Lewis acidic Fe3+-driven catalytic active Ni3+ formation in Fe-free metal-organic framework for enhanced electrochemical glucose sensing.

Manipulating metal valence states and porosity in the metal-organic framework (MOF) by alloying has been a unique tool for creating high-valent metal sites and pore environments in a structure that are inaccessible by other methods, favorable for accelerating the catalytic activity towards sensing applications. Herein, we report Fe3+-driven formation of catalytic active Ni3+ species in the amine-crafted benzene-dicarboxylate (BDC-NH2)-based MOF as a high-performance electrocatalyst for glucose sensing. This work took the benefit of different bonding stability between BDC-NH2 ligand, and Fe3+ and Ni2+ metal precursor ions in the heterometallic NixFe(1-x)-BDC-NH2 MOF. The FeCl3 that interacts weakly with ligand, oxidizes the Ni2+ precursor to Ni3+-based MOF owing to its Lewis acidic behavior and was subsequently removed from the structure supported by Ni atoms, during solvothermal synthesis. This enables to create mesopores within a highly stable Ni-MOF structure with optimal feed composition of Ni0.7Fe0.3-BDC-NH2. The Ni3+-based Ni0.7Fe0.3-BDC-NH2 demonstrates superior catalytic properties towards glucose sensing with a high sensitivity of 13,435 µA mM-1 cm-2 compared to the parent Ni2+-based Ni-BDC-NH2 (10897 µA mM-1cm-2), along with low detection limit (0.9 µM), short response time (≤5 s), excellent selectivity, and higher stability. This presented approach for fabricating high-valent nickel species, with a controlled quantity of Fe3+ integrated into the structure allowing pore engineering of MOFs, opens new avenues for designing high-performing MOF catalysts with porous framework for sensing applications.

Atypical performance of CoO-accelerated interface tweaking in hierarchical cobalt phosphide/oxide@P-doped rGO heterostructures for hybrid supercapacitors.

Designing two-dimensional (2D) heterostructures based on suitable energy materials is a promising strategy to achieve high-performance supercapacitors with hybridized transition metal and carbonaceous-based electrodes. The influence of each component and its content on the capacitor performance necessitates deeper insights. In this study, a 2D/2D heterostructure made of hierarchical pseudocapacitive cobalt phosphide/oxide and P-doped reduced graphene oxide (PrGO) nanosheets (CoP/CoO@PrGO) was fabricated using porous zeolitic-imidazolate framework precursor. The decoration of 2D leaf-like CoP/CoO hybrid onto PrGO could create a unique interface with a large number of active sites, CoO-driven creation of pseudocapacitive surface POx species, and high P content (∼3 at.%) in PrGO, thus promoting the Faradaic reaction, electrical conductivity, and overall charge storage. This framework yields a high specific capacitance of 405 F g-1 at 5 A g-1 and excellent cycling stability (over 100 % after 10,000 cycles), superior to those of pristine CoP@PrGO (300 F g-1 at 5 A g-1). Furthermore, the fabricated asymmetric supercapacitor delivers reasonable energy density of 4.2 Wh kg-1 at a power density of 785 W kg-1 and cycling stability of âˆ¼100 % after 10,000 cycles. Therefore, CoP/CoO@PrGO with its unique interfacial properties can promote the development of heterostructure electrode for high-performance supercapacitors.

Composition engineering of ZIF-derived cobalt phosphide/cobalt monoxide heterostructures for high-performance asymmetric supercapacitors.

The fabrication of interpenetrated heterostructures from desirable energy materials for the development of efficient supercapacitors is promising yet challenging. Herein, a leaf-shaped cobalt phosphide/cobalt oxide heterostructure, (CoPx)1-y/CoOy (0.44 > y > 0.06), was synthesized from 2D-zeolitic-imidazolate-framework (ZIF-Co-L) molecular precursor via phosphidation of the Co3O4 intermediate. The efficient construction of heterostructure through the variation of surface/bulk composition significantly alters the interfacial properties and electronic structure, yielding enhanced supercapacitor performance. Further, gas-phase phosphidation entails a core-shell formation mechanism via gas diffusion, regulated by the Kirkendall effect. The optimized heterostructure (y = 0.10) exhibits remarkable interfacial properties derived from the CoO/Co0/CoP interface, thus facilitating a high specific capacitance (467 F g-1 at 5 A g-1) and excellent cycling stability (~91% after 10000 cycles) at 30 A g-1. A further increase in the cyclability (~107%) was achieved by employing a graphene hybrid. Further, an asymmetric supercapacitor device was fabricated, that delivers reasonably high energy density of 12.7 Wh kg-1 at a power density of 370 W kg-1 and cycling stability of ~93% after 10000 cycles. This study reports on the modulation of interfacial properties of CoPx/CoO heterostructure to enhance energy storage performance via bulk/surface compositional variation, thereby providing a strategy to develop heterostructure electrodes for high-performance supercapacitor.

A Complementary Co-Ni Phosphide/Bimetallic Alloy-Interspersed N-Doped Graphene Electrocatalyst for Overall Alkaline Water Splitting.

Echinops-like bimetallic CoNiP-CoNi alloy is synthesized from a metal-organic framework (MOF) and serves as an efficient catalyst for the oxygen evolution reaction (OER), with a low overpotential of 300 mV in 1 M KOH at 10 mA cm-2 (η10 ). The cooperative effect of Ni and Co metal, as well as the interfacial properties of the integrated semiconducting phosphide/metallic alloy and electronic conductivity of the MOF-derived carbon regulate the performance of the catalyst. Moreover, the bimetallic CoNiP/CoNi alloy catalyst is interspersed with N-doped graphene, forming a triad catalyst that demonstrates superior activity towards the hydrogen evolution reaction (η10 =150 mV) and excellent durability, owing to interfacial effects of the triad catalyst, large electrochemical active surface area, and enhanced conductivity from N-doped graphene. The stability of the carbon-containing catalyst during OER (oxidation) is altered by the high reactivity of heteroatom dopant. The assembled CoNiP/CoNi/N-RGO||CoNiP/CoNi water electrolyzer delivers a reasonable cell potential of 1.76 V at 10 mA cm-2 . The synthesized bimetallic CoNiP/CoNi alloy-based triad catalyst thus demonstrates excellent electrocatalytic activity and high durability suitable for efficient alkaline water splitting.

Scanty graphene-driven phase control and heteroatom functionalization of ZIF-67-derived CoP-draped N-doped carbon/graphene as a hybrid electrode for high-performance asymmetric supercapacitor.

Zeolitic imidazolate framework (ZIF)-derived materials have been explored as promising electrode for energy storage, owing to their tunable composition, high porous structure, and heteroatom-based active sites. Herein, we report cobalt phosphide-draped N-doped carbon/graphene hybrid (CoP-NPC/GS) synthesized from ZIF-67 precursor via a single-step in-situ carbonization and phosphidation. The CoP-NPC/GS hybrid performed as a promising positive electrode with superior electrochemical performance - high capacitance (165 F g-1 at 7 A g-1 compared to 97 F g-1 for CoP-NPC), enhanced rate capability, and promoted cycling stability (~88% after 10,000 cycles). Excellent performance of the CoP-NPC/GS was derived from scanty graphene (2 wt%)-driven compositional variation, which promotes the redox-active CoP phase and higher nitrogen content offering enhanced electronic conductivity. Besides, CoP-NPC/GS performed well as a negative electrode, derived from double-layer capacitance of porous carbon, realizing a capacitance of ~71 F g-1 at 1 A g-1 but inferior to CoP-NPC, which was regulated by pyridinic nitrogen-induced pseudocapacitance. A fabricated CoP-NPC/GS||CoP-NPC asymmetric device displayed an energy density of 10 Wh Kg-1 at 700 W kg-1, with excellent cyclability (~100%) till 11,000 cycles. This study clarifies the role of scanty graphene on the phase control and heteroatom functionalization of phosphide-based electrode, beneficial for enhanced supercapacitive performance.