Synthesis and Characterisation of High Performing Heteroatom Doped Carbon Catalyst for Oxygen Reduction Reaction (ORR) in Alkaline Fuel Cells

Ramya, Krishnan

Alkaline fuel cell (AFC) routing platinum-free electrocatalysts are one of the potential frontiers to enable its use in widespread applications. PGM catalysts have always been preferred and widely utilised due to their enhanced intrinsic activity and superior performance. Its high cost and less abundance brought attention to heteroatom doped carbon-based electrocatalysts that offer comparable performance, tunable selectivity and simple synthesis route. The lack of efficient catalysts hampers the performance, peak power density and longevity of the cell due to sluggish ORR activity.

In this article, Heteroatom-doped carbon (F, N/F and N/S/F) is prepared using PVDF-HFP polymer as a precursor. The polymer is mixed with urea or ThioUrea concerning the required dopant and pyrolyzed at 900 ^ºC for 3 hours at a heating rate of 5 deg per min in an inert atmosphere. The enhanced performance is obtained from the N/F- doped carbon which shows an onset potential (E = 1.04V vs. RHE), a diffusion-limited current density(j) of 6.12 mA/cm² in 0.1M KOH, which is comparatively better than the F-doped and N/S/F-doped carbon. The number of electrons (n) involved in the ORR activity was calculated to be 3.99, 3.98, 3.85 for N/F-C, N/S/F-C and F-C respectively. This suggests a 4e^- pathway indicating efficient operation for the Alkaline electrochemical cell. The systematic studies exhibit an increased ORR activity in the case of the N/F-doped carbon electro-catalyst due to a combined synergistic effect of hetero-atoms and high surface area. Heteroatom doping and the activity in the carbon material were confirmed by all the necessary physical and electrochemical characterisations.

Keywords: Hydrogen, Alkaline Fuel cell, AFC, Oxygen reduction reaction, ORR catalyst