Iron, nitrogen‐codoped carbon (Fe−N−C) nanocomposites have emerged as viable electrocatalysts for the oxygen reduction reaction (ORR) due to the formation of FeNxCy coordination moieties. In this study, results from first‐principles calculations show a nearly linear correlation of the energy barriers of key reaction steps with the Fe magnetic moment. Experimentally, when single Cu sites are incorporated into Fe−N−C aerogels (denoted as NCAG/Fe−Cu), the Fe centers exhibit a reduced magnetic moment and markedly enhanced ORR activity within a wide pH range of 0–14. With the NCAG/Fe−Cu nanocomposites used as the cathode catalyst in a neutral/quasi‐solid aluminum–air and alkaline/quasi‐solid zinc–air battery, both achieve a remarkable performance with an ultrahigh open‐circuit voltage of 2.00 and 1.51 V, large power density of 130 and 186 mW cm−2, and good mechanical flexibility, all markedly better than those with commercial Pt/C or Pt/C‐RuO2 catalysts at the cathode.
Biological
applications of poly(vinyl alcohol) hydrogels (PVA)
are limited because the pure polymer has low hardness and poor mechanical
properties. The quality of most PVA hydrogels can be enhanced by addition
of molecules that form strong covalent or noncovalent cross-links
between the PVA chains. Natural materials as cross-linking agents
are attracting interest because of their degradability, cell compatibility,
and environmental friendliness. Herein, we report the use of hydrophobic
luteolin (LUT) in the facile fabrication of a type of hybrid PVA hydrogel.
Even at low LUT concentration (0.04 wt %), the strong hydrogen bonding
formed between PVA and LUT caused gelation at 25 °C after the
reagents were mixed at high temperature. The effects of LUT concentration,
freezing and thawing, and pH on hydrogels mechanics were evaluated,
and a possible mechanism of hydrogel formation was deduced. Notably,
after freezing and thawing, the elongation (600%) and tensile strength
(0.812 MPa) of the PVA/LUT hydrogels were superior to those of common
PVA hydrogels. Our study reveals a hydrophobic biocrosslinker for
PVA hydrogels that has potential applications in medicine. We expect
that this contribution will promote screening of other biocrosslinkers
for PVA hydrogels.
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