Chemical Origin of Effective Functionalization of Single Atom-MXene Catalysts

Abstract

The chemical and atomic structures of the Cu-, Ni,- or CuNi-embedded MXene (Ti3C2Tx, T=O or OH) nanosheet catalysts are examined by using various characterization methods to demonstrate the chemical origin of their composition-dependent evolution. The results of combined X-ray spectroscopy studies and the electrochemical test reveal that Cu ions in (Cu or CuNi):MXene remain active having +1 valence and form metallic Cu–Cu bonds to enhance the catalytic activity for nitrate reduction. By contrast, Ni ions in (Ni or CuNi):MXene tend to remain bound to O as in Ni2+Ox staying inactive, and furthermore, hinder the catalytic activity of Cu when co-doped on MXene. It is also demonstrated that chemistry of MXene itself varies by donating electrons from Ti2+/3+ to Cu2+ to stabilize the active Cu+ ions. These findings support a combinational mechanism in which both the abundant metallic bonds and the cooperative chemical reconstruction happened via MXene–to–Cu charge transfer facilitate the single atom-aided functionalization of MXene catalyst.