Interlayer Injection of Low-Valence Zn Atoms to Activate MXene-Based Micro-Redox Capacitors With Battery-Type Voltage Plateaus

Abstract

Insufficient and unstable energy output is the bottleneck issue radically restricting the application of micro-supercapacitors (MSCs). Herein, an interlayer atom injection strategy that can anchor low-valence Zn atoms (Zn^δ⁺, 0 < δ <2) on O-terminals of Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> (MXene) flakes within the MXene/silver-nanowires hybrid cathode of symmetric MSCs is first presented. Combining the polyacrylamide/ZnCl<inf>2</inf> hydrogel electrolyte rich in Cl⁻ and Zn²⁺ ions, the matched Zn^δ⁺/Zn²⁺ (−0.76 V vs SHE) and Ag/AgCl (0.23 V vs SHE), redox couples between the symmetrical electrodes are activated to offer faradaic charge storage beside ions-intercalation involved pseudocapacitance. Thus, a battery-type voltage plateau (≈0.9 V) appears in the discharge curve of a fabricated pseudo-symmetric micro-redox capacitor, simultaneously achieving energy density enhancement (117 µWh cm⁻² at 0.5 mA cm⁻²) and substantially improved power output stability (46% of the energy from the plateau region) relative to that before activation (98 µWh cm⁻² without voltage platform). The work provides a fire-new strategy to overcome the performance bottlenecks confronting conventional MSCs.