Dehydroxylation Driven Reactivity in Kaolinite: Unraveling Strain Structure Interplay for Enhanced Electrocatalytic Water Splitting

Abstract

Kaolinite is an earth-derived natural mineral and is available in latent reactive form, which can be transformed into aluminosilicate, capable of catalytic functions through a simple thermal activation process. The Al 3+ in kaolinite changes its coordination environment making it highly suitable for catalytic processes. The kaolinite heated to 100 °C (KAO@100) exhibited the best OER activity, achieving an overpotential of 280 mV at 10 mA cm⁻², due to the retention of surface hydroxyl groups and favorable surface that promote OH⁻ adsorption. On the other hand, the kaolinite heated at 900 °C (KAO@900) demonstrated superior HER activity with a low overpotential of 174 mV, which is due to the dehydroxylation driven phase transformation to metakaolinite, where the rearranged Al-O coordination, increased defect density, and improved charge transfer characteristics. The temperature dependent microstructural evolution is correlated with catalytic activity, where compressive strain and structural disorder at higher temperatures enhance HER, whereas lightly strained hydroxyl rich structures favor OER. The two electrode full cell configuration required only 1.68 V to achieve 10 mA cm⁻² for overall water splitting. These findings demonstrate that thermally engineered kaolinite is a promising, scalable, and sustainable electrocatalyst for green hydrogen production.