Pyrolytic Transformation of Zn-TAL Metal-Organic Framework into Hollow Zn-N-C Spheres for Improved Oxygen Reduction Reaction Catalysis.

Metal-organic frameworks (MOFs) are promising precursors for creating metal-nitrogen-carbon (M-N-C) electrocatalysts with high performance, though maintaining their structure during pyrolysis is challenging. This study examines the transformation of a Zn-based MOF into an M-N-C electrocatalyst, focusing on the preservation of the carbon framework and the prevention of Zn aggregation during pyrolysis. A highly porous Zn-N-C electrocatalyst derived from Zn-TAL MOF (where TAL stands for the TalTech-UniTartu Alliance Laboratory) was synthesized via optimized pyrolysis, yielding notable electrocatalytic activity toward oxygen reduction reaction (ORR). Scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) analyses confirmed that the carbon framework preserved its integrity and remained free of Zn metal aggregates, even at elevated temperatures. Rotating disc electrode (RDE) tests in an alkaline solution showed that the optimized Zn-N-C electrocatalyst demonstrated ORR activity on par with commercial Pt/C electrocatalysts. In an anion-exchange membrane fuel cell (AEMFC), the Zn-N-C material pyrolyzed at 1000 °C exhibited a peak power density of 553 mW cm at 60 °C. This work demonstrates that Zn-TAL MOF is an excellent precursor for forming hollow Zn-N-C structures, making it a promising high-performance Pt-free electrocatalyst for fuel cells.