Reduced Graphene Oxide Coating with Anticorrosion and Electrochemical Property-Enhancing Effects Applied in Hydrogen...

Low-capacity retention is the most prominent problem of the magnesium nickel alloy (Mg₂Ni), which prevents it from being commercially applied. Here, we propose a practical method for enhancing the cycle stability of the Mg₂Ni alloy. Reduced graphene oxide (rGO) possesses a graphene-based structure, which could provide high-quality barriers that block the hydroxyl in the aqueous electrolyte; it also possesses good hydrophilicity. rGO has been successfully coated on the amorphous-structured Mg₂Ni alloy via electrostatic assembly to form the rGO-encapsulated Mg₂Ni alloy composite (rGO/Mg₂Ni). The experimental results show that ζ potentials of rGO and the modified Mg₂Ni alloy are totally opposite in water, with values of -11.0 and +22.4 mV, respectively. The crumpled structure of rGO sheets and the contents of the carbon element on the surface of the alloy are measured using scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometry. The Tafel polarization test indicates that the rGO/Mg₂Ni system exhibits a much higher anticorrosion ability against the alkaline solution during charging/discharging. As a result, high-capacity retentions of 94% (557 mAh g^-1) at the 10th cycle and 60% (358 mAh g^-1) at the 50th cycle have been achieved, which are much higher than the results on Mg₂Ni capacity retention combined with the absolute value reported so far to our knowledge. In addition, both the charge-transfer reaction rate and the hydrogen diffusion rate are proven to be boosted with the rGO encapsulation. Overall, this work demonstrates the effective anticorrosion and electrochemical property-enhancing effects of rGO coating and shows its applicability in the Mg-based hydrogen storage system.