Dual-Atom Co/Ni Electrocatalyst Anchored at the Surface-Modified Ti₃C₂T_<i>x</i> MXene Enables Efficient Hydrogen and Oxygen Evolution Reactions.

Abstract

Dual-atom catalytic sites on conductive substrates offer a promising opportunity for accelerating the kinetics of multistep hydrogen and oxygen evolution reactions (HER and OER, respectively). Using MXenes as substrates is a promising strategy for depositing those dual-atom electrocatalysts, if the efficient surface anchoring strategy ensuring metal-substrate interactions and sufficient mass loading is established. We introduce a surface-modification strategy of MXene substrates by preadsorbing L-tryptophan molecules, which enabled attachment of dual-atom Co/Ni electrocatalyst at the surface of Ti₃C₂T_<i>x</i> by forming N-Co/Ni-O bonds, with mass loading reaching as high as 5.6 wt %. The electron delocalization resulting from terminated O atoms on MXene substrates, N atoms in L-tryptophan anchoring moieties, and catalytic metal atoms Co and Ni provides an optimal adsorption strength of intermediates and boosts the HER and OER kinetics, thereby notably promoting the intrinsic activity of the electrocatalyst. CoNi-Ti₃C₂T_<i>x</i> electrocatalyst displayed HER and OER overpotentials of 31 and 241 mV at 10 mA cm^-2, respectively. Importantly, the CoNi-Ti₃C₂T_<i>x</i> electrocatalyst also exhibited high operational stability for both OER and HER over 100 h at an industrially relevant current density of 500 mA cm^-2. Our study provided guidance for constructing dual-atom active metal sites on MXene substrates to synergistically enhance the electrochemical efficiency and stability of the energy conversion and storage systems.