Developing a cost-effective material to replace Pt catalysts for hydrogen evolution reaction (HER) holds great promising for clean energy technologies. In this work, we developed a simple way to prepare nanoporous Si by argon ion irradiation at 90 keV to fluences of 0.5, 1, 2 x 10(17) ions/cm(2). After post-irradiation annealing at 700 degrees C in vacuum (2 x 10(-4) pa) for 5 h, the nanoporous Si was formed which displays largely enhanced electrocatalytic water splitting compared with the unirradiated Si. We also investigated the influence of fluence on morphology and the HER performance of the electrocathodes. It was found that 1 x 10(17) Ar+ ions/cm(2) irradiated Si showed the highest HER performance. The largely enhanced HER activity comes from the unique morphology which results by Ar+ ions irradiation and post irradiation annealing. We further fabricated electrocathodes by coating Ni film on the nanoporous Si, significant improvement of the HER performance compared with Ni coated planar Si was found. Using the ion irradiation technology, we developed a new method to fabricate electrocathode with large specific surface area for largely enhanced hydrogen evolution reaction activities. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.