A critical routine for memristors applied to neuromorphic computing is to approximate synaptic dynamic behaviors as closely as possible. A type of homogenous bilayer memristor with a structure of W/HfO y /HfO x /Pt is designed and constructed in this paper. The memristor replicates the structure and oxygen vacancy (V O ) distribution of a complete synapse and its Ca 2+ distribution, respectively, after the forming process. The detailed characterizations of its atomic structure and phase transformation in and near the conductive channel demonstrate that the crystallite kinetics are adaptively coupled with the V O migration prompted by directional external bias. The extrusion (injection) of the V O s and the subsequent crystallite coalescence (separation), phase transformation, and alignment (misalignment) resemble closely the Ca 2+ flux and neurotransmitter dynamics in chemical synapses. Such adaptation and similarity allow the memristor to emulate diverse synaptic plasticity. This study supplies a kinetic process of conductive channel theory for bilayer memristors. In addition, our memristor has very low energy consumption (5-7.5 fJ per switching for a 0.5 µm diameter device, compatible with a synaptic event) and is therefore suitable for large-scale integration used in neuromorphic networks.
A series of silica supported Pd (Pd/SiO
2
) catalysts
were prepared in various HCl concentrations (
C
HCl
) of the impregnation solution with different electrostatic
interactions between Pd precursor and support, and their catalytic
properties were evaluated by the selective hydrogenation of nitrile
butadiene rubber (NBR). The results show that with the
C
HCl
increasing from 0.1 to 5 M, the particle size of Pd
nanoparticles dramatically decreases from 24.2 to 5.1 nm and stabilizes
at ∼5 nm when
C
HCl
is higher than
2 M. Using the catalysts prepared with a high
C
HCl
(>2 M), an excellent hydrogenation degree (HD) of ∼94%
with 100% selectivity to C=C can be acquired under mild conditions.
Interestingly, the HD could be remarkably increased from 65 to 92%
by increasing only
C
Cl
–
from 0.1 to 2 M with the addition of NaCl while keeping
C
H
+
at 0.1 M. This is because
PdCl
4
2–
is the predominant existing form
of precursor at high
C
Cl
–
, which has a strong electrostatic attraction with the positively
charged support favorable for the formation of small-sized Pd nanoparticles
over silica. Notably, Pd leaching behavior during the hydrogenation
reaction is closely related to
C
H
+
, and the higher the
C
H
+
, the less Pd residues are detected in the
hydrogenated NBR. Our contribution is to provide a facile strategy
to synthesize effective and stable Pd/SiO
2
catalysts via
adjusting the electrostatic interaction, which exhibits a high activity
and selectivity for NBR hydrogenation.
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