A new methodology for evaluating the performances of electrocatalysts for rechargeable Li-O2 batteries: (Ru-Sn)O2@graphene nanowalls/Ti electrodes as an example

[Display omitted] •CV with various ESL effectively evaluates the catalysis of air cathodes.•The Ru-enriched (Ru-Sn)O2 is the best bifunctional catalyst for Li-O2 cells.•The Sn-enriched (Ru-Sn)O2 shows a higher ORR activity than Ru-enriched (Ru-Sn)O2. The bi-functional activities of electrocatalysts for the oxygen reduction reaction (ORR) and discharge products decomposition in the typical organic electrolyte of rechargeable Li-O2 batteries are proposed to be effectively evaluated by cyclic voltammetry (CV) with varying the lower potential limit. The free-standing Ru-Sn oxides-decorated graphene nanowalls are employed as examples to demonstrate this interesting methodology. Both Ru-enriched and Sn-enriched Ru-Sn oxides (RTO73 and RTO37) show higher bi-functional activities than two mono-oxides and pure graphene from CV and confirmed by the charge–discharge results. The full cell performances such as rate capability, cycle life and charge–discharge voltage gaps can be correlated to the findings from CV.