Superhydrophilic molybdenum nitride nanoplate arrays enable rapid cerium reaction kinetics

Abstract

The cerium-based redox flow batteries (RFBs) have great potential for efficient energy storage applications, so the development of highly active and cheap catalysts has become an indispensable work due to the sluggish kinetics of cerium redox reactions. In this work, we prepare a superhydrophilic molybdenum nitride (MoN) nanoplate arrays (NPAs) decorated graphite felt (GF) electrode (MNGF) for cerium-based RFBs by a generalized and high-yield route in terms of scalable impregnation method and facile nitriding reaction. Interestingly, the 3D micro-nano hierarchical NPAs with open and ordered structure ensure entirely exposing active sites toward cerium electrolyte and contribute to the direct and complete contact of every nanoplate with cerium electrolyte. Moreover, in the contact angle measurements, the electrolyte droplet instantaneously soaked into the surface of MNGF in a very short time (within 0.3 s) and the electrolyte solution contact angle of MNGF is ultrasmall, even near 0°, as compared to 102.6° for MoO2 decorated GF (MOGF), 113.4° for air-oxidized GF (AGF), and 121.9° for pristine GF, suggesting that MNGF is superhydrophilic. The highly catalytic MoN NPAs with ingenious open and ordered structure and superhydrophilicity enable the MNGF to possess excellent catalytic activity toward Ce4+/Ce3+ electrochemical reactions. When applied to the cerium-zinc RFBs, the energy efficiency of MNGF is increased by 46.8% relative to pristine GF at 40 mA cm−2. The viable strategy proposed here, for the first time, applies the superhydrophilic materials concept into catalyst design for RFBs and provides a new perspective on the performance boost of RFBs.