The thermoelectric figure-of-merit (ZT) for GeTe powder is able to be raised from ∼0.8 to 1.37 at high temperature near ∼500 °C by tuning the Ge vacancy level through a reversible in situ route.
An optimized two-step melt-quenching synthesis method is proposed for GeTe to show a highly reproducible high ZT ∼ 2.35 at 800 K (in Ge0.9Sb0.1Te) through simultaneous carrier concentration and microstructural control.
Tuning
the electronic structure of perovskite oxides via aliovalent
substitution is a promising strategy to attain inexpensive and efficient
electrocatalysts for energy conversion and storage devices. Herein,
following the d-band center positions and using a simple sol–gel
method followed by a pyrolysis step, LaNi1–x
Co0.5x
Fe0.5x
O3 (LNFCO-x; x = 0.0, 0.4, 0.5, and 0.6) electrocatalysts are designed and synthesized
for oxygen redox reactions in 1 M KOH. Among them, LNFCO-0.5 has exhibited
the lowest overpotential and the highest charge transfer kinetics
in oxygen redox reactions. Overall, a 90 mV lower overpotential was
observed in oxygen redox activity of LNFCO-0.5 compared to that of
pristine LaNiO3. The mass activity of LNFCO-0.5 in the
oxygen reduction reaction (at 0.7 V vs RHE) and oxygen evolution reaction
(1.60 V vs RHE) was calculated to be 2.5 and 2.13 times higher than
that of LaNiO3, respectively. The bifunctionality index
(potential difference between the oxygen evolution at a current density
of 10 mA cm–2 and the oxygen reduction at a current
density of −1 mA cm–2) of LNFCO-0.5 was found
to be 0.98. The substitution of Fe and Co for the Ni-site shifted
the d-band center close to the Fermi level, which can increase the
binding strength of the *OH intermediate in the rate-determining step.
Also, the surface was enriched with Fe3+Δ, Co3+, and partially oxidized Ni3+ states, which is
susceptible to tune the eg-orbital filling for superior
oxygen redox activity.
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