Modulation of the electrocatalytic performance of rGO/CoCuFe[Ni(CN) 4 ] pillared with pyridine derivatives in Zinc-air batteries

Abstract

Composites consisting of cobalt, iron, and copper tetracyanonickelates, pillared with different organic ligands, were obtained via chemical precipitation and subsequently exfoliated in a rGO suspension. Exfoliation and the presence of organic ligands modify the crystal structure and morphology of tetracyanonickelate particles, thereby enabling a uniform distribution of TCNs on rGO sheets. FTIR and Raman spectroscopy reveal a blueshift of ν(CN), attributed to charge density redistribution from the equatorial coordinated ligand, which also changes the chemical environment of the metals in the composites, as evidenced by XPS. Three-electrode characterization reveals that the coordination of 4-aminopyridine boosts both OER and ORR with average Tafel slopes of 68 mV‧dec-1 (OER) and 73 mV‧dec-1 (ORR), and overpotentials of 0.40 and 0.41 V for OER (@ 10 mA‧cm-2) and ORR (@ 1 mA‧cm-2), respectively. After assembling the Zn-air battery, the TCN-NH2Py stood among the other composites, with higher discharge potential plateaus, greater stability, and a voltage gap of 0.87 V at 5 mA‧cm-2. The battery achieves a capacity of 795.56 mA‧h‧g-1 at a current density of 5 mA‧cm-2, consistent with prior studies. N2 physisorption reveals that NH2Py-derived hydroxide exhibits the highest surface area (83.34 m2/g) and pore volume (0.2683 cm3/g), enhancing electrolyte penetration and active site exposure. Finally, characterization of the positive electrode after cycling demonstrates that multimetallic tetracyanonickelate acts as a precatalyst for specific Fe-Cu-Co-Ni hydroxides, while the pyridine derivatives tune the electrocatalytic performance by shifting the hydroxide's d-band center. Complementary DC/AC magnetic measurements reveal distinct spin configurations that correlate with the optimized electronic structure of NH2Py-OH, providing direct evidence of the local structural disorder underpinning its superior performance.