Ab initio characterization of hybrid MOF-MXenes surfaces: The case of Cu-pyridyl on Ti₂CO₂

Hybrid MOF-MXenes appear as an appealing system for electrocatalytic reactions. The combination of a MXene substrate with a metal-embedded organic 2D network prevents the metal sintering and provides the material with unique redox surface properties. In this work we characterize by periodic density functional theory the geometry, energetics, and electronic structure of a superstructure containing copper atoms, pyridine, and 1,3,5-tris(pyridyl)benzene molecules supported on a Ti2CO2 substrate. The adsorption of each individual adsorbate is energetically favorable, and their coadsorption stabilizes the overall system, with an electron transfer from the adsorbates to the support and a charge of similar to+0.68 |e| for Cu. The (co)adsorption systems are found to be more reducible than the bare support, as observed in the work function values and the oxygen vacancy formation energy. Interestingly, the formation of oxygen vacancies close to the position of Cu is found to be the most energetically favorable, inducing the migration of the Cu atom to fill the vacancy and become negatively charged, similar to-0.40 |e|. This effect may play an important role in electrocatalytic processes by (de)stabilizing intermediates adsorbed on Cu sites, as in the ORR reaction.