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"Zeng, Jie"
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Graphene/MoS2/FeCoNi(OH)x and Graphene/MoS2/FeCoNiPx multilayer-stacked vertical nanosheets on carbon fibers for highly efficient overall water splitting
Development of excellent and cheap electrocatalysts for water electrolysis is of great significance for application of hydrogen energy. Here, we show a highly efficient and stable oxygen evolution reaction (OER) catalyst with multilayer-stacked hybrid structure, in which vertical graphene nanosheets (VGSs), MoS
2
nanosheets, and layered FeCoNi hydroxides (FeCoNi(OH)
x
) are successively grown on carbon fibers (CF/VGSs/MoS
2
/FeCoNi(OH)
x
). The catalyst exhibits excellent OER performance with a low overpotential of 225 and 241 mV to attain 500 and 1000 mA cm
−2
and small Tafel slope of 29.2 mV dec
−1
. Theoretical calculation indicates that compositing of FeCoNi(OH)
x
with MoS
2
could generate favorable electronic structure and decrease the OER overpotential, promoting the electrocatalytic activity. An alkaline water electrolyzer is established using CF/VGSs/MoS
2
/FeCoNi(OH)
x
anode for overall water splitting, which generates a current density of 100 mA cm
−2
at 1.59 V with excellent stability over 100 h. Our highly efficient catalysts have great prospect for water electrolysis.
While water-splitting electrocatalysis offers a renewable means for carbon-neutral energy production, it is a challenge to design efficient, active, and stable catalysts. Here, authors prepare multilayer composite nanosheet materials as bifunctional water-splitting electrocatalysts.
Journal Article
Water enables mild oxidation of methane to methanol on gold single-atom catalysts
As a 100% atom-economy process, direct oxidation of methane into methanol remains as a grand challenge due to the dilemma between activation of methane and over-oxidation of methanol. Here, we report that water enabled mild oxidation of methane into methanol with >99% selectivity over Au single atoms on black phosphorus (Au
1
/BP) nanosheets under light irradiation. The mass activity of Au
1
/BP nanosheets reached 113.5 μmol g
catal
−1
in water pressured with 33 bar of mixed gas (CH
4
:O
2
= 10:1) at 90 °C under light irradiation (1.2 W), while the activation energy was 43.4 kJ mol
−1
. Mechanistic studies revealed that water assisted the activation of O
2
to generate reactive hydroxyl groups and •OH radicals under light irradiation. Hydroxyl groups reacted with methane at Au single atoms to form water and CH
3
* species, followed by oxidation of CH
3
* via •OH radicals into methanol. Considering the recycling of water during the whole process, we can also regard water as a catalyst.
It is important but challenging to oxidize methane by O
2
into methanol under ambient conditions. Here, the authors achieved mild oxidation of methane into methanol over Au single atoms on black phosphorus nanosheets with the help of water under light irradiation.
Journal Article
Post-stress bacterial cell death mediated by reactive oxygen species
Antimicrobial efficacy, which is central to many aspects of medicine, is being rapidly eroded by bacterial resistance. Since new resistance can be induced by antimicrobial action, highly lethal agents that rapidly reduce bacterial burden during infection should help restrict the emergence of resistance. To improve lethal activity, recent work has focused on toxic reactive oxygen species (ROS) as part of the bactericidal activity of diverse antimicrobials. We report that when Escherichia coli was subjected to antimicrobial stress and the stressor was subsequently removed, both ROS accumulation and cell death continued to occur. Blocking ROS accumulation by exogenous mitigating agents slowed or inhibited poststressor death. Similar results were obtained with a temperature-sensitive mutational inhibition of DNA replication. Thus, bacteria exposed to lethal stressors may not die during treatment, as has long been thought; instead, death can occur after plating on drug-free agar due to poststress ROS-mediated toxicity. Examples are described in which (i) primary stress-mediated damage was insufficient to kill bacteria due to repair; (ii) ROS over-came repair (i.e., protection from anti-ROS agents was reduced by repair deficiencies); and (iii) killing was reduced by anti-oxidative stress genes acting before stress exposure. Enzymatic suppression of poststress ROS-mediated lethality by exogenous catalase supports a causal rather than a coincidental role for ROS in stress-mediated lethality, thereby countering challenges to ROS involvement in anti-microbial killing. We conclude that for a variety of stressors, lethal action derives, at least in part, from stimulation of a self-amplifying accumulation of ROS that overwhelms the repair of primary damage.
Journal Article
Electrochemical deposition as a universal route for fabricating single-atom catalysts
Single-atom catalysts (SACs) exhibit intriguing catalytic performance owing to their maximized atom utilizations and unique electronic structures. However, the reported strategies for synthesizing SACs generally have special requirements for either the anchored metals or the supports. Herein, we report a universal approach of electrochemical deposition that is applicable to a wide range of metals and supports for the fabrication of SACs. The depositions were conducted on both cathode and anode, where the different redox reactions endowed the SACs with distinct electronic states. The SACs from cathodic deposition exhibited high activities towards hydrogen evolution reaction, while those from anodic deposition were highly active towards oxygen evolution reaction. When cathodically- and anodically-deposited Ir single atoms on Co
0.8
Fe
0.2
Se
2
@Ni foam were integrated into a two-electrode cell for overall water splitting, a voltage of 1.39 V was required at 10 mA cm
−2
in alkaline electrolyte.
While single-atom catalysts exhibit intriguing catalytic performances and electronic structures, syntheses are often tailored to a particular system. Here, authors report electrochemical deposition as a universal approach for the fabrication of single-atom catalysts over range of metals and supports.
Journal Article
Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages
Supported platinum intermetallic compound catalysts have attracted considerable attention owing to their remarkable activities and durability for the oxygen reduction reaction in proton-exchange membrane fuel cells. However, the synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. In this study, we perform in-situ high-temperature X-ray diffraction studies to investigate the structural evolution in the impregnation synthesis of carbon-supported intermetallic catalysts. We identify the phase-transition-temperature (
T
PT
)-dependent evolution process that involve concurrent (for alloys with high
T
PT
) or separate (for alloys with low
T
PT
) alloying/ordering stages. Accordingly, we realize the synthesis of highly ordered intermetallic catalysts by adopting a separate annealing protocol with a high-temperature alloying stage and a low-temperature ordering stage, which display a high mass activity of 0.96 A mg
Pt
–1
at 0.9 V in H
2
–O
2
fuel cells and a remarkable durability.
The synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. Here the authors identify phase-transition-temperature-dependent evolution process in the synthesis of intermetallic Pt catalysts and propose a separate alloying/ordering annealing synthetic protocol.
Journal Article
Ambient-pressure hydrogenation of CO2 into long-chain olefins
The conversion of CO
2
by renewable power-generated hydrogen is a promising approach to a sustainable production of long-chain olefins (C
4+
=
) which are currently produced from petroleum resources. The decentralized small-scale electrolysis for hydrogen generation requires the operation of CO
2
hydrogenation in ambient-pressure units to match the manufacturing scales and flexible on-demand production. Herein, we report a Cu-Fe catalyst which is operated under ambient pressure with comparable C
4+
=
selectivity (66.9%) to that of the state-of-the-art catalysts (66.8%) optimized under high pressure (35 bar). The catalyst is composed of copper, iron oxides, and iron carbides. Iron oxides enable reverse-water-gas-shift to produce CO. The synergy of carbide path over iron carbides and CO insertion path over interfacial sites between copper and iron carbides leads to efficient C-C coupling into C
4+
=
. This work contributes to the development of small-scale low-pressure devices for CO
2
hydrogenation compatible with sustainable hydrogen production.
The conversion of CO2 by renewable power-generated hydrogen is a promising approach to a sustainable production of long-chain olefins. Here the authors report a Cu-Fe catalyst which achieves the hydrogenation of CO2 into long-chain olefins under ambient pressure via the synergy of carbide mechanism and CO insertion mechanism.
Journal Article
Cdc25A inhibits autophagy-mediated ferroptosis by upregulating ErbB2 through PKM2 dephosphorylation in cervical cancer cells
Cervical cancer is the leading cause of cancer-related deaths in women, and treatment for cervical cancer is very limited. Emerging evidence suggests that targeting ferroptosis is a promising way to treat cancer. Here, we investigated the role of ferroptosis in cervical cancer, with a focus on the Cdc25A/PKM2/ErbB2 axis. Cervical cancer cells were treated with sorafenib to induce ferroptosis. Cellular MDA/ROS/GSH/iron detection assays were used to measure ferroptosis. MTT assays were performed to assess cell viability. qRT-PCR, western blot, and immunostaining assays were performed to measure the levels of proteins. Autophagy was monitored by fluorescence microscopy. Nuclear and cytosolic fractions were isolated to examine the location of PKM2 modifications. Co-IP experiments were conducted to determine the Cdc25A/PKM2 interaction. ChIP assays were performed to measure the binding affinity between H3K9Ac and the ErbB3 promoter, and a dual luciferase assay was performed to examine the transcriptional activity of ErbB2. A nude mouse xenograft model was used to examine the effects of the Cdc25A/ErbB2 axis on tumour growth in vivo. Cdc25A was elevated in human cervical cancer tissues but was reduced during sorafenib-induced ferroptosis of cervical cancer cells. Overexpression of Cdc25A inhibited sorafenib-induced ferroptosis by dephosphorylating nuclear PKM2 and suppressing autophagy. Cdc25A regulated autophagy-induced ferroptosis by increasing ErbB2 levels via the PKM2–pH3T11–H3K9Ac pathway. Cdc25A increased the resistance of cervical cancer to sorafenib, while knockdown of ErbB2 blocked these effects. Cdc25A suppressed autophagy-dependent ferroptosis in cervical cancer cells by upregulating ErbB2 levels through the dephosphorylation of PKM2. These studies revealed that Cdc25A/PKM2/ErbB2 pathway-regulated ferroptosis could serve as a therapeutic target in cervical cancer.
Journal Article
Selectively anchoring single atoms on specific sites of supports for improved oxygen evolution
The homogeneity of single-atom catalysts is only to the first-order approximation when all isolated metal centers interact identically with the support. Since the realistic support with various topologies or defects offers diverse coordination environments, realizing real homogeneity requires precise control over the anchoring sites. In this work, we selectively anchor Ir single atoms onto the three-fold hollow sites (Ir
1
/T
O
–CoOOH) and oxygen vacancies (Ir
1
/V
O
–CoOOH) on defective CoOOH surface to investigate how the anchoring sites modulate catalytic performance. The oxygen evolution activities of Ir
1
/T
O
–CoOOH and Ir
1
/V
O
–CoOOH are improved relative to CoOOH through different mechanisms. For Ir
1
/T
O
–CoOOH, the strong electronic interaction between single-atom Ir and the support modifies the electronic structure of the active center for stronger electronic affinity to intermediates. For Ir
1
/V
O
–CoOOH, a hydrogen bonding is formed between the coordinated oxygen of single-atom Ir center and the oxygenated intermediates, which stabilizes the intermediates and lowers the energy barrier of the rate-determining step.
While single-atom catalysts offer well-defined structures, the homogeneity of the active sites is determined by localized coordination environments. Here, authors anchor Ir single atoms onto different sites on CoOOH and show how their distinct coordinations activate oxygen-evolving electrocatalysis
Journal Article