Balancing the piezoelectric coefficient and carrier concentration of materials is key in the field of piezocatalysis. In this work, Bi₂WO₆ material with both piezoelectric and semiconductor properties was chosen as a model material. A one-step ethylene glycol (EG)-assisted solvothermal method was used to synthesize Bi₂WO₆ with oxygen vacancies. By controlling the solvothermal time and temperature, the oxygen vacancy concentration (C_OV) was regulated. As C_OV increases, the piezoelectric coefficient decreases, the carrier concentration increases, and the hydrogen production rate first increases but then decreases. When C_OV reaches 1.45×10¹² spins·mg⁻¹, the corresponding piezoelectric coefficient and carrier concentration are 13.9 pm·V⁻¹ and 2.90×10²⁰ cm⁻³, respectively. The optimal hydrogen production rate per power of 2.21 μmol·g⁻¹·h⁻¹·W⁻¹ is equivalent to or even better than that of most reported piezocatalysts. The piezoelectric coefficient and carrier concentration, as two factors, jointly determine the piezocatalytic performance. The findings of this research can provide important and deep-seated insights for better piezocatalysts in the future.

Potassium ion-based dual-graphite batteries (KDGBs) emerge as promising devices for large-scale applications due to their high voltage, low cost, and environmental friendliness. However, conventional KPF₆/carbonate-based electrolytes suffer from severe oxidation decomposition, low concentration, and flammability, which limit the capacity and cyclability of KDGBs. Herein, a nonflammable potassium bis(fluorosulfonyl)imide/triethyl phosphate (KFSI/TEP) electrolyte was designed for KDGBs. When the salt-to-solvent molar ratio increases to 1:1.3, graphite cathode operated at the cut-off potential of 5.2 V exhibits much enhanced capacity, excellent rate capability (26.4 mAh∙g⁻¹ at 1.0 A∙g⁻¹), and superior cyclability with 98% capacity retention after 350 cycles. Inorganic compounds-rich electrode/electrolyte interphase layers derived from the preferential decomposition of FSI⁻ anions ensure good compatibility of the 1:1.3 KFSI/TEP electrolyte with K metal and graphite anodes. Based on this electrolyte, as-assembled KDGBs show high operation voltage of 4.3 V and good cycling performance. This work provides feasibility for developing long-life and safe-operation DGBs.