(a) Demonstration of the different current waveforms. (b) The maximal ripple factor of different current waveforms. (c) Hydrogen generation efficiency as a function of amplitude. j_DC is the mean current density (offset), and f is the frequency of the waveform. (d) Hydrogen generation efficiency as a function of frequency at different ripple factors. The graph represents the results obtained with square waveform. (Reproduced from Ref. [58]. Copyright©2017, Springer Nature Limited).