M2(CHOO)4 paddlewheel of metal organic frameworks (M = Co, Mo, Ir) with open metal sites as anode materials of Na/K ion batteries: a theoretical study.

The adsorption of Na/Na+ and K/K+ on the three open metal site formate paddlewheels (PWs) of metal-organic frameworks with different metals from the first row of TM (Co-PW), the second row of TM (Mo-PW), and the third row of TM (Ir-PW) were examined to determine if they could be used in NIBs and KIBs. Na/Na+ and K/K+ adsorption energies were measured in the range of −203.5 to −42.1 kJ/mol and −208.4 to −43.7 kJ/mol, respectively. Co-PW cannot serve as a suitable example for NIBs and KIBs since atomic Na and K are both adsorbed more favourably than ionic ones. Ir-PW is suitable only for NIBs with a positive ΔEcell of −14.3 kJ/mol for Na/Na+ adsorption. Mo-PW is a potential candidate as anode material for both Na-ion batteries (NIBs) and K-ion batteries (KIBs) with Ecell of −91.0 and −34.8 kJ/mol with related Vcell of 1.97 and 0.75 V because both Na+ and K+ are much more feasible to adsorption on Mo-PW than Na and K. Although four atoms of Na and K with a theoretical capacity of 288.2 mAh/g toward sodium and potassium can be exothermally adsorbed on the Mo-PW, the ΔEcell and Vcell of the fourth K are close to zero. [ABSTRACT FROM AUTHOR]