Upcycling scrap iron into ultrafine iron sulphide nanostructures and their application in electrochemical hydrogen production

Energy and environment pollution control are two burning areas where researchers' attention is drawn towards generation of clean energy without producing secondary waste. The efficient utilization of waste materials is a growing concern for sustainable energy technologies. In this study, waste iron is repurposed to synthesize iron pyrite (FeS₂), a promising material for electrochemical hydrogen evolution reaction (HER) application. Scrap iron wire was digested in HCl to extract iron, followed by micellization, calcination and sulphurisation to form ultrafine spherical nanoparticles of FeS₂ (12 nm). Electrochemical measurements indicate that FeS₂ exhibits notable catalytic activity for HER in acidic media, characterized by a low overpotential of 283 mV and a Tafel slope of 66 mV dec^-1. FeS₂ coated over graphite substrate demonstrates hydrophilic nature with a low contact angle of 40° ensuring the higher chemical accessibility of active sites for electrolyte contact for HER. The electrocatalyst shows good retention of potentiostatic current density for over 48 h, proving its robustness. This finding ensures successful recycling of waste iron into a functional FeS₂ electrocatalyst besides highlighting its potential as an environmentally friendly and economically viable approach for clean energy generation.