With good operation flexibility and scalability, vanadium redox‐flow batteries (VRBs) stand out from various electrochemical energy storage (EES) technologies. However, traditional electrodes in VRBs, such as carbon and graphite felt with low electrochemical activities, impede the interfacial charge transfer processes and generate considerable overpotential loss, which significantly decrease the energy and voltage efficiencies of VRBs. Herein, by using a facile electrodeposition technique, Prussian blue/carbon felt (PB/CF) composite electrodes with high electrochemical activity for VRBs are successfully fabricated. The PB/CF electrode exhibits excellent electrochemical activity toward VO2+/VO2+ redox couple in VRB with an average cell voltage efficiency (VE) of 90% and an energy efficiency (EE) of 88% at 100 mA cm−2. In addition, due to the uniformly distributed PB particles that are strongly bound to the surface of carbon fibers in CF, VRBs with the PB/CF electrodes show much better long‐term stabilities compared with the pristine CF‐based battery due to the redox‐mediated catalysis. A VRB stack consisting of three single cells (16 cm2) is also constructed to assess the reliability of the redox‐mediated PB/CF electrodes for large‐scale application. The facile technique for the high‐performance electrode with redox‐mediated reaction is expected to shed new light on commercial electrode design for VRBs.
Vanadium redox flow batteries (VRFBs) are widely applied in energy storage systems (e.g., wind energy, solar energy), while the poor activity of commonly used carbon-based electrode limits their large-scale application. In this study, the graphene modified carbon felt (G/CF) with a large area of 20 cm × 20 cm has been successfully prepared by a chemical vapor deposition (CVD) strategy, achieving outstanding electrocatalytic redox reversibility of the VRFBs. The decorating graphene can provide abundant active sites for the vanadium redox reactions. Compared with the pristine carbon felt (CF) electrode, the G/CF composite electrode possesses more defective sites on surface, which enhances activity toward VO 2+ /VO 2 + couple and electrochemical performances. For instance, such G/CF electrode delivered remarkable voltage efficiency (VE) of 88.4% and energy efficiency (EE) of 86.4% at 100 mA•cm −2 , much higher than CF electrode by 2.1% and 3.78%, respectively. The long-term cycling stability of G/CF electrode was further investigated and a high retention value of 47.6% can be achieved over 600 cycles. It is demonstrated that this work develops a promising and effective strategy to synthesize the large size of carbon electrode with high performances for the next-generation VRFBs.
To describe the commonly existing coupling between adsorption dynamics and fluid flow, a nonequilibrium molecular model is developed, upon which we systematically investigate the dynamical adsorption of ionic components from confined flows onto the charged surfaces of nanoscale pores, and find that a competition relation exists between the adsorption and flow. Promoting flow speed suppresses the adsorption amount, while enhancing adsorption strength reduces the flow speed. With the increase of flow speed, the contact density of co‐ion is enhanced while that of counterion is suppressed, leading to overall enhanced accumulation charge densities at pore surfaces. Besides, the accumulation charge density increases monotonically with the applied voltage in large pores, while displays a nontrivial relation with the applied voltage in small pores of several ion sizes. This work not only extends the theoretical framework of nonequilibrium molecular theories, but also provides novel insights into the regulation of interfacial dynamic processes.
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