To relieve our strong reliance on fossil fuels and to reduce greenhouse effects, there is an ever-growing interest in using electrocatalytic water splitting to produce green, renewable, and environment-benign hydrogen fuel via the hydrogen evolution reaction. For commercially feasible water electrolysis, it is imperative to develop electrocatalysts that perform as efficiently as Pt but using only earth-abundant commercial materials. However, the highest performance current catalysts consist of nanostructures made by using complex methods. Here we report a porous nickel diselenide (NiSe2) catalyst that is superior for water electrolysis, exhibiting much better catalytic performance than most first-row transition metal dichalcogenide-based catalysts, well-studied MoS2, and WS2-based catalysts. Indeed NiSe2 performs comparably to the state-of-the-art Pt catalysts. We fabricate NiSe2 directly from commercial nickel foam by acetic acid-assisted surface roughness engineering. To understand the origin of the high performance, we use first-principles calculations to identify the active sites. This work demonstrates the commercial possibility of hydrogen production via water electrolysis using porous bulk NiSe2 catalysts.