In situ coupling metallophilic Zn sites and interfacial LiCl stabilizer to achieve one-step reversible hydrogen storage in Li/Na dual-cation borohydride

Abstract

Dual-cation borohydrides composed of alkali or alkaline-earth metals attract considerable attention for hydrogen storage, thanks to their high hydrogen capacity and low eutectic melt point; however, they still suffer from high-temperature-dependent dehydrogenation and poor reversibility. In-situ catalyzation and nanoconfinemnt are effective for easing these problems, but a simple and efficient method is required to achieve their coulping. Here inspired from the structural stabilization and performance improvement roles on anodes of metal batteries by constructing metallophilic Zn sites and interfacial LiCl layers, we develop a 0.62LiBH4-0.38NaBH4 system with ZnCl2 as reactive additives by one-step ball milling. In-situ evolved LiCl and Zn(BH4)2 are surprisingly identified as interfacial stabilizers and metastable phases to disperse borohydride particles and to trigger hydrogen release below 100 °C, respectively. Further formed Zn from the decomposition of Zn(BH4)2 acts as catalytic nucleation sites to promote the one-step and reversible (de)hydrogenation of LiBH4 and NaBH4, without producing high chemical potential intermediates, benefiting from the strong affinity of Zn towards Li and Na. These factors contribute to a cyclic stability of nearly 70 %, the highest for dual-cation borohydrides reported so far. The present work provides new insights and a feasible scheme for developing promising borohydride-based storage systems towards practical application.