To calculate the Ti vacancy formation energy for Ti3C2T2, unit cells with one removed Ti atom were prepared, cells parameters were fixed, and atomic positions were relaxed. The Ti vacancy formation energy was defined as 𝐸 V = 𝐸 defect -𝐸 perfect + 𝜇 Ti , where 𝐸 V stands for the Ti vacancy formation energy, 𝐸 defect is the free energy of system with vacancy, 𝐸 perfect is the free energy of the original MXene.