Porous CoP/Co2P heterostructure for efficient hydrogen evolution and application in magnesium/seawater battery

Hydrogen evolution reaction (HER), serving as the cathodic reaction of magnesium (Mg)/seawater battery, could not only produce clean hydrogen directly from seawater but also generate electricity. However, the kinetics of the hydrogen evolution directly from the neutral seawater is sluggish, and leads to unsatisfied HER and battery performance. Herein, a unique porous CoP/Co2P heterostructure electrode was fabricated via a template-free strategy. As demonstrated, the optimized porous CoP/Co2P heterostructure exhibits superior activity for HER, with low overpotential of 87, 133 and 454 mV at 10 mA cm−2 in acidic, alkaline and seawater media, respectively. An Mg/seawater battery fabricated with the porous CoP/Co2P heterostructure cathode displays promising performance, with a peak power density of 6.28 mW cm−2, approaching to the platinum cathode, and a satisfied stability in a 24 h stability test, which is the best non-noble metal cathode reported. The superior battery performance could be attributed to the large active interfaces and the high specific surface area of the porous CoP/Co2P heterostructure electrode, which guarantee a low polarization of the cathodic HER.