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 MgH2 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 MgH2 indued by its poor thermal conductivity, effectively elevates the temperature of MgH2 upon solar irradiation. The "hydrogen pump" effect of Ti and TiHx species that are in situ formed on the surface of MXene from the reduction of MgH2 , 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 MgH2 . Based on the combination of photothermal and catalytic effect of Cu@MXene, a reversible hydrogen storage capacity of 5.9 wt% is achieved for MgH2 after 30 cycles using solar irradiation as the only energy source.

Light-Driven Reversible Hydrogen Storage in Light-Weight Metal Hydrides Enabled by Photothermal Effect.

Requiring high temperature for hydrogen storage is the main feature impeding practical application of light metal hydrides. Herein, to lift the restrictions associated with traditional electric heating, light is used as an alternative energy input, and a light-mediated catalytic strategy coupling photothermal and catalytic effects is proposed. With NaAlH4 as the initial target material, TiO2 nanoparticles uniformly distribute on carbon nanosheets (TiO2 @C), which couples the catalytic effect of TiO2 and photothermal property of C, is constructed to drive reversible hydrogen storage in NaAlH4 under light irradiation. Under the catalysis of TiO2 @C, complete hydrogen release from NaAlH4 is achieved within 7 min under a light intensity of 10 sun. Furthermore, owing to the stable catalytic and photothermal effect of TiO2 @C, NaAlH4 delivers a reversible capacity of 4 wt% after 10 cycles with a capacity retention of 85% under light irradiation only. The proposed strategy is also applicable to other light metal hydrides such as LiAlH4 and MgH2 , validating its universality. The concept of light-driven hydrogen storage provides an alternative approach to electric heating, and the light-mediated catalytic strategy proposed herein paves the way to the design of reversible high-density hydrogen storage systems that do not rely on artificial energy.