Low-cost bio-inspired electrocatalyst for rechargeable metal-air battery

Indian scientists have synthesized a bio-inspired electrocatalyst that can help develop efficient, low-cost renewable energy conversion and storage technologies such as fuel cells, biofuel cells, and metal-air batteries. 

The electrocatalyst—developed by Dr Ramendra Sundar Dey and his team at the Institute of Nano Science and Technology (INST), Mohali—is based on iron (Fe), manganese (Mn) and N-doped fish gill derived carbon (Fe/Mn/N-FGC). It has a unique porous structure and could provide conductive carbon networks after heat treatment. 

The catalyst, when used as an air cathode in zinc-air battery, was able to show active oxygen reduction reaction (ORR) in a wide range of pH (pH< 1, 7, and >13) and outperformed platinum-on-carbon (Pt/C) catalyst.

Study findings

Transition-metal atoms and/or heteroatom-doped carbon nanostructures are a crucial alternative to find a nonprecious metal catalyst for electrocatalytic ORR. 

In their study, for the first time, the INST scientists demonstrated the formation of binary (Fe-Mn) active sites in hierarchically porous nanostructure composed of Fe, Mn, and N-doped fish gill derived carbon.

They fabricated a homemade rechargeable Zn−air battery (ZAB) with the catalyst as an air cathode, which showed almost stable charge−discharge voltage plateaus after rigorous cycling for a long duration. It surpassed the commercial Pt/C based ZAB performance.

The Fe/Mn/N-FGC catalyst showed onset potential (Eonset) of 1.03 V and half-wave potential (E1/2) of 0.89 V, slightly better than commercial Pt/C (Eonset = 1.01 V, E1/2 = 0.88 V) in alkaline medium (pH > 13). The remarkable ORR performance is attributed to the synergistic effect of Fe-Mn dual metal center, as evidenced by X-ray absorption spectroscopic study. 

The scientists found that the reason behind the outstanding performance of this catalyst is the presence of Fe−Mn based binary moiety, which is beneficial for the Oxygen (O2) binding and boosting ORR catalytic performances in alkaline medium by weakening the Oxygen-Oxygen bonds.

The researchers have suggested that the careful selection of transition metals and heteroatoms together with engineering the synthesis protocol could lead to highly active low-cost electrocatalyst for energy conversion devices.

The results of the strategy to synthesize the bioinspired electrocatalyst have been published in the journal Inorganic Chemistry published by the American Chemical Society.