Metal single‐atom materials with their high atom utilization efficiency and unique electronic structures usually show remarkable catalytic performances in many crucial chemical reactions. Herein, a ...facile and easily scalable “impregnation‐carbonization‐acidification” strategy for fabricating a class of single‐atom‐anchored (including cobalt and nickel single atoms) monolith as superior binder‐free electrocatalysts for developing high‐performance wearable Zn–air batteries is reported. The as‐prepared single atoms, supported by N‐doped carbon flake arrays grown on carbon nanofibers assembly (M SA@NCF/CNF), demonstrate the dual characteristics of excellent catalytic activity (reversible oxygen overpotential of 0.75 V) and high stability, owing to the greatly improved active sites' accessibility and optimized single‐sites/pore‐structures correlations. Furthermore, wearable Zn–air battery based on Co SA@NCF/CNF air electrode displays superior stability under deformation, satisfactory energy storage capacity, and good practicality to be utilized as an integrated battery system. Theoretical calculations reveal a mechanism for the promotion of the catalytic performances on single atomic sites by lowering the overall oxygen reduction/evolution reaction barriers comparing to metal cluster co‐existing configuration. These findings provide a facile strategy for constructing free‐standing single‐atom materials as well as the engineering of high‐performance binder‐free catalytic electrodes.
A class of single‐atom‐anchored hierarchically porous monoliths for flexible energy storage is prepared by a facile and easily scalable “impregnation–carbonization–acidification” strategy. It exhibits excellent bifunctional electrocatalytic activity for oxygen reduction/evolution reactions. Wearable zinc–air batteries based on this binder‐free monolith show low overpotential and high mechanical stability.
Developing efficient bifunctional electrocatalysts toward oxygen/hydrogen evolution reactions is crucial for electrochemical water splitting toward hydrogen production. The high‐performance ...electrocatalysts depend on the catalytically active and highly accessible reaction sites and their structural robustness, while the rational design of such electrocatalysts with desired features avoiding tedious manufacture is still challenging. Here, a facile method is reported to synthesize mesoporous and heterostructured transition metal oxides strongly anchored on a nickel skeleton (MH‐TMO) containing identified Fe–Cu oxide interfaces with high intrinsic activity, easy accessibility for reaction intermediates, and long‐term stability for alkaline oxygen/hydrogen evolution reactions. The MH‐TMO with the electrocatalytically active Fe–O–Cu bridge has an optimal oxygen binding energy to facilitate adsorption/desorption of oxygen intermediates for oxygen molecules. Associated with the high mass transport through the nanoporous structure, MH‐TMO exhibits impressive oxygen evolution reaction catalysis, with an extremely low overpotential of around 0.22 V at 10 mA cm−2 and low Tafel slope (44.5 mV dec−1) in 1.0 M KOH, realizing a current density of 100 mA cm−2 with an overpotential as low as 0.26 V. As a result, the alkaline electrolyzer assembled by the bifunctional MH‐TMO catalysts operates with an outstanding overall water‐splitting output (1.49 V@10 mA cm−2), outperforming one assembled with noble‐metal‐based catalysts.
A facile method based on a lattice‐matching strategy is reported to synthesize Fe–Cu oxides with high mesoporosity and unique heterostructure. The established structure possesses high activity for the oxygen evolution reaction with an extremely low overpotential of around 0.22 V at 10 mA cm−2 as well as electrocatalytic bifunctionality for high‐performance water splitting with an outstanding overall output (1.49 V@10 mA cm−2).
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•Applications of intermittent aeration in N removal are critically reviewed.•Strategies and mechanisms of enhanced N removal efficiency are presented.•Variations in N transformation ...and microbial interactions are discussed.•Advantages of intermittent aeration in the integrated anammox process are outlined.•Directions for future work in N removal with intermittent aeration are suggested.
Intermittent aeration has been shown to be one of the most effective and cost-effective strategies for biological wastewater treatment. This review presents an overview of the application and advantages of intermittent aeration, with the mechanisms of improvement in process stability discussed. Intermittent aeration was applied to maximize the utilization of organic carbon for denitrification rather than oxidized by O2. Under that condition, advanced nitrogen removal and sludge settleability were achieved and the energy consumption and N2O emissions were reduced. With the discovery that nitrite oxidation bacteria are selectively inhibited while ammonium oxidation bacteria are less affected under intermittent aeration conditions, intermittent aeration has been applied to the partial nitrification process. Furthermore, the non-aerated phases of intermittent aeration have been found to facilitate the synergism of anaerobic ammonium oxidizing bacteria (AnAOB) and denitrifying bacteria, providing a suitable environment for AnAOB growth. Therefore, intermittent aeration is considered to be an effective operational strategy for anammox-based processes, such as single-stage partial nitrification-anammox. In addition, simultaneous nutrient removal and sludge reduction could also be achieved. In order to regulate the synergism of microbial species, dissolved oxygen (DO) concentrations and the durations of aerated and non-aerated periods can be adjusted based on the monitored parameters such as nitrogen concentrations, pH and oxidation reduction potential profiles. Finally, the current limitations, gaps in knowledge and the areas requiring further research are proposed.
•Simultaneous nitrogen and carbon removal was achieved in the SAD process.•Contributions of anammox and denitrification to nitrogen removal were determined.•Anammox and denitrifying bacteria ...dominated at low and high CODs, respectively.•Brocadia sinica could grow with organic matter and tolerate high NO3− concentrations.
A sequencing batch reactor (SBR) was used to test the simultaneous anammox and denitrification process. Optimal nitrogen removal was achieved with chemical oxygen demand (COD) of 150mg/L, during which almost all of ammonia, nitrite and nitrate could be removed. Organic matter was a key factor to regulate the synergy of anammox and denitrification. Both experimental ΔNO2−-N/ΔNH4+-N and ΔNO3−-N/ΔNH4+-N values deviated from their theoretical values with increasing COD. Denitrifying bacteria exhibited good diversity and abundance, but the diversity of anammox bacteria was less abundant. Brocadia sinica was able to grow in the presence of organic matter and tolerate high nitrite concentration. Anammox bacteria were predominant at low COD contents, while denitrifying bacteria dominated the microbial community at high COD contents. Anammox and denitrifying bacteria could coexist in one reactor to achieve the simultaneous carbon and nitrogen removal through the synergy of anammox and denitrification.
Seeking a multifunctional electrocatalyst composed of earth-abundant elements for highly hydrogen and oxygen evolution reaction and oxygen reduction reaction (HER, OER and ORR) is technically ...imperative for the electrocatalytic applications. Herein, we report HER, OER and ORR electrocatalytic performances of metal-organic framework (MOF) derived cobalt nanoparticles encapsulated in nitrogen-doped carbon and carbon nanotube (Co@NC/CNT). The optimized Co@NC/CNT hybrid shows superior HER and OER activities with a small overpotential of 137 mV and 302 mV at a current density of 10 mA cm−2, respectively. Furthermore, the Co@NC/CNT as an air-cathode in secondary Zn-air battery demonstrates a confined potential gap of 0.88 V over 200 h and a maximum power density of 53.4 mW cm−2, which are much better than those of Pt/C. The outstanding performances are attributed to the synergistic effects from Co, and N embedded into carbon and CNT. More importantly, the unique surface structure contributes to expose many active sites for superior catalytic activity through allowing a large number of electrons. These outcomes not only prove a facile approach for the preparation of metals/carbon hybrid but also disclose its huge possible as a multifunctional electrocatalyst for sustainable energy systems.
•Co@NC/CNT derived from metal-organic framework (MOF) is designed and prepared.•Co@NC/CNT as a tri-functional electrocatalyst exhibits superior HER, OER and ORR activity.•The outstanding performance is attributed to the synergistic offerings from Co, and N embedded into carbon and CNT.•The result provides huge possible as a multi-functional electrocatalyst for sustainable energy systems.
Developing of inexpensive, high-efficient, and earth-abundant bifunctional catalysts for water splitting is of great significance for green and sustainable energy development. Herein, a bifunctional ...hybrid electrocatalyst of Ni3ZnC0.7 nanodots in-situ grown on nitrogen-doped carbon nanotube (Ni3ZnC0.7/NCNT) arrays is synthesized by a one-step template strategy with 1, 3, 5-triamino-2, 4, 6-trinitrobenzene serving as carbon/nitrogen sources, ZnO nanorods as template and zinc source, and nickel foam as substrate and nickel source. Benefiting from the introduction of Ni3ZnC0.7 nanodots and nitrogen doping to the carbon nanotubes, the Ni3ZnC0.7/NCNT-700 arrays exhibit superior hydrogen evolution reaction and oxygen evolution reaction catalytic activity in terms of low overpotential (203 mV and 380 mV vs RHE at 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction, respectively). When the Ni3ZnC0.7/NCNT-700 is served as both anode and cathode catalysts for overall water splitting, a potential of 1.66 V is needed to deliver a current density of 10 mA cm−2, and it also displays negligible degradation after 24 h of operation in alkaline solution. The present work not only provides an efficient bifunctional electrocatalyst for overall water splitting, but also offers a new strategy to design and synthetize the bimetallic carbide.
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Highlights
A binder-free and freestanding all-climate cathode FeS
2
@C/CNT in aluminum-ion batteries working from −25 to 50 °C with exceptional flexibility, enhanced capacity retention (above ...117 mAh g
−1
) and rate capacity even at a low temperature of −25 °C.
High rate capacity (above 151 mAh g
−1
at 2 A g
−1
) and robust long-term stability (above 80 mAh g
−1
after 2,000 cycles at 1 A g
−1
) at room temperature.
DFT simulation verifies that the well-designed structure restricts FeS
2
pulverization and facilitates the kinetic process of active ion.
Aluminum-ion batteries (AIBs) are promising next-generation batteries systems because of their features of low cost and abundant aluminum resource. However, the inferior rate capacity and poor all-climate performance, especially the decayed capacity under low temperature, are still critical challenges toward high-specific-capacity AIBs. Herein, we report a binder-free and freestanding metal–organic framework-derived FeS
2
@C/carbon nanotube (FeS
2
@C/CNT) as a novel all-climate cathode in AIBs working under a wide temperature window between −25 and 50 °C with exceptional flexibility. The resultant cathode not only drastically suppresses the side reaction and volumetric expansion with high capacity and long-term stability but also greatly enhances the kinetic process in AIBs with remarkable rate capacity (above 151 mAh g
−1
at 2 A g
−1
) at room temperature. More importantly, to break the bottleneck of the inherently low capacity in graphitic material-based all-climate AIBs, the new hierarchical conductive composite FeS
2
@C/CNT highly promotes the all-climate performance and delivers as high as 117 mAh g
−1
capacity even under −25 °C. The well-designed metal sulfide electrode with remarkable performance paves a new way toward all-climate and flexible AIBs.
Electrochemical CO
2
reduction (ECR) is one of the most effective methods to obtain carbonaceous chemicals and reduce greenhouse gases passingly under the ambient condition. However, efficient ...electrocatalysts featured with high selectivity and stability are still lacking. A novel molecule-mediated Ag electrocatalyst with capped thiols is rationally designed for high-performance ECR. The thiol-capped and carbon-supported Ag nanostructures (Ag-TC) are formed by
in situ
electrochemical reduction from three-dimentional (3D) Ag-thiol metal-organic compound with cysteine as the anchor agent and carbon source. Ag-TC exhibits high selectivity and stability for CO
2
conversion to CO (86.7%), which is more catalytically active than that of common Ag nanoparticles. The function of thiols for ECR is proved by replacing cysteine with alanine without thiol group. Meanwhile, alternatively replacing and removing the surface molecules on the Ag foil further demonstrate the effect of thiols. This work enlightens the promise of
in situ
construction method for molecule capped metal electrocatalyst towards selective and stable ECR.
Due to the increasingly urgent demand for effective wastewater denitrification and dephosphorization systems, there is a need to improve the performance of existing biological treatment technologies. ...As a bacteria‐level communication mechanism, quorum sensing (QS) synchronizes gene expression in a density‐dependent manner and regulates bacterial physiological behavior. On this basis, the QS‐based bacterial communication mechanism and environmental factors affecting QS are discussed. This paper reviews the influence of QS on sludge granulation, biofilm formation, emerging contaminants (ECs) removal, and horizontal gene transfer in sewage treatment system. Furthermore, the QS inhibition strategies are compared. Based on the coexistence and balance of QQ and QS in the long‐term operation system, QQ, as an effective tool to regulate the growth density of microorganisms, provides a promising exogenous regulation strategy for residual sludge reduction and biofilm pollution control. This paper reviews the potential of improving wastewater treatment efficiency based on QS theory and points out the feasibility and prospect of exogenous regulation strategy.
Practitioner Points
The mechanism of bacterial communication based on QS and the environmental factors affecting QS were discussed.
The application of QS and QQ in improving the sludge performance of biological treatment systems was described.
The significance of QS and QQ coexistence in sewage treatment process was described.
The QS of microorganisms is conducive to promoting the formation of particles and biofilms. On the contrary, when the QQ is dominant in the system, it can effectively alleviate biofilm pollution. The regulation of QS and QQ is a dynamic process in the long‐term operation of the reactor.
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