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

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 Ti3C2Tx MXenes to boost the catalytic activity toward HCOOH dehydrogenation. Impressively, Ti3C2Tx MXenes after treating with air at 250 °C (Ti3C2Tx-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 Ti3C2Tx MXenes with different coverages of surface oxygen atoms. Increasing the oxygen coverage on the surface of Ti3C2Tx 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.