3 research outputs found
Carborane-thiol protected copper nanoclusters: stimuli-responsive materials with tunable phosphorescence
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Direct Measurement of Helicoid Surface States in RhSi Using Nonlinear Optics.
Despite the fundamental nature of the edge state in topological physics, direct measurement of electronic and optical properties of the Fermi arcs of topological semimetals has posed a significant experimental challenge, as their response is often overwhelmed by the metallic bulk. However, laser-driven currents carried by surface and bulk states can propagate in different directions in nonsymmorphic crystals, allowing for the two components to be easily separated. Motivated by a recent theoretical prediction G. Chang et al., Phys. Rev. Lett. 124, 166404 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.166404, we have measured the linear and circular photogalvanic effect currents deriving from the Fermi arcs of the nonsymmorphic, chiral Weyl semimetal RhSi over the 0.45-1.1 eV incident photon energy range. Our data are in good agreement with the predicted spectral shape of the circular photogalvanic effect as a function of photon energy, although the direction of the surface photocurrent departed from the theoretical expectation over the energy range studied. Surface currents arising from the linear photogalvanic effect were observed as well, with the unexpected result that only two of the six allowed tensor element were required to describe the measurements, suggesting an approximate emergent mirror symmetry inconsistent with the space group of the crystal
A Metal-Free Covalent Organic Polymer for Electrocatalytic Hydrogen Evolution
Metal-free catalysis
for electrocatalytic hydrogen evolution from
water is very demanding for the production of sustainable and clean
fuel. Herein, we report the synthesis of a porphyrin-based metal-free
covalent organic polymer (TpPAM) through a simple condensation between
triformyl phloroglucinol (Tp) and 5,10,15,20-tetraÂ(4-aminophenyl)-21<i>H</i>,23<i>H</i>-porphyrin (PAM). The as-prepared
porous TpPAM exhibited superior activity for the hydrogen evolution
reaction (HER) current density of 10 mA cm<sup>–2</sup> at
a low overpotential of 250 mV and a small Tafel slope of 106 mV decade<sup>–1</sup>, which are better than those of related metal-free
electrocatalysts. The high HER activity of TpPAM was investigated
in-depth via theoretical density functional theory (DFT) calculations.
The theoretical findings were correlated with the experimental results,
and these were in good agreement for high HER catalytic efficiency
of the porous TpPAM polymer. The Faradaic efficiency of the TpPAM-based
electrode was found to be 98%, which is very close to the ideal value
of 100%, reflecting its potential for practical implementation. Moreover,
the as-synthesized catalyst showed good stability by retaining 91%
of the initial current density after 1000 cycles