The development of efficient small-molecule electrocatalysts for the hydrogen evolution reaction (HER) is crucial in advanced water splitting and fuel cell applications. The use of effective molecular electrocatalysts for HER and allied reactions is limited by a lack of electrical conductivity, which strongly hinders their activity. Here, we report a series of N-heterocyclic carbene (NHC)-coordinated silver(I) (8 and 9) and ruthenium(II) (10 and 11) small-molecule electrocatalysts varied by the NHC ligand field as highly effective HER catalysts. Silver complexes 8 and 9 were prepared by the in situ deprotonation of triazolium salts (6 and 7), while ruthenium complexes 10 and 11 were prepared through transmetalation protocol using former derivatives. Both types of complexes were thoroughly characterized by various spectral and analytical techniques. Both salts were studied for their structure using the single-crystal X-ray diffraction technique. Among others, ruthenium complexes 10 and 11 evidenced an overpotential (η10) of −175 and −209 mV vs RHE to reach a benchmark current density of 10 mA cm–2, while silver derivatives 8 and 9 displayed an overpotential of −291 and −394 mV vs RHE, respectively. Their respective η50 values are in the range −287 to −496 mV vs RHE with comparative Tafel slope values (94.3–208.4 mV dec–1) with a decrease in the performance to 265 mV vs RHE (η10 for 10) over 18 h of HER operation. Alongside, hydrogen oxidation is evidenced by a significant current density observed at the platinum ring electrode. Finally, the promising HER performance of silver and ruthenium-NHC complexes is attributed to the confined coordination geometry around the metal atom (linear or three-legged piano stool), the steric bulk offered by the NHC ligand, surface morphology (well-ordered discrete microgranules/tubes to highly porous films), and the charge-transfer resistance (Rct: 119.8–191.6 Ω).
It is challenging to create an electrocatalyst for water electrolysis that is long-lasting, highly efficient, and inexpensive for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, we have synthesized an ordered NiFe-layered double hydroxide (LDH)/RuSe2 heterostructure for electrochemical water splitting reaction. The synthesized heterostructure electrode NiFeLDH/RuSe2 exhibits exceptional HER and OER performance as it produces a current density of 10 mA cm–2 at 60 and 268 mV overpotential, respectively. Very low Tafel slope values of 70 and 69 mV dec–1 for the HER and OER, respectively, imply a fast charge transfer process. Additionally, for the HER and OER processes, even after 40 h, the synthesized NiFeLDH/RuSe2 heterostructure electrodes demonstrate long-term endurance. Insights into interfacial electron transfer are provided by Mott–Schottky experiments, which signifies the creation of the p–n junction in NiFeLDH/RuSe2, which helps in the transition of electrons from n-type NiFeLDH to p-type RuSe2. The formation of the heterojunction enhances the active sites to adsorb H+ and OH– ions, and hence better OER and HER processes are achieved. Transmission electron microscopy clearly depicts the formation of different interfaces at multiple points that was assigned to the interplanar distance of NiFeLDH and RuSe2.
The functionalization of materials for ultrasensitive detection of heavy metal ions (HMIs) in the environment is crucial. Herewith, we have functionalized inexpensive and environmentally friendly Fe3O4 nanoparticles with D-valine (Fe3O4–D–Val) by a simple co-precipitation synthetic approach characterized by XRD, FE-SEM, and FTIR spectroscopy. The Fe3O4–D–Val sensor was used for the ultrasensitive detection of Cd+2, Pb+2, and Cu+2 in water samples. This sensor shows a very low detection limit of 11.29, 4.59, and 20.07 nM for Cd+2, Pb+2, and Cu+2, respectively. The detection limits are much lower than the values suggested by the world health Organization. The real water samples were also analyzed using the developed sensor.
One pot reduction and functionalization of graphene oxide (GO) with L-cysteine (L-cys-rGO) at the edges and basal planes of the carbon layers are presented. The L-cys-rGO was characterized by X-ray diffraction studies (XRD), X-ray photoelectron spectroscopy (XPS), attenuated infrared spectroscopy (ATIR), and Raman spectroscopy. The surface morphology was studied by scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). The L-cys-rGO was further utilized for the simultaneous electrochemical quantification of environmentally harmful metal ions such as, Cd2+, Pb2+, Cu2+ and Hg2+. Detection limits obtained for these metal ions were 0.366, 0.416, 0.261 and 1.113 μg L−1 respectively. The linear range obtained for Cd2+, Cu2+ and Hg2+ was 0.4 to 2.0 μM and for Pb2+ was 0.4 to 1.2 μM. The detection limits were found to be less than the World Health Organization (WHO) limits. The developed protocol was applied for the determination of the above metal ions in various environmental samples and the results obtained were validated by atomic absorption spectroscopy (AAS).
Abstract The work reported here exploits the extraordinary features of graphene nanoribbons (GNR) and well‐known conductive polypyrrole (PPy) polymer to develop a very good electrochemically active composite for sensing metal ions. A strong hydrogen bond and π‐π interaction between the two components facilitates an enhanced conductive 3D network that has been used to design and fabricate an electrochemical sensor for selective and sensitive determination of Pb 2+ ions by differential pulse voltammetry (DPV). The probe has been further extended to simultaneously detect Zn 2+ , Cd 2+ , As 2+ , Cu 2+ , Pb 2+ , Fe 2+ and Hg 2+ ions. Moreover, the larger effective surface area, higher porosity and chelating groups of composite promotes better adsorption‐stripping process of Pb 2+ ions, leading to a high detection limit of 0.03 nM with a sensitivity of 0.7557 μA μM −1 cm −2 . This study is extended to detect heavy metal ions in lake water samples, demonstrating promising applications in real time (environmental) samples, and the study shows a deviation of ≈10 %, when validated with atomic absorption spectroscopy studies.
The demand for the development of electrochemical energy storage systems from abundant, renewable, eco-friendly, and cost-effective materials has been the focal and driving point in the advancement of electronic devices. This task and demand can be addressed with a resource that is abundant and possesses the attributes of being developed into efficient electrochemical energy storage systems. Lignin and cellulose, which are collectively known as lignocellulose, are the two most abundant biopolymers available, and they possess the attributes and the qualities to meet this demand. Lignocellulose biopolymers possess unique characteristics such as mechanical flexibility, porosity, and tunability because of their abundant and diverse functional groups. These qualities enable suitable pairing with electronically conducting polymers as enhanced materials for the development of sustainable energy storage devices. This Review highlights the challenges and the utilization of lignocellulose with electronically conducting polymers in supercapacitors applications and battery applications in various capacities as electrodes, separators, binders, and electrolytes.
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