Redox flow batteries (RFBs) are one of the most promising long-term energy storage technologies which utilize the redox reaction of active species to realize charge and discharge. With the decoupled power and energy components, RFBs exhibit high battery pile construction flexibility and long lifespan. However, the inherent slow electrochemical kinetics of the current widely applied redox active species severely impedes the power output of RFBs. Developing high performance electrocatalysts for these redox active species would boost the power output and energy efficiency of RFBs. Here, we present a critical review of nanoelectrocatalysts to improve the sluggish kinetics of different redox active species, mainly including the chemical components, structure and integration methods. The relationship between the physicochemical properties of nanoelectrocatalysts and the power output of RFBs is highlighted. Finally, the future design of nanoelectrocatalysts for commercial RFBs is proposed.