Fabrication of Co3O4 pseudocapacitor electrodes from nanoscale cobalt–organic frameworks

Cellulose Nanofiber-Alginate Biotemplated Cobalt Composite Multifunctional Aerogels for Energy Storage Electrodes

Tunable porous composite materials to control metal and metal oxide functionalization, conductivity, pore structure, electrolyte mass transport, mechanical strength, specific surface area, and magneto-responsiveness are critical for a broad range of energy storage, catalysis, and sensing applications. Biotemplated transition metal composite aerogels present a materials approach to address this need. To demonstrate a solution-based synthesis method to develop cobalt and cobalt oxide aerogels for high surface area multifunctional energy storage electrodes, carboxymethyl cellulose nanofibers (CNF) and alginate biopolymers were mixed to form hydrogels to serve as biotemplates for cobalt nanoparticle formation via the chemical reduction of cobalt salt solutions. The CNF-alginate mixture forms a physically entangled, interpenetrating hydrogel, combining the properties of both biopolymers for monolith shape and pore size control and abundant carboxyl groups that bind metal ions to facilitate biotemplating. The CNF-alginate hydrogels were equilibrated in CaCl2 and CoCl2 salt solutions for hydrogel ionic crosslinking and the prepositioning of transition metal ions, respectively. The salt equilibrated hydrogels were chemically reduced with NaBH4, rinsed, solvent exchanged in ethanol, and supercritically dried with CO2 to form aerogels with a specific surface area of 228 m2/g. The resulting aerogels were pyrolyzed in N2 gas and thermally annealed in air to form Co and Co3O4 porous composite electrodes, respectively. The multifunctional composite aerogel's mechanical, magnetic, and electrochemical functionality was characterized. The coercivity and specific magnetic saturation of the pyrolyzed aerogels were 312 Oe and 114 emu/gCo, respectively. The elastic moduli of the supercritically dried, pyrolyzed, and thermally oxidized aerogels were 0.58, 1.1, and 14.3 MPa, respectively. The electrochemical testing of the pyrolyzed and thermally oxidized aerogels in 1 M KOH resulted in specific capacitances of 650 F/g and 349 F/g, respectively. The rapidly synthesized, low-cost, hydrogel-based synthesis for tunable transition metal multifunctional composite aerogels is envisioned for a wide range of porous metal electrodes to address energy storage, catalysis, and sensing applications.

In situ formation of Co3O4 nanoparticles embedded N-doped porous carbon nanocomposite: a robust material for electrocatalytic detection of anticancer drug flutamide and supercapacitor application

The one-step synthesis of heteroatom-doped porous carbons is reported with the in situ formation of cobalt oxide nanoparticles for dual electrochemical applications (i.e., electrochemical sensor and supercapacitor). A single molecular template of zeolitic imidazole framework-67 (ZIF-67) was utilized for the solid-state synthesis of cobalt oxide nanoparticle-decorated nitrogen-doped porous carbon (Co₃O₄@NPC) nanocomposite through a facile calcination treatment. For the first time, Co₃O₄@NPC nanocomposite derived from ZIF-67 has been applied as an electrode material for the efficient electrochemical detection of anticancer drug flutamide (FLU). The cyclic voltammetry studies were performed in the operating potential from 0.15 to - 0.65 V (vs. Ag/AgCl). Interestingly, the fabricated drug sensor exhibited a very low reduction potential (- 0.42 V) compared to other  reported sensors. The fabricated sensor exhibited good analytical performance in terms of low detection limit (12 nM), wide linear range (0.5 to 400 μM), and appreciable recovery results (~ 98%, RSD 1.7% (n = 3)) in a human urine sample. Hereafter, we also examined the supercapacitor performance of the Co₃O₄@NPC-modified Ni foam in a 1M KOH electrolyte, and noticeable a specific capacitance of 525 F g^-1 at 1.5 A g^-1 was attained, with long-term cycling stability. The Co₃O₄@NPC nanocomposite supercapacitor experiments outperform the associated MOF-derived carbons and the Co₃O₄-based nanostructure-modified electrodes.

Metal–organic framework derived petal-like Co3O4@CoNi2S4 hybrid on carbon cloth with enhanced performance for supercapacitors

Starting from 2D Co-based metal-organic frameworks, novel petal-like core-shell Co₃O₄@CoNi₂S₄ nanowall arrays are synthesized on carbon cloth using a facile two-step method and investigated as promising electrode materials for supercapacitors.

Porous Co3O4 nanoparticles derived from a Co(ii)-cyclohexanehexacarboxylate metal–organic framework and used in a supercapacitor with good cycling stability

Porous Co₃O₄ nanoparticles were obtained by calcination the Co-based MOF precursors. It exhibited good pseudocapacitive performance in an alkaline medium and displayed slightly enhanced capacitance after 2500 cycles.