Ternary FeNiS2 ultrathin nanosheets as an electrocatalyst for both oxygen evolution and reduction reactions

High-performance and cost-effective electrocatalysts are essential for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we provide the first report about a facile colloidal method to fabricate 2D ultrathin ternary FeNiS2 nanosheets (NSs). When serving as an OER catalyst under alkaline conditions, they exhibited superior electrocatalytic performance over RuO2 and achieved a current density of 10 mA cm−2 with a potential of 1.54 V and a Tafel slope of 46 mV decade−1. Meanwhile, an ORR catalytic activity was also achieved with an onset potential of 0.78 V, a Tafel slope of 107 mV decade−1, and a high selectivity with electron transfer number of 3.92 and H2O2% of 3.6% at 0.3 V under neutral conditions, which were comparable to those of the commercial Pt/C. The ternary FeNiS2-NSs were superior over the binary FeS NSs and Ni9S8 nanorods synthesized via the same routes. More importantly, with the resistance for the corrosion and poison from the alkaline and phosphate buffer solution, the FeNiS2 NSs exhibited superior stability without apparent OER or ORR catalytic activity loss over long-term operation. Their enhanced electrocatalytic performance compared to their binary counterparts indicate that a new strategy to prepare high performance OER and ORR catalysts was developed. In addition, the as-prepared FeNiS2 NSs could serve as a noble-metal-free catalyst for OER or ORR with good electrocatalytic activities and long-term stability for practical applications.