utilization. As proof-of-concept demonstrations, CoP-NCs are employed here as effective photothermal agents to ablate cancer cells by utilizing their ability of near-infrared heat conversion, and as photoactive material for self-powered photoelectrochemical sensing by taking advantage of their ability of photon-to-electricity conversion.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu²⁺) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd²⁺ and S^2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu²⁺ ions. The photoelectrode response for Cu²⁺ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu²⁺ ion detection.

Electrodeposition of nickel nanoflowers on screen-printed electrodes and their application to non-enzymatic determination of sugars

Nickel nanoflowers were electrodeposited on screen-printed carbon electrodes for the non-enzymatic catalytic detection of sugars.

Photoelectrochemical bioanalysis: the state of the art

This review provides a panoramic snapshot of the state of the art in the dynamically developing field of photoelectrochemical bioanalysis.