New strategy to synthesize oxygen vacancy-rich CoFe nanoneedles for overall water splitting and urea electrolysis.

• CoFe nanoneedles with rich oxygen vacancies were synthesised by CaH 2 reduction method. • The CoFe-250 exhibits an high OER activity with an overpotential of 230 mV at 10 mA cm−2 in 1 M KOH. • An extremely attractive cell voltage of 1.47 V was achieved for 10 mA cm−2 for overall water splitting. • The overall energy consumption was decreased by 12.2 % compared to water splitting. Developing highly efficient electrocatalysts for overall water splitting and urea oxidation reaction (UOR) is of significant importance to achieve hydrogen production. Herein, CoFe nanoneedles with abundant oxygen vacancies were prepared on Ni foam by hydrothermal method and CaH 2 reduction method at different temperature in an evacuated (≈10−2 Pa) pyrex tube. The CoFe-250 exhibits an excellent OER activity with an overpotential of 230 mV at 10 mA cm−2 in 1 M KOH and the symmetrical overall splitting electrolyzer using CoFe-250 as both anode and cathode dilivers 10 mA cm−2 at the voltage of 1.47 V in 1 M KOH. More impressively, the overall water-urea electrolysis only requires 1.6 V to deliver 100 mA cm−2 and reduces the overall energy consumption by 12.2 % in 1 M KOH with a 0.33 M urea. This work provides a highly active overall water splitting and UOR electrocatalysts for hydrogen production in an economic way. [ABSTRACT FROM AUTHOR]