The proper choice of nonprecious transition metals as single atom catalysts (SACs) remains unclear for designing highly efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, reported is an activity correlation with catalysts, electronic structure, in order to clarify the origin of reactivity for a series of transition metals supported on nitrogen‐doped graphene as SACs for HER by a combination of density functional theory calculations and electrochemical measurements. Only few of the transition metals (e.g., Co, Cr, Fe, Rh, and V) as SACs show good catalytic activity toward HER as their Gibbs free energies are varied between the range of –0.20 to 0.30 eV but among which Co‐SAC exhibits the highest electrochemical activity at 0.13 eV. Electronic structure studies show that the energy states of active valence dz2 orbitals and their resulting antibonding state determine the catalytic activity for HER. The fact that the antibonding state orbital is neither completely empty nor fully filled in the case of Co‐SAC is the main reason for its ideal hydrogen adsorption energy. Moreover, the electrochemical measurement shows that Co‐SAC exhibits a superior hydrogen evolution activity over Ni‐SAC and W‐SAC, confirming the theoretical calculation. This systematic study gives a fundamental understanding about the design of highly efficient SACs for HER.
Robust and photostable single photon emitters (SPEs) underpin a number of promising quantum information science and technologies. [1][2][3][4] Solid-state quantum light sources are highly sought after for their ease of integration into onchip architectures, and rapid progress has been made recently with a variety of solidstate sources such as quantum dots, [5,6] color centers in diamond, [7,8] silicon carbide, [9,10] rare-earth materials, [11] carbon nanotubes, [12] and layered van der Waals materials. [3] One of the most promising candidates are quantum emitters in hexagonal boron nitride (hBN), which have recently emerged as a robust solid-state platform capable of hosting bright, [13][14][15][16][17] linearly polarized, [13,18] and optically stable SPEs operating at room temperature with high photon purity. [19,20] While the zerophonon lines (ZPLs) of hBN quantum emitters have been known to display a wide spread of energies (≈1.6-2.4 eV), implying the existence of multiple defect species, [15,18,[21][22][23] recent progress utilizing chemical vapor deposition (CVD) has shown that this spread can be reduced to ≈100 meV. [24,25] This reduced ZPL energy distribution is useful both for applications and for basic studies of the defects responsible for the emissions. However, to fully understand and exploit the diversity of emissions reported in hBN further advances in controlling the observed emission spectra and emitter density are required.In order to target the incorporation of particular structural defects during CVD growth, a method to modify the dominant defect formation processes is required. In situ monitoring of hBN growth on Cu has clarified that hBN growth is subject to complex interaction between the precursor species, and the catalyst surface/bulk. [26] As a result, controlling the interactions between the precursor species and the catalyst is critical to achieve highly crystalline hBN growth, but also offers a promising avenue to controlled defect engineering during CVD growth of hBN. In other material systems such as InAs/ GaAs quantum dots modifying catalyst properties such as lattice mismatch during epitaxial growth has been definitively linked to defect creation. [27] Similarly graphene is known to be dependent of the interactions with the catalyst bulk/surface, where growth depends strongly on the relative phase of the catalyst and the supply of carbon in and out of the catalyst, controlling both defect formation and density. [28,29] Despite added complications for CVD growth of hBN, especially due to Luminescent defects in hexagonal boron nitride (hBN) have emerged as promising single photon emitters (SPEs) due to their high brightness and robust operation at room temperature. The ability to create such emitters with well-defined optical properties is a cornerstone toward their integration into on-chip photonic architectures. Here, an effective approach is reported to fabricate hBN SPEs with desired emission properties in distinct spectral regions via the manipulation of boron diffusion through ...
With the increasing demand for wearable and implantable electronics, structured sensors with exceptional performance in sensitivity, stretchability, biocompatibility, and adhesion to the biological surfaces have become essential.
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