Search

The electrocatalytic oxygen reduction reaction (ORR) is the vital process at the cathode of next-generation electrochemical storage and conversion technologies, such as metal–air batteries and fuel cells. Single-metal-atom and nitrogen co-doped carbonaceous electrocatalysts (M–N–C) have emerged as attractive alternatives to noble-metal platinum for catalyzing the kinetically sluggish ORR due to their high electrical conductivity, large surface area, and structural tunability at the atomic level, however, their application is limited by the low intrinsic activity of the metal–nitrogen coordination sites (M–Nx) and inferior site density. In this Perspective, we summarize the recent progress and milestones relating to the active site engineering of single atom carbonous electrocatalysts for enhancing the ORR activity. Particular emphasis is placed on the emerging strategies for regulating the electronic structure of the single metal site and populating the site density. In addition, challenges and perspectives are provided regarding the future development of single atom carbonous electrocatalysts for the ORR and their utilization in practical use., This Perspective summarizes and highlights the recent progress and milestones relating to the active site engineering of single atom carbonous electrocatalysts for enhancing the electrocatalytic oxygen reduction reaction activity.

Large blue rectangular crystals of the 2D layered coordination polymer 1 have been obtained. The interest for this complex is two-fold. First, complex 1 is made of 2D layers packing along the (0–11) direction favored by the presence of lattice and coordinated water molecules. And second, nanostructures that could be derived by delamination are potentially suitable for catalytic purposes. Therefore it represents an excellent example to study the role of interlayer solvent molecules on the ultrasound-assisted delamination of functionally-active 2D metal-organic frameworks in water, a field of growing interest. With this aim, ultrasound-assisted delamination of the crystals was optimized with time, leading to stable nanosheet colloidal water suspensions with very homogeneous dimensions. Alternative bottom-up synthesis of related nanocrystals under ultrasound sonication yielded similar shaped crystals with much higher size dispersions. Finally, experimental results evidence that the nanostructures have higher catalytic activities in comparison to their bulk counterparts, due to larger metallic center exposition. These outcomes confirm that the combination of liquid phase exfoliation and a suitable synthetic design of 2D coordination polymers represents a very fruitful approach for the synthesis of functional nanosheets with an enhancement of catalytic active sites, and in general, with boosted functional properties., This work was supported by grant RTI2018-098027-B-C21 from the Spanish Government funds and by the European Regional Development Fund (ERDF). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). Noemí Contreras Pereda’s project that gave rise to these results received the support of a fellowship from “laCaixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/ES17/11600012. Renhao Dong acknowledgements the financial support from ERC Starting Grant (FC2DMOF, No. 852909) and DFG project (SPP 1928, COORNETs).

Electrocatalytic oxygen reduction reaction (ORR) is the vital process for next-generation electrochemical energy storage and conversion technologies, e.g., metal-air batteries and fuel cells. During the ORR, the O-2* and O* intermediates principally combine with protons to form OOH* and OH* species, respectively, which are the proton-coupled electron transfer processes. Unfortunately, under alkaline conditions, the protons are essentially generated from the sluggish water dissociation process, which unavoidably limits the ORR kinetics. Herein, we design and synthesize a nitrogen-doped hierarchically porous carbon with homogeneously distributed ultrafine alpha-MoC nanoparticles (alpha-MoC/NHPC) as a model electrocatalyst. Theoretical investigations unveil that alpha-MoC on NHPC could efficiently reduce the energy barrier of the water dissociation process to generate protons, eventually promoting the proton-coupled ORR kinetics. In a 0.1 M KOH aqueous solution, alpha-MoC/NHPC exhibits excellent ORR performance with a high half-wave potential of 0.88 V (vs. reversible hydrogen electrode), which outperforms those for NHPC and commercial Pt/C. Moreover, as the air electrode in a zinc-air battery, alpha-MoC/NHPC presents a large peak power density of 200.3 mW cm(-2)and long-term stability. Thereby, our approach to engineering proton-feeding centers paves a new avenue towards the understanding of ORR kinetics and the development of high-performance ORR electrocatalysts.

Highly effective electrocatalysts promoting CO2 reduction reaction (CO2RR) is extremely desirable to produce value-added chemicals/fuels while addressing current environmental challenges. Herein, we develop a layer-stacked, bimetallic two-dimensional conjugated metal-organic framework (2D c-MOF) with copper-phthalocyanine as ligand (CuN4) and zinc-bis(dihydroxy) complex (ZnO4) as linkage (PcCu-O8-Zn). The PcCu-O8-Zn exhibits high CO selectivity of 88%, turnover frequency of 0.39 s−1 and long-term durability (>10 h), surpassing thus by far reported MOF-based electrocatalysts. The molar H2/CO ratio (1:7 to 4:1) can be tuned by varying metal centers and applied potential, making 2D c-MOFs highly relevant for syngas industry applications. The contrast experiments combined with operando spectroelectrochemistry and theoretical calculation unveil a synergistic catalytic mechanism; ZnO4 complexes act as CO2RR catalytic sites while CuN4 centers promote the protonation of adsorbed CO2 during CO2RR. This work offers a strategy on developing bimetallic MOF electrocatalysts for synergistically catalyzing CO2RR toward syngas synthesis., Effective electrocatalyst is crucial in promoting CO2 reduction to address current energy/environmental issue. Here, the authors develop bimetallic layered two-dimensional conjugated metal-organic framework to synergistically and efficiently electro-catalyze CO2 to CO toward syngas synthesis.

A simple, one-step and amplified Hg2+ detection strategy based on DNAzyme motor was described here. Fluorophore labeled DNA probes and long arm DNA are immobilized on the AuNPs by Au-S bond. The fluorescent signal of DNA probe is significantly quenched by AuNPs. In the presence of Hg2+, thymine-Hg2+-thymine (T-Hg2+-T) interaction can causes the duplex structure of split E-DNA and then form an entire E-DNA. Then the E-DNA can bind with fluorophore labeled DNA to form Mg2+-dependent DNAzyme structure. With the assistance of Mg2+, the fluorophore labeled DNA can be circularly cleaved by DNAzyme and then leave from the AuNPs surface. The recycling cleavage and binding processes caused processive moving of E-DNA on AuNPs surface and significant fluorescent signal recovery. A good linear relationship was obtained between fluorescence intensity and Hg2+ concentration in the range from 0.1 nM to 5 nM. The limit of detection was calculated to be 30 pM. This strategy was successfully used for detection of Hg2+ in Chinese herbs (Atractylodes macrocephala Koidz), showing a promising practical application future.

A novel fluorescent and colorimetric strategy with enzyme-free dual amplification was developed for ultra-sensitively detection of uranyl in river waters samples. The enzyme-strand recycling and hairpin catalytic assembly (HCA) reaction were used as dual enzyme-free amplification strategies. Three hairpins labeled with fluorophore can absorb on the surface of gold nanoparticles (AuNPs) to prevent them from aggregation in salt solution and quench the fluorescent signal simultaneously. In the presence of UO22+, the HCA reaction between hairpins was induced to form rigid DNA triangles, resulting in the aggregation of AuNPs with a red to blue color change and a “turn-on” fluorescent signal. The limit of detection was as low as 0.1 pM. Importantly, this strategy provided colorimetric and fluorescent dual signals for lower false-positives and higher anti-interference ability. It was successfully used for detection of uranyl in real waters samples.

Herein, a fast and visible colorimetric method for bisphenol A (BPA) detection was developed using hemin-functionalized reduced graphene oxide (H–rGO) composites and aptamer. The aptamer can be stably adsorbed on the surface of H–rGO, preventing H–rGO from salt-induced aggregation. However, in the presence of BPA, the aptamer can bind with BPA; this results in the aggregation of H–rGO. Consequently, the supernatant contains a little H–rGO and shows light blue color after the chromogenic reaction. The color difference can be used for the quantitative detection of BPA. The designed aptasensor displayed a linear response for BPA in the range from 5 nM to 100 nM with a detection limit of 2 nM. This colorimetric aptasensing platform offered great advantages, including label-free conditions and visible result readout platform, for quick screening of BPA for on-site analysis and in-house diagnosis.

Owing to their earth abundance, high atom utilization, and excellent activity, single iron atoms dispersed on nitrogen-doped carbons (Fe-N-C) have emerged as appealing alternatives to noble-metal platinum (Pt) for catalyzing the oxygen reduction reaction (ORR). However, the ORR activity of current Fe-N-C is seriously limited by the low density and inferior exposure of active Fe-Nx species. Here, a novel zinc-mediated template synthesis strategy is demonstrated for constructing densely exposed Fe-Nx moieties on hierarchically porous carbon (SA-Fe-NHPC). During the thermal treatment of 2,6-diaminopyridine/ZnFe/SiO2 complex, the zinc prevents the formation of iron carbide nanoparticles and the SiO2 template promotes the generation of hierarchically pores for substantially improving the accessibility of Fe-Nx moieties after subsequent leaching. As a result, the SA-Fe-NHPC electrocatalysts exhibit an unprecedentedly high ORR activity with a half-wave potential (E1/2 ) of 0.93 V in a 0.1 m KOH aqueous solution, which outperforms those for Pt/C catalyst and state-of-the-art noble metal-free electrocatalysts. As the air electrode in zinc-air batteries, the SA-Fe-NHPC demonstrates a large peak power density of 266.4 mW cm-2 and superior long-term stability. Therefore, the developed zinc-mediated template synthesis strategy for boosting the density and accessibility of Fe-Nx species paves a new avenue toward high-performance ORR electrocatalysts.

Rechargeable sodium-iodine (Na-I2 ) batteries are attracting growing attention for grid-scale energy storage due to their abundant resources, low cost, environmental friendliness, high theoretical capacity (211 mAh g-1 ), and excellent electrochemical reversibility. Nevertheless, the practical application of Na-I2 batteries is severely hindered by their poor cycle stability owing to the serious dissolution of polyiodide in the electrolyte during charge/discharge processes. Herein, the atomic modulation of metal-bis(dihydroxy) species in a fully conjugated phthalocyanine copper metal-organic framework (MOF) for suppression of polyiodide dissolution toward long-time cycling Na-I2 batteries is demonstrated. The Fe2 [(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Cu] MOF composited with I2 (Fe2 -O8 -PcCu/I2 ) serves as a cathode for a Na-I2 battery exhibiting a stable specific capacity of 150 mAh g-1 after 3200 cycles and outperforming the state-of-the-art cathodes for Na-I2 batteries. Operando spectroelectrochemical and electrochemical kinetics analyses together with density functional theory calculations reveal that the square planar iron-bis(dihydroxy) (Fe-O4 ) species in Fe2 -O8 -PcCu are responsible for the binding of polyiodide to restrain its dissolution into electrolyte. Besides the monovalent Na-I2 batteries in organic electrolytes, the Fe2 -O8 -PcCu/I2 cathode also operates stably in other metal-I2 batteries like aqueous multivalent Zn-I2 batteries. Thus, this work offers a new strategy for designing stable cathode materials toward high-performance metal-iodine batteries.