Electrochemical Flocculation Integrated Hydrogen Evolution Reaction of Fe@N‐Doped Carbon Nanotubes on Iron Foam for Ultralow Voltage Electrolysis in Neutral Media

Hydrogen (H2) production is a key step in solving the energy crisis in the future. Electrocatalytic water splitting suffers from sluggish anodic oxygen evolution reaction (OER) kinetics leading to low energy conversion efficiency. Herein, a strategy is presented that integrates anodic electrochemical flocculation with cathodic hydrogen production from water splitting in 0.5 m Na2SO4. Iron encapsulated in a nitrogen‐doped carbon nanotubes array on iron foam (Fe@N‐CNT/IF) is employed as an electrode for the hydrogen evolution reaction (HER), and the Fe@N‐CNT/IF possesses superior HER activity requiring an overpotential of 525 mV to achieve 10 mA cm−2, which is close to that of 20 wt% Pt/C. Benefiting from the lower oxidation potential of iron (E°Fe/Fe2+, 0.44 V) than that of OER (E0OH‐/O2, 1.23 V), the cell voltage for integrated electrochemical flocculation and H2 production is significantly reduced by 1.31 V relative to overall water splitting to achieve 20 mA cm−2. More important, the production of electrochemical flocculation can be applied to water purification, because of the excellent adsorption capacity. Finally, metal–carbon electrocatalysts are prepared again by pyrolysis of flocculation adsorbents containing toxic heavy metals and organics. This result provides a new direction for designing a heterogeneous electrolysis system for energy conversion and environmental treatment applications. A strategy is presented that integrates anodic electrochemical flocculation with cathodic hydrogen production from water splitting in neutral media. Hydrogen is produced at the cathode electrocatalyzed by iron encapsulated in a nitrogen‐doped carbon nanotubes array on iron foam, while simultaneously oxidizing iron and generating flocculant for absorbing contaminants. Metal–carbon electrocatalysts are obtained again by controlled pyrolysis of recyclable flocculation.