Solar-Driven Reversible Hydrogen Storage.

The lack of safe and efficient hydrogen storage is a major bottleneck for large-scale application of hydrogen energy. Reversible hydrogen storage of light-weight metal hydrides with high theoretical gravimetric and volumetric hydrogen density is one ideal solution but requires extremely high operating temperature with large energy input. Herein, taking MgH 2 as an example, a concept is demonstrated to achieve solar-driven reversible hydrogen storage of metal hydrides via coupling the photothermal effect and catalytic role of Cu nanoparticles uniformly distributed on the surface of MXene nanosheets (Cu@MXene). The photothermal effect of Cu@MXene, coupled with the "heat isolator" role of MgH 2 indued by its poor thermal conductivity, effectively elevates the temperature of MgH 2 upon solar irradiation. The "hydrogen pump" effect of Ti and TiH x species that are in situ formed on the surface of MXene from the reduction of MgH 2 , on the other hand, plays a catalytic role in effectively alleviating the kinetic barrier and hence decreasing the operating temperature required for reversible hydrogen adsorption and desorption of MgH 2 . Based on the combination of photothermal and catalytic effect of Cu@MXene, a reversible hydrogen storage capacity of 5.9 wt% is achieved for MgH 2 after 30 cycles using solar irradiation as the only energy source.