Surface defect-engineered Fe doping in layered Co-based complex as highly efficient bifunctional electrocatalysts for overall water splitting

The electrocatalytic splitting of water to produce hydrogen is regarded as an efficient and promising strategy but is limited by its large overpotential; thus, a highly efficient electrocatalyst is urgently needed. Mixed metal doping is an important strategy in defect engineering because the heteroatoms can change the intrinsic structure to form defects by affecting the atomic coordination mode and adjusting the electronic structure, which is often accompanied by morphological changes. Herein, two-dimensional layered bimetallic Co-pydc containing axially coordinated water molecules was selected by producing surface defects through Fe doping in Co centers as bifunctional electrocatalysts for OER and HER. The optimized Co0.59Fe0.41-pydc possesses outstanding OER performance with the lowest overpotential of 262 mV to reach j = 10 mA cm-2, and Co0.75Fe0.25-pydc possesses superior HER performance with the lowest overpotential of 96 mV at j = 10 mA cm-2. Furthermore, the overall water splitting device assembled with Co0.59Fe0.41-pydc@NF//Co0.59Fe0.41-pydc@NF affords a current density of 10 mA cm-2 at only 1.687 V. This work emphasizes the surface defects formed by tuning the electronic structure of metal centres accompanied with morphological changes of bimetallic dopants for efficient overall water splitting.

Pyridine 3,5-dicarboxylate-based metal-organic frameworks as an active electrode material for battery-supercapacitor hybrid energy storage devices

Efficient energy storage and conversion is crucial for a sustainable society. Battery-supercapacitor hybrid energy storage devices offer a promising solution, bridging the gap between traditional batteries and supercapacitors. In this regard, metal-organic frameworks (MOFs) have emerged as the most versatile functional compounds owing to their captivating structural features, unique properties, and extensive diversity of applications in energy storage. MOF properties are governed by the structure and topological characteristics, which are influenced by the types of ligands and metal nodes. Herein, MOFs based on pyridine 3,5-dicarboxylate (PYDC) ligand in combination with copper and cobalt are electrochemically analyzed. Owing to the promising initial characterization of Cu-PYDC-MOF, a battery supercapacitor hybrid device was fabricated, comprising Cu-PYDC-MOF and activated carbon (AC) electrodes. The device showcased energy and power density of 17 W h kg -1 and 2550 W kg -1, respectively. Dunn's model was employed to gain deeper insights into the capacitive and diffusive contributions of the device. With their performance and versatility, the PYDC-based MOFs stand at the forefront of energy technology, ready to power a brighter future for upcoming generations.

New metal–organic frameworks derived from pyridine-3,5-dicarboxylic acid: structural diversity arising from the addition of templates into the reaction systems

The effect of aminoalcohol/polyol template molecules in the formation of MOFs based on bipositive metal ions and pyridine-3,5-dicalboxylate ligand was investigated providing access to a series of new multidimensional coordination polymers.

Stimulus-responsive reversible thermochromism and exciplex emission of a Zn(ii) complex and selective sensing of NH3 gas

A Zn(ii) complex exhibits reversible thermochromism and emission switch, and the resulting free radical species responds fast and selectively toward NH₃.

Excellent supercapacitor and sensor performance of robust cobalt phosphinate ferrocenyl organic framework materials achieved by intrinsic redox and structure properties

A new Co coordination polymer with phosphinates and Fc fragments was synthesized, which can be used as a water sensor and sorbent and also as a supercapacitor electrode.

Solvent-mediated supramolecular templated assembly of a metal organophosphonate via a crystal–amorphous–crystal transformation

Three monophosphonoester-based supramolecular assemblies were synthesized and fully characterized. These complexes showed a reversible crystal–amorphous–crystal transformation with changes in their emission properties.

Solvent-Induced Reversible Crystal-to-Amorphous Transformation Properties of Cobalt(II) 4-Aminomethylpyridine-Sulfate with Chromotropism

The crystalline CoII coordination compound with empirical formula [Co(Hampy)2(H2O)4](SO4)2(H2O)3 (1); ampy = 4-aminomethylpyridine was obtained. The structure contains a mononuclear [Co(Hampy)2(H2O)4]4+ cation unit, two sulfate ions, and three lattice water molecules. The Co2+ cation shows an elongated octahedral geometry comprised of four oxygen atoms from water molecules at equatorial positions and two nitrogen atoms from Hampy ligands which are protonated at NH2. Each mononuclear cation unit is assembled by intermolecular hydrogen bonding and π–π stacking interactions by the coordinated and lattice water molecules, amino group, and sulfate anions to form a 3D supramolecular network. Investigations of the dynamic structural behaviour demonstrate that the title compound exhibits a solvent-induced reversible crystal-to-amorphous transformation with chromotropism when exposed to water and methanol vapour. This indicates that the dehydrated amorphous form, [Co(Hampy)2(SO4)2] 1A, may be utilised as an indicator for humidity and methanol vapour.