<p>Aqueous redox flow batteries are promising for long-duration energy storage. However, many of them (e.g. sulfur-based and organic-based flow batteries) suffer from sluggish kinetics with low energy efficiency and insufficient capacity utilization. Here, we propose relay catalysis as a universal strategy to achieve high reaction rates while minimizing overpotential, enabling high capacity and energy efficiency. Inspired by sequential electron transfer in cellular respiration, relay catalysis employs a low-overpotential catalyst (e.g., isoalloxazine) to initiate the reaction, seamlessly transferring control to a high-activity catalyst (e.g., quinone) to sustain charge propagation, breaking the trade-off between overpotential and catalytic rate. Using this strategy, we demonstrate polysulfide-ferrocyanide flow batteries with near full polysulfide utilization (S₄^2–/S₂^2–, 64 Ah L^–1_negolyte) and high stability over 3 months (&gt; 500 cycles at 20 mA cm^–2, decay rate 0.00071% per cycle, 0.003% per day). We further extend this strategy to organosulfide- and azo-based batteries with various relay-catalyst couples. By mimicking biological electron relays, this approach not only redefines homogeneous catalysis for energy storage but also establishes a transformative platform for designing flow batteries with enhanced performance and scalability.</p>