Two-Dimensional Graphdiyne-Confined Platinum Catalyst for Hydrogen Evolution and Oxygen Reduction Reactions.

Pt-based materials are the state-of-the-art catalysts for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR); however, there is still much room to improve the catalytic activity and enhance the stability of Pt-based catalysts. In this work, two-dimensional (2D) graphdiyne (GDY) with uniform distributed pores was applied to cover the Pt surface for catalyzing HER and ORR through density functional theory (DFT) calculations. The 2D confinement induced by GDY was found to improve the catalytic performance of the Pt catalyst from three aspects: (1) the 2D covering layer increases the stability of the Pt catalyst through forming the heterogeneous interface of GDY/Pt(111); (2) GDY/Pt(111) shows better catalytic activities of HER and ORR, with the smaller average overpotential values of 0.26 and 0.51 V, respectively, compared with those (0.29 V for HER, 0.62 V for ORR) on the Pt catalyst; (3) the confinement effect of GDY weakens the adsorption energy of CO to -1.81 eV (average value) from -2.14 eV on Pt(111), inhibiting CO poisoning. This work sheds new light on 2D confinement effects for HER and ORR, which opens up a new strategy for improving the catalytic performance of Pt-based catalysts.

Transition metal-N4 embedded black phosphorus carbide as a high-performance bifunctional electrocatalyst for ORR/OER.

Designing highly active electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important challenge in energy conversion and storage technology. In this work, based on computational screening over doping of 23 kinds of transition metals (TMs), we use first-principles study to explore the ORR and OER activity of TM-N4 embedded black phosphorus carbide monolayer (b-PC). The results show that its catalytic performance highly depends on the number of electrons in the d orbital and the number of valence electrons of introduced TM atom. Moreover, we found that Co-N4-bPC (ηORR = 0.31 V; ηOER = 0.22 V), Rh-N4-bPC (ηORR = 0.33 V; ηOER = 0.62 V), and Ir-N4-bPC (ηORR = 0.21 V; ηOER = 0.21 V) can be promising candidates as bifunctional catalysts for both the ORR and OER and can be comparable or superior to TM-N4-graphene in terms of overpotential. They experience no structural distortion at 500 K. Moreover, the exfoliation energy of b-PC is lower than that of graphene, and these three promising candidates show much lower formation energy than TM-N4-graphene. Our study provides a systematical method for designing and developing high performance 2D material-based single atom catalysts (SACs) beyond graphene.

Role of graphene in enhancing the mechanical properties of TiO2/graphene heterostructures.

Graphene has been integrated in many heterogeneous structures in order to take advantage of its superior mechanical properties. However, the complex mechanical response of heterogeneous films incorporating graphene is not well understood. Here, we studied the mechanical behavior of atomic layer deposition (ALD) synthesized TiO2/graphene, as a representative building block of a typical composite, to understand the mechanical behavior of heterostructures using an experiment-computational approach. The inclusion of graphene was found to significantly enhance the Young's modulus of TiO2/graphene hetero-films for films below a critical thickness of 3 nm, beyond which the Young's modulus approaches that of pure TiO2 film. A rule-of-mixtures was found to reasonably estimate the modulus of the TiO2/graphene hetero-film. Experimentally, these hetero-films were observed to fail via brittle fracture. Complimentary density functional theory and finite element modeling demonstrates strong adhesion at the graphene TiO2 interface and that graphene serves as a reinforcement, providing the hetero-film with an ability to sustain significantly high stresses at the point of failure initiation. The results and methodology described herein can contribute to the rational design of strong and reliable ultrathin hetero-films for versatile applications.

Photothermal Catalyst Engineering: Hydrogenation of Gaseous CO2 with High Activity and Tailored Selectivity.

This study has designed and implemented a library of hetero-nanostructured catalysts, denoted as Pd@Nb2O5, comprised of size-controlled Pd nanocrystals interfaced with Nb2O5 nanorods. This study also demonstrates that the catalytic activity and selectivity of CO2 reduction to CO and CH4 products can be systematically tailored by varying the size of the Pd nanocrystals supported on the Nb2O5 nanorods. Using large Pd nanocrystals, this study achieves CO and CH4 production rates as high as 0.75 and 0.11 mol h-1 gPd-1, respectively. By contrast, using small Pd nanocrystals, a CO production rate surpassing 18.8 mol h-1 gPd-1 is observed with 99.5% CO selectivity. These performance metrics establish a new milestone in the champion league of catalytic nanomaterials that can enable solar-powered gas-phase heterogeneous CO2 reduction. The remarkable control over the catalytic performance of Pd@Nb2O5 is demonstrated to stem from a combination of photothermal, electronic and size effects, which is rationally tunable through nanochemistry.