Faculty Publications

Now showing 1 - 3 of 3

The structural and surface modification of zeolitic imidazolate frameworks towards reduction of encapsulated CO2
(Royal Society of Chemistry, 2018) Payra, S.; Challagulla, S.; Reddy, R.R.; Chakraborty, C.; Tarafder, K.; Ghosh, B.; Roy, S.
ZIF-8, a metal organic framework with a sodalite topological structure, is a widely studied crystalline microporous material due to its thermal and chemical stability. However, the existing studies mostly focus on understanding the porosity and bulk structure of ZIF-8, ignoring the external facets of the porous crystal, which are the first points of interaction between adsorbent and guest adsorbate. This paper reports on understanding the preferential exposure of thermodynamically stable and unstable facets as a function of synthetic methodology. The comprehensive and combinatorial investigation of experimental and theoretical studies shows that the high energy {112} facets of ZIF-8 efficiently reduce the encapsulated CO2 to fuel compared to the {011} facets. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Structure-sensitive electrocatalytic reduction of co2 to methanol over carbon-supported intermetallic ptzn nano-alloys
(American Chemical Society service@acs.org, 2020) Payra, S.; Shenoy, S.; Chakraborty, C.; Tarafder, K.; Roy, S.
The electrochemical reduction of CO2 (CO2RR) to produce valuable synthetic fuel like CH3OH not only mitigates the accumulated greenhouse gas from the environment but is also a promising direction toward attenuating our continuous reliance on fossil fuels. However, CO2RR to yield CH3OH suffers because of large overpotential, competitive H2 evolution reaction (HER), and poor product selectivity. In this regard, intermetallic alloy catalysts open up a wide possibility of fine-tuning the electronic property and attain appropriate structures that facilitate selective CO2RR. Here, we report for the first time the CO2RR over carbon-supported PtZn nano-alloys and probed the crucial role of structures and interfaces as active sites. PtZn/C, Pt3Zn/C, and PtxZn/C (1 < x < 3) synthesized from the metal-organic framework material were characterized structurally and morphologically. The catalysts demonstrated structure dependency toward CH3OH selectivity, as the mixed-phase PtxZn/C outperformed the phase-pure PtZn/C and Pt3Zn/C. The structure-dependent reaction mechanism and the kinetics were elucidated over the synthesized catalysts with the help of detail experiments and associated density functional theory calculations. Results showed that in spite of low electrochemically active surface area, PtxZn could not only have facilitated the single electron transfer to adsorbed CO2 but also showed better binding of the intermediate CO2 •- over its surface. Moreover, the lower bond energy between the mixed-phase surface and -OCH3 compared to the phase-pure catalysts has enabled higher CH3OH selectivity over PtxZn. This work opens a wide possibility of studying the role of interfaces between phase-pure nano-alloys toward CO2RR. © 2020 American Chemical Society
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 Chemistry

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