Dimethyl formamide pillared cobalt tetracyanonickelate coupled with rGO as a bifunctional pre-electrocatalyst for Zn-air batteries

•A new pillared structure was obtained by coordinating DMF to cobalt ions in the solid.•Cobalt tetracyanonickelate is responsible for promoting the oxygen evolution reaction.•rGO displaces the on-set for the oxygen reduction reaction towards higher potentials.•Synergy between rGO and CoTCN improves the discharging voltage of the zinc-air battery.•Assembled zinc-air battery displays a specific capacity of 760 mA h g−1 at 5 mA cm−2. 2D-Hofmann-type MOFs are gaining interest due to their ability to incorporate transition metals and organic ligands, which enhance electrochemical and electrocatalytic properties. However, they mainly catalyze the OER and must be paired with another material to obtain bifunctional catalytic activity. Composites were created with different ratios of cobalt tetracyanonickelate and rGO through chemical precipitation in an ultrasonically dispersed rGO in H2O:DMF solution. The addition of rGO alters the crystalline structure and morphology of cobalt tetracyanonickelate. Three-electrode characterization indicates that pristine materials individually enhance the OER (CoTCN) and ORR (rGO), while their combination exhibits bifunctionality with Tafel slopes of 66 mV‧dec−1 (OER) and 81 mV‧dec−1 (ORR), and overpotentials of 0.4 V for both processes. In assembled Zn-air batteries, the 1:1 composite outperformed the others, achieving higher potential plateaus, stability, a voltage gap of 0.96 V, and a specific capacity of 760 mA‧h‧g−1 at 5 mA‧cm−2. Finally, post-mortem analysis indicates that cobalt tetracyanonickelate acts as a precatalyst for Co and Ni hydroxides. [Display omitted]