One-Step Hydrothermally Synthesized Ni₁₁(HPO₃)₈(OH)₆/Co₃(HPO₄)₂(OH)₂ Heterostructure with Enhanced Rate Performance for Hybrid Supercapacitor Applications

Abstract

Transition metal phosphate is the prospective electrode material for supercapacitors (SCs). It has an open frame construction with spacious cavities and wide aisles, resulting in excellent electric storage capacity. However, the inferior rate behavior and cycling stability of transition metal phosphate materials in alkaline environments pose significant barriers to their application in SCs. Herein, Ni11(HPO3)8(OH)6/Co3(HPO4)2(OH)2 heterostructured materials synthesized through a one-step hydrothermal process exhibiting remarkable rate capability coupled with exceptional cycling endurance. Ni11(HPO3)8(OH)6/Co3(HPO4)2(OH)2 samples exhibit a micron-scale structure composed of sheet-like compositions and unique pore structure. The multistage pore structure is favorable for promoting the diffusion of protons and ions, enhancing the sample’s electrochemical storage capacity. Upon conducting electrochemical tests, it was observed that Ni11(HPO3)8(OH)6/Co3(HPO4)2(OH)2 composite electrode surpassed both the standalone Ni11(HPO3)8(OH)6 and Co3(HPO4)2(OH)2 electrode, achieving a remarkable specific capacity of 163 mAh g−1 with exceptional stability and efficiency at 1 A g−1. Notably, this electrode also exhibits superior rate performance, maintaining 82.5% and 71% of its original full capacity even at 50 A g−1 and 100 A g−1, respectively. Furthermore, it demonstrates superior stability in cycling, retaining a capacity of 92.7% at 10 A g−1 after 5000 cycles. Moreover, Ni11(HPO3)8(OH)6/Co3(HPO4)2(OH)2 and porous carbon (PC) were assembled into a hybrid supercapacitor (HSC). Electrochemical tests reveal an impressive power density of up to 36 kW kg−1 and an exceptional energy density of up to 47.4 Wh kg−1 for the HSC. Moreover, Ni11(HPO3)8(OH)6/Co3(HPO4)2(OH)2//PC HSC exhibits robust capacity retention stability of 92.9% after enduring 10,000 cycles at 3 A g−1, demonstrating its remarkable durability. This work imparts viewpoints into the design of transition metal phosphate heterostructured materials.

Keywords

• high-rate performance
• hybrid supercapacitor
• nickel cobalt phosphate
• heterostructure