Strategies for liquid-liquid extraction of oxide particles for applications in supercapacitor electrodes and thin films

Bottom-up and top-down liquid-liquid extraction methods have been developed for the transfer of colloidal metal oxide particles, synthesized in an aqueous phase, to organic phases. In such methods the agglomeration of the particles during the drying stage was avoided. Hexadecylamine was used as an extractor for MnO₂ particles in the bottom-up extraction to the 1-butanol phase and top-down extraction to the dichloromethane phase. The reduction of particle agglomeration facilitated the fabrication of MnO₂-carbon nanotube composite electrodes for electrochemical supercapacitors with enhanced mixing of the individual components and active mass as high as 35mgcm^-2. Electrochemical testing results showed superior performance of the composite MnO₂-carbon nanotube electrodes, prepared by the bottom-up strategy. The new strategies allowed the fabrication of advanced electrodes, which showed a capacitance of 5.48Fcm^-2 at a scan rate of 2mVs^-1, good capacitance retention at high scan rates and low resistance. In another conceptually new bottom-up strategy colloidal titania particles were modified during synthesis with 2,3,4-trihydroxybenzaldehyde, which allowed strong catecholate-type bonding to the Ti atoms on the particle surface. The Schiff base reaction with hexadecylamine at the liquid-liquid interface allowed for particle extraction. The extraction strategies developed in this investigation pave the way for agglomerate-free processing of advanced films, coatings and devices by colloidal methods.