Synthesis of Ni-Co Metal-Organic Framework (Ni-Co MOF) Structures by High-Power, Continuous Laser-Induced Rapid...

Metal-organic bimetallic frameworks of Ni-Co, having metal content of 2:1 and 1:2 molar ratios, respectively, have been synthesized via a rapid laser method with a continuous-wave Nd:YVO₄ laser (λ = 975 nm) under 88-90 °C in a DMF/H₂O solution in 70 min. The structure, porosity, and photophysical, electrochemical, and dielectric characteristics of the frameworks and their reduced graphene oxide (rGO) composites in the form of powders and UV-cured PEGMEA/PEGDA films have been investigated. Framework Ni2Co1MOF demonstrated a BET surface area equal to 88.3 m² g^-1 and a total pore volume of 0.022 cm³ g^-1, whereas framework Ni1Co2MOF exhibited a BET surface area of 52.5 m² g^-1 and a total pore volume of 0.016 cm³ g^-1. The incorporation of rGO from 1 to 10 wt.% into the framework changed the charge transport and polarization properties of the materials. The electrochemical investigations of the 10 wt.% rGO-Ni1Co2MOF composite in 0.5 M HCl demonstrated a specific capacitance of 32.3 F g^-1 at 10 mV s^-1, and it preserved 98% of the electrochemical response after 400 cycles, in comparison with 96% for the 10 wt.% rGO-Ni2Co1MOF. The electrochemical responses consisted of both diffusion-controlled ion transport and pseudocapacitance. The introduction of rGO in 1 to 10 wt.% in the polymer composite improved the conductivity and Maxwell-Wagner-Sillars interface polarization at low frequencies in the case of low rGO concentrations, whereas overly high rGO content led to aggregation and the decreased influence of the conductive phase. The main contribution of the present work is the fast sub-100 °C synthesis approach for compositionally tunable Ni-Co frameworks/rGO materials and the relationships between the metal ratio, porous structure, interfacial charge transport, and dielectric response.