Polymorphic engineering in FeS₂ enabling enhanced catalytic activity for oxygen evolution reaction

Developing efficient and long-lasting non-noble metal electrocatalysts for the oxygen evolution reaction (OER) stands as a primary challenge in the commercialization of water electrolysis technology. Herein, we report the construction of polymorphic FeS₂ (p/m-FeS₂) integrating pyrite-type FeS₂ (p-FeS₂) with marcasite-type FeS₂ (m-FeS₂) as a promising OER catalyst. Compared with p-FeS₂, p/m-FeS₂ shows significantly enhanced alkaline OER activity along with exceptional durability. In-depth studies reveal that introducing the metastable m-FeS₂ promotes the complete reconstruction of p/m-FeS₂ into highly active FeOOH species, contributing to its boosted OER performance. The optimized p/m-FeS₂ achieves a current density of 10 mA cm⁻² at 280 mV overpotential with a small Tafel slope of 86 mV dec⁻¹, compared to p-FeS₂ requiring a higher overpotential of 400 mV with a Tafel slope of 127 mV dec⁻¹. This phase transition strategy offers insights into the rational design of high-efficiency Fe-based OER electrocatalysts and stimulates the pursuit of cost-effective and eco-friendly alternatives to meet the demands of future sustainable development.