Effectively enhanced catalytic effect of sulfur doped Ti3C2 on the kinetics and cyclic stability of hydrogen storage in MgH2

Abstract

Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH₂. Herein, the sulfur doped Ti₃C₂ (S-Ti₃C₂) was successfully prepared by heat treatment of Ti₃C₂ MXene under Ar/H₂S atmosphere to facilitate the hydrogen release and uptake from MgH₂. The S-Ti₃C₂ exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH₂. The addition of 5 wt% S-Ti₃C₂ into MgH₂ resulted in a reduction of 114 °C in the starting dehydriding temperature compared to pure MgH₂. MgH₂ + 5 wt% S-Ti₃C₂ sample could quickly release 6.6 wt% hydrogen in 17 min at 220 °C, and 6.8 wt% H₂ was absorbed in 25 min at 200 °C. Cyclic testing revealed that MgH₂ + 5 wt% S-Ti₃C₂ system achieved a reversible hydrogen capacity of 6.5 wt%. Characterization analysis demonstrated that Ti-species (Ti⁰, Ti²⁺, Ti–S, and Ti³⁺) as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH₂, and sulfur doping can effectively improve the stability of Ti⁰ and Ti³⁺, contributing to the improvement of cyclic stability of MgH₂. This study provides strategy for the construction of catalysts for hydrogen storage materials.