Femtosecond-laser structuring of Ni electrodes for highly active hydrogen evolution

Hydrogen production by alkaline water electrolysis has attracted great attention due to the feasibility of large scale H-2 production and the use of non-precious electrode materials. In particular, efficient electrodes towards the hydrogen evolution reaction (HER) consist of porous or skeletal Ni-based catalysts. In this contribution, a unique surface processing technique using a femtosecond (fs) laser pulse process was utilized to enlarge the surface area of Ni aiming to enhance significantly the HER-activity. Fs laser structured Ni surfaces were processed using different laser process parameters (e.g. fluence, spot size and scan line overlap). Surface morphology was studied by scanning electron microscopy. Under the chosen process conditions arrays of conical surface structures were obtained, which are significantly covered by redeposited particles using a fluence far above the ablation threshold. Electrochemical investigations (CV, EIS, steady-state polarization curves) conducted in 29.9 wt.-% KOH at 333 K (industrial conditions) point out that the fs laser structured electrodes reveal a high and adjustable surface area with a roughness factor between 6 and 73. The roughness of the fs laser structured surfaces has a significant impact on the HER leading to a reduced overpotential (eta(300) = 280 mV, reduction by approximately 45 % compared to smooth Ni). In fact, the results clearly show the feasibility of the fs laser pulse technique for processing highly structured electrodes without affecting the intrinsic HER-activity significantly.