Arunava Majumdar, Postdoctoral Faculty Sponsor
A General Strategy to Immobilize Single-Atom Catalysts to Metal-Organic Frameworks for Enhanced Photocatalysis.
Advanced materials (Deerfield Beach, Fla.)
Single-atom catalysts (SACs) are being witnessed a rapid development due to their high activity and selectivity toward diverse reactions. However, it remains a grand challenge in the general synthesis of SACs, particularly featuring identical chemical microenvironment and on the same support. Herein, we have developed a universal synthetic protocol to immobilize SACs to metal-organic frameworks (MOFs). Significantly, by means of SnO2 as a mediator or adaptor, not only different single-atom metal sites, such as Pt, Cu and Ni, etc., can be installed, but also the MOF supports can be changed (for example, UiO-66-NH2 , PCN-222, and DUT-67) to afford M1 /SnO2 /MOF architecture. Taking UiO-66-NH2 as a representative, the Pt1 /SnO2 /MOF exhibit 5 times higher activity toward photocatalytic H2 production than the corresponding Pt nanoparticles (2.5nm) stabilized by SnO2 /UiO-66-NH2 . Remarkably, despite featuring identical parameters in chemical microenvironment and support in M1 /SnO2 /UiO-66-NH2 , the Pt1 catalyst possesses a hydrogen evolution rate of 2167 mumol·g-1 ·h-1 , superior to the Cu1 and Ni1 counterparts, which is attributed to the differentiated hydrogen binding free energies, as supported by density-functional theory (DFT) calculations. To our knowledge, this is the first report on the universal approach to the stabilization of SACs with identical chemical microenvironment on the identical support. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/adma.202109203
View details for PubMedID 34883530
- Water or Anion? Uncovering the Zn2+ Solvation Environment in Mixed Zn(TFSI)(2) and LiTFSI Water-in-Salt Electrolytes ACS ENERGY LETTERS 2021; 6 (10): 3458-3463
- Direct methane activation by atomically thin platinum nanolayers on two-dimensional metal carbides NATURE CATALYSIS 2021; 4 (10): 882-891
Tailoring the Local Environment of Platinumin Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation.
Angewandte Chemie (International ed. in English)
Single-atom Pt 1 /CeO 2 catalyst by atom trapping (AT, 800 o C in air) shows excellent thermal stability, however, it is inactive for CO oxidation at low temperatures due to over-stabilization of Pt 2+ in a highly symmetric square-planar Pt 1 O 4 coordination. Reductive activation forming Pt nanoparticles (NPs) results in enhanced activity, however, NPs are easily oxidized leading to drastic activity loss. Here we show that tailoring the local environment of isolated Pt 2+ via thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (> 1200 o C) in an inert atmosphere induce surface reconstruction of CeO 2 , generating Pt single atoms in an asymmetric Pt 1 O 4 configuration. Originating from this unique coordination, Pt 1 delta+ in a partially reduced state dynamically evolved during CO oxidation, resulting in an exceptional low-temperature performance. The CO oxidation reactivity on the Pt 1 /CeO 2 _TS catalyst is retained under oxidizing conditions.
View details for DOI 10.1002/anie.202108585
View details for PubMedID 34346155
Water-in-Salt LiTFSI Aqueous Electrolytes. 1. Liquid Structure from Combined Molecular Dynamics Simulation and Experimental Studies.
The journal of physical chemistry. B
The concept of water-in-salt electrolytes was introduced recently, and these systems have been successfully applied to yield extended operation voltage and hence significantly improved energy density in aqueous Li-ion batteries. In the present work, results of X-ray scattering and Fourier-transform infrared spectra measurements over a wide range of temperatures and salt concentrations are reported for the LiTFSI (lithium bis(trifluoromethane sulfonyl)imide)-based water-in-salt electrolyte. Classical molecular dynamics simulations are validated against the experiments and used to gain additional information about the electrolyte structure. Based on our analyses, a new model for the liquid structure is proposed. Specifically, we demonstrate that at the highest LiTFSI concentration of 20 m the water network is disrupted, and the majority of water molecules exist in the form of isolated monomers, clusters, or small aggregates with chain-like configurations. On the other hand, TFSI- anions are connected to each other and form a network. This description is fundamentally different from those proposed in earlier studies of this system.
View details for DOI 10.1021/acs.jpcb.1c02189
View details for PubMedID 33904299
- Elucidation of the Active Sites in Single-Atom Pd-1/CeO2 Catalysts for Low-Temperature CO Oxidation ACS CATALYSIS 2020; 10 (19): 11356–64
Interfacial Speciation Determines Interfacial Chemistry: X-ray-Induced Lithium Fluoride Formation from Water-in-salt Electrolytes on Solid Surfaces.
Angewandte Chemie (International ed. in English)
Super-concentrated "water-in-salt" electrolytes recently spurred resurgent interest for high energy density aqueous lithium-ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Here we investigated LiTFSI/H 2 O electrolyte interfacial decomposition pathways in the "water-in-salt" and "salt-in-water" regimes using synchrotron X-rays, which produce electrons at the solid-electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X-ray diffraction. We observed the surface-reduction of TFSI - at super-concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron-induced reduction was revealed to be concentration-dependent interfacial chemistry that only occurs among closely contact ion-pairs, which constitutes the rationale behind the "water-in-salt" concept.
View details for DOI 10.1002/anie.202007745
View details for PubMedID 32881197
- NASICON Na3V2(PO4)(3) Enables Quasi-Two-Stage Na+ and Zn2+ Intercalation for Multivalent Zinc Batteries CHEMISTRY OF MATERIALS 2020; 32 (7): 3028–35