Iminodiacetonitrile induce-synthesis of two-dimensional PdNi/Ni@carbon nanosheets with uniform dispersion and strong interface bonding as an effective bifunctional eletrocatalyst in air-cathode

Developing highly-active, stable and conductive bifunctional electrocatalysts towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a key step for rechargeable Zn-air batteries. From unique molecular structure of iminodiacetonitrile (IDAN), herein we design and build a novel organometallic coordination polymer (OCP) for the synthesis of hierarchical N-doped carbon nanosheets anchored PdNi/Ni hybrids (PdNi/Ni@N-C). The cyano ligands in IDAN can form a low spin planar tetragonal complex with M²⁺ (M=Pd and Ni) by dsp² hybridization, while the amino ligands tend to form a high spin tetrahedral complex with M²⁺ by sp³ hybridization, which not only induce the formation of 2D carbon nanosheets, but also strengthen metal-carbon interaction after the pyrolysis. The optimized PdNi/Ni@N-C can function as an outstanding bifunctional electrocatalyst, presenting a positive half-wave potential of 0.89 V towards ORR and a low overpotential of 360 mV at 10 mA cm⁻² towards OER, out-performing commercial precious-metal benchmarks. Theoretical calculations are performed to analyze the alloying effects of PdNi and identify the potential active sites for ORR/OER. Furthermore, the PdNi/Ni@N-C as an air-cathode can enable rechargeable liquid and flexible all-solid-state Zn–air batteries to achieve higher power density and longer cycle life than costly Pd/C+RuO₂-driven batteries. This work offers a potential molecular design strategy for the development of efficient electrocatalysts for energy storage and conversion.