Constructing dual hydroxide ion conduction channels with sulfonated hollow carbon spheres for alkaline zinc-based flow battery membrane

Alkaline zinc-based flow batteries (AZFBs) have emerged as a promising candidate for large-scale energy storage due to their low cost and high energy density. However, the pursuit of high power density in AZFBs has been hindered by the lack of ion conductive membranes (ICMs) capable of delivering high and stable ion conduction, a challenge that has yet to be fully addressed. Herein, we designed an innovative sulfonated hollow carbon sphere (SHCS)-embedded ICM designed specifically for AZFBs. By combining a hydrophilic polymer with SHCS, the membrane achieved exceptional ion conductivity through dual ion conduction channels. The sulfonic acid groups on SHCS and the polymer side chains created interconnected water networks, enabling efficient ion transport. Additionally, hollow structure and alkali resistance of SHCS provided stable ion pathways. As a result, the proposed membrane exhibited a superior OH⁻ conductivity of 10.28 mS cm⁻¹, surpassing the pure polymer membrane (4.69 mS cm⁻¹). In AZFB tests, it achieved an 88.9 % voltage efficiency at 80 mA cm⁻² and operated for over 1570 cycles (1130 h). This work offers a breakthrough in designing high-performance ICMs, advancing high power density AZFBs for energy storage.