Cathodic electrochemical activation of CoO nanoarrays: a smart strategy to significantly boost the hydrogen evolution activity.

Co(hydro)oxides show unsatisfactory catalytic activity for the hydrogen evolution reaction (HER) in alkaline media, and it is thus highly desirable but still remains a challenge to design and develop Co(hydro)oxide derived materials as superb hydrogen-evolving catalysts using a facile, rapid and less energy-intensive method. Here, we propose a cathodic electrochemical activation strategy toward greatly boosted HER activity of a CoO nanoarray via room-temperature cathodic polarization in sodium hypophosphite solution. After activation, the overpotential significantly decreases from 260 to 73 mV to drive a geometrical catalytic current density of 10 mA cm in 1.0 M KOH. Notably, this activated electrode also shows strong long-term electrochemical durability with the retention of its catalytic activity at 100 mA cm for at least 40 h.