Effect of the biaxial strain on the electronic structure, quantum capacitance of NH3 adsorption on pristine Hf2CO2 MXene using first-principles calculations

The adsorption of NH3 molecule on Hf2CO2 monolayer is investigated by first-principles calculation. The possible adsorption sites are all considered. The results show that TH-PH system (N atom of NH3 molecule on the top site over Hf atom) is the most suitable adsorption system among all the possible configurations. The recovery times of TH-PH system are very short in the strain range from −2% to +2%. TH-PH system under −2% strain changes from chemical adsorption to physical adsorption and is suitable to be used for NH3 detection due to the high sensitivity and short recovery time. The analysis of the effective mass indicates that applying strain can improve electron transfer in the valence band. The quantum capacitance of TH-PH system under strain is further explored. Hf2CO2 under strain is a potential cathode material for asymmetric supercapacitors. The introduction of the strain can generally improve the maximum Cdiff of Hf2CO2 MXene.