Successive ionic layer adsorption and reaction–deposited copper sulfide electrocatalyst for high-power polysulfide-based aqueous flow batteries

With the widespread exploitations of renewable energy sources, electrochemical energy storage (EES) systems that could store electric energy in large quantity and buffer the impact of intermittently generated electricity from wind and solar, become increasingly important for the resilience and quality of power grids. Among various EES systems, redox flow batteries (RFBs) offer greater promise for reliable and durable grid-scale storage of electricity owing to their salient feature of decoupled energy storage and power generation. However, the deployments of RFBs are severely impeded by the high material and system costs. Polysulfide has been studied as a low-cost, highly soluble, and robust anodic redox species for RFBs, although it suffers from sluggish reaction kinetics. Here, we report a feasible successive ionic layer adsorption and reaction method to graft the copper sulfide electrocatalyst on the graphite felt electrode, which substantially promotes the redox reaction of polysulfide. With [Fe(CN)6]4−/3− as the catholyte and polysulfide as the anolyte, an RFB with a power density of 116 mW cm−2 at 220 mA cm−2 and an energy efficiency of 77.7% at 50 mA cm−2 has been attained, markedly superior to the reported ones. With the considerably improved performance, the polysulfide-[Fe(CN)6]4−/3− flow battery has been demonstrated to be a cost-effective solution for large-scale energy storage.