These correspond to 4.8 times the mass activity of Ir black  0:79Amg 1 @1:55VRHE (Fig. 3a) and are comparable to the values 0:38Amg 1 @1:53VRHE 13, and 0:7Amg 1 @1:5VRHE 12 from recent studies, while these studies did not demonstrate device applications for water electrolysis.