Mn-doped nickel-iron phosphide heterointerface nanoflowers for efficient alkaline freshwater/seawater splitting at high current densities

To realize highly efficient and stable hydrogen production at high current densities, more efforts are devoted to developing outstanding water-splitting electrocatalysts. Herein, through a facile hydrothermal-phosphorization method, Mn-doped Ni2P/Fe2P was rationally designed and prepared as a high-performance bifunctional elec-trocatalyst for alkaline freshwater/seawater splitting. In alkaline seawater (freshwater) electrolyte, it merely needs low overpotentials of 358 (335) and 470 (405) mV to reach 1000 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. This electrocatalyst also shows excellent stability even at a high OER current density of 500 mA cm-2 for 200 h. Regarding the alkaline overall seawater splitting, Mn-doped Ni2P/Fe2P presents a low cell voltage of 2.02 V at 500 mA cm-2 and outstanding stability for 120 h at the same current. The X-ray absorption fine structure (XAFS) experimental analysis verifies that the Mn doping and Ni2P/Fe2P heterointerfaces can efficiently optimize the electrocatalyst's electronic structure, leading to the improved intrinsic OER and HER activities. Meanwhile, the 3D nanoflower structure provides abundant exposed active sites, and the Mn doping and heterointerfaces can create more active sites. Besides, the high corrosion resistance resulting from nickel-iron phosphides makes the electrocatalyst become a good candidate for seawater splitting. This study provides a simple path to fabricate highly active and robust non-noble electrocatalysts for freshwater/seawater splitting at high current densities.