Surface Electronegativity as an Activity Descriptor to Screen Oxygen Evolution Reaction Catalysts of Li-O2 Battery

Electrostatic and Electronic Effects on Doped Nickel Oxide Nanofilms for Water Oxidation

An ideal water-splitting electrocatalyst is inexpensive, abundant, highly active, stable, selective, and durable. The anodic oxygen evolution reaction (OER) is the main bottleneck for H2 production with a complex and not fully resolved mechanism, slow kinetics, and high overpotential. Nickel oxide-based catalysts (NiOx) are highly active and cheaper than precious metal catalysts. However, rigorous catalyst tests and DFT calculations are still needed to rationally optimize NiOx catalysts. In this work, we combine plasma-enhanced atomic layer deposition (PE-ALD) and density functional theory (DFT) to address the role of dopants in promoting NiOx OER activity. Ultrathin films of NiOx doped with Zn2+, Al3+, and Sn4+ presented improved intrinsic activity, stability, and durability for the OER. The results show a low to high catalytic performance of ZnNiOx < NiOx < AlNiOx < SnNiOx, which we attribute to an increase in the concentration of valence band (VB) holes combined with conduction band (CB) electron conductivity, characterized by electrochemical impedance spectroscopy (EIS). The influence of doping on the electronic structure and catalytic activity was investigated using advanced characterization techniques and density functional theory (DFT) calculations (PEB0/pob-TZVP). DFT complements the experimental results, showing that the dopant charge states and orbital hybridization enhance the OER by improving the charge carrier concentration and mobility, thus allowing optimal binding energies and charge dynamics and delocalization. Our findings demonstrate the potential of PE-ALD-doped nanofilms NiOx and DFT to rationally design and develop catalysts for sustainable energy applications.

Application of South African heulandite (HEU) zeolite for the adsorption and removal of Pb2+ and Cd2+ ions from aqueous water solution: Experimental and computational study

The capacity of South African Heulandite (HEU) zeolite to remove Pb2+ and Cd2+ ions from aqueous solution was investigated using batch experiments and molecular simulations studies. The effect of different factors on the adsorption of these ions onto the zeolite was investigated; contact time, initial metal ion concentration and the amount of HEU adsorbent. Molecular simulations was done using Monte Carlo and density functional theory. Experimental results obtained indicate that the maximum adsorption for the two ions occur at pH 5 and after 240 min of contact time. The percent removal based on contact time of Pb2+ and Cd2+ ions from water by the heulandite zeolite were 99.7 and 76.7 %, respectively. The adsorption of two metal ions onto the HEU zeolite follows the Langmuir adsorption isotherm. From the molecular simulation findings, the adsorption of Pb2+ ions onto the HEU window is equidistant from the two adjacent oxygen atoms within the HEU structure while the Cd2+ ion is adsorbed in the upper left side of the 8-ring HEU window. It was observed that the performance of the zeolite can significantly be improved by doping with germanium, aluminum, thallium indium, and sodium cations. These results indicate that the application of HEU zeolite as an adsorbent holds a great promise in heavy metal removal from aqueous solutions.

Localized charge-induced ORR/OER activity in doped fullerenes for Li-air battery applications

Non-aqueous Li-air batteries have garnered significant interest in recent years. The key challenge lies in the development of efficient catalysts to overcome the sluggish kinetics associated with the oxygen reduction reaction (ORR) during discharge and the oxygen evolution reaction (OER) during charging at the cathode. In this work, we conducted a comprehensive study on B/N-doped and BN co-doped fullerenes using first-principles analysis. Our results show significant changes in the geometries, electronic properties, and catalytic behaviors of doped and co-doped fullerenes. The coexistence of boron and nitrogen boosts the formation energy, enhancing stability compared to pristine and single-doped structures. C179B exhibits minimal overpotentials (0.98 V), implying superior catalyst performance for ORR and OER in LABs and significantly better performance than Pt (111) (3.48 V) and standard graphene (3.51 V). The electron-deficient nature of the B atom makes it provide its vacant 2pz orbital for conjugation with the p-electrons of nearby carbon atoms. Consequently, boron serves as a highly active site due to the localization of positive charge, which improves the adsorption of intermediates through oxygen atoms. Moreover, the higher activity of B-doped systems than N-doped systems in lithium-rich environments is opposite to the observed trend in the reported PEM fuel cells. This work introduces doped and co-doped fullerenes as LAB catalysts, offering insights into their tunable ORR/OER activity via doping with various heteroatoms and fullerene size modulation.

Active learning guides discovery of a champion four-metal perovskite oxide for oxygen evolution electrocatalysis

Multi-metal oxides in general and perovskite oxides in particular have attracted considerable attention as oxygen evolution electrocatalysts. Although numerous theoretical studies have been undertaken, the most promising perovskite-based catalysts continue to emerge from human-driven experimental campaigns rather than data-driven machine learning protocols, which are often limited by the scarcity of experimental data on which to train the models. This work promises to break this impasse by demonstrating that active learning on even small datasets-but supplemented by informative structural-characterization data and coupled with closed-loop experimentation-can yield materials of outstanding performance. The model we develop not only reproduces several non-obvious and actively studied experimental trends but also identifies a composition of a perovskite oxide electrocatalyst exhibiting an intrinsic overpotential at 10 mA cm-2oxide of 391 mV, which is among the lowest known of four-metal perovskite oxides.

Experimental and Computational Approaches for the Structural Study of Novel Ca-Rich Zeolites from Incense Stick Ash and Their Application for Wastewater Treatment

At present, chemical Si/Al sources are mainly used as precursor materials for the manufacturing of zeolites. Such precursor materials are quite expensive for commercial synthesis. Here, we have reported the synthesis of Ca-based zeolite from incense stick ash waste by the alkali-treatment method for the first time. Incense stick ash (ISA) was used as a precursor material for the synthesis of low Si zeolites by the alkali-treatment method. The as-synthesized zeolites were characterized by various instruments like particle size analyzer (PSA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray fluorescence (XRF). FTIR and XRD helped in the identification of the microstructure and crystalline nature of the zeolites and also confirmed the synthesis of Ca-based zeolite with two thetas at 25.7°. The microscopic analysis by FESEM and TEM exhibited that the size of synthesized Ca-rich zeolites varies from 200 to 700 nm and they are aggregated and cuboidal in shape. Additionally, structural, electronic, and density of states’ characteristics of gismondine (Ca2Al4Si4O16·9H2O) structures were evaluated by computational simulations (first principle, density functional theorem). The structural optimization of structures was carried out in the first stage under the lowest condition of total energy and forces acting on atoms for the lattice constant, as well as the available experimental and theoretical findings. The present research approach predicted the transformation of ISA waste into a value-added mineral, i.e., zeolite, which was further used for the removal of both heavy metals and alkali metals from fly ash-based wastewater using inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Photocatalytic Conversion of Methane: Recent Advancements and Prospects

Abundant and affordable methane is not only a high-quality fossil fuel, it is also a raw material for the synthesis of value-added chemicals. Solar-energy-driven conversion of methane offers a promising approach to directly transform methane to valuable energy sources under mild conditions, but remains a great challenge at present. In this Review, recent advances in the photocatalytic conversion of methane are systematically summarized. Insights into the construction of effective semiconductor-based photocatalysts from the perspective of light-absorption units and active centers are highlighted and discussed in detail. The performance of various photocatalysts in the conversion of methane is presented, with the photooxidation classified according to the oxidant systems. Lastly, challenges and future perspectives in the photocatalytic oxidation of methane are described.

Monodispersed Ruthenium Nanoparticles on Nitrogen-Doped Reduced Graphene Oxide for an Efficient Lithium-Oxygen Battery

Lithium-oxygen batteries with ultrahigh energy densities have drawn considerable attention as next-generation energy storage devices. However, their practical applications are challenged by sluggish reaction kinetics aimed at the formation/decomposition of discharge products on battery cathodes. Developing effective catalysts and understanding the fundamental catalytic mechanism are vital to improve the electrochemical performance of lithium-oxygen batteries. Here, uniformly dispersed ruthenium nanoparticles anchored on nitrogen-doped reduced graphene oxide are prepared by using an in situ pyrolysis procedure as a bifunctional catalyst for lithium-oxygen batteries. The abundance of ruthenium active sites and strong ruthenium-support interaction enable a feasible discharge product formation/decomposition route by modulating the surface adsorption of lithium superoxide intermediates and the nucleation and growth of lithium peroxide species. Benefiting from these merits, the electrode provides a drastically increased discharge capacity (17,074 mA h g^-1), a decreased charge overpotential (0.51 V), and a long-term cyclability (100 cycles at 100 mA g^-1). Our observations reveal the significance of the dispersion and coordination of metal catalysts, shedding light on the rational design of efficient catalysts for future lithium-oxygen batteries.