Rapid self-reconstruction of nickel in amorphous nickel borate nanosheets for efficient oxygen evolution in alkaline seawater splitting

Abstract

Enhancing the transformation of true (Ni²⁺ to Ni³⁺) active site in amorphous nickel borate (NiB) is the paramount importance in alkaline water/ seawater splitting. In this study, we strengthen the oxygen evolution reaction (OER) performance of amorphous NiB nanosheets by adding Fe. The incorporated Fe enriches conductivity which facilitating formation of real active site in the NiFeB. This unique nanosheet structure of NiFeB features more active sites and large open surface area that permit the better electrolyte diffusion. The optimized electrocatalyst demonstrates impressive OER activity with an ultra-low overpotential of 180 mV (50 mA cm⁻²), a small Tafel slope (63 mV dec⁻¹) also exhibits exceptional durability over 24 h in alkaline water. Similarly, in alkaline seawater, the catalyst displays a low over potential of 185 mV to reach 50 mA cm⁻², a small Tafel slope 46 mV dec⁻¹ and excellent durability over 24 h. For the hydrogen evolution reaction in alkaline water, the amorphous NiFe0.5B nanosheet shows low overpotential as 290 mV at 10 mA cm⁻², a small Tafel slope 195 mV dec⁻¹. In overall alkaline seawater splitting, the catalyst delivers 50 mA cm⁻² at the lowest cell voltage of 1.63 V with exceptional stability. This work provides valuable insights into the cost-effective design of amorphous transition metal borate OER catalyst for seawater splitting.