Destruction of a Copper Metal-Organic Framework to Induce CuPt Growth as a Heterojunction Catalyst for Hydrogen Peroxide Sensing.

Assembling bimetallic alloys (BAs) with metal-organic frameworks (MOFs) to form heterojunctions has emerged as a promising strategy for the construction of highly active electrocatalysts. However, the current approaches to prepare BA@MOF heterojunctions suffer from poor controllability. In this work, a fascinating method involving partial thermal reduction and galvanic replacement to induce CuPt growth on a CuHHTP MOF (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene) is reported in order to construct a CuPt@CuHHTP heterojunction. The size of the CuPt nanoparticles can be effectively regulated by modifying the reduction temperature. The resultant CuPt NP@CuHHTP heterojunction nanoarrays exhibit high electrocatalytic activity and potential as an electrochemical H2 O2 sensor with a low detection limit (5 nM), high sensitivity (6.942 mA ⋅ mM-1 ⋅ cm-2 ), and outstanding selectivity. This in situ approach provides not only new insights into the preparation of BA@MOF-based heterojunctions but also an effective approach for the optimization of the catalytic performance of MOFs and related materials.

Enhanced Proton Transfer in Proton-Exchange Membranes with Interconnected and Zwitterion-Functionalized Covalent Porous Material Structures.

Excellent proton-conductive accelerators are indispensable for efficient proton-exchange membranes (PEMs). Covalent porous materials (CPMs), with adjustable functionalities and well-ordered porosities, show much promise as effective proton-conductive accelerators. In this study, an interconnected and zwitterion-functionalized CPM structure based on carbon nanotubes and a Schiff-base network (CNT@ZSNW-1) is constructed as a highly efficient proton-conducting accelerator by in situ growth of SNW-1 onto carbon nanotubes (CNTs) and subsequent zwitterion functionalization. A composite PEM with enhanced proton conduction is acquired by integrating CNT@ZSNW-1 with Nafion. Zwitterion functionalization offers additional proton-conducting sites and promotes the water retention capacity. Moreover, the interconnected structure of CNT@ZSNW-1 induces a more consecutive arrangement of ionic clusters, which significantly relieves the proton transfer barrier of the composite PEM and increases its proton conductivity to 0.287 S cm-1 under 95 % RH at 90 °C (about 2.2 times that of the recast Nafion, 0.131 S cm-1 ). Furthermore, the composite PEM displays a peak power density of 39.6 mW cm-2 in a direct methanol fuel cell, which is significantly higher than that of the recast Nafion (19.9 mW cm-2 ). This study affords a potential reference for devising and preparing functionalized CPMs with optimized structures to expedite proton transfer in PEMs.

Synergistic Combination of Fermi Level Equilibrium and Plasmonic Effect for Formic Acid Dehydrogenation.

Developing an efficient catalyst for formic acid (FA) dehydrogenation is a promising strategy for safe hydrogen storage and transportation. Herein, we successfully developed trimetallic NiAuPd heterogeneous catalysts through a galvanic replacement reaction and a subsequent chemical reduction process to boost hydrogen generation from FA decomposition at room temperature by coupling Fermi level engineering with plasmonic effect. We demonstrated that Ni worked as an electron reservoir to donate electrons to Au and Pd driven by Fermi level equilibrium whereas plasmonic Au served as an optical absorber to generate energetic hot electrons and a charge-redistribution mediator. Ni and Au worked cooperatively to promote the charge heterogeneity of surface-active Pd sites, leading to enhanced chemisorption of formate-related intermediates and eventually outstanding activity (342 mmol g-1 h-1 ) compared with bimetallic counterpart. This work offers excellent insight into the rational design of efficient catalysts for practical hydrogen energy exploitation.

Natural oxidase-mimicking copper-organic frameworks for targeted identification of ascorbate in sensitive sweat sensing.

Sweat sensors play a significant role in personalized healthcare by dynamically monitoring biochemical markers to detect individual physiological status. The specific response to the target biomolecules usually depends on natural oxidase, but it is susceptible to external interference. In this work, we report tryptophan- and histidine-treated copper metal-organic frameworks (Cu-MOFs). This amino-functionalized copper-organic framework shows highly selective activity for ascorbate oxidation and can serve as an efficient ascorbate oxidase-mimicking material in sensitive sweat sensors. Experiments and calculation results elucidate that the introduced tryptophan/histidine fundamentally regulates the adsorption behaviors of biomolecules, enabling ascorbate to be selectively captured from complex sweat and further efficiently electrooxidized. This work provides not only a paradigm for specifically sweat sensing but also a significant understanding of natural oxidase-inspired MOF nanoenzymes for sensing technologies and beyond.

In situ electrochemical reductive construction of metal oxide/metal-organic framework heterojunction nanoarrays for hydrogen peroxide sensing.

Transition metal oxide/metal-organic framework heterojunctions (TMO@MOF) that combine the large specific surface area of MOFs with TMOs' high catalytic activity and multifunctionality, show excellent performances in various catalytic reactions. Nevertheless, the present preparation approaches of TMO@MOF heterojunctions are too complex to control, stimulating interests in developing simple and highly controllable methods for preparing such heterojunction. In this study, we propose an in situ electrochemical reduction approach to fabricating Cu2O nanoparticle (NP)@CuHHTP heterojunction nanoarrays with a graphene-like conductive MOF CuHHTP (HHTP is 2,3,6,7,10,11-hexahydroxytriphenylene). We have discovered that size-controlled Cu2O nanoparticles could be in situ grown on CuHHTP by applying different electrochemical reduction potentials. Also, the obtained Cu2O NP@CuHHTP heterojunction nanoarrays show high H2O2 sensitivity of 8150.6 µA·mM-1·cm2 and satisfactory detection performances in application of measuring H2O2 concentrations in urine and serum samples. This study offers promising guidance for the synthesis of MOF-based heterojunctions for early cancer diagnosis.

Cobalt-gluconate-derived high-density cobalt sulfides nanocrystals encapsulated within nitrogen and sulfur dual-doped micro/mesoporous carbon spheres for efficient electrocatalysis of oxygen reduction.

The exploration of an efficient nonprecious electrocatalyst for oxygen reduction reaction (ORR) is critical to the commercialization of various electrochemical energy-conversion devices. Herein, a cobalt-gluconate-derived nitrogen and sulfur dual-doped micro/mesoporous carbon sphere (Co9S8/N, S-MCS) with encapsulated high-density cobalt sulfide (Co9S8) nanocrystals is developed by annealing and subsequent high-temperature vulcanization. Particularly, the vulcanization temperature has a critical impact on the formation of high-density Co9S8 nanocrystals. Benefiting from the favorable material characteristics of large surface area, abundant micro/mesopores and high graphitic nanostructures, as well as the synergistic effects between high-density Co9S8 nanocrystals and N, S-dual doped graphitic carbon shells, the resulting catalyst demonstrates superior ORR catalytic activity and durability compared to platinum/carbon (Pt/C) catalyst. More notably, the proposed approach can be extended potentially to fabricate other transition metal sulfide (or oxide, carbide) based electrocatalysts.

Iron Sulfide Nanoparticles Embedded Into a Nitrogen and Sulfur Co-doped Carbon Sphere as a Highly Active Oxygen Reduction Electrocatalyst.

The unique micro/mesoporous spherical nanostructure composed of non-noble metal nanoparticles encapsulated within a heteroatom-doped carbon matrix provides great advantages for constructing advanced non-precious oxygen reduction (ORR) electrocatalysts. Herein, a promising oxygen electrocatalyst comprising iron sulfide (Fe1-xS) nanoparticles embedded into a nitrogen and sulfur co-doped carbon sphere (Fe1-xS/NS-CS) is successfully explored through a simple and fast polymerization between methylolmelamines (MMA) and ammonium ferric citrate (AFC) as well as a high-temperature vulcanization process. Moreover, the proposed polymerization reaction can be finished completely within a very short time, which is useful for large-scale manufacturing. Impressively, the developed Fe1-xS/NS-MCS catalyst demonstrates outstanding ORR catalytic activity in terms of a more positive onset and half-wave potential as well, as much a better methanol tolerance and stability, in comparison with that of Pt/C benchmarked catalyst. The remarkable ORR electrocatalytic properties are strongly associated with the favorable characteristic spherical N, the S co-doped porous graphitic carbon nanoskeleton incorporated with the Fe1-xS nanoparticle-encapsulation structure.

Assembling Metal-Organic Frameworks into the Fractal Scale for Sweat Sensing.

Many natural organizations with some special functional properties possess fractal tissues which display nearly the same at every scale. The benefit of mimicking fractal structure in synthetic functional materials warrants further exploration. To tackle this challenge, we assemble metal-organic frameworks (MOFs) into fractal structures by using a bottom-up approach inspired from evaporation-driven crystallization. Such hierarchically branched MOFs exhibit some unexpected performances in electrochemistry, and can be a versatile biosensor for sweat analysis. Our work provides an interesting and efficient example for fabricating fractal MOFs as well as uncovering their new properties. This fractal-guided strategy can be extended to synthesize and explore new characteristics of other materials, holding potential in various applications including sensors, catalysis, and energy storage.