Bifunctional PGM-free electrocatalysts for seawater batteries

Abstract

Seawater batteries (SWBs) are an emerging energy storage solution that leverages the abundant and cost-effective sodium ions present in seawater. However, their performance is often constrained by the sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) at the seawater cathode. To overcome these limitations, a series of platinum group metal (PGM)-free bifunctional electrocatalysts was developed to enhance OER/ORR catalytic activity and overall power performance. Metal-doped nitrogen carbon nanoparticles (M-N-C), namely FeNiNC, FeNC, and NiNC, were synthesized via a simple precipitation method followed by heat treatment, yielding an amorphous structure that promotes improved capacitive behavior. The use of low-cost biomass derived from hazelnut shells as a carbon-based material, modified with Fe and/or Ni, resulted in a highly efficient catalyst. Particularly, FeNiNC exhibited an ORR activity of 0.87 V vs. RHE at half-potential and an OER activity of 1.57 V vs. RHE at a current density of 10 mA cm⁻². Electrochemical characterization demonstrated that SWBs incorporating the FeNiNC catalyst achieved significantly enhanced power output and cycling stability, maintaining performance for 350 hours.