Aerogels; Bimetallic selenides; MXene; Graphene; Supercapacitor; Water splitting

In this work, multifunctional Ti3C2 MXene@Graphene composite aerogel fabricated with bimetallic NiCo2Se4 (denoted as NCSe@MGA) have been prepared by hydrothermal method with the assistance of wet-chemical approach. 3D spatial arrangement of NCSe microspheres in hierarchical aerogel structure improved the exposed electroactive surface area. High surface to volume ratio and luxuriant 3D porous framework of aerogel enabled fast multi-dimensional ion-phase transport. Ti3C2 MXene@Graphene composite aerogel act as flexible skeleton to facilitate strain release and restrained the pulverization of NCSe during electrochemical tests. As a result, NCSe@MGA exhibited high specific capacity of 352.4 mAh g(-1) at 1 A g(-1) with 99.6% initial coulombic efficiency, and maintained capacity retention rate to 91.5% after 5000 consecutive cycles at 12 A g(-1). In case of electrocatalytic water splitting, NCSe@MGA realized 10 mA cm(-2) current at significantly low overpotentials of 78 and 201 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The value of Tafel slope was as low as 55 mV dec(-1) (HER) and 79 mV dec(-1) (OER), demonstrating fast kinetics. For both half reactions, no significant decay of current density was observed during 10 h electrolysis test. The synergistic effects stemming from intimate contact among NCSe, MXene and Graphene ultimately boosted the electrochemical activity of NCSe@MGA in comparison to NCSe and NCSe@GA. This study proposes a feasible strategy to design 3D electrode materials with optimal properties for multi-range technological applications.