NiCo 2 O 4 /MXene Hybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reaction

Abstract For the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt‐based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo 2 O 4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo 2 O 4 /MXene) was developed. The successful integration of NiCo 2 O 4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo 2 O 4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo 2 O 4 /MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm 2 , and a small Tafel slope of 64 mV/dec compared to NiCo 2 O 4 , MXene and NiCo 2 O 4 +MXene (physically mixed). Additionally, NiCo 2 O 4 /MXene displays an ORR limiting current density of −4 mA/cm 2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo 2 O 4 , MXene and NiCo 2 O 4 +MXene (physically mixed).