Synergistic energy storage in Ni/Mn carbonate-hydroxide bilayer electrodes for asymmetric supercapacitors

Abstract

The electrochemical performance of the supercapacitor electrodes was enhanced by integrating a 3D Ni foam substrate with transition metal carbonate–hydroxide composites possessing improved surface wettability. In this study, two types of active materials were synthesized individually, with Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf> forming nanowires and NiMn(CO<inf>3</inf>)(OH)<inf>2</inf> forming nanoplates. These materials were used to fabricate both single-layer electrodes and bilayer electrode architectures. In the single-layer configuration, the Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf> electrode delivered a specific capacity of 128.3 mAh g−1, while the NiMn(CO<inf>3</inf>)(OH)<inf>2</inf> electrode exhibited 74.5 mAh g−1 at a current density of 3 A g−1. In contrast, the bilayer structures showed substantially improved performance. The Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf>–NiMn(CO<inf>3</inf>)(OH)<inf>2</inf> electrode achieved 201.4 mAh g−1, and the NiMn(CO<inf>3</inf>)(OH)<inf>2</inf>–Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf> electrode reached 172.2 mAh g−1 The enhanced performance resulted from the increased effective surface area and the complementary electrochemical reactions facilitated by the bilayer configuration. The cycling stabilities of the two bilayer electrodes, Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf>–NiMn(CO<inf>3</inf>)(OH)<inf>2</inf> and NiMn(CO<inf>3</inf>)(OH)<inf>2</inf>–Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf>, were determined to be 89.6 % and 84.3 %, respectively. In addition, an asymmetric supercapacitor with a Ni<inf>2</inf>(CO<inf>3</inf>)(OH)<inf>2</inf>–NiMn(CO<inf>3</inf>)(OH)<inf>2</inf> positive electrode and a graphene negative electrode exhibited an energy density of 39.6 Wh kg−1 and a power density of 580.7 W kg−1 at a current density of 2 A g−1. These results highlight the potential of supercapacitors based on a bilayer electrode structure. © 2026 Elsevier B.V.