Enhanced OER catalytic activity of single metal atoms supported by the pentagonal NiN2 monolayer: insight from density functional theory calculations.

Two-dimensional material-supported single metal atom catalysts have been extensively studied and proved effective in electrocatalytic reactions in recent years. In this work, we systematically investigate the OER catalytic properties of single metal atoms supported by the NiN2 monolayer. Several typical transition metals with high single atom catalytic activity, such as Fe, Co, Ru, Rh, Pd, Ir, and Pt, were selected as catalytic active sites. The energy calculations show that transition metal atoms (Fe, Co, Ru, Rh, Pd, Ir, and Pt) are easily embedded in the NiN2 monolayer with Ni vacancies due to the negative binding energy. The calculated OER overpotentials of Fe, Co, Ru, Rh, Pd, Ir and Pt embedded NiN2 monolayers are 0.92 V, 0.47 V, 1.13 V, 0.66 V, 1.25 V, 0.28 V, and 0.94 V, respectively. Compared to the 0.57 V OER overpotential of typical OER noble metal catalysts IrO2, Co@NiN2 and Ir@NiN2 exhibit high OER catalytic activity due to lower overpotential, especially for Ir@NiN2. The high catalytic activity of the Ir embedded NiN2 monolayer can be explained well by the d-band center model. It is found that the adsorption strength of the embedded TM atoms with intermediates follows a linear relationship with their d-band centers. Besides, the overpotential of the Ir embedded NiN2 monolayer can be further reduced to 0.24 V under -2% biaxial strain. Such findings are expected to be employed in more two-dimensional material-supported single metal atom catalyzed reactions.

Smart Textiles Based on MoS2 Hollow Nanospheres for Personal Thermal Management.

Two-dimensional transition metal dichalcogenides are of particular interest in high-performance photothermal conversion, yet there remains a huge challenge in their practical application in smart textiles for healthcare, energy, and personal protection. Herein, we controllably prepared MoS2 hollow nanospheres with a high photothermal conversion efficiency of 36% via a microemulsion-hydrothermal method, which was further applied to construct photothermal fibers for personal thermal management after a hot-blast dip-drying process. Because of the prominent photothermal effect, the temperature of the photothermal fibers sharply increases from the room temperature value of 25.0 to 55.5 °C in 60 s under near-infrared illumination with a power density of 500 W/cm2. Furthermore, the photothermal fiber pad demonstrated an obvious temperature enhancement of 38.0 °C from a skin temperature of 22.0 °C after it was irradiated by natural sunlight for 60 s. Significantly, the antibacterial elimination rates of the photothermal fibers for Escherichia coli and Staphylococcus aureus are ∼99.9 and ∼99.8%, respectively. This strategy affords an avenue toward the practical application of photothermal materials in smart fibers for personal thermoregulation.