Achieving high energy density with all pseudocapacitive asymmetric materials as energy storage device: Metallic ruthenium confined in MOF-derived N-doped porous carbon as positive and free-standing Ti3C2 film as negative electrode

Abstract

Herein, we report for the first time the transformation of non-conductive ruthenium (Ru)-based metal-organic frameworks (Ru-MOFs) into MOF-derived metallic Ru encapsulated by a nitrogen-doped graphitic carbon matrix (Ru@N-doped C), forming a nano-heterostructured interface. This unique feature offered by Ru@N-doped C facilitates the generation of abundant redox-active sites (Ru) while promoting efficient ion transport through well-defined diffusion channels (N-doped C) in sulfuric acid (H2SO4, 1 M). The resultant Ru@N-doped C electrode exhibits a faradaic (non-diffusion-limited) charge storage mechanism, and the calculated specific capacitance (211.1 F g-1 at 1 A g-1) outperforms other pristine ruthenium dioxide (RuO2)-based electrodes. The synergistic integration of highly conductive N-doped carbon with metallic Ru enhances both redox activity and ion diffusion kinetics, while maintaining excellent rate capability. When Ru@N-doped C (positive electrode) is integrated with pseudocapacitive Ti3C2 MXene free-standing film (negative electrode), it exhibits all pseudo-capacitive asymmetric device configurations and delivers superior specific capacitance (194.3 F g-1 at 1 A g-1), accompanied by faradaic efficiency (90 %) and capacitive retention (109 %). The asymmetric (ASC) device demonstrates high energy density (60.7 Wh kg-1) and power density of 1294 W kg-1, which outperforms other reported RuO2-based devices.