Modulating oxygen coverage of Ti3C2Tx MXenes to boost catalytic activity for HCOOH dehydrogenation

Abstract

As a promising hydrogen carrier, formic acid (HCOOH) is renewable, safe and nontoxic. Although noble-metal-based catalysts have exhibited excellent activity in HCOOH dehydrogenation, developing non-noble-metal heterogeneous catalysts with high efficiency remains a great challenge. Here, we modulate oxygen coverage on the surface of Ti₃C₂T_x MXenes to boost the catalytic activity toward HCOOH dehydrogenation. Impressively, Ti₃C₂T_x MXenes after treating with air at 250 °C (Ti₃C₂T_x-250) significantly increase the amount of surface oxygen atoms without the change of crystalline structure, exhibiting a mass activity of 365 mmol·g^-1·h^-1 with 100% of selectivity for H₂ at 80 °C, which is 2.2 and 2.0 times that of commercial Pd/C and Pt/C, respectively. Further mechanistic studies demonstrate that HCOO* is the intermediate in HCOOH dehydrogenation over Ti₃C₂T_x MXenes with different coverages of surface oxygen atoms. Increasing the oxygen coverage on the surface of Ti₃C₂T_x MXenes not only promotes the conversion from HCOO* to CO₂* by lowering the energy barrier, but also weakens the adsorption energy of CO₂ and H₂, thus accelerating the dehydrogenation of HCOOH.