Novel Graphene Hydrogel/B-Doped Graphene Quantum Dots Composites as Trifunctional Electrocatalysts for Zn-Air Batteries and Overall Water Splitting

Herein, a facile, one-step hydrothermal route to synthesize novel all-carbon-based composites composed of B-doped graphene quantum dots anchored on a graphene hydrogel (GH-BGQD) is demonstrated. The obtained GH-BGQD material has a unique 3D architecture with high porosity and large specific surface area, exhibiting abundant catalytic active sites of B-GQDs as well as enhanced electrolyte mass transport and ion diffusion. Therefore, the prepared GH-BGQD composites exhibit a superior trifunctional electrocatalytic activity toward the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction with excellent long-term stability and durability comparable to those of commercial Pt/C and Ir/C catalysts. A flexible solid-state Zn-air battery using a GH-BGQD air electrode achieves an open-circuit voltage of 1.40 V, a stable discharge voltage of 1.23 V for 100 h, a specific capacity of 687 mAh g(-1), and a peak power density of 112 mW cm(-2). Also, a water electrolysis cell using GH-BGQD electrodes delivers a current density of 10 mA cm(-2) at cell voltage of 1.61 V, with remarkable stability during 70 h of operation. Finally, the trifunctional GH-BGQD catalyst is employed for water electrolysis cell powered by the prepared Zn-air batteries, providing a new strategy for the carbon-based multifunctional electrocatalysts for electrochemical energy devices.