Lower Charge Transfer Resistance Research Articles

Interface engineering of laminated redox-copolymers for electrochemical remediation of perfluoroalkyl substances

Redox polymers now show promise for selective removal of perfluoroalkyl substances from a complex aqueous matrix at high energy efficiency and no secondary pollution. However, self-agglomeration of redox polymers is a dominating barrier to constructing a low-cost, stable system in practical applications. Herein, we introduce polymer interface engineering strategy to enhance the activity of amine functionalities and nitrous oxide radicals in copolymers composed of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine. The grafted laminated redox polymer on multi-walled carbon nanotubes (termed MWCNT-g-P(TMPMA-co-TMA)) via free-radical polymerization demonstrated a 19.1–59.9 % increase in the electrosorption capacity with a maximum value (Qm) of 725.09 mg g−1 and a pseudo-first-order rate constant k1 = 1.46 min−1 and sustainable regeneration efficiency at ∼80 %. The core–shell structure of MWCNT-g-P(TMPMA-co-TMA) with a laminated redox polymer layer of ∼5 nm processed a low charge transfer resistance, which is expected to contribute to the enhanced capture performance and stability. An integrated system consisting of a MWCNT-g-P(TMPMA-co-TMA) electrode and a boron-doped diamond electrode can efficiently separate and degrade trace-concentration PFOA from industrial wastewater at high mineralization efficiency. This work provides insight into the design and optimization of redox active materials for water purification and beyond.

Selective electro-capacitive deionization of Yb(III) by nanospherical N-doped carbon supported nickel‑iron bimetallic oxide, nitride and phosphide

The separation of rare earth elements from the mining waste water is highly important but still facing challenge. In this study, three different porous composite electrode materials were well-designed by decorating the nickel‑iron bimetallic oxide, nitride or phosphide onto nitrogen-doped carbon nanosphere, respectively (termed as NiFeO@NC, NiFeN@NC and NiFeP@NC), and utilized in capacitive deionization device for electrosorption of Yb(III) from water under the low-voltage electric field. The characterization and electrochemical results indicated that the incorporation of N or P atom lead to the reduced specific surface area and the enhanced electrochemical properties (i.e., larger specific capacitance, lower charge transfer resistance). In addition, NiFeN@NC and NiFeP@NC exhibited the excellent electrosorption capacities of Yb(III) with 105.24 mg·g−1 and 90.31 mg·g−1, respectively, under conditions of a flow rate of 20 mL·min−1, a voltage of 1.2 V, and pH of 5.0, which was extremely higher than NiFeO@NC (i.e., 50.7 mg·g−1). Moreover, all these three materials also demonstrated the remarkable electrosorption selectivity of Yb(III) from the mixed solution, and the robust durability with over 90 % of initial capacities after ten consecutive electrosorption-desorption cycles. Furthermore, the XPS characterizations and electrosorption results revealed that the electrosorption mechanism mainly depended on the synergistic effects of intrinsic Faraday redox reaction, electric double layer capacitance and active binding sites. Therefore, this work provided a feasible strategy for the separation of rare earth elements from aqueous solution, and the prospective applications related to the recovery of rare earth elements from mining wastes or spent permanent magnets in future life.

Reversible Li-ion trade-off in ultrathick sulfur cathodes for practical lean Li–S batteries

The use of low electrolyte volume is beneficial to improve energy density but severely limits access over obscured sulfur, along with sluggish ion kinetics and aggravated polarization, as the ion imbalance across the multicomponent interface of thick sulfur cathodes at a lean electrolyte viciously dominates the sulfur electrokinetics. Herein, we demonstrate that an ion imbalance at the interfaces of a thick electrode with a lean electrolyte can be compensated by the ion trade-off strategy utilizing a cationic ion conductive active binder. It ensures sustained lithium-ion donation/release over the vicinity of slow electrolyte percolation to realize an ion-enriched sulfur–binder–electrolyte interface. The in-situ evolved ionic interface essentially activates the inaccessible sulfur, bringing about additional capacity and low ion and charge transfer resistances. The active binder adopts sulfur cathodes housing 8.1 mg cm–2 with an E/S ratio of 6 µL mg–1 electrochemically utilized 60.89 % sulfur, corresponding to a 1020 mAh g–1 capacity. The lean Li–S pouch cell delivers an energy density of 324 Wh kg–1, demonstrating the efficacy of ion trade-off to ease the interfacial barrier. This study would open up a new paradigm in potentially designing thick electrodes for multiple high energy density batteries.

Development of novel plasma process for modification of solid and liquid interfaces for high-energy-density Cu-MnOx supercapacitor electrodes

Supercapacitors are known for their fast-charging capabilities and high-power density, though their energy density is lower compared to common batteries. Modifying the interface of manganese oxide (MnOx) electrodes by incorporating copper (Cu) is a promising method to enhance the energy density of supercapacitors, though it is not yet fully implemented due to the high electrical resistance inherent to MnOx. This work addresses this challenge by incorporating copper oxide into MnOx. A custom-designed atmospheric-pressure plasma device is used to induce super-hydrophilicity in the carbon cloth substrate, thereby improving MnOx electrodeposition. The copper sulfate precursor solution is also treated with direct plasma discharge to increase the copper doping rate in MnOx. The resulting Cu-MnOx supercapacitor electrodes, with copper oxide incorporated into the material, exhibit significantly lower charge transfer resistance and impedance, indicating an improved electrolyte/electrode interface. The assembled asymmetric supercapacitor, featuring Cu-MnOx as the cathode and activated carbon as the anode, demonstrates a specific capacitance of 92.3 F/g at 1 A g-1, a power density of 700 W/kg, and an energy density of 25.13 Wh/kg. This approach is promising for developing next-generation plasma processing technologies and energy storage materials and devices, as well as easy-to-implement surface modifications for improved wettability.

Performance evaluation of a dynamic electrooxidation systems with magnetically functionalised UiO-66-NH2 and Ti/Sb–SnO2 for methotrexate treatment

Novel conductive MOF magnetic particles Fe3O4@UiO-66-NH2@PANI (FUP) were prepared and combined with Ti/Sb–SnO2 electrodes to construct a dynamic system with improved electrochemical oxidation efficiency. Electrochemical tests revealed that the Ti/Sb–SnO2–FUP electrodes showed a high active specific surface area and low charge transfer resistance. Investigation of the effects of parameters such as dynamic particle loading, magnetic separation time, initial concentration, Na2SO4 dosage and solution pH on the methotrexate (MTX) degradation rate revealed that the degradation rate reached 97.5%. Electron paramagnetic resonance spectroscopy revealed that the Ti/Sb–SnO2–FUP electrodes could produce abundant hydroxyl radicals, possibly due to the unique pore structure of UiO-66-NH2 and the semiconductor structure of aniline. Finally, the decomposition pathway of MTX and ecotoxicity of the intermediates were analysed through LC-MS/MS and Toxicity Estimation Software Tool theoretical calculations combined with genotoxicity experiments. The results showed that Ti/Sb–SnO2–FUP could effectively reduce the toxicity of the intermediates. In this work, a dynamic electrooxidation system was developed using magnetic Ti/Sb–SnO2 electrodes coupled with MOFs, providing a new idea to improve the oxidative degradation efficiency of electrooxidation systems.

Development of carbon dots supported on Zr-MOFs nano-composites for effective oxygen evolution reaction

Efficient hydrogen generation from water splitting is a key component of the hydrogen economy. It has been extensively researched for decades how electrochemically splitting water using electrocatalysts might provide a sustainable and environmentally friendly hydrogen energy source. Sluggish kinetics of the oxygen evolution reaction (OER) hinders the process of overall water splitting. Although metal-organic frameworks (MOFs) are attractive for generation of effective OER electrocatalysts, their activity is significantly hindered by their inherent lower conductivity. Here, we demonstrate a Zr-MOF-based composite with carbon dots (CDs) in order to increase their OER activity. Its exceptional morphology with higher porosity and greater surface area results in enhanced electrochemical activity. It reveals tremendously low onset potential, i.e., 1.40 V vs. RHE, and a remarkably small overpotential of 1.45 V vs. RHE to attain benchmark current density. It exhibited a minimal Tafel value of 37 mV/dec, conquering state-of-the-art catalysts for OER. The fabricated electrocatalyst demonstrated a lower charge transfer resistance (Rct) of 0.248 Ω, with exceptional durability for about 20 h in chronoamperometric studies and for up to 1500 CV cycles. All these results demonstrated that as-fabricated Zr-MOF-based composite is a probable and potential candidate for OER.

Hierarchical design of self-standing FeNi-based metallic glass by in-situ surface amorphous oxide construction for durable and efficient oxygen evolution

As the driving force to accelerate water electrolysis in commercialization, electrocatalysts concurrently satisfying electrocatalytic activity, mechanical flexibility and low cost are essential in the design to lower the kinetic barriers of oxygen evolution reaction (OER). Herein, we present a strategy to in situ construct amorphous metal oxide layers on different compositions of self-standing non-precious FexNiyP20 (at.%) metallic glasses (AMO-MG). With the mechanical flexibility, the processed FexNiyP20 MGs, particularly at Fe30Ni50P20, reaches low OER overpotentials of 238 at a current density of 10 mA cm−2 and a Tafel slope of 33 mV dec−1 in 1.0 M KOH solution while preserving a long-term durability exceeding 60 h. Further studies indicate these robust OER activities appear to be directly linked with the unique surface patterns of the in situ formed AMO layer providing abundant active sites, low charge transfer resistance and superior structural-integration. Modelling analysis further shows that both Fe and Ni sites in AMO layer act as active sites leading to a strong charge transfer for effective H2O adsorption and an optimization of rate-determining step of OER process. Such in situ AMO-MG hierarchical structure therefore provides a novel structure-integration strategy and win–win situation to design and commercialize high-performance alloy catalysts for OER.

Synergistic Enhancements of Zn-ZIF with Nano Zinc Oxide for Hydrogen adsorption, energy storage, and photocatalytic technologies

Creating the porous Zinc-Zeolitic Imidazolate Framework (Zn-ZIF) using a solvothermal technique addresses the need for advanced materials with distinctive properties and cost-effectiveness in modern applications. The PXRD, SEM, UV-DRS, TEM, and TGA/DTG are used to characterize different concentrations of Zn-ZIF. Zn-ZIF's crystalline structure and phase purity have been verified by PXRD. Using diffuse reflectance spectra, the Kubelka-Monk function determined the band gaps of the Zn-ZIF samples, and scanning electron microscopy revealed a more porous structure. At 77 K and 1 bar, the Zn-ZIF solution with a 2:1 ratio had the highest hydrogen storage capacity (1.71 wt%). The electrochemical behavior of several Zn-ZIF electrodes in a 6 M KOH electrolyte was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments. The Zn-ZIF electrode with a 2:1 ratio exhibits a low charge transfer resistance and a high proton diffusion coefficient (D) of 1.687 × 10−4 cm2 s−1. The characteristics of the 2:1 synthesized Zn-ZIF electrode as a supercapacitor were investigated. Our analysis of the generated Zn-ZIF material's specific capacitance values after 2000 cycles revealed an impressive retention rate of nearly 89 %, with values of 296.6 Fg-1. In addition, we examined the photocatalytic activities of the as-synthesized material by exposing it to ultraviolet light and seeing how it degraded organic dyes such as Cango-Red (CR) dye. With a photocatalytic efficacy of 95.06 % for CR dye, Zn-ZIF (2:1 ratio) is the most effective. These findings should provide new knowledge for researchers interested in developing novel Zn-ZIF materials for photocatalytic, energy storage, and hydrogen storage applications.

Fabrication of Ti/Zr-SnO2/PbO2-Nd Electrode for Efficient Electrocatalytic Degradation of Alizarine Yellow R

Introduction: A novel attempt to degrade alizarine yellow R (AYR) by lead dioxide (PbO2)/ neodymium (Nd) coated Ti anode was investigated. Method: Ti/Zr-SnO2/PbO2-Nd electrode showed high oxygen evolution potential, high current density, and neutral conditions, which favored the degradation of AYR. The PbO2-Nd layer on Ti/Zr-SnO2 was further characterized by scanning electron microscopy, and X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The electrochemical properties of Ti/Zr- SnO2/PbO2-Nd electrode were evaluated by cyclic voltammetry, AC impedance spectroscopy, and accelerated life test. Result: The relatively higher oxygen evolution overpotential (~1.80 V) of the developed electrode can effectively suppress the occurrence of surface side reactions and oxygen evolution. A relatively lower charge transfer resistance (Rct, 18.0 Ω) of Ti/Zr-SnO2/PbO2-Nd electrode could be found. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited an accelerated lifetime of 110 min under a very high current density of 10,000 A/m2. The doping of Nd could produce loosely-stacked sheet-like structures, thus, the number of active sites on the electrode surface increases. Conclusion: Moreover, an outstanding conductivity of Ti/Zr-SnO2/PbO2-Nd electrode was obtained, which favored the electron transfer and catalytic activity of the modified electrode. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited improved electrochemical performances and higher oxygen evolution potential, and the highest oxygen evolution potential is 1.80 V. Under the current density of 30 mA/cm2, the electrocatalytic degradation of 92.3% could be achieved in 180 min. The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater. conclusion: The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater.

Bio-functionalized conductive poly(acrylic acid):poly(3,4-Ethylenedioxythiophene)-Prussian blue hybrid transducer for biosensors and bioelectronics interfaces

This study presents an innovative organic-inorganic hybrid transducer of poly(acrylic acid) (PAA), poly(3,4-ethylenedioxythiophene) (PEDOT) and Prussian blue (PB) nanocatalysts. The transducer demonstrated functionality conducive to enzyme conjugation and exhibited favorable electrochemical properties for biosensor signal transduction. Fabricated by a one-tube chemical redox method, the PAA:PEDOT-PB transducer showed long-term electrocatalytic and structural stability. The performance of the transducer was characterized by high transduction activity and low charge transfer resistance, particularly for H2O2 reduction. It achieves a linear detection range from 1.0 μM to 4.0 mM, with a sensitivity of 494 ± 10 μA mM−1 cm−1 and a LOD of 0.34 μM. The PAA:PEDOT-PB transducer featured a high density of carboxyl groups (DCOOH = 14.64 ± 0.05 μmol cm−2) that promoted the immobilization of the H2O2-dependent oxidase enzyme lactate oxidase (LOx) with an EDC/S–NHS coupling agent. The LOx-PAA:PEDOT-PB transducer was developed for lactate biosensing. The transducer provided high LOx-enzyme affinity (KMapp = 1.47 ± 0.05 mM), and a rapid response time (10 s) for lactate detection across a concentration range of 5.0 μM to 4.0 mM, showing a sensitivity of 223 ± 3 μA mM−1 cm−1 and an LOD of 1.45 μM. The LOx-PAA:PEDOT-PB transducer was integrated with a flexible screen-printed electrode, incorporating a wireless, battery-free near-field communication potentiostat module to measure lactate in artificial sweat on a skin model via smartphone. The PAA:PEDOT-PB transducer could enable connections with multiple bio-recognition molecules through polycarboxylic acid groups, providing potential avenues for the development of advanced biosensors.

Tailoring the electrochemical performance of novel BaS and their N-rGO composites for developing next-generation pseudocapacitor electrodes

The exploration of prospective versatile materials with desired morphology for energy storage applications has been reckoned to be a foremost challenge for researchers of the era. In this study, the metal sulfides and their composite with N-rGO are synthesized by facile hydrothermal approach. X-ray diffraction (XRD) pattern of the sample having cubic phase confirms its high crystallinity and purity. Photoelectron Spectroscopy (XPS) depicts utterly the constituent elements and states. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) portray porous-type morphology with a high surface area.I-V measurements ensure the high conductivity of these composites whereas Fourier Transform Infrared Spectroscopy (FTIR) displays the presence of the vibrational bonds. Zeta potential of BaS is determined to be moderately negative, suggesting the existence of negatively charged entities on its surface. Brunauer-Emmett-Teller (BET) corroborates that N-rGO based composite contains a mesoporous structure with an average pore size (2.01 nm) elongated the large surface area (82.21 m2/g). The thermal stability of the composite is envisioned via Thermal gravimetric analysis (TGA). So far as the electrochemical analysis, CV results are much enough to affirm the pseudocapacitive nature of all the fabricated electrodes. An impressive cyclic stability, retaining 98.1 % of its initial capacitance over 10000th cycles is determined through N-rGO based electrode. GCD test unveils exceptional Cs of 913.34 F/g at 1 A/g with Energy density (Ed) 62.106 Wh/kg and Power density (Pd) 2896.47 W/kg and EIS provides valuable insights, showing a small semi-circle in the Nyquist plot, which indicates low charge transfer resistance. The results from the two-electrode experiment indicate that BaS/N-rGO has a specific capacitance (Cs) of 533.96 F/g at 1 A/g. Finally, our symmetrical solid-state supercapacitors exhibit exceptional capacitive performance to power LED. These results confidently indicate that the incorporation of N-rGO with metal sulfides presents promising prospects for the next-generation supercapacitor electrodes to excel the energy storage technological applications.

Elevating Oxygen Evolution using Iron Phthalocyanine Infused Vanillic acid Electrocatalyst.

Oxygen evolution reaction (OER) is the bottle neck step in water splitting reaction towards the realization of hydrogen based clean energy production and storage. Metal air batteries and polymer electrolyte membrane fuel cells (PEMFC) are the alternative green energy systems that utilise O2 and H2 in the production of continuous and high energy output without the utilization of carbon based fuels which are the major sources of pollution. Transition metal based N4 organics are explored extensively as oxygen electrocatalysts i. e., OER and oxygen reduction reaction (ORR) catalysts because of their ease of synthesis, tuneable properties, low cost and high performance with long term stability. Here, vanillic acid functionalized iron phthalocyanine (FeVAPc) was synthesised and characterised by various spectroscopic techniques. The novel FeVAPc exhibited good thermal stability and was coated on Ni foam for OER studies. The scanning electron microscopy images showed net-work like surface morphology and the X-ray photoelectron spectroscopy indicated the presence of Fe in +3 oxidation state. The Ni/FeVAPc demonstrated excellent electrocatalytic activity for OER with overpotential of 312 mV at 10 mA.cm-2 current density in 1.0 M KOH electrolyte. The designed organic based catalyst exhibited lesser Tafel slope value which is nearer to the benchmark catalyst, IrO2. The proposed catalyst exhibited good stability as phthalocyanines are highly stable and do not undergo decomposition even in strong acidic and basic corrosive media. Integration of FeVAPc onto the Ni foam resulted in higher mass activity, lower charge transfer resistance, high active surface area leading to enhanced conductivity and activity. The fabricated Ni/FeVAPc is an appropriate cost-effective, efficient and stable catalyst for OER towards industrial applications.

Corrosion behavior of predominant Halodesulfovibrio in a marine SRB consortium and its mitigation using ZnO nanoparticles

Formation of Sulfate Reducing Bacteria (SRB) biofilm accelerates microbiologically influenced corrosion (MIC). The aim of this study was to investigate both the corrosivity of a marine SRB consortium on carbon steel coupons and its mitigation in the presence of ZnO. Metagenomics analysis revealed that Halodesulfovibrio (78.9%) was predominant and could be related to MIC. The analysis also showed a remarkable shift from a highly corrosive SRB consortium in the control bioreactors to a far less corrosive consortium when ZnO was added to the bioreactors. Further results indicated that the corrosion rate of the SRB consortium was 8.17 mpy on the carbon steel coupons. In the ZnO-treated bioreactors, the count of SRB and MIC in the carbon steel coupons simultaneously reduced. Moreover, Confocal Laser Scanning Microscopy and profilometry analysis determined that ZnO could significantly decrease the amount of biofilm and the corrosion rate. Electrochemical experiments revealed higher corrosion current density (icorr) and lower charge transfer resistance (Rct) in the control bioreactors relative to the ZnO-treated bioreactors. We introduce Halodesulfovibrio as a potentially important corrosive genus in a marine SRB consortium. Additionally, ZnO could be considered a proper candidate to control the corrosion induced by Halodesulfovibrio.

Enhance electrochemical sensing of ascorbic acid and dopamine using V-CuO/GO nanocomposite

The electrochemical detection of Ascorbic acid and dopamine is crucial due to their vital roles in biological processes. Both biomolecules coexist in the human body and have the same oxidation potential, leading to electrode fouling and overlapping of oxidation potential. Accurate detection enables monitoring their levels in biological samples, aiding in disease diagnosis and treatment. This study presents the fast and green synthesis of a highly sensitive and selective electrochemical biosensor for the simultaneous detection of dopamine and ascorbic acid. The change in spherical cluster morphology into nanorods enhances the electrode's electroactive surface area, enhancing sensor sensitivity and selectivity. Electrochemical characterization techniques, including cyclic voltammetry and electrochemical impedance spectroscopy, demonstrated excellent electron transportation and low charge transfer resistance. The sensor exhibited simultaneous detection with a low limit of detection of 8 µM for dopamine and 6.9 µM for ascorbic acid, with a wide linear working range. Additionally, the sensor showed excellent selectivity and repeatability with a vast potential gap at simultaneous detection, making it suitable for clinical and food industry applications.

A flexible solid-state asymmetric supercapacitor device comprising cobalt hydroxide and biomass-derived porous carbon.

Development in the field of alternative and renewable energy sources is becoming necessary considering the current energy demands of the growing technologies. The main challenge associated with the produced energy is to store it for future use, such that it can be used when needed. Supercapacitors are among the electrochemical energy storage systems that provides higher power density, faster charging-discharging, high specific capacitance (C S), and long cycling life. Herein, the fabrication of a flexible solid-state asymmetric supercapacitor (ASC) device is reported, where Co(OH)2 hollow spheres and biomass-derived porous carbon (PC) are the cathode and anode, respectively. Co(OH)2 is a highly redox active material, whereas PC is an electric double-layer capacitive (EDLC) material. In this device, aqueous KOH solution (electrolyte) encapsulated in PVA gel (separator) was used to bind the electrodes. This Co(OH)2//PC ASC device exhibited a high C S of 260 F g-1 (at 2 A g-1). It retained ∼91% of the initial C S value (at 6 A g-1) till ∼5000 cycles. Electrochemical impedance spectroscopy (EIS) study confirmed low internal resistance (0.95 Ω) and charge transfer resistance (1.41 Ω) values of Co(OH)2//PC. These results indicate that the high electron transfer process in the electrode-electrolyte interface during the electrochemical reaction, which is responsible for the excellent performance of this ASC device. The high-performance Co(OH)2//PC ASC device exhibited an energy density of 76.7 W h kg-1 at a power density of 1416.9 W kg-1. To demonstrate its practical use, LED lights were illuminated using this Co(OH)2//PC ASC device.

Combined experimental and density functional theory approaches to address different mechanisms of nitrogen and sulfur doping on the enhancement of capacitive performance of hierarchical porous biochars

Activated carbon derived from biomass as hierarchical porous biochars (HPB) has been developed as electrode materials for supercapacitors. Nitrogen is known as the doping element that enhances quantum capacitance, but the mechanisms of sulfur doping on the quantum capacitance enhancement remain ambiguous. In this study, conventional approaches to assess the characteristics and capacitive performance of biochars were combined with density functional theory (DFT) calculations to assess different mechanisms of nitrogen and sulfur doping. The Bbiochar samples were prepared from the pyrolyzed fish bone powder at 800 °C without additional doping possessed a specific capacitance of 240 F g−1 at 1 A/g within 1 M H2SO4. Interestingly, additional nitrogen doping through urea mixing and additional sulfur doping through thiosulfate mixing prior to the pyrolysis enhanced the specific capacitance of biochar samples to exceed 400 F g−1 under the same condition. The urea mixed sample possessed low porosity but high charge transfer resistance, while the thiosulfate mixed sample possessed high porosity but low charge transfer resistance. The different underlying mechanisms were discussed through DFT calculations on graphene models designed based on the x-ray photoelectron spectroscopy (XPS) results. Nitrogen-doped configurations with topological defects mainly stored charge at the dangling atoms and possessed a relatively high quantum capacitance. Meanwhile, doped configurations of oxidized sulfur groups required relatively low formation energy and possessed large bond dipoles, corresponding to larger pore size and surface area of the thiosulfate mixed biochars. Understanding the contrary between effects of nitrogen and sulfur doping could resolve the bottleneck on enhancing the performance of electronic double layer supercapacitors.

Multiphasic titania photoanode: A facile phase assisted approach to enhance the photoelectrochemical and photovoltaic performance

A facile low-temperature method has been proposed and utilized to synthesize pristine and multiphasic titania. Increasing reactant acid content led to the phase transition of titania from pristine anatase to triphasic anatase-rutile-brookite mixed phase; then to biphasic anatase-rutile mixed phase and ultimately pristine rutile. Morphological differences between the samples led to different dye loading on the Dye Sensitized Solar Cell (DSSC) photoanodes, with anatase showing highest loading. However, the Electrochemical Impedance Spectroscopic (EIS) analyses revealed that the triphasic titania photoanode showed superior charge transport ability as evidenced by the lowest charge transfer resistance and highest carrier lifetime. This led to the triphasic DSSC showing a photoconversion efficiency of 4.23 % which is 45 % greater than the reference DP25 DSSC and 72 % better than that of the anatase DSSC despite having a 24 % lower dye loading. These factors suggest that the charge transport properties precede the dye loading capability of the photoanode in determining the DSSC performance. The intimate ternary interfacial junction between the anatase, rutile and brookite phases may be responsible for the enhanced charge transport properties of the triphasic titania. Thus, it is essential to ensure superior photoanode charge transport characteristics to enhance the DSSC performance.

Boosting HER performance of ZIF-67 via optimizing synthesis parameters in alkaline medium

Electrochemical water splitting offers a promising route to sustainable hydrogen production. Metal-Organic Frameworks (MOFs) have emerged as potential electrocatalysts due to their tunable structure and composition. We investigated the electrocatalytic activity of ZIF-67 for the hydrogen evolution reaction (HER) in alkaline media. Synthesis parameters, including temperature, reaction time, acidity, molar ratio of 2-methylimidazole (2-MIM) to cobalt source, cobalt source type, addition method of 2-MIM, and solvent type, were systematically varied to optimize the electrocatalytic properties of ZIF-67. The synthesized ZIF-67 electrocatalysts were characterized using BET, FESEM, EDS, TEM, XRD, FTIR, and UV–vis spectroscopy. The electrocatalytic properties were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry methods. The optimized ZIF-67 electrocatalyst exhibited remarkable performance, with a low overpotential of 171 mV, a small Tafel slope of 82 mV.dec−1, a low charge transfer resistance of 97 Ω, a high double-layer capacitance of 13.5 mF cm−2, and high stability for 15 h at the current density of 10 mA cm−2. The enhanced electrocatalytic activity of the optimized ZIF-67 was attributed to its high surface area, tunable pore structure, and the presence of active cobalt sites.

CuO/Sb2S3 Nanoarchitectures for Enhanced Charge Generation/Separation for Photoelectrochemical Hydrogen Evolution

Developing an efficient photocathode system using abundant earth materials is crucial for the effective process of Photoelectrochemical (PEC) water splitting. Achieving successful charge transfer between heterojunctions is a key consideration in creating an innovative photocathode that considers cost-effectiveness, material abundance, and PEC performance. In our study, we synthesized a p-type narrow band gap photocathode using copper oxide (CuO) with an energy gap (Eg) of 1.5 eV through a hydrothermal method. We then enhanced its performance by decorating it with antimony sulfide (Sb2S3) nanospheres (NSs) using a simple chemical bath deposition (CBD) technique, resulting in the formation of a CuO/Sb2S3 NSs heterojunction.The fabricated heterojunction demonstrated superior PEC performance compared to the bare CuO. Specifically, we observed a significant increase in photocurrent density for the CuO/Sb2S3 NSs photocathode (J = -1 mA.cm-2) compared to CuO alone (J = -0.3 mA.cm-2) at a standard potential of 0 V vs RHE in a 0.5 M Na2SO4 solution with a pH of 6.85. This improvement can be attributed to the enhanced generation and separation of charge carriers. Furthermore, the CuO/Sb2S3 heterojunction exhibited remarkable photostability over a period of 2.5 h, with no degradation in photocurrent density. The Sb2S3 acted as a sensitizer, reducing the recombination rate of electron-hole pairs (e-/h+) within the CuO/Sb2S3 NSs, thereby enhancing the overall performance. The CuO/Sb2S3 NSs photocathode exhibited an ABPE% of 0.1%, while the ABPE% for CuO alone was 0.03%. This indicates a significant improvement in the performance of the CuO/Sb2S3 NSs photocathode. Onset potential (Eonset) was also observed to shift in a positive direction in CuO/Sb2S3 NSs as compared to CuO only. Eonset for the films followed a trend having CuO/Sb2S3 NSs (0.85 VRHE) > CuO (0.78 VRHE). Notably, this improvement is attributed to increased light absorption and a reduced recombination rate compared to the pristine CuO photocathode. Moreover, electrochemical impedance spectroscopy (EIS) studies provided evidence of enhanced electron transfer rates occurring at the interface between the heterojunction and the electrode/electrolyte interface. UV-Visible and photoluminescence (PL) emission spectra results indicated that the CuO/Sb2S3 NSs heterojunction exhibited an extended absorption spectrum and a reduced rate of recombination, further supporting the enhanced performance. Additionally, electrochemical impedance spectroscopy studies revealed lower charge transfer resistance in the CuO/Sb2S3 NSs heterojunction compared to CuO alone.These findings open up new avenues for the development of novel photocathodic materials and heterojunctions utilizing copper-based binary oxides/chalcogenides for efficient solar harvesting applications.References(1) Kumar, M.; Singh, A.; Meena, B.; Sahu, P. K.; Subrahmanyam, C. Decoration of Spherical Sb2S3 over CuO Nanoflakes for Efficient Photoelectrochemical Hydrogen Generation. Results Eng. 2023, 101513. https://doi.org/10.1016/j.rineng.2023.101513.(2) Kumar, M.; Meena, B.; Subramanyam, P.; Suryakala, D.; Subrahmanyam, C. Emerging Copper-Based Semiconducting Materials for Photocathodic Applications in Solar Driven Water Splitting. Catalysts 2022, 12 (10), 1198. https://doi.org/10.3390/catal12101198.(3) Kumar, M.; Meena, B.; Subramanyam, P.; Suryakala, D.; Subrahmanyam, C. Recent Trends in Photoelectrochemical Water Splitting: The Role of Cocatalysts. NPG Asia Mater. 2022, 14 (1), 88. https://doi.org/10.1038/s41427-022-00436-x. Figure 1

Integrating Electrochemical Analysis and Machine Learning for Enhanced Discovery of Conductive MOFs: A Database-Driven Approach

Metal-organic frameworks (MOFs) are highly versatile structures composed of metal ions linked by organic molecules. They offer a broad range of applications in electronics and light-based technologies due to their flexibility. However, the connection between metal ions and organic components often hinders efficient charge movement, which is essential for electrical conduction. To address this challenge, researchers have been innovatively designing MOFs to enhance their conductivity, which is typically low. This process is complex and time-consuming. To overcome these barriers, and to save both time and costs, we integrated machine learning (ML) with electrochemical testing. Our aim was to pinpoint ion and electron conductive MOFs from the Computation-Ready, Experimental Metal–Organic Framework (CoREMOF) Database, which contains over 14,000 MOFs. The ML approach predicted 84 intrinsically conductive MOFs, which were then subjected to rigorous experimental validation through synthesis and conductivity performance testing. Further experimental data confirmed that only two conductive MOFs, containing copper and pyrazole structures with carbonyl groups, exhibited both proton and electron conductivity. The differences between them lie solely in the preparation techniques and solvents used. Sample 1 was prepared using hydrothermal methods and alcohol as the solvent, and NH4@1 was prepared with an ammonium solution at room temperature. To understand deeper their intrinsic conductivity and semiconductor properties, we employed temperature-dependent conductivity and electrochemical measurements, including Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Linear Sweep Voltammetry (I-V), and Mott-Schottky analysis. The EIS data showed a smaller semicircular arc for synthesized NH4@1, indicating its lower charge transfer resistance due to the presence of two different positive charge carriers on its surface. We investigated the effect of increasing positive charge carriers by raising the humidity up to 98% RH. EIS data showed that increasing positive charge has a significantly reduced charge transfer resistance of sample 1 compared to NH4@1. Because NH4@1 consists of ammonium and H3O+ simultaneously, causing saturation of positive charges and increasing charge transfer resistance. Mott-Schottky analysis further elucidated the electrical properties of compounds 1 and NH4@1, revealing their p-type behavior with negative slopes and flat band potentials of 0.61 V and 0.9 V, respectively. The CV analysis of pyrazole carboxylic acid in a 0.1 M KOH solution, using three reference electrodes, revealed reduction and oxidation peaks vs. Ag/AgCl. These peaks highlight the redox behavior of the linker, generating a stable carboxylate anion (-COO−) that facilitates charge hopping. This reversible redox activity is crucial for the charge transport mechanism within the MOFs. CV analyses confirmed the presence of different copper oxidation states in both compounds, with cathodic peaks indicating the reduction from Cu(II) to Cu(I), suggesting active charge transfer. Extensive electrochemical studies, encompassing both Mott-Schottky and EIS analyses, provided deeper insights into charge carriers and transfer resistance, areas not extensively explored in previous research on intrinsically conductive MOFs. Our results underscore the critical role of experimental validation of ML predictions in accelerating the discovery and characterization of conductive MOFs for potential applications in batteries.