Faculty Publications
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Item The role of synthesis vis-à-vis the oxygen vacancies of Co3O4 in the oxygen evolution reaction(Royal Society of Chemistry, 2022) Roy, S.; Devaraj, N.; Tarafder, K.; Chakraborty, C.; Roy, S.The oxygen evolution reaction over oxide vacancy-induced spinel Co3O4 is a topic of tremendous scientific attention owing to the favourable adsorption of water, as also shown here through DFT calculations. However, the inclusion of an optimum amount of oxygen-ion vacancies at the surface and in the bulk of Co3O4 remains a synthetic challenge in order to enhance the efficacy of the oxygen evolution reaction. Here, we have attempted a single-step scalable approach of solution combustion synthesis to incorporate the oxide ion vacancies in high-surface-area Co3O4. To benchmark the catalyst, we also synthesized Co3O4 using elevated-temperature calcination routes. Detailed structural and surface analyses revealed the significant presence of oxide ion vacancies in the combustion-synthesized material. The solution combustion synthesized Co3O4 due to the presence of oxygen-ion vacancies exhibited an excellent oxygen evolution reactivity with a lower overpotential and higher current density compared with the other Co3O4 materials synthesized using calcination routes. Tafel slope calculations indicated that the formation of surface hydroxyl species through water dissociation over the oxide ion vacancies is the rate-determining step of the overall reaction. The mechanistic role of the oxygen-ion vacancies in the oxygen evolution reaction was further explored via DFT studies. © 2022 The Royal Society of ChemistryItem Mechanistic insight and first principle analysis of cation-inverted zinc ferrite nanostructure: A paradigm for ppb-level room temperature NOx sensor(Elsevier B.V., 2024) Nath, V.G.; Ray, S.; Rodney, J.D.; Prakasha Bharath, S.; Roy, S.; Tarafder, K.; Subramanian, A.; Chul Kim, B.Herein, we adopted a new paradigm for developing a high-performance gas sensor by leveraging the mixed spinel ZnFe2O4 structure (mZFO) to enhance the adsorption of NOx molecules. Material characterization reveals the formation of the mZFO due to the cation inversion in lattice sites. The estimated value of the inversion degree is observed to shift from 0.78 to 0.39 with an increase in the calcination temperature. The mZFO nanoparticles calcined at 500 °C show exceptional sensing performance due to their suitable grain size (∼2 times Debye length), neck diameter, and surface area. The sensing studies conducted at various NOx concentrations indicate that the sensor can detect ppb level of NOx with a detection limit of about 9 ppb at room temperature. The detailed sensing mechanism is elucidated based on the density functional theory calculations (DFT) and Bader charge analysis. The outstanding sensor performance is attributed to the formation of a mixed spinel structure, wherein the adsorption energy of NOx (∼-0.6 eV) in the presence of surface adsorbed oxygen is higher than that of the normal spinel structure (∼-0.1 eV). Furthermore, the sensor exhibited a fast response and recovery times (7 and 92 s at 800 ppb NO2), excellent stability, and selectivity. The practical suitability of the mZFO sensor was studied by analyzing the vehicle exhaust emissions. We strongly believe this work would pave a novel approach to developing a high-potential gas sensor by modifying the cation distributions in the spinel ferrites. © 2024 Elsevier B.V.