Hierarchical porous metals (HPMs) are advanced functional materials used in various applications. However, the current fabrication methods require extra sacrificial materials and generate chemical waste. Here, a facile gaseous oxidation-reduction (GOR) approach was developed to directly transform commercial metals into HPMs. Taking cobalt (Co) as a typical example, a series of hierarchical porous Co foils (HPCF) with controlled porous structures were successfully sculptured. Larger micron-sized pores were formed spontaneously by utilizing different oxidation rates between grain and grain boundaries for the oxidation, and nanoscale pores originated from volume contraction and spontaneous rearrangement of the metal atoms during reduction. This straightforward GOR approach avoids multiple processes and harsh chemical etching and generates water vapor as the only processing byproduct, making it a facile, green process, suitable for large-scale fabrication. When HPCF were used as self-supporting electrodes for the oxygen evolution reaction, DFT calculations and in situ spectroscopy indicated that abundant vacancy defects contained within the hierarchical pores enhanced *OH adsorption and promoted the reconstruction of highly active CoOOH nanosheets. As a result, the CoOOH/HPCF electrode demonstrated outstanding performance of 190 mV at 10 mA cm−2 and exceptional durability of 500 h at 100 mA cm−2, outperforming most reported nonprecious metal oxygen evolution reaction electrodes.