Calcination-induced five-coordinated Al sites on montmorillonite as anchoring points for Ru nanoparticles toward enhanced alkaline hydrogen electrocatalysis

Abstract

Montmorillonite (MMT) is a promising catalyst support due to its two-dimensional layered structure and abundant surface groups. However, aluminum (Al) species in MMT predominantly exist as coordinatively saturated Al^VI, lacking active anchoring sites. Herein, a calcination-induced dehydroxylation strategy was employed to transform Al^VI into highly reactive five-coordinated Al^V sites within the octahedral sheets, constructing an activated MMT support (MMT700). Solid-state ²⁷Al MAS NMR spectroscopy directly confirmed the formation of Al^V at the expense of Al^VI. As a proof of concept, Ru nanoparticles supported on MMT700 catalyst (Ru/MMT700) was fabricated and evaluated for alkaline hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). In 0.1 M KOH, Ru/MMT700 exhibited the HER overpotential of 42.49 mV at 10 mA cm⁻² and a low Tafel slope of 39.28 mV dec⁻¹. The HOR exchange current density reached 1.21 mA cm⁻², with excellent stability retained after 1000 cycles. Structural analyses indicated that Al^V sites promoted the stable dispersion of Ru species and modulated the Ru electronic structure via Al^V-mediated Ru-O-Al-like interfacial coordination, forming Ru^δ+ species that optimized hydrogen-intermediate adsorption. This work established a novel strategy of tuning the coordination environment of MMT and provided new insights for the functional utilization of clay minerals.