Multi-site trifunctional hydrangea-like electrocatalysts for efficient industrial-level water/urea electrolysis with current density exceeding 1000 mA cm(-2)

Splitting water into hydrogen by electrolysis using renewable electricity is one of the promising routes for green hydrogen production. The key dilemma for this electrochemical route is the extremely high overpotentials required for oxygen evolution reaction at the anode. Innovative strategies are desirable to fabricate inexpensive metal-based multifunctional catalysts with robust catalytic performance and large-current durability for electrochemical hydrogen production in freshwater or urea-containing water. Here we report the rational design and synthesis of hydrangea-like CoP/Ni3FeN heterostructure arrays as excellent multifunctional electrocatalysts for both alkaline water and urea electrolysis. This catalyst presents superb trifunctional catalytic activities and outstanding large-current durability in basic media, requiring ultralow potentials of -0.160, 1.538 and 1.419 V to facilitate hydrogen, oxygen evolution and urea oxidation reactions (HER, OER and UOR) at an extremely large current density of 1000 mA cm(-2), respectively. Remarkably, the as-constructed two-electrode cells using this electrocatalyst as both the cathode and anode demand extremely low cell voltages of 1.577 and 1.668 V to deliver 500 mA cm(-2) stably for urea and water electrolysis, respectively, suggesting its superb activity and outstanding stability for trifunctional catalysis. Operando Raman spectroscopic studies in combination with density functional theory calculations validate that the CoP/Ni3FeN hybrid can greatly facilitate the formation of active metal (oxy)hydroxide species for both OER and UOR, and also reduce the adsorption energy barriers of *H2O and *H intermediates for HER. This work provides an effective pathway for developing multifunctional catalysts for electrochemical hydrogen production at low voltages whenever fresh or urea-containing water is available.

Automated summary

Splitting water into hydrogen using renewable electricity is a promising route for green hydrogen production. However, the high overpotentials required for oxygen evolution reaction at the anode pose a challenge. In this study, hydrangea-like CoP/Ni3FeN heterostructure arrays were designed and synthesized as excellent electrocatalysts for both alkaline water and urea electrolysis, showing superb catalytic activities and outstanding durability at ultralow potentials. These findings provide an effective pathway for developing multifunctional catalysts for electrochemical hydrogen production at low voltages.