Transition metals such as Ni with a low cost and a highly efficient activity to water splitting, are favorable catalysts for alkaline water electrolysis, and often prepared in porous to boost the electrolysis performance, while a the mass transportation is inevitable limited. Here, we report a method to prepare porous Ni electrodes with improved performance. Ni electrodes with pore-graded structures were obtained from a blend of Ni and Al via high-pressure cold spray. The gradient porosity was realized by varying the addition of Al and applying chemical etching. The obtained electrodes were annealed before the etching to eliminate the residual stress and strengthen the adhesion of layers. The size distribution and connectivity of pores were characterized by scanning electron microscopy (SEM) and industrial Computed Tomography (CT). The effect of gradient porosity on the electrocatalytic activity toward HER/OER was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results revealed that the prepared pore-graded electrodes exhibited a superior HER/OER performance than normal porous electrodes. Sample N321A with a negative gradient exhibited the best HER/OER performance when tested with an annulus counter electrode of Nickel foam. While sample N123A with a positive gradient exhibited the highest HER/OER performance when tested with a carbon rob counter electrode. All prepared electrodes showed an excellent durability that after 500 cycles of HER/OER test the overpotential increased only by around 20 mV.

Alkaline water electrolysis; High pressure cold spray; gradient porous; ; HER/OER; Mass transportation.