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 an rGO suspension. Exfoliation and the presence of organic ligands modify the crystal structure and morphology of the tetracyanonickelate particles, thereby enabling the uniform distribution of TCNs on rGO sheets. FTIR and Raman spectroscopy reveal a blueshift in ν(CN), attributed to the 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 the 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 the OER (at 10 mA cm⁻²) and ORR (at 1 mA cm⁻²), respectively. After assembling a Zn–air battery, TCN-NH₂Py composite exhibited the higher discharge potential plateaus, greater stability, and a voltage gap of 0.87 V at 5 mA cm⁻². The battery achieved a capacity of 795.56 mA h g⁻¹ at a current density of 5 mA cm⁻², consistent with prior studies. N₂ physisorption measurements reveal that the NH₂Py-derived hydroxide exhibits the highest surface area (83.34 m² g⁻¹) and pore volume (0.2683 cm³ g⁻¹), 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 d-band center of the hydroxide. Complementary DC and 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.