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Item Doped nickel-based nanocatalysts for electrochemical water splitting: a review(ACS, 2025-10) Pande, SurojitThe growing demand for clean energy solutions to address fossil fuel depletion and global warming has increased the pace for the search for sustainable alternatives. To address this situation, hydrogen energy is emerging as a promising method due to its zero pollution and high energy density. Electrocatalytic water splitting is a promising technology for large-scale hydrogen production. Generally, electrocatalysts work well for either the HER or the OER, but not both. Developing catalysts that can be efficiently used for overall water splitting is necessary for commercial viability. Nickel-based materials, specifically when doped with metals (e.g., Fe, Co, W, Cu, Ru, and Ir) and nonmetals (e.g., C, F, and P), have shown great potential because of their versatile chemical properties, corrosion resistance, and structural stability. This review provides a comprehensive overview of recent advancements in doped nickel-based electrocatalysts, which focuses on nickel oxides, chalcogenides, phosphides, nitrides, and single-atom catalysts (SACs). It discusses fundamental mechanisms of HER and OER, strategies for enhancing electrocatalytic performance through doping, defect engineering, and electronic structure modulation. It also discusses the effect of nonmetal and metal doping on activity and stability. The review also emphasizes the importance of systematic experimental approaches like doping ratios, accurate surface area corrections, and operando methods to better understand the relationship between electronic structure and electrocatalytic performance. It also highlights the research gaps and the future directions that aim to advance the design of efficient, stable, and cost-effective nickel-based electrocatalysts, which can contribute to the development of sustainable hydrogen energy production.Item Sulfur/nitrogen-codoped carbon-dot-modified wo3 nanosheets toward enhanced charge-carrier separation in a saline water-splitting reaction(ACS, 2023-11) Basu, MrinmoyeeHydrogen (H2) is considered to be a future fuel because of its high energy density and could replace fossil fuels. It can be produced in a greener way by using abundant solar light and saline water and applying a photoelectrochemical (PEC) pathway. To produce green H2, WO3 2D nanosheets are developed, and their performance in saline water splitting is studied under PEC conditions. WO3 is very efficient in absorbing visible light from solar irradiation; however, it suffers from low charge-transfer rates, which inhibits its PEC performance. To increase the charge transportation ability, WO3 is sensitized with sulfur/nitrogen-codoped carbon dots (SNCDs). Impedance analysis indicates an enhanced charge transportation ability of the formed heterostructure. The best-obtained heterostructure of WO3 and SNCDs exhibits nearly 1.62 times more photocurrent density than bare WO3. Bare WO3 nanosheets can produce a photocurrent density of 1.59 mA/cm2 at 1.39 V vs Ag/AgCl. The best-obtained heterostructure of WO3 and SNCDs can produce photocurrent density of 2.57 mA/cm2 at 1.39 V vs Ag/AgCl. A type II staggered heterostructure of WO3/SNCDs leads to improved PEC activity. Enhanced carrier density and lowered charge-transfer resistances are observed from Mott–Schottky and PEC impedance analyses, respectively. The carrier density increases nearly 84 times in the heterostructure. The heterostructure exhibits effective photostability under uninterrupted illumination for 2 h.Item Bifunctional Tungsten-Doped Ni(OH)2/NiOOH Nanosheets for Overall Water Splitting in an Alkaline Medium(ACS, 2022-02) Pande, SurojitThe development of a cost-effective and proficient bifunctional electrocatalyst is highly fascinating. Herein, we have synthesized a tungsten (W6+)-doped vertically grown nanosheet-like structure of Ni(OH)2/NiOOH on carbon cloth for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity in KOH solution. Doping with W6+ ions in Ni(OH)2/NiOOH is performed by electrodeposition, followed by the hydrothermal method. Various amounts of the dopant (W6+) are used to confirm the role of W, but the W0.1Ni(OH)2/NiOOH nanosheet shows the highest efficiency in electrocatalysis. The surface composition and the oxidation state of the developed electrocatalyst are confirmed by inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy analyses. After doping, the lattice suffers a tensile strain, which is confirmed by Raman and X-ray powder diffraction analyses. Field emission scanning electron microscopy and transmission electron microscopy analyses confirm the nanosheet morphology of W0.1Ni(OH)2/NiOOH. The electrocatalyst, W0.1Ni(OH)2/NiOOH, has a lower value of overpotential of 56 and 293 mV to obtain current densities of 10 and 50 mA/cm2 for HER and OER, respectively, in a basic medium. The corresponding Tafel slope values are 63.5 and 48.2 mV dec–1 for HER and OER, respectively. In W0.1Ni(OH)2/NiOOH, the W6+ ion is a d0 system that behaves as a strong Lewis acid and helps in electron pulling from Ni2+ ions, which facilitates the formation of Ni3+ ions as an active site for HER and OER. The electron pulling nature of the W6+ ion is further confirmed from Bader’s charge analysis. Moreover, the synergistic effect between Ni2+ and W6+ ions plays an important role in a higher electrocatalytic efficiency. Density functional theory calculations revealed an increase in the Gibbs free energy of H adsorption in the presence of W, suggesting an enhanced HER activity for W0.1Ni(OH)2/NiOOH.Item Co-Doped Ni9S8 Nanostructures for Electrocatalytic Water Splitting over a Wide pH Range(ACS, 2022-07) Pande, SurojitAs a replacement for renewable energy sources, an earth-abundant electrocatalyst for water splitting is effectively explored. In this work, Ni9S8 and cobalt-doped Ni9S8 nanostructures are fabricated on carbon cloth using the hydrothermal technique. The developed electrocatalysts are characterized through various techniques, for example, powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy , the Brunauer–Emmett–Teller method, and inductively coupled plasma atomic emission spectroscopy. Tuning of cobalt doping is performed to obtain the best optimized ratio of Co/Ni for electrocatalytic activity. All the developed materials are used for a water splitting reaction in an alkaline electrolyzer, and Co0.05Ni8.95S8 is an optimized material for both hydrogen and oxygen evolution. The electrocatalyst Co0.05Ni8.95S8 only requires −0.151 V versus RHE (reversible hydrogen electrode) to obtain a 10 mA/cm2 current density in the hydrogen evolution reaction (HER), and in the oxygen evolution reaction (OER), it requires 1.557 V versus RHE to generate a 30 mA/cm2 current density. The corresponding Tafel slope values for the HER and OER are 125 and 49.8 mV/dec, respectively, obtained by using Co0.05Ni8.95S8 electrocatalysts in 1.0 M KOH solution. The stability of Co0.05Ni8.95S8 is also checked, and it is stable for up to 60 and 80 h for the HER and OER, respectively. The cell voltage of 1.89 V is required to generate a 10 mA/cm2 current density for the overall water splitting reaction. The electrocatalyst is also used for the HER and OER in a wide pH range for practical applicability. The overall experimental findings were verified by theoretical calculations, which state that the higher metallic nature of Co-doped Ni9S8 facilitates efficient electrocatalytic activity. The optimum Gibbs free energy and hydrogen and oxygen coverage calculations also prove that the optimized Co0.05Ni8.95S8 electrocatalyst exhibits the best HER and OER activity. Therefore, this work provides a robust electrocatalyst for the electrocatalytic water splitting reaction.Item Fe-Doped NiCo2Se4 Nanorod Arrays as Electrocatalysts for Overall Electrochemical Water Splitting(ACS, 2023-02) Pande, SurojitThe development of efficient, affordable, and earth-abundant bifunctional electrocatalysts is vital for the water-splitting reaction. In this article, we have fabricated NiCo2Se4 and Fe-doped NiCo2Se4 through a simple hydrothermal route on the surface of carbon cloth with nanorod morphology. The developed electrocatalyst was thoroughly investigated by various techniques like PXRD, XPS, FESEM, ICP-AES, and TEM analysis. The optimized Fe0.2NiCo1.8Se4 has worked finest for hydrogen and oxygen evolution in an alkaline medium; it entails a potential of 148 mV and 1.656 V vs RHE to obtain 50 and 100 mA/cm2 current densities for HER and OER, respectively. The Tafel slope values for HER and OER are 85.7 and 56.3 mV/dec, respectively. This catalyst is stable under an alkaline medium for 48 h. The best HER and OER activity recommends the catalyst as a bifunctional in an alkaline medium, and the developed cell consisting of a doped sample requires 1.51 V to generate a 10 mA/cm2 current density with 24 h of stability. The Fe0.2NiCo1.8Se4 catalyst has a good Faradaic efficiency of 89.9% for overall water splitting. The nanorod morphology has a specific role in enhancing the electron transportation and conductivity of Fe0.2NiCo1.8Se4. The doping with Fe in NiCo2Se4 enhances the active sites and increases its electrocatalytic performance. The SCN– poisoning effect on metal ions in Fe0.2NiCo1.8Se4 suggests that Fe, Co, and Ni metals have a prominent impact on the overall electrocatalytic activity. Additionally, DFT investigation indicates that after Fe doping in a NiCo2Se4 zero band gap, minimum Gibbs free energy, maximum hydrogen, and oxygen coverage calculations are accountable for the higher conductivity of the system. This research provides a simple approach for synthesizing a Fe-doped ternary NiCo2Se4 nanorod array on the surface of carbon cloth, which is highly active and stable for water splitting in an alkaline medium.Item Doping of MoS2 by “Cu” and “V”: An Efficient Strategy for the Enhancement of Hydrogen Evolution Activity(ACS, 2021-04) Basu, Mrinmoyee; Pande, SurojitTo replace Pt-based compounds in the electrocatalytic hydrogen evolution reaction (HER), MoS2 has already been established as an efficient catalyst. The electrocatalytic activity of MoS2 is further improved by tuning the morphology and the electronic structure through doping, which helps the band energy position to be modified. Presently, thin sheets of MoS2 (MoS2-TSs) are synthesized via a microwave technique. Thin sheets of MoS2 can outperform nanosheets of MoS2 in the HER. Further, the efficiency of the thin sheets is improved by doping with different metals like Cu, V, Zn, Mn, Fe, Sn, etc. “Cu”- and “V”-doped MoS2-TSs are highly efficient for the HER. At a fixed potential of −0.588 V vs RHE, Cu-doped MoS2 (Cu-MoS2-TS), V-doped MoS2 (V-MoS2-TS), and MoS2-TS can generate current densities of 327.46, 308.45, and 127.82 mA/cm2, respectively. The electrochemically active surface area increases nearly 7.7-fold and 2.5-fold for Cu-MoS2-TS and V-MoS2-TS than for MoS2-TS, respectively. Cu-MoS2-TS shows exceptionally high electrocatalytic stability up to 140 h in an acidic medium (0.5 M H2SO4). First-principles calculations using density functional theory (DFT) are performed, which are well matched with the experimental observations. DFT calculations dictate that after doping with “V” and “Cu” both valance band maxima and conduction band minima are uplifted, which indicates the higher hydrogen-ion-reducing ability of M-MoS2-TS (M = Cu, V) compared to bare MoS2-TS.Item Electronic Structures and Optical Properties of p-Type/n-Type Polymer Blends: Density Functional Theory Study(ACS, 2020-04) Ghosh, SarbaniA blend made of p-type and n-type polymers can act as bipolar/ambipolar material composites that transport both electrons and holes. Although several experimental efforts are currently devoted to p-/n-type blends of conducting polymers, theoretical studies of these systems are missing to a large extent. In the current paper, using the density functional theory (DFT) and the time-dependent DFT, we calculate electronic and optical properties of a p-type/n-type polymeric blend, where we have chosen the poly(3,4-ethylenedioxythiophene)/benzimidazo-benzophenanthroline ladder (PEDOT/BBL) as a model composite system. We demonstrate that in the blend, PEDOT acts as an electron donor and BBL acts as an electron acceptor under doped conditions. However, no charge transfer between the chains takes place for an undoped composite system. Due to a significant difference in the electron affinities and the ionization energies of PEDOT and BBL, the electronic properties of a negatively (positively) doped PEDOT/BBL blend are primarily governed by the chains where negative (positive) charges are localized, i.e., the BBL chains (the PEDOT chains). However, this is no longer valid for the optical absorption where the electronic transition occurs between the two chains and, therefore, the calculated UV–vis–near-infrared (NIR) absorption spectra of the negatively (positively) doped PEDOT/BBL blend are rather different compared to the corresponding spectra of the single BBL chains (PEDOT chains). The electronic coupling between the photoexcited state and the final charge-transfer state of the blend was calculated to be ∼0.08 eV. The results presented here are generic to a wide class of p-type/n-type combinations, which was further confirmed by calculations performed on the polythiophene (PT)/BBL blendItem Experimental and Theoretical Investigation into the Polaron Structure of K-Doped Polyfluorene Films(ACS, 2020-12) Ghosh, SarbaniThe evolution of the electronic structure and optical transition upon n-doping of poly(9,9-dioctylfluorene) (PFO) films is elucidated with photoelectron spectroscopy, optical absorption, density functional theory (DFT), and time-dependent DFT (TD-DFT) calculations. Optical absorption measurements extending into near infrared show two low-energy absorption features at low doping ratios and an additional peak at a higher energy of ∼2.2 eV that disappears with increasing doping ratios. A gap state (i.e., polaronic state) close to the Fermi level and a significantly destabilized highest valence band appear in the experimentally measured ultraviolet photoelectron spectra. These experimental results are interpreted by the TD-DFT calculations, which show that the lower energy peaks originate from the excitation from polaronic states to the conduction band, while the higher energy peak mainly originates from the destabilized valence band to conduction band transitions and only appears at low doping ratios (cred ≤ 50%, 0.5 potassium atom per fluorene monomer). The DFT calculations further indicate that polaron pairs rather than bipolarons are preferentially formed at high doping ratios. Comparing the results of doped glassy and β-phase films, we find that the ordered segments in the β-phase film disappear due to the dopant (potassium) insertion, resulting in a similar polaronic structure.Item qPlus atomic force microscopy of the Si(100) surface: Buckled, split-off, and added dimers(AIP, 2009-08) Gangopadhyay, SubhashisDimer configurations at the Si(100) surface have been studied with noncontact atomic force microscopy in the qPlus mode at 77 K, using both large (10 nm peak to peak) and small (0.5 nm peak to peak) oscillation amplitudes. In addition to the , , and reconstructions of the pristine surface, a variety of defect types including ad-dimers, vacancies, and split-off dimers have been imaged. Our data appear at odds with the currently accepted structural model for split-off dimers. At low oscillation amplitudes the degree of apparent dimer buckling can be “tuned” by varying the frequency shift set point.Item Reduction of threshold electric field on doping nematic liquid crystal with functionalized CNT(AIP, 2013-06) Manjuladevi, V.; Gupta, Raj KumarNematic Liquid crystals are orientationally ordered fluids whose average orientation direction can be manipulated on application of electric and magnetic fields. Carbon nanotube (CNT), a highly shape anisotropic object can find numerous industrial application because of its interesting electronic and mechanical properties. The self-organizing properties of nematics can be used to align CNTs dispersed in them. We have dispersed functionalized CNTs in nematic liquid crystal and carried out experimental studies. We will present results of electro-optic switching of CNT-LC dispersion. We have observed that addition of functionalized CNTs in the liquid crystal (LC) has led to reduction of threshold electric field.