Innovative Electrochemical Strategies for Hydrogen Production: From Electricity Input to Electricity Output.

Renewable H production by water electrolysis has attracted much attention due to its numerous advantages. However, the energy consumption of conventional water electrolysis is high and mainly driven by the kinetically inert anodic oxygen evolution reaction. An alternative approach is the coupling of different half-cell reactions and the use of redox mediators. In this review, we, therefore, summarize the latest findings on innovative electrochemical strategies for H production. First, we address redox mediators utilized in water splitting, including soluble and insoluble species, and the corresponding cell concepts. Second, we discuss alternative anodic reactions involving organic and inorganic chemical transformations. Then, electrochemical H production at both the cathode and anode, or even H production together with electricity generation, is presented. Finally, the remaining challenges and prospects for the future development of this research field are highlighted.