Phosphorous-doped nickel-cobalt bimetallic molybdate/three-dimensional hierarchical porous carbon for high-efficiency solid-state supercapacitors

Abstract

The limited electrical conductivity and insufficient quantity of electrochemically active sites in transition-metal oxides impede their extensive utilization in high-performance supercapacitors. Herein, we present a successful synthesis of phosphorus-doped NixCo1-xMoO4 (P-NCMO) on three-dimensional hierarchical porous carbon (HPC) derived from enzymatically hydrolyzed lignin through a co-precipitation pathway and subsequent phosphorylation process. The electrochemical performance was improved by optimizing the content of P doping. Additionally, the incorporation of phosphorus into P-NCMO led to a decrease in Co-O bonding energy and facilitated the formation of molybdenum species with lower oxidation states, thereby enhancing surface redox chemistry and improving electrochemical performance. As a result, the optimized HPC/P-NCMO-2 electrode exhibits a high specific capacity of 1003 C g−1 at a current density of 1 A g−1, and it maintains 89.87 % of its initial capacity after 10,000 cycles at a current density of 1 A g−1. The optimized HPC/P-NCMO-2 assembled as the positive electrode and activated carbon as the negative electrode in an asymmetric supercapacitor delivers a high energy density of 94.7 Wh kg−1 at a power density of 800 W kg−1, while maintaining excellent cycle life.