Cost-effective ion-tuning of Birnessite structures for efficient ORR electrocatalysts

Birnessite structured MnOx with tuned potassium, copper and water content in the interlayer spacing is produced by a simple and cost-effective method. The new structures are investigated by XRD, Raman spectroscopy, SEM, EDX, HRTEM, DLS, TG, and DSC. Our study demonstrates a successful intercalation process to produce birnessites with mixed interlayer cations. Both Birnessite and Cu2+/Birnessite structure have a nanosheet-like morphology where the sizes of the copper-treated birnessite nanoparticles are drastically decreased compared to the copper ion free structures. The specific surface area is increased from 21.6 m2/g to 77.8 m2/g in the presence of copper as a result of a longer ageing process. Our study reveals that the electron transfer numbers of Birnessite and Cu2+/Birnessite are about 3.40 and 3.65, respectively in the oxygen reduction reaction. Both as-synthesized pristine Birnessite and copper tuned Birnessite are a promising candidate for a cheap, noble metal-free electrocatalyst for fuel cell applications.