Nanoflower MnxNi2−xP as efficient bifunctional catalyst for hydrogen production with urea-assisted energy-saving in alkaline freshwater and seawater

To achieve efficient and stable hydrogen production while addressing the corrosive effects of seawater on electrodes, integrating the energy-saving urea oxidation reaction (UOR) with the hydrogen evolution reaction (HER) presents a promising low-energy solution. However, developing low-cost, high-performance bifunctional electrocatalysts for both HER and UOR remains a significant challenge. In this work, we prepared bifunctional electrocatalysts featuring Mn_xNi_2−xP nanoflower structures grown on nickel foam using a simple hydrothermal phosphatization method. These catalysts demonstrated excellent performance in alkaline freshwater and seawater, with notably low overpotentials of 251 and 257 mV for HER, and 1.33 and 1.37 V for UOR. Combining its bifunctional activity in UOR and HER in a two-electrode system, an energy saving of 0.19 V potential compared to water electrolysis through water oxidation can be acquired to reach 100 mA cm⁻² current density. Moreover, the catalyst also maintains fairly stable after long-term testing, indicating its potential for efficient and energy-saving hydrogen production. Our study reveals that the synergistic interaction between Ni and Mn metals enhances the electronic structure of the electrocatalysts, significantly boosting both UOR and HER activities. Additionally, Mn doping alters the morphological structure, creating nanoflowers with abundant active sites, while nickel-iron phosphides improve the catalyst's corrosion resistance in seawater. This work provides valuable insights into the design of low-cost, stable non-precious metal electrocatalysts for seawater and freshwater splitting, combining hydrogen evolution with urea-assisted energy-saving.