Experimental and Theoretical Insights of Anion Regulation in MOF-Derived Ni-Co-Based Nanosheets for Supercapacitors and Anion Exchange Membrane Water Electrolyzers.

The anionic components have a significant role in regulating the electrochemical properties of mixed transition-metal (MTM)-based materials. However, the relationship between the anionic components and their inherent electrochemical properties in MTM-based materials is still unclear. Herein, we report the anion-dependent supercapacitive and oxygen evolution reaction (OER) properties of in situ grown binary Ni-Co-selenide (Se)/sulfide (S)/phosphide (P) nanosheet arrays (NAs) over nickel foam starting from MOF-derived Ni-Co layered double hydroxide precursors. Among them, the Ni-Co-Se NAs exhibited the best specific capacity (289.6 mA h g-1 at 4 mA cm-2). Furthermore, a hybrid device constructed with Ni-Co-Se NAs delivered an excellent energy density (74 W h kg-1 at 525 W kg-1) and an ultra-high power density (10 832 W kg-1 at 46 W h kg-1) with outstanding durability (∼94%) for 10 000 cycles. Meanwhile, the Ni-Co-Se NAs showed superior electrocatalytic OER outputs with the lowest overpotential (235 mV at 10 mA cm-2) and Tafel slope. In addition, Ni-Co-Se NAs outperformed IrO2 as an anode in an anion exchange membrane water electrolyzer at a high current density (>1.0 A cm-2) and exhibited a stable performance up to 48 h with a 99% Faraday efficiency. Theoretical analyses validate that the Se promotes OH adsorption and improves the electrochemical activity of the Ni-Co-Se through a strong electronic redistribution/hybridization with an active metal center due to its valence 4p and inner 3d orbital participations. This study will provide in-depth knowledge of bifunctional activities in MTM-based materials with different anionic substitutions.

Morphology-dependent adsorption energetics of Ru nanoparticles on hcp-boron nitride (001) surface - a first-principles study.

Active B5-sites on Ru catalysts can be exploited for various catalytic applications; in particular, the epitaxial formation of Ru nanoparticles with hexagonal planar morphologies on hexagonal boron nitride sheets increases the number of active B5-sites along the nanoparticle edges. The energetics of adsorption of Ru nanoparticles on hexagonal boron nitride were investigated using density functional theory calculations. Then, to understand the fundamental reason for this morphology control, adsorption studies and charge density analysis were performed on fcc and hcp Ru nanoparticles heteroepitaxially formed on a hexagonal boron nitride support. Among the explored morphologies, hcp Ru(0001) nanoparticles exhibited the highest adsorption strength of -31.656 eV. To verify the hexagonal planar morphologies of the hcp-Ru nanoparticles, three different hcp-Ru(0001) nanoparticles-Ru60, Ru53, and Ru 41-were adsorbed onto the BN substrate. In agreement with the experimental studies, the hcp-Ru60 nanoparticles exhibited the highest adsorption energy owing to their long-range and perfect hexagonal match with the interacting hcp-BN(001) substrate.

Unveiling the positive effect of mineral induced natural organic matter (NOM) on catalyst properties and catalytic dechlorination performance: An experiment and DFT study.

Herein, we report the significant effects of natural organic matter contained in natural zeolite (Z-NOM) on the physicochemical characteristics of a Ni/Fe@natural zeolite (NF@NZ) catalyst and its decontamination performance toward the dechlorination of trichloroethylene (TCE). Z-NOM predominantly consists of humic-like substances and has demonstrable utility in the synthesis of bimetallic catalysts. Compared to NF@NZ600C (devoid of Z-NOM), NF@NZ had increased dispersibility and mobility and showed significant enhancement in the catalytic dechlorination of TCE owing to the encapsulation of Ni0/Fe0 nanoparticles by Z-NOM. The results of corrosion experiments, spectroscopic analyses, and H2 production experiments confirmed that Ni0 acted as an efficient cocatalyst with Fe0 to enhance the dechlorination of TCE to ethane, and Z-NOM-capped Ni0 showed improved adsorption of TCE and atomic hydrogen on their reactive sites and oxidation resistance. The density functional theory (DFT) studies have substantiated the improved adsorption of TCE due to the presence of NOM (especially by COOH structure) and the enhanced charge density at the Ni site in the Ni/Fe bimetal alloy for the stronger adsorption of hydrogen atoms that ultimately enhanced the TCE reduction reaction. These findings illustrate the efficiency of NOM containing natural minerals toward the synthesis of bimetallic catalysts for practical applications.

Role of Chemical Structure of Support in Enhancing the Catalytic Activity of a Single Atom Catalyst Toward NRR: A Computational Study.

Using the periodic density functional theory-based methodology, we propose a potential catalytic system for dinitrogen activation, viz., single metal atoms (Mo, Fe, and V) supported on graphene-based sheets. Graphene-based sheets show an excellent potential toward the anchoring of single atoms on them (Mo, Fe, and V) with adsorption energies ranging between 1.048 and 10.893 eV. Factors such as defects and BN doping are noted to enhance the adsorption energies of single metal atoms on the support. The adsorption of a dinitrogen molecule on metal atom-anchored graphene-based supports is seen to be highly favorable, ranging between 0.620 and 2.278 eV. The adsorption is driven through a direct hybridization between the d orbitals of the metal atom (Mo, Fe, and V) on the support and the p orbital of the molecular nitrogen. Noticeably, BN-doped graphene supporting a single metal atom (Mo, Fe, and V) activates the N2 molecule with a red shift in the N-N stretching frequency (1,597 cm-1 as compared to 2,330 cm-1 in the free N2 molecule). This red shift is corroborated by an increase in the N-N bond length (1.23 Å from 1.09 Å) and charge transfer to an N2 molecule from the catalyst.