Activating silicon for high hydrogen conversion and sustainable anode recovery.

Abstract

The hydrolysis/methanolysis of silicon has received considerable attention to achieve efficient and on-demand hydrogen conversion. However, the intense covalent network and highly localized electrons in pure Si impede its reactivity with water (H₂O) or methanol (CH₃OH), thereby hindering the hydrogen release. In this work, we report the synthesis of Zintl phase alkalis-Si alloys via simple ball-milling or sintering, showing eminent performance in enhancement of H₂O/CH₃OH dissociation. Experiments combined with DFT calculations have revealed that the obtained Zintl phase alloys exhibit discrete Si clusters containing well-defined unpaired electrons that efficiently facilitate the interaction between reductant and solvent molecules. Such an effect thereby reduces the activation barrier of H₂O/CH₃OH dissociation to yield active intermediates containing Si-H structure, which significantly promotes the hydrogen release with favorable kinetics and efficiency. The optimal Zintl Li₂₁Si₅ alloy achieves ultrahigh Si utilization rates of 86.9% in water and 98.1% in methanol at 25 °C, respectively. Remarkably, even at an extremely low temperature of -40 °C, a substantial hydrogen yield of 1.091 L g^-¹ in methanol is retained. Furthermore, the desirable Zintl phase-water reaction inspires an economic-friendly "charge-hydrolysis-separation" strategy, for effectively recovering the valuable lithium, graphite, Si and Cu resources from the degraded lithium-ion batteries.