Hydrothermally grown α-MnO2 nanorods as highly efficient low cost counter-electrode material for dye-sensitized solar cells and electrochemical sensing applications

Electrochemical Sensing Strategies for Synthetic Orange Dyes

This review explores electrochemical sensing strategies for synthetic orange dyes, addressing the growing need for sensitive and selective detection methods in various industries. We examine the fundamental principles underlying the electrochemical detection of these compounds, focusing on their redox behavior and interaction with electrode surfaces. The review covers a range of sensor designs, from unmodified electrodes to advanced nanomaterial-based platforms. Chemically modified electrodes incorporating polymers and molecularly imprinted polymers are discussed for their enhanced selectivity. Particular attention is given to nanomaterial-based sensors, including those utilizing carbon nanotubes, graphene derivatives, and metal nanoparticles, which have demonstrated exceptional sensitivity and wide linear ranges. The potential of biological-based approaches, such as DNA interaction sensors and immunosensors, is also evaluated. Current challenges in the field are addressed, including matrix effects in complex samples and long-term stability issues. Emerging trends are highlighted, including the development of multi-modal sensing platforms and the integration of artificial intelligence for data analysis. The review concludes by discussing the commercial potential of these sensors in food safety, environmental monitoring, and smart packaging applications, emphasizing their importance in ensuring the safe use of synthetic orange dyes across industries.

Voltammetric determination of hydrogen peroxide at decorated palladium nanoparticles/poly 1,5-diaminonaphthalene modified carbon-paste electrode

In this work, palladium nanoparticles (PdNPs)/p1,5-DAN/ carbon paste electrode (CPE) and p1,5-DAN/CPE sensors have been developed for determination of hydrogen peroxide. Both sensors showed a highly sensitive and selective electrochemical behaviour, which were derived from a large specific area of poly 1,5 DAN and super excellent electroconductibility of PdNPs. PdNPs/p1,5-DAN/CPE exhibited excellent performance over p1,5-DAN/CPE. Thus, it was used for detecting hydrogen peroxide (H2O2) with linear ranges of 0.1 to 250 µM and 0.2 to 300 µM as well as detection limits (S/N = 3) of 1.0 and 5.0 nM for square wave voltammetry (SWV) and cyclic voltammetry (C.V) techniques, respectively. The modified CPE has good reproducibility, adequate catalytic activity, simple synthesis and stability of peak response during H2O2 oxidation on long run that exceeds many probes. Both reproducibility and stability for H2O2 detection are attributable to the PdNPs immobilized on the surface of p1,5-DAN/CPE. The modified CPE was used for determining H2O2 in real specimens with good stability, sensitivity, and reproducibility.

Fabrication of Carbon Nanofiber Incorporated with CuWO4 for Sensitive Electrochemical Detection of 4-Nitrotoluene in Water Samples

In the current work, copper tungsten oxide (CuWO₄) nanoparticles are incorporated with carbon nanofiber (CNF) to form CNF/CuWO₄ nanocomposite through a facile hydrothermal method. The prepared CNF/CuWO₄ composite was applied to the electrochemical detection of hazardous organic pollutants of 4-nitrotoluene (4-NT). The well-defined CNF/CuWO₄ nanocomposite is used as a modifier of glassy carbon electrode (GCE) to form CuWO₄/CNF/GCE electrode for the detection of 4-NT. The physicochemical properties of CNF, CuWO₄, and CNF/CuWO₄ nanocomposite were examined by various characterization techniques, such as X-ray diffraction studies, field emission scanning electron microscopy, EDX-energy dispersive X-ray microanalysis, and high-resolution transmission electron microscopy. The electrochemical detection of 4-NT was evaluated using cyclic voltammetry (CV) the differential pulse voltammetry detection technique (DPV). The aforementioned CNF, CuWO₄, and CNF/CuWO₄ materials have better crystallinity with porous nature. The prepared CNF/CuWO₄ nanocomposite has better electrocatalytic ability compared to other materials such as CNF, and CuWO₄. The CuWO₄/CNF/GCE electrode exhibited remarkable sensitivity of 7.258 μA μM^-1 cm^-2, a low limit of detection of 86.16 nM, and a long linear range of 0.2-100 μM. The CuWO₄/CNF/GCE electrode exhibited distinguished selectivity, acceptable stability of about 90%, and well reproducibility. Meanwhile, the GCE/CNF/CuWO₄ electrode has been applied to real sample analysis with better recovery results of 91.51 to 97.10%.

Selective Voltammetric Sensor for the Simultaneous Quantification of Tartrazine and Brilliant Blue FCF

Tartrazine and brilliant blue FCF are synthetic dyes used in the food, cosmetic and pharmaceutical industries. The individual and/or simultaneous control of their concentrations is required due to dose-dependent negative health effects. Therefore, the paper presents experimental results related to the development of a sensing platform for the electrochemical detection of tartrazine and brilliant blue FCF based on a glassy carbon electrode (GCE) modified with MnO₂ nanorods, using anodic differential pulse voltammetry. Homogeneous and stable suspensions of MnO₂ nanorods have been obtained involving cetylpyridinium bromide solution as a cationic surfactant. The MnO₂ nanorods-modified electrode showed a 7.9-fold increase in the electroactive surface area and a 72-fold decrease in the electron transfer resistance. The developed sensor allowed the simultaneous quantification of dyes for two linear domains: in the ranges of 0.10-2.5 and 2.5-15 μM for tartrazine and 0.25-2.5 and 2.5-15 μM for brilliant blue FCF with detection limits of 43 and 41 nM, respectively. High selectivity of the sensor response in the presence of typical interference agents (inorganic ions, saccharides, ascorbic and sorbic acids), other food dyes (riboflavin, indigo carmine, and sunset yellow), and vanillin has been achieved. The sensor has been tested by analyzing soft and isotonic sports drinks and the determined concentrations were close to those obtained involving the chromatography technique.

Hydrothermal Synthesis of MnO2/Reduced Graphene Oxide Composite for 4-Nitrophenol Sensing Applications

Recently, the electrochemical sensing approach has attracted materials/electrochemical scientists to design and develop electrode materials for the construction of electrochemical sensors for the detection of para-nitrophenol (4-NP). In the present study, we have prepared a hybrid composite of MnO2 and rGO (MnO2/rGO) using a hydrothermal approach. The morphological features of the prepared MnO2/rGO composite were studied by scanning electron microscopy, whereas the phase purity and formation of the MnO2/rGO composite were authenticated via the powder X-ray diffraction method. Energy-dispersive X-ray spectroscopy was also employed to analyze the elemental composition of the prepared MnO2/rGO composite. In further studies, a glassy carbon electrode (GCE) was modified with MnO2/rGO composite (MnO2/rGO/GCE) and explored as 4-nitrophenol (4-NP) sensor. The fabricated MnO2/rGO/GCE exhibited a reasonably good limit of detection of 0.09 µM with a sensitivity of 0.657 µA/µMcm2. The MnO2/rGO/GCE also demonstrates good selectivity, stability and repeatability in 50 cycles.

Design and Fabrication of α-MnO2-Nanorods-Modified Glassy-Carbon-Electrode-Based Serotonin Sensor

Serotonin is a very important monoamine neurotransmitter, which takes part in biological and psychological processes. In the present scenario, design and fabrication of a serotonin electrochemical sensor is of great significance. In this study, we have synthesized α-MnO₂ via a hydrothermal synthesis method using potassium permanganate as a precursor. The physiochemical properties, such as structural and phase-purity of the prepared α-MnO₂, were investigated by various characterization techniques and methods (powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy). Furthermore, the serotonin sensor was fabricated using α-MnO₂ as an electrode modifier or electro-catalyst. The bare glassy carbon electrode (GCE) was adopted as a working substrate, and its active carbon surface was modified with the synthesized α-MnO₂. This modified GCE (α-MnO₂/GCE = MGCE) was explored as a serotonin sensor. The electrochemical investigations showed that the MGCE has excellent electro-catalytic properties towards determination of serotonin. The MGCE exhibits an excellent detection limit (DL) of 0.14 µM, along with good sensitivity of 2.41 µAµM^-1 cm^-2. The MGCE also demonstrated excellent selectivity for determination of serotonin in the presence of various electro-active/interfering molecules. The MGCE also exhibits good cyclic repeatability, stability, and storage stability.

Fabrication of Nitrogen-Doped Reduced Graphene Oxide Modified Screen Printed Carbon Electrode (N-rGO/SPCE) as Hydrogen Peroxide Sensor

In recent years, the electrochemical sensing approach has attracted electrochemists because of its excellent detection process, simplicity, high sensitivity, cost-effectiveness, and high selectivity. In this study, we prepared nitrogen doped reduced graphene oxide (N-rGO) and characterized it using various advanced techniques such as XRD, SEM, EDX, Raman, and XPS. Furthermore, we modified the active surface of a screen printed carbon electrode (SPCE) via the drop-casting of N-rGO. This modified electrode (N-rGO/SPCE) exhibited an excellent detection limit (LOD) of 0.83 µM with a decent sensitivity of 4.34 µAµM-1cm-2 for the detection of hydrogen peroxide (H2O2). In addition, N-rGO/SPCE also showed excellent selectivity, repeatability, and stability for the sensing of H2O2. Real sample investigations were also carried out that showed decent recovery.

Novel gamma-irradiated chitosan-doped reduced graphene-CuInS2 composites as counter electrodes for dye-sensitized solar cells

To address the issues associated with traditional counter electrodes, a novel gamma-irradiated chitosan-doped reduced graphene-CuInS₂ composite (Chi@RGO-CIS) was used as the counter electrode (CE). The system was fabricated following a simple hydrothermal method. The prepared Chi@RGO-CIS was characterized by various spectroscopic and microscopic techniques. The synergistic effect between chitosan, CuInS₂, and reduced graphene oxide can help in producing a large surface area. It can also help in the generation of catalytic sites toward I-/I₃-redox electrolytes. We used a composite (based on electrical considerations) to study the effect of the amount of graphene on the characteristics and photovoltaic efficiency of the Chi@RGO-CIS composites. The solar cell assembled with 1.5% Chi@RGO-CIS exhibited an efficiency of 12.21%. The efficiency was higher than that of a Pt-based device (9.96%) fabricated under the same conditions. Hence, Chi@RGO-CIS can be potentially used as the CE of dye-sensitized solar cells (DSSCs). It can be used as a substitute for Pt in DSSCs.

To address the issues associated with traditional counter electrodes, a novel gamma-irradiated chitosan-doped reduced graphene-CuInS₂ composite (Chi@RGO-CIS) was used as the counter electrode (CE).

Experimental and Computational Study of Zr and CNC-Doped MnO2 Nanorods for Photocatalytic and Antibacterial Activity

Cellulose nanocrystals (CNC), MnO₂, CNC-doped MnO₂, and Zr/CNC-doped MnO₂ were prepared with a hydrothermal method to assess their photocatalytic and antibacterial properties. Various characterizations were undertaken to determine the phase composition, the existence of functional units, optical characteristics, elemental analysis, surface topography, and microstructure of the prepared materials. Sample crystallinity was improved, whereas a decrease in crystallite size was observed with increasing amounts of dopants. Incorporation of dopants (CNC and Zr) into MnO₂ instigated a transformation in morphology from nanoclusters to nanorods with different diameters. Furthermore, photocatalytic activity experiments indicated a more effective degradation of methylene blue (MB) dye with CNC-doped MnO₂ and Zr/CNC-codoped MnO₂ while enhancing the bacterial efficacy for both G +ve and G -ve. Density functional theory was utilized to model the structures and elucidate their bonding and charge transfer mechanisms. The Zr/CNC-MnO₂ system showed charge depletion around Mn atoms, while charges were observed to accumulate around oxygen atoms.

Spherical silver oxide nanoparticles for fabrication of electrochemical sensor for efficient 4-Nitrotoluene detection and assessment of their antimicrobial activity

This research article reports an economic and affordable microwave-assisted synthesis of spherical silver oxide nanoparticles (Ag₂O NPs) (80-90 nm) for an efficient electrochemical sensing of a hazardous organic pollutant 4-nitrotoluene (4-NT). Such well-characterized Ag₂O NPs were utilized to modify gold (Au) electrode in order to fabricate Ag₂O-NPs/Au sensor to detect 4-NT using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) techniques. Ag₂O-NPs/Au sensor exhibited a distinguished electrical response as a function of varying 4-NT concentration in neutral medium samples. Ag₂O-NPs/Au sensor demonstrated an ultrahigh sensitivity as 15.33 μA (μM)^-1 cm^-2, a low detection limit of 62.3 nM, and linear response in detection ranges of 0.6-5.9 μM and 37-175 μM. The sensing performance of fabricated Ag₂O-NPs/Au sensor is reproducible, reusable, selective in presence of other chemical species, and validated using real samples. The Ag₂O/Au sensor had much rapid and easy fabrication process and offered much lower LOD for 4-NT detection than many previously reported sensors. Along with efficient electrochemical activity, the spherical Ag₂O NPs also exhibit remarkable antimicrobial activity against harmful gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus) bacteria. Herein projected efficient Ag₂O-NPs/Au electrochemical sensor for 4-NT is affordable with the capability of scaling up to perform point-of-care 4-NT testing needed for successful environmental monitoring and water quality assurance.

Interfacial Electronic Effects in Co@N-Doped Carbon Shells Heterojunction Catalyst for Semi-Hydrogenation of Phenylacetylene

Metal-supported catalyst with high activity and relatively simple preparation method is given priority to industrial production. In this work, this study reported an easily accessible synthesis strategy to prepare Mott-Schottky-type N-doped carbon encapsulated metallic Co (Co@N_p+gC) catalyst by high-temperature pyrolysis method in which carbon nitride (g-C₃N₄) and dopamine were used as support and nitrogen source. The prepared Co@N_p+gC presented a Mott-Schottky effect; that is, a strong electronic interaction of metallic Co and N-doped carbon shell was constructed to lead to the generation of Mott-Schottky contact. The metallic Co, due to high work function as compared to that of N-doped carbon, transferred electrons to the N-doped outer shell, forming a new contact interface. In this interface area, the positive and negative charges were redistributed, and the catalytic hydrogenation mainly occurred in the area of active charges. The Co@N_p+gC catalyst showed excellent catalytic activity in the hydrogenation of phenylacetylene to styrene, and the selectivity of styrene reached 82.4%, much higher than those of reference catalysts. The reason for the promoted semi-hydrogenation of phenylacetylene was attributed to the electron transfer of metallic Co, as it was caused by N doping on carbon.

Design and fabrication of cost-effective and sensitive non-enzymatic hydrogen peroxide sensor using Co-doped δ-MnO2 flowers as electrode modifier

The development of a cost-effective and highly sensitive hydrogen peroxide sensor is of great importance. Electrochemical sensing is considered the most sensitive technique for hydrogen peroxide detection. Herein, we reported a cost-effective and highly sensitive hydrogen peroxide sensor using Co-doped δ-MnO₂ (Co@δ-MnO₂) flower-modified screen-printed carbon electrode. The δ-MnO₂ and Co@δ-MnO₂ flowers were synthesized by employing a hydrothermal approach. Advanced techniques such as PXRD, SEM, FTIR, Raman, UV, EDX, BET, and TEM were utilized to confirm the formation of δ-MnO₂ and Co-doped δ-MnO₂ flowers. The fabricated sensor exhibited an excellent detection limit (0.12 μM) and sensitivity of 5.3 μAμM^-1 cm^-2.Graphical abstract.

Ultrasonic synthesis of α-MnO2 nanorods: An efficient catalytic conversion of refractory pollutant, methylene blue

In this work, uniform α-MnO₂ nanorods were synthesized via a simple hydrothermal followed by ultrasonication method using ultrasonic bath (20 kHz, 100 W) without using any surfactant and template. The crystallographic phases and surface morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transition electron microscopy (TEM) analysis, respectively. Functional group identification and chemical states of α-MnO₂ nanorods were confirmed by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The as-synthesized uniform nanorods of α-MnO₂ exhibit excellent catalytic conversion of toxic organic contaminant (methylene blue (MB)) in the presence of NaBH₄ as reductant. The α-MnO₂ exhibits excellent stability up to four repeated catalytic cycles with nearly 92% conversion. The kinetic rate constant (k), and turnover frequency (TOF) were 0.736 min^-1 and 0.02 mmol mg^-1 min^-1, respectively. In addition, the fast electron transfer mechanism were investigated and discussed. These results open a new avenue for developing various metal oxide catalysts, which are expected to be very useful catalytic conversions.

Hybrid of Graphene based on quaternary Cu2ZnNiSe4 -WO3 Nanorods for Counter Electrode in Dye-sensitized Solar Cell Application

A novel nanohybrid of graphene-based Cu₂ZnNiSe₄ with WO₃ nanorods (G-CZNS@W) was successfully synthesized via a simple hydrothermal method to use as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The characterization technique confirmed the structural and morphologies of the G-CZNS@W nanohybrid, which could show rapid electrons transfer pathway through the WO₃ nanorods. Moreover, the as-fabricated G-CZNS@W nanohybrid exhibited synergetic effect between G-CZNS and a WO₃ nanorod, which could affect the electrocatalytic activity towards triiodide reaction. The nanohybrid exhibits an excellent photovoltaic performance of 12.16%, which is higher than that of the standard Pt electrode under the same conditions. The G-CZNS@W nanohybrid material as CE thus offers a promising low-cost Pt-free counter electrode for DSSC.

Metal Oxide Oxidation Catalysts as Scaffolds for Perovskite Solar Cells

Whilst the highest power conversion efficiency (PCE) perovskite solar cell (PSC) devices that have reported to date have been fabricated by high temperature sintering (>500 °C) of mesoporous metal oxide scaffolds, lower temperature processing is desirable for increasing the range of substrates available and also decrease the energy requirements during device manufacture. In this work, titanium dioxide (TiO₂) mesoporous scaffolds have been compared with metal oxide oxidation catalysts: cerium dioxide (CeO₂) and manganese dioxide (MnO₂). For MnO₂, to the best of our knowledge, this is the first time a low energy band gap metal oxide has been used as a scaffold in the PSC devices. Thermal gravimetric analysis (TGA) shows that organic binder removal is completed at temperatures of 350 °C and 275 °C for CeO₂ and MnO₂, respectively. By comparison, the binder removal from TiO₂ pastes requires temperatures >500 °C. CH₃NH₃PbBr₃ PSC devices that were fabricated while using MnO₂ pastes sintered at 550 °C show slightly improved PCE (η = 3.9%) versus mesoporous TiO₂ devices (η = 3.8%) as a result of increased open circuit voltage (V_oc). However, the resultant PSC devices showed no efficiency despite apparently complete binder removal during lower temperature (325 °C) sintering using CeO₂ or MnO₂ pastes.

A highly sensitive and selective hydroquinone sensor based on a newly designed N-rGO/SrZrO3 composite

Herein, we have reported a novel composite of nitrogen doped reduced graphene oxide (N-rGO) and strontium zirconate (SrZrO3). This new composite (N-rGO/SrZrO3) was synthesized using the reflux method. The physicochemical properties of N-rGO/SrZrO3 were determined using different advanced techniques such XRD, FE-SEM, EDX, FTIR and BET. Furthermore, a glassy carbon electrode was modified with N-rGO/SrZrO3 (GCE-2). This modified electrode was employed for the sensing of HQ. The electrochemically active surface area (ECSA) of this modified electrode (GCE-2) was calculated by employing the Randles-Sevcik equation. Furthermore, GCE-2 exhibited a good detection limit (0.61 μM) including high selectivity towards HQ.

Recent trends of MnO2-derived adsorbents for water treatment: a review

Over the years, manganese dioxide (MnO₂) and its different allotropes have gained significant research attention in the field of wastewater treatment because of their exciting physicochemical properties.

Fabrication of a hydrazine chemical sensor based on facile synthesis of doped NZO nanostructure materials

In this approach, nickel-doped zinc oxide (NZO) nanostructure materials were synthesized by the solution method in the basic phase.

Enhanced Electrocatalytic Behaviour of Poy(aniline-co-2-hydroxyaniline) Coated Electrodes for Hydrogen Peroxide Electrooxidation

Polymer-coated electrodes are widely used for the detection and oxidation of hydrogen peroxide (H2O2). Conducting polyaniline (PANI), poly (2-hydroxyanilne) (PHA), and their copolymer poly(aniline-co-2-hydroxyaniline) (PACHA) were electrochemically synthesized on a gold substrate for H2O2 detection and analysis. Cyclic voltammetry (CV), square wave voltammetry (SWV), and differential pulse voltammetry (DPV) techniques were used for electroanalysis. Both PACHA and PANI greatly reduced the gold overpotential for H2O2 oxidation with enhanced current densities. The PACHA- and PANI-coated electrodes showed oxidative peaks at 0.30 and 0.50 V, respectively, in the presence of 1.4 × 10−6 M H2O2, while PHA-coated electrodes exhibited no response. The fabricated electrodes displayed a linear response towards H2O2 in range of 2 × 10−7 to 1.4 × 10−6 M, with very low detection limits (LODs) of 1 × 10−7 M (for PACHA) and 1.15 × 10−7 M (for PANI) evaluated from CV data. In case of SWV and DPV, the LODs were found to be 1.78 × 10−7 M (for PACHA) and 1 × 10−7 M (for PANI), respectively. The materials exhibit high sensitivity of 650 A/Mcm2 and show good stability. The PACHA-coated electrode shows better capacitance (1.84 × 10−3 F) than PHA- (2.52 × 10−4 F) and PANI-coated (1.17 × 10−3 F) electrodes.

Pt-free, low-cost and efficient counter electrode with carbon wrapped VO2(M) nanofiber for dye-sensitized solar cells

The present study reports the use of one-dimensional carbon wrapped VO₂(M) nanofiber (VO₂(M)/C) as a cost-effective counter electrode for dye-sensitized solar cells (DSSCs); where M denotes monoclinic crystal system. Uniform short length nanofiber was synthesised by a sol-gel based simple and versatile electrospinning and post carbonization technique. The investigation of nanostructure and morphological analysis were performed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) with EDAX. The electrochemical response was comprehensively characterized by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization. The electrochemical analysis of the VO₂(M)/C nanofiber counter electrode exhibits significant electrocatalytic activity towards the reduction of triiodide and low charge transfer resistance at the electrode-electrolyte interface. The DSSCs fabricated with carbon-wrapped VO₂(M) nanofiber CE showed high power conversion efficiency of 6.53% under standard test condition of simulated 1SUN illumination at AM1.5 G, which was comparable to the 7.39% observed for conventional thermally decomposed Pt CE based DSSC under same test conditions. This result encourages the next step of modification and use of low-cost VO₂(M) as an alternate counter electrode for DSSCs to achieve a substantial efficiency for future energy demand.

High surface area 3D-MgO flowers as the modifier for the working electrode for efficient detection of 4-chlorophenol

We report for the first time, magnesium oxide (MgO) 3D-flowers, synthesized by a simple reflux method. The synthesized MgO 3D-flowers were characterized by powder X-ray diffraction (PXRD), ultra-violet visible (UV-vis) spectroscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) mapping to confirm their purity, morphology and elemental composition. The synthesized MgO 3D-flowers had a very high specific surface area of 218 m2 g-1 as confirmed by the N2 adsorption-desorption isotherm. These MgO 3D-flowers were employed as an electrode modifier for the construction of an electrochemical sensor to detect 4-chlorophenol (4-CP). The active surface area of the glassy carbon electrode (GCE) was modified with MgO 3D-flowers with the assistance of 0.1% Nafion (MgO 3D-flowers/GCE) and the MgO 3D-flowers/GCE sensor shows an excellent electrocatalytic behavior towards 4-CP. The constructed MgO 3D-flowers/GCE sensor exhibits the limits of detection (LOD) of 45 nM, 68 nM, and 52 nM, and sensitivities of 2.84 μA μM-1 cm-2, 5.94 μA μM-1 cm-2, and 10.67 μA μM-1 cm-2 in cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) techniques, respectively. The modified MgO 3D-flowers/GCE sensor displays excellent performance in terms of sensitivity, selectivity, repeatability and reproducibility. The excellent electrocatalytic activity of the proposed MgO 3D-flowers/GCE sensor was attributed to the high specific surface area, surface electron transfer ability and the presence of the edges/corner defects of MgO 3D-flowers.

Bifunctional Photo-Supercapacitor with a New Architecture Converts and Stores Solar Energy as Charge

Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO₂ is used as the solar cell. Poly(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO₂) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO₂ coatings, which serve as the CEs for the TiO₂/hb/CdS photoanode and yet another PEDOP@MnO₂ electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm^-2) illumination, the TiO₂/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO₂ electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g^-1, an energy density of 13.2 Wh kg^-1, and a power density of 360 W kg^-1 at a discharge current density of 1 A g^-1. During the self-discharge process, PEDOP@MnO₂-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO₂/hb/CdS photoanode with the PEDOP@MnO₂ CE in an aqueous polysulfide-silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.

Visible light driven water splitting through an innovative Cu-treated-δ-MnO2 nanostructure: probing enhanced activity and mechanistic insights

In this study, we have fabricated nanostructured thin films of δ-MnO2 on FTO glass substrates by a facile, room-temperature and low cost chemical bath deposition method. A copper treatment procedure in the synthesis steps results in a film of Cu-δ-MnO2, which displays significant photoactivity when used as a photocathode for hydrogen evolution reaction, with a photocurrent of 3.59 mA cm-2 (at 0 V vs. RHE) in a mild acidic solution. Furthermore, the electrodes also display significant electrocatalytic activity towards water oxidation reaching up to 10 mA cm-2 (at only 1.67 V vs. RHE). The Cu-δ-MnO2 film has been thoroughly characterized via various physicochemical, optical and electrochemical techniques, and an attempt has been made to explain the conductivity mechanism. It is suggested that Cu treatment enhances the photoactivity of δ-MnO2 films through a series of surface dominated processes, which facilitate reduced recombination and enhanced hole consumption at the interface of the electrode and electrolyte. These results establish birnessite-based manganese dioxides as suitable candidates for electrodes in water splitting cells and pave the way for atomic-level engineering of earth abundant materials to reach the ultimate goal of low-cost, sustainable generation of hydrogen.

Enhanced electrocatalytic performance of nickel diselenide grown on graphene toward the reduction of triiodide redox couples

The promising activity of nickel diselenide (NiSe₂) towards electrocatalysis has made it especially attractive in energy conversion fields. However, NiSe₂ with high electrocatalytic performance always requires complicated fabrication or expensive conductive polymers, resulting in the scale-up still being challenging. Herein, we introduce a simple and cost-effective synthesis of NiSe₂ dispersed on the surface of graphene (NiSe₂/RGO NPs). NiSe₂/RGO NPs exhibited enhanced electrocatalytic performance and long-term stability for the reduction reaction of triiodide redox couples in dye-sensitized solar cells (DSSCs). Leveraging the advantageous features, the DSSC fabricated with NiSe₂/RGO NPs as CE had a smaller charge-transfer resistance (R_ct) value and higher short-circuit current density and fill factor than naked NiSe₂ NPs. Additionally, NiSe₂/RGO NPs achieved a PCE of 7.76%, higher than that of pure NiSe₂ (6.51%) and even exceeding that of Pt (7.56%). These prominent features demonstrated that the NiSe₂/RGO NPs in this work are a promising cheap and efficient electrocatalyst to replace state-of-the-art Pt.

The promising activity of nickel diselenide (NiSe₂) towards electrocatalysis has made it especially attractive in energy conversion fields.