Electrocatalysis最新文献

Abstract

Ammonia (NH₃) is one of the most used chemicals. Industrially, ammonia is produced by hydrogenation of N₂ through the Haber–Bosch process, a process in which enormous amounts of CO₂ are released and requires a huge energy consumption (~ 2% of the total global energy). Therefore, it is of paramount importance to explore more sustainable and environmentally friendly routes to produce NH₃. The electrochemical nitrogen reduction reaction (NRR) to ammonia represents a promising alternative that is receiving great attention but still needs to be significantly improved to be economically competitive. In this work, the NRR is studied on Pt–Rh nanoparticle–based electrodes. Carbon-supported Pt–Rh nanoparticles (2–4 nm) with different Pt:Rh atomic compositions were synthesized and subsequently airbrushed onto carbon Toray paper to fabricate electrodes. The electrochemical NRR experiments were performed in a H-cell in 0.1 M Na₂SO₄ solution. The results obtained show interesting faradaic efficiencies (FE) towards NH₃ which range between 5 and 23% and reasonable and reliable NH₃ yield values of about 4.5 µg h⁻¹ mg_cat⁻¹, depending on the atomic composition of the electrocatalysts and the metal loading. The electrodes also showed good stability and recyclability (constant FE and NH₃ yield in five consecutive experiments).

Herein, we present a novel blended solid polymer electrolyte system composed of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) and polymethyl methacrylate (PMMA) with the addition of phenothiazine (PZ) as an additive and iodide/triiodide (I^-/I₃^-) as a redox couple in nanocrystalline TiO₂ dye-sensitized solar cells (DSSCs). The characterization of the blended solid polymer electrolyte was conducted using techniques such as XRD, FTIR, SEM, and current-voltage (I-V) measurements. Our analyses revealed a decrease in the degree of crystallinity in PVDF-co-HFP/PMMA-based blended solid polymer electrolytes due to the incorporation of PZ, as observed through XRD, FTIR, and SEM. The electrical conductivity of the optimized solid polymer electrolyte film was determined using complex impedance spectroscopy, showing a maximum ionic conductivity value of 3.2 × 10^-7 Scm^-1 at ambient temperature (298 K). DSSCs based on nanocrystalline TiO₂ were fabricated, and the cell parameters, including short-circuit current density (J_sc), open-circuit voltage (V_oc), fill factor (ff), and photovoltaic energy conversion efficiency (η), were evaluated. The DSSC fabricated with the polymer electrolyte exhibited values of 9.3 mA/cm², 800 mV, 0.56, and 5.2% for J_sc, Voc, ff, and η, respectively, under 80 mW/cm² at AM 1.5 simulated solar irradiation.

Graphical Abstract

The determination of complex structure helps to explore its reaction mechanism and provides design strategies for guiding synthesis of high-performance hydrogen evolution reaction (HER) electrocatalysts. A new mononuclear Ni(II) complex, [Ni(p-MOPhH₂IDC)₂(H₂O)₂], was synthesized by the reaction of p-MOPhH₃IDC (2-(4-methoxyphenyl)-1 H-imidazole-4,5-dicarboxylic acid) and Ni(NO₃)₂·6H₂O under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV-vis spectroscopy. The structure analysis revealed that the nickel center was six-coordinated octahedron coordination geometry. The electrochemical properties of the Ni(II) complex-doped carbon paste electrode (Ni-CPE) were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in 0.5 M H₂SO₄ electrolyte. The HER measurements show that the η₁₀^298K (overpotential, 10 mA cm^–2) of the Ni-CPE was positively shifted by 265 mv compared with the bare-CPE (without complex). The Tafel slope of the Ni-CPE was 187 mV dec^− 1. These indicated that the Ni-CPE was effective for HER electrocatalytic reaction. In addition, the electrochemical sensing performances of the Ni-CPE towards H₂O₂ were found to have a linear response from 0.5 µM to 4.0 mM with a detection limit of 0.036 µM. The above studies prove that the Ni(II) complex can be used as an effective bi-functional molecular electrocatalyst for HER and H₂O₂ sensing, and provide a new approach for designing efficient, non-precious metal electrochemical catalysts.

Graphical Abstract

A new mononuclear Ni(II) complex, [Ni(p-MOPhH₂IDC)₂(H₂O)₂], was synthesized under solvothermal conditions. The electrochemical properties of the Ni(II) complex-doped carbon paste electrode (Ni-CPE) were investigated. In the HER study, the Ni-CPE has more positive overpotentials (η₁₀^293K), smaller Tafel slopes and lower activation energies in the HER process compared to the bare-CPE, demonstrating that the Ni-CPE has effective electrocatalytic hydrogen evolution activity. Moreover, electrochemical sensing performance shows that Ni-CPE has good detection ability for H₂O₂ and exhibit good stability and anti-interference properties. Therefore, the Ni-CPE can be used as an effective bifunctional electrocatalyst.

The present work involves the design and validation of an electrochemical sensor for precise and selective sensing of nicotinamide adenine dinucleotide (NADH). The designed electrochemical sensor consists of TCNQ and Pd-Co@NC nanocomposite–modified electrodes (TCNQ-Pd-Co@NC/CPE). The designed electrode was validated by cyclic voltammetry, amperometry, and electrochemical impedance spectroscopy (EIS). The results revealed potent electrocatalytic activity towards NADH oxidation and sensing. Cyclic voltammetry revealed the superior capability of TCNQ-Pd-Co@NC-based carbon paste electrode in electron transfer than TCNQ-Co@NC/CPE and TCNQ/CPE, validating better conductivity of TCNQ-Pd-Co@NC/CPE for NADH sensing. Amperometry study provided a wide linear range of 10 to 250 µM for NADH detection with a low detection limit (LOD) of 5.17 µM and a sensitivity of 21.5 µA mM. EIS study revealed the lowest R_ct value of 12.5 × 10² for TCNQ-Pd-Co@NC/CPE compared to TCNQ-Co@NC/CPE and TCNQ/CPE, demonstrating high electron transfer capability and thus sensitivity towards NADH. Besides this, the modified TCNQ-Pd-Co@NC-based carbon paste electrodes offered exceptional selectivity, reproducibility, and stability over time. Therefore, designed TCNQ-Pd-Co@NC nanocomposite–based carbon paste electrodes can be efficiently used for precise and selective NADH sensing.

Graphical Abstract

Abstract

The electronic coupling effect by interfacial engineering between noble metal and transition metal tungstates is considered an effective strategy for improving electrocatalytic activity. Herein we introduced a new hybrid electrocatalyst consisting of Pd nanoparticle supported on NiWO₄ nanocrystals modified carbon for efficient alcohol electro-oxidation reaction. Bimetallic oxide resulted as an efficient interface modulator for Pd over mono metallic oxides. The synthesised catalyst, Pd over nickel tungstate modified Vulcan, exhibited well-dispersed homogeneous Pd particles. The catalytic effectiveness for the electro-oxidation of methanol and ethanol was found to be enhanced around ten times (1202.48 mA/mg_Pd) and six times (1508.24 mA/mg_Pd), respectively compared to Pd deposited over C catalyst. The enhanced electrochemical property owing to electronic modification and improved surface area, by the strong coupling of Pd with nickel tungstate and carbon support conferred excellent catalytic performance for the synthesised catalyst.

Abstract

Hydrogen is a clean fuel with high energy density, considered one of the alternative energy sources of the future. Hydrogen evolution reaction (HER) could produce pure hydrogen on a large scale while striving for effective electrocatalysts. Here, binary and ternary mixed transition metals (Mn, Co, and Ni) were synthesized by an electrodeposition method and employed as efficient HER electrocatalysts. It was found that the combination of transition metals could positively tune the corresponding morphology and activity rather than using single metals. Namely, NiMn electrocatalysts with an onset potential of 83 mV and a Tafel slope of 103 (frac{mV}{dec}) showed superior activity toward HER in alkaline media compared to the other developed electrocatalysts. This high activity was related to improved intrinsic activity, higher energy efficiency, and enhanced conductivity thanks to the synergy between manganese and nickel. NiMn electrocatalyst also displayed a durable and stable performance, rendering it a promising electrocatalyst for efficient electrocatalysis of HER.

Oxygen defect engineering is a reliable and efficient approach to modulate the electronic structure of metal oxides for the improvement of catalytic efficiency. In this work, carbon nitride supported titanium dioxide nanoparticle, with the space group of I41/amd, was prepared using a high temperature synthesis route. Transmission electron microscope study revealed that titanium dioxide particle were dispersed uniformly on the carbon nitride network. The X-ray photoelectron spectroscopy analysis predicted the formation of oxygen defects in the matrix of titanium oxide, and it also indicated the presence of titanium ions with mixed valence states. The synthesized hybrid system was evaluated as an electrocatalyst for the electrochemical detection of epinephrine using cyclic voltammetric and square wave voltammetric techniques. A custom-made device was also fabricated using synthesized hybrid material for the purpose of evaluating the electrochemical sensing of epinephrine in a pharmaceutical sample.

Pharmaceutical wastewater containing contaminants like aspirin, ofloxacin, and amoxicillin are emerging as a worldwide issue due to its significant effects on the ecosystem and public health. In this study, wastewater containing aspirin was treated by using Mn₃O₄ etched graphite felt (EGF) as a cathode in an MFC-powered electro-Fenton system. The electrochemical characterization of etched electrodes revealed that etching at 400 °C for 1.5 h showed the highest electrochemical activity and rapid electron transfer with a peak current of − 0.058A. The physicochemical characterization exhibited a porous morphology with high defect concentration (I_D/I_G ratio of 1.56) and increased specific surface area and superhydrophilicity, proving its ability to regenerate Fe²⁺ on the cathodic surface and promote H₂O₂ generation. MFC exhibits a maximum power density of 0.053 W/m² and a current density of 0.516 A/({{text{m}}}^{2}). Under optimized conditions of 0.7 mM iron concentration, pH 3, and 100 Ω resistance, the MFC-powered electro-Fenton system showed a maximum of 95.85% aspirin degradation in 30 h with a highest H₂O₂ generation of 11.84 mg/l. The results highlight the potential of EGF electrodes as efficient cathodes in MFC-powered electro-Fenton systems and suggest that this technology can be opted as an energy-saving system for degrading pharmaceuticals such as aspirin from wastewater.

Graphical abstract

The problem of water shortage is becoming increasingly serious. Looking for efficient and environmentally friendly water treatment technology has become the focus of today’s municipal engineering field. The ultraviolet-assisted electrocatalytic system is considered to be a new and efficient process. In this study, ultraviolet radiation was introduced into the self-made double-chamber dynamic diaphragm system electrolytic cell, and the synergistic effect of electrocatalytic reaction and ultraviolet radiation was used to achieve efficient degradation of rhodamine B. The effects of initial concentration, electrolytic voltage, and electrolyte concentration on the degradation efficiency were further studied. The optimal conditions were established by statistical methods such as the response surface method. After 60 min, the decolorization rate of rhodamine B in the positive and negative chambers of the electrolytic cell reached more than 98%. In addition, the intermediate products in the degradation process were analyzed by LC-MS to explore the degradation mechanism of rhodamine B. The experimental results show that the UV-assisted electrocatalytic membrane system process has potential in the field of water treatment and provides a new and efficient treatment scheme for solving the problem of water shortage.

Graphical Abstract

Abstract

Tungsten oxide (WO₃) is a promising photoanode material capable of water oxidation under visible-light irradiation. Although WO₃ is usually prepared via sintering at 500 °C–550˚C, this work shows that high-temperature sintering (i.e., at 600 °C) can lead to efficient output at the WO₃ photoanode. The material characteristics such as the crystal system, surface structure, film thickness, and optical properties were essentially independent of the sintering temperatures employed. However, the high-temperature-sintered WO₃ showed low charge transfer resistance at the electrode–electrolyte interface, resulting in improved charge injection efficiency for water oxidation at the WO₃ photoanode. WO₃ sintered at 550 °C and 600 °C showed the similar visible Raman spectra with strong band intensities, indicative of improved crystallinity in WO₃ bulk particularly in the comparison with WO₃ sintered at 450 °C. However, the ultraviolet Raman spectrum exhibited intense bands for only the WO₃ prepared at 600 °C, indicating the enhanced crystallization of the WO₃ outermost surface. Thus, the high crystallinity in the WO₃ bulk and at its surface results in efficient photoanodic output owing to the suppression of electron–hole recombination.