Synergistic effect between strongly coupled CoAl layered double hydroxides and graphene for the electrocatalytic reduction of oxygen

[Display omitted] •CoAl-LDHs were synthesized on the surface of graphene oxide in situ.•The oxygen reduction reaction activity of the catalyst was investigated.•The synergistic effect between CoAl-LDHs and rGO is discussed in detail.•The roles of Co2+ in the LDHs were clarified. Precious metal-free electrocatalysts with high efficiency and durability for the oxygen reduction reaction (ORR) are strongly desired in the field of energy technology. Herein, the CoAl layered double hydroxides (CoAl-LDHs)/reduced graphene oxide (rGO) composites were successfully prepared by growing CoAl-LDHs on the surface of GO in situ via coprecipitation and subsequently hydrothermal treatment. The structure, composition, morphology and ORR catalytic activity of the CoAl-LDHs/rGO composites were investigated as a function of mass ratios of CoAl-LDHs and GO. The results show that there is an optimum mass ratio of CoAl-LDHs and GO (wCoAl-LDHs:wGO=1:5) for the ORR catalytic activity, where the electron transfer number for ORR at the CoAl-LDHs/rGO composites reaches to 3.5, closing to the full four-electron process. The synergistic effect between CoAl-LDHs and rGO is discussed in detail and the discussion is instructive for the construction of the better transition metal oxides/carbon composite-based ORR catalysts.