Exploring low-cost and high-performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe3 C nanoparticles encapsulated in mesoporous Fe-N-doped carbon nanofibers, which is synthesized by a cost-effective method using carbonaceous nanofibers, pyrrole, and FeCl3 as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of -0.02 V and half-wave potential of -0.140 V) closely comparable to the state-of-the-art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.
Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe3C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl3 as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of −0.02 V and half‐wave potential of −0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.
Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high-energy density Li metal-based batteries. Herein, a novel tri-layer separator design that significantly enhances the cycling stability and safety of Li metal-based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper-making process, is directly laminated on each side of a plasma-treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri-layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose-based tri-layer separator design thus significantly facilitates the realization of high-energy density Li metal-based batteries.
Despite
a large number of publications describing biosensors based
on electrochemical impedance spectroscopy (EIS), little attention
has been paid to the stability and reproducibility issues of the sensor
interfaces. In this work, the stability and reproducibility of faradaic
EIS analyses on the aptamer/mercaptohexanol (MCH) self-assembled monolayer
(SAM)-functionalized gold surfaces in ferri- and ferrocyanide solution
were systematically evaluated prior to and after the aptamer-probe
DNA hybridization. It is shown that the EIS data exhibited significant
drift, and this significantly affected the reproducibility of the
EIS signal of the hybridization. As a result, no significant difference
between the charge transfer resistance (R
CT) changes induced by the aptamer-target DNA hybridization and that
caused by the drift could be identified. A conditioning of the electrode
in the measurement solution for more than 12 h was required to reach
a stable R
CT baseline prior to the aptamer-probe
DNA hybridization. The monitored drift in R
CT and double layer capacitance during the conditioning suggests that the MCH SAM on the gold surface
reorganized to a thinner but more closely packed layer. We also observed
that the hot binding buffer used in the following aptamer-probe DNA
hybridization process could induce additional MCH and aptamer reorganization,
and thus further drift in R
CT. As a result,
the R
CT change caused by the aptamer-probe
DNA hybridization was less than that caused by the hot binding buffer
(blank control experiment). Therefore, it is suggested that the use
of high temperature in the EIS measurement should be carefully evaluated
or avoided. This work provides practical guidelines for the EIS measurements.
Moreover, because SAM-functionalized gold electrodes are widely used
in biosensors, for example, DNA sensors, an improved understanding
of the origin of the observed drift is very important for the development
of well-functioning and reproducible biosensors.
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