Effect of Ni/tubular g-C3N4 on hydrogen storage properties of MgH2

Additive doping is one of the effective methods to overcome the shortcomings of MgH 2 on the aspect of relatively high operating temperatures and slow desorption kinetics. In this paper, hollow g-C 3 N 4 (TCN) tubes with a diameter of 2 μm are synthesized through the hydrothermal and high-temperature pyrolysis methods, and then nickel is chemically reduced onto TCN to form Ni/TCN composite at 278 K. Ni/TCN is then introduced into the MgH 2 /Mg system by means of hydriding combustion and ball milling. The MgH 2 –Ni/TCN composite starts to release hydrogen at 535 K, which is 116 K lower than the as-milled MgH 2 (651 K). The MgH 2 –Ni/TCN composite absorbs 5.24 wt% H 2 within 3500 s at 423 K, and takes up 3.56 wt% H 2 within 3500 s, even at a temperature as low as 373 K. The apparent activation energy ( E a ) of the MgH 2 decreases from 161.1 to 82.6 kJ/mol by the addition of Ni/TCN. Moreover, the MgH 2 –Ni/TCN sample shows excellent cycle stability, with a dehydrogenation capacity retention rate of 98.0% after 10 cycles. The carbon material enhances sorption kinetics by dispersing and stabilizating MgH 2 . Otherwise, the phase transformation between Mg 2 NiH 4 and Mg 2 NiH 0.3 accelerates the re/dehydrogenation reaction of the composite.