Subha Sadhu

Ammonia (NH₃) is vital in agriculture and industry, yet its large-scale production remains energy-intensive and environmentally hostile. Herein, for the first time we report the development of lead-free nontoxic hexagonal methylammonium iodobismuthate metal halide perovskite (MABI) as a highly efficient and sustainable electrocatalyst for green ammonia production from nitrate reduction. The unique structure of MABI, featuring an isolated BiI₆ octahedron stabilized by a methylammonium cation, offers a highly tunable electronic environment required for nitrogen activation and hydrogenation. The experimental and computational studies categorically established the formation of an interconnected pure hexagonal structure with a band gap of ∼2.1 eV. Electrocatalytic nitrate reduction revealed that MABI displays a remarkable ammonia yield (27.53 μg mg^-1 h^-1) with excellent stability and a quite impressive Faradaic efficiency (40%). This work highlights the potential of halide bismuthate perovskites as an alternative to traditional catalysts to produce ammonia in ambient conditions that address the dual challenges of energy efficiency and environmental sustainability.

In this work we have incorporated MoS₂ quantum dots having outstanding optoelectronic properties with methyl ammonium lead iodide (MAPI) to form a composite absorber material for photovoltaic applications.

Two polymorphs of titania were synthesized by varying the reaction conditions. Enhanced HER in rutile nanorods was seen compared to that in anatase granules due to enhanced charge separation and faster diffusion of charge.

Perovskites in general are known to possess ionic conductivity and ion movement has been postulated to be directly or indirectly responsible for their lack of long-term stability and unusual behavior, including hysteresis. Therefore, understanding ion migration in perovskites is of major importance in improving their performance. Ion movement in HOIPs may occur extrinsically, i.e. from one of the contacts, or take the form of ion migration, where an ion is displaced from an occupied to a vacant site. Numerous studies confirmed the rotational movement of the MA ions within the inorganic cage formed by the PbI₂octahedra, which has been associated to the temperature and frequency dependence of the complex permittivity. To test the relationship between MA rotation and the frequency dispersion in the dielectric response in HOIP materials, we conducted a series of experiments in which the hydrogen atoms in MAI were selectively substituted with deuterium. Our results (Figure 1) unambiguously demonstrate that deuteration of the ammonium group leads to a large inverse kinetic isotope effect indicative of proton tunneling in HOIP materials. Deuteration of the methyl group in MA induces a normal secondary KIE that is consistent with these findings.^1,2 REFERENCES 1. Y.-F. Chen, Y.-T. Tsai, L. Hirsch, D. M. Bassani J. Am. Chem. Soc., 2017, 139, 16359 – 16364. 2. S. Sadhu, K. Aqueche, T. Buffeteau,J.-M. Vincent,L. Hirsch,D. M. BassaniMat. Horiz., 2018, DOI: 10.1039/C8MH01119B. Figure 1

Correction for ‘Unexpected surface interactions between fluorocarbons and hybrid organic inorganic perovskites evidenced by PM-IRRAS and their application towards tuning the surface potential' by Subha Sadhu et al., Mater. Horiz., 2019, DOI: 10.1039/c8mh01119b.

The chemical nature and orientation of fluorinated monolayers on CH₃NH₃PbI₃ perovskites is probed through XPS and PM-IRRAS measurements. We show that even perfluoro-n-alkanes interact with the HOIP surface to form stable monolayers with well-defined orientation and that the surface potential of CH₃NH₃PbI₃ can be easily tuned over a 150 mV range using various fluorinated porphyrin monolayers.

We report an investigation of lead halide perovskite CH₃NH₃PbBr₃ nanocrystals and associated ligand molecules by combining several different state-of-the-art experimental techniques, including synchrotron radiation-based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials, we could directly obtain complete band alignment to vacuum of both CH₃NH₃PbBr₃ nanocrystals and the ligands widely used in their preparation. We discuss the possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to those of bulk material. The experimental results were supported by DFT calculations.

The optical and structural properties of hybrid perovskites can be tuned by the post-synthetic introduction of new cations. To advance the development of this approach, knowledge of the reaction mechanism is essential, but has not yet been elucidated. Here, the effect of n-octylamine on three-dimensional (3D) methylammonium lead bromide (MAPbBr₃) was investigated by in situ X-ray photoelectron spectroscopy. Spectroscopic analysis indicated equimolar substitutions between octylammonium (OcA⁺) and methylammonium (MA⁺) cations that cause the formation of two-dimensional (2D) octylammonium lead bromide ((OcA)₂PbBr₄). The introduction of methylamine reversed these changes, and the cation exchange between MA⁺ and OcA⁺ caused the reverse conversion to MAPbBr₃.

In comparison to the one-dimensional (1D) semiconductor nanostructures, the hierarchical, three-dimensional (3D) microstructures, composed of the arrays of 1D nanostructures as building blocks, show quite unique physicochemical properties due to efficient photon capture and enhanced surface to volume ratio, which aid in advancing the performance of various optoelectronic devices. In this contribution, we report the fabrication of surfactant-free, radially assembled, 3D titania (rutile-phase) microsphere arrays (3D-TMSAs) composed of bundles of single-crystalline titania nanowires (NWs) directly on fluorine-doped conducting oxide (FTO) substrates with tunable architecture. The effects of growth parameters on the morphology of the 3D-TMSAs have been studied thoroughly. The 3D-TMSAs grown on the FTO-substrate showed superior photon-harvesting owing to the increase in light-scattering. The photocatalytic and photon to electron conversion efficiency of dye-sensitized solar cells (DSSC), where the optimized 3D-TMSAs were used as an anode, showed around 44% increase in the photoconversion efficiency compared to that of Degussa P-25 as a result of the synergistic effect of higher surface area and enhanced photon scattering probability. The TMSA film showed superhydrophilicity without any prior UV irradiation. In addition, the presence of bundles of almost parallel NWs led to the formation of arrays of microcapacitors, which showed stable dielectric performance. The fabrication of single-crystalline, oriented, self-assembled TMSAs with bundles of titania nanowires as their building blocks deposited on transparent conducting oxide (TCO) substrates has vast potential in the area of photoelectrochemical research.