Bipolar Hydrogen Production by Hybrid Water Electrolysis

Abstract Hybrid water electrolysis systems (HWEs) replace sluggish oxygen evolution reaction by thermodynamically favorable alternatives for anodic value‐added chemical conversion, while achieving cathodic hydrogen production at a more reduced cell voltage. Nonetheless, large‐scale deployment of such systems is hampered by a market‐size mismatch between cathodic and anodic products and a low hydrogen atom economy. Bipolar hydrogen production (BHP) emerges as a unique type of HWEs, to realize both cathodic and paradoxical anodic hydrogen co‐production by means of one‐electron‐transfer oxidative reactions. BHP can lead to ultralow cell voltage, high electron and atom efficiency, and market‐matchable of anode and cathode products. This review highlights the ingenious reaction design, selectivity regulation, and mechanistic tailoring of this seemingly counterintuitive electrochemistry. Additionally exemplified are some integrated self‐powered aldehyde reforming and nitrate conversion systems. Finally, current challenges and future prospects are outlined to guide further development.