Versatile double hydrophilic block copolymer: dual role as synthetic nanoreactor and ionic and electronic conduction layer for ruthenium oxide nanoparticle supercapacitors

Abstract

The facile synthetic approach to ruthenium oxide nanoparticles using double hydrophilic block copolymers (DHBCs) and their application toward the supercapacitor are presented. Nanostructured hydrous ruthenium oxide (RuO₂) nanoparticles are synthesized using a double hydrophilic block copolymer of poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA) as a template, forming a micelle upon addition of the ruthenium precursor, which then transformed into RuO₂ nanoparticles of controlled dimension with reducing agents. The synthesized hydrous RuO₂·xH₂O nanoparticles are very stable for several months without any noticeable aggregates. Furthermore, we have demonstrated their utility in application as supercapacitors. Through annealing at 400 °C, we found that the crystallinity of RuO₂ nanoparticles increases considerably with a simultaneous transformation of the surrounding double hydrophilic block copolymer into ionic and electronic conducting buffer layers atop RuO₂ nanoparticles, which contribute to the significant enhancement of the overall specific capacitance from 106 to 962 F g⁻¹ at 10 mV s⁻¹. The RuO₂ nanoparticles annealed at 400 °C also exhibit a superior retention of capacitance over 1000 cycles at very high charge–discharge rates at 20 A g⁻¹. We envision that the double hydrophilic block copolymer will provide a facile and general tool in creating functional nanostructures with controlled dimensions that are useful for various applications.