Department of Chemistry
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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 Nickel Cobaltite Nanostructures with Enhanced Supercapacitance Activity(ACS, 2014-07-08) Basu, MrinmoyeeHerein, we report a strategy for controlled synthesis of functional nanomaterials desired for energy conversion and power storage applications. NiCo2O4 nanostructures with square sheets, hexagonal sheets, and spherical form have been synthesized using a solvothermal route by tuning of reaction conditions as well as selection of hydrolyzing agents. The synthesized nanostructures exhibited significant shape dependent electrochemical behavior with improved supercapacitance as well as good electrocatalytic properties toward oxygen evolution reaction. Among all the three morphologies, the square sheets, assembled from nanoparticles ∼5 nm diameter, exhibited higher specific capacitance with good stability. Due to high surface area (∼100 m2/g) and the mesoporous nature of the square sheets, NiCo2O4 reveals better pseudocapacitance.Item CoSe2 Embedded in C3N4: An Efficient Photocathode for Photoelectrochemical Water Splitting(ACS, 2016-09-16) Basu, MrinmoyeeAn efficient H2 evolution catalyst is developed by grafting CoSe2 nanorods into C3N4 nanosheets. The as-obtained C3N4–CoSe2 heterostructure can show excellent performance in H2 evolution with outstanding durability. To generate phatocathode for photoelectrochemical water splitting CoSe2 grafted in C3N4 was decorated on the top of p-Si microwires (MWs). p-Si/C3N4–CoSe2 heterostructure can work as an efficient photocathode material for solar H2 production in PEC water splitting. In 0.5 M H2SO4, p-Si/C3N4–CoSe2 can afford photocurrent density −4.89 mA/cm2 at “0” V vs RHE and it can efficiently work for 3.5 h under visible light. Superior activity of C3N4–CoSe2 compared to CoSe2 toward H2 evolution is explained with the help of impedance spectroscopy.Item Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution(ACS, 2016) Basu, MrinmoyeeThis study employed silicon@cobalt dichalcogenide microwires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co(OH)2 MWs were utilized as precursors to synthesize Si@CoX2 (X = S or Se) photocathodes. Si@CoS2 and Si@CoSe2 MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co(OH)2, respectively. The CoX2 outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX2 layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS2 photocathode showed a photocurrent density of −3.22 mA cm–2 at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe2 MWs revealed moderate photocurrent density of −2.55 mA cm–2. However, Si@CoSe2 presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX2 MWs. Si@CoS2 electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe2 MWs gradually increased to −5 mA cm–2 after chronoamperometry characterization owing to the amorphous structure generation.Item Ag2S/Ag Heterostructure: A Promising Electrocatalyst for the Hydrogen Evolution Reaction(ACS, 2017) Basu, Mrinmoyee; Pande, Surojit; Gangopadhyay, SubhashisDifferent metal chalcogenides, being a potential candidate for hydrogen evolution catalysts, have attracted enormous attention in the field of water splitting. In the present study, Ag2S/Ag is revealed as an efficient catalyst for hydrogen evolution. When a sacrificial template of the CuS nanostructure is used, Ag2S/Ag heterostructures are synthesized following a simple wet-chemical technique. Two different routes, wet chemical and hydrothermal, are followed to modulate the morphology of the CuS templates from flower ball to wirelike structures, which subsequently results in the formation of Ag2S nanostructure. Finally, the Ag layer is deposited on Ag2S with the help of a photoreduction technique. The unique heterostructure of Ag2S/Ag shows efficient catalytic activity in the H2 evolution reaction. A Ag2S/Ag wire can successfully generate a 10 mA/cm2 current density at a −0.199 V potential. Ag2S/Ag contains the micronanostructure where nanoplates of Ag2S/Ag assemble to give rise to microstructures such as flower balls and wire.Item Shape-Controlled Hematite: An Efficient Photoanode for Photoelectrochemical Water Splitting(ACS, 2019-04-11) Basu, MrinmoyeePhotoelectrochemical water splitting has gained considerable interest in the past few decades because of its potential for harvesting solar light for H2 production. For harvesting solar light, the design of a semiconductor photoelectrode is the critical parameter to control performance. In this regard, vertically aligned, interconnected 2D nanosheets of α-Fe2O3 show the most efficient activity for PEC water splitting as compared to other morphologies like thick sheets and nanorods as the former absorb more light, provide less path length for photon penetration, and a short minority carrier (hole) diffusion length. Compared to thick sheets and nanorods, the separation efficiency of Fe2O3 nanosheet is 7.3, which is higher than the structures as mentioned above, at 1.23 V vs RHE. To further legitimize the efficacy of α-Fe2O3 nanosheet vis-à-vis the thick sheets and nanorods, Mott–Schottky analysis is performed to calculate carrier densities of 8.68 × 1020, 8.68 × 1019, and 2.89 × 1020 cm–3.Item 2D Thin Sheet Heterostructures of MoS2 on MoSe2 as Efficient Electrocatalyst for Hydrogen Evolution Reaction in Wide pH Range(ACS, 2020-03-09) Basu, MrinmoyeeTwo-dimensional layered transition metal dichalcogenides, MoSe2 and MoS2, have drawn potential attention in the field of water splitting. Coupling of MoS2 and MoSe2 provides a sustainable route to improve the electrocatalytic activity for the hydrogen evolution reaction (HER). Here, the heterostructures of thin sheets (ts) of MoSe2 and MoS2 are combined to develop the MoSe2-ts@MoS2-ts heterostructure via multiple-step methodology. First, thin sheets of MoSe2 are synthesized following the stepwise hydrothermal method. After the successful synthesis of MoSe2-ts, MoS2-ts is synthesized on it to develop the heterostructure: MoSe2-ts@MoS2-ts. By tuning the amount of MoS2-ts and MoSe2-ts in the heterostructure separately, the optimum condition is obtained for HER. The unique heterostructure is efficient for HER under wide pH conditions like 1 M KOH, pH-7 phosphate buffer, 3.5% saline water, and finally 0.5 M H2SO4. MoSe2-ts@MoS2-ts can generate 10 mA/cm2 current density under the application of −0.186 V vs RHE with a low Tafel value of 71 mV/decade. The formation of the heterojunction plays an essential role in facilitating charge transportation. Furthermore, the heterostructure provides the more active sites for the adsorption of hydrogen to generate H2. An excess amount of any of the bare counter parts in the heterostructure leads to a decrease in electrocatalytic efficiency because of the lowered heterojuction formation. MoSe2-ts@MoS2-ts has very high stability during the electrocatalytic reaction, which is determined from 1000 consecutive cycles and a 24 h prolonged scan. MoSe2-ts@MoS2-ts can generate 147 μmol of H2 in ∼50 min of reaction time with 100% Faradaic efficiency.